Geographic Characteristics of Tropical Cyclone Diurnal Cycle

Tropical cyclones (TCs) are among the most severe weather systems and can lead to catastrophic damage to human lives, properties, and society. TCs have significant geographic characteristics. Satellite observations from passive microwave sensors (PMW) provide the only method of global coverage of TC life cycles to display their geographic characteristics. These PMW sensors are the Advanced Microwave Scanning Radiometer (AMSR), Tropical Rainfall Measuring Mission microwave imager (TMI), Global Precipitation Measurement microwave imager (GMI), Special Sensor Microwave Imager (SSM/I), and Special Sensor Microwave Imager/Sounder (SSMIS), which provide accurate measurements of TC intensity, center position, eyewall, and spiral convection zones because of PMW’s ability to penetrate clouds. Multi-satellite sensors are required to provide a near real-time global coverage of TCs because each Low Earth Orbit (LEO) sensor only takes observations twice per day over a given location. The Naval Research Laboratory-Monterey (NRL-MRY) TC web page is the one-stop site where people can search for all available TC microwave sensor observations and associated numerical weather prediction (NWP) TC forecasts for current TCs and historical TC datasets. They also create a unified TC brightness temperature (TB) database dated back to 1987. A comprehensive analysis of this database reveals the detailed TC diurnal properties from a perspective of satellite PMW measurements. Results show that in general TCs have a clear diurnal variability with a primary peak in 3-6 LST and secondary peak in 15-18 LST, which are corresponding to the large intensifying periods in a 3-hour timeframe. The maximum wind speed (Vmax) used for defining TC intensity categories further confirms the TC’s diurnal cycle for a 3-hour lag of diurnal phase with TBs. The radical propagation of TC TB diurnal cycle exhibits the TC convective zone’s diurnal evolution. These diurnal properties have significant geographic characteristics. The detailed descriptions of TC’s diurnal cycle will be presented at the meeting along with discussion of the ambient wind impacts on TC diurnal cycle.