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Relationships between tropical cyclone intensity and satellite based indicators of inner core convection: 85 GHz ice scattering signature and lightning
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A key component in the maintenance and intensification of tropical cyclones is the transverse circulation, which transports mass and momentum and provides latent heat release via inner core convective updrafts. This study examines these updrafts indirectly, using satellite-borne observations of the scattering of upwelling microwave radiation by precipitation sized ice and satellite-borne observations of lightning. The observations are then compared to tropical cyclone intensity and the resulting relationships are assessed. The size of ice particles is tied to updraft strength, in that stronger updrafts produce more supercooled liquid water, leading to larger graupel through riming. Large graupel and a high supercooled liquid water content are necessary ingredients for charge separation, leading to lightning. Various parameters derived from the inner core ice scattering signature are computed for regions encircling hurricanes and typhoons, and observations of lightning activity or inactivity are analyzed. As expected, increasing ice scattering signature is found to correspond to increasing tropical cyclone intensity. However, the highest correlations do not involve indicators of convective intensity, as they were expected to. Instead, the highest correlations with tropical cyclone intensity result from the ice scattering signature parameters most closely associated with the areal extent of at least moderate precipitation rates. Correlations tend to be of the same sign for both present cyclone intensity at the time of the satellite overpass and subsequent intensity change. Correlations are higher for future cyclone intensity than for either of these. These correlations are much higher for the Atlantic and the Eastern North Pacific than for the Western North Pacific. It is hypothesized that processes involved with the most intense or rapidly intensifying tropical cyclones (more commonly found in the Western North Pacific) are responsible for these differences. The lightning observations are more limited than the microwave observations, because the short amount of time in which lightning can be detected may not adequately represent a particular storms electrical activity. These observations reveal no clear relationships between electrical activity and tropical cyclone intensity. In the examination of case studies, the paradoxical situation of much greater lightning activity in rainbands than in eyewalls is noted.
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Cecil, Daniel Joseph (1997). Relationships between tropical cyclone intensity and satellite based indicators of inner core convection: 85 GHz ice scattering signature and lightning. Master's thesis, Texas A&M University. Available electronically from
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