Enhancing the Understanding of Nocturnal Convective System Morphological Evolution

大型雷暴团，被称为“中尺度对流系统”（MCS），经常发生在美国中部的夜间，带来破坏性的恶劣天气，但也带来了该地区生长季节农业所需的大部分降雨。 通过计算机模型对MCS的预测往往不是很准确，特别是当它们从几个强烈的雷暴，往往在傍晚，到一个更大的风暴和稳定的雨在夜间，再次接近黎明时，MCS通常消散。MCS的演变与雨水蒸发形成的冷空气池有关，冷池受风暴附近的温度和湿度以及在云中形成降水的过程的影响。 影响MCS演变的其他因素包括风随高度的变化，附近天气锋的存在，甚至更小尺度的大气特征，如重力波，这些重力波与该地区夜间经常发展的更快的风相互作用，称为低空急流。该项目将研究所有这些过程如何影响MCS演变，加深了解将改善对MCS降雨的预测，这些降雨往往会导致洪水和恶劣天气。 这项研究将支持几个研究生，纳入本科课程，并在推广到公众和国家气象局办公室。夜间MCS的准确预测，特别是它们的降雨和形态演变，仍然是难以捉摸的。将水平网格间距从3公里细化到1公里，可以增加WRF模拟的线性系统的数量，与观测结果更好地吻合，但是这些线是在错误的情况下，在错误的时间产生的，并且通常在层状雨的描述中存在问题。在高增长期，问题尤其多，然后又走向消散。随着反射率更高的连续区域的发展，谱线数量增加，这可能是因为沿沿着冷池边界的升力分辨率更高。这可能是几个影响冷池的因素，如近风暴傍晚边界层特征和对流内的微物理过程中发挥了重要作用的高档增长形态演变，沿着环境风切变和边界的定位。重力波、钻孔、侵入流及其与低空急流的相互作用也会影响演变。影响层状区域形成的因素也可能起到一定的作用，可以解释在MCSs生命周期后期模拟模式的模型问题。该项目将使用三个模型，WRF，FV 3-SAR和CM 1，沿着观察，以提高对夜间形态演变的理解，并揭示阻碍某些模式和它们之间转换的准确模拟的主要问题。该奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

Large thunderstorm clusters, known as “Mesoscale Convective Systems” (MCSs), often occur at night in the central United States, bringing damaging severe weather but also much of the rainfall needed for agriculture during the growing season in this region. Forecasting of MCSs by computer models is often not very accurate, especially when they are growing from a few intense thunderstorms, often in early evening, to a much larger region of storms and steady rain during the night, and again toward dawn when MCSs usually dissipate. The evolution of MCSs is related to the pool of cool air that forms from evaporation of the rain, and that cool pool is influenced by the temperature and humidity near the storm, and the processes that form precipitation in the cloud. Other factors influencing MCS evolution include changes in wind with height, the presence of nearby weather fronts, and even smaller-scale atmospheric features like gravity waves that interact with a current of faster wind that often develops at night over this region, known as the low-level jet. The project will study how all of these processes influence MCS evolution, and the improved understanding will improve forecasting of MCS rainfall that often causes flooding and severe weather. The research will support several graduate students, be incorporated into undergraduate courses, and be presented in outreach to the public and National Weather Service offices. Accurate prediction of nocturnal MCSs, particularly their rainfall and morphological evolution, remains elusive. A refinement of horizontal grid spacing from 3 to 1 km has been found to increase the number of linear systems simulated by WRF, agreeing better with observations, but the lines were produced in the wrong cases, at the wrong times, and usually with problems in the depiction of stratiform rain. Problems are particularly abundant during the upscale growth period, and again toward dissipation. The increase in number of lines occurs as more continuous zones of higher reflectivity develop, possibly because of better resolution of lift along cold pool boundaries. It is likely that several factors affecting the cold pools, such as near-storm evening boundary layer characteristics and microphysical processes within convection play an important role in the upscale growth morphological evolution, along with the ambient wind shear and positioning of boundaries. Gravity waves, bores, intrusion currents, and their interaction with the low-level jet also influence evolution. Factors influencing stratiform region formation may also play a role that could explain model problems in simulating mode late in the life cycle of MCSs. The project will use three models, WRF, FV3-SAR, and CM1, along with observations to improve understanding of nocturnal morphological evolution and reveal the primary problems preventing accurate simulation of some modes and transitions between them.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.