D. Posselt IHOP Spring Workshop 24-26 March 2003

Simulation of an IHOP Simulation of an IHOP Convective Initiation CaseConvective Initiation Case

for GIFTS Preparationfor 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 Langley Research Center

D. Posselt 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

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 rapidly-evolving water vapor structures

• Develop GIFTS data analysis techniques for CI applications

GIFTS high spatial and temporal resolution water vapor measurements indicate vast potential for early detection and diagnosis of CI

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

King Air

Proteus

P3

D. Posselt IHOP Spring Workshop 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

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

Simulated atmospheric fields generated using the 5th generation Penn State/NCAR Mesoscale Modeling system (MM5) initialized from 10 km RUC analyses

D. Posselt IHOP Spring Workshop 24-26 March 2003

Simulation Results

Cloud and water vapor features

• Color-shaded plot depicts 2-meter 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

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

Forward Model

Radiances

Model Atmosphere

D. Posselt IHOP Spring Workshop 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 Retrieved mixing ratio: 1800 UTC

D. Posselt IHOP Spring Workshop 24-26 March 2003

Simulated vs. Retrieved Water Vapor: 700 hPa

“True” mixing ratio: 1830 UTC Retrieved mixing ratio: 1830 UTC

D. Posselt IHOP Spring Workshop 24-26 March 2003

Simulated vs. Retrieved Water Vapor: 700 hPa

“True” mixing ratio: 1900 UTC Retrieved mixing ratio: 1900 UTC

D. Posselt IHOP Spring Workshop 24-26 March 2003

Simulated vs. Retrieved Water Vapor: 700 hPa

“True” mixing ratio: 1930 UTC Retrieved mixing ratio: 1930 UTC

D. Posselt IHOP Spring Workshop 24-26 March 2003

Simulated vs. Retrieved Water Vapor: 700 hPa

“True” mixing ratio: 2000 UTC Retrieved mixing ratio: 2000 UTC

D. Posselt 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

1800-2200 UTC

D. Posselt IHOP Spring Workshop 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 productDetails:• 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.

1800-2200 UTC

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 (streamlinesstreamlines), 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)