5:15 PM - 6:45 PM
[AAS03-P02] The Coriolis parameter dependence of tropical cyclone formation under radiative-convective quasi-equilibrium in the f-plane and its variation with domain size
The formation process of tropical cyclones is intricately related to various factors, including thermal factors such as SST and mechanical factors such as planetary vorticity and vertical shear. Among these, the planetary vorticity (Coriolis parameter) contributes to the rotation and structure formation of tropical cyclones, and it is a statistical fact that the number of tropical cyclones occurring is small near the equator, where its value is small.
However, it is not fully understood whether the size of the Coriolis parameter contributes to tropical cyclone formation. Therefore, in this study, we investigated the size of the Coriolis parameter necessary for tropical cyclone formation by preparing ideal conditions that exclude the influence of environmental fields such as vertical shear and land. Using the cloud-resolving model SCALE-RM to simulate a radiative-convection equilibrium system with rotation, we investigate whether there is a threshold for the Coriolis parameter for tropical cyclone formation and whether this threshold depends on the region size. did. The experiments conducted can be broadly divided into three types.
First, (i) we investigated the existence of a threshold value for the Rioli parameters necessary for tropical cyclone formation by changing the length of one side of the square region from 96 km to 960 km at a horizontal resolution of 4 km.
Next, (ii) we investigated whether the threshold of the Coriolis parameter required for tropical cyclone formation changes by changing the horizontal resolution.Finally, (iii) we expanded the region size and conducted experiment (i).
As a result of (i), we were able to confirm the Coriolis parameter threshold at which tropical cyclone formation could be confirmed in all experiments, with area sizes ranging from 96km square to 960km square. In (iii), this threshold decreased as the region size increased.
When similar experiments were conducted with the area size further expanded to 1600 km, 3200 km, and 4800 km square, the formation of tropical cyclones was confirmed even with Coriolis parameters near the equator. In addition, considering these area sizes as the spatial scale necessary for the formation of a tropical cyclone, and plotting the area size [km] on the horizontal axis and the Coriolis parameter threshold [s-1] on the vertical axis, it is possible to plot the area with the equivalent depth constant. It was found that the value was close to the evaluated Rossby deformation radius.
However, it is not fully understood whether the size of the Coriolis parameter contributes to tropical cyclone formation. Therefore, in this study, we investigated the size of the Coriolis parameter necessary for tropical cyclone formation by preparing ideal conditions that exclude the influence of environmental fields such as vertical shear and land. Using the cloud-resolving model SCALE-RM to simulate a radiative-convection equilibrium system with rotation, we investigate whether there is a threshold for the Coriolis parameter for tropical cyclone formation and whether this threshold depends on the region size. did. The experiments conducted can be broadly divided into three types.
First, (i) we investigated the existence of a threshold value for the Rioli parameters necessary for tropical cyclone formation by changing the length of one side of the square region from 96 km to 960 km at a horizontal resolution of 4 km.
Next, (ii) we investigated whether the threshold of the Coriolis parameter required for tropical cyclone formation changes by changing the horizontal resolution.Finally, (iii) we expanded the region size and conducted experiment (i).
As a result of (i), we were able to confirm the Coriolis parameter threshold at which tropical cyclone formation could be confirmed in all experiments, with area sizes ranging from 96km square to 960km square. In (iii), this threshold decreased as the region size increased.
When similar experiments were conducted with the area size further expanded to 1600 km, 3200 km, and 4800 km square, the formation of tropical cyclones was confirmed even with Coriolis parameters near the equator. In addition, considering these area sizes as the spatial scale necessary for the formation of a tropical cyclone, and plotting the area size [km] on the horizontal axis and the Coriolis parameter threshold [s-1] on the vertical axis, it is possible to plot the area with the equivalent depth constant. It was found that the value was close to the evaluated Rossby deformation radius.