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Abstract Based on the hourly output from the 2000–2014 simulations of the National Center for Atmospheric Research's vertically extended version of the Whole Atmosphere Community Climate Model in specified dynamics configuration, we examine the roles of planetary waves (PWs), gravity waves, and atmospheric tides in driving the mean meridional circulation (MMC) in the lower thermosphere (LT) and its response to the sudden stratospheric warming phenomenon with an elevated stratopause in the northern hemisphere. Sandwiched between the two summer‐to‐winter overturning circulations in the mesosphere and the upper thermosphere, the climatological LT MMC is a narrow gyre that is characterized by upwelling in the middle winter latitudes, equatorward flow near 120 km, and downwelling in the middle and high summer latitudes. Following the onset of the sudden stratospheric warmings, this gyre reverses its climatological direction, resulting in a “chimney‐like” feature of un‐interrupted polar descent from the altitude of 150 km down to the upper mesosphere. This reversal is driven by the westward‐propagating PWs, which exert a brief but significant westward forcing between 70 and 125 km, exceeding gravity wave and tidal forcings in that altitude range. The attendant polar descent potentially leads to a short‐lived enhanced transport of nitric oxide into the mesosphere (with excess in the order of 1 parts per million), while carbon dioxide is decreased.
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The Influence of Obliquely Propagating Monsoon Gravity Waves in the Southern Polar Summer Mesosphere After Stratospheric Sudden Warmings in the Winter Stratosphere
Abstract Oblique propagation of gravity waves (GWs) refers to the latitudinal propagation (or vertical propagation away from their source) from the low‐latitude troposphere to the polar mesosphere. This propagation is not included in current gravity wave parameterization schemes, but may be an important component of the global dynamical structure. Previous studies have revealed a high correlation between observations of GW pseudomomentum flux (GWMF) from monsoon convection and Polar Mesospheric Clouds (PMCs) in the northern hemisphere. In this work, we report on data and model analysis of the effects of stratospheric sudden warmings (SSWs) in the northern hemisphere, on the oblique propagation of GWs from the southern hemisphere tropics, which in turn influence PMCs in the southern summer mesosphere. In response to SSWs, the propagation of GWs at the midlatitude winter hemisphere is enhanced. This enhancement appears to be slanted toward the equator with increasing altitude and follows the stratospheric eastward jet. The oblique propagation of GWs from the southern monsoon regions tends to start at higher altitudes with a sharper poleward slanted structure toward the summer mesosphere. The correlation between PMCs in the summer southern hemisphere and the zonal GWMF from 50°N to 50°S exhibits a pattern of high‐correlation coefficients that connects the winter stratosphere with the summer mesosphere, indicating the influence of Interhemispheric Coupling mechanism. Temperature and wind anomalies suggest that the dynamics in the winter hemisphere can influence the equatorial region, which in turn, can influence the oblique propagation of monsoon GWs.
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- Award ID(s):
- 1855476
- PAR ID:
- 10375592
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Atmospheres
- Volume:
- 126
- Issue:
- 5
- ISSN:
- 2169-897X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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