Quantifying the Effects of Land Surface Characteristics on Rainband Structures of a Modeled Landfalling Tropical Cyclone

As tropical cyclones (TCs) can produce varying rainfall amounts during landfall, it is important to understand how land surface conditions can contribute to the energetics of a TC to better predict rainfall patterns as the storm moves over land. Different land-surface properties have been shown to influence the heat and moisture fluxes within the planetary boundary layer, which change the development of deep cumulus clouds and can influence the TC structure accordingly. However, fewer studies have examined the effects that different land surface profiles can have on TCs, especially in a realistic atmospheric setting. This study performs multiple simulations of a landfalling TC using WRF3.4.1 modifies only the land cover and soil type to better understand how changes in roughness length (RL) and moisture availability (MA) modify the planetary boundary layer (PBL) and affect rainfall production within the TC. The calculation of spatial metrics on simulated radar reflectivity reveals differences in timing of development and configuration the TC rainbands among the multiple simulations.

The simulated TC is from the Hurricane Nature Run 2 (HNR2), which is a component of a Joint Observing System Simulation Experiments Nature Run (JONR). The HNR2 is a simulated hurricane that experienced significant land interaction during its development as well as during landfalls over Florida and the southeast United States. Four experiments were conducted using the exact physical schemas used by HNR2. For the entire experiment period, the land surface of United States is covered by a single combination of RL and MA. The resulting spatial patterns of simulated reflectivity are evaluated using by measuring their dispersion from the storm center, their closure around the storm center, and their fragmentation.

The accumulated hourly precipitation totals within 500 km from the storm center show that the WH case has the highest amount over all while the DH case has the lowest amount. The three-day total precipitation showed noticeable differences in the precipitation extent over land. For the interval of 200 mm to 300 mm, with the same low RL, the wet case shows a wider extent than the dry case. For the interval of 300 mm to 400 mm, the drier cases show smaller area compared with the wetter cases with the same RL. Wet and rough cases exhibit a more dispersed structure compared with the dry and smooth cases. Driers cases feature a more fragmented structure, while rougher cases have the circulation center more exposed to the environmental air mass, meaning less closure.

By applying geographic spatial analysis and shape metrics to the metrological model outputs, this research provides quantitative evidence of TC structural changes resulting from interaction with different land surface conditions. These results demonstrate how land surface and PBL interaction can influence the structure of a larger-scale system.