ESRL Global Systems Division

Moisture Transport by the Low-Level Jet

FSL scientists have completed two research flights during the International H2O Project (IHOP) to study the transport of water vapor over the central United States by the low-level jet (LLJ). The objectives for these missions were to map moisture and horizontal winds during LLJ episodes in order to understand the evolution of the LLJ and moisture fields during the development of the daytime convective boundary layer, and to characterize the impact of this transport on the initiation and development of convection. The DLR Falcon and Flight International Learjet aircraft flew a rectangular pattern around the low-level jet on the mornings of 3 and 9 June 2002. Moisture flux associated with the LLJ was provided by aircraft dropsondes at 55 km spacing, supplemented by 1- to 3-hourly special soundings taken at 10 NWS sites and 5 CART/ARM sounding sites. Fine-scale moisture transport was mapped along the track of the Falcon from two lidar instruments - the DLR Water Vapor Differential Absorption Lidar (DIAL) and the NOAA/ETL High-Resolution Coherent Solid State Doppler Lidar (HRDL). DIAL measures water vapor and aerosols below flight level, while the HRDL gives range-resolved and backscatter intensity suitable to estimate winds transverse to the flight path. Additional moisture data were taken with two NASA airborne systems, the LASE (Lidar Atmospheric Sensing Experiment) flown on the NASA DC-8 and the NAST (NPOESS Aircraft Sounder Testbed) on the Proteus. NAST comprises a suite of airborne infrared and microwave spectrometers being developed for future instruments proposed to fly on the future National Polar-orbiting Operational Environmental Satellite System (NPOESS) satellite. Infrared radiance measurements obtained from the NAST-I interferometer were used to retrieve detailed atmospheric temperature and water vapor profiles. FSL scientists will compute moisture budgets and perform diagnostic and numerical modeling studies of these cases to test the hypothesis that warm-season quantitative precipitation forecast skill could be significantly improved by better characterization of the four-dimensional water vapor field and its transport by the LLJ.

For more information about the 9 June 2002 LLJ mission, go to the IHOP 2002 Field Catalog web site and click on the Mission Scientist Summary for 12:45 UTC 9 June. The flight track is presented there, along with sample measurements taken by the DIAL and LASE showing variations in moisture along the west-east flight track, which included passage over the dryline. The LASE relative aerosol data also show strong evidence of a smoke plume in western Kansas above 4 km MSL emanating from wildfires burning in Colorado. Also appearing is an analysis of total precipitable water (PW) fields from the 4-km resolution LAPS (Local Analysis and Prediction System) that was run every three hours at FSL in support of IHOP. These PW fields may be compared with the DIAL and LASE measurements. For a look at some of the aircraft measurements taken from the 3 June 2002 mission, click on the Mission Scientist Summary for 10:00 UTC 3 June. Aircraft data obtained from both missions, as well as many of the other special IHOP moisture measurement systems, will be compared to the LAPS and RUC (Rapid Update Cycle) model analyses in order to improve the analysis of moisture and the short-range prediction of convection and heavy precipitation.

Contributors to this report include Steven Koch, Cecilia Girz, Ed Tollerud, Brian Jamison, Fernando Caracena, and Adrian Marroquin of FSL's Forecast Research Division.

Contact information
Name: Steven Koch
Tel: 303-497-5487