Extended Abstract (68K)5B.6
Characteristics of oceanic tropical convection at Kwajalein
Jasmine Cetrone, University of Washington, Seattle, WA; and R. A. Houze
Over tropical oceans precipitating clouds occur in ensembles that include a broad range of phenomena, from shallow isolated cells to large mesoscale convective systems with stratiform precipitation areas. Often one type or another of these clouds is investigated singularly. However, the clouds of this wide range of sizes and characteristics work in concert to redistribute the mass, heat, moisture, and momentum of the large-scale tropical circulation. Only a few studies have comprehensively characterized the ensemble properties of convective clouds over the tropical oceans. This study analyzes the ensemble properties of the precipitating cloud population described by a unique data set obtained over the tropical western Pacific Ocean. At Kwajalein Atoll, an S-band research radar has been operating since 1998 to collect data in support of the TRMM satellite. These radar data have excellent qualities, including high sensitivity, fine vertical and temporal resolution, and calibration matching with the TRMM satellite radar. An intensive field observation campaign, the Kwajalein Experiment (KWAJEX), supplemented the multi-year data set for the period 23 July through 15 September 1999. We use the entire data set to characterize the radar echo population in the vicinity of Kwajalein. We employ echo identification and tracking techniques to describe the characteristics of the precipitating cloud population at Kwajalein in terms of the horizontal dimensions of echoes, echo heights, the degree to which echoes are elongated, and spatial orientation of echo bands. We determine the statistics of echo motion by tracking the echoes. Preliminary results indicate that the echoes exhibit a lognormal distribution of all their temporal and spatial dimensions. Analysis indicates that the echoes are consistently about twice as long as they are wide. Echo tracking shows that, depending on echo size, 39 to 92% appear and disappear as a result of mergers and splits, and that the echoes generally follow an east-southeast to west-northwest track, aligned with the prevailing low-level trade winds. Application of a standard algorithm will determine the subdivision of echoes into convective and stratiform components. The apportionment of the total convective and stratiform precipitation amounts according to echo sizes, shapes, heights, and durations will be determined. In an extension of this work we will determine if the virtual radar echoes produced in a cloud resolving model simulation of Kwajalein convection exhibit statistics similar to those exhibited by the real radar echoes.
Session 5B, CONVECTION, waves, and precipitation III
Tuesday, 4 May 2004, 8:00 AM-9:30 AM, Napoleon I Room
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