10:45 AM - 12:15 PM
[AAS02-P10] Impact of Drag Coefficient on Typhoon Strength and Internal Structure
Keywords:Typhoon, Non numerical model, Drag Coefficient
A project ”Moonshot Goal 8” supported by Japan Science and Technology Agency was established to study the possible weakening of typhoon intensity due to artificial interventions.
One such measure is to increase the sea surface drag by using obstacles such as large ships.
The maximum potential intensity theory suggests that the equilibrium intensity decreases as the surface drag coefficient increases if the surface enthalpy exchange is unaffected.
However, numerical studies to test it, especially in a realistic atmosphere are limited.
Previous fine-resolution simulations (e.g., with a sub-kilometer grid) tend to agree with the theoretical indication, but the number of cases is limited.
Studies with coarse-resolution models exhibit mixed results.
Also, no studies have been conducted to elucidate the effect of surface drag coefficient change in a limited oceanic region.
Therefore, we aim to conduct a comprehensive study on how tropical cyclones would react to surface drag change over limited regions that can be set in various ways.
As a first step, we conducted preliminary numerical simulations of Typhoon FAXAI in 2019.
The lowest pressure of FAXAI was 955 hPa, and the maximum wind speed was 43 ms-1.
Here we ran the Scalable Computing for Advanced Library and Environment (SCALE) at a coarse resolution of 5 km for FAXAI.
SCALE has many libraries to change parameters easily.
Therefore, we set some different drag coefficient (CD) over the whole simulation area and analyzed the strength and structure of FAXAI.
The resultant minimum central pressure was nearly insensitive to CD, but the maximum winds were weakened by about 60 % of the control run (CTL) when CD was set to 1.5 to 3.5 times that in CTL.
Also, the radii of average winds of 15ms-1 were decreased by about 20 %.
However, if CD was set to four or five times, the result was that the size was about 1.5 times, and the wind speed was developed about 1.4 times.
Changes in CD have created different effects between central pressure, maximum wind speed, and size.
As a result, it was found that CDs have not only negative effects that weaken the strength, but also positive effects on typhoons.
We will conduct further studies until the meeting.
This research was supported by JST Moonshot R&D Grant Number JPMJMS2282.
One such measure is to increase the sea surface drag by using obstacles such as large ships.
The maximum potential intensity theory suggests that the equilibrium intensity decreases as the surface drag coefficient increases if the surface enthalpy exchange is unaffected.
However, numerical studies to test it, especially in a realistic atmosphere are limited.
Previous fine-resolution simulations (e.g., with a sub-kilometer grid) tend to agree with the theoretical indication, but the number of cases is limited.
Studies with coarse-resolution models exhibit mixed results.
Also, no studies have been conducted to elucidate the effect of surface drag coefficient change in a limited oceanic region.
Therefore, we aim to conduct a comprehensive study on how tropical cyclones would react to surface drag change over limited regions that can be set in various ways.
As a first step, we conducted preliminary numerical simulations of Typhoon FAXAI in 2019.
The lowest pressure of FAXAI was 955 hPa, and the maximum wind speed was 43 ms-1.
Here we ran the Scalable Computing for Advanced Library and Environment (SCALE) at a coarse resolution of 5 km for FAXAI.
SCALE has many libraries to change parameters easily.
Therefore, we set some different drag coefficient (CD) over the whole simulation area and analyzed the strength and structure of FAXAI.
The resultant minimum central pressure was nearly insensitive to CD, but the maximum winds were weakened by about 60 % of the control run (CTL) when CD was set to 1.5 to 3.5 times that in CTL.
Also, the radii of average winds of 15ms-1 were decreased by about 20 %.
However, if CD was set to four or five times, the result was that the size was about 1.5 times, and the wind speed was developed about 1.4 times.
Changes in CD have created different effects between central pressure, maximum wind speed, and size.
As a result, it was found that CDs have not only negative effects that weaken the strength, but also positive effects on typhoons.
We will conduct further studies until the meeting.
This research was supported by JST Moonshot R&D Grant Number JPMJMS2282.