Passive Microwave Signatures of Tropical Cyclone Symmetry as Related to Intensity Change

Multiple recent works have highlighted the tendency of tropical cyclones to possess a relatively symmetric inner-core preceding rapid intensification, often with a ring-like appearance. Disparate hypotheses have come forth relating to the relative importance of such symmetric inner core features at 37 GHz, predominantly sensitive to emission from rain, and 85 GHz, predominantly sensitive to ice. In an effort to rectify the potential importance of warm rain and ice processes, here over two decades of passive microwave overpasses of tropical cyclones from the Special Sensor Microwave/Imager (SSM/I) and Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) are evaluated in an effort to examine their structure and relative symmetry of each scene as related to future intensity change.

To accomplish this a computationally efficient, objective algorithm to quantify ring presence at varying microwave frequencies has been devised. Through this algorithm the statistical significance of ring presence at 37 GHz vertically polarized temperatures, 85 GHZ polarization corrected temperatures, and 37 GHz Naval Research Laboratory false color scenes is evaluated relative to intensity change. Further, scenes with rings can have their centers fixed for each respective frequency to allow transformation into polar coordinates and subsequent analyses related to axisymmetric versus asymmetric components for intensity change. Results will also focus on sensitivity of the aforementioned frequencies and products to environmental parameters and potential implications for interpretation of resultant brightness temperature products.