Gravity Wave Momentum Flux Derived By Combining COSMIC Radio Occultation And ERA-Interim Reanalysis Data

Gravity waves are one of the most basic fluctuations in the atmosphere,and their spatiotemporal distribution changes have an important impact on the global atmosphere temperature,wind field,water vapor and atmospheric circulation.The vertical flux of the horizontal wavelength of the gravity wave,that is,the gravity momentum flux,is an irreplaceable parameter that characterizes the gravity wave activity.GNSS radio occultation dry temperature data is globally distribution with high vertical resolution and high precision,and has high precision from the upper troposphere to the lower stratosphere,which is of great value for the study of global gravity wave activity.In this paper,in view of the limited spatiotemporal resolution of the observation data from the occultation missions,which cannot meet the occultation profile group that requires spatiotemporal matching when extracting the gravity momentum flux on the long-term scale,the COSMIC occultation dry temperature data and ERA-Interim reanalyzes the horizontal wind field data to study the spatiotemporal characteristics of long-term momentum flux.We first propose a method of extracting gravity momentum flux by combining two types of data.The background temperature and background wind field are obtained by performing zonal S transformation on the occultation and wind fields with 0-6 zonal wave number information retained.Based on this,the temperature and wind perturbations resulted from gravity wave are extracted.Furthermore,the gravitational wave buoyancy frequency,vertical wavelength and potential energy are obtained from the temperature perturbation,and the gravity wave natural frequency is obtained from the wind perturbation.The above parameters are used to obtain the horizontal wavelength,and finally obtain the magnitude of the momentum flux.As the method is verified,the COSMIC occultation and ERA-Interim wind field data from June 2006 to May 2013 were processed for seven consecutive years,and the global distribution of momentum fluxes in the three altitude ranges of 20-25 km,25-30 km and 30-35 km with their seasonal and interannual variations are analyzed.The results indicate that although the magnitude of the momentum flux decreases with the increase of the height as a whole,the distribution pattern of the momentum flux in each altitude interval and its seasonal and inter-annual variation are consistent.In addition,the gravity wave activity hotspot area has the most significant distribution of momentum flux in the height range of 20-25 km.There are two high peaks in the global distribution of momentum flux.As for the spatial variation,the maximum of momentum flux occurs over the 60 ° latitude zone where the east hemisphere prevails in winter,and the second maximum occurs in the subtropical region where deep convection occurs in summer.The momentum flux in the subtropical region is affected by the zonal wind,and there is an obvious quasi-two-year oscillation(QBO)phenomenon.Compared with the existing gravity flux research based on satellite data,the results of this paper have made breakthroughs in the height range,latitude range and time length of the gravity wave activity studied.