TIIMES Gravity Wave Retreat

1
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
Larry Coy John McCormack Code 7646 NRL DC Tim
Hogan Code 7532 NRL Monterey, CA Ag Stephens
Bryan Lawrence Rutherford Appleton Lab, U. K.
Dong Wu NASA/JPL, Pasadena, CA Jim Doyle Code
7533 NRL Monterey, CA
2
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, doi10.1029/2004GL019562, 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, doi10.1029/2004JD0050
  90, 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
So whats 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
• We still are not able (and most studies never
  attempt) to invert a measured gravity wave
  radiance oscillation R (TB) into intrinsic
  unsmeared gravity wave properties (e.g.,
  temperature amplitude, vertical flux of
  horizontal pseudomomentum density)
• We dont understand which 3D gravity waves are
  visible and invisible to AMSU-A
• Can we formulate an accurate 3D forward model of
  in-orbit detection of gravity waves in AMSU-As
  swath-scanned radiance maps?
• Can we validate 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 algorithms that fully characterize the
  intrinsic (unsmeared) properties of gravity waves
  resolved in AMSU-A (or radiances from other swath
  scanners)

4
AMSU-A Scan Pattern
5
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

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Temperature Weighting Functions From Our Full 3D
Forward Model for AMSU-A Channel 9
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3D Weighting Functions and the Instruments
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).
8
AMSU-A Beam Visibilities to Gravity
Waves(Normalized Fourier Transforms of 3D
Weighting Functions)
Consider a gravity wave of lh 400 km, lz12 km.
The beam spectra above predict gravity wave
visibilities of 10-13
9
Complete 3D Forward Model Simulations Confirm
These Spectral Predictions
TB(Xj,Yj)/TPEAK

• Gravity Wave lh 400 km, lz12 km
• Peak Visibility Perturbations of 13

This means this lower stratospheric gravity wave
with TPEAK 5K should yield a Channel 9
brightness temperature perturbations TB 0.65
K Since Channel 9 NEDT 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
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 TPEAK 7 K at 90 hPa Gravity
Wave Structure Extensively Validated Using
Radiosonde and Aircraft Data Acquired During NASA
SOLVE II mission
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Stratospheric Mountain Waves over Scandinavia 14
January 2003

• Horizontal structure of wave field in the
  stratosphere

12
ECMWF IFS, NOGAPS-ALPHA and COAMPS Hindcast T
Fields 14 Jan 2003 1200 UTC
13
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

14
Simulated 1200 UTC AMSU-A Radiance Perturbations
by Forward Modeling 3D Model Temperature Fields

• ECMWF IFS NOGAPS-ALPHA
  COAMPS AMSU-A Data

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

• AMSU-A Observations

NOGAPS-ALPHA Hindcasts
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Cross Sectional Comparisons
17
Cross Sections Through Wave Field
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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.

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Summary and Conclusions

• Weve 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 models 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