1. PRELIMINARY VALIDATION OF IAPP MOISTURE RETRIEVALS USING DOE ARM MEASUREMENTS Wayne Feltz, Thomas Achtor, Jun Li and Harold Woolf Cooperative Institute for Meteorological Satellite Studies (CIMSS), University of Wisconsin- Madison UW-Madison Global atmospheric temperature and moisture retrievals from the Advanced TIROS Operational Sounder (ATOVS) radiance data are produced routinely at CIMSS using the International ATOVS Processing Package (IAPP). (See lower center panel for more details on IAPP software.) The University of Wisconsin - Madison Space Science and Engineering Center (SSEC) has a downlink capability to acquire global ATOVS radiances in near real-time for IAPP processing. To assess the accuracy of the IAPP retrievals, comparisons are made to measurements from the U. S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Program site in the U. S. Southern Great Plains (SGP) (see http://www.arm.gov/). A study to create the comparison data set was started in September 2001. The IAPP moisture output is compared to spatially and temporally co-located radiosonde and microwave radiometer (MWR) data at the ARM site. A case study example of a cold frontal passage is also presented. Participation within the ARM program has allowed independent, high quality validation opportunities for satellite derived products. INTRODUCTION The scatter plot compares MWR total water vapor values to the AVN model forecast (red triangles) and the IAPP ATOVS physical retrieval values (black stars). RMS and bias values for 205 temporal and spatial matches are shown. IAPP physical retrievals show modest improvement over the AVN model TPW first guess in mean difference (0.1 mm or 5%) and better improvement in RMS (0.4 mm or 12%). IAPP physical retrievals indicate good accuracy when compared to MWR measurements, especially considering the different spatial characteristics of the measurements. Comparison of Moisture Profile Calculations from IAPP and SGP Radiosondes Cold Frontal Passage Example Demonstrating ATOVS Vertical Temperature and Moisture Retrievals with DOE ARM Measurements Validation Source: Co-located SGP central facility radiosonde moisture profiles Satellite Product: ATOVS IAPP derived moisture profiles, using surface observations and AVN model first guess Co-location criteria: 1 1/2 hours and 1 degree lat/lon Validation Source: Radiosondes, AERI (Atmospheric Emitted Radiance Interferometer) Satellite Products: ATOVS IAPP Temperature and Moisture Fields Further Information on the International ATOVS Processing Package (IAPP) The IAPP uses radiances from HIRS/3 and AMSU -A and -B, preprocessed using the AAPP to level 1-D format, for retrieval. The retrieval algorithm is a physical simultaneous technique described by Li et al., 1998, 10 th Proceedings of the International TOVS Study Conference, Boulder, CO. To obtain IAPP source code, contact tom.achtor@ssec.wisc.edu.tom.achtor@ssec.wisc.edu DOE ARM Southern Great Plains Instrument Site Microwave Radiometer (MWR) Comparison of Total Precipitable Water Vapor (TPW) Calculations from IAPP and MWR Validation Source: DOE SGP Microwave Radiometer (MWR) Total Precipitable Water Vapor (TPW) Satellite Product: ATOVS IAPP derived TPW, using surface observations and AVN model first guess Co-location criteria: 5 minutes and 1/2 degree lat/lon. Above are two examples from the comparison data set. Each diagram shows the temperature and moisture profiles for the radiosonde (black), the Aviation Model first guess (red) and the final IAPP physical retrieval (blue). The IAPP retrieval improves upon the AVN first guess when compared to the radiosonde validation source, especially in the upper troposphere. The improvement in water vapor profiles can be shown statistically with 59 coincident radiosonde - ATOVS matches. This figure shows the mean bias (left) and the RMS difference (right) for the Aviation Model first guess (red) and the IAPP final physical retrieval (black) when compared with coincident radiosondes. A 50% improvement in bias and a 25% improvement in RMS is indicated in the IAPP moisture retrieval in the mid and upper troposphere, largely due to a moist bias in the model. On 12/5/01 a cold front moved through the SGP ARM site domain. A ground-based AERI instrument located at the SGP central facility retrieved boundary layer temperature and moisture structure during this frontal passage. A time-height cross section of AERI potential temperature and water vapor mixing ratio indicate rapid cooling and drying around 1900 UTC. Wind barbs from the NOAA 404 MHz wind profiler near Lamont, Oklahoma are plotted on the upper cross section. The wind profiler indicates the frontal passage, as winds veer from southwest to northwest. This case can also be examined using ATOVS temperature and moisture profiles as shown below. Near 0000 UTC the cold front has cleared the central facility. Note the cooling within the boundary layer and the drying through the entire atmospheric column. The surface data from 2200 UTC indicates temperatures over 17C, while the radiosonde profile from a later time shows the nocturnal inversion developing. At 1730 UTC (11:30 CST) both profiles (although still 2 hours apart) indicate the boundary layer moisture has decreased while the temperature profiles indicate warm boundary layer conditions still exist. Surface data and the satellite image indicate the cold front is approaching the central facility site. In the early morning, the SGP central facility was in the warm sector with southerly winds and 15C dewpoint. The radiosonde profile indicates a cloud at 750 hPa at 1130 UTC; the ATOVS profile from 2 hours earlier indicates cirrus clouds. The satellite image from 1445 UTC shows the high clouds east of the site which are indicated by the ATOVS profile from 0930 UTC. Location of DOE ARM site Acknowledgments: The work has been supported through NOAA grant NA67EC0100. The AERI, MWR, and radiosonde data were obtained from the Atmospheric Radiation Measurement (ARM) program sponsored by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Environmental Sciences Division.