scholarly journals Temporal variability of tidal and gravity waves during a record long 10 day continuous lidar sounding

2017 ◽  
Author(s):  
Kathrin Baumgarten ◽  
Michael Gerding ◽  
Gerd Baumgarten ◽  
Franz-Josef Lübken
Keyword(s):  
Gravity Waves ◽  
General Circulation ◽  
Middle Atmosphere ◽  
Wave Interaction ◽  
Weather Conditions ◽  
General Circulation Models ◽  
Driving Mechanism ◽  
Lidar Measurement ◽  
Large Variability ◽  
Tidal Waves

Abstract. Gravity waves (GW) as well as solar tides are a key driving mechanism for the circulation in the Earth's atmosphere. The propagation of gravity waves is strongly infected by tidal waves as they modulate the mean background wind field and vice versa, which is not yet fully understood and not implemented in many circulation models. The daylight capable Rayleigh-Mie-Raman (RMR) lidar at Kühlungsborn (54° N, 12&deg E) typically provides temperature data to investigate both wave phenomena during one full day or several consecutive days in the middle atmosphere between 30 and 75 km altitude. Outstanding weather conditions in May 2016 allowed for an unprecedented 10-day continuous lidar measurement which shows a large variability of gravity waves and tides on time scales of days. Using a 1-dimensional spectral filtering technique, gravity and tidal waves are separated according to their specific periods or vertical wavelengths, and their temporal evolution is studied. During the measurement a strong 24 h-wave occurs only between 40 and 60 km and vanishes after a few days. The disappearance is related to an enhancement of gravity waves with periods of 4–8 h. Wind data provided by ECMWF are used to analyze the meteorological situation at our site. The local wind structure changes during the observation period, which leads to different propagation conditions for gravity waves in the last days of the measurement and therefore a strong GW activity. The analysis indicates a further change in wave-wave interaction resulting in a minimum of the 24 h tide. The observed variability of tides and gravity waves on timescales of a few days clearly demonstrates the importance of continuous measurements with high temporal and spatial resolution to detect interaction phenomena, which can help to improve parametrization schemes of GW in general circulation models.

scholarly journals Temporal variability of tidal and gravity waves during a record long 10-day continuous lidar sounding

2018 ◽  
Vol 18 (1) ◽  
pp. 371-384 ◽  
Author(s):  
Kathrin Baumgarten ◽  
Michael Gerding ◽  
Gerd Baumgarten ◽  
Franz-Josef Lübken
Keyword(s):  
Gravity Waves ◽  
General Circulation ◽  
Middle Atmosphere ◽  
Weather Conditions ◽  
General Circulation Models ◽  
Driving Mechanism ◽  
Lidar Measurement ◽  
Large Variability ◽  
Tidal Waves ◽  
Measurement Period

Abstract. Gravity waves (GWs) as well as solar tides are a key driving mechanism for the circulation in the Earth's atmosphere. The propagation of gravity waves is strongly affected by tidal waves as they modulate the mean background wind field and vice versa, which is not yet fully understood and not adequately implemented in many circulation models. The daylight-capable Rayleigh–Mie–Raman (RMR) lidar at Kühlungsborn (54∘ N, 12∘ E) typically provides temperature data to investigate both wave phenomena during one full day or several consecutive days in the middle atmosphere between 30 and 75 km altitude. Outstanding weather conditions in May 2016 allowed for an unprecedented 10-day continuous lidar measurement, which shows a large variability of gravity waves and tides on timescales of days. Using a one-dimensional spectral filtering technique, gravity and tidal waves are separated according to their specific periods or vertical wavelengths, and their temporal evolution is studied. During the measurement period a strong 24 h wave occurs only between 40 and 60 km and vanishes after a few days. The disappearance is related to an enhancement of gravity waves with periods of 4–8 h. Wind data provided by ECMWF are used to analyze the meteorological situation at our site. The local wind structure changes during the observation period, which leads to different propagation conditions for gravity waves in the last days of the measurement period and therefore a strong GW activity. The analysis indicates a further change in wave–wave interaction resulting in a minimum of the 24 h tide. The observed variability of tides and gravity waves on timescales of a few days clearly demonstrates the importance of continuous measurements with high temporal and spatial resolution to detect interaction phenomena, which can help to improve parametrization schemes of GWs in general circulation models.

scholarly journals A two-dimensional Stockwell Transform for gravity wave analysis of AIRS measurements

2016 ◽  
Author(s):  
N. P. Hindley ◽  
N. D. Smith ◽  
C. J. Wright ◽  
N. J. Mitchell
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Momentum Flux ◽  
General Circulation ◽  
Middle Atmosphere ◽  
Critical Role ◽  
General Circulation Models ◽  
Two Dimensional ◽  
Wave Analysis ◽  
Stockwell Transform

Abstract. Gravity waves play a critical role in the dynamics of the middle atmosphere due to their ability to transport energy and momentum from their sources to great heights. The accurate parametrization of gravity wave momentum flux is of key importance to general circulation models. For the last decade, the nadir-viewing Atmospheric Infrared Sounder (AIRS) aboard NASA’s Aqua satellite has made global, two-dimensional (2-D) measurements of stratospheric radiances in which gravity waves can be detected. Current methods for gravity wave analysis of these data can introduce unwanted biases. Here, we present a new analysis method. Our method uses a 2-D Stockwell transform (2DST) to determine gravity wave horizontal wavelengths and directions in both directions simultaneously. We demonstrate that our method can accurately recover horizontal wavelengths and directions from a specified wave field. We show that the use of an elliptical spectral windowing function in the 2DST, in place of a Gaussian, can dramatically improve the recovery of wave amplitude. We measure momentum flux in two granules of AIRS measurements in two regions known to be intense hot spots of gravity wave activity: (i) the Drake Pas- sage/Antarctic Peninsula and (ii) the isolated mountainous island of South Georgia. We show that our 2DST method provides improved spatial localisation of key gravity wave properties over current methods. The added flexibility offered by alternative spectral windowing functions and scaling parameters presented here extend the usefulness of our 2DST method to other areas of geophysical data analysis.

scholarly journals Ozone-Gravity Wave Interaction in the Upper Stratosphere/Lower Mesosphere

2022 ◽  
Author(s):  
Axel Gabriel
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
General Circulation ◽  
Low Frequency ◽  
Wave Interaction ◽  
General Circulation Models ◽  
Intrinsic Frequency ◽  
Night Time ◽  
Ozone Photochemistry ◽  
Middle Stratosphere

Abstract. The increase in amplitudes of upward propagating gravity waves (GWs) with height due to decreasing density is usually described by exponential growth; however, recent measurements detected a much stronger increase in gravity wave potential energy density (GWPED) during daylight than night-time (increase by a factor of about 4 to 8 between middle stratosphere and upper mesosphere), which is not well understood up to now. This paper suggests that ozone-gravity wave interaction in the upper stratosphere/lower mesosphere is largely responsible for this phenomenon. The coupling between ozone-photochemistry and temperature is particularly strong in the upper stratosphere where the time-mean ozone mixing ratio is decreasing with height; therefore, an initial uplift of an air parcel must lead to a local increase in ozone and in the heating rate compared to the environment, and, hence, to an amplification of the initial uplift. Standard solutions of upward propagating GWs with linear ozone-temperature coupling are formulated suggesting local amplitude amplifications during daylight of 5 to 15 % for low-frequency GWs (periods ≥4 hours), as a function of the intrinsic frequency which decreases if ozone-temperature coupling is included. Subsequently, for horizontal wavelengths larger than 500 km and vertical wavelengths smaller than 5 km, the cumulative amplification during the upward level-by-level propagation leads to much stronger amplitudes in the GW perturbations (factor of about 1.5 to 3) and in the GWPED (factor of about 3 to 9) at upper mesospheric altitudes. The results open a new viewpoint for improving general circulation models with resolved or parameterized GWs.

scholarly journals Exploiting the weekly cycle as observed over Europe to analyse aerosol indirect effects in two climate models

2009 ◽  
Vol 9 (21) ◽  
pp. 8493-8501 ◽  
Author(s):  
J. Quaas ◽  
O. Boucher ◽  
A. Jones ◽  
G. P. Weedon ◽  
J. Kieser ◽  
...  
Keyword(s):  
Indirect Effects ◽  
General Circulation ◽  
Climate Models ◽  
General Circulation Models ◽  
Cloud Microphysics ◽  
Liquid Water Path ◽  
Large Variability ◽  
Aerosol Indirect Effects ◽  
Weekly Cycle ◽  
Model Control

Abstract. A weekly cycle in aerosol pollution and some meteorological quantities is observed over Europe. In the present study we exploit this effect to analyse aerosol-cloud-radiation interactions. A weekly cycle is imposed on anthropogenic emissions in two general circulation models that include parameterizations of aerosol processes and cloud microphysics. It is found that the simulated weekly cycles in sulfur dioxide, sulfate, and aerosol optical depth in both models agree reasonably well with those observed indicating model skill in simulating the aerosol cycle. A distinct weekly cycle in cloud droplet number concentration is demonstrated in both observations and models. For other variables, such as cloud liquid water path, cloud cover, top-of-the-atmosphere radiation fluxes, precipitation, and surface temperature, large variability and contradictory results between observations, model simulations, and model control simulations without a weekly cycle in emissions prevent us from reaching any firm conclusions about the potential aerosol impact on meteorology or the realism of the modelled second aerosol indirect effects.

scholarly journals Net effect of the QBO in a chemistry climate model

2008 ◽  
Vol 8 (21) ◽  
pp. 6505-6525 ◽  
Author(s):  
H. J. Punge ◽  
M. A. Giorgetta
Keyword(s):  
General Circulation ◽  
Climate Models ◽  
Climate Model ◽  
Middle Atmosphere ◽  
Meridional Circulation ◽  
Vortex Formation ◽  
General Circulation Models ◽  
Quasi Biennial Oscillation ◽  
The Mean ◽  
The Tropics

Abstract. The quasi-biennial oscillation (QBO) of zonal wind is a prominent mode of variability in the tropical stratosphere. It affects not only the meridional circulation and temperature over a wide latitude range but also the transport and chemistry of trace gases such as ozone. Compared to a QBO less circulation, the long-term climatological means of these quantities are also different. These climatological net effects of the QBO can be studied in general circulation models that extend into the middle atmosphere and have a chemistry and transport component, so-called Chemistry Climate Models (CCMs). In this work we show that the CCM MAECHAM4-CHEM can reproduce the observed QBO variations in temperature and ozone mole fractions when nudged towards observed winds. In particular, it is shown that the QBO signal in transport of nitrogen oxides NOx plays an important role in reproducing the observed ozone QBO, which features a phase reversal slightly below the level of maximum of the ozone mole fraction in the tropics. We then compare two 20-year experiments with the MAECHAM4-CHEM model that differ by including or not including the QBO. The mean wind fields differ between the two model runs, especially during summer and fall seasons in both hemispheres. The differences in the wind field lead to differences in the meridional circulation, by the same mechanism that causes the QBO's secondary meridional circulation, and thereby affect mean temperatures and the mean transport of tracers. In the tropics, the net effect on ozone is mostly due to net differences in upwelling and, higher up, the associated temperature change. We show that a net surplus of up to 15% in NOx in the tropics above 10 hPa in the experiment that includes the QBO does not lead to significantly different volume mixing ratios of ozone. We also note a slight increase in the southern vortex strength as well as earlier vortex formation in northern winter. Polar temperatures differ accordingly. Differences in the strength of the Brewer-Dobson circulation and in further trace gas concentrations are analysed. Our findings underline the importance of a representation of the QBO in CCMs.

scholarly journals Intercomparison of Gravity Waves in Global Convection-Permitting Models

2019 ◽  
Vol 76 (9) ◽  
pp. 2739-2759 ◽  
Author(s):  
Claudia Christine Stephan ◽  
Cornelia Strube ◽  
Daniel Klocke ◽  
Manfred Ern ◽  
Lars Hoffmann ◽  
...  
Keyword(s):  
Gravity Waves ◽  
General Circulation ◽  
Primary Source ◽  
General Circulation Models ◽  
Systematic Change ◽  
Model Formulation ◽  
Difficult Challenge ◽  
Atmospheric Gravity ◽  
Coarse Grids ◽  
Horizontal Grid

AbstractLarge uncertainties remain with respect to the representation of atmospheric gravity waves (GWs) in general circulation models (GCMs) with coarse grids. Insufficient parameterizations result from a lack of observational constraints on the parameters used in GW parameterizations as well as from physical inconsistencies between parameterizations and reality. For instance, parameterizations make oversimplifying assumptions about the generation and propagation of GWs. Increasing computational capabilities now allow GCMs to run at grid spacings that are sufficiently fine to resolve a major fraction of the GW spectrum. This study presents the first intercomparison of resolved GW pseudomomentum fluxes (GWMFs) in global convection-permitting simulations and those derived from satellite observations. Six simulations of three different GCMs are analyzed over the period of one month of August to assess the sensitivity of GWMF to model formulation and horizontal grid spacing. The simulations reproduce detailed observed features of the global GWMF distribution, which can be attributed to realistic GWs from convection, orography, and storm tracks. Yet the GWMF magnitudes differ substantially between simulations. Differences in the strength of convection may help explain differences in the GWMF between simulations of the same model in the summer low latitudes where convection is the primary source. Across models, there is no evidence for a systematic change with resolution. Instead, GWMF is strongly affected by model formulation. The results imply that validating the realism of simulated GWs across the entire resolved spectrum will remain a difficult challenge not least because of a lack of appropriate observational data.

Estimation of hydrological response to future climate change in a cold watershed

2018 ◽  
Vol 10 (1) ◽  
pp. 78-88 ◽  
Author(s):  
Jian Sha ◽  
Zhong-Liang Wang ◽  
Yue Zhao ◽  
Yan-Xue Xu ◽  
Xue Li
Keyword(s):  
Climate Change ◽  
General Circulation ◽  
Water System ◽  
Coupled Model ◽  
Weather Conditions ◽  
General Circulation Models ◽  
Future Climate ◽  
Future Climate Change ◽  
Research Station ◽  
Hydrological Process

Abstract The vulnerability of the natural water system in cold areas to future climate change is of great concern. A coupled model approach was applied in the headwater watershed area of Yalu River in the northeastern part of China to estimate the response of hydrological processes to future climate change with moderate data. The stochastic Long Ashton Research Station Weather Generator was used to downscale the results of general circulation models to generate synthetic daily weather series in the 2050s and 2080s under various projected scenarios, which were applied as input data of the Generalized Watershed Loading Functions hydrological model for future hydrological process estimations. The results showed that future wetter and hotter weather conditions would have positive impacts on the watershed runoff yields but negative impacts on the watershed groundwater flow yields. The freezing period in winter would be shortened with earlier snowmelt peaks in spring. These would result in less snow cover in winter and shift the monthly allocations of streamflow with more yields in March but less in April and May, which should be of great concern for future local management. The proposed approach of the coupled model application is effective and can be used in other similar areas.

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