11:30 AM - 11:45 AM
[AAS02-04] Impact of Vertical Wind Shear on the Internal Structure of Tropical Cyclones During the Development Phase
Keywords:Typhoon, Tropical cyclone, Vertical wind shear, Idealized experiment
Vertical wind shear has a significant impact on the development of tropical cyclones. In general, vertical wind shear is known to suppress tropical cyclone development; however, under moderate vertical wind shear, development can still occur. Various hypotheses have been proposed in previous studies regarding the mechanisms of tropical cyclone development under vertical wind shear. However, there remain gaps in understanding, particularly between observational data and idealized experiments. In particular, the response of weak tropical cyclones—defined here as those with an intensity below or around the threshold value for classification as a typhoon (17 m/s)—to vertical shear is complex due to the dominance of moist processes, necessitating further research.
In this study, we investigated the development and structural changes of weak tropical cyclones under vertical shear through idealized experiments. Additionally, we conducted experiments by varying the intensity, radius of maximum wind, and height of the vortices to examine differences in their responses to vertical wind shear.
For numerical modeling, we used Plane-NICAM, a non-hydrostatic model on an f-plane. The computational domain was rhombus-shaped with a side length of 4096 km and a grid spacing of 8 km. The Coriolis parameter was set to a value corresponding to 15°N latitude, and the sea surface temperature (SST) was set to 28°C. The vertical distribution of temperature and humidity in the basic state was determined through a radiative-convective equilibrium experiment. Since Plane-NICAM applies periodic boundary conditions at the northern and southern boundaries, special adjustments were necessary to impose vertical wind shear while maintaining thermal equilibrium and geostrophic balance.
As initial vortex conditions representing weak tropical cyclones, we used five different axisymmetric vortices. The reference vortex was set with a maximum wind speed of 15 m/s. In addition to this reference vortex, we tested four other variations: a stronger vortex, a weaker vortex, a vortex with a larger radius of maximum wind, and a vortex with a lower height. For each of these vortices, we conducted experiments by varying the vertical wind shear magnitude from 0 m/s to 20 m/s.
For the reference vortex, development was observed when the vertical wind shear magnitude was 11 m/s or less, whereas no development occurred when it was 12 m/s or more. Notably, in experiments with vertical shear magnitudes of 10 m/s and 11 m/s, significant delays in development were observed. This suggests that there is a range of threshold values for vertical shear magnitude that determine whether development occurs. Additionally, before development began, counterclockwise precession and re-alignment of the vortex were observed, which are consistent with previous studies.
Furthermore, experiments with the other vortices demonstrated that the response to vertical wind shear varies depending on the internal structure of the vortex, such as its intensity, radius of maximum wind, and height.
Future challenges include conducting experiments with higher resolution in a more systematic manner to obtain more precise results. Additionally, further investigation is needed to deepen our understanding of the underlying mechanisms.
In this study, we investigated the development and structural changes of weak tropical cyclones under vertical shear through idealized experiments. Additionally, we conducted experiments by varying the intensity, radius of maximum wind, and height of the vortices to examine differences in their responses to vertical wind shear.
For numerical modeling, we used Plane-NICAM, a non-hydrostatic model on an f-plane. The computational domain was rhombus-shaped with a side length of 4096 km and a grid spacing of 8 km. The Coriolis parameter was set to a value corresponding to 15°N latitude, and the sea surface temperature (SST) was set to 28°C. The vertical distribution of temperature and humidity in the basic state was determined through a radiative-convective equilibrium experiment. Since Plane-NICAM applies periodic boundary conditions at the northern and southern boundaries, special adjustments were necessary to impose vertical wind shear while maintaining thermal equilibrium and geostrophic balance.
As initial vortex conditions representing weak tropical cyclones, we used five different axisymmetric vortices. The reference vortex was set with a maximum wind speed of 15 m/s. In addition to this reference vortex, we tested four other variations: a stronger vortex, a weaker vortex, a vortex with a larger radius of maximum wind, and a vortex with a lower height. For each of these vortices, we conducted experiments by varying the vertical wind shear magnitude from 0 m/s to 20 m/s.
For the reference vortex, development was observed when the vertical wind shear magnitude was 11 m/s or less, whereas no development occurred when it was 12 m/s or more. Notably, in experiments with vertical shear magnitudes of 10 m/s and 11 m/s, significant delays in development were observed. This suggests that there is a range of threshold values for vertical shear magnitude that determine whether development occurs. Additionally, before development began, counterclockwise precession and re-alignment of the vortex were observed, which are consistent with previous studies.
Furthermore, experiments with the other vortices demonstrated that the response to vertical wind shear varies depending on the internal structure of the vortex, such as its intensity, radius of maximum wind, and height.
Future challenges include conducting experiments with higher resolution in a more systematic manner to obtain more precise results. Additionally, further investigation is needed to deepen our understanding of the underlying mechanisms.