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PubAg

Main content area


1. API Overview

Our RESTful Web Service gives you access to the publications and related information we hold in the PUBAG repository. The API provides one module: the Search module, which returns articles that match desired search criteria.


2. Gaining Access

Anyone may access and use the API. However, a data.gov API key must be incorporated into each API request. You can apply for a key from Data.gov here: api.data.gov.


3. Rate Limits

We currently limit the number of API requests to a default rate of 1,000 requests per hour per API Key. Exceeding this limit will cause your API key to be temporarily blocked for one hour. More detailed information on rate limits may be found here. Please contact us if you feel you need a higher request rate setting.


4. Using the API

Anyone may access the PubAg API using either the DEMO_KEY or an api.data.gov API key. The DEMO_KEY (api_key=DEMO_KEY) can be used for initially exploring the API prior to signing up for a Data.gov key. It has much lower rate limits, however, so you are encouraged to sign up for your own API key if you plan to use the API for more extensive searching at: https://api.data.gov/signup.

The rate limits for the DEMO_KEY are:

  1. Hourly Limit: 30 requests per IP address per hour
  2. Daily Limit: 50 requests per IP address per day

Additionally, "curl" can be used for each request.


a. API Module: Search

Use this module to search the publications and related information we hold in the PUBAG repository. The links that are underlined are live links.

URL syntax

Construct your URL for search requests as follows:

https://api.nal.usda.gov/pubag/rest/search/?query={}[&parameters]

Request Parameters

  • query
    This is the only required parameter for the search module.

    Example API Query URL: https://pubag-stage2.nal.usda.gov/api/rest/search/?query=journal:climate&api_key=DEMO_KEY
    {
      "responseHeader":{
        "zkConnected":true,
        "status":0,
        "QTime":1841,
        "params":{
          "q":"journal:climate",
          "fl":"id,abstract,aris,author,author_lastname,author_primary,chorus_url,chorusOpen,dataset,dataset_availability,date,doi,doi_url,endpage,format,handle_url,issn,issue,journal_name,language,last_modified_date,mesh_ss,nalt_all,page,pmcid_url,pmid_url,publication_year,publisher,startpage,subject,text_availability,title,url,usda_authored_publication,usda_funded_publication,volume",
          "start":"0",
          "sort":"id asc",
          "rows":"20",
          "wt":"javabin",
          "version":"2"}},
      "response":{"numFound":6734,"start":0,"numFoundExact":true,"docs":[
          {
            "date":"2014-12",
            "nalt_all":["atmospheric precipitation",
              "climate",
              "climate models",
              "decision support systems",
              "linear models",
              "model validation",
              "neural networks",
              "simulation models",
              "time series analysis"],
            "subject":["atmospheric precipitation",
              "climate",
              "climate models",
              "decision support systems",
              "linear models",
              "model validation",
              "neural networks",
              "simulation models",
              "time series analysis",
              "Ontario",
              "Quebec"],
            "author_lastname":["Gaitan",
              "Hsieh",
              "Cannon"],
            "last_modified_date":"2015-01-28T23:08:58.199Z",
            "language":["English"],
            "title":"Comparison of statistically downscaled precipitation in terms of future climate indices and daily variability for southern Ontario and Quebec, Canada",
            "startpage":"3201",
            "usda_authored_publication":false,
            "id":"1128445",
            "text_availability":"Citation in PubAg",
            "doi_url":"https://doi.org/10.1007/s00382-014-2098-4",
            "issue":"no. 12 ",
            "author":["Carlos F. Gaitan",
              "William W. Hsieh",
              "Alex J. Cannon"],
            "format":"text",
            "endpage":"3217",
            "journal_name":"Climate dynamics",
            "abstract":"Given the coarse resolution of global climate models, downscaling techniques are often needed to generate finer scale projections of variables affected by local-scale processes such as precipitation. However, classical statistical downscaling experiments for future climate rely on the time-invariance assumption as one cannot know the true change in the variable of interest, nor validate the models with data not yet observed. Our experimental setup involves using the Canadian regional climate model (CRCM) outputs as pseudo-observations to estimate model performance in the context of future climate projections by replacing historical and future observations with model simulations from the CRCM, nested within the domain of the Canadian global climate model (CGCM). In particular, we evaluated statistically downscaled daily precipitation time series in terms of the Peirce skill score, mean absolute errors, and climate indices. Specifically, we used a variety of linear and nonlinear methods such as artificial neural networks (ANN), decision trees and ensembles, multiple linear regression, and k-nearest neighbors to generate present and future daily precipitation occurrences and amounts. We obtained the predictors from the CGCM 3.1 20C3M (1971–2000) and A2 (2041–2070) simulations, and precipitation outputs from the CRCM 4.2 (forced with the CGCM 3.1 boundary conditions) as predictands. Overall, ANN models and tree ensembles outscored the linear models and simple nonlinear models in terms of precipitation occurrences, without performance deteriorating in future climate. In contrast, for the precipitation amounts and related climate indices, the performance of downscaling models deteriorated in future climate.",
            "pmid_url":"http://www.ncbi.nlm.nih.gov/pubmed/?term=",
            "url":"http://dx.doi.org/10.1007/s00382-014-2098-4",
            "volume":"v. 43 ",
            "publication_year":"2014",
            "usda_funded_publication":false,
            "issn":"0930-7575",
            "page":"pp. 3201-3217",
            "author_primary":"Carlos F. Gaitan",
            "doi":"10.1007/s00382-014-2098-4"},
          {
            "date":"2014-12",
            "nalt_all":["El Nino",
              "latitude",
              "models",
              "stratosphere",
              "surface water temperature",
              "troposphere"],
            "subject":["El Nino",
              "latitude",
              "models",
              "stratosphere",
              "surface water temperature",
              "troposphere"],
            "author_lastname":["Hurwitz",
              "Calvo",
              "Garfinkel",
              "Butler",
              "Ineson",
              "Cagnazzo",
              "Manzini",
              "Peña-Ortiz"],
            "last_modified_date":"2015-01-28T23:08:57.860Z",
            "language":["English"],
            "title":"Extra-tropical atmospheric response to ENSO in the CMIP5 models",
            "startpage":"3367",
            "usda_authored_publication":false,
            "id":"1128446",
            "text_availability":"Citation in PubAg",
            "doi_url":"https://doi.org/10.1007/s00382-014-2110-z",
            "issue":"no. 12 ",
            "author":["Margaret M. Hurwitz",
              "Natalia Calvo",
              "Chaim I. Garfinkel",
              "Amy H. Butler",
              "Sarah Ineson",
              "Chiara Cagnazzo",
              "Elisa Manzini",
              "Cristina Peña-Ortiz"],
            "format":"text",
            "endpage":"3376",
            "journal_name":"Climate dynamics",
            "abstract":"The seasonal mean extra-tropical atmospheric response to El Niño/Southern Oscillation (ENSO) is assessed in the historical and pre-industrial control CMIP5 simulations. This analysis considers two types of El Niño events, characterized by positive sea surface temperature (SST) anomalies in either the central equatorial Pacific (CP) or eastern equatorial Pacific (EP), as well as EP and CP La Niña events, characterized by negative SST anomalies in the same two regions. Seasonal mean geopotential height anomalies in key regions typify the magnitude and structure of the disruption of the Walker circulation cell in the tropical Pacific, upper tropospheric ENSO teleconnections and the polar stratospheric response. In the CMIP5 ensembles, the magnitude of the Walker cell disruption is correlated with the strength of the mid-latitude responses in the upper troposphere i.e., the North Pacific and South Pacific lows strengthen during El Niño events. The simulated responses to El Niño and La Niña have opposite sign. The seasonal mean extra-tropical, upper tropospheric responses to EP and CP events are indistinguishable. The ENSO responses in the MERRA reanalysis lie within the model scatter of the historical simulations. Similar responses are simulated in the pre-industrial and historical CMIP5 simulations. Overall, there is a weak correlation between the strength of the tropical response to ENSO and the strength of the polar stratospheric response. ENSO-related polar stratospheric variability is best simulated in the “high-top” subset of models with a well-resolved stratosphere.",
            "pmid_url":"http://www.ncbi.nlm.nih.gov/pubmed/?term=",
            "url":"http://dx.doi.org/10.1007/s00382-014-2110-z",
            "volume":"v. 43 ",
            "publication_year":"2014",
            "usda_funded_publication":false,
            "issn":"0930-7575",
            "page":"pp. 3367-3376",
            "author_primary":"Margaret M. Hurwitz",
            "doi":"10.1007/s00382-014-2110-z"},
          {
            "date":"2014-12",
            "nalt_all":["rain",
              "spring"],
            "subject":["rain",
              "spring",
              "Central Africa"],
            "author_lastname":["Kamsu-Tamo",
              "Janicot",
              "Monkam",
              "Lenouo"],
            "last_modified_date":"2015-01-28T23:08:58.555Z",
            "language":["English"],
            "title":"Convection activity over the Guinean coast and Central Africa during northern spring from synoptic to intra-seasonal timescales",
            "startpage":"3377",
            "usda_authored_publication":false,
            "id":"1128447",
            "text_availability":"Citation in PubAg",
            "doi_url":"https://doi.org/10.1007/s00382-014-2111-y",
            "issue":"no. 12 ",
            "author":["P. H. Kamsu-Tamo",
              "S. Janicot",
              "D. Monkam",
              "A. Lenouo"],
            "format":"text",
            "endpage":"3401",
            "journal_name":"Climate dynamics",
            "abstract":"This study proposes an overview of the main synoptic, medium-range and intraseasonal modes of convection and precipitation in northern spring (March–June 1979–2010) over West and Central Africa, and to understand their atmospheric dynamics. It is based on daily National Oceanic and Atmospheric Administration outgoing longwave radiation and Cloud Archive User Service Tb convection data, daily TRMM and Global Precipitation Climatology Project rainfall products and daily ERA-Interim reanalysis atmospheric fields. It is first shown that mesoscale convective systems can be modulated in terms of occurrences number and intensity at such time scales. Based on empirical orthogonal function analyses on the 2–90-day filtered data it is shown that the main mode of convective and rainfall variability is located along the Guinean coast with a moderate to weak extension over Central Africa. Corresponding regressed deseasonalised atmospheric fields highlight an eastward propagation of patterns consistent with convectively coupled equatorial Kelvin wave dynamics. Then a singular spectrum analysis combined with a Hierarchical Ascendant Classification enable to define objectively the main spectral bands of variability within the 2–90-day band, and highlight three main bands, 2–8-, 8–22- and 20–90-day. Within these three bands, space–time spectral decomposition is used to identify the relative impacts of convectively coupled equatorial Kelvin, Rossby and inertia–gravity waves, as well as Madden–Julian Oscillation (MJO) signal. It confirms that eastward propagating signals (convectively coupled equatorial Kelvin wave and MJO) are highly dominant in these convection and precipitation variability modes over the Guinean coast during northern spring. So, while rain-producing individual systems are moving westward, their activity are highly modulated by sub-regional and regional scales envelops moving to the east. This is a burning issue for operational forecasting centers to be able to monitor and predict such eastward propagating envelops of convective activity.",
            "pmid_url":"http://www.ncbi.nlm.nih.gov/pubmed/?term=",
            "url":"http://dx.doi.org/10.1007/s00382-014-2111-y",
            "volume":"v. 43 ",
            "publication_year":"2014",
            "usda_funded_publication":false,
            "issn":"0930-7575",
            "page":"pp. 3377-3401",
            "author_primary":"P. H. Kamsu-Tamo",
            "doi":"10.1007/s00382-014-2111-y"},
          {
            "date":"2014-12",
            "nalt_all":["memory",
              "evapotranspiration",
              "stream flow",
              "models",
              "watersheds",
              "soil water",
              "summer",
              "surface temperature",
              "weather forecasting",
              "energy balance",
              "climate",
              "prediction"],
            "subject":["memory",
              "evapotranspiration",
              "stream flow",
              "models",
              "watersheds",
              "soil water",
              "summer",
              "surface temperature",
              "weather forecasting",
              "energy balance",
              "climate",
              "prediction",
              "Europe"],
            "author_lastname":["Orth",
              "Seneviratne"],
            "last_modified_date":"2019-12-04T17:11:30.369Z",
            "language":["English"],
            "title":"Using soil moisture forecasts for sub-seasonal summer temperature predictions in Europe",
            "startpage":"3403",
            "usda_authored_publication":false,
            "id":"1128448",
            "text_availability":"Citation in PubAg",
            "doi_url":"https://doi.org/10.1007/s00382-014-2112-x",
            "issue":"no. 12 ",
            "author":["René Orth",
              "Sonia I. Seneviratne"],
            "format":"text",
            "endpage":"3418",
            "journal_name":"Climate dynamics",
            "abstract":"Soil moisture exhibits outstanding memory characteristics and plays a key role within the climate system. Especially through its impacts on the evapotranspiration of soils and plants, it may influence the land energy balance and therefore surface temperature. These attributes make soil moisture an important variable in the context of weather and climate forecasting. In this study we investigate the value of (initial) soil moisture information for sub-seasonal temperature forecasts. For this purpose we employ a simple water balance model to infer soil moisture from streamflow observations in 400 catchments across Europe. Running this model with forecasted atmospheric forcing, we derive soil moisture forecasts, which we then translate into temperature forecasts using simple linear relationships. The resulting temperature forecasts show skill beyond climatology up to 2 weeks in most of the considered catchments. Even if forecasting skills are rather small at longer lead times with significant skill only in some catchments at lead times of 3 and 4 weeks, this soil moisture-based approach shows local improvements compared to the monthly European Centre for Medium Range Weather Forecasting (ECMWF) temperature forecasts at these lead times. For both products (soil moisture-only forecast and ECMWF forecast), we find comparable or better forecast performance in the case of extreme events, especially at long lead times. Even though a product based on soil moisture information alone is not of practical relevance, our results indicate that soil moisture (memory) is a potentially valuable contributor to temperature forecast skill. Investigating the underlying soil moisture of the ECMWF forecasts we find good agreement with the simple model forecasts, especially at longer lead times. Analyzing the drivers of the temperature forecast skills we find that they are mainly controlled by the strengths of (1) the soil moisture-temperature coupling and (2) the soil moisture memory. We find a negative relationship between these controls that weakens the forecast skills, nevertheless there is a middle ground between both controls in several catchments, as shown by our results.",
            "pmid_url":"http://www.ncbi.nlm.nih.gov/pubmed/?term=",
            "url":"http://dx.doi.org/10.1007/s00382-014-2112-x",
            "volume":"v. 43 ",
            "publication_year":"2014",
            "usda_funded_publication":false,
            "issn":"0930-7575",
            "page":"pp. 3403-3418",
            "author_primary":"René Orth",
            "doi":"10.1007/s00382-014-2112-x"},
          {
            "date":"2014-12",
            "nalt_all":["data collection",
              "monsoon season",
              "summer",
              "water resources"],
            "subject":["data collection",
              "monsoon season",
              "summer",
              "water resources",
              "India"],
            "author_lastname":["Sushama",
              "Ben Said",
              "Khaliq",
              "Nagesh Kumar",
              "Laprise"],
            "last_modified_date":"2015-01-28T23:08:58.724Z",
            "language":["English"],
            "title":"Dry spell characteristics over India based on IMD and APHRODITE datasets",
            "startpage":"3419",
            "usda_authored_publication":false,
            "id":"1128449",
            "text_availability":"Citation in PubAg",
            "doi_url":"https://doi.org/10.1007/s00382-014-2113-9",
            "issue":"no. 12 ",
            "author":["L. Sushama",
              "S. Ben Said",
              "M. N. Khaliq",
              "D. Nagesh Kumar",
              "R. Laprise"],
            "format":"text",
            "endpage":"3437",
            "journal_name":"Climate dynamics",
            "abstract":"Selected characteristics of dry spells and associated trends over India during the 1951–2007 period is studied using two gridded datasets: the Indian Meteorological Department (IMD) and the Asian Precipitation-Highly Resolved Observational Data Integration Towards Evaluation of the water resources (APHRODITE) datasets. Two precipitation thresholds, 1 and 3 mm, are used to define a dry day (and therefore dry spells) in this study. Comparison of the spatial patterns of the dry spell characteristics (mean number of dry days, mean number of dry spells, mean and maximum duration of dry spells) for the annual and summer monsoon period obtained with both datasets agree overall, except for the northernmost part of India. The number of dry days obtained with APHRODITE is larger for this region compared to IMD, which is consistent with the smaller precipitation for the region in APHRODITE. These differences are also visible in the spatial patterns of mean and maximum dry spell durations. Analysis of field significance associated with trends, at the level of 34 predefined meteorological subdivisions over the mainland, suggests better agreement between the two datasets in positive trends associated with number of dry days for the annual and summer monsoon period, for both thresholds. Important differences between the two datasets are noted in the field significance associated with the negative trends. While negative trends in annual maximum duration of dry spells appear field significant for the desert regions according to both datasets, they are found field significant for two regions (Punjab and South Interior Karnataka) for the monsoon period for both datasets. This study, in addition to providing information on the spatial and temporal patterns associated with dry spell characteristics, also allows identification of regions and characteristics where the two datasets agree/disagree.",
            "pmid_url":"http://www.ncbi.nlm.nih.gov/pubmed/?term=",
            "url":"http://dx.doi.org/10.1007/s00382-014-2113-9",
            "volume":"v. 43 ",
            "publication_year":"2014",
            "usda_funded_publication":false,
            "issn":"0930-7575",
            "page":"pp. 3419-3437",
            "author_primary":"L. Sushama",
            "doi":"10.1007/s00382-014-2113-9"},
          {
            "date":"2014-12",
            "nalt_all":["El Nino",
              "La Nina",
              "Landsat",
              "air temperature",
              "altitude",
              "case studies",
              "cold",
              "glaciers",
              "ice",
              "monitoring",
              "remote sensing",
              "snow"],
            "subject":["El Nino",
              "La Nina",
              "Landsat",
              "air temperature",
              "altitude",
              "case studies",
              "cold",
              "glaciers",
              "ice",
              "monitoring",
              "remote sensing",
              "snow",
              "Andes region",
              "Ecuador"],
            "author_lastname":["Veettil",
              "Leandro Bayer Maier",
              "Bremer",
              "de Souza"],
            "last_modified_date":"2015-01-28T23:08:59.156Z",
            "language":["English"],
            "title":"Combined influence of PDO and ENSO on northern Andean glaciers: a case study on the Cotopaxi ice-covered volcano, Ecuador",
            "startpage":"3439",
            "usda_authored_publication":false,
            "id":"1128450",
            "text_availability":"Citation in PubAg",
            "doi_url":"https://doi.org/10.1007/s00382-014-2114-8",
            "issue":"no. 12 ",
            "author":["Bijeesh Kozhikkodan Veettil",
              "Éder Leandro Bayer Maier",
              "Ulisses Franz Bremer",
              "Sergio Florencio de Souza"],
            "format":"text",
            "endpage":"3448",
            "journal_name":"Climate dynamics",
            "abstract":"This paper describes the application of remote sensing in monitoring the fluctuations in one of the mountain glaciers in the Ecuadorean Andes during the past few decades using ASTER, EO-1 ALI, Landsat MSS, TM and ETM + images. Satellite images were used to calculate the snow line altitudes (SLAs) during the period 1979–2013. Cotopaxi ice covered volcano was studied as representative of Ecuadorian glaciers in the eastern cordillera. Precipitation and air temperature data from various gauging stations within the range of 30 km from the study site and monthly discharge and water level data from a gauging station were also utilized in this study. Anomalies in precipitation and temperature were found to be slightly different in the Cotopaxi region compared to nearby Antizana in the same cordillera and Chimborazo region in the western cordillera. An attempt to correlate the El Niño—southern oscillation phenomenon with the glacier fluctuations in Ecuadorian Andes was done successfully. Cold and warm regimes of Pacific Decadal Oscillation is also considered. The calculated glacier fluctuations obtained were similar to that performed on the nearby Antizana 15 in the eastern cordillera during 1995–2002. Precipitation and temperature anomalies were similar with Antizana 15. It is evident from the research that SLAs were highly fluctuated between the period of occurrence of El Niño and La Niña events. It is also seen that the glacier fluctuations show a negative mass balance trend in during the warm regime of Pacific Decadal Oscillation during the past three decades. Glaciated areas were advanced during the La Nina events in the cold regime of PDO during 1998–2002.",
            "pmid_url":"http://www.ncbi.nlm.nih.gov/pubmed/?term=",
            "url":"http://dx.doi.org/10.1007/s00382-014-2114-8",
            "volume":"v. 43 ",
            "publication_year":"2014",
            "usda_funded_publication":false,
            "issn":"0930-7575",
            "page":"pp. 3439-3448",
            "author_primary":"Bijeesh Kozhikkodan Veettil",
            "doi":"10.1007/s00382-014-2114-8"},
          {
            "date":"2014-12",
            "nalt_all":["air temperature",
              "climate models",
              "global warming",
              "greenhouse gas emissions",
              "ice",
              "melting"],
            "subject":["air temperature",
              "climate models",
              "global warming",
              "greenhouse gas emissions",
              "ice",
              "melting"],
            "author_lastname":["Chen",
              "von Storch",
              "Zeng",
              "Du"],
            "last_modified_date":"2015-01-28T23:08:58.967Z",
            "language":["English"],
            "title":"Polar Low genesis over the North Pacific under different global warming scenarios",
            "startpage":"3449",
            "usda_authored_publication":false,
            "id":"1128451",
            "text_availability":"Citation in PubAg",
            "doi_url":"https://doi.org/10.1007/s00382-014-2117-5",
            "issue":"no. 12 ",
            "author":["Fei Chen",
              "Hans von Storch",
              "Lili Zeng",
              "Yan Du"],
            "format":"text",
            "endpage":"3456",
            "journal_name":"Climate dynamics",
            "abstract":"Following an earlier climatological study of North Pacific Polar Lows by employing dynamical downscaling of NCEP1 reanalysis in the regional climate model COSMO-CLM, the characteristics of Polar Low genesis over the North Pacific under different global warming scenarios are investigated. Simulations based on three scenarios from the Special Report on Emissions Scenarios were conducted using a global climate model (ECHAM5) and used to examine systematic changes in the occurrence of Polar Lows over the twenty first century. The results show that with more greenhouse gas emissions, global air temperature would rise, and the frequency of Polar Lows would decrease. With sea ice melting, the distribution of Polar Low genesis shows a northward shift. In the scenarios with stronger warming there is a larger reduction in the number of Polar Lows.",
            "pmid_url":"http://www.ncbi.nlm.nih.gov/pubmed/?term=",
            "url":"http://dx.doi.org/10.1007/s00382-014-2117-5",
            "volume":"v. 43 ",
            "publication_year":"2014",
            "usda_funded_publication":false,
            "issn":"0930-7575",
            "page":"pp. 3449-3456",
            "author_primary":"Fei Chen",
            "doi":"10.1007/s00382-014-2117-5"},
          {
            "date":"2014-12",
            "nalt_all":["Sahel",
              "meteorological data",
              "models",
              "monsoon season",
              "rain",
              "summer"],
            "subject":["Sahel",
              "meteorological data",
              "models",
              "monsoon season",
              "rain",
              "summer",
              "Gulf of Guinea",
              "India"],
            "author_lastname":["Sperber",
              "Annamalai"],
            "last_modified_date":"2015-01-28T23:08:59.515Z",
            "language":["English"],
            "title":"The use of fractional accumulated precipitation for the evaluation of the annual cycle of monsoons",
            "startpage":"3219",
            "usda_authored_publication":false,
            "id":"1128452",
            "text_availability":"Citation in PubAg",
            "doi_url":"https://doi.org/10.1007/s00382-014-2099-3",
            "issue":"no. 12 ",
            "author":["Kenneth R. Sperber",
              "H. Annamalai"],
            "format":"text",
            "endpage":"3244",
            "journal_name":"Climate dynamics",
            "abstract":"Using pentad rainfall data we demonstrate the benefits of using accumulated rainfall and fractional accumulated rainfall for the evaluation of the annual cycle of rainfall over various monsoon domains. Our approach circumvents issues related to using threshold-based analysis techniques for investigating the life-cycle of monsoon rainfall. In the Coupled Model Intercomparison Project-5 models we find systematic errors in the phase of the annual cycle of rainfall. The models are delayed in the onset of summer rainfall over India, the Gulf of Guinea, and the South American Monsoon, with early onset prevalent for the Sahel and the North American Monsoon. This, in combination with the rapid fractional accumulation rate, impacts the ability of the models to simulate the fractional accumulation observed during summer. The rapid fractional accumulation rate and the time at which the accumulation begins are metrics that indicate how well the models concentrate the monsoon rainfall over the peak rainfall season, and the extent to which there is a phase error in the annual cycle. The lack of consistency in the phase error across all domains suggests that a “global” approach to the study of monsoons may not be sufficient to rectify the regional differences. Rather, regional process studies are necessary for diagnosing the underlying causes of the regionally-specific systematic model biases over the different monsoon domains. Despite the afore-mentioned biases, most models simulate well the interannual variability in the date of monsoon onset, the exceptions being models with the most pronounced dry biases. Two methods for estimating monsoon duration are presented, one of which includes nonlinear aspects of the fractional accumulation. The summer fractional accumulation of rainfall provides an objective way to estimate the extent of the monsoon domain, even in models with substantial dry biases for which monsoon is not defined using threshold-based techniques.",
            "pmid_url":"http://www.ncbi.nlm.nih.gov/pubmed/?term=",
            "url":"http://dx.doi.org/10.1007/s00382-014-2099-3",
            "volume":"v. 43 ",
            "publication_year":"2014",
            "usda_funded_publication":false,
            "issn":"0930-7575",
            "page":"pp. 3219-3244",
            "author_primary":"Kenneth R. Sperber",
            "doi":"10.1007/s00382-014-2099-3"},
          {
            "date":"2014-12",
            "nalt_all":["El Nino",
              "climate",
              "cold",
              "mathematical models",
              "stratosphere",
              "time series analysis",
              "troposphere",
              "winter"],
            "subject":["El Nino",
              "climate",
              "cold",
              "mathematical models",
              "stratosphere",
              "time series analysis",
              "troposphere",
              "winter"],
            "author_lastname":["Graf",
              "Zanchettin",
              "Timmreck",
              "Bittner"],
            "last_modified_date":"2015-01-28T23:08:59.327Z",
            "language":["English"],
            "title":"Observational constraints on the tropospheric and near-surface winter signature of the Northern Hemisphere stratospheric polar vortex",
            "startpage":"3245",
            "usda_authored_publication":false,
            "id":"1128453",
            "text_availability":"Citation in PubAg",
            "doi_url":"https://doi.org/10.1007/s00382-014-2101-0",
            "issue":"no. 12 ",
            "author":["Hans-F. Graf",
              "Davide Zanchettin",
              "Claudia Timmreck",
              "Matthias Bittner"],
            "format":"text",
            "endpage":"3266",
            "journal_name":"Climate dynamics",
            "abstract":"A composite analysis of Northern Hemisphere’s mid-winter tropospheric anomalies under the conditions of strong and weak stratospheric polar vortex was performed on NCEP/NCAR reanalysis data from 1948 to 2013 considering, as additional grouping criteria, the coincidental states of major seasonally relevant climate phenomena, such as El Niño-Southern Oscillation (ENSO), Quasi Biennial Oscillation and strong volcanic eruptions. The analysis reveals that samples of strong polar vortex nearly exclusively occur during cold ENSO states, while a weak polar vortex is observed for both cold and warm ENSO. The strongest tropospheric and near-surface anomalies are found for warm ENSO and weak polar vortex conditions, suggesting that internal tropospheric circulation anomalies related to warm ENSO constructively superpose on dynamical effects from the stratosphere. Additionally, substantial differences are found between the continental winter warming patterns under strong polar vortex conditions in volcanically-disturbed and volcanically-undisturbed winters. However, the small-size samples obtained from the multi-compositing prevent conclusive statements about typical patterns, dominating effects and mechanisms of stratosphere-troposphere interaction on the seasonal time scale based on observational/reanalysis data alone. Hence, our analysis demonstrates that patterns derived from observational/reanalysis time series need to be taken with caution as they not always provide sufficiently robust constraints to the inferred mechanisms implicated with stratospheric polar vortex variability and its tropospheric and near-surface signature. Notwithstanding this argument, we propose a limited set of mechanisms that together may explain a relevant part of observed climate variability. These may serve to define future numerical model experiments minimizing the sample biases and, thus, improving process understanding.",
            "pmid_url":"http://www.ncbi.nlm.nih.gov/pubmed/?term=",
            "url":"http://dx.doi.org/10.1007/s00382-014-2101-0",
            "volume":"v. 43 ",
            "publication_year":"2014",
            "usda_funded_publication":false,
            "issn":"0930-7575",
            "page":"pp. 3245-3266",
            "author_primary":"Hans-F. Graf",
            "doi":"10.1007/s00382-014-2101-0"},
          {
            "date":"2014-12",
            "nalt_all":["air temperature",
              "cold",
              "global warming",
              "latitude",
              "topography",
              "troposphere",
              "wind direction"],
            "subject":["air temperature",
              "cold",
              "global warming",
              "latitude",
              "topography",
              "troposphere",
              "wind direction",
              "Europe"],
            "author_lastname":["He",
              "Huang",
              "Ji"],
            "last_modified_date":"2015-01-28T23:08:59.699Z",
            "language":["English"],
            "title":"Impact of land–sea thermal contrast on interdecadal variation in circulation and blocking",
            "startpage":"3267",
            "usda_authored_publication":false,
            "id":"1128454",
            "text_availability":"Citation in PubAg",
            "doi_url":"https://doi.org/10.1007/s00382-014-2103-y",
            "issue":"no. 12 ",
            "author":["Yongli He",
              "Jianping Huang",
              "Mingxia Ji"],
            "format":"text",
            "endpage":"3279",
            "journal_name":"Climate dynamics",
            "abstract":"The impact of asymmetric thermal forcing associated with land–sea distribution on interdecadal variation in large-scale circulation and blocking was investigated using observations and the coupled model intercomparison project outputs. A land–sea index (LSI) was defined to measure asymmetric zonal thermal forcing; the index changed from a negative to a positive anomaly in the 1980s. In the positive phase of the LSI, the 500 hPa geopotential height decreased in the polar regions and increased in the mid-latitudes. The tropospheric planetary wave activity also became weaker and exerted less easterly forcing on the westerly wind. These circulation changes were favorable for westerly wind acceleration and reduced blocking. In the Atlantic, the duration of blocking decreased by 38 % during the positive LSI phase compared with that during the negative phase; in Europe, the number of blocking persisting for longer than 10 days during the positive LSI phase was only half of the number during the negative phase. The observed surface air temperature anomaly followed a distinctive “cold ocean/warm land” (COWL) pattern, which provided an environment that reduced, or destroyed, the resonance forcing of topography and was unfavorable for the development and persistence of blocking. In turn, the responses of the westerly and blocking could further enhance continental warming, which would strengthen the “cold ocean/warm land” pattern. This positive feedback amplified regional warming in the context of overall global warming.",
            "pmid_url":"http://www.ncbi.nlm.nih.gov/pubmed/?term=",
            "url":"http://dx.doi.org/10.1007/s00382-014-2103-y",
            "volume":"v. 43 ",
            "publication_year":"2014",
            "usda_funded_publication":false,
            "issn":"0930-7575",
            "page":"pp. 3267-3279",
            "author_primary":"Yongli He",
            "doi":"10.1007/s00382-014-2103-y"},
          {
            "date":"2014-12",
            "nalt_all":["Cedrus libani subsp. brevifolia",
              "Pinus brutia",
              "Pinus nigra",
              "drought",
              "forest resources",
              "greenhouse gases",
              "growth rings",
              "time series analysis",
              "trees",
              "warm season",
              "water stress"],
            "subject":["Cedrus libani subsp. brevifolia",
              "Pinus brutia",
              "Pinus nigra",
              "drought",
              "forest resources",
              "greenhouse gases",
              "growth rings",
              "time series analysis",
              "trees",
              "warm season",
              "water stress",
              "Cyprus",
              "Northern Africa"],
            "author_lastname":["Touchan",
              "Christou",
              "Meko"],
            "last_modified_date":"2015-01-28T23:09:00.103Z",
            "language":["English"],
            "title":"Six centuries of May–July precipitation in Cyprus from tree rings",
            "startpage":"3281",
            "usda_authored_publication":false,
            "id":"1128455",
            "text_availability":"Citation in PubAg",
            "doi_url":"https://doi.org/10.1007/s00382-014-2104-x",
            "issue":"no. 12 ",
            "author":["Ramzi Touchan",
              "Andreas K. Christou",
              "David M. Meko"],
            "format":"text",
            "endpage":"3292",
            "journal_name":"Climate dynamics",
            "abstract":"A May–July precipitation nested reconstruction for the period AD 1415–2010 was developed from multi-century tree-ring records of Pinus nigra, Pinus brutia, and Cedrus brevifolia for Cyprus. Calibration and verification statistics for the period 1917–2010 show a good level of skill, and split-sample validation over 1917–2010 supports temporal stability of the tree-ring signal for precipitation. Smoothed annual time series of reconstructed precipitation and a tally of drought events in a moving time window indicate that the calibration period is not representative of the full range of drought variability. While convective precipitation in the warm season may be driven strongly by local factors, composite maps of geopotential height anomaly for dry years and wet years support large-scale atmospheric-flow influence related to height anomalies over the broader region of northeast Africa and the eastern Mediterranean. Emerging positive trend in reconstruction residuals may be an early sign of exacerbation of drought stress on trees by recent warming in May–July. Future warming expected from increases in greenhouse gases poses a threat to forest resources in Cyprus and elsewhere in the Mediterranean.",
            "pmid_url":"http://www.ncbi.nlm.nih.gov/pubmed/?term=",
            "url":"http://dx.doi.org/10.1007/s00382-014-2104-x",
            "volume":"v. 43 ",
            "publication_year":"2014",
            "usda_funded_publication":false,
            "issn":"0930-7575",
            "page":"pp. 3281-3292",
            "author_primary":"Ramzi Touchan",
            "doi":"10.1007/s00382-014-2104-x"},
          {
            "date":"2014-12",
            "nalt_all":["General Circulation Models",
              "La Nina",
              "atmospheric circulation",
              "climatic factors",
              "global warming",
              "rain",
              "surface water temperature"],
            "subject":["General Circulation Models",
              "La Nina",
              "atmospheric circulation",
              "climatic factors",
              "global warming",
              "rain",
              "surface water temperature"],
            "author_lastname":["Chung",
              "Power"],
            "last_modified_date":"2015-07-31T13:17:37.258Z",
            "language":["English"],
            "title":"Precipitation response to La Niña and global warming in the Indo-Pacific",
            "startpage":"3293",
            "usda_authored_publication":false,
            "id":"1128456",
            "text_availability":"Citation in PubAg",
            "doi_url":"https://doi.org/10.1007/s00382-014-2105-9",
            "issue":"no. 12 ",
            "author":["Christine T. Y. Chung",
              "Scott B. Power"],
            "format":"text",
            "endpage":"3307",
            "journal_name":"Climate dynamics",
            "abstract":"Recent studies have highlighted the nonlinear rainfall response to El Niño sea surface temperature (SST) events in the Indo-Pacific region and how this response might change over coming decades. Here we investigate the response to La Niña SST anomalies with and without global warming by performing idealised SST-forced experiments with an atmospheric general circulation model. The La Niña SST anomaly is multiplied by a factor 2 a 4 and added to climatological SSTs. Similar experiments using El Niño SST anomalies were previously performed, in which large nonlinearities in the precipitation response were evident. We find that: (i) Under current climatic conditions, as 1≤a≤4 increases, the precipitation responds in three ways: the intertropical convergence zone (ITCZ) dries and moves poleward, the maximum precipitation along the equator moves west, and the South Pacific convergence zone (SPCZ) narrows, intensifies, and elongates. For weak (α=1) La Niña events, the precipitation anomalies approximately mirror those from the El Niño events along the ITCZ and SPCZ, though there are some marked differences in the central-eastern Pacific. For stronger La Niña events (α>1]), precipitation responds nonlinearly to SST anomalies, though the nonlinearities are smaller and differ spatially from the nonlinearities in the El Niño runs. (ii) The addition of a global warming SST pattern increases rainfall in the western Pacific and SPCZ, enhances the narrowing of the SPCZ, and increases the nonlinear response in the western Pacific. However, large La Niña events reduce the impact of global warming along the central-eastern equatorial Pacific as the global warming and La Niña SST anomalies have opposite signs in that region. (iii) The response to La Niña SST anomalies is driven primarily by changes in the atmospheric circulation, whereas the response to the global warming SST pattern is mainly driven by increases in atmospheric moisture. (iv) Large changes in La Niña-driven rainfall anomalies can occur in response to global warming, even if the La Nina SST anomalies relative to the warmer background state are completely unchanged.",
            "pmid_url":"http://www.ncbi.nlm.nih.gov/pubmed/?term=",
            "url":"http://dx.doi.org/10.1007/s00382-014-2105-9",
            "volume":"v. 43 ",
            "publication_year":"2014",
            "usda_funded_publication":false,
            "issn":"0930-7575",
            "page":"pp. 3293-3307",
            "author_primary":"Christine T. Y. Chung",
            "doi":"10.1007/s00382-014-2105-9"},
          {
            "date":"2014-12",
            "nalt_all":["drought",
              "drying",
              "plateaus",
              "rain",
              "sea level",
              "spring",
              "subsidence",
              "summer",
              "topography",
              "uncertainty",
              "wind"],
            "subject":["drought",
              "drying",
              "plateaus",
              "rain",
              "sea level",
              "spring",
              "subsidence",
              "summer",
              "topography",
              "uncertainty",
              "wind",
              "Mexico"],
            "author_lastname":["Bhattacharya",
              "Chiang"],
            "last_modified_date":"2015-01-28T23:09:00.596Z",
            "language":["English"],
            "title":"Spatial variability and mechanisms underlying El Niño-induced droughts in Mexico",
            "startpage":"3309",
            "usda_authored_publication":false,
            "id":"1128457",
            "text_availability":"Citation in PubAg",
            "doi_url":"https://doi.org/10.1007/s00382-014-2106-8",
            "issue":"no. 12 ",
            "author":["Tripti Bhattacharya",
              "John C. H. Chiang"],
            "format":"text",
            "endpage":"3326",
            "journal_name":"Climate dynamics",
            "abstract":"The El Niño Southern Oscillation plays a key role in modulating interannual rainfall variability in Mexico. While El Niño events are linked to drought in Mexico, uncertainty exists about the spatial pattern and causal mechanisms behind El Niño-induced drought. We use lead/lag correlation analysis of rainfall station data to identify the spatial pattern of drought associated with the summer before, and the spring following, the peak of warm SST anomalies in the eastern equatorial Pacific. We also use atmospheric fields from the North American Regional Reanalysis to calculate the anomalous moisture budget and diagnose the mechanisms associated with El Niño-induced drought in Mexico. We find that reduced rainfall occurs in Mexico in both the summer before and the spring after a peak El Niño event, especially in regions of climatologically strong convection. The teleconnection in the developing phase of El Niño is primarily driven by changes in subsidence resulting from anomalous convection in the equatorial Pacific. The causes of drought during the decaying phase of El Niño events are varied: in some years, descent anomalies dominate other moisture budget terms, while in other years, drying of the boundary layer on the Mexican plateau is important. We suggest that the latter may result from the interaction of weakened southeasterly winds in the Intra-Americas Sea with high topography along the Atlantic coast of Mexico. Weakened winds are likely driven by a reduced sea level pressure gradient between the Atlantic and the Pacific. Changes in easterly wave activity may contribute to drought in the developing phase of El Niño, but may be less important in the decaying phase of El Niño.",
            "pmid_url":"http://www.ncbi.nlm.nih.gov/pubmed/?term=",
            "url":"http://dx.doi.org/10.1007/s00382-014-2106-8",
            "volume":"v. 43 ",
            "publication_year":"2014",
            "usda_funded_publication":false,
            "issn":"0930-7575",
            "page":"pp. 3309-3326",
            "author_primary":"Tripti Bhattacharya",
            "doi":"10.1007/s00382-014-2106-8"},
          {
            "date":"2014-12",
            "nalt_all":["El Nino",
              "surface water temperature",
              "sea level",
              "variance",
              "methodology",
              "time series analysis",
              "climate models",
              "climate",
              "prediction"],
            "subject":["El Nino",
              "surface water temperature",
              "sea level",
              "variance",
              "methodology",
              "time series analysis",
              "climate models",
              "climate",
              "prediction"],
            "author_lastname":["Gehne",
              "Kleeman",
              "Trenberth"],
            "last_modified_date":"2019-12-04T17:11:30.465Z",
            "language":["English"],
            "title":"Irregularity and decadal variation in ENSO: a simplified model based on Principal Oscillation Patterns",
            "startpage":"3327",
            "usda_authored_publication":false,
            "id":"1128458",
            "text_availability":"Citation in PubAg",
            "doi_url":"https://doi.org/10.1007/s00382-014-2108-6",
            "issue":"no. 12 ",
            "author":["Maria Gehne",
              "Richard Kleeman",
              "Kevin E. Trenberth"],
            "format":"text",
            "endpage":"3350",
            "journal_name":"Climate dynamics",
            "abstract":"A new method of estimating the decay time, mean period and forcing statistics of El Niño-Southern Oscillation (ENSO) has been found. It uses a two-dimensional stochastically forced damped linear oscillator model with the model parameters estimated from a Principal Oscillation Pattern (POP) analysis and associated observed power spectra. It makes use of extended observational time series of 150 years of sea surface temperature (SST) and sea level pressure (SLP) as well as climate model output. This approach is motivated by clear physical relationships that SST and SLP POP patterns have to the ENSO cycle, as well as to each other, indicating that they represent actual physical modes of the climate system. Moreover, the leading POP mode accounts for 20–50 % of the variance on interannual time scales. The POP real part is highly correlated with several Niño indices near zero lag while the imaginary part exhibits a 6–9 month lead time and thus is a precursor. The observed POP power spectra show markedly different behavior for the peak and precursor, the former having more power at ENSO frequencies and the latter dominating at low frequencies. The results realistically suggest a period of oscillation of 4–6 years and a decay time of 8 months, which corresponds to the practical ENSO prediction limit. A fundamental finding of this approach is that the difference between the observed peak and precursor spectra at low frequencies can be related to the forcing statistics using the simple model, as well as to the difference between patterns of decadal and interannual variability in the Pacific.",
            "pmid_url":"http://www.ncbi.nlm.nih.gov/pubmed/?term=",
            "url":"http://dx.doi.org/10.1007/s00382-014-2108-6",
            "volume":"v. 43 ",
            "publication_year":"2014",
            "usda_funded_publication":false,
            "issn":"0930-7575",
            "page":"pp. 3327-3350",
            "author_primary":"Maria Gehne",
            "doi":"10.1007/s00382-014-2108-6"},
          {
            "date":"2014-12",
            "nalt_all":["General Circulation Models",
              "climate",
              "heat",
              "hurricanes",
              "wind"],
            "subject":["General Circulation Models",
              "climate",
              "heat",
              "hurricanes",
              "wind",
              "South China Sea"],
            "author_lastname":["Wang",
              "Wang",
              "Han",
              "Li",
              "Wu"],
            "last_modified_date":"2015-01-28T23:09:00.790Z",
            "language":["English"],
            "title":"Effects of tropical cyclones on large-scale circulation and ocean heat transport in the South China Sea",
            "startpage":"3351",
            "usda_authored_publication":false,
            "id":"1128459",
            "text_availability":"Citation in PubAg",
            "doi_url":"https://doi.org/10.1007/s00382-014-2109-5",
            "issue":"no. 12 ",
            "author":["Xidong Wang",
              "Chunzai Wang",
              "Guijun Han",
              "Wei Li",
              "Xinrong Wu"],
            "format":"text",
            "endpage":"3366",
            "journal_name":"Climate dynamics",
            "abstract":"In this study, we investigate the influence of tropical cyclones (TCs) on large-scale circulation and ocean heat transport in the South China Sea (SCS) by using an ocean general circulation model at a 1/8° resolution during 2000–2008. The model uses a data assimilation system to assimilate observations in order to improve the representation of SCS circulation. The results reveal an unexpected deep SCS circulation anomaly induced by TCs, which suggests that effects of TC can penetrate deeper into the ocean. This deep effect may result from the near inertial oscillations excited by TCs. The inertial oscillations can propagate downward to the oceanic interior. The analyses confirm that TCs have two effects on ocean heat transport of the SCS. Firstly, the wind stress curl induced by TCs affects the structure of SCS circulation, and then changes heat transport. Secondly, TCs pump surface heat downward to the thermocline, increasing the heat injection from the atmosphere to the ocean. Two effects together amplify the outflow of the surface heat southward away the SCS through the Mindoro and Karimata Straits. The TC-induced heat transports through the Mindoro, Balabac and Karimata Straits account for 20 % of the total heat transport through three straits. An implication of this study is that ocean models need to simulate the TC effect on heat transport in order to correctly evaluate the role of the SCS through flow in regulating upper ocean circulation and climate in the Indonesian maritime continent and its adjacent regions.",
            "pmid_url":"http://www.ncbi.nlm.nih.gov/pubmed/?term=",
            "url":"http://dx.doi.org/10.1007/s00382-014-2109-5",
            "volume":"v. 43 ",
            "publication_year":"2014",
            "usda_funded_publication":false,
            "issn":"0930-7575",
            "page":"pp. 3351-3366",
            "author_primary":"Xidong Wang",
            "doi":"10.1007/s00382-014-2109-5"},
          {
            "date":"2014-12",
            "nalt_all":["models",
              "tropics",
              "wind"],
            "subject":["models",
              "tropics",
              "wind",
              "Angola",
              "Atlantic Ocean"],
            "author_lastname":["Toniazzo",
              "Woolnough"],
            "last_modified_date":"2015-01-28T23:09:01.294Z",
            "language":["English"],
            "title":"Development of warm SST errors in the southern tropical Atlantic in CMIP5 decadal hindcasts",
            "startpage":"2889",
            "usda_authored_publication":false,
            "id":"1142583",
            "text_availability":"Citation in PubAg",
            "doi_url":"https://doi.org/10.1007/s00382-013-1691-2",
            "issue":"no. 11 ",
            "author":["Thomas Toniazzo",
              "Steve Woolnough"],
            "format":"text",
            "endpage":"2913",
            "journal_name":"Climate dynamics",
            "abstract":"SST errors in the tropical Atlantic are large and systematic in current coupled general-circulation models. We analyse the growth of these errors in the region of the south-eastern tropical Atlantic in initialised decadal hindcasts integrations for three of the models participating in the Coupled Model Inter-comparison Project 5. A variety of causes for the initial bias development are identified, but a crucial involvement is found, in all cases considered, of ocean-atmosphere coupling for their maintenance. These involve an oceanic “bridge” between the Equator and the Benguela-Angola coastal seas which communicates sub-surface ocean anomalies and constitutes a coupling between SSTs in the south-eastern tropical Atlantic and the winds over the Equator. The resulting coupling between SSTs, winds and precipitation represents a positive feedback for warm SST errors in the south-eastern tropical Atlantic.",
            "pmid_url":"http://www.ncbi.nlm.nih.gov/pubmed/?term=",
            "url":"http://dx.doi.org/10.1007/s00382-013-1691-2",
            "volume":"v. 43 ",
            "publication_year":"2014",
            "usda_funded_publication":false,
            "issn":"0930-7575",
            "page":"pp. 2889-2913",
            "author_primary":"Thomas Toniazzo",
            "doi":"10.1007/s00382-013-1691-2"},
          {
            "date":"2014-12",
            "nalt_all":["data collection",
              "heat transfer",
              "hydrologic cycle",
              "surface water temperature",
              "trade winds",
              "tropics"],
            "subject":["data collection",
              "heat transfer",
              "hydrologic cycle",
              "surface water temperature",
              "trade winds",
              "tropics"],
            "author_lastname":["Servain",
              "Caniaux",
              "Kouadio",
              "McPhaden",
              "Araujo"],
            "last_modified_date":"2015-01-28T23:09:00.996Z",
            "language":["English"],
            "title":"Recent climatic trends in the tropical Atlantic",
            "startpage":"3071",
            "usda_authored_publication":false,
            "id":"1142584",
            "text_availability":"Citation in PubAg",
            "doi_url":"https://doi.org/10.1007/s00382-014-2168-7",
            "issue":"no. 11 ",
            "author":["Jacques Servain",
              "Guy Caniaux",
              "Yves K. Kouadio",
              "Michael J. McPhaden",
              "Moacyr Araujo"],
            "format":"text",
            "endpage":"3089",
            "journal_name":"Climate dynamics",
            "abstract":"A homogeneous monthly data set of sea surface temperature (SST) and pseudo wind stress based on in situ observations is used to investigate the climatic trends over the tropical Atlantic during the last five decades (1964–2012). After a decrease of SST by about 1 °C during 1964–1975, most apparent in the northern tropical region, the entire tropical basin warmed up. That warming was the most substantial (>1 °C) in the eastern tropical ocean and in the longitudinal band of the intertropical convergence zone. Surprisingly, the trade wind system also strengthened over the peirod 1964–2012. Complementary information extracted from other observational data sources confirms the simultaneity of SST warming and the strengthening of the surface winds. Examining data sets of surface heat flux during the last few decades for the same region, we find that the SST warming was not a consequence of atmospheric heat flux forcing. Conversely, we suggest that long-term SST warming drives changes in atmosphere parameters at the sea surface, most notably an increase in latent heat flux, and that an acceleration of the hydrological cycle induces a strengthening of the trade winds and an acceleration of the Hadley circulation. These trends are also accompanied by rising sea levels and upper ocean heat content over similar multi-decadal time scales in the tropical Atlantic. Though more work is needed to fully understand these long term trends, especially what happens from the mid-1970’s, it is likely that changes in ocean circulation involving some combination of the Atlantic meridional overtuning circulation and the subtropical cells are required to explain the observations.",
            "pmid_url":"http://www.ncbi.nlm.nih.gov/pubmed/?term=",
            "url":"http://dx.doi.org/10.1007/s00382-014-2168-7",
            "volume":"v. 43 ",
            "publication_year":"2014",
            "usda_funded_publication":false,
            "issn":"0930-7575",
            "page":"pp. 3071-3089",
            "author_primary":"Jacques Servain",
            "doi":"10.1007/s00382-014-2168-7"},
          {
            "date":"2014-12",
            "nalt_all":["General Circulation Models",
              "momentum",
              "spring",
              "surface water temperature",
              "troposphere",
              "wind"],
            "subject":["General Circulation Models",
              "momentum",
              "spring",
              "surface water temperature",
              "troposphere",
              "wind",
              "South America"],
            "author_lastname":["Richter",
              "Behera",
              "Doi",
              "Taguchi",
              "Masumoto",
              "Xie"],
            "last_modified_date":"2015-01-28T23:09:01.658Z",
            "language":["English"],
            "title":"What controls equatorial Atlantic winds in boreal spring?",
            "startpage":"3091",
            "usda_authored_publication":false,
            "id":"1142585",
            "text_availability":"Citation in PubAg",
            "doi_url":"https://doi.org/10.1007/s00382-014-2170-0",
            "issue":"no. 11 ",
            "author":["Ingo Richter",
              "Swadhin K. Behera",
              "Takeshi Doi",
              "Bunmei Taguchi",
              "Yukio Masumoto",
              "Shang-Ping Xie"],
            "format":"text",
            "endpage":"3104",
            "journal_name":"Climate dynamics",
            "abstract":"The factors controlling equatorial Atlantic winds in boreal spring are examined using both observations and general circulation model (GCM) simulations from the coupled model intercomparison phase 5. The results show that the prevailing surface easterlies flow against the attendant pressure gradient and must therefore be maintained by other terms in the momentum budget. An important contribution comes from meridional advection of zonal momentum but the dominant contribution is the vertical transport of zonal momentum from the free troposphere to the surface. This implies that surface winds are strongly influenced by conditions in the free troposphere, chiefly pressure gradients and, to a lesser extent, meridional advection. Both factors are linked to the patterns of deep convection. Applying these findings to GCM errors indicates, that, consistent with the results of previous studies, the persistent westerly surface wind bias found in most GCMs is due mostly to precipitation errors, in particular excessive precipitation south of the equator over the ocean and deficient precipitation over equatorial South America. Free tropospheric influences also dominate the interannual variability of surface winds in boreal spring. GCM experiments with prescribed climatological sea-surface temperatures (SSTs) indicate that the free tropospheric influences are mostly associated with internal atmospheric variability. Since the surface wind anomalies in boreal spring are crucial to the development of warm SST events (Atlantic Niños), the results imply that interannual variability in the region may rely far less on coupled air–sea feedbacks than is the case in the tropical Pacific.",
            "pmid_url":"http://www.ncbi.nlm.nih.gov/pubmed/?term=",
            "url":"http://dx.doi.org/10.1007/s00382-014-2170-0",
            "volume":"v. 43 ",
            "publication_year":"2014",
            "usda_funded_publication":false,
            "issn":"0930-7575",
            "page":"pp. 3091-3104",
            "author_primary":"Ingo Richter",
            "doi":"10.1007/s00382-014-2170-0"},
          {
            "date":"2014-12",
            "nalt_all":["coastal water",
              "eddy covariance",
              "evaporation",
              "freshwater",
              "mathematical models",
              "mixing",
              "rivers",
              "salinity",
              "seasonal variation",
              "trade winds"],
            "subject":["coastal water",
              "eddy covariance",
              "evaporation",
              "freshwater",
              "mathematical models",
              "mixing",
              "rivers",
              "salinity",
              "seasonal variation",
              "trade winds",
              "Africa",
              "Gulf of Guinea"],
            "author_lastname":["Berger",
              "Treguier",
              "Perenne",
              "Talandier"],
            "last_modified_date":"2015-01-28T23:09:01.489Z",
            "language":["English"],
            "title":"Dynamical contribution to sea surface salinity variations in the eastern Gulf of Guinea based on numerical modelling",
            "startpage":"3105",
            "usda_authored_publication":false,
            "id":"1142586",
            "text_availability":"Citation in PubAg",
            "doi_url":"https://doi.org/10.1007/s00382-014-2195-4",
            "issue":"no. 11 ",
            "author":["Henrick Berger",
              "Anne Marie Treguier",
              "Nicolas Perenne",
              "Claude Talandier"],
            "format":"text",
            "endpage":"3122",
            "journal_name":"Climate dynamics",
            "abstract":"In this study, we analyse the seasonal variability of the sea surface salinity (SSS) for two coastal regions of the Gulf of Guinea from 1995 to 2006 using a high resolution model (1/12°) embedded in a Tropical Atlantic (1/4°) model. Compared with observations and climatologies, our model demonstrates a good capability to reproduce the seasonal and spatial variations of the SSS and mixed layer depth. Sensitivity experiments are carried out to assess the respective impacts of precipitations and river discharge on the spatial structure and seasonal variations of the SSS in the eastern part of the Gulf of Guinea. In the Bight of Biafra, both precipitations and river runoffs are necessary to observe permanent low SSS values but the river discharge has the strongest impact on the seasonal variations of the SSS. South of the equator, the Congo river discharge alone is sufficient to explain most of the SSS structure and its seasonal variability. However, mixed layer budgets for salinity reveal the necessity to take into account the horizontal and vertical dynamics to explain the seasonal evolution of the salinity in the mixed layer. Indeed evaporation, precipitations and runoffs represent a relatively small contribution to the budgets locally at intraseasonal to seasonal time scales. Horizontal advection always contribute to spread the low salinity coastal waters offshore and thus decrease the salinity in the eastern Gulf of Guinea. For the Bight of Biafra and the Congo plume region, the strong seasonal increase of the SSS observed from May/June to August/September, when the trade winds intensify, results from a decreasing offshore spread of freshwater associated with an intensification of the salt input from the subsurface. In the Congo plume region, the subsurface salt comes mainly from advection due to a strong upwelling but for the Bight of Biafra, entrainment and vertical mixing also play a role. The seasonal evolution of horizontal advection in the Bight of Biafra is mainly driven by eddy correlations between salinity and velocities, but it is not the case in the Congo plume.",
            "pmid_url":"http://www.ncbi.nlm.nih.gov/pubmed/?term=",
            "url":"http://dx.doi.org/10.1007/s00382-014-2195-4",
            "volume":"v. 43 ",
            "publication_year":"2014",
            "usda_funded_publication":false,
            "issn":"0930-7575",
            "page":"pp. 3105-3122",
            "author_primary":"Henrick Berger",
            "doi":"10.1007/s00382-014-2195-4"},
          {
            "date":"2014-12",
            "nalt_all":["climate models",
              "heat transfer",
              "latitude",
              "simulation models",
              "surface water temperature",
              "tropics",
              "wind"],
            "subject":["climate models",
              "heat transfer",
              "latitude",
              "simulation models",
              "surface water temperature",
              "tropics",
              "wind"],
            "author_lastname":["Xu",
              "Chang",
              "Richter",
              "Kim",
              "Tang"],
            "last_modified_date":"2015-01-28T23:09:01.896Z",
            "language":["English"],
            "title":"Diagnosing southeast tropical Atlantic SST and ocean circulation biases in the CMIP5 ensemble",
            "startpage":"3123",
            "usda_authored_publication":false,
            "id":"1142587",
            "text_availability":"Citation in PubAg",
            "doi_url":"https://doi.org/10.1007/s00382-014-2247-9",
            "issue":"no. 11 ",
            "author":["Zhao Xu",
              "Ping Chang",
              "Ingo Richter",
              "Who Kim",
              "Guanglin Tang"],
            "format":"text",
            "endpage":"3145",
            "journal_name":"Climate dynamics",
            "abstract":"Warm sea-surface temperature (SST) biases in the southeastern tropical Atlantic (SETA), which is defined by a region from 5°E to the west coast of southern Africa and from 10°S to 30°S, are a common problem in many current and previous generation climate models. The Coupled Model Intercomparison Project Phase 5 (CMIP5) ensemble provides a useful framework to tackle the complex issues concerning causes of the SST bias. In this study, we tested a number of previously proposed mechanisms responsible for the SETA SST bias and found the following results. First, the multi-model ensemble mean shows a positive shortwave radiation bias of ~20 W m⁻², consistent with models’ deficiency in simulating low-level clouds. This shortwave radiation error, however, is overwhelmed by larger errors in the simulated surface turbulent heat and longwave radiation fluxes, resulting in excessive heat loss from the ocean. The result holds for atmosphere-only model simulations from the same multi-model ensemble, where the effect of SST biases on surface heat fluxes is removed, and is not sensitive to whether the analysis region is chosen to coincide with the maximum warm SST bias along the coast or with the main SETA stratocumulus deck away from the coast. This combined with the fact that there is no statistically significant relationship between simulated SST biases and surface heat flux biases among CMIP5 models suggests that the shortwave radiation bias caused by poorly simulated low-level clouds is not the leading cause of the warm SST bias. Second, the majority of CMIP5 models underestimate upwelling strength along the Benguela coast, which is linked to the unrealistically weak alongshore wind stress simulated by the models. However, a correlation analysis between the model simulated vertical velocities and SST biases does not reveal a statistically significant relationship between the two, suggesting that the deficient coastal upwelling in the models is not simply related to the warm SST bias via vertical heat advection. Third, SETA SST biases in CMIP5 models are correlated with surface and subsurface ocean temperature biases in the equatorial region, suggesting that the equatorial temperature bias remotely contributes to the SETA SST bias. Finally, we found that all CMIP5 models simulate a southward displaced Angola–Benguela front (ABF), which in many models is more than 10° south of its observed location. Furthermore, SETA SST biases are most significantly correlated with ABF latitude, which suggests that the inability of CMIP5 models to accurately simulate the ABF is a leading cause of the SETA SST bias. This is supported by simulations with the oceanic component of one of the CMIP5 models, which is forced with observationally derived surface fluxes. The results show that even with the observationally derived surface atmospheric forcing, the ocean model generates a significant warm SST bias near the ABF, underlining the important role of ocean dynamics in SETA SST bias problem. Further model simulations were conducted to address the impact of the SETA SST biases. The results indicate a significant remote influence of the SETA SST bias on global model simulations of tropical climate, underscoring the importance and urgency to reduce the SETA SST bias in global climate models.",
            "pmid_url":"http://www.ncbi.nlm.nih.gov/pubmed/?term=",
            "url":"http://dx.doi.org/10.1007/s00382-014-2247-9",
            "volume":"v. 43 ",
            "publication_year":"2014",
            "usda_funded_publication":false,
            "issn":"0930-7575",
            "page":"pp. 3123-3145",
            "author_primary":"Zhao Xu",
            "doi":"10.1007/s00382-014-2247-9"}]
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