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Title:Convective structure and its evolution in tropical cyclones as observed by passive microwave sensors in relation to intensity change
Author(s):Harnos, Daniel
Advisor(s):Nesbitt, Stephen W.
Department / Program:Atmospheric Sciences
Discipline:Atmospheric Sciences
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):tropical cyclones
passive microwave sensors
rapid intensification
Abstract:The use of passive microwave sensors in analysis of tropical cyclones provide unique insight into the microphysical attributes and system structure opposed to other instruments that are only able to detect information about the cloud top. With the ability to infer information about key microphysical processes and structure at high resolution, these platforms provide a glimpse into tropical cyclone development and intensification over systems’ life cycles. In particular, passive microwave observations have the potential to depict crucial precursors of rapid intensification (RI; defined as a wind increase of 30 kt/24 hr). A dataset with a common resolution of 8 km across all channels is developed for the Special Sensor Microwave Imager (SSM/I) from 1987-2008 and Tropical Rainfall Measuring Mission Microwave Imager (TMI) for 1997-2008. Statistical metrics are calculated for each storm overpass using 85 GHz and 37 GHz polarization corrected temperatures as well as microwave rain rate estimates. These products are examined as a function of azimuth and annuli in true-north, storm-relative motion, and shear-relative coordinates and evaluated in terms of intensity (wind speed) and intensity change (wind speed change over time). To examine predictive potential of these sensors, the brightness temperature statistics are evaluated in terms of linear correlations between intensity and its change. Highest values occur on the order of 0.7, and are seen at radii of 110 km between median values for 85 GHz PCT and rain rates with observed intensity. An increase in skill is evident following the initial satellite overpass, suggesting a lag between latent heating at the time of overpass and the resultant intensification. Despite this, correlation is consistently less skillful for evaluations of intensity change with values at short time changes of around 0.3. The distribution of statistical values are also evaluated in the context of the dataset with median values at the 110 km distance showing the greatest distinction of 85 GHz PCTs and rain rates for storms at the onset of RI and those that are not, with less variation seen for percentiles > 90% that are indicative of isolated convective activity. With the differentiation in structure noted between RI and non-RI storms, composites are created for each of the brightness temperature products, with a distinct modest convective ring structure evident at the onset of RI that is not present in the non-RI class. Over time this convective ring shows a tendency to contract and intensify over the 24 hour period examined for RI, with the increased latent heating over a more focused area acting to increase the system intensity. Through these evaluations the continued importance spatial convective coverage and axisymmetricization is underscored in intensity and intensity change evaluation, with a lack of signal seen in more isolated convective predictors.
Issue Date:2011-01-21
Rights Information:Copyright 2010 Daniel Harnos
Date Available in IDEALS:2013-01-22
Date Deposited:2010-12

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