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Abstract We investigate the effects on the mesosphere and thermosphere from a strong mountain wave (MW) event over the wintertime Southern Andes using a gravity wave (GW)‐resolving global circulation model. During this event, MWs break and attenuate atz∼50–80 km, thereby creating local body forces that generate large‐scale secondary GWs having concentric ring structure with horizontal wavelengthsλH=500–2,000 km, horizontal phase speedscH=70–100 m/s, and periodsτr∼3–10 hr. These secondary GWs dissipate in the upper mesosphere and thermosphere, thereby creating local body forces. These forces have horizontal sizes of 180–800 km, depending on the constructive/destructive interference between wave packets and the overall sizes of the wave packets. The largest body force is atz=80–130 km, has an amplitude of ∼2,400 m/s/day, and is located ∼1,000 km east of the Southern Andes. This force excites medium‐ and large‐scale “tertiary GWs” having concentric ring structure, withλHincreasing with radius from the centers of the rings. Near the Southern Andes, these tertiary GWs havecH=120–160 m/s,λH=350–2,000 km, andτr∼4–9 hr. Some of the larger‐λHtertiary GWs propagate to the west coast of Africa with very large phase speeds ofcH≃420 m/s. The GW potential energy density increases exponentially atz∼95–115 km, decreases atz∼115–125 km where most of the secondary GWs dissipate, and increases again atz>125 km from the tertiary GWs. Thus, strong MW events result in the generation of medium‐ to large‐scale fast tertiary GWs in the mesosphere and thermosphere via this multistep vertical coupling mechanism.
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Characteristics of the Quiet‐Time Hot Spot Gravity Waves Observed by GOCE Over the Southern Andes on 5 July 2010
Abstract We analyze quiet‐time data from the Gravity Field and Ocean Circulation Explorer satellite as it overpassed the Southern Andes atz≃275 km on 5 July 2010 at 23 UT. We extract the 20 largest traveling atmospheric disturbances from the density perturbations and cross‐track winds using Fourier analysis. Using gravity wave (GW) dissipative theory that includes realistic molecular viscosity, we search parameter space to determine which hot spot traveling atmospheric disturbances are GWs. This results in the identification of 17 GWs having horizontal wavelengthsλH = 170–1,850 km, intrinsic periodsτIr = 11–54 min, intrinsic horizontal phase speedscIH = 245–630 m/s, and density perturbations 0.03–7%. We unambiguously determine the propagation direction for 11 of these GWs and find that most had large meridional components to their propagation directions. Using reverse ray tracing, we find that 10 of these GWs must have been created in the mesosphere or thermosphere. We show that mountain waves (MWs) were observed in the stratosphere earlier that day and that these MWs saturated atz∼ 70–75 km from convective instability. We suggest that these 10 Gravity Field and Ocean Circulation Explorer hot spot GWs are likely tertiary (or higher‐order) GWs created from the dissipation of secondary GWs excited by the local body forces created from MW breaking. We suggest that the other GW is likely a secondary or tertiary (or higher‐order) GW. This study strongly suggests that the hot spot GWs over the Southern Andes in the quiet‐time middle winter thermosphere cannot be successfully modeled by conventional global circulation models where GWs are parameterized and launched in the troposphere or stratosphere.
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- Award ID(s):
- 1834222
- PAR ID:
- 10375080
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Space Physics
- Volume:
- 124
- Issue:
- 8
- ISSN:
- 2169-9380
- Page Range / eLocation ID:
- p. 7034-7061
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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