The Meiyu-Baiu front is the main weather system that influences the Yangtze-Huai River area of China in early summer. Convective cells along the Meiyu-Baiu front are very active and often lead to regional flooding disasters. In this study, the multiscale window transform (MWT) and MWT-based multiscale energetics analysis are utilized to investigate the dynamic energy transfers during a typical Meiyu-Baiu rainstorm. It is found that baroclinic instability in the lower stratosphere is possibly a primary trigger for the rainstorm and its diurnal variation. The kinetic energy source for a single rainstorm case varies in its evolution. During shallow convection, the rainstorm itself is a kinetic energy (KE) source. The baroclinic canonical transfer from the rainstorm window brings a lot of available potential energy (APE) to the background flow window, and is further converted into the background flow KE. In contrast, during deep convection, the primary source of KE is the background flow. The barotropic canonical transfer from the background flow contributes to the APE, thus bringing KE into the rainstorm. Implications on Meiyu-Baiu rainstorm forecasting are also discussed.

Various cloud systems responsible for snowfall along the western coast of Japan are formed over the Sea of Japan. In the present study, stratiform snow clouds associated with a mid-level trough were investigated using an instrumented aircraft and dual Doppler radars. The snow clouds exhibited a double-layer structure with thermo-dynamically and kinematically different characteristics. The top height and base height of the clouds were 4.5 km and 0.9 km at temperatures of −29 °C and −5 °C, respectively. The layer below 2 km mean sea level (MSL) had turbulent air, which reflected its convectively unstable stratification. The maximum updraft exceeded 4 m s⁻¹ at approximately 1 km MSL, and the maximum cloud water content was 0.6 g m⁻³. The layer above 2 km was less turbulent and characterized by a weak updraft of < 2 m s⁻¹ and maximum cloud water content of 0.1 g m⁻³. These values were considerably lower than those in the lower layer. The weak updraft was likely caused by an approaching mid-level trough. Ice crystal and precipitation particle concentrations, measured using two-dimensional cloud and precipitation optical array probes, respectively, were almost constant with height and measured several tens of particles L⁻¹ and several particles L⁻¹, respectively. Precipitation particles grew by the seeder-feeder mechanism in the two-layer stratiform snow cloud. In the upper layer (2–4.5 km), precipitation particles increased in size by vapor deposition and showed a remarkable broadening of size distributions toward large sizes. In the lower layer (0.9–2 km MSL), the precipitation particles grew further via accretion of supercooled cloud droplets and produced denser particles like graupel with no substantial change in the size distribution. Below 0.9 km MSL, particle concentrations decreased at all sizes due to sublimation and melting.

Currently, the Regional Specialized Meteorological Center Tokyo applies the satellite-based Dvorak technique using the relationship developed by Koba et al. (1990) for one of the important sources of tropical cyclone (TC) intensity analysis. To improve TC intensity analysis, we revisited Koba’s relationship used for estimating the minimum sea level pressure (MSLP) considering case selection, aircraft data treatment, current intensity (CI) numbers, and additional explanatory variables. The root mean squared difference (RMSD) of the MSLP between the aircraft data and the concurrent estimates based on the original formula of Koba et al. (1990) is approximately 13.0 hPa. The RMSD reduced by 28 % to 9.3 hPa in the revised regression model that used CI numbers analyzed through modern methods and additional explanatory parameters (development rate, size, latitude, and environmental pressure) with careful treatment of the aircraft data. The signs of the coefficients in the proposed model suggest that the actual MSLP change lags the change in the corresponding CI number. The large TC at high latitudes with lower environmental pressure has a low MSLP for a given CI number. Cross-validation results supported the superiority of the proposed model. The current approach is simple but substantially improves the quality of the TC intensity analysis, leading to improved TC forecasts through TC bogus, wave models, storm surge models, and forecast verification.

The impact of the directional propagation of mesoscale convective systems (MCSs) on precipitation structures during the pre-summer rainy season in South China remains unclear. Using multi-satellite datasets, this study aims to reveal the features and mechanisms of precipitation influenced by MCS propagation from the perspective of both cloud microphysics and diurnal forcing of land-atmospheric system. The study region mainly consists of three contiguous coastal regions (A1, B1, and C1 from southwest to northeast). Controlled by the steering flow, MCSs tend to move from region A1 to C1 with a direction parallel to the coastline with a speed of 50 km h⁻¹. Although regions A1 and C1 are both hilly regions, the results show that region A1 is the only key region for initiation and development of MCS, while MCSs in region C1 mainly come from the upstream regions. The directional propagation of MCS causes the propagation of diurnal rainfall peaks, while strong precipitation may accelerate the dissipation of MCS in region C1. The activities of MCSs enhanced ice-phased precipitation processes by spreading more droplets and therefore near-surface rainfall in regions B1 and C1, whereas the hilly surface in region C1 further promoted liquid-phased processes by uplifting southerly low-level flow. Of all the thermodynamic parameters, the daytime vertically moistest layer above the boundary layer over the coastal regions plays a key role in the initiation and development of MCS. These results contribute to a deeper understanding of MCS-related precipitations over coastal regions.