Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 6 11 2006 10.5194/acp-6-3325-2006 http://www.atmos-chem-phys.net/6/3325/2006/ http://www.atmos-chem-phys.net/6/3325/2006/acp-6-3325-2006.html http://www.atmos-chem-phys.net/6/3325/2006/acp-6-3325-2006.pdf 3325 3341 2006-08-14 Imaging gravity waves in lower stratospheric AMSU-A radiances, Part 1: Simple forward model S. D. Eckermann stephen.eckermann@nrl.navy.mil D. L. Wu E. O. Hulburt Center for Space Research, Naval Research Laboratory, Washington, D.C., USA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA Using a simplified model of in-orbit radiance acquisition by the Advanced Microwave Sounding Unit (AMSU-A), we derive three-dimensional temperature weighting functions for Channel 9 measurements (peaking at ~60–90 hPa) at all 30 cross-track beam positions and use them to investigate the sensitivity of these radiances to gravity waves. The vertical widths of the weighting functions limit detection to waves with vertical wavelengths of ≳10 km, with slightly better vertical wavelength sensitivity at the outermost scan angles due to the limb effect. Fourier Transforms of two-dimensional cross-track weighting functions reveal optimal sensitivity to cross-track wavelengths at the near-nadir scan angles, where horizontal measurement footprints are smallest. This sensitivity is greater for the AMSU-A on the Aqua satellite than for the identical instruments on the NOAA meteorological satellites, due to a lower orbit altitude and thus smaller horizontal footprints from antenna spreading. Small cross-track asymmetries in the radiance response to gravity waves are found that peak at the mid-range scan angles, with more symmetric responses at near-nadir and far off-nadir scan angles. Three-dimensional simulations show gravity wave oscillations imaged in horizontal AMSU-A radiance maps swept out by the scan pattern and satellite motion. A distorting curvature is added to imaged wave phase lines due to vertical variations in weighting function peaks with cross-track scan angle. This wave distortion is analogous to the well-known "limb darkening" and "limb brightening" of microwave radiances acquired from purely vertical background temperature profiles by cross-track scanners. Waves propagating along track are more visible in these images at the outermost scan angles than those propagating cross track, due to oversampling and narrower widths of the horizontal measurement footprints in the along track direction. Based on nominal noise floors and representative lower stratospheric wave temperature amplitudes, our modeling indicates that Channel 9 AMSU-A radiances can resolve and horizontally image gravity waves with horizontal wavelengths of ≳150 km and vertical wavelengths of ≳10 km. Alexander, M. J.: Interpretations of observed climatological patterns in stratospheric gravity wave variance, J. Geophys. Res., 103, 8627–8640, 1998. Alexander, M. J. and Rosenlof, K. H.: Gravity-wave forcing in the stratosphere: Observational constraints from the Upper Atmosphere Research Satellite and implications for parameterization in global models, J. Geophys. Res., 108(D19), 4597, doi:10.1029/2003JD003373, 2003. Dewan, E. M., Picard, R. H., O'Neil, R. R., Gardiner, H. A., Gibson, J., Mill, J. D., Richards, E., Kendra, M., and Gallery, W. O.: MSX satellite observations of thunderstorm-generated gravity waves in mid-wave infrared images of the upper stratosphere, Geophys. Res. Lett., 25, 939–942, 1998. Eckermann, S. D. and Preusse, P.: Global measurements of stratospheric mountain waves from space, Science, 286, 1534–1537, 1999. Eckermann, S. D., Hirota, I., and Hocking, W. K.: Gravity-wave and equatorial-wave morphology of the stratosphere derived from long-term rocket soundings, Quart. J. Roy. Meteorol. Soc., 121, 149–186, 1995. Eckermann, S. D., Dörnbrack, A., Vosper, S. B., Flentje, H., Mahoney, M. J., Bui, T. P., and Carslaw, K. S.: Mountain wave-induced polar stratospheric cloud forecasts for aircraft science flights during SOLVE/THESEO 2000, Wea. Forecasting, 21, 42–68, 2006a. Eckermann, S. D., Wu, D. L., Doyle, J. D., Burris, J. F., McGee, T. J., Hostetler, C. A., Coy, L., Lawrence, B. N., Stephens, A., McCormack, J. P., and Hogan, T. F.: Imaging gravity waves in lower stratospheric AMSU-A radiances, Part: 2 Validation case study, Atmos. Chem. Phys., 6, 3343–3362, 2006b. Fetzer, E. J. and Gille, J. C.: Gravity wave variance in LIMS temperatures. Part I: Variability and comparison with background winds, J. Atmos. Sci., 51, 2461–2483, 1994. Fritts, D. C. and Alexander, M. J.: Gravity wave dynamics and effects in the middle atmosphere, Rev. Geophys., 41(1), 1003, doi:10.1029/2001RG000106, 2003. Goldberg, M. D., Crosby, D. S., and Zhou, L.: The limb adjustment of AMSU-A observations: methodology and validation, J. Appl. Meteorol., 40, 70–83, 2001. Grody, N. C.: Remote sensing of the atmosphere from satellites using microwave radiometry, in: Atmospheric Remote Sensing by Microwave Radiometry, edited by: Janssen, M. A., Wiley, New York, 259–334, 1993. Grody, N. C. and Pellegrino, P. P.: Synoptic-scale studies using the Nimbus 6 scanning microwave radiometer, J. Appl. Meteorol., 16, 816–826, 1977. Hertzog, A., Vial, F., Dörnbrack, A., Eckermann, S. D., Knudsen, B. M., and Pommereau, J.-P.: In-situ observations of gravity waves and comparisons with numerical simulations during the SOLVE/THESEO 2000 campaign, J. Geophys. Res., 107(D20), 8292, doi:10.1029/2001JD001025, 2002. Houghton, J. T., Taylor III, F. W., and Rodgers, C. D.: Remote sounding of atmospheres, Cambridge Univ. Press, 343pp, 1984. Jiang, J. H., Eckermann, S. D., Wu, D. L., and Ma, J.: A search for mountain waves in MLS stratospheric limb radiances from the Northern Hemisphere: data analysis and global mountain wave modeling, J. Geophys. Res., 109, D03107, doi:10.1029/2003JD003974, 2004. Kidder, S. Q. and Vonder Haar, T. H.: Satellite Meteorology: An Introduction, Academic Press, San Diego, 466pp, 1995. Kidder, S. Q., Goldberg, M. D., Zehr, R. M., DeMaria, M., Purdom, J. F. W., Velden, C. S., Grody, N. C., and Kusselson, S. J.: Satellite analysis of tropical cyclones using the Advanced Microwave Sounding Unit (AMSU), Bull. Am. Meteorol. Soc., 81, 1241–1259, 2000. Lambrigtsen, B. H.: Calibration of the AIRS microwave instruments, IEEE Trans. Geosci. Remote Sens., 41, 369–378, 2003. Mann, G. W., Carslaw, K. S., Chipperfield, M. P., Davies, S., and Eckermann, S. D.: Large NAT particles and denitrification caused by mountain waves in the Arctic stratosphere, J. Geophys. Res., 110, D08202, doi:10.1029/2004JD005271, 2005. McLandress, C., Alexander, M. J., and Wu, D.: Microwave limb sounder observations of gravity waves in the stratosphere: a climatology and interpretation, J. Geophys. Res., 105, 1947–1967, 2000. Mo, T.: Prelaunch calibration of the Advanced Microwave Sounding Unit-A for NOAA-K, IEEE Trans. Microwave Theory Tech., 44, 1460–1469, 1996. Mo, T.: AMSU-A antenna pattern corrections, IEEE Trans. Geosci. Remote Sens., 37, 103–112, 1999. Parkinson, C. L.: Aqua: An Earth-observing satellite mission to examine water and other climate variables, IEEE Trans. Geosci. Remote Sens., 41, 173–183, 2003. Poon, R. K. L.: A power law fit to oxygen absorption at 60 GHz and its application to remote sensing of atmospheric temperature, Radio Sci., 15, 25–33, 1980. Preusse, P., Eckermann, S. D., and Offermann, D.: Comparison of global distributions of zonal-mean gravity wave variance inferred from different satellite instruments, Geophys. Res. Lett., 27, 3877–3880, 2000. Rosenkranz, P. W., Hutchison, K. D., Hardy, K. R., and Davis, M. S.: An assessment of the impact of satellite microwave sounder incidence angle and scan geometry on the accuracy of atmospheric temperature profile retrievals, J. Atmos. Ocean. Tech., 14, 488–494, 1997. Staelin, D. H.: Inversion of passive microwave remote sensing data from satellites, in: Inversion Methods in Atmospheric Remote Sounding, edited by: Deepak, A., Academic, New York, 361–394, 1977. Tsuda, T., Nishida, M., Rocken, C., and Ware, R. H.: A global morphology of gravity wave activity in the stratosphere revealed by the GPS occultation data (GPS/MET), J. Geophys. Res., 105, 7257–7273, 2000. Wang, L. and Geller, M. A.: Morphology of gravity-wave energy as observed from 4 years (1998–2001) of high vertical resolution U. S. radiosonde data, J. Geophys. Res., 108(D16), 4489, doi:10.1029/2002JD002786, 2003. Waters, J. W., Kunzi, K. F., Pettyjohn, R. L., Poon, R. K. L., and Staelin, D. H.: Remote sensing of atmospheric temperature profiles with the Nimbus 5 microwave spectrometer, J. Atmos. Sci., 32, 1953–1969, 1975. Wu, D. L.: Mesoscale gravity wave variances from AMSU-A radiances, Geophys. Res. Lett., 31, L112114, doi:10.1029/2004GL019562, 2004. Wu, D. L. and Waters, J. W.: Satellite observations of atmospheric variances: A possible indication of gravity waves, Geophys. Res. Lett., 23, 3631–3634, 1996a. Wu, D. L. and Waters, J. W.: Gravity-wave-scale temperature fluctuations seen by the UARS MLS, Geophys. Res. Lett., 23, 3289–3292, 1996b. Wu, D. L. and Zhang, F.: A study of mesoscale gravity waves over the North Atlantic with satellite observations and a mesoscale model, J. Geophys. Res., 109, D22104, doi:10.1029/2004JD005090, 2004. Wu, D. L., Preusse, P., Eckermann, S. D., Jiang, J. H., de la Torre Juarez, M., Coy, L., and Wang, D. Y.: Remote sounding of atmospheric gravity waves with satellite limb and nadir techniques, Adv. Space Res., 37, 2269–2277, 2006.