1. TIIMES Gravity Wave Retreat, National Center for Atmospheric Research, Boulder, CO, 19 June - 6 July 2006 TIIMES Gravity Wave Retreat Explicitly-Resolved Stratospheric Gravity Waves in Swath-Scanned Radiance Imagery and High-Resolution Numerical Weather Prediction (NWP) Model Runs Steve Eckermann Naval Research Laboratory (NRL), Washington, DC Dong Wu NASA/JPL, Pasadena, CA Jim Doyle Code 7533 NRL Monterey, CA Larry Coy & John McCormack Code 7646 NRL DC Tim Hogan Code 7532 NRL Monterey, CA Ag Stephens & Bryan Lawrence Rutherford Appleton Lab, U. K.

2. TIIMES Gravity Wave Retreat, National Center for Atmospheric Research, Boulder, CO, 19 June - 6 July 2006 Gravity Waves in Swath-Scanned Stratospheric Radiances: Background Isolation of gravity waves in the stratospheric radiances channels of the Advanced Microwave Sounding Unit (AMSU-A) was pioneered by Dong Wu and colleagues circa 2004… –Wu, D. L., Mesoscale gravity wave variances from AMSU-A radiances, Geophys. Res. Lett., 31, L12114, doi:10.1029/2004GL019562, 2004. –Wu, D. L., and F. Zhang, 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. Isolation of gravity waves in stratospheric radiances from higher-resolution infrared swath-scanners (e.g., AIRS) is being pioneered by Joan Alexander and colleagues… –Alexander, M. J., and C. Barnet, Using Satellite Observations to Constrain Parameterizations of Gravity Wave Effects for Global Models, J. Atmos. Sci., (in press), 2006.

3. TIIMES Gravity Wave Retreat, National Center for Atmospheric Research, Boulder, CO, 19 June - 6 July 2006 So what’s new here re: AMSU-A?… Do we fully understand the gravity wave-induced radiance structure resolved in pushbroom stratospheric radiance imagery acquired by AMSU-A?No… 1.We still are not able (and most studies never attempt) to invert a measured gravity wave radiance oscillation R’ (T’ B ) into intrinsic unsmeared gravity wave properties (e.g., temperature amplitude, vertical flux of horizontal pseudomomentum density) 2.We don’t understand which 3D gravity waves are visible and invisible to AMSU-A formulate an accurate 3D forward model Can we formulate an accurate 3D forward model of in-orbit detection of gravity waves in AMSU-A’s swath-scanned radiance maps? validate that model observationally Can we validate that model observationally for an AMSU-A observation of a gravity wave of known intrinsic properties? develop inversion algorithms Can we use a validated forward model to develop inversion algorithms that fully characterize the intrinsic (unsmeared) properties of gravity waves resolved in AMSU-A (or radiances from other swath scanners)

4. TIIMES Gravity Wave Retreat, National Center for Atmospheric Research, Boulder, CO, 19 June - 6 July 2006 AMSU-A Scan Pattern

5. TIIMES Gravity Wave Retreat, National Center for Atmospheric Research, Boulder, CO, 19 June - 6 July 2006 AMSU-A Scan Cycle 30 step and stare measurements in eqipsaced sequential cross-track scan angles between ±48.33 o. One measurement per 0.2025s, 8 second duty cycle

6. TIIMES Gravity Wave Retreat, National Center for Atmospheric Research, Boulder, CO, 19 June - 6 July 2006 Temperature Weighting Functions From Our Full 3D Forward Model for AMSU-A Channel 9

7. TIIMES Gravity Wave Retreat, National Center for Atmospheric Research, Boulder, CO, 19 June - 6 July 2006 3D Weighting Functions and the Instrument’s “Visibility” to Gravity Waves In other words, the 3D Fourier Transform of the AMSU-A weighting function W j (X,Y,Z) at beam position j defines the “visibility” of AMSU-A to a gravity wave of given three- dimensional wavenumber (k X,k Y,k Z ).

8. TIIMES Gravity Wave Retreat, National Center for Atmospheric Research, Boulder, CO, 19 June - 6 July 2006 AMSU-A Beam “Visibilities” to Gravity Waves (Normalized Fourier Transforms of 3D Weighting Functions) Consider a gravity wave of h = 400 km, z =12 km. The beam spectra above predict gravity wave visibilities of ~10-13%

9. TIIMES Gravity Wave Retreat, National Center for Atmospheric Research, Boulder, CO, 19 June - 6 July 2006 Complete 3D Forward Model Simulations Confirm These Spectral Predictions 1.Gravity Wave: h = 400 km, z =12 km Peak Visibility Perturbations of ±13% T’ B (X j,Y j )/T PEAK This means this lower stratospheric gravity wave with T PEAK = 5K should yield a Channel 9 brightness temperature perturbations T’ B ~ ±0.65 K Since Channel 9 NE  T ~ 0.16 K, then this gravity wave should theoretically appear and be imaged as an oscillation as above in AMSU-A Channel 9 radiances

10. TIIMES Gravity Wave Retreat, National Center for Atmospheric Research, Boulder, CO, 19 June - 6 July 2006 Stratospheric Mountain Waves over Scandinavia: 14 January 2003 NOGAPS-ALPHA T239L60 Hindcast Simulation Initialized on 14 January 2003 at 0000 UTC 3 hourly fields from 0000 UTC to 2400 UTC Horizontal wavelength ~400 km Vertical Wavelength ~12 km T PEAK ~7 K at 90 hPa Gravity Wave Structure Extensively Validated Using Radiosonde and Aircraft Data Acquired During NASA SOLVE II mission

11. TIIMES Gravity Wave Retreat, National Center for Atmospheric Research, Boulder, CO, 19 June - 6 July 2006 Stratospheric Mountain Waves over Scandinavia: 14 January 2003 Horizontal structure of wave field in the stratosphere

12. TIIMES Gravity Wave Retreat, National Center for Atmospheric Research, Boulder, CO, 19 June - 6 July 2006 ECMWF IFS, NOGAPS-ALPHA and COAMPS ® Hindcast T’ Fields: 14 Jan 2003 1200 UTC

13. TIIMES Gravity Wave Retreat, National Center for Atmospheric Research, Boulder, CO, 19 June - 6 July 2006 AMSU-A Measured Channel 9 Brightness Temperature Perturbations Computed a large-scale mean radiance field computed using –11 point (~650 km) along- track running average –6 th order polynomial fits cross-track to smoothed fields (to capture limb effects) –Additional 5 point along track smoothing Isolated perturbations as

14. TIIMES Gravity Wave Retreat, National Center for Atmospheric Research, Boulder, CO, 19 June - 6 July 2006 Simulated 1200 UTC AMSU-A Radiance Perturbations by Forward Modeling 3D Model Temperature Fields ECMWF IFS NOGAPS-ALPHA COAMPS ® AMSU-A Data ECMWF IFS NOGAPS-ALPHA COAMPS ® AMSU-A Data

15. TIIMES Gravity Wave Retreat, National Center for Atmospheric Research, Boulder, CO, 19 June - 6 July 2006 Time Evolution of Brightness Temperature Perturbations: AMSU-A vs. Forward Modeled NOGAPS-ALPHA AMSU-A ObservationsNOGAPS-ALPHA Hindcasts

16. TIIMES Gravity Wave Retreat, National Center for Atmospheric Research, Boulder, CO, 19 June - 6 July 2006 Cross Sectional Comparisons

17. TIIMES Gravity Wave Retreat, National Center for Atmospheric Research, Boulder, CO, 19 June - 6 July 2006 Cross Sections Through Wave Field

18. TIIMES Gravity Wave Retreat, National Center for Atmospheric Research, Boulder, CO, 19 June - 6 July 2006 For Full Details, see…. Eckermann, S. D., D. L. Wu, J. D. Doyle, L. Coy, J. P. McCormack, A. Stephens, B. N. Lawrence, and T. F. Hogan, Imaging gravity waves in lower stratospheric AMSU-A radiances, SPARC Newsletter, 26, 30-33, 2006. Eckermann, S. D., and D. L. Wu, Imaging gravity waves in lower stratospheric AMSU-A radiances, Part 1: Simple forward model, Atmos. Chem. Phys. Discuss., 6, 1953- 2001, 2006. Eckermann, S. D., D. L. Wu, J. D. Doyle, J. F. Burris, T. J. McGee, C. A. Hostetler, L. Coy, B. N. Lawrence, A. Stephens, J. P. McCormack, and T. F. Hogan, Imaging gravity waves in lower stratospheric AMSU-A radiances, Part 2: Validation case study, Atmos. Chem. Phys. Discuss., 6, 2003-2058, 2006.

19. TIIMES Gravity Wave Retreat, National Center for Atmospheric Research, Boulder, CO, 19 June - 6 July 2006 Summary and Conclusions We’ve developed 3D forward model of the in-orbit radiance acquisition by AMSU-A and used it to predictions the gravity wave structures that are visible and invisible to AMSU-A swath-scanned imagery The model predicts absolute (not relative) amplitudes, phases and horizontal wavelengths of waves’ radiance signal in swath imagery A well-observed stratospheric mountain wave over Scandinavia on 14 January 2003 was “hindcast” using NWP models These 3D NWP temperature fields were used to “simulate” the actual AMSU-A overpasses and radiance acquisition from Channel 9 on this day (NWP fields validated against suborbital observations) The forward model reproduces both the amplitude and phase of the radiance structures actually observed by AMSU-A on this day This study provides an initial validation of our forward model’s prediction of the visibility of AMSU-A Channel 9 to this gravity wave event. FUTURE WORK?  extend forward model to Channels 10-14 using prototype Community Radiative Transfer Model (pCTRM)  study additional wave cases through full depth of the stratosphere  compare & cross-correlate with synchronous AIRS imagery on EOS Aqua