Hydrologic Responses to a Shrinking Arctic Sea Ice Cover

这项工作将验证这样一个假设：北极海冰和北部高纬度积雪的消失将引发北极地区降水(P)和净降水（P- e）的季节性、空间分布和量级的变化，这些变化与随之而来的温度变化一起，对北冰洋的淡水收支和格陵兰冰盖的物质平衡产生影响。研究人员预计：(a)海冰的减少将导致北冰洋和周边海域可用水蒸气的增加，这在秋冬季节最为明显，此时冰层形成的延迟和冰层变薄将促进进入大气的热量和水分的大量垂直通量；(b)海冰和陆地积雪的消失将引起北极环流型态的变化，从而引起水汽辐合型态的变化，这种变化在秋季和冬季是由垂直热通量增强引起的，而在暖季是由北冰洋及其周围陆地的温差加热改变引起的；(c)在北冰洋的“下风”以及（目前）部分被冰覆盖的东格陵兰海和巴芬湾附近，格陵兰冰盖将通过对积累和表面融化的影响感受到这些变化。分析工具将是Polar WRF，这是最近开发的一种针对极地应用进行优化的区域气候模式。将对几个北极地区进行控制模拟，重点关注最近几年的特点是9月份海冰范围极低，NCEP/NCAR再分析提供的侧向强迫和卫星观测规定的海冰条件。生成的关键水文变量（可降水量、降水量、水汽通量辐合、净降水量、温度）和大气环流场将与一系列海冰和积雪变化实验的结果进行对比。这些模拟将包括：在整个年周期中，具有冬季气候最大冰范围和冰浓度的模拟；规定的冰范围和冰浓度的减少量大于观测值；在年周期中保持100%和0%的陆地积雪，但有观测到的海冰条件；以及观测到的海冰条件，但夏季开阔水域的海面温度升高。

This effort will test the hypothesis that the loss of arctic sea ice and northern high latitude snow cover will invoke changes in the seasonality, spatial distribution and magnitudes of precipitation (P) and net precipitation (P-E) over the Arctic, which along with attendant changes in temperature, have ramifications for the freshwater budget of the Arctic Ocean and the mass balance of the Greenland ice sheet.The researchers expect that: (a) sea ice loss will lead to an increase in available water vapor over the Arctic Ocean and peripheral seas, most pronounced in autumn and winter, when delayed ice formation and thinner ice will promote large vertical fluxes of heat and moisture into the atmosphere; (b) loss of sea ice and terrestrial snow cover will invoke changes in arctic circulation patterns and hence patterns of water vapor convergence, driven in autumn and winter by enhanced vertical heat fluxes and during the warm season by altered differential heating over the Arctic Ocean and surrounding land; (c) in lying "downwind" of the Arctic Ocean as well as adjacent to the (presently) partially ice-covered East Greenland Sea and Baffin Bay, the Greenland ice sheet will feel these changes both through impacts on accumulation and surface melt.The analysis tool will be Polar WRF, a recently developed regional climate model optimized for polar applications. Control simulations will be conducted for several arctic domains, focusing on recent years which are characterized by extremely low September sea ice extent, with lateral forcing supplied from the NCEP/NCAR reanalysis, and sea ice conditions prescribed from satellite-based observations. Generated fields of key hydrologic variables (precipitable water, precipitation, vapor flux convergence, net precipitation, temperature) and atmospheric circulation will be contrasted with those from a series of experiments with altered sea ice and snow cover. These will include simulations with climatological maximum winter ice extent and concentration through the annual cycle, prescribed reductions in ice extent and concentration larger than those observed, 100% and 0% terrestrial snow cover maintained over the annual cycle but with observed sea ice conditions, and observed sea ice conditions but with increased sea surface temperature over open water areas in summer.