- 著者
- LI Tsung-Han WANG Yuqing
- 出版者
- Meteorological Society of Japan
- 雑誌
- 気象集誌. 第2輯 (ISSN:00261165)
- 巻号頁・発行日
- pp.2021-028, (Released:2021-01-15)
- 被引用文献数
- 9
In Part I of this series of studies, we demonstrated that the intensification rate of a numerically simulated tropical cyclone (TC) during the primary intensification stage is insensitive to surface drag coefficient. This leads to the question of what is the role of the boundary layer in determining the TC intensification rate given sea surface temperature and favorable environmental conditions. This part attempts to answer this question based on both a boundary layer model and a full-physics model as used in Part I. Results from a boundary layer model suggest that TCs with a smaller radius of maximum wind (RMW) or of lesser strength (i.e., more rapid radial decay of tangential wind outside the RMW) can induce stronger boundary-layer inflow and stronger upward motion at the top of the boundary layer. This leads to stronger condensational heating inside the RMW with higher inertial stability, and thus favorable for higher intensification rate. Results from full-physics model simulations show that the TC vortex initially with a smaller RMW or of lesser strength has a shorter initial spinup stage due to faster moistening of the inner core and intensifies more rapidly during the primary intensification stage. This is because the positive indirect effect of boundary layer dynamics depends strongly on vortex structure but the dissipation effect of surface friction depends little on vortex structure. As a result, the intensification rate of the simulated TC is very sensitive to the initial TC structure.
- 著者
- LI Tsung-Han WANG Yuqing
- 出版者
- Meteorological Society of Japan
- 雑誌
- 気象集誌. 第2輯 (ISSN:00261165)
- 巻号頁・発行日
- pp.2021-027, (Released:2021-01-15)
- 被引用文献数
- 11
This study examines the role of boundary layer dynamics in tropical cyclone (TC) intensification by numerical simulations. The hypothesis is that although surface friction has a negative effect on TC intensification because of frictional dissipation (direct effect), it contributes positively to TC intensification by determining the amplitude and radial location of eyewall updrafts/convection (indirect effect). Results from a boundary layer model show that TCs with larger surface drag coefficient (CD) can induce stronger and more inwardly penetrated boundary-layer inflow and upward motion at the top of the boundary layer. This can lead to stronger and more inwardly located condensational heating inside the radius of maximum wind with higher inertial stability, and is favorable for more rapid intensification. Results from full-physics model simulations using the TC Model version 4 (TCM4) demonstrate that the intensification rate of a TC during the primary intensification stage is insensitive to CD if CD is changed in a reasonable range. This is because the increased/reduced positive contribution by the indirect effect of surface friction to TC intensification due to increased/reduced CD is roughly offset by the increased/reduced negative (direct) dissipation effect due to surface friction. However, greater surface friction can significantly shorten the initial spin-up period through stronger frictional moisture convergence and Ekman pumping and thus faster moistening of the inner core column of the TC vortex, but would lead to a weaker storm in the mature stage.