An Study Of Inertia Gravity Waves Observed By Radiosondes At High Latitudes

Atmospheric gravity waves have an important influence on atmospheric circulation and thermal structure.Inertial gravity waves are low-frequency gravity waves.At present,there are extensive reports on inertial gravity wave activities at low and middle latitudes.Due to the observational constraints,there are few studies on inertial gravity waves at high latitudes.This paper uses 8-year radiosonde observation at the Nome Ap station(64.5 ° N,165.43° E)in Alaska,to study the characteristics of inertial gravity waves in the low stratosphere over high latitudes.Based on the hodograph technique and Lomb-Scargle spectral analysis,the quasi-monochromatic inertial gravity waves in the low stratosphere were extracted from the zonal wind,meridional wind and temperature profiles,and the wave parameters and their seasonal changes were statistically analyzed.According to the momentum flux analysis at the different stations,the effect of inertial gravity waves on the background atmosphere in the high latitudinal region was quantitatively evaluated.The main conclusions of this study are as follows:1.This paper statistically studied the parameter distribution of low stratospheric inertial gravity waves at Nome Ap site.The horizontal wavelength of inertial gravity waves is mainly distributed in the range of 50～1050 km,accounting for 80.8% between50～550 km.The vertical wavelength is mainly distributed in the range of 1～7 km,accounting for 82.5% between 1～4 km.The average horizontal and vertical wavelengths are 359 km and 2.87 km,respectively.Inertial gravity waves with an eigenfrequency in the range of 1 to 2.5f(corresponding to the eigenperiod range of 5.3-13.3 h)account for80.1% of the total,and its average value is 2.14 times the inertial frequency f,corresponding to an intrinsic period of 6.2h.The extracted inertial gravity wave satisfies the linear theory of gravity wave,indicating that the inertial gravity wave in the low stratosphere has been far away from the excitation region and exhibits the characteristics of free propagation.2.The seasonal variation of inertial gravity wave activity in the lower stratosphere at Nome Ap site is analyzed.The average horizontal wavelength of 355 km in winter is slightly larger than the average of 343 km in summer.The seasonal variation of wavelength may be related to the excitation source and the background atmosphere.Correspondingly,the eigenfrequency in winter is slightly higher than that in summer,which is consistent with the dispersion relationship of gravity waves.In autumn and winter,the westward propagating inertial gravity waves are prodominant,while in summer,the eastward propagating waves are slightly dominant.The difference in propagation direction resulte from the filtering effects of the background wind.The upward propagating inertial gravity waves are absolutely dominant,and the downward propagating gravity wave obviously increases during winter.This is because the intense polar vortex activity in winter excites the upward and downward propagating inertial gravity waves.Wave energy also is strong in winter but weak in summer.3.The effects of inertial gravity wave momentum flux on the background atmosphere is investigated.At the Nome Ap site,the vertical flux of latitudinal momentum is significantly greater in autumn and winter than in spring and summer,and the meridional momentum flux is relatively small throughout the year.The average latitudinal momentum for many years has a large net vertical flux of-0.30 m Pa,indicating that gravity wave activity at high latitudes has a drag effect on the polar stratospheric vortex.The observation at other high latitude stations show that the momentum flux exhibits similar characteristics,further confirming that the gravity wave activity in high latitudes can put a westward drag on the polar stratospheric background wind field.