Response of convection to forcing that creates a cold pool

It is known that the dynamics of cold pools generated by the evaporation of raindrops in the mixed layer play an important role in the excitation of convection in the atmosphere. In this study, we quantify the effect of evaporation cooling of raindrops on the magnitude and scale of cold pools. Assuming non-adiabatic cooling due to the evaporation of raindrops, we investigate the convection response when a cooling source is forced into the mixed layer by numerical simulations. The numerical model SCALE is used to achieve a radiative-convective equilibrium state with a horizontal grid spacing of 1 km in a 96 km × 96 km double-period domain, with a uniform forcing near the center in the x-direction and the y-direction. The forcing provides a constant cooling source - 1 K/h in the region below 1 km height. The results show that for a forcing width of 2 km or more, convection is localized at both ends of the region in the x-direction, indicating that the effect of the forcing extends over the entire region. When the forcing width is 1 km, the convective suppression area is generally limited to half of the region. The case of a circular forcing in the region's center was also examined. The temperature drop at the lowest level in the forcing region is a few degrees. The balance between the strength of the mass flux and the heat supply from the sea surface determines the area of expansion of the cold pool.

A similar forcing was applied to Typhoon Hagibis in 2019 using the stretch-NICAM. A circular region of force is applied to a fixed position. The nature of the forcing that effectively affects the eyewalls and the spiral bands will be investigated. This research was supported by JST Moonshot R&D Grant Number JPMJMS2282.