Contribution of Vertical Advection to Supergradient Wind in Tropical Cyclone Boundary Layer: A Numerical Study

Abstract

The existence of supergradient wind in the interior of the boundary layer is a distinct feature of a tropical cyclone (TC). Although the vertical advection is shown to enhance supergradient wind in TC boundary layer (TCBL), how and to what extent the strength and structure of supergradient wind are modulated by vertical advection are not well understood. In this study, both a TCBL model and an axisymmetric full-physics model are used to quantify the contribution of vertical advection process to the strength and vertical structure of supergradient wind in TCBL. Results from the TCBL model show that the removal of vertical advection of radial wind reduces both the strength and height of supergradient wind by slightly more than 50%. The removal of vertical advection of agradient wind reduces the height of the supergradient wind core by ~30% but increases the strength of supergradient wind by ~10%. Results from the full-physics model show that the removal of vertical advection of radial wind or agradient wind reduces both the strength and height of supergradient wind but the removal of that of radial wind produces a more substantial reduction (52%) than the removal of that of agradient wind (35%). However, both the intensification rate and final intensity of the simulated TCs in terms of maximum 10-m wind speed show little differences in experiments with and without the vertical advection of radial or agradient wind, suggesting that supergradient wind contributes little to either the intensification rate or the steady-state intensity of the simulated TC.

Effect of the Initial Vortex Structure on Intensity Change During Eyewall Replacement Cycle of Tropical Cyclones: A Numerical Study

“…The mean radial advection contributes positively to the azimuthal mean tangential wind tendency in the boundary layer and negatively immediately above due to the outflow layer associated with the upward advection of supergradient winds from the boundary layer in both the inner and outer eyewall updrafts (Fig. 9b, Li et al [36] ; Fei et al [37] ). The negative tangential wind tendency immediately above the boundary layer in the outwardly tilted eyewalls is largely offset by the positive tendency induced by vertical advection, which also partly offsets the positive tangential wind tendency due to mean radial advection in the boundary layer (Fig.…”

Assessment of Different Boundary Layer Parameterization Schemes in Numerical Simulations of Typhoon Nida (2016) Based on Aircraft Observations

“…Compared with other boundary schemes, the U-wind simulations in the eye area of the YSU and MYNN schemes were more similar to the observation/result of an ideal typhoon model (shown in Figure 9). Here, the ideal typhoon model means the vertical typhoon structure analyzed in Emanuel et al (1986) [26,27], Chen et al (2019) [20], and Fei et al (2021) [28], where the eye area sinks and both sides of the eye area rise. Under the action of guided wind circulation, the northeast to southwest of the U-wind boundary layer in the eye area showed an east-to-west wind transition, with an easterly jet near a height of 6000 m on the northeast side of the eye area and weak westerly winds on the southwest side of the upper levels.…”