Multi-model ensembles for upper atmosphere modelling

200 ~ 1000 km高度的中性大气密度日变化率可达80%，在磁暴期间可变化1 ~ 2个数量级。目前使用的高层大气预测模型在应用于卫星轨道预测时，可能会导致轨道参数的很大不确定性（即一天之后的位置误差在千米数量级）。由于缺乏适当高度的中性大气测量，这类模型（即时预报和预报）的准确性进一步受到限制。如果没有能力更准确地预测轨道轨迹，从而更好地规划卫星避免碰撞的机动行动，轨道碰撞可能会变得频繁，足以造成级联，即所谓的凯斯勒综合症。这有可能阻止使用低地球轨道，使用多模型集合正在成为改进大气密度模型性能从而改进轨道预测的一种可能方式。最初的MME工作表明，总中性密度的RMS误差显著降低（约60%）。拟议的方案将旨在展示在更广泛的条件下使用MME;使MME的建设正式化;并将其使用范围扩大到电离层和热层密度。工作实习将在Dstl进行，并将重点放在测试新模型对数据。

The neutral atmospheric density from 200 to 1000 km altitude can change by 80% diurnally as well as by one to two orders of magnitude during geomagnetic storms. The upper atmosphere forecast models currently in use can result in large uncertainties in the orbital parameters when applied to satellite orbit forecasts (i.e. positional errors on the order of kilometres after a day). The accuracy of such models (nowcast and forecast) is further limited by the lack of neutral atmosphere measurements at the appropriate altitudes. Without the capability to more accurately predict orbital trajectories, and thereby better plan satellite collision avoidance manoeuvres, orbital collisions could become frequent enough to cause a cascade, known as the Kessler Syndrome. This has the potential to prevent the use of low Earth orbit (LEO).The use of multi-model ensembles (MMEs) is emerging as a possible way to improve the performance of atmospheric density models and thereby improve orbital predictions. Initial MME work has demonstrated a significant reduction in the RMS errors of total neutral density (by approximately 60%). The proposed programme will aim to demonstrate the use of MMEs over wider range of conditions; formalise the construction of the MME; and expand the use to ionospheric as well as thermospheric densities. Work placements will be undertaken at Dstl and will be focused on testing the new models against data.