Abstract
The satellite passive microwave (PMW) sensor brightness temperatures (TBs) of all tropical cyclones (TCs) from 1987–2012 have been carefully calibrated for inter-sensor frequency differences, center position fixing using the Automated Rotational Center Hurricane Eye Retrieval (ARCHER) scheme, and application of the Backus–Gilbert interpolation scheme for better presentation of the TC horizontal structure. With additional storm motion direction and the 200–850 hPa wind shear direction, a unique and comprehensive TC database is created for this study. A reliable and detailed climatology for each TC category is analyzed and discussed. There is significant annual variability of the number of storms at hurricane intensity, but the annual number of all storms is relatively stable. Results based on the analysis of the 89 GHz horizontal polarization TBs over oceans are presented in this study. An eyewall contraction is clearly displayed with an increase in TC intensity. Three composition schemes are applied to present a reliable and detailed TC climatology at each intensity category and its geographic characteristics. The global composition relative to the North direction is not able to lead a realistic structure for an individual TC. Enhanced convection in the down-motion quadrants relative to direction of TC motion is obvious for Cat 1–3 TCs, while Cat 4–5 TCs still have a concentric pattern of convection within 200 km radius. Regional differences are evident for weak storms. Results indicate the direction of TC movement has more impact on weak storms than on Cat 4–5 TCs. A striking feature is that all TCs have a consistent pattern of minimum TBs at 89 GHz in the downshear left quadrant (DSLQ) for the northern hemisphere basins and in the downshear right quadrant (DSRQ) for the southern hemisphere basin, regarding the direction of the 200–850 hPa wind shear. Tropical depression and tropical storm have the minimum TBs in the downshear quadrants. The axis of the minimum TBs is slightly shifted toward the vertical shear direction. There is no geographic variation of storm structure relative to the vertical wind shear direction except over the southern hemisphere which shows a mirror image of the storm structure over the northern hemisphere. This study indicates that regional variation of storm structure relative to storm motion direction is mainly due to differences of the vertical wind shear direction among these basins. Results demonstrate the direction of the 200–850 hPa wind shear plays a critical role in TC structure.
Highlights
A tropical cyclone (TC) can be one of the most impactful weather systems, causing catastrophic damages to human lives, society, transportation, properties, etc. [1,2]
TC structure relative to the 200–850 hPa wind shear direction has a consistent pattern with convection located in downshear left quadrant (DSLQ) among these basins except the SH basin where convection is located in downshear right quadrant (DSRQ)
The TMI and Sensor Microwave Imager (SSM/I) TBs at 85 GHz and Sensor Microwave Imager and Sounder (SSMIS) TBs at 91 GHz TBs are calibrated to 89 GHz so that SSM/I, SSMIS, TMI and AMSR-E used in this study have a consistent high frequency channel at 89 GHz
Summary
A tropical cyclone (TC) can be one of the most impactful weather systems, causing catastrophic damages to human lives, society, transportation, properties, etc. [1,2]. Hurricane Katrina in 2005, with a maximum wind speed of 280 km hr−1, impacted most of the southeast United States (US), making landfall in the greater New Orleans area. It is the costliest hurricane in US history, killing an estimated 1245–1836 people and causing damages of $149 billion US dollars [3]. TCs can attain very strong wind speeds, greater than 260 km hr−1, and bring heavy precipitation. Most TC damage is caused by the force of its strong wind, storm surge, and flash flooding. Flooding from US landfalling TCs is the leading cause of death related to severe storms [4]. To mitigate the potential impact of TCs, appropriate preparations should be taken based on accurate monitoring and predictions of TC intensity, structure and precipitation
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