Extraction And Numerical Simulation Of Gravity Waves In The Middle Atmosphere

Atmospheric gravity waves are very important fluctuations in the middle atmosphere,and their global distribution characteristics are related not only to the methods used to extract the gravity wave disturbances,but also to the sensitivity of detection instruments from which extracted gravity wave spectrum.The Lomb least squares fitting method(LS)and Fourier transform filter method(IF)are used in the horizontal direction,superimposed on the wavelet analysis(WT)and high-pass filtering(HF)in the vertical direction,then select a method of horizontal and vertical separately to combine into four methods.We focuses on the extraction of gravity wave signal,using the above four methods or extracted from different satellite observations,to analyze the global distribution characteristics of gravity wave activity.In addition,due to insufficient resolution of satellite data,we combine with the mesoscale numerical prediction model WRF,analyze a convection-induced gravity wave event over North China on August 4,2010.The main conclusions are as follows:(1)Due to the interpolation error of IF method,the potential energy of gravity wave obtained by using IF method is larger than that by LS method,lead to that the LS method is superior than IF method in horizontal direction.On the basis of LS method in the horizontal direction,WT and HF methods were used to obtain the potential energy of gravity wave in the vertical direction respectively,and their global distribution patterns were basically similar.The WT method has errors in the lower and upper layers so that covers quasi-biennial oscillation in the equatorial region.Since the dominant vertical wavelength of gravity wave is larger below 50 km,the HF method loses the information of gravity wave with longer vertical wavelength,so that the potential energy value of gravity wave obtained by this method in the lower stratosphere is about 1/4 smaller than that obtained by WT method,and this underestimation of gravity wave activity cannot be ignored.Therefore,only using LS method in the horizontal direction will not produce errors,and can retain major of the gravity wave,and the characteristics of gravity wave obtained by this method is the most accurate.(2)Using LS method,the global distribution patterns of gravity wave potential energy obtained from SABER and COSMIC satellites are generally similar,but the potential energy obtained from COSMIC satellite data is significantly larger than the SABER satellite results.The absence of zonal scanning points is an important reason for the significantly decrease of SABER potential energy value.The horizontal resolution has a significant effect on the magnitude of gravity wave potential energy,while it has little effect on the distribution pattern of gravity wave activity.The sensitivity of the two satellites to the gravity wave spectrum is different.At 30 km altitude,the dominant vertical wavelength of gravity wave extracted from SABER satellite is larger than the result of the COSMIC satellite,indicating that the SABER satellite is more likely to capture gravity wave signals with longer vertical wavelengths,while the COSMIC satellite is more sensitive to gravity wave information with shorter vertical wavelengths.This feature makes the gravity wave activity detected by COSMIC satellites higher at low latitudes and underestimated at high latitudes.(3)A case study of gravity waves excited by deep convection is studied by combined with COSMIC satellite and WRF model.The WRF model can well the form and structure,vertical and horizontal wavelengths of gravity waves.The gravity waves excited by this event are mainly medium and low frequency gravity waves in the stratosphere.The vertical wavelengths of gravity waves are mainly 9-11 km,and the horizontal The wavelength is 650-800 km in the stratosphere.Due to the insufficient resolution of satellite data,it is difficult to capture all gravity wave,so that the potential energy per unit mass and momentum flux of gravity wave obtained by COSMIC satellite data are significantly smaller than the results of WRF simulation.The results of the WRF simulations show that about 62% of the momentum is concentrated in the lower stratosphere at an altitude of 15-25 km.During the occurrence of convection activity,the potential energy per unit mass of gravity wave in the lower stratosphere always maintained a large value,while that in the upper stratosphere decreased rapidly after the convection weakened,and it increased rapidly with the next convection once again.The response of potential energy per unit mass of stratospheric gravity wave to convection at different heights was mainly related to the development height of convection and the background wind field.When the convection development was shallow,the excited gravity wave was easily dissipated in the low-level westerly wind.However,when the convection developed to 16 km or higher,the excited gravity wave was close to the zero wind layer,and it could be rapidly uploaded in the easterly wind,resulting in the rapid increase of gravity wave potential energy per unit mass in the upper layer.