TIIMES Gravity Wave Retreat, National Center for Atmospheric Research, Boulder, CO, 19 June - 6 July 2006 TIIMES Gravity Wave Retreat Explicitly-Resolved.

TIIMES Gravity Wave Retreat, National Center for Atmospheric Research, Boulder, CO, 19 June - 6 July 2006TIIMES Gravity Wave Retreat, National Center for Atmospheric Research, Boulder, CO, 19 June - 6 July 2006

TIIMES Gravity Wave Retreat

Explicitly-Resolved Stratospheric Gravity Explicitly-Resolved Stratospheric Gravity Waves in Swath-Scanned Radiance Imagery Waves in Swath-Scanned Radiance Imagery

and High-Resolution Numerical Weather and High-Resolution Numerical Weather Prediction (NWP) Model RunsPrediction (NWP) Model Runs

Steve EckermannSteve EckermannNaval Research Laboratory (NRL), Washington, DC

Dong WuNASA/JPL, Pasadena, CA

Jim DoyleCode 7533 NRL Monterey, CA

Larry Coy & John McCormack

Code 7646 NRL DC

Tim HoganCode 7532 NRL Monterey, CA

Ag Stephens & Bryan LawrenceRutherford Appleton Lab, U. K.


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.


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…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

Can we formulate an accurate 3D forward modelformulate an accurate 3D forward model of in-orbit detection of gravity waves in AMSU-A’s swath-scanned radiance maps?

Can we validate that model observationallyvalidate that model observationally for an AMSU-A observation of a gravity wave of known intrinsic properties?

Can we use a validated forward model to develop inversion algorithmsdevelop inversion algorithms that fully characterize the intrinsic (unsmeared) properties of gravity waves resolved in AMSU-A (or radiances from other swath scanners)


AMSU-A Scan Pattern


AMSU-A Scan Cycle• 30 step and stare measurements in eqipsaced sequential cross-track scan angles between ±48.33o. One

measurement per 0.2025s, 8 second duty cycle


Temperature Weighting Functions From Our Full 3D Forward Model for AMSU-A Channel 9


3D Weighting Functions and the Instrument’s “Visibility” to Gravity Waves

In other words, the 3D Fourier Transform of the AMSU-A weighting function Wj(X,Y,Z)

at beam position j defines the “visibility” of AMSU-A to a gravity wave of given three-dimensional wavenumber (kX,kY,kZ).


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%


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(Xj,Yj)/TPEAK

This means this lower stratospheric gravity wave with TPEAK = 5K should yield a Channel 9 brightness temperature perturbations T’B ~ ±0.65 K

Since Channel 9 NET ~ 0.16 K, then this gravity wave should theoretically appear and be imaged as an oscillation as above in AMSU-A Channel 9 radiances


Stratospheric Mountain Waves over Scandinavia: 14 January 2003

NOGAPS-ALPHA NOGAPS-ALPHA T239L60 Hindcast T239L60 Hindcast

Simulation Initialized Simulation Initialized on 14 January 2003 on 14 January 2003

at 0000 UTCat 0000 UTC

3 hourly fields from 0000 UTC to 2400 UTC

Horizontal wavelength ~400 km

Vertical Wavelength ~12 km

TPEAK ~7 K at 90 hPa

Gravity Wave Structure Extensively Validated Using Radiosonde and Aircraft Data Acquired During NASA SOLVE II mission


Stratospheric Mountain Waves over Scandinavia: 14 January 2003

Horizontal structure of wave field in the stratosphere


ECMWF IFS, NOGAPS-ALPHA and COAMPS® Hindcast T’ Fields: 14 Jan 2003 1200 UTC


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 – 6th order polynomial fits

cross-track to smoothed fields (to capture limb effects)

– Additional 5 point along track smoothing

• Isolated perturbations as


Simulated 1200 UTC AMSU-A Radiance Perturbations by Forward Modeling 3D Model Temperature Fields

ECMWF IFS NOGAPS-ALPHA COAMPSECMWF IFS NOGAPS-ALPHA COAMPS®® AMSU-A DataAMSU-A Data


Time Evolution of Brightness Temperature Perturbations: AMSU-A vs. Forward Modeled NOGAPS-ALPHA

AMSU-A Observations NOGAPS-ALPHA Hindcasts


Cross Sectional Comparisons


Cross Sections Through Wave Field


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.


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?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

TIIMES Gravity Wave Retreat, National Center for Atmospheric Research, Boulder, CO, 19 June - 6 July 2006 TIIMES Gravity Wave Retreat Explicitly-Resolved.

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