Sensitivity of Axisymmetric Tropical Cyclone Spinup Time to Dry Air Aloft

Abstract

The sensitivity of tropical cyclone spinup time to the initial entropy deficit of the troposphere is examined in an axisymmetric hurricane model. Larger initial entropy deficits correspond to less moisture above the initial lifting condensation level of a subcloud-layer parcel. The spinup time is quantified in terms of thresholds of integrated horizontal kinetic energy within a radius of 300 km and below a height of 1.5 km. The spinup time increases sublinearly with increasing entropy deficit, indicating the greatest sensitivity lies with initial moisture profiles closer to saturation. As the moisture profile approaches saturation, there is a large increase in the low-level, area-averaged, vertical mass flux over the spinup period because of the predominance of deep convection. Higher entropy deficit experiments have a greater amount of cumulus congestus and reduced vertical mass flux over a longer duration. Consequently, the secondary circulation takes longer to build upward, and the radial influx of angular momentum is reduced. There is also a reduction in the conversion of potential available enthalpy to horizontal kinetic energy, as a result of reduced flow down the radial pressure gradient early in the spinup period. Later in the spinup period, the low-level vortex spins up relatively quickly near the nascent radius of maximum wind in the high-entropy deficit experiments, whereas the low-level vortex spins up over a wider area in the low-entropy deficit experiments.

Monitoring and prediction of hurricane tracks using GPS tropospheric products

“…The results confirm that temporal changes in GPS-IWV are strongly linked to a hurricane's path and may facilitate the tracking and monitoring of hurricane activities at least several hours before the arrival of a storm. These findings are in agreement with Tang et al (2016) in showing that TC development projections could be improved through the monitoring of water vapor in the lower and middle atmosphere. During Hurricanes Harvey and Irma, IWV values ranged mostly between 60 and 80 mm.…”

The Control of Environmental Stratification on the Hurricane Maximum Potential Intensity

“…As discussed in Kieu et al (2013) and Tang et al (2016), this feature can be attributed to the time required for the model to moisten the lower troposphere before the storm central region becomes saturated for deep convection to develop. Results show very similar V max among all the experiments during the quasi-steady stage.…”

“…The only significant difference among these moisture-varying experiments is the onset of rapid intensification that tends to be delayed in an initially drier environment. As discussed in Kieu et al (2013) and Tang et al (2016), this feature can be attributed to the time required for the model to moisten the lower troposphere before the storm central region becomes saturated for deep convection to develop.…”

Evolution of convective characteristics during tropical cyclogenesis

“…Another possibility is that the seasonal average sounding employed here is already moist enough to bypass the congestus phase. In an axisymmetric framework, Tang et al (2016) found a prolongation of the shallow and cumulus congestus phases when the atmosphere is drier initially.…”

“…In an axisymmetric framework, Tang et al . (2016) found a prolongation of the shallow and cumulus congestus phases when the atmosphere is drier initially.…”