THIS PROPOSAL FALLS UNDER: A.26 WEATHER AND ATMOSPHERIC DYNAMICS TOPIC 2.1 DIFFICULT-TO-RETRIEVE WEATHER SPECIFICALLY TO IMPROVE UNDERSTANDING OF LIGHT RAINFALL PROCESSES AND ASSOCIATED DROP SIZE DISTRIBUTION SHAPES AND VARIABILITY WITH THE GOAL OF IMPROVEMENT OF PRECIPITATION RETRIEVALS BY DPR-GMI COMBINED ALGORITHM AT LIGHT RAIN RATES. UNDER THESE CONDITIONS THE ENSEMBLE-BASED OPTIMAL ESTIMATION SCHEME OF THE ALGORITHM GENERALLY DEFAULTS TO THE APRIORI DROP SIZE DISTRIBUTION (DSD) STATE WHICH MAY NOT BE VALID IN THE MID-TO-HIGH LATITUDES LEADING TO SYSTEMATIC BIASES IN RAIN RATE (GENERALLY AN UNDERESTIMATE) WHEN COMPARED WITH OTHER SATELLITE BASED METHODS. UNBIASED LIGHT PRECIPITATION ESTIMATES ARE IMPORTANT SINCE IT DOMINATES THE FREQUENCY OF OCCURRENCE ESPECIALLY IN THE MID-TO-HIGH LATITUDES OVER OCEAN (TYPICALLY THE FREQUENCY OF OCCURRENCE OF R<0.5 MM/H RANGES FROM 55-65% WHILE THE CONTRIBUTION TO RAIN ACCUMULATION IS AROUND 4-7%). THE FIRST OBJECTIVE IS TO DETERMINE AN ACCURATE APRIORI DSD STATE WHICH WILL MAKE THE COMBINED ALGORITHM ESTIMATES OF RAINFALL MORE STABLE AND CONSISTENT WITH CLIMATOLOGY. IN ADDITION TO PROFILES OF RAIN RATE THE COMBINED ALGORITHM ALSO PROVIDES ESTIMATES OF TWO PARAMETERS OF AN ASSUMED THREE-PARAMETER GAMMA DSD MODEL. THE PARAMETERS ARE THE NORMALIZED INTERCEPT PARAMETER AND THE MASS-WEIGHTED-MEAN DIAMETER THE THIRD SHAPE PARAMETER IS ASSUMED CONSTANT. THE SECOND OBJECTIVE IS TO EXAMINE THE APPLICABILITY OF THE FIXED SHAPE GAMMA DISTRIBUTION MODEL AND TO PROVIDE FOR MORE ACCURATE CONSTRAINTS FOR THE CO-VARIABILITY OF THE NORMALIZED INTERCEPT PARAMETER AND THE MASS-WEIGHTED MEAN DIAMETER AS WELL AS THE DISTRIBUTION OF THE INTERCEPT PARAMETER AND TO USE GROUND RADARS FOR VALIDATION OF THE COMBINED ALGORITHM PRECIPITATION RETRIEVALS. IT IS NOW WELL-ESTABLISHED THAT A SIGNIFICANT FRACTION OF LIGHT RAINFALL AT MID-TO-HIGH LATITUDES OVER OCEANS IS MISSED BY THE COMBINED ALGORITHM DUE TO LIMITED SENSITIVITY OF THE DUAL PRECIPITATION RADAR OR DUE TO THE SHALLOW NATURE OF THE PRECIPITATION. HOWEVER THE LOW FREQUENCY CHANNELS OF THE MICROWAVE RADIOMETERS ON THE CORE SATELLITE HAVE BEEN FOUND TO CORRELATE WELL WITH THE DIFFERENTIAL PATH INTEGRATED ATTENUATION AT THE TWO FREQUENCIES OF THE DUAL PRECIPITATION RADAR WHICH MAKES IT POSSIBLE TO CONSTRUCT A RADIOMETER-CENTRIC COMBINED ALGORITHM TO MEASURE LIGHT RAIN. THE THIRD OBJECTIVE IS TO SUPPORT THIS DEVELOPMENT USING POLARIMETRIC AND DUAL-WAVELENGTH GROUND RADAR RETRIEVALS OF LIQUID WATER PATH AND PATH INTEGRATED ATTENUATION AND DIFFERENTIAL PATH INTEGRATED ATTENUATION BETWEEN KU AND KA-BANDS LEADING TO SIMULATION OF BRIGHTNESS TEMPERATURES AND TO DERIVE BRIGHTNESS TEMPERATURE-RAIN RATE RELATIONSHIPS. MOREOVER OBSERVING SYSTEM SIMULATION EXPERIMENTS MAKING USE OF THE GROUND RADAR RETRIEVALS WILL BE USED TO GET INSIGHT INTO THE PERFORMANCE OF RADIOMETER ESTIMATES OF PIA AS WELL AS TO VALIDATE THESE ESTIMATES. THE PROPOSED MEASUREMENT SITE IS THE COASTAL OCEANIC WALLOPS ISLAND PRECIPITATION RESEARCH FACILITY. THIS FACILITY IS HEAVILY INSTRUMENTED WITH SCANNING POLARIMETRIC NASA S-BAND RADAR AND THE NASA DUAL-POLARIMETRIC/DUAL-WAVELENGTH RADAR. THE SURFACE MEASUREMENTS INCLUDE A NEW NASA OPTICAL ARRAY PROBE COLLOCATED WITH A 2D-VIDEO DISDROMETER AS WELL AS A NETWORK OF PARSIVEL OTHER 2D-VIDEO AND RAIN GAGES. THE RAIN TYPES INCLUDE LIGHT RAIN ORIGINATING FROM STRATIFORM WITH BRIGHT-BAND RAIN WITHOUT BRIGHT-BAND BUT ECHO TOP TEMPERATURES COLDER THAN 0C PURE WARM RAIN AND MARINE STRATOCUMULUS DRIZZLE (MORE PREVALENT IN THE OCEANIC SITES BELOW). THE NON-NASA OCEANIC DSD DATA BASE AVAILABLE IS FROM OCEANRAIN USING AN OPTICAL DISDROMETER DESIGNED FOR USE ON SHIPS. OUR FOCUS IS ON THE S. HEMISPHERE MID-TO-HIGH LATITUDES TRACKS SSW OF PERTH IN 2016 AND MORE RECENTLY SOUTH OF TASMANIA IN 2018. DURING THE LATTER CRUISE THE RV INVESTIGATOR HAD A C-BAND POLARIMETRIC RADAR WITH A NUMBER OF GPM SATELLITE OVERPASSES.

Colorado State University, Fort Collins CO

Investigators