Spring Soil Temperature Anomalies in the Western United States and Summer Droughts in the Southern Plains

这个项目试图了解美国南部平原(大致相当于内布拉斯加州、密苏里州、俄克拉何马州、阿肯色州、德克萨斯州和路易斯安那州)降水变化的原因。该地区是美国最容易发生干旱的地区之一，该地区的干旱对经济产生了重大影响。这个项目检验了这样一种假设，即美国西部春季次表层土壤温度异常导致南部平原在随后的夏季发生降雨变化。这种假设关系是，西部温暖的次表层土壤温度通过其在温暖的地表温度中的表现，在上层大气中产生气旋式环流，向东传播，在地温异常的东部和南部产生6月增强的降水，而对于寒冷的次表层土壤温度则相反(即干旱)。该项目要研究的另一个问题是冻土对降水对土壤温度的响应的影响。该项目测试了在区域气候模式(RCM)中更好地表示冻土在多大程度上可以导致该模式模拟的西部土壤温度和南部平原降水之间存在更强的关系。该提案的初步工作已经证明了地下土壤温度的影响，在该项目下进行的工作将通过一系列模型模拟实验进行后续工作。实验将在一种模式配置下进行，其中全球大气模式(NOAA/NCEP全球预报系统模式，简称GFS)将与被称为天气研究和预报(WRF)模式的RCM相结合，在该模式中，陆地表面过程由简化的简单生物圈(SSIB)模式模拟。实验通常使用施加的海面温度和海冰，使用GFS模型生成特定年份的全球模拟，该模型反过来用于指定WRF模拟的横向边界条件。这些实验测试了所有本地和远程影响对南部平原降水的影响，包括西部各州的土壤条件以及海洋表面温度(SST)的波动。海温，包括那些与厄尔尼诺有关的海温，可以通过其对西部土壤温度的影响，直接或间接地影响南部平原的降水。由于南部平原干旱的经济和社会影响，以及需要更好的方法来预测干旱的程度和持续时间，这项工作具有更广泛的影响。该项目还将支持一名博士后研究人员，从而支持该研究领域的下一代科学家。

This project seeks to understand the causes of precipitation variability in the US Southern Plains (roughly equivalent to Nebraska, Missouri, Oklahoma, Arkansas, Texas, and Louisiana). This area is among the most drought-prone in the US, and droughts in the region have substantial economic impacts. This project examines the hypothesis that Spring subsurface soil temperature anomalies in the Western US in produce rainfall changes in the Southern Plains in the subsequent summer. The hypothesized relationship is such that warm subsurface soil temperature in the West, through its manifestation in warm land surface temperature, generates a cyclonic circulation in the overlying atmosphere, which propagates eastward to produce enhanced June rainfall to the east and south of the soil temperature anomaly, with the opposite result (i.e. drought) for cold subsurface soil temperature. A further issue to be examined in the project is the effect of frozen soil on the precipitation response to soil temperature. The project tests the extent to which a better representation of frozen soil in regional climate models (RCMs) can lead to a stronger relationship between Western soil temperature and Southern Plains precipitation simulated by the model. Preliminary work for the proposal has shown evidence for the effect of subsurface soil temperature, and work performed under the project will follow up with a set of model simulation experiments. The experiments will be conducted with a model configuration in which a global atmospheric model (the NOAA/NCEP Global Forecast System model, or GFS) will be combined with an RCM known as the Weather Research and Forecasting (WRF) model, in which land surface processes are simulated by the Simplified Simple Biosphere (SSiB) model. Experiments typically use imposed sea surface temperatures and sea ice to produce a global simulation for a particular year using the GFS model, which is in turn used to specify lateral boundary conditions for WRF simulations. The experiments test the influence of all local and remote effects on Southern Plains precipitation, including soil conditions in the Western states and also sea surface temperature (SST) fluctuations. SSTs, including those associated with El Nino can affect Southern Plains precipitation both directly and indirectly, through their influence on soil temperature to the West.The work has broader impacts due to the economic and societal impact of drought in the Southern Plains and the desirability of better methods to predict the extent and duration of droughts. The project will also support a post-doctoral researcher, thereby supporting the next generation of scientists in this research area.