| Atmospheric gravity waves(AGWs)can play an important role in the middle and upper atmosphere,and the parameterization has been an important issue for studying GWs.Atmospheric gravity waves not only act on lower altitudes in the upper middle and upper atmosphere(such as stratosphere),but even in some cases cause certain effects on the ionosphere.For example,the traveling ionospheric disturbances(TIDs),as the important part of ionospheric weather,are mainly induced by atmospheric gravity waves(AGWs).There have been a lot of researches on the certain case to study the propagation and the possible wave sources of TIDs.Due to the data limitations on spatiotemporal coverage,it has become a difficult problem how to use satellites data to extract and parameterize GWs and TIDs globally and statistically.Temperature profiles provided by the Constellation Observing System for Meteorology,Ionosphere and Climate(COSMIC)global positioning system(GPS)satellite constellation were used to study an eight-year series(2007 to 2015)of gravity wave(GW)potential energy in the stratosphere(18-30 km)around the Tibetan Plateau(TP).We found that with increasing altitude,the GW potential energy values in the stratosphere caused by convection decreases.The importance of GWs that are stimulated by topography is enhanced in this area.In the TP,which was considered to lack strong topographical GW activity,clear activity existed in the spring and winter of all studied years.Based on the latitudinal zone of the TP,the distribution of GW potential energy is highly consistent with the elevation of the local topography.The activities of topographical GWs are strongly filtered as they propagate upward to the area of zero speed wind.The analysis indicates that in the TP,clear orographic GW excitation exists and propagates upward to the upper stratosphere,where it is greatly influenced by the wind.The vertical parameters of gravity waves can be easily obtained by using occultation observation data.However,to obtain more information of gravity waves,the extraction of horizontal parameters becomes a very big challenge.We made use of the favorable conditions of satellite flight between year 2006 and 2007 after COSMIC launch,and applied the multichannel maximum entropy method(MMEM)to stratospheric temperature data,which helps to obtain a more real horizontal wavelength than previous work.We successfully extracted a series of parameters of GWs,and provided a series of valuable results for the global spatial distribution and seasonal variation of GWs in the stratosphere.Our comparisons with previous studies demonstrate that the characteristics of GWs parameters may be less dependent on the difference of approaches to data and patterns.The GW amplitude,potential energy and momentum flux showed an apparent seasonal variation with localized maxima in the summertime subtropics and in the high latitudes of winter hemisphere.The comparison of the GW parameters with the elevation in the mountainous regions of northern hemisphere indicates that except for the Andes,which has been fully observed and studied by previous work,the topography GWs are also active in the middle and high latitudes in the northern hemisphere.On this basis,we used the MMEM method to extract the parameters of waves with the ionospheric electron density,and obtained the global spatial and seasonal variation of waves in the ionosphere.As far as we know,this is the first time that the method has been used to study the ionospheric waves with COSMIC TEC profiles.The results show that the ionospheric wave amplitude increased at the low and high latitudes and decreased in the mid-latitudes.And the ionospheric wave vertical and horizontal wavelength increased in the mid-latitudes and decreased at the low and high latitudes.Besides,the ionospheric wave amplitude and vertical wavelength in the mid-latitudes of the Northern Hemisphere increased in winter and decreased in summer,and their magnitudes also increased in the regions where the elevation is higher. |
PDF Full Text Request