Atmosphere-cryosphere coupled model development and its application for regional climate studies

Presence of snow strongly affects the surface energy budget in mid-to-high latitudes during the transition period of winter to spring. Snow's high albedo dramatically reduces the amount of shortwave radiative energy available at the surface, and its low thermal conductivity significantly restricts exchanges of heat between soil and the atmosphere. Synoptic waves propagating over the Northern Plains are a major source of snow storms and flash flooding during this period. The presence of snow and its melt from winter to spring affects the propagation of synoptic waves and the amount of precipitation over this region. Here we investigate the effect of snow cover, soil frost, and snowmelt on the atmosphere over cold land and implements a multi-layer Soil-Snow-Vegetation Model (SSVM) coupled to an atmospheric Purdue Regional Model (PRM). We have applied a one-dimensional, multi-layer land surface model based on the conservations of heat and water substance inside the soil and snow for use with the regional climate model. Compared to the current land-surface scheme, the new SSVM shows significant improvement in both moisture and temperature simulation for the months of March and April, which affects the surface energy budget and the hydrological cycle. The effect of including cryosphere model physics lowers the surface temperature by the initial frozen soil conditions and by the reduction of incoming solar radiation at the surface due to higher albedo over the snow covered region. These effects change the horizontal temperature gradients, and in turn change the location of synoptic weather systems passing over the cold land region. In addition, the partitioning of incoming radiative energy into the sensible and latent heat fluxes is sensitive to snowmelt and soil freeze/thaw conditions during the early stage of the model simulations. Overall, the regional climate simulation of March and April 1997 with the inclusion of the detailed frozen soil and snow processes improves the synoptic and local circulations during the cold season. Both spatial and temporal analysis of PRM-SSVM indicate that the coupling of these processes are important when simulating cold season surfaces with frozen soil and snow cover.