scholarly journals Gravity wave influence on NLC: experimental results from ALOMAR, 69° N

2013 ◽  
Vol 13 (7) ◽  
pp. 20049-20079
Author(s):  
H. Wilms ◽  
M. Rapp ◽  
P. Hoffmann ◽  
J. Fiedler ◽  
G. Baumgarten
Keyword(s):  
Kinetic Energy ◽  
Gravity Wave ◽  
Gravity Waves ◽  
Wave Activity ◽  
Set Covering ◽  
Full Data ◽  
Data Set ◽  
Strong Activity ◽  
Volume Measurements ◽  
Weak Activity

Abstract. The influence of gravity waves on noctilucent clouds (NLC) at ALOMAR (69° N) is analyzed by relating gravity wave activity to NLC occurrence from common-volume measurements. Gravity wave kinetic energies are derived from MF-radar wind data and filtered into different period ranges by wavelet transformation. From the data set covering the years 1999–2011 a direct correlation between gravity wave kinetic energy and NLC occurrence is not found. I.e., NLC appear independently of the simultaneously measured gravity wave kinetic energy. In addition, gravity wave activity is divided into weak and strong activity as compared to a 13 yr mean. The NLC occurrence rates during strong and weak activity are calculated separately for a given wave period and compared to each other. Again, for the full data set no dependence of NLC occurrence on relative gravity wave activity is found. However, concentrating on 12 h of NLC detections during 2008, we do find an NLC-amplification with strong long-period gravity wave occurrence. Our analysis hence confirms previous findings that in general NLC at ALOMAR are not predominantly driven by gravity waves while exceptions to this rule are at least possible.

scholarly journals Gravity wave influence on NLC: experimental results from ALOMAR, 69° N

2013 ◽  
Vol 13 (23) ◽  
pp. 11951-11963 ◽  
Author(s):  
H. Wilms ◽  
M. Rapp ◽  
P. Hoffmann ◽  
J. Fiedler ◽  
G. Baumgarten
Keyword(s):  
Kinetic Energy ◽  
Gravity Wave ◽  
Gravity Waves ◽  
Wavelet Transformation ◽  
Wave Activity ◽  
Strong Activity ◽  
Full Dataset ◽  
Volume Measurements ◽  
Weak Activity ◽  
Mf Radar

Abstract. The influence of gravity waves on noctilucent clouds (NLC) at ALOMAR (69° N) is analysed by relating gravity wave activity to NLC occurrence from common-volume measurements. Gravity wave kinetic energies are derived from MF-radar wind data and filtered into different period ranges by wavelet transformation. From the dataset covering the years 1999–2011, a direct correlation between gravity wave kinetic energy and NLC occurrence is not found, i.e., NLC appear independently of the simultaneously measured gravity wave kinetic energy. In addition, gravity wave activity is divided into weak and strong activity as compared to a 13 yr mean. The NLC occurrence rates during strong and weak activity are calculated separately for a given wave period and compared to each other. Again, for the full dataset no dependence of NLC occurrence on relative gravity wave activity is found. However, concentrating on 12 h of NLC detections during 2008, we do find an NLC-amplification with strong long-period gravity wave occurrence. Our analysis hence confirms previous findings that in general NLC at ALOMAR are not predominantly driven by gravity waves while exceptions to this rule are at least possible.

scholarly journals Seasonal changes in gravity wave activity measured by lidars at mid-latitudes

2008 ◽  
Vol 8 (22) ◽  
pp. 6775-6787 ◽  
Author(s):  
M. Rauthe ◽  
M. Gerding ◽  
F.-J. Lübken
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Low Frequency ◽  
Weather Conditions ◽  
Wave Activity ◽  
Data Set ◽  
Atmospheric Physics ◽  
Adverse Weather Conditions ◽  
Comprehensive Information ◽  
Adverse Weather

Abstract. More than 230 nights of temperature measurements between 1 and 105 km have been performed at the Leibniz-Institute of Atmospheric Physics in Kühlungsborn with a combination of two different lidars, i.e. a Rayleigh-Mie-Raman lidar and a potassium lidar. About 1700 h of measurements have been collected between 2002 and 2006. Apart from some gaps due to the adverse weather conditions the measurements are well distributed throughout the year. Comprehensive information about the activity of medium- and low-frequency gravity waves was extracted from this data set. The dominating vertical wavelengths found are between 10 and 20 km and do not show any seasonal variation. In contrast the temperature fluctuations due to gravity waves experience a clear annual cycle with a maximum in winter. The most significant differences exist around 60 km where the fluctuations in winter are more than two times larger than they are in summer. Only small seasonal differences are observed above 90 km and below 35 km. Generally, the fluctuations grow from about 0.5 K up to 8 K between 20 and 100 km. Damping of waves is observed at nearly all altitudes and in all seasons. The planetary wave activity shows a similar structure in altitude and season as the gravity wave activity which indicates that similar mechanisms influencing different scales. Combining the monthly mean temperatures and the fluctuations we show that the transition between winter and summer season and vice versa seems to start in the mesopause region and to penetrate downward.

scholarly journals Seasonal changes in gravity wave activity measured by lidars at mid-latitudes

2008 ◽  
Vol 8 (4) ◽  
pp. 13741-13773 ◽  
Author(s):  
M. Rauthe ◽  
M. Gerding ◽  
F.-J. Lübken
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Low Frequency ◽  
Weather Conditions ◽  
Wave Activity ◽  
Data Set ◽  
Atmospheric Physics ◽  
Adverse Weather Conditions ◽  
Comprehensive Information ◽  
Adverse Weather

Abstract. More than 230 nights of temperature measurements between 1 and 105 km have been performed at the Leibniz-Institute of Atmospheric Physics in Kühlungsborn with a combination of two different lidars, i.e. a Rayleigh-Mie-Raman lidar and a potassium lidar. About 1700 h of measurements have been collected between 2002 and 2006. Apart from some gaps due to the adverse weather conditions the measurements are well distributed throughout the year. Comprehensive information about the activity of medium- and low-frequency gravity waves was extracted from this data set. The dominating vertical wavelengths found are between 10 and 20 km and do not show any seasonal variation. In contrast the temperature fluctuations due to gravity waves experience a clear annual cycle with a maximum in winter. The most significant differences exist around 60 km where the fluctuations in winter are more than two times larger than they are in summer. Only small seasonal differences are observed above 90 km and below 35 km. Generally, the fluctuations grow from about 0.5 K up to 8 K between 20 and 100 km. Damping of waves is observed at nearly all altitudes and in all seasons. The planetary wave activity shows a similar structure in altitude and season as the gravity wave activity which indicates a strong coupling between the processes of the different scales. Combining the monthly mean temperatures and the fluctuations we show that the transition between winter and summer season and vice versa seems to start in the mesopause region and to penetrate downward.

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

2017 ◽  
Vol 17 (4) ◽  
pp. 2901-2920 ◽  
Author(s):  
Lars Hoffmann ◽  
Reinhold Spang ◽  
Andrew Orr ◽  
M. Joan Alexander ◽  
Laura A. Holt ◽  
...  
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Lower Stratosphere ◽  
Michelson Interferometer ◽  
Temperature Fluctuations ◽  
Wave Activity ◽  
Cloud Formation ◽  
Small Scale ◽  
Data Set ◽  
The Right

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.

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

2016 ◽  
Author(s):  
Lars Hoffmann ◽  
Reinhold Spang ◽  
Andrew Orr ◽  
M. Joan Alexander ◽  
Laura A. Holt ◽  
...  
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Lower Stratosphere ◽  
Michelson Interferometer ◽  
Temperature Fluctuations ◽  
Wave Activity ◽  
Cloud Formation ◽  
Small Scale ◽  
Data Set ◽  
Medium Range Weather Forecast

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 comprises observations of the Atmospheric InfraRed Sounder (AIRS) aboard NASA's Aqua satellite during 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 most sensitive to temperature fluctuations at about 17–32 km 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 cause 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 Forecast (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.

scholarly journals Influence of the cloud-level neutral layer on the vertical propagation of topographically generated gravity waves on Venus

2019 ◽  
Vol 71 (1) ◽  
Author(s):  
Takeru Yamada ◽  
Takeshi Imamura ◽  
Tetsuya Fukuhara ◽  
Makoto Taguchi
Keyword(s):  
Layer Thickness ◽  
Gravity Wave ◽  
Local Time ◽  
Gravity Waves ◽  
Analytical Approach ◽  
Wave Activity ◽  
Neutral Layer ◽  
Low Latitudes ◽  
Vertical Propagation ◽  
The Waves

AbstractThe reason for stationary gravity waves at Venus’ cloud top to appear mostly at low latitudes in the afternoon is not understood. Since a neutral layer exists in the lower part of the cloud layer, the waves should be affected by the neutral layer before reaching the cloud top. To what extent gravity waves can propagate vertically through the neutral layer has been unclear. To examine the possibility that the variation of the neutral layer thickness is responsible for the dependence of the gravity wave activity on the latitude and the local time, we investigated the sensitivity of the vertical propagation of gravity waves on the neutral layer thickness using a numerical model. The results showed that stationary gravity waves with zonal wavelengths longer than 1000 km can propagate to the cloud-top level without notable attenuation in the neutral layer with realistic thicknesses of 5–15 km. This suggests that the observed latitudinal and local time variation of the gravity wave activity should be attributed to processes below the cloud. An analytical approach also showed that gravity waves with horizontal wavelengths shorter than tens of kilometers would be strongly attenuated in the neutral layer; such waves should originate in the altitude region above the neutral layer.

scholarly journals A statistical study of gravity waves from radiosonde observations at Wuhan (30° N, 114° E) China

2005 ◽  
Vol 23 (3) ◽  
pp. 665-673 ◽  
Author(s):  
S. D. Zhang ◽  
F. Yi
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Extreme Values ◽  
Dynamical Instability ◽  
Strong Wind ◽  
Data Set ◽  
Height Range ◽  
Wave Parameters ◽  
Thermal Structures ◽  
Radiosonde Observation

Abstract. Several works concerning the dynamical and thermal structures and inertial gravity wave activities in the troposphere and lower stratosphere (TLS) from the radiosonde observation have been reported before, but these works were concentrated on either equatorial or polar regions. In this paper, background atmosphere and gravity wave activities in the TLS over Wuhan (30° N, 114° E) (a medium latitudinal region) were statistically studied by using the data from radiosonde observations on a twice daily basis at 08:00 and 20:00 LT in the period between 2000 and 2002. The monthly-averaged temperature and horizontal winds exhibit the essential dynamic and thermal structures of the background atmosphere. For avoiding the extreme values of background winds and temperature in the height range of 11-18km, we studied gravity waves, respectively, in two separate height regions, one is from ground surface to 10km (lower part), and the other is within 18-25km (upper part). In total, 791 and 1165 quasi-monochromatic inertial gravity waves were extracted from our data set for the lower and upper parts, respectively. The gravity wave parameters (intrinsic frequencies, amplitudes, wavelengths, intrinsic phase velocities and wave energies) are calculated and statistically studied. The statistical results revealed that in the lower part, there were 49.4% of gravity waves propagating upward, and the percentage was 76.4% in the upper part. Moreover, the average wave amplitudes and energies are less than those at the lower latitudinal regions, which indicates that the gravity wave parameters have a latitudinal dependence. The correlated temporal evolution of the monthly-averaged wave energies in the lower and upper parts and a subsequent quantitative analysis strongly suggested that at the observation site, dynamical instability (strong wind shear) induced by the tropospheric jet is the main excitation source of inertial gravity waves in the TLS.

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

2015 ◽  
Vol 8 (11) ◽  
pp. 4645-4655 ◽  
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.

scholarly journals Seasonal variations in gravity wave activity at three locations in Brazil

2009 ◽  
Vol 27 (3) ◽  
pp. 1059-1065 ◽  
Author(s):  
B. R. Clemesha ◽  
P. P. Batista ◽  
R. A. Buriti da Costa ◽  
N. Schuch
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Close Correlation ◽  
Temporal Variations ◽  
Wave Activity ◽  
Vertical Shear ◽  
Equatorial Station ◽  
Wave Forcing ◽  
Santa Maria ◽  
Fluctuating Wind

Abstract. Using the variance in meteor radar winds as a measure of gravity wave activity, we investigate the temporal variations in gravity waves at three locations in Brazil: São João do Cariri (7.3° S, 36.4° W), Cachoeira Paulista (22.7° S, 45.0° W) and Santa Maria (29.7° S, 53.7° W). The technique used is that of Hocking (2005) which makes it possible to separate the zonal and meridional components of the fluctuating wind velocity. We find that the seasonal variation of the fluctuating wind is similar to that of the amplitude of the diurnal tide, showing a predominantly semi-annual variation, stronger at Cachoeira Paulista and Santa Maria than at the quasi-equatorial station, Cariri. Both with respect to the seasonal trend and shorter term variations, strong coupling between gravity wave activity and tides is indicated by a remarkably close correlation between the fluctuating velocity and the vertical shear in the tidal winds. It is not clear as to whether this is caused by gravity wave forcing of the tides or whether it results from in situ generation of gravity waves by tidal wind shear.

scholarly journals Intercomparison of stratospheric gravity wave observations with AIRS and IASI

2014 ◽  
Vol 7 (12) ◽  
pp. 4517-4537 ◽  
Author(s):  
L. Hoffmann ◽  
M. J. Alexander ◽  
C. Clerbaux ◽  
A. W. Grimsdell ◽  
C. I. Meyer ◽  
...  
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Global Scale ◽  
Wave Activity ◽  
Spatial And Temporal Patterns ◽  
Atmospheric Infrared Sounder ◽  
Substantial Impact ◽  
Stratospheric Temperature ◽  
Consistent Picture ◽  
Time Variations

Abstract. Gravity waves are an important driver for the atmospheric circulation and have substantial impact on weather and climate. Satellite instruments offer excellent opportunities to study gravity waves on a global scale. This study focuses on observations from the Atmospheric Infrared Sounder (AIRS) onboard the National Aeronautics and Space Administration Aqua satellite and the Infrared Atmospheric Sounding Interferometer (IASI) onboard the European MetOp satellites. The main aim of this study is an intercomparison of stratospheric gravity wave observations of both instruments. In particular, we analyzed AIRS and IASI 4.3 μm brightness temperature measurements, which directly relate to stratospheric temperature. Three case studies showed that AIRS and IASI provide a clear and consistent picture of the temporal development of individual gravity wave events. Statistical comparisons based on a 5-year period of measurements (2008–2012) showed similar spatial and temporal patterns of gravity wave activity. However, the statistical comparisons also revealed systematic differences of variances between AIRS and IASI that we attribute to the different spatial measurement characteristics of both instruments. We also found differences between day- and nighttime data that are partly due to the local time variations of the gravity wave sources. While AIRS has been used successfully in many previous gravity wave studies, IASI data are applied here for the first time for that purpose. Our study shows that gravity wave observations from different hyperspectral infrared sounders such as AIRS and IASI can be directly related to each other, if instrument-specific characteristics such as different noise levels and spatial resolution and sampling are carefully considered. The ability to combine observations from different satellites provides an opportunity to create a long-term record, which is an exciting prospect for future climatological studies of stratospheric gravity wave activity.

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