A Modeling Study of the Effects of Vertical Wind Shear on the Raindrop Size Distribution in Typhoon Nida (2016)

Abstract

In this study, the effects of vertical wind shear (VWS) on the raindrop size distribution in tropical cyclone are investigated, based on the theoretical analyses that intense VWS, which commonly appears in the lower layers of tropical cyclones, can enhance the collisional breakup of raindrops. This is achieved by comparing the numerical sensitivity experiments of Typhoon Nida (2016) using Weather Research and Forecasting model against the polarimetric radar and disdrometer observations. In the control run with the default Morrison microphysics, unrealistic large raindrops are produced with excessively large differential reflectivity and heavier precipitation. An obvious decrease of raindrop size is present when the constant value of cloud droplet number concentration reduces from 250 to 30 cm−3 (NC30), leading to more comparable microphysics characteristics with the observations due to the enhancement of autoconversion rate from cloud droplets to raindrops; however, some unrealistic large‐sized raindrops still exist. A semiempirical raindrop collection/breakup parameterization is further proposed in NC30_WS run by modifying the threshold diameter of raindrops at which breakup occurs as a function of VWS. The certain improvements of simulating raindrop size distribution and precipitation in Typhoon Nida are present in NC30_WS run, owing to the efficient collisional breakup and the induced stronger raindrop evaporation cooling. Our results indicate that the combined effects of reasonable cloud droplet numbers as well as reliable raindrop breakup parameterization are pronounced and highlight the impacts of VWS on raindrop size distribution, which should be involved in current microphysical schemes to forecast the TCs more accurately.

Evaluating the Variability of Simulated Raindrop Size Distributions in the “21·7” Henan Extremely Heavy Rainfall Event

“…Based on the reduction of simulated STD( D m ), we suppose limited DSD variability in the schemes is highly likely to be caused by unrealistic constrictions related to warm‐rain processes. Previous studies have revealed that the self‐collection (breakup) processes are commonly parameterized by simplified empirical formulas in microphysics schemes, and the key parameters of which have a critical impact on the values of DSD parameters (Deng et al., 2019; Morrison et al., 2012; Planche et al., 2019; Saleeby et al., 2022). Take THOM for example, the self‐collection (breakup) formula is presented as: $$$\mathrm{d}{N}_{rcol}=2{E}_{c}{N}_{r}W,$$$ where d N rcol denotes the raindrop number concentration tendency via self‐collection (breakup), N r denotes the existing raindrop number concentration.…”

Simulating the impact of typhoons on air‐sea CO2 fluxes on the northern coastal area of the South China Sea

“…This suggests that SST played a primary role in pCO 2sea during the initial limited time period of Typhoon Merbok. Furthermore, there was no significant slowdown in the temperature-induced pCO 2sea relative to non-temperature factors during the second step of Typhoon Nida (figure 8), indicating that SST may not only be affected by deeper water but may also be influenced by other factors such as heavy rainfall, which could cause a decrease in SST (Deng et al 2019, Feng et al 2021.…”

A Study of the Effects of Anthropogenic Gaseous Emissions on the Microphysical Properties of Landfalling Typhoon Nida (2016) over China

“…With the development of cloud and precipitation observations, polarimetric radar has gradually been used to validate the model in simulating the raindrop characteristics within the TC system [32][33][34]. The horizontal reflectivity factor (Z H , unit: dBZ) is a variable that represents both particle size and number concentration in the detective volume, while the differential reflectivity (Z DR , unit: dB) only expresses the size information of particles.…”