Seasonal cycle of orographic gravity wave occurrence above small islands in the Southern Hemisphere: Implications for effects on the general circulation

Alexander, M. Joan; Grimsdell, Alison W.

doi:10.1002/2013jd020526

Cited by 83 publications

(135 citation statements)

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“…In this study we analyze satellite observations of stratospheric gravity wave activity at 18 orographic hotspots located in the Southern Hemisphere. The study closely follows recent work of Alexander and Grimsdell (2013), which analyzed the seasonal cycle of orographic gravity wave occurrence above remote islands in the southern oceans. Further motivation to study stratospheric gravity wave activity at mid-and high latitudes during winter arises from the fact that gravity waves play an important role in the formation of polar stratospheric clouds (PSCs).…”

Section: Introductionmentioning

confidence: 63%

“…In order to identify orographic waves in as objective and consistent a manner as possible, the visual inspections follows criteria defined by Alexander and Grimsdell (2013). In particular, there must be a clear difference in the wave pattern near the hotspot to distinguish orographic waves from waves from other sources, i.e., the location of the hotspot should be clearly indicated by the position of the wave pattern.…”

Section: Two-box Methods For the Detection Of Mountain Wavesmentioning

confidence: 99%

“…As a second test we compared the detection results from the two-box method with the event statistic of Alexander and Grimsdell (2013). The study of Alexander and Grimsdell (2013) were identified by visual inspection of AIRS 15 µm brightness temperature perturbation maps.…”

Section: Two-box Methods For the Detection Of Mountain Wavesmentioning

confidence: 99%

“…In the winter hemisphere orographic and jet sources play a more important role, and small-scale orographic hotspots may provide a significant contribution to the total gravity wave drag that is currently not well-represented in global climate models McLandress et al, 2012;Alexander and Grimsdell, 2013;Vosper, 2015). More comprehensive observations may help to develop and improve parameterizations to better incorporate the wave drag even for such small sources.…”

Section: Introductionmentioning

confidence: 99%

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

2016

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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)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(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 midfall 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.

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Section: Introductionmentioning

confidence: 63%

Section: Two-box Methods For the Detection Of Mountain Wavesmentioning

confidence: 99%

Section: Two-box Methods For the Detection Of Mountain Wavesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

2016

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“…A relatively low cutoff was selected here to also make weak wave signals visible. Following the approach of Alexander and Grimsdell (2013), we performed a cross-check for the orographic wave events to confirm that these are indeed cases with substantial true gravity wave amplitudes. We computed the vertical wavelength λ z from the gravity wave dispersion relation for stationary waves, assuming that the ground-based frequency and phase speed are zero:…”

Section: A Survey Of Gravity-wave-induced Psc Formation Eventsmentioning

confidence: 99%

A decadal satellite record of gravity wave activity in the lower stratosphere to study polar stratospheric cloud formation

et al. 2017

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Abstract. Atmospheric gravity waves yield substantial small-scale temperature fluctuations that can trigger the formation of polar stratospheric clouds (PSCs). This paper introduces a new satellite record of gravity wave activity in the polar lower stratosphere to investigate this process. The record is comprised of observations of the Atmospheric Infrared Sounder (AIRS) aboard NASA's Aqua satellite from January 2003 to December 2012. Gravity wave activity is measured in terms of detrended and noise-corrected 15 µm brightness temperature variances, which are calculated from AIRS channels that are the most sensitive to temperature fluctuations at about 17-32 km of altitude. The analysis of temporal patterns in the data set revealed a strong seasonal cycle in wave activity with wintertime maxima at mid-and high latitudes. The analysis of spatial patterns indicated that orography as well as jet and storm sources are the main causes of the observed waves. Wave activity is closely correlated with 30 hPa zonal winds, which is attributed to the AIRS observational filter. We used the new data set to evaluate explicitly resolved temperature fluctuations due to gravity waves in the European Centre for Medium-Range Weather Forecasts (ECMWF) operational analysis. It was found that the analysis reproduces orographic and non-orographic wave patterns in the right places, but that wave amplitudes are typically underestimated by a factor of 2-3. Furthermore, in a first survey of joint AIRS and Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) satellite observations, nearly 50 gravity-wave-induced PSC formation events were identified. The survey shows that the new AIRS data set can help to better identify such events and more generally highlights the importance of the process for polar ozone chemistry.

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Radiosonde observations of gravity waves in the lower stratosphere over Davis, Antarctica

et al. 2014

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and 2012 are used to compile a climatology of lower stratosphere inertial gravity wave characteristics. Wavelet analysis extracts single wave packets from the wind and temperature perturbations. Wavelet parameters, combined with linear gravity wave theory, allow for the derivation of a wide range of wave characteristics. Observational filtering associated with this analysis preferentially selects inertial gravity waves with vertical wavelengths less than 2-3 km. The vertical propagation statistics show strong temporal and height variations. The waves propagate close to the horizontal and are strongly advected by the background wind in the wintertime. Notably, around half of the waves observed in the stratosphere above Davis between early May and mid-October propagate downward. This feature is distributed over the observed stratospheric height range. Based on the similarity between the upward and downward propagating waves and on the vertical structure of the nonlinear balance residual in the polar winter stratosphere, it is concluded that a source due to imbalanced flow that is distributed across the winter lower stratosphere best explains the observations. Calculations of kinetic and potential energies and momentum fluxes highlight the potential for variations in results due to different analysis techniques.

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Seasonal cycle of orographic gravity wave occurrence above small islands in the Southern Hemisphere: Implications for effects on the general circulation

Cited by 83 publications

References 43 publications

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

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

A decadal satellite record of gravity wave activity in the lower stratosphere to study polar stratospheric cloud formation

Radiosonde observations of gravity waves in the lower stratosphere over Davis, Antarctica

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