Finding the right Mathematical Model for Atmospheric Convection

地球上一些最极端的天气与深层对流风暴有关，深层对流风暴是由水蒸气变成液态云水或冰时释放的热量驱动的。这些风暴最初是小而湍急的涡流，后来发展成猛烈的雷暴。风暴可以组织成更大的结构，如狂风线和热带气旋。然而，这个规模越来越大的组织在一定程度上仍然受到发生在最小动荡尺度上的过程的控制。在用于预报天气的模型中，最小的尺度不能准确地表示，这损害了天气预报的准确性。这个专题的目的是评估表示最小尺度的新方法。学生将评估两种类型的平均对于导出表示与对流有关的亚格子尺度变异性的方程的适用性。条件平均假设每个网格盒的动量、温度和密度两个值，以表示大气中对流活跃(多云)和稳定(晴朗天空)区域的条件。成交量平均法包括预测均值、标准差和变量之间的相关性。该项目将首先评估哪种平均技术最能代表低分辨率的高分辨率数据。然而，数据的表示只是个开始。最大的挑战在于使用体积或条件平均方程建立预测模型，以及预测小尺度、湍流运动和深对流之间的转换。学生将使用两种平均技术开发现有的模式，并将提出和测试预测大气对流稳定区域和对流活动区域之间过渡的新想法。结果将与高分辨率对流模型进行比较。该项目是Circle-A项目的一部分。“硬灰区对流的参数化”，这是NERC/Met办公室方案“了解和代表尺度上的大气对流”的一部分。因此，这名学生将成为全国网络的一部分。这是一个为模型开发做出贡献的机会，这些模型将直接提供给天气和气候预报。

Some of the most extreme weather on the planet is associated with deep convective storms driven by the heat released when water vapour turns into liquid cloud water or ice. These storms start out as small turbulent eddies which grow into violent thunderstorms. Storms can organise into much larger structures such as squall lines and tropical cyclones. This ever-larger scale organisation nevertheless remains, in part, controlled by processes occurring at the smallest turbulent scales. The smallest scales are not represented accurately in models used to predict the weather, which compromises the accuracy of weather forecasts. This project is aimed at evaluating new approaches to the representation of the smallest scales.The student will assess the suitability of two types of averaging for deriving equations that represent the sub-grid scale variability associated with convection. Conditional averaging assumes two values of momentum, temperature and density per grid box in order to represent the conditions in both the convectively active (cloudy) and stable (clear sky) regions of the atmosphere. Volume averaging involves predicting means, standard deviations and correlations between variables. The project will start by assessing which averaging technique can best represent high resolution data at low resolution. However the representation of the data is just the start. The big challenge lies in creating prediction models using volume or conditionally averaged equations and in predicting the transition between small scale, turbulent motion and deep convection. The student will develop existing models using both averaging techniques and will propose and test new ideas for predicting the transition between convectively stable and convectively active regions of the atmosphere. The results will be compared with high resolution models of convection.This project is part of ``Project Circle-A. Parametrizing Convection in the Hard Grey Zone'' at Reading which is part of the NERC/Met Office programme ``Understanding and Representing Atmospheric Convection across Scales''. The student will therefore be part of a national network. This is an opportunity to contribute to model development that will directly feed in to weather and climate forecasting.