AIRS/Aqua Observations of Gravity Waves

Introduction

This data repository provides access to gravity wave observations of the Atmospheric Infrared Sounder (AIRS) aboard NASA's Aqua satellite. Aqua was launched in May 2002 into a nearly polar, low earth orbit (705 km altitude, 100 min orbit period, 14.4 orbits per day). AIRS is an infrared nadir sounder with across-track scanning capabilities. Each across-track scan covers 1780 km ground distance and consists of 90 footprints. Two adjacent scans are separated by 18 km along-track distance. The footprint size varies between 14 x 14 km2 at nadir and 21 x 42 km2 at the scan extremes. AIRS measurements cover three wavelength bands in the 3.74-15.4 μm spectral range.

Information on stratospheric gravity wave activity is derived from radiance measurements in the 4.3 and 15 μm CO2 fundamental bands. These bands typically get optically thick in the mid stratosphere, e. g., the 4.3 μm measurements are most sensitive to atmospheric temperatures at about 30-40 km altitude. In order to extract the gravity wave signals, background signals due to large-scale temperature gradients or planetary waves are removed with a detrending procedure. Measurement noise is significantly reduced by averaging the radiance measurements of multiple AIRS channels. AIRS is sensitive only to gravity waves with rather long vertical wavelengths (λz≥10-15 km) but provides good horizontal resolution (λx≥30 km) due to the nadir observation geometry.

Two specific data products are provided in this repository: (i) The 4.3 and 15 micron brightness temperature data products are derived by averaging AIRS radiance measurements of three selected channel sets in the 4.3 and 15 micron wavebands and converting them to brightness temperatures. Brightness temperature perturbations due to gravity waves are determined by applying the polynomial fit method described above. The brightness temperature data sets have relatively coarse vertical resolution and gravity wave vertical wavelength sensitivity, but have low measurement noise due to multichannel averaging. (ii) The 3-D stratospheric temperature retrieval data set is derived by applying a nonlinear radiative transfer model and an optimal estimation retrieval scheme to retrieve vertical temperature profiles for the individual footprints of the AIRS measurements. The retrieval scheme provides better vertical resolution than the brightness temperature products, but is more sensitive to noise.

These data files provide more detailed information on the characteristics of the brightness temperature data sets:

These data files provide more detailed information on the characteristics of the 3-D stratospheric temperature retrievals:

Browse images

The browse images provided on this web site show global maps of stratospheric gravity wave activity in terms of 4.3 μm brightness temperature perturbations. Data are shown separately for nighttime (01:30 LT) and daytime (13:30 LT) observations. Note that the brightness temperature perturbations shown in the maps are usually much smaller than real gravity wave temperature amplitudes, because of the vertical smoothing effect of the nadir observation geometry. In the browse images we restricted the range of the brightness temperature perturbations to make also weaker wave events visible.

Next to orography and jet sources, deep convection and thunderstorms may be a significant source of stratospheric gravity wave activity. AIRS radiance measurements in the 8.1 μm spectral window region can be used to detect clouds and convection. In cloud-free scenes the 8.1 μm measurements are sensitive to surface temperatures. In cloudy scenes the measurements indicate cloud top temperatures, which are usually much lower than surface temperatures.

Data access

The gravity wave data sets provided on this web site have been created using AIRS/Aqua L1B Infrared (IR) geolocated and calibrated radiances V005 distributed by the NASA Goddard Earth Sciences Data and Information Services Center (GES DISC). Please see the GES DISC website for further information on the AIRS/Aqua operational data products. Note that this data repository provides access to non-operational research data products, which are dedicated to the research on stratospheric gravity waves.

Legal notes

The data sets and browse images provided on this web site are licensed under a Creative Commons Attribution 4.0 International License. You are free to share the material in any medium or format and adapt it for any purpose, even commercially. You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use. You may not apply legal terms or technological measures that legally restrict others from doing anything the license permits. The licensor cannot revoke these freedoms as long as you follow the license terms. The data are distributed in the hope that it will be useful, but without any warranty. Please follow the link to see the terms and conditions of the license:

References

This data repository can be cited via the following doi:

Hoffmann, Lars, 2021, "AIRS/Aqua Observations of Gravity Waves", https://doi.org/10.26165/JUELICH-DATA/LQAAJA, Jülich DATA, V1.

Further information and citation, if the 4.3 and 15 μm brightness temperature data are used in publications:

Hoffmann, L., X. Xue, and M. J. Alexander, A global view of stratospheric gravity wave hotspots located with Atmospheric Infrared Sounder observations, J. Geophys. Res. Atmos., 118, 416-434, https://doi.org/10.1029/2012JD018658, 2013.

Hoffmann, L., Alexander, M. J., Clerbaux, C., Grimsdell, A. W., Meyer, C. I., Rößler, T., and Tournier, B.: Intercomparison of stratospheric gravity wave observations with AIRS and IASI, Atmos. Meas. Tech., 7, 4517–4537, https://doi.org/10.5194/amt-7-4517-2014, 2014.

Hoffmann, L., Spang, R., Orr, A., Alexander, M. J., Holt, L. A., and Stein, O.: A decadal satellite record of gravity wave activity in the lower stratosphere to study polar stratospheric cloud formation, Atmos. Chem. Phys., 17, 2901-2920, https://doi.org/10.5194/acp-17-2901-2017, 2017.

Further information and citation, if the 3-D stratospheric temperature retrieval data are used in publications:

Hoffmann, L., and Alexander, M. J., Retrieval of stratospheric temperatures from Atmospheric Infrared Sounder radiance measurements for gravity wave studies, J. Geophys. Res., 114, D07105, https://doi.org/10.1029/2008JD011241, 2009.

Contact

We encourage any scientist interested in the data set to contact us for discussions on how you like to use the data. This might help to reduce the risk of mistaken applications and helps us to track the distribution and areas of applications of the data set.

Please do not hesitate to contact us if you have any further questions:

Dr. Lars Hoffmann

Forschungszentrum Jülich
Jülich Supercomputing Centre
52425 Jülich
Germany

e-mail: l.hoffmann@fz-juelich.de

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