# Presentation: 053682

## Radiance Assimilation Activities at SPoRT

- Will McCarty
- SPoRT SAC
- Wednesday June 13, 2007

## Motivation for Radiance Assimilation

- SPoRT emphasis on short-term regional weather forecast improvements
- Value of AIRS radiances
- supplement raobs in data sparse regions (over oceans and between raobs)
- Aqua platform provides asynoptic observations over CONUS
_**Regional**_ assimilation allows to the use of more satellite measurements (every cloud-free footprint) spatially and spectrally
- Smaller-scale features in the data are retained
- Challenges in identifying the proper utilization of the measurements, relative to global methodologies

## Radiance Assimilation

- Advantages of Radiance Assimilation
- By theory, radiances will have a larger impact in a variational system than profiles
- Direct measurement is being used, not a retrieved product
- No additional error from retrieval process impacting data
- Disadvantages of Radiance Assimilation
- Computationally expensive
- Less intuitive
- Many issues (sfc , cloud contamination) inherent to both

## Radiance Assimilation @ SPoRT

- SPoRT and JCSDA
- Emphasize _**transition**_ of NASA technologies to operations
- SPoRT focus – short-range (0-48 hr), mesoscale
- JCSDA focus – Medium-range (48+ hr), global
- Assimilation of NASA measurements to improve initial conditions
- Improved initial condition lead towards improved forecasts
- Collaboration on AIRS assimilation in within North American Model (NAM) Data Assimilation System (NDAS)

## Collaboration with JCSDA

- McCarty at JCSDA summer of 2006
- Spent working onsite at the JCSDA, under the direction of then-director John Le Marshall
- Developed a working knowledge of the Gridpoint Statistical Interpolation (GSI) 3D-VAR system
- Multi-agency development
- At NCEP, currently the Regional and Global Data Assimilation System
- Data Assimilation workshop - July 2007

- Computational resources
- Resources from JCSDA and NCEP/EMC (S. Lord) have been made available to allow SPoRT focus with national-scale office resources

## Expected SPoRT Contributions to JCSDA

- Assess system configuration
- Assess differences in bias adjustments between the NAM system and the GFS system
- Evaluate thinning methodologies between regional and global model assimilation applications
- spatial
- spectral
- Evaluate impact of AIRS data at regional scale
- Data density and coverage
- Cloud-free radiance detection

## Flow Chart of Radiance Assimilation Research

- Focus on specific problems
- Assess the use of AIRS in the NDAS (GSI and WRF-NMM)
- Consider spatial (horizontal) and spectral (vertical) characteristics for optimal impact on regional model
- Consider the sorting technique, an aggressive approach to assessing cloud contamination
- Develop algorithm
- Implement algorithm in DA system
- Basic outline of Ph. D. research, anticipated to be finished in Spring of 2008

## Spatial Concerns

- Spatial Thinning
- Global system – 180 km thinning, based on warmest from 3x3 IFOV
- Regional system can utilize larger number of radiances spatially, due

- 	to finer grid-spacing and smaller domain

- SPoRT configuration considers every (15km) IFOV to maximize impact

## Spectral Concerns

- More aggressive than approach inherent in GSI
- Utilizes the high spectral (thus vertical) resolution of AIRS
- Current technique is applicable to all thermal infrared sounders

- _Cloud Contamination_
- CO2 sorting technique developed to identify cloud-free radiances
- run locally in NRT
- implemented within the GSI system
- Developed to maximize the amount of information content in cloudy portions of the atmosphere

## Spectral Concerns

- Spectral Thinning
- Currently, AIRS 281 channel subset is considered
- However, sorting method, situational background errors (EnKF), could be considered for proper definition of subset on a per-IFOV basis, to optimally select AIRS channels used for assimilation
- Many channels in operational subset (281 of 2378 channels) chosen for _**global**_ applications
- Upper atmosphere channels
- NAM TOA (2 hPa) > GFS TOA (~0.25 hPa)
- Ozone channels
- No Ozone in the NAM
- These channels are not applicable as they revert to climatology

## Domain and Analysis

- NAM-12 Grid
- Denoted by dashed line
- Allows for use of operational NAM as control
- 12 km gridspacing
- Fits action of transition of research to operations

- Analysis System
- GSI 3D-VAR system
- Operational NAM Data Assimilation System (NDAS)
- Universal DA system used by NOAA and NASA for numerous models, including GFS, WRF-NMM (NAM), WRF-ARW (WRFRUC), and GEOS-5

## Current Status

- Ongoing Validation
- Initial validation is being performed
- Problem with validating an analysis is the use of an independent dataset
- Currently using GOES sounder measurements
- Initial results demonstrate that more work is needed to address aforementioned concerns

## Future Work

- Continue to investigate appropriate use of AIRS radiances at regional scales in an experimental NDAS system
- Include more cloud-free channels (tune CO2 sorting approach)
- Maximize / optimize the amount of data available for assimilation
- Forecast validation based on improved analyses
- Demonstrate impact of regional scale methodologies on forecast