Gravity-Wave-Driven Seasonal Variability of Temperature Differences between ECMWF IFS and Rayleigh Lidar Measurements in the Lee of the Southern Andes

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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Local time variation of gravity wave momentum fluxes and their relationship with the tides derived from LIDAR measurements

Journal of Atmospheric and Solar-Terrestrial Physics ◽

10.1016/j.jastp.2015.10.018 ◽

2015 ◽

Vol 135 ◽

pp. 136-142 ◽

Cited By ~ 3

Author(s):

Ryan Agner ◽

Alan Z. Liu

Keyword(s):

Gravity Wave ◽

Local Time ◽

Time Variation ◽

Lidar Measurements ◽

Momentum Fluxes ◽

Wave Momentum

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Evaluation of methods for gravity wave extraction from middle-atmospheric lidar temperature measurements

Atmospheric Measurement Techniques ◽

10.5194/amt-8-4645-2015 ◽

2015 ◽

Vol 8 (11) ◽

pp. 4645-4655 ◽

Cited By ~ 30

Author(s):

B. Ehard ◽

B. Kaifler ◽

N. Kaifler ◽

M. Rapp

Keyword(s):

Gravity Wave ◽

Gravity Waves ◽

Spectral Response ◽

Synthetic Data ◽

Temperature Measurements ◽

Data Set ◽

Wide Range ◽

Lidar Measurements ◽

Background Temperature ◽

Wave Induced

Abstract. This study evaluates commonly used methods of extracting gravity-wave-induced temperature perturbations from lidar measurements. The spectral response of these methods is characterized with the help of a synthetic data set with known temperature perturbations added to a realistic background temperature profile. The simulations are carried out with the background temperature being either constant or varying in time to evaluate the sensitivity to temperature perturbations not caused by gravity waves. The different methods are applied to lidar measurements over New Zealand, and the performance of the algorithms is evaluated. We find that the Butterworth filter performs best if gravity waves over a wide range of periods are to be extracted from lidar temperature measurements. The running mean method gives good results if only gravity waves with short periods are to be analyzed.

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Advanced hodograph-based analysis technique to derive gravity-wave parameters from lidar observations

Atmospheric Measurement Techniques ◽

10.5194/amt-13-479-2020 ◽

2020 ◽

Vol 13 (2) ◽

pp. 479-499

Author(s):

Irina Strelnikova ◽

Gerd Baumgarten ◽

Franz-Josef Lübken

Keyword(s):

Gravity Wave ◽

Wave Theory ◽

Linear Wave ◽

Data Set ◽

Background Removal ◽

Analysis Technique ◽

Lidar Measurements ◽

Meridional Winds ◽

Linear Fit ◽

Removal Technique

Abstract. An advanced hodograph-based analysis technique to derive gravity-wave (GW) parameters from observations of temperature and winds is developed and presented as a step-by-step recipe with justification for every step in such an analysis. As the most adequate background removal technique the 2-D FFT is suggested. For an unbiased analysis of fluctuation whose amplitude grows with height exponentially, we propose applying a scaling function of the form exp (z∕(ςH)), where H is scale height, z is altitude, and the constant ς can be derived by a linear fit to the fluctuation profile and should be in the range 1–10. The most essential part of the proposed analysis technique consists of fitting cosine waves to simultaneously measured profiles of zonal and meridional winds and temperature and subsequent hodograph analysis of these fitted waves. The linear wave theory applied in this analysis is extended by introducing a wave packet envelope term exp⁡(-(z-z0)2/2σ2) that accounts for limited extent of GWs in the observational data set. The novelty of our approach is that its robustness ultimately allows for automation of the hodograph analysis and resolves many more GWs than can be inferred by the manually applied hodograph technique. This technique allows us to unambiguously identify upward- and downward-propagating GWs and their parameters. This technique is applied to unique lidar measurements of temperature and horizontal winds measured in an altitude range of 30 to 70 km.

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Gravity waves observed from the Equatorial Wave Studies (EWS) campaign during 1999 and 2000 and their role in the generation of stratospheric semiannual oscillations

Annales Geophysicae ◽

10.5194/angeo-24-2481-2006 ◽

2006 ◽

Vol 24 (10) ◽

pp. 2481-2491 ◽

Cited By ~ 10

Author(s):

V. Deepa ◽

G. Ramkumar ◽

B. V. Krishna Murthy

Keyword(s):

Gravity Wave ◽

Gravity Waves ◽

Propagation Characteristics ◽

Mean Flow ◽

Vertical Wavelength ◽

Flow Acceleration ◽

Equatorial Wave ◽

The Mean ◽

Phase Propagation ◽

Rayleigh Lidar

Abstract. The altitude profiles of temperature fluctuations in the stratosphere and mesosphere observed with the Rayleigh Lidar at Gadanki (13.5° N, 79.2° E) on 30 nights during January to March 1999 and 21 nights during February to April 2000 were analysed to bring out the temporal and vertical propagation characteristics of gravity wave perturbations. The gravity wave perturbations showed periodicities in the 0.5–3-h range and attained large amplitudes (4–5 K) in the mesosphere. The phase propagation characteristics of gravity waves with different periods showed upward wave propagation with a vertical wavelength of 5–7 km. The mean flow acceleration computed from the divergence of momentum flux of gravity waves is compared with that calculated from monthly values of zonal wind obtained from RH-200 rockets flights. Thus, the contribution of gravity waves towards the generation of Stratospheric Semi Annual Oscillation (SSAO) is estimated.

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