scholarly journals A Comparison between Gravity Wave Momentum Fluxes in Observations and Climate Models

2013 ◽  
Vol 26 (17) ◽  
pp. 6383-6405 ◽  
Author(s):  
Marvin A. Geller ◽  
M. Joan Alexander ◽  
Peter T. Love ◽  
Julio Bacmeister ◽  
Manfred Ern ◽  
...  
Keyword(s):  
High Resolution ◽  
Gravity Wave ◽  
Gravity Waves ◽  
Climate Models ◽  
Radiosonde Data ◽  
Wave Source ◽  
Wide Range ◽  
Momentum Fluxes ◽  
High Resolution Models ◽  
Wave Momentum

Abstract For the first time, a formal comparison is made between gravity wave momentum fluxes in models and those derived from observations. Although gravity waves occur over a wide range of spatial and temporal scales, the focus of this paper is on scales that are being parameterized in present climate models, sub-1000-km scales. Only observational methods that permit derivation of gravity wave momentum fluxes over large geographical areas are discussed, and these are from satellite temperature measurements, constant-density long-duration balloons, and high-vertical-resolution radiosonde data. The models discussed include two high-resolution models in which gravity waves are explicitly modeled, Kanto and the Community Atmosphere Model, version 5 (CAM5), and three climate models containing gravity wave parameterizations, MAECHAM5, Hadley Centre Global Environmental Model 3 (HadGEM3), and the Goddard Institute for Space Studies (GISS) model. Measurements generally show similar flux magnitudes as in models, except that the fluxes derived from satellite measurements fall off more rapidly with height. This is likely due to limitations on the observable range of wavelengths, although other factors may contribute. When one accounts for this more rapid fall off, the geographical distribution of the fluxes from observations and models compare reasonably well, except for certain features that depend on the specification of the nonorographic gravity wave source functions in the climate models. For instance, both the observed fluxes and those in the high-resolution models are very small at summer high latitudes, but this is not the case for some of the climate models. This comparison between gravity wave fluxes from climate models, high-resolution models, and fluxes derived from observations indicates that such efforts offer a promising path toward improving specifications of gravity wave sources in climate models.

Gravity wave intermittency derived from HIRDLS and SABER satellite limb soundings

2020 ◽  
Author(s):  
Manfred Ern ◽  
Peter Preusse ◽  
Martin Riese
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Climate Models ◽  
Spatial Scales ◽  
Wave Activity ◽  
Background Flow ◽  
Wave Source ◽  
Gini Coefficients ◽  
Broadband Emission ◽  
Wave Distribution

<p>Sources of atmospheric gravity waves are mostly located in the troposphere and the lower stratosphere. Gravity waves propagate away from their sources, re-distribute energy and momentum in the atmosphere, and exert drag on the atmospheric background flow where they dissipate. Therefore they are important drivers of the atmospheric circulation. In climate models, their effect on the background circulation is usually parameterized because of their relatively short horizontal and vertical wavelengths that are of the order of 10-1000km and 1-100km, respectively. Gravity wave parametrizations are very simplified. For example, they often neglect the fact that gravity wave source processes and gravity wave propagation conditions can vary on short temporal and spatial scales. Therefore the global distribution of gravity wave activity is very intermittent, which has also important consequences where gravity waves dissipate and exert drag on the background flow, and which should be accounted for in parametrizations.<br>For guiding models, global observations of the gravity wave distribution and its intermittency are needed. We derive gravity wave potential energies and absolute momentum fluxes from observations of the High Resolution Dynamics Limb Sounder (HIRDLS) and the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) satellite instruments. As a measure of intermittency, we calculate global distributions of Gini coefficients. We find that our results are qualitatively in good agreement with previous findings from satellite, and similar in magnitude to intermittency obtained from previous superpressure balloon campaigns. In the stratosphere, strongest intermittency is found over orographic gravity wave sources, followed by gravity wave activity in the polar night jets. Intermittency in the tropical stratosphere is weakest. However, in the tropical upper mesosphere intermittency is increased, which is likely caused by the modulation of the gravity wave distribution by tides.</p>

scholarly journals Stratospheric gravity-waves over the mountainous island of South Georgia: testing a high-resolution dynamical model with 3-D satellite observations and radiosondes

2020 ◽  
Author(s):  
Neil P. Hindley ◽  
Corwin J. Wright ◽  
Alan M. Gadian ◽  
Lars Hoffmann ◽  
John K. Hughes ◽  
...  
Keyword(s):  
High Resolution ◽  
Southern Ocean ◽  
Gravity Wave ◽  
Gravity Waves ◽  
Wave Activity ◽  
Satellite Observations ◽  
Total Flux ◽  
Mean Flow ◽  
South Georgia ◽  
Momentum Fluxes

Abstract. Atmospheric gravity waves are key drivers of the transfer of energy and momentum between the layers of the Earth’s atmosphere. The accurate representation of these waves in General Circulation Models (GCMs) however has proved very challenging. This is because large parts of the gravity wave spectrum are at scales that are near or below the resolution of global GCMs. This is especially relevant for small isolated mountainous islands such as South Georgia (54° S, 36° W) in the Southern Ocean. Observations reveal the island to be an intense source of stratospheric gravity waves, but their momentum fluxes can be under-represented in global models due to its small size. This is a crucial limitation, since the inadequate representation of gravity waves near 60° S during winter has been linked to the long-standing "cold-pole problem", where the southern stratospheric polar vortex breaks up too late in spring by several weeks. Here we address a fundamental question: when a model is allowed to run at very high spatial resolution over South Georgia, how realistic are the simulated gravity waves compared to observations? To answer this question, we present a 3-D comparison between satellite gravity wave observations and a high resolution model over South Georgia. We use a dedicated high-resolution run (1.5 km horizontal grid, 118 vertical levels) of the Met Office Unified Model over South Georgia and coincident 3-D satellite observations from NASA AIRS/Aqua during July 2013 and June–July 2015. First, model winds are validated with coincident radiosonde observations. The AIRS observational filter is then applied to the model output to make the two data sets comparable. A 3-D S-transform method is used to measure gravity-wave amplitudes, wavelengths, directional momentum fluxes and intermittency in the model and observations. Our results show that although the timing of gravity wave activity in the model closely matches observations, area-averaged momentum fluxes are generally up to around 25 % lower than observed. Further, we find that 72 % of the total flux in the model region is located downwind of the island, compared to only 57 % in the AIRS measurements. Directly over the island, the model exhibits higher individual flux measurements but these fluxes are more intermittent than in observations, with 90 % of the total flux carried by just 22 % of wave events, compared to 32 % for AIRS. Observed gravity wave fluxes also appear to dissipate more quickly with increasing height than in the model, suggesting a greater role for wave-mean flow interactions in reality. Finally, spectral analysis of the wave fields suggests that the model over-estimates gravity wave fluxes at short horizontal scales directly over the island, but under-estimates fluxes from larger horizontal scale non-orographic waves in the region, leading to a lower average value overall. Our results indicate that, although increasing model resolution is important, it is also important to ensure that variability in the background wind vector and role of non-orographic waves are accurately simulated in order to achieve realistic gravity wave activity over the Southern Ocean in future GCMs.

scholarly journals Intraseasonal to interannual variability of Kelvin wave momentum fluxes as derived from high-resolution radiosonde data

2017 ◽  
Author(s):  
Jeremiah P. Sjoberg ◽  
Thomas Birner ◽  
Richard H. Johnson
Keyword(s):  
Time Series ◽  
High Resolution ◽  
Momentum Flux ◽  
Radiosonde Data ◽  
Boreal Summer ◽  
Vertical Resolution ◽  
Madden Julian Oscillation ◽  
Kelvin Wave ◽  
Momentum Fluxes ◽  
Wave Momentum

Abstract. Observational estimates of Kelvin wave momentum fluxes in the tropical lower stratosphere remains challenging. Here we extend a method based on linear wave theory to estimate time series of these momentum fluxes from high-resolution radiosonde data. Testing the sensitivity to vertical resolution, our estimated momentum fluxes are found to be most sensitive to vertical resolution greater than 1 km, largely due to overestimation of the vertical wavelength. Estimates of momentum fluxes derived from reanalyses and coarse-resolution satellite data are notably larger. Daily time series are produced for sounding sites operated by the U.S. Department of Energy (DOE) and from the recent Dynamics of the Madden-Julian Oscillation (DYNAMO) field campaign. Our momentum flux estimates are found to be robust to different data sources and processing, and in quantitative agreement with estimates from prior studies. Climatological analysis is performed over the selected 11 year span of data from the ARM sites. Analyses for the available 11-year span of data reveal the expected seasonal cycle of momentum flux maxima in boreal winter and minima in boreal summer and variability associated with the quasi-biennial oscillation (QBO) of maxima during easterly phase and minima during westerly phase. Analysis of Madden-Julian Oscillation (MJO) active periods suggests that the MJO provides a nontrivial increase in lowermost stratospheric momentum fluxes, though statistical significance is not found due to the small number of events observed in the available time series.

scholarly journals On the Relation between Gravity Waves and Wind Speed in the Lower Stratosphere over the Southern Ocean

2017 ◽  
Vol 74 (4) ◽  
pp. 1075-1093 ◽  
Author(s):  
Riwal Plougonven ◽  
Valérian Jewtoukoff ◽  
Alvaro de la Cámara ◽  
François Lott ◽  
Albert Hertzog
Keyword(s):  
Wind Speed ◽  
Probability Density ◽  
Gravity Wave ◽  
Gravity Waves ◽  
Probability Density Functions ◽  
Density Functions ◽  
Simple Relationship ◽  
Momentum Fluxes ◽  
Strong Winds ◽  
Wave Momentum

Abstract The relationship between gravity wave momentum fluxes and local wind speed is investigated for oceanic regions at high southern latitudes during austral spring. The motivation is to better describe the gravity wave field by identifying a simple relationship between gravity waves and the large-scale flow. The tools used to describe the gravity waves are probability density functions of the gravity wave momentum fluxes. Three independent datasets covering high latitudes in the Southern Hemisphere springtime are analyzed: simulations with a mesoscale model, analyses from the European Centre for Medium-Range Weather Forecasts, and observations from superpressure balloons of the Concordiasi campaign in 2010. A remarkably robust relation is found, with stronger momentum fluxes much more likely in regions of strong winds. The tails of the probability density functions are well described as lognormal. The median momentum flux increases linearly with background wind speed: for winds stronger than 50 m s−1, the median gravity wave momentum fluxes are about 4 times larger than for winds weaker than 10 m s−1. From model output, this relation is found to be relevant from the tropopause to the midstratosphere at least. The flux dependence on wind speed shows a somewhat steeper slope at higher altitude. Several different processes contribute to this relation, involving both the distribution of sources and the effects of propagation and filtering. It is argued that the location of tropospheric sources is the main contributor in the upper troposphere and lowermost stratosphere and that lateral propagation into regions of strong winds becomes increasingly important above.

scholarly journals Sensitivity of Gravity Wave Fluxes to Interannual Variations in Tropical Convection and Zonal Wind

2017 ◽  
Vol 74 (9) ◽  
pp. 2701-2716 ◽  
Author(s):  
M. Joan Alexander ◽  
David A. Ortland ◽  
Alison W. Grimsdell ◽  
Ji-Eun Kim
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Momentum Flux ◽  
Large Scale ◽  
Climate Models ◽  
Interannual Variations ◽  
Model Framework ◽  
Quasi Biennial Oscillation ◽  
Regional Variations ◽  
Wave Momentum

Abstract Using an idealized model framework with high-frequency tropical latent heating variability derived from global satellite observations of precipitation and clouds, the authors examine the properties and effects of gravity waves in the lower stratosphere, contrasting conditions in an El Niño year and a La Niña year. The model generates a broad spectrum of tropical waves including planetary-scale waves through mesoscale gravity waves. The authors compare modeled monthly mean regional variations in wind and temperature with reanalyses and validate the modeled gravity waves using satellite- and balloon-based estimates of gravity wave momentum flux. Some interesting changes in the gravity spectrum of momentum flux are found in the model, which are discussed in terms of the interannual variations in clouds, precipitation, and large-scale winds. While regional variations in clouds, precipitation, and winds are dramatic, the mean gravity wave zonal momentum fluxes entering the stratosphere differ by only 11%. The modeled intermittency in gravity wave momentum flux is shown to be very realistic compared to observations, and the largest-amplitude waves are related to significant gravity wave drag forces in the lowermost stratosphere. This strong intermittency is generally absent or weak in climate models because of deficiencies in parameterizations of gravity wave intermittency. These results suggest a way forward to improve model representations of the lowermost stratospheric quasi-biennial oscillation winds and teleconnections.

scholarly journals GRACILE: a comprehensive climatology of atmospheric gravity wave parameters based on satellite limb soundings

2018 ◽  
Vol 10 (2) ◽  
pp. 857-892 ◽  
Author(s):  
Manfred Ern ◽  
Quang Thai Trinh ◽  
Peter Preusse ◽  
John C. Gille ◽  
Martin G. Mlynczak ◽  
...  
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
General Circulation ◽  
Climate Models ◽  
General Circulation Models ◽  
Atmospheric Gravity Wave ◽  
Data Set ◽  
Wave Source ◽  
Global Data ◽  
Satellite Instruments

Abstract. Gravity waves are one of the main drivers of atmospheric dynamics. The spatial resolution of most global atmospheric models, however, is too coarse to properly resolve the small scales of gravity waves, which range from tens to a few thousand kilometers horizontally, and from below 1 km to tens of kilometers vertically. Gravity wave source processes involve even smaller scales. Therefore, general circulation models (GCMs) and chemistry climate models (CCMs) usually parametrize the effect of gravity waves on the global circulation. These parametrizations are very simplified. For this reason, comparisons with global observations of gravity waves are needed for an improvement of parametrizations and an alleviation of model biases. We present a gravity wave climatology based on atmospheric infrared limb emissions observed by satellite (GRACILE). GRACILE is a global data set of gravity wave distributions observed in the stratosphere and the mesosphere by the infrared limb sounding satellite instruments High Resolution Dynamics Limb Sounder (HIRDLS) and Sounding of the Atmosphere using Broadband Emission Radiometry (SABER). Typical distributions (zonal averages and global maps) of gravity wave vertical wavelengths and along-track horizontal wavenumbers are provided, as well as gravity wave temperature variances, potential energies and absolute momentum fluxes. This global data set captures the typical seasonal variations of these parameters, as well as their spatial variations. The GRACILE data set is suitable for scientific studies, and it can serve for comparison with other instruments (ground-based, airborne, or other satellite instruments) and for comparison with gravity wave distributions, both resolved and parametrized, in GCMs and CCMs. The GRACILE data set is available as supplementary data at https://doi.org/10.1594/PANGAEA.879658.

scholarly journals GRACILE: A comprehensive climatology of atmospheric gravity wave parameters based on satellite limb soundings

2018 ◽  
Author(s):  
Manfred Ern ◽  
Quang Thai Trinh ◽  
Peter Preusse ◽  
John C. Gille ◽  
Martin G. Mlynczak ◽  
...  
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
General Circulation ◽  
Climate Models ◽  
General Circulation Models ◽  
Atmospheric Gravity Wave ◽  
Data Set ◽  
Wave Source ◽  
Global Data ◽  
Satellite Instruments

Abstract. Gravity waves are one of the main drivers of atmospheric dynamics. The spatial resolution of most global atmospheric models, however, is too coarse to properly resolve the small scales of gravity waves, which range from tens to a few thousand kilometers horizontally, and from below 1 km to tens of kilometers vertically. Gravity wave source processes involve even smaller scales. Therefore, general circulation models (GCMs) and chemistry climate models (CCMs) usually parametrize the effect of gravity waves on the global circulation. These parametrizations are very simplified. For this reason, comparisons with global observations of gravity waves are needed for an improvement of parametrizations and an alleviation of model biases. We present a gravity wave climatology based on atmospheric infrared limb emissions observed by satellite (GRACILE). GRACILE is a global data set of gravity wave distributions observed in the stratosphere and the mesosphere by the infrared limb sounding satellite instruments High Resolution Dynamics Limb Sounder (HIRDLS) and Sounding of the Atmosphere using Broadband Emission Radiometry (SABER). Typical distributions (zonal averages and global maps) of gravity wave vertical wavelengths and along-track horizontal wavenumbers are provided, as well as gravity wave temperature variances, potential energies and absolute momentum fluxes. This global data set captures the typical seasonal variations of these parameters, as well as their spatial variations. The GRACILE data set is suitable for scientific studies, and it can serve for comparison with other instruments (ground based, airborne, or other satellite instruments) and for comparison with gravity wave distributions, both resolved and parametrized, in GCMs and CCMs. The GRACILE data set is available as supplementary data at https://doi.org/10.1594/PANGAEA.879658.

scholarly journals Spatial and seasonal variability of medium- and high-frequency gravity waves in the lower atmosphere revealed by US radiosonde data

2014 ◽  
Vol 32 (9) ◽  
pp. 1129-1143 ◽  
Author(s):  
S. D. Zhang ◽  
C. M. Huang ◽  
K. M. Huang ◽  
F. Yi ◽  
Y. H. Zhang ◽  
...  
Keyword(s):  
Energy Density ◽  
Gravity Waves ◽  
Seasonal Variability ◽  
High Frequency ◽  
Lower Atmosphere ◽  
Radiosonde Data ◽  
High Latitudes ◽  
Middle Latitudes ◽  
Momentum Fluxes ◽  
Horizontal Momentum

Abstract. We extended the broad spectral method proposed by Zhang et al. (2013) for the extraction of medium- and high-frequency gravity waves (MHGWs). This method was applied to 11 years (1998–2008) of radiosonde data from 92 stations in the Northern Hemisphere to investigate latitudinal, continuous vertical and seasonal variability of MHGW parameters in the lower atmosphere (2–25 km). The latitudinal and vertical distributions of the wave energy density and horizontal momentum fluxes as well as their seasonal variations exhibit considerable consistency with those of inertial gravity waves. Despite the consistency, the MHGWs have much larger energy density, horizontal momentum fluxes and wave force, indicating the more important role of MHGWs in energy and momentum transportation and acceleration of the background. For the observed MHGWs, the vertical wavelengths are usually larger than 8 km; the horizontal wavelengths peak in the middle troposphere at middle–high latitudes. These characteristics are obviously different from inertial gravity waves. The energy density and horizontal momentum fluxes have similar latitude-dependent seasonality: both of them are dominated by a semiannual variation at low latitudes and an annual variation at middle latitudes; however at high latitudes, they often exhibit more than two peaks per year in the troposphere. Compared with the inertial GWs, the derived intrinsic frequencies are more sensitive to the spatiotemporal variation of the buoyancy frequency, and at all latitudinal regions they are higher in summer. The wavelengths have a weaker seasonal variation; an evident annual cycle can be observed only at middle latitudes.

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