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Importance of the resolution of surface topography vis-à-vis atmospheric and surface processes in the simulation of the climate of Himalaya-Tibet highland

Jain, Shipra, Mishra, Saroj K., Salunke, Popat, Sahany, Sandeep
Climate dynamics 2019 v.52 no.7-8 pp. 4735-4748
air temperature, climate, climate models, landscapes, probability distribution, seasonal variation, topography, troposphere
As Himalaya-Tibet Highland (HTH), a spatially extensive and complex terrain, plays influential roles in the regional and global climate, its representation in climate models is a decisive factor in climate simulations. It is established that higher spatial resolution improves the simulation of several seasonal mean features over this region, but how much improvement comes from the better representation of surface topography and how much comes from the better modeling of the atmospheric and surface processes are still not clear. To understand this, three sets of 6-member ensemble simulations are conducted using the NCAR Community Atmosphere Model version 5.1 (CAM5.1) at: (1) 1.9° × 2.5° resolution (Coarse), (2) 0.47° × 0.63° resolution (Fine), and (3) topography is prescribed at the Coarse resolution and rest of the model processes are computed at the Fine resolution (Hybrid). The Coarse resolution overlooks most of the intricate features of the topography with a severe bias of ~ 1–2 km but Fine resolution does a much better job in their representations. Surface air temperatures are found to be strongly dependent on the resolution of topography and therefore it is desirable to resolve topography in models for the realistic simulation and projection of temperatures. Rest of the variables, viz. seasonal mean, seasonal cycle and probability distribution of precipitation; tropospheric temperature and moisture; Tibetan anticyclone, show remarkable improvements with the increase in resolution of the atmospheric and surface processes. Influence of the resolution of topography is found to be limited to the model levels adjacent to the surface, and for higher model levels, the resolution of the atmospheric and surface processes is noted to play a more crucial role.