HR: 1340h
AN: AE33A-0184    [Abstracts]
TI: TRMM Observations of the Basic Relationship Between Ice Water Path and Lightning
AU: Christian, H
EM: hugh.christian@nasa.gov
AF: NASA Marshall Space Flight Center, Earth Sciences Directorate 320 Sparkman Dr., Huntsville, AL 35805 United States
AU: Petersen, W A
EM: walt.petersen@msfc.nasa.gov
AF: ESSC/NSSTC University of Alabama Huntsville, 320 Sparkman Dr., Huntsville, AL 35899 United States
AU: * Boccippio, D J
EM: dennis.boccippio@nasa.gov
AF: NASA Marshall Space Flight Center, Earth Sciences Directorate 320 Sparkman Dr., Huntsville, AL 35805 United States
AB: Space-based lightning and radar observations are used to address the relationship between lightning and precipitation ice water mass (e.g., integrated amounts of graupel and hail), and the degree to which this relationship remains constant between global tropical ocean, coastal and continental convective regimes. Considering the close microphysical coupling between cloud electrification, lightning, and the ice phase, we hypothesize that regardless of regime there should be little difference in the relationship between convective ice-phase precipitation mass and lightning flash density (in contrast to the well documented variability between lightning and rainfall amount, where the microphysical coupling is often much weaker). To investigate our hypothesis we examined three years (1998-2000) of Tropical Rainfall Measurement Mission (TRMM) Lightning Imaging Sensor (LIS) flash density (FD) and TRMM Precipitation Radar (PR) reflectivity (Z) data for southern and northern hemisphere summer seasons (July-Aug., Dec.-Feb.). First, ice water contents (IWCs) were computed for PR range gates located at heights above the -10 C level using Z-IWC relationships based on exponential ice particle size distributions and ice particle densities adjusted as a function of precipitation type (convective or stratiform) and Z. Next, ice water paths (IWPs; ice mass in a column) were computed by vertically integrating IWC upward from the -10C level to radar echo top. Pixel-level IWP, FD and rainfall were subsequently averaged and gridded at a resolution of 0.5 x 0.5 degrees for comparison. When the grid-box IWPs were binned by FD and then globally averaged for land, ocean and coastal regimes, correlations between FD and IWP were found to be quite large (R$>$0.9) for all three regimes. Best-fit lines between FD and IWP for all three regimes were nearly identical, exhibiting differences in slope (a metric of "ice-yield" as opposed to "rain-yield") of less than 20% with nearly identical intercepts of ~0.01 kg/m^2 (an apparent lower threshold in IWP for achieving a detectable FD with LIS in a 0.5 x 0.5 Deg. grid cell). Appropriate power law fits between averaged FD and mean rainfall rate for all three regimes were also quite good (R$>$0.8); however, in contrast to the FD-IWP relationship. the rainfall-FD relationships by regime were markedly different. The results suggest that 1) when averaged over all oceans, land and coastal regimes there is no discernable difference in the relationship between ice-phase precipitation mass and FD between ocean, coastal and land regimes (in contrast to rainfall); and 2) to first order, the physical assumptions of precipitation-based charging and mixed phase precipitation development are robust, suggesting that lightning data may be a useful variable for inclusion in combined algorithms developed to retrieve precipitation ice water content (at least over the large scales examined herein).
DE: 3324 Lightning
DE: 3354 Precipitation (1854)
DE: 3374 Tropical meteorology
DE: 3304 Atmospheric electricity
SC: Atmospheric and Space Electricity [AE]
MN: 2004 AGU Fall Meeting