scholarly journals Numerical Modeling of the Generation of Tertiary Gravity Waves in the Mesosphere and Thermosphere During Strong Mountain Wave Events Over the Southern Andes

2019 ◽  
Vol 124 (9) ◽  
pp. 7687-7718 ◽  
Author(s):  
Sharon L. Vadas ◽  
Erich Becker
Keyword(s):  
Numerical Modeling ◽  
Gravity Waves ◽  
Mountain Wave ◽  
Southern Andes

scholarly journals Numerical Simulation of Mountain Waves over the Southern Andes. Part I: Mountain Wave and Secondary Wave Character, Evolutions, and Breaking

2020 ◽  
Vol 77 (12) ◽  
pp. 4337-4356
Author(s):  
Thomas S. Lund ◽  
David C. Fritts ◽  
Kam Wan ◽  
Brian Laughman ◽  
Han-Li Liu
Keyword(s):  
Gravity Waves ◽  
Acoustic Waves ◽  
Critical Level ◽  
Lower Thermosphere ◽  
Secondary Wave ◽  
Computational Domain ◽  
Mean Flow ◽  
Mountain Wave ◽  
Southern Andes ◽  
Ship Wave

AbstractThis paper addresses the compressible nonlinear dynamics accompanying increasing mountain wave (MW) forcing over the southern Andes and propagation into the mesosphere and lower thermosphere (MLT) under winter conditions. A stretched grid provides very high resolution of the MW dynamics in a large computational domain. A slow increase of cross-mountain winds enables MWs to initially break in the mesosphere and extend to lower and higher altitudes thereafter. MW structure and breaking is strongly modulated by static mean and semidiurnal tide fields exhibiting a critical level at ~114 km for zonal MW propagation. Varying vertical group velocities for different zonal wavelengths λx yield initial breaking in the lee of the major Andes peaks for λx ~ 50 km, and extending significantly upstream for larger λx approaching the critical level at later times. The localized extent of the Andes terrain in latitude leads to “ship wave” responses above the individual peaks at earlier times, and a much larger ship-wave response at 100 km and above as the larger-scale MWs achieve large amplitudes. Other responses above regions of MW breaking include large-scale secondary gravity waves and acoustic waves that achieve very large amplitudes extending well into the thermosphere. MW breaking also causes momentum deposition that yields local decelerations initially, which merge and extend horizontally thereafter and persist throughout the event. Companion papers examine the associated momentum fluxes, mean-flow evolution, gravity wave–tidal interactions, and the MW instability dynamics and sources of secondary gravity waves and acoustic waves.

scholarly journals Numerical simulation of mountain waves over the southern Andes, Part 2: Momentum fluxes and wave/mean-flow interactions

2021 ◽  
Author(s):  
David C. Fritts ◽  
Thomas S. Lund ◽  
Kam Wan ◽  
Han-Li Liu
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Acoustic Waves ◽  
Large Scale ◽  
Mean Flow ◽  
Mountain Wave ◽  
Southern Andes ◽  
Mountain Waves ◽  
Momentum Fluxes ◽  
Flow Interactions

AbstractA companion paper by Lund et al. (2020) employed a compressible model to describe the evolution of mountain waves arising due to increasing flow with time over the Southern Andes, their breaking, secondary gravity waves and acoustic waves arising from these dynamics, and their local responses. This paper describes the mountain wave, secondary gravity wave, and acoustic wave vertical fluxes of horizontal momentum, and the local and large-scale three-dimensional responses to gravity breaking and wave/mean-flow interactions accompanying this event. Mountain wave and secondary gravity wave momentum fluxes and deposition vary strongly in space and time due to variable large-scale winds and spatially-localized mountain wave and secondary gravity wave responses. Mountain wave instabilities accompanying breaking induce strong, local, largely-zonal forcing. Secondary gravity waves arising from mountain wave breaking also interact strongly with large-scale winds at altitudes above ~80km. Together, these mountain wave and secondary gravity wave interactions reveal systematic gravity-wave/mean-flow interactions having implications for both mean and tidal forcing and feedbacks. Acoustic waves likewise achieve large momentum fluxes, but typically imply significant responses only at much higher altitudes.

scholarly journals Can gravity waves significantly impact PSC occurrence in the Antarctic?

2009 ◽  
Vol 9 (22) ◽  
pp. 8825-8840 ◽  
Author(s):  
A. J. McDonald ◽  
S. E. George ◽  
R. M. Woollands
Keyword(s):  
Antarctic Peninsula ◽  
Gravity Waves ◽  
Clustering Algorithm ◽  
Small Scale ◽  
Temperature Threshold ◽  
Aerosol Extinction ◽  
Polar Stratospheric Clouds ◽  
Mountain Wave ◽  
Stratospheric Clouds ◽  
The Antarctic

Abstract. A combination of POAM III aerosol extinction and CHAMP RO temperature measurements are used to examine the role of atmospheric gravity waves in the formation of Antarctic Polar Stratospheric Clouds (PSCs). POAM III aerosol extinction observations and quality flag information are used to identify Polar Stratospheric Clouds using an unsupervised clustering algorithm. A PSC proxy, derived by thresholding Met Office temperature analyses with the PSC Type Ia formation temperature (TNAT), shows general agreement with the results of the POAM III analysis. However, in June the POAM III observations of PSC are more abundant than expected from temperature threshold crossings in five out of the eight years examined. In addition, September and October PSC identified using temperature thresholding is often significantly higher than that derived from POAM III; this observation probably being due to dehydration and denitrification. Comparison of the Met Office temperature analyses with corresponding CHAMP observations also suggests a small warm bias in the Met Office data in June. However, this bias cannot fully explain the differences observed. Analysis of CHAMP data indicates that temperature perturbations associated with gravity waves may partially explain the enhanced PSC incidence observed in June (relative to the Met Office analyses). For this month, approximately 40% of the temperature threshold crossings observed using CHAMP RO data are associated with small-scale perturbations. Examination of the distribution of temperatures relative to TNAT shows a large proportion of June data to be close to this threshold, potentially enhancing the importance of gravity wave induced temperature perturbations. Inspection of the longitudinal structure of PSC occurrence in June 2005 also shows that regions of enhancement are geographically associated with the Antarctic Peninsula; a known mountain wave "hotspot". The latitudinal variation of POAM III observations means that we only observe this region in June–July, and thus the true pattern of enhanced PSC production may continue operating into later months. The analysis has shown that early in the Antarctic winter stratospheric background temperatures are close to the TNAT threshold (and PSC formation), and are thus sensitive to temperature perturbations associated with mountain wave activity near the Antarctic peninsula (40% of PSC formation). Later in the season, and at latitudes away from the peninsula, temperature perturbations associated with gravity waves contribute to about 15% of the observed PSC (a value which corresponds well to several previous studies). This lower value is likely to be due to colder background temperatures already achieving the TNAT threshold unaided. Additionally, there is a reduction in the magnitude of gravity waves perturbations observed as POAM III samples poleward of the peninsula.

scholarly journals Mesospheric Mountain Wave Activity in the Lee of the Southern Andes

2020 ◽  
Author(s):  
Pierre-Dominique Pautet ◽  
Michael J. Taylor ◽  
David C. Fritts ◽  
Diego Janches ◽  
Natalie Kaifler ◽  
...  
Keyword(s):  
Wave Activity ◽  
Mountain Wave ◽  
Southern Andes

scholarly journals Numerical Modeling of the Propagation of Infrasonic Acoustic Waves Through the Turbulent Field Generated by the Breaking of Mountain Gravity Waves

2019 ◽  
Vol 46 (10) ◽  
pp. 5526-5534 ◽  
Author(s):  
R. Sabatini ◽  
J. B. Snively ◽  
C. Bailly ◽  
M. P. Hickey ◽  
J. L. Garrison
Keyword(s):  
Numerical Modeling ◽  
Gravity Waves ◽  
Acoustic Waves ◽  
Turbulent Field

scholarly journals Stratospheric gravity waves at Southern Hemisphere orographic hotspots: 2003–2014 AIRS/Aqua observations

2016 ◽  
Vol 16 (14) ◽  
pp. 9381-9397 ◽  
Author(s):  
Lars Hoffmann ◽  
Alison W. Grimsdell ◽  
M. Joan Alexander
Keyword(s):  
Gravity Wave ◽  
Southern Hemisphere ◽  
Antarctic Peninsula ◽  
Gravity Waves ◽  
General Circulation ◽  
Wave Activity ◽  
Small Scale ◽  
Mountain Wave ◽  
Kerguelen Islands ◽  
The Antarctic

Abstract. Stratospheric gravity waves from small-scale orographic sources are currently not well-represented in general circulation models. This may be a reason why many simulations have difficulty reproducing the dynamical behavior of the Southern Hemisphere polar vortex in a realistic manner. Here we discuss a 12-year record (2003–2014) of stratospheric gravity wave activity at Southern Hemisphere orographic hotspots as observed by the Atmospheric InfraRed Sounder (AIRS) aboard the National Aeronautics and Space Administration's (NASA) Aqua satellite. We introduce a simple and effective approach, referred to as the “two-box method”, to detect gravity wave activity from infrared nadir sounder measurements and to discriminate between gravity waves from orographic and other sources. From austral mid-fall to mid-spring (April–October) the contributions of orographic sources to the observed gravity wave occurrence frequencies were found to be largest for the Andes (90 %), followed by the Antarctic Peninsula (76 %), Kerguelen Islands (73 %), Tasmania (70 %), New Zealand (67 %), Heard Island (60 %), and other hotspots (24–54 %). Mountain wave activity was found to be closely correlated with peak terrain altitudes, and with zonal winds in the lower troposphere and mid-stratosphere. We propose a simple model to predict the occurrence of mountain wave events in the AIRS observations using zonal wind thresholds at 3 and 750 hPa. The model has significant predictive skill for hotspots where gravity wave activity is primarily due to orographic sources. It typically reproduces seasonal variations of the mountain wave occurrence frequencies at the Antarctic Peninsula and Kerguelen Islands from near zero to over 60 % with mean absolute errors of 4–5 percentage points. The prediction model can be used to disentangle upper level wind effects on observed occurrence frequencies from low-level source and other influences. The data and methods presented here can help to identify interesting case studies in the vast amount of AIRS data, which could then be further explored to study the specific characteristics of stratospheric gravity waves from orographic sources and to support model validation.

Alpine gravity waves: Lessons from MAP regarding mountain wave generation and breaking

2007 ◽  
Vol 133 (625) ◽  
pp. 917-936 ◽  
Author(s):  
Ronald B. Smith ◽  
James D. Doyle ◽  
Qingfang Jiang ◽  
Samantha A. Smith
Keyword(s):  
Gravity Waves ◽  
Wave Generation ◽  
Mountain Wave
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