The Climatology And Variability Of Stratospheric Gravity Waves Based On COSMIC Radio Occultation Observations

It is well known that gravity waves(GWs.)are one of the fundamental fluctuations in the atmosphere.GWs transport energy,momentum,chemical and atmospheric constituents horizontally and vertically and play a major role in the variability of the temperature field,the wind field and the global atmospheric circulation.Global Positioning System(GPS)radio occultation(RO)technique can provide amounts of atmospheric parameter profiles with global coverage,high vertical resolution and longterm stability and has been applied in the study of gravity wave(GW)activities.This thesis aims to study the global distribution,the seasonal variation,the spatial and temporal variability of global stratospheric GWs,the GW activity anomalies during stratospheric sudden warming(SSW)and the relationship with GW and the height and temperature of tropopause using the Global Positioning System(GPS)radio occultation(RO)data derived from the Constellation Observing System for Meteorology,Ionosphere and Climate(COSMIC)mission during September 2006 to June 2016.The main results of this thesis are as follows:The global distributions of averaged seasonal means GW potential energy(Ep)over 20-30 km and 30-38 km show similar spatial patterns and seasonal variations.Ep is large at tropical and subtropical latitudes(30°S-30°N)in all seasons,as well as at middle and high latitudes in winter hemisphere.GW Ep and the outgoing longwave radiation(OLR)(a proxy for deep convection)are negatively correlated at equatorial regions,suggesting that convection is the primary source of GWs in the Tropics.GWs propagate upward and poleward from the equatorial troposphere to higher stratosphere.At latitudes of near 50°N and 50°S,GWs are mainly generated by the meridional mountains.Whether they propagate upward or not depends on the zonal wind over their formation regions.Intense eastward wind,which mainly happens in winter hemisphere,is favorable for the upward propagation of GWs,while weak westerly winds or easterly winds,which is apparent in summer hemisphere,filters out most of the GWs.This can explain the seasonal variations of GWs at middle and high latitudes.In contrast to low-latitude region,the seasonal cycle of GWs at the middle and high latitudes are more distinct.The influence of quasi-biennial oscillation(QBO)on GW activity in the tropics is examined.GW Ep enhances closely following the occurrence of Minor SSW events,while during Major events,GW Ep may not enhance or even weaken.The anomaly of GW Ep produced by SSW events can be explained by the filtering effect of zonal winds.GWs are crucial factors affecting the structures of the tropopause.At the middle and high latitudes,the upward propagation of GW lifts the tropopause,leading to a high and cold tropopause.While at tropical latitudes,both convections and GWs have impacts on the temperature and heights of the tropopause.