skip to main content


Title: 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.

 
more » « less
Award ID(s):
1834222
NSF-PAR ID:
10375080
Author(s) / Creator(s):
 ;  ;  ;  ;  ;  
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
More Like this
  1. Abstract

    We present a new version of the high‐resolution Kühlungsborn Mechanistic general Circulation Model (KMCM) extended toz ∼ 450 km. This model is called HIAMCM (HI Altitude Mechanistic general Circulation Model) and explicitly simulates gravity waves (GWs) down to horizontal wavelengths ofλh  165 km. We find predominant tertiary GWs in the winter thermosphere at middle/high latitudes. These GWs typically have horizontal wavelengthsλh ∼ 300–1,100 km, ground‐based periods25–90 min, and intrinsic horizontal phase speedscIh ∼ 250–350 m s−1. Abovez∼ 200 km, the predominant GW horizontal propagation directions are roughly against the background winds from the diurnal tide; the GWs propagate mainly poleward at midnight, eastward at 6 local time (LT), equatorward at noon, and westward at 18 LT. Wintertime GWs atz∼ 300 km having 165 km λh≤ 330 km create a large hot spot over the Southern Andes/Antarctic Peninsula that agrees well with quiet time satellite measurements. Due to cancelation effects, the time‐averaged zonal mean Eliassen‐Palm flux divergence from the resolved GWs in the thermosphere is negligible compared to that of the tides and compared to the zonal component of the time‐averaged zonal mean ion drag. We also find that the thermospheric GWs dissipate mainly from macroturbulent diffusion and, abovez∼ 200 km, from molecular diffusion, whereas the tides dissipate mainly from ion drag. The averaged dissipative heating in the thermosphere due to tides is much stronger than that due to GWs.

     
    more » « less
  2. 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.

     
    more » « less
  3. Abstract

    In this study, we analyze the thermospheric density data provided by the Gravity Field and Steady‐State Ocean Circulation Explorer during June–August 2010–2013 at ∼260 km altitude and the Challenging Minisatellite Payload during June–August 2004–2007 at ∼370 km altitude to study high latitude traveling atmospheric disturbances (TADs) in austral winter. We extract the TADs along the satellite tracks from the density for varyingKp, and linearly extrapolate the TAD distribution toKp = 0; we call these the geomagnetic “quiet time” results here. We find that the quiet time spatial distribution of TADs depends on the spatial scale (along‐track horizontal wavelength) and altitude. Atz∼ 260 km, TADs with ≤ 330 km are seen mainly around and slightly downstream of the Southern Andes‐Antarctic region, while TADs with > 800 km are distributed fairly evenly around the geographic South pole at latitudes ≥60°S. Atz∼ 370 km, TADs with ≤ 330 km are relatively weak and are distributed fairly evenly over Antarctica, while TADs with > 330 km make up a bipolar distribution. For the latter, the larger size lobe is centered at ∼60°S, and is located around, downstream and somewhat upstream of the Andes/Antarctic Peninsula, while the smaller lobe is located over the Antarctic continent at 90°–150°E. We also find that the TAD morphology forKp ≥ 2 and > 330 km depends strongly on geomagnetic activity, likely due to auroral activity, with greatly enhanced TAD amplitudes with increasingKp.

     
    more » « less
  4. Abstract

    We examine the total electron content (TEC) from GPS receivers over the United States on March 25–26, 2015. We observe partial to nearly fully concentric rings of traveling ionospheric disturbances (TIDs) with centers close to deep convection. Many of these TIDs have observed horizontal phase speedscH > 300 m/s, suggesting they are induced by gravity waves (GWs) created in the thermosphere. We investigate the largest‐amplitude concentric TIDs at 23:00 UT on March 25 and 01:20 UT on March 26. We find thatcHand the GW periodτrincrease linearly with radius and the horizontal wavelength,λH, increases quadratically with radius. This is expected if the GWs are excited by point sources. For these GWs,cH = 150–530 m/s,τr ∼ 8–40 min, andλH ∼ 100–500 km. Using reverse ray‐tracing, no GW withcH > 200 m/s propagates belowz = 100 km, 73% of the GWs in the first case cannot propagate belowz ∼ 100 km, all of the GWs in the second case cannot propagate belowz ∼ 100 km, and the inferred thermospheric point sources are ∼2–4° from deep convection. Because the underlying GWs are most likely excited by a point source and most must be created in the thermosphere, we find that these concentric TIDs are most likely induced by GWs generated in the thermosphere, including those withcH = 150–200 m/s. Their close proximity to deep convection and the TEC map asymmetries suggest these TIDs are likely induced by secondary GWs from local horizontal body forces created by the dissipation of primary GWs from deep convection.

     
    more » « less
  5. Abstract

    A new Cloud Imaging and Particle Size (CIPS) gravity wave (GW) variance data set is available that facilitates automated analysis of GWs entering the mesosphere. This work examines several years of CIPS GW variances from 50 to 55 km in the context of the Arctic and Antarctic polar vortices. CIPS observes highest GW activity in the vortex edge region where horizontal wind speeds are largest, consistent with previously published GW climatologies in the stratosphere and mesosphere. CIPS observes the well‐documented planetary wave (PW)‐1 patterns in GW activity in both hemispheres. In the Northern Hemisphere, maximum GW activity occurs over the North Atlantic and western Europe. In the Southern Hemisphere, maximum GW activity stretches from the Andes over the South Atlantic and Indian Oceans, as expected. In the NH, CIPS GW spatial patterns are highly correlated with horizontal wind speed. In the SH, CIPS GW patterns are less positively correlated with the winds due to increased zonal symmetry and orographic forcing. The Andes Mountains and Antarctic Peninsula, South Georgia Island, Kerguelen/Heard Islands, New Zealand, and Tasmania are persistent sources of orographic GWs. Atmospheric Infrared sounder observations of stratospheric GWs are analyzed alongside CIPS to explore vertical GW coherence and to infer GW propagation and sources. NH midlatitude GW activity is reduced during the January 2021 SSW, as expected. This reduction in GWs leads to a simultaneous reduction in traveling ionospheric disturbances (TIDs), providing more evidence that weak polar vortex events with weak GW activity leads to reduced daytime TID activity.

     
    more » « less