The Spatial and Temporal Variability of Global Stratospheric Gravity Waves and Their Activity during Sudden Stratospheric Warming Revealed by COSMIC Measurements

Abstract

This study investigates the spatial and temporal variability of global stratospheric gravity waves (GWs) and the characteristics of GW activity during sudden stratospheric warming (SSW) using the GPS radio occultation measurements from the COSMIC mission during September 2006 to May 2013. Corresponding to the COSMIC RO observational window and analysis method, GW potential energy (Ep) with vertical scales no shorter than ∼2 km is resolved. It is found that the distributions of GW Ep over 20–30 km and 30–38 km show similar spatial and seasonal variations. The variations of GW Ep with altitude and latitude along the westerly wind are identified in different seasons over 60◦–80◦W. In the middle and high latitudes, seasonal cycles are distinct in the time–latitude and time–altitude distributions of GW activities, which show larger Ep in winters when westerly wind dominates and smaller Ep in summers when easterly wind dominates. The influence of quasi-biennial oscillation on GW activity is recognized in the tropics. GW Ep enhances closely following the occurrence of minor SSW events; while during major events, GW Ep may not enhance, and sometimes may even weaken, in the regions where reversals of zonal wind occur, probably caused by the filtering impact of the 0 m s⁻¹ wind level on the GWs.

摘 要

本文利用进行 GPS 掩星观测的 COSMIC 任务于 2006 年 9 月至 2013 年 5 月期间的干温廓线, 研究了全球平流层重力波的时空变化及其在平流层爆发性增温(SSW)期间的活动特征. 与 COSMIC 掩星观测窗口及分析方法相对应, 本文所研究的重力波垂直波长大于 2 km. 基于所提取的重力波势能, 发现20–30km和30–38km两个高度层的势能呈现相似的空间变化和季节变化特征. 以60°W–80°W 经度带为例, 西风对重力波势能随高度和纬度的变化在不同季节都有明显影响. 在中高纬度区域, 重力波势能的时间-纬度和时间-高度分布均呈现明显的季节变化特征; 在热带, QBO 对重力波活动的影响较显著. 不同类型 SSW 事件对重力波活动的影响不同: 次增温事件后, 重力波势能一般会增强; 主增温事件后, 重力波势能可能无显著增强, 在风场反转的区域甚至可能削弱, 这可能是由于零风场线对重力波活动的过滤作用.