Climate impacts of parameterizing subgrid variation and partitioning of land surface heat fluxes to the atmosphere with the NCAR CESM1.2

[摘要] All current global climate models (GCMs) utilize onlygrid-averaged surface heat fluxes to drive the atmosphere, and thus theirsubgrid horizontal variations and partitioning are absent. This can resultin many simulation biases. To address this shortcoming, a novelparameterization scheme considering the subgrid variations of the sensibleand latent heat fluxes to the atmosphere and the associated partitioning isdeveloped and implemented into the National Center for Atmospheric Research(NCAR) Climate Earth System Model 1.2 (CESM1.2). Compared to the defaultmodel, in addition to the improved boreal summer precipitation simulationover eastern China and the coastal areas of the Bay of Bengal, thelong-standing overestimations of precipitation on the southern and easternmargins of the Tibetan Plateau (TP) in most GCMs are alleviated. Theimproved precipitation simulation on the southern margin of the TP is fromsuppressed large-scale precipitation, while that on the eastern edge of theTP is due to decreased convective precipitation. Moisture advection isblocked toward the southern edge of the TP, and the anomaly of anticyclonicmoisture transport over northern China extends westward, suppressing localconvection on the eastern edge of the TP. The altered large-scalecirculation in the lower atmosphere resulting from anomalous heating and coolingin the planetary boundary layer is responsible for the change in moisturetransport. The performance of other key variables (e.g., surface energyfluxes, clouds and 2 m temperature) is also evaluated thoroughly using thedefault CESM1.2, the new scheme and the scheme stochastically allocatingthe subgrid surface heat fluxes to the atmosphere (i.e., without subgridpartitioning included). This study highlights the importance of subgridsurface energy variations and partitioning to the atmosphere in simulatingthe hydrological and energy cycles in GCMs.

[学科分类] 土木及结构工程学