A Novel Framework to Understand Tropical Cyclone Behavior

Tropical Cyclones (TCs) typically begin to weaken once interacting with land surfaces. However, certain TCs, such as Tropical Storm (TS) Erin (2007), undergo intensification overland perplexingly. Prior research uncovered multiple factors for Erin’s overland intensification, including positive surface moisture anomalies resulting in a hypothesized ”brown ocean” effect and interactions with synoptic features. While these factors are notable, our research has further hypothesized that diurnal variability plays a notable role on the timing of TS Erin’s intensification. Previous studies on the diurnal cycle in TCs have established a nocturnal preference for rapid intensification and deep convection over the ocean. However, research into how cloud-radiative feedback and the diurnal cycle affect overland TC behavior is much scarcer, despite the direct impacts on human populations. We seek to address that gap using TS Erin as a case study. The diurnal cycle has impacts on both the Great Plains Low-Level Jet and cloud-radiative feedback, which both play a role in providing the ingredients for intensification, and thus understanding the relative role each plays could help improve our understanding of overland TC behavior. We investigate the role of these components through a diabatic heating framework. The use of the vertically integrated frozen moist static energy budget has been theorized to explain physical drivers of convection during self-aggregation in tropical environments, with external sources coming from radiative fluxes and surface fluxes. We examine the potential role of these diabatic sources in a set of sensitivity tests on TS Erin using the Weather Research & Forecasting (WRF) model. Results indicate that longwave radiation dominating at night in the absence of shortwave radiation contributed the most to TS Erin’s timing of intensification, while changes in surface fluxes had the most impact on the magnitude of TS Erin’s intensification. As a result, expanding on this framework could identify environments of favorability for intensification with regards to landfalling and post-landfall TCs.