Diurnal Pulse Climatology
Description: This study used storm-centered IR brightness temperature imagery to create a climatology of tropical cyclone diurnal pulses in the Atlantic basin from 1982-2017, thus generalizing and expanding the results of Dunion et al. (2014). Pulses were defined objectively by determining critical thresholds for the magnitude of the IR differences, areal coverage of cold-cloud tops, and longevity. Some days without cooling pulses had events of the opposite sign, here labeled warming pulses, that propagated outward at the same speed as their cooling pulse counterparts. Only 12.2% of days had no pulses that met the criteria, indicating that pulsing is nearly ubiquitous in tropical cyclones.
Electrically Active Pulses
Description: This study used storm-centered IR brightness temperature imagery and WWLLN lightning data to create a climatology of electrically active tropical cyclone diurnal pulses in the Atlantic basin from 2005-2017. Pulses were defined objectively by determining critical thresholds for the lightning flash density, areal coverage, and longevity within a pulse. It was found that electrically active (ACT) pulses occurred around 61% of the time, primarily when pulses propagated outward on the right-of-shear side of the storm, the dominant quadrant for outer-rainband lighting activity, and on days with overall more favorable environments for deep convection.
Hurricane Harvey (2017)
Description: This study used storm-centered IR brightness temperatures, WWLLN lightning data, 85--91-GHz channels on microwave satellite imagers, NEXRAD radar reflectivity, and the HRRR to study two electrically active diurnal pulses in Hurricane Harvey (2017). The pulses were found to share many similar characteristics, including those associated with tropical squall lines, supporting the tropical squall line interpretation of diurnal pulses put forth in recent studies. A hypothesis for ACT pulse initiation was then introduced, tested, and confirmed: inner rainbands that propagated outward into a more favorable environment for deep convection reinvigorated into ACT pulses that had tropical squall line characteristics.
