Abstract
Atmospheric gravity waves play a crucial role in affecting atmospheric circulation, energy transportation, thermal structure, and chemical composition. Using ERA5 temperature data, the present study investigates the tropospheric to the lower mesospheric gravity wave potential energy (EP) over the equatorial region to understand the vertical coupling of the atmosphere. EP is mainly controlled by two factors. The first is zonal wind through wave–mean flow interactions, and thus EP has periodic variations that are correlated to the zonal wind oscillations and enhances around the altitudes of zero-wind shears where the zonal wind reverses. The second is the convections caused by atmospheric circulations and warm oceans, resulting in longitudinal variability in EP. The lower stratospheric and the lower mesospheric EP are negatively correlated. However, warm oceanic conditions can break this wave energy coupling and further enhance the lower mesospheric EP.
Highlights
Gravity waves transport energy and momentum from the lower to the middle and even the upper atmosphere, affecting the atmospheric circulations and energy budget [3]. They are related to several geophysical phenomena in the middle and upper atmosphere, such as the stratospheric quasi-biennial oscillation (QBO) [12,13,14], the upper stratospheric and lower mesospheric semiannual oscillations (SAO) [15,16,17], polar stratospheric clouds [18], sudden stratospheric warming events [19,20,21], elevated stratopause events [22,23], and mesospheric temperature inversions [24,25,26]
Different from that EP is lower around 20 km altitude, and a low EP region appears at 27–30 km altitude the stratospheric SAO (SSAO), the EP values around the easterly shear of the second mesospheric SAO (MSAO)
The semiannual and annual variations in EP are relatively regular since the corresponding oscillations in the background zonal wind are mainly triggered by solar radiation [10], and EP properly varies with the zonal wind (Figure 5)
Summary
ERA5 is the latest (5th generation) of the atmospheric reanalysis dataset released by ECMWF from 2017. T is the vertical temperature profile retrieved from ERA5, and we employed a 2–10 km (the common vertical wavelengths of gravity waves in the stratosphere [3,60]) band-stop filter to filter out the wave components from T, and the result is the background temperature T. Since we employed a 2–10 km filter to retrieve the wave component, the sliding window, i.e., the spacing between zmin and zmax is set to 2 km (the shortest wavelength) in the present study. 45–80 km altitude) as analyzed in the present study; the temperature inversion at the tropopause and stratopause will be wrongly recognized as wave structures. Thereby, the mesospheric EP is possibly underestimated in the present study
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