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MCS rainfall forecast accuracy as a function of large-scale forcing

机译：MCS降雨预报准确性与大规模强迫的关系

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The large-scale forcing associated with 20 mesoscale convective system (MCS) events has been evaluated to determine how the magnitude of that forcing influences the rainfall forecasts made with a 10-km grid spacing version of the Eta Model. Different convective parameterizations and initialization modifications were used to simulate these Upper Midwest events. Cases were simulated using both the Betts-Miller-Janjic (BMJ) and the Kain-Fritsch (KF) convective parameterizations, and three different techniques were used to improve the initialization of mesoscale features important to later MCS evolution. These techniques included a cold pool initialization, vertical assimilation of surface mesoscale observations, and an adjustment to initialized relative humidity based on radar echo coverage. As an additional aspect in this work, a morphology analysis of the 20 MCSs was included.Results suggest that the model using both schemes performs better when net large-scale forcing is strong, which typically is the case when a cold front moves across the domain. When net forcing is weak, which is often the case in midsummer situations north of a warm or stationary front, both versions of the model perform poorly. Runs with the BMJ scheme seem to be more affected by the magnitude of surface frontogenesis than the KF runs. Runs with the KF scheme are more sensitive to the CAPE amount than the BMJ runs. A fairly well-defined split in morphology was observed, with squall lines having trailing stratiform regions likely in scenarios associated with higher equitable threat scores (ETSs) and nonlinear convective clusters strongly dominating the more poorly forecast weakly forced events.
机译：已对与20次中尺度对流系统（MCS）事件相关的大规模强迫进行了评估，以确定该强迫的大小如何影响以Eta模型的10 km网格间距版本做出的降雨预报。不同的对流参数化和初始化修改被用来模拟这些上中西部事件​​。使用Betts-Miller-Janjic（BMJ）和Kain-Fritsch（KF）对流参数化对案例进行了模拟，并使用三种不同的技术来改善对中尺度特征的初始化，这对于以后的MCS演化很重要。这些技术包括冷池初始化，表面中尺度观测值的垂直同化以及根据雷达回波覆盖范围对初始化的相对湿度进行调整。作为这项工作的另一个方面，其中包括对20个MCS的形态分析。结果表明，当净大尺度强力较强时，使用两种方案的模型都表现更好，这通常是冷锋跨域移动时的情况。当净强迫很弱时（这通常在盛夏或静止锋以北的仲夏情况下），两个模型的性能都较差。与KF运行相比，使用BMJ方案运行似乎更受表面锋生程度的影响。与BMJ运行相比，使用KF方案运行对CAPE量更为敏感。观察到形态上相当明确的分裂，风线可能在与较高的公平威胁评分（ETS）和非线性对流星团相关联的场景中具有尾随的层状区域，强烈主导着预报较差的弱强迫事件。

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