Abstract
The spatial–temporal distribution of the global gravity wave (GW) potential energy (Ep) at the lower stratosphere of 20–35 km is studied using the dry temperature profiles from multi- Global Navigation Satellite System (GNSS) radio occultation (RO) missions, including CHAMP, COSMIC, GRACE, and METOP-A/B/C, during the 14 years from 2007 to 2020, based on which the linear trends of the GW Ep and the responses of GW Ep to solar activity, quasi biennial oscillation (QBO), and El Niño-Southern Oscillation (ENSO) are analyzed using the multivariate linear regression (MLR) method. It is found that the signs and the magnitudes of the trends of GW Ep during each month vary at different altitude ranges and over different latitudes. At 25–35 km of the middle and high latitudes, GW Ep values generally show significant negative trends in almost all months, and the values of the negative trends become smaller in the regions closer to the poles. The distribution of the deseasonalized trends in the monthly zonal-mean GW Ep demonstrates that the GW activities are generally declining from 2007 to 2020 over the globe. The responses of GW Ep to solar activity are found to be mostly positive at 20–35 km over the globe, and the comparison between the distribution pattern of the deseasonalized trends in the GW activities and that of the responses of GWs to solar activity indicates that the sharp decline in solar activity from 2015 to 2017 might contribute to the overall attenuation of gravity wave activity during the 14 years. Significant negative responses of GW Ep to QBO are found at 30–35 km over 30° S–25° N, and the negative responses extend to the mid and high latitudes in the southern hemisphere at 20–30 km. The responses of GW Ep to QBO change to be significantly positive at 20–30 km over 15° S–15° N, which demonstrates that the zonal wind field should be the main factor affecting the GW activities at 20–30 km over the tropics. The responses of GW Ep at 20–35 km to ENSO are found to be positive over 15° S–15° N, while at 30–35 km over 15° N–30° N and at 20–35 km near 50° N, significant negative responses of GW Ep to ENSO exist.
Highlights
What needs to be mentioned is that Ern et al [67] and Liu et al [9] both observed negative responses in gravity wave (GW) Ep to F10.7 indexes at the altitude range of 30–35 km above low and middle latitudes by using the SABER temperature data, which are different from our results, while the time periods researched by Ern et al [67] and by Liu et al [9] are
We suggest that a possible reason why our results are inconsistent with those of Ern et al [67] and Liu et al [9] is that the solar activity weakened sharply during 2015 to 2017, which partially contributed to the general weakening of GW activities after 2016
By using multi-mission Global Navigation Satellite System (GNSS) radio occultation (RO) data from 2007 to 2020, the present study studies from different RO missions, firstly, the global distributions of the seasonal means of GW
Summary
Gravity waves (GWs), which are fluctuations generated by buoyancy and gravity under stable stratification in the atmosphere, are an important component of the atmospheric system and a critical driving mechanism in the lower and middle atmosphere through drag and diffusion processes [1,2]. The sources for generating GWs include deep convection, jet stream, flow over topography, and wind shear, etc. Energy and momentum in the troposphere can be transported by the GWs to the middle atmosphere due to the effect of background wind [4]. The break in GWs can enhance the local eddy diffusions, which will have impacts on the local distribution of atmospheric species [5,6]
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