Understanding the Dynamical Changes by an Artificial Cold Pool on an Approaching Typhoon using the Nonhydrostatic Icosahedral Atmospheric Model (NICAM)

Tropical cyclones are highly destructive natural disasters that can be very costly, therefore, making them a grave concern to any society. As a part of the Moonshot project of the Typhoon Control Research aiming for a safe and prosperous society, a series of experiments are conducted using the stretched version of the Nonhydrostatic Icosahedral Atmospheric Model (NICAM) with a minimum grid spacing of 1.4km to see the impact an artificial forcing would have on an approaching typhoon. Each experiment has an artificial forcing with a different intensity to induce a cold pool positioned at 27 degrees North Latitude and 138 degrees East longitude, in the pathway of typhoon Hagibis. The experiments run for two days (48 hours) prior to landfall in Japan. The intensities provide a constant cooling source of 1K/hr, 2K/hr, 10K/hr and 20K/hr where each are circular in shape with a radius of 50km. For the first 6 hours the cold pool has no impact on typhoon Hagibis in each of the experiments due to the fact that it is still in the outer regions. As the cyclones continues approaching Japan, there is some distortion of the eye where it takes on irregular shapes. All experiments increase in sea level pressure at the times from 7 to 14 hours. This is a sign that there is some weakening occurring. Once the cold pool is in the eye of the typhoon which occurs from 20 to 24 hours, there is a sharp increase in surface pressure with the greatest being observed in the 20K/hr and 10K/hr. The left side of the typhoon experiences a greater impact of the cold pool than the right side. Although, in some cases, there are very little changes being observed. Unsurprisingly, the experiments for 10K/hr and 20K/hr show a greater impact than 1K/hr and 2K/hr. After 24 hours it is very clear that the 2 larger intensities had a significant impact on weakening the cyclone by producing larger sea level pressures. Although the cyclone does not change in size, the distribution of the wind intensities in the eyewall show changes and the reduction in the wind speed tends to be more evident on the left side of the typhoon. Although, there is a reduction in wind speed in some parts of the typhoon, when the typhoon hits Japan it is not at an appreciable weaken state. The 1K/hr and 2K/hr experiments show very little difference. A cooler environment should reduce the intensity of an approaching tropical cyclone, however, our results prove that the cooling force can only have an impact if it is of a certain intensity. These results are promising. Although there is no overall reduction in strength, the artificial cold pool has proven to show some weakening in the approaching typhoon. Improvements are being made to the forcing such as changing the location of the cold pool and using evaporative rain to generate the artificial cold pool.

This research was supported by JST Moonshot R&D Grant Number JPMJMS2282