Impacts of Radiation and Upper-Tropospheric Temperatures on Tropical Cyclone Structure and Intensity

Abstract

Potential intensity theory predicts that the upper-tropospheric temperature acts as an important constraint on tropical cyclone (TC) intensity. The physical mechanisms through which the upper troposphere impacts TC intensity and structure have not been fully explored, however, due in part to limited observations and the complex interactions between clouds, radiation, and TC dynamics. In this study, idealized Weather Research and Forecasting Model ensembles initialized with a combination of three different tropopause temperatures and with no radiation, longwave radiation only, and full diurnal radiation are used to examine the physical mechanisms in the TC–upper-tropospheric temperature relationship on weather time scales. Simulated TC intensity and structure are strongly sensitive to colder tropopause temperatures using only longwave radiation, but are less sensitive using full radiation and no radiation. Colder tropopause temperatures result in deeper convection and increased ice mass aloft in all cases, but are more intense only when radiation was included. Deeper convection leads to increased local longwave cooling rates but reduced top-of-the-atmosphere outgoing longwave radiation, such that the total radiative heat sink is reduced from a Carnot engine perspective in stronger storms. We hypothesize that a balanced response in the secondary circulation described by the Eliassen equation arises from upper-troposphere radiative cooling anomalies that lead to stronger tangential winds. The results of this study further suggest that radiation and cloud–radiative feedbacks have important impacts on weather time scales.

The Sensitivity of Eyewall Replacement Cycles to Shortwave Radiation

“…In the full‐physics idealized simulations performed by Trabing et al. (2019), TCs developed a secondary eyewall without any added perturbations to the model. In Trabing et al.…”

“…The experimental setup for the idealized WRF simulations can be found in Trabing et al. (2019) but will be briefly summarized here for completeness. The simulations were conducted with two‐way nested, doubly‐periodic domains with 18, 6, and 2 km resolution in the horizontal and 30 stretched vertical levels reaching 25 km in altitude.…”

“…To investigate the influences of radiation on SEFs and ERCs, idealized experiments are conducted using the Advanced Research version of the Weather Research and Forecasting (WRF-ARW; version 3.7.1; Skamarock et al, 2008) model. In the full-physics idealized simulations performed by Trabing et al (2019), TCs developed a secondary eyewall without any added perturbations to the model. In Trabing et al (2019), ensembles were performed with full radiation, longwave only radiation, and no radiation with three different tropopause temperatures each.…”

“…In the full-physics idealized simulations performed by Trabing et al (2019), TCs developed a secondary eyewall without any added perturbations to the model. In Trabing et al (2019), ensembles were performed with full radiation, longwave only radiation, and no radiation with three different tropopause temperatures each. From the ensemble members that underwent an ERC, the first ensemble member is selected from the experiment with a tropopause temperature of 199.6 K to be the "Control" for this study.…”

The Role of Radiation in Accelerating Tropical Cyclogenesis in Idealized Simulations

“…Cooling at the tropopause and above can lead to significant changes in the potential intensity of TCs (e.g., Ramsay 2013;Wang et al 2014). Temperatures in the upper troposphere have recently been linked to changes in ice species, upper-level vertical mass flux and the height of the TC's upper-tropospheric outflow (Trabing et al 2019). Radiation's impacts on the Brunt-Väisälä frequency have been linked to potential vorticity near the tropopause, which has implications for the rapid intensification of TCs (Duran and Molinari 2019).…”