Comparison of AIRS L2 Profiles to Ground-Based Soundings Brad Zavodsky SPoRT Meeting 30 January 2008

1. Comparison of AIRS L2 Profiles to Ground-Based Soundings Brad Zavodsky SPoRT Meeting 30 January 2008

2. Motivation/Background • SPoRT is planning to generate an Atmospheric Infrared Radiometer (AIRS) L2 profile product for the Huntsville NWS • Rawinsonde/AIRS intercomparisons done for global coverage (e.g. Tobin et al. 2006, Divakarla et al. 2006), but we are concerned with how AIRS behaves in the SEUS at different times of the year • Challenge: AIRS observations occur at asynoptic times meaning there are very few radiosonde observations for direct comparison • Solution 1: Use Microwave Profiling Radiometer (MPR) data collected at the NSSTC, Redstone Arsenal radiosonde (RSA) data, and AIRS in a three-way process to gain insight into performance of AIRS • Solution 2: Use “bookend” and temporally-interpolated radiosondes to see how AIRS performs in a dynamic environment

3. Instrumentation AIRS MPR RSA Radiosonde • On Aqua EOS • Infrared and Microwave* • Generates T and Td profiles twice daily up to TOA • Vertical resolution: • 2378 channels • 54 pressure levels • Temperature accuracy: • 1.0K in 1-km layers • Moisture accuracy: • 15% RH in 2-km layers • On MIPS located at NSSTC • Microwave • Generates T and Td profiles every 1 minute up to 10 km • Vertical resolution: • 100 m below 1 km; 250 m above 1 km • Temperature accuracy: • 1.0K below 2 km; 1.5-2.0K above 2 km • Moisture accuracy: • 0.2-0.3gm-3 below 2 km; 1.0-1.5gm-3 above 2 km • Vaisala RS92-SGP launched from Redstone Arsenal • Generates T and Td profiles at 12Z on weekdays up to 10 hPa • Vertical resolution: • variable • Temperature accuracy: • 0.2-0.5K • Moisture accuracy: • 2-5% RH

4. March 2007 AM AIRS may be observing cool layer above residual unstable PBL RSA-MPRAIRS-MPR Using MPR as Conduit • No ground truth at AIRS time, so use MPR as “truth” • How will MPR compare to direct measurement from radiosonde? • Linearly interpolate RSA and AIRS to MPR height coordinates • Compare RSA to MPR at RSA time (≈12Z) (RSA ≈ 10 km from MPR) • Compare AIRS to MPR at AIRS time (≈06-09Z) (closest AIRS ≤ 50 km from MPR) • Assume instrument biases at one time similar to biases at other times • Compare relative differences between the biases to determine how AIRS may compare to a radiosonde in the SEUS • AIRS and RSA are similarly biased compared to MPR at most levels lending credibility to AIRS • AIRS appears cooler and more moist than radiosondes for AM overpasses in March 2007

5. AIRS in a Changing Airmass • An AIRS sounding should exhibit the characteristics of its two bounding radiosondes • Logarithmically interpolate RAOB to AIRS pressure levels • Linear interpolation in time • Cold front swept through SEUS on 2-3 March 2007 • 12Z 20o cooler than 00Z below 600 hPa • 12Z 30-50o drier than 00Z below 400 hPa • AIRS produces approximate T and Td profile expected from the bounding radiosondes for this case • AIRS T nearly identical to interpolated RAOB • AIRS Td exhibits characteristics of changing moisture field 3 March 2007 Peachtree City, GA 0000Z RAOB 1200Z RAOB0741Z AIRS0741Z RAOB AIRS depicts top of dry layer AIRS depicts sharp drying in lower layers

6. Conclusions/Future Work • SPoRT is planning to generate an AIRS L2 profile product for the Huntsville NWS • Quality of AIRS profiles is being assessed in a couple of manners: • MPR/AIRS/RSA comparisons: • AIRS and RSA exhibit similar biases when compared to MPR qualitatively validating the quality of the AIRS soundings • AIRS comparisons to bounding radiosondes: • AIRS can successfully depict a dynamic atmosphere (i.e. nearly identical T and similar characteristics of Td sounding for cold front case) • Future work: • Start one day delay web posting of AIRS and radiosondes for continued comparison • Work to understand where/when AIRS performs best in SEUS to assist in forecaster training