Modeling the Summertime Climate of Southwest Asia: The Role of Land Surface Processes in Shaping the Climate of Semiarid Regions
Title :
Modeling the Summertime Climate of Southwest Asia: The Role of Land Surface Processes in Shaping the Climate of Semiarid Regions
https://dspace.mit.edu/bitstream/handle/1721.1/72524/Marcella-2012-Modeling%20the%20Summert.pdf?sequence=2&isAllowed=yPresented is a study on the role of land surface processes in determining the summertime climate over thensemiarid region of southwest Asia. In this region, a warm surface air temperature bias of 3.58C is simulated innthe summer by using the standard configuration of Regional Climate Model version 3 (RegCM3). Biases arenalso simulated in surface albedo (underestimation), shortwave incident radiation (overestimation), and vapornpressure (underestimation). Based on satellite measurements documented in NASA’s surface radiationnbudget (SRB) dataset, a correction in surface albedo by 4% is introduced in RegCM3 to match the observednSRB data. Increasing albedo values results in a nearly 18C cooling over the region. In addition, by incorporatingnRegCM3’s dust module and including subgrid variability for surface wind, shortwave incidentnradiation bias originally of about 45 W m22 is reduced by 30 W m22. As a result, the reduction of shortwavenincident radiation cools the surface by 0.68C. Finally, including a representation for the irrigation andnmarshlands of Mesopotamia produces surface relative humidity values closer to observations, thus eliminatingna nearly 5-mb vapor pressure dry bias over some of the region. Consequently, the representation ofnirrigation and marshlands results in cooling of nearly 18C in areas downwind of the actual land-cover change.nAlong with identified biases in observational datasets, these combined processes explain the 3.58C warm biasnin RegCM3 simulations. Therefore, it is found that accurate representations of surface albedo, dust emissions,nand irrigation are important in correctly modeling summertime climates of semiarid regions.