Simulation of an IHOP
Convective Initiation Case
for GIFTS Preparation
Derek J. Posselt1, Erik Olson1, Wayne F. Feltz1, Russ Dengel1,
Gail Dengel1, John R. Mecikalski1, Robert Aune1,
Brian Osborne1, Robert O. Knuteson1, and William L. Smith2
1Cooperative
Institute for Meteorological Satellite Studies,
Space Science and Engineering Center, University of Wisconsin–Madison
2NASA
D. Posselt
Langley Research Center
IHOP Spring Workshop
24-26 March 2003
Outline
•
•
•
•
•
•
Introduction to GIFTS
Choice of case: 12 June 2002
Evaluation of CI simulation
GIFTS simulated radiances
Uses of simulated radiances and retrievals
Future Work
D. Posselt
IHOP Spring Workshop
24-26 March 2003
Geosynchronous Imaging Fourier
Transform Spectrometer (GIFTS)
GIFTS Details:
•
•
•
•
Next generation geostationary imager/sounder with launch as early as 2006
Spectral resolution as high as 0.625 cm-1
Designed for horizontal resolution of 4 km, vertical resolution of 1-2 km, and
maximum temporal resolution of 11 seconds
Potential for much more rapid and high-resolution retrievals of temperature,
moisture, and wind than are available with any current geostationary instrument.
Pre-Launch Tasks:
•
•
•
•
Produce simulations of several different atmospheric cases
Use simulated atmosphere in the GIFTS forward radiative transfer model to
obtain top of the atmosphere radiances
Retrieve temperature, water vapor and winds from these radiances, and compare
them with the original simulated atmosphere to assess retrieval accuracy
Develop uses for radiance observations and retrieved quantities in advance of
launch
D. Posselt
IHOP Spring Workshop
24-26 March 2003
GIFTS IHOP 2002 CI Objectives
GIFTS high spatial and temporal resolution water vapor
measurements indicate vast potential for early detection
and diagnosis of CI
IHOP Case Objectives:
• Produce simulated atmosphere to be used for GIFTS preparation
• Demonstrate GIFTS potential to observe moisture convergence prior
to convective initiation
• Demonstrate GIFTS usefulness for observation of fine-scale rapidlyevolving water vapor structures
• Develop GIFTS data analysis techniques for CI applications
D. Posselt
IHOP Spring Workshop
24-26 March 2003
Case: 12 June 2002
Convective initiation occurred at approximately 2100 UTC along a
weak low-level trough stretching southwest to northeast through the
Oklahoma panhandle
Case Specifics for GIFTS Simulation:
• Environment mostly clear preceding convection
• CI occurred associated with strong, but small•
•
scale water vapor gradient
CI well-predicted and well-forced, leading to
relative ease of simulation
Occurred during a day specifically targeted for
study of convective initiation during IHOP 2002
D. Posselt
IHOP Spring Workshop
King Air
P3
Proteus
24-26 March 2003
GOES-11 Imagery
10-minute (approximate) 10.7 micron GOES-11 imagery
clearly depicting wind-shift boundary and CI
D. Posselt
IHOP Spring Workshop
24-26 March 2003
MM5 Configuration
Simulated atmospheric fields generated using the 5th generation
Penn State/NCAR Mesoscale Modeling system (MM5) initialized
from 10 km RUC analyses
Configuration details:
• 4 km grid spacing, 60 vertical levels
• Initialized 0600 UTC, 24-hour duration
• Goddard microphysics
• MRF boundary layer
• No cumulus parameterization
• RRTM radiation
• OSU-Land surface model
• Nudged toward RUC analyses during
6-hour spin-up period
D. Posselt
IHOP Spring Workshop
24-26 March 2003
Simulation Results
Cloud and water vapor features
• Color-shaded plot depicts 2meter mixing ratio
• White iso-surfaces encompass
cloud boundaries
• Wind vectors valid at 1.5 km
height
D. Posselt
IHOP Spring Workshop
24-26 March 2003
Simulation Results
Observed GOES-11 imagery
Simulated GOES-11 imagery
1900 UTC
1900 UTC
D. Posselt
IHOP Spring Workshop
24-26 March 2003
Simulation Results
Observed GOES-11 imagery
Simulated GOES-11 imagery
2000 UTC
2000 UTC
D. Posselt
IHOP Spring Workshop
24-26 March 2003
Simulation Results
Observed GOES-11 imagery
Simulated GOES-11 imagery
2100 UTC
2100 UTC
D. Posselt
IHOP Spring Workshop
24-26 March 2003
Simulation Results
Observed GOES-11 imagery
Simulated GOES-11 imagery
2200 UTC
2200 UTC
D. Posselt
IHOP Spring Workshop
24-26 March 2003
Simulation Results
Observed GOES-11 imagery
Simulated GOES-11 imagery
2300 UTC
2300 UTC
D. Posselt
IHOP Spring Workshop
24-26 March 2003
GIFTS Simulated Radiances and
Retrievals
Model
Atmosphere
Procedure
• Generate
•
•
•
•
simulated
atmospheric
fields
representative of desired case
Using GIFTS forward radiative transfer model,
produce top of atmosphere radiances from
simulated atmospheric fields
Retrieve temperature and water vapor from top
of atmosphere radiances
Compare retrievals with “truth” atmosphere to
assess accuracy of retrieval method
Develop applications based on simulated
radiances and retrievals
D. Posselt
IHOP Spring Workshop
Forward
Model
Radiances
24-26 March 2003
Top of Atmosphere Brightness
Temperatures
Output from GIFTS forward radiative transfer model:
10.7 micron brightness temperatures
10-min time resolution 1800-2200 UTC
D. Posselt
IHOP Spring Workshop
24-26 March 2003
Simulated vs. Retrieved
Water Vapor: 700 hPa
“True” mixing ratio: 1800 UTC
D. Posselt
Retrieved mixing ratio: 1800 UTC
IHOP Spring Workshop
24-26 March 2003
Simulated vs. Retrieved
Water Vapor: 700 hPa
“True” mixing ratio: 1830 UTC
D. Posselt
Retrieved mixing ratio: 1830 UTC
IHOP Spring Workshop
24-26 March 2003
Simulated vs. Retrieved
Water Vapor: 700 hPa
“True” mixing ratio: 1900 UTC
D. Posselt
Retrieved mixing ratio: 1900 UTC
IHOP Spring Workshop
24-26 March 2003
Simulated vs. Retrieved
Water Vapor: 700 hPa
“True” mixing ratio: 1930 UTC
D. Posselt
Retrieved mixing ratio: 1930 UTC
IHOP Spring Workshop
24-26 March 2003
Simulated vs. Retrieved
Water Vapor: 700 hPa
“True” mixing ratio: 2000 UTC
D. Posselt
Retrieved mixing ratio: 2000 UTC
IHOP Spring Workshop
24-26 March 2003
Uses of Simulated Data
• Band differencing for CI detection
– John Mecikalski and Kris Bedka
– Subtraction of one spectral band from another
to detect features associated with CI
• Wind retrievals
– Chris Velden, Dave Stettner, Russ Dengel, Gail
Dengel
– Tracking retrieved water vapor gradients to
produce derived winds
D. Posselt
IHOP Spring Workshop
24-26 March 2003
Band Differencing: 5.9-11 micron
5.9 micron weighting function peaks in upper troposphere (~300 mb)
11 micron window channel much less sensitive to water vapor absorption
Details:
• Low clouds or clear scene: brightness
temperature difference usually << 0
• High, cold clouds: difference = 0
• Cloud top at or above tropopause: difference
may be > 0
• Has been used to locate overshooting tops in
geostationary satellite imagery and to monitor
temporal trends in cloud top height
• Large temporal change in this band difference
often an indicator of CI
D. Posselt
IHOP Spring Workshop
1800-2200 UTC
24-26 March 2003
Band Differencing: 8.5-11 micron
Key: Differences in real and imaginary indices of refraction for liquid vs. ice
• Very small difference at 8.5 microns
• Maximum difference at 11 microns
• Band combination used in MODIS cloud phase product
1800-2200 UTC
Details:
•
•
•
•
Ice clouds: positive difference
Water clouds: slightly negative difference
Mixed phase: values near zero
Clear sky: strongly negative differences, due to
contribution of terrestrial radiation at 11 microns
• Band combination also highly dependent on
effective radius of the size distribution
• Ice clouds with smaller particles: greater
(positive) differences.
D. Posselt
IHOP Spring Workshop
24-26 March 2003
Winds From GIFTS Simulated
Retrievals
Using existing techniques, simulated water vapor retrievals
are being used to obtain water vapor gradient-track winds
700 hPa
500 hPa
Mixing ratio (gray shaded), model winds (streamlines), and retrieved winds (barbs)
D. Posselt
IHOP Spring Workshop
24-26 March 2003
Future Work
• Rerun initializing from IHOP reanalyses
• Continued assessment of GIFTS utility for CI
detection
• Rerun GIFTS forward model with improved cloud
microphysics (improved scattering, multiple ice
habits)
• Develop derived products from simulated data
(stability, etc)
• Simulation of other cases (THORPEX)
D. Posselt
IHOP Spring Workshop
24-26 March 2003