Unexpected climatological behavior of MLT gravity wave momentum flux in the lee of the Southern Andes hot spot

Abstract. During austral winter the mountains of the southern Andes and Antarctic Peninsula are a known hot spot of intense gravity wave momentum flux. There also exists a long leeward region of increased gravity wave energy that sweeps eastwards from the mountains out over the Southern Ocean, the source of which has historically proved difficult to determine. In this study we use Global Positioning System (GPS) Radio Occultation (RO) data from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) satellite constellation to investigate the distribution, variability and sources of waves in the hot spot region and over the Southern Ocean. We present evidence that suggests a southward focusing of waves into the stratospheric jet from sources to the north. We also describe a wavelet analysis technique for the quantitative identification of individual waves from COSMIC temperature profiles. This analysis reveals different geographical regimes of wave amplitude and short-timescale variability in the wave field over the Southern Ocean. Finally, we take advantage of the large numbers of closely spaced pairs of profiles from the deployment phase of the COSMIC constellation in 2006 to make estimates of gravity wave horizontal wavelengths. We show that, given sufficient numbers of these pairs, GPS-RO can then produce physically reasonable estimates of stratospheric gravity wave momentum flux in the hot spot region that are consistent with other studies. The results are discussed in the context of previous satellite and modelling studies to build up a better picture of the nature and origins of waves in the southern winter stratosphere.

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The southern stratospheric gravity wave hot spot: individual waves and their momentum fluxes measured by COSMIC GPS-RO

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-7797-2015 ◽

2015 ◽

Vol 15 (14) ◽

pp. 7797-7818 ◽

Cited By ~ 47

Author(s):

N. P. Hindley ◽

C. J. Wright ◽

N. D. Smith ◽

N. J. Mitchell

Keyword(s):

Southern Ocean ◽

Gravity Wave ◽

General Circulation ◽

Hot Spot ◽

Polar Vortex ◽

General Circulation Models ◽

Wave Drag ◽

Southern Andes ◽

Analysis Technique ◽

Modelling Studies

Abstract. Nearly all general circulation models significantly fail to reproduce the observed behaviour of the southern wintertime polar vortex. It has been suggested that these biases result from an underestimation of gravity wave drag on the atmosphere at latitudes near 60° S, especially around the "hot spot" of intense gravity wave fluxes above the mountainous Southern Andes and Antarctic peninsula. Here, we use Global Positioning System radio occultation (GPS-RO) data from the COSMIC satellite constellation to determine the properties of gravity waves in the hot spot and beyond. We show considerable southward propagation to latitudes near 60° S of waves apparently generated over the southern Andes. We propose that this propagation may account for much of the wave drag missing from the models. Furthermore, there is a long leeward region of increased gravity wave energy that sweeps eastwards from the mountains over the Southern Ocean. Despite its striking nature, the source of this region has historically proved difficult to determine. Our observations suggest that this region includes both waves generated locally and orographic waves advected downwind from the hot spot. We describe and use a new wavelet-based analysis technique for the quantitative identification of individual waves from COSMIC temperature profiles. This analysis reveals different geographical regimes of wave amplitude and short-timescale variability in the wave field over the Southern Ocean. Finally, we use the increased numbers of closely spaced pairs of profiles from the deployment phase of the COSMIC constellation in 2006 to make estimates of gravity wave horizontal wavelengths. We show that, given sufficient observations, GPS-RO can produce physically reasonable estimates of stratospheric gravity wave momentum flux in the hot spot that are consistent with measurements made by other techniques. We discuss our results in the context of previous satellite and modelling studies and explain how they advance our understanding of the nature and origins of waves in the southern stratosphere.

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Impact of Global Warming on Gravity Wave Momentum Flux in the Lower Stratosphere

SOLA ◽

10.2151/sola.2005-049 ◽

2005 ◽

Vol 1 ◽

pp. 189-192 ◽

Cited By ~ 2

Author(s):

Shingo Watanabe ◽

Tatsuya Nagashima ◽

Seita Emori

Keyword(s):

Global Warming ◽

Gravity Wave ◽

Momentum Flux ◽

Lower Stratosphere ◽

Wave Momentum

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Characterization of Momentum Transport Associated with Organized Moist Convection and Gravity Waves

Journal of the Atmospheric Sciences ◽

10.1175/2010jas3418.1 ◽

2010 ◽

Vol 67 (10) ◽

pp. 3208-3225 ◽

Cited By ~ 28

Author(s):

Todd P. Lane ◽

Mitchell W. Moncrieff

Keyword(s):

Gravity Wave ◽

Gravity Waves ◽

Momentum Flux ◽

Tropical Convection ◽

Momentum Transport ◽

Moist Convection ◽

Convective Systems ◽

Convective Momentum Transport ◽

Convective Organization ◽

Wave Momentum

Abstract Tropical convection is inherently multiscalar, involving complex fields of clouds and various regimes of convective organization ranging from small disorganized cumulus up to large organized convective clusters. In addition to being a crucial component of the atmospheric water cycle and the global heat budget, tropical convection induces vertical fluxes of horizontal momentum. There are two main contributions to the momentum transport. The first resides entirely in the troposphere and is due to ascent, descent, and organized circulations associated with precipitating convective systems. The second resides in the troposphere, stratosphere, and farther aloft and is caused by vertically propagating gravity waves. Both the convective momentum transport and the gravity wave momentum flux must be parameterized in general circulation models; yet in existing parameterizations, these two processes are treated independently. This paper examines the relationship between the convective momentum transport and convectively generated gravity wave momentum flux by utilizing idealized simulations of multiscale tropical convection in different wind shear conditions. The simulations produce convective systems with a variety of regimes of convective organization and therefore different convective momentum transport properties and gravity wave spectra. A number of important connections are identified, including a consistency in the sign of the momentum transports in the lower troposphere and stratosphere that is linked to the generation of gravity waves by tilted convective structures. These results elucidate important relationships between the convective momentum transport and the gravity wave momentum flux that will be useful for interlinking their parameterization in the future.

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