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Buoy, island stations, and platform stations play a crucial role in advancing atmospheric and ocean sciences by providing essential marine observational data. This paper explores the potential impact of assimilating sea-based observation data from the South China Sea and the coast on forecasts of heavy rainfall during annually first rainy seasons in South China. In addition to ground station observations, seabased observations are added to conduct continuous cycle assimilation experiments. The experiment results suggest that the continuous cycle assimilation scheme significantly improves precipitation forecasting compared to the cold-start assimilation scheme. The assimilation of additional sea-based observations effectively enhances the humidity field and wind field at the lower levels of the analysis field, thereby improving the water vapor transport and dynamic conditions in the South China Sea region. While the assimilation of sea-based observations does not show significant improvement in precipitation forecasts over land areas, it notably enhances precipitation forecasts for coastal and offshore regions, particularly for heavy rainfall forecasts at 18 - and 24-hour lead times. Overall, the inclusion of sea-based observations positively contributes to the prediction of heavy rainfall along the coastal and offshore regions of the South China Sea during annually first rainy seasons. This study provides an important basis for the CMA-MESO model to achieve more operational assimilation of sea-based observations, improve heavy rainfall forecasting in South China, and conduct marine observation experiments in the South China Sea. [ABSTRACT FROM AUTHOR]

Using the ERA5 reanalysis data, observational data from automated weather stations, and local radar data, this paper presents a comparative study to analyze the rainfall, weather patterns, physical parameters, and radar echo characteristics during two extreme torrential rainfall events on May 20--22, 2020 (Process 1) and on June 6--8, 2020 (Process 2) in the Shenzhen-Shanwei Special Cooperation Zone (SSCZ). The results show that both of the two events occurred under the background of favorable largescale circulation, and low-level jet (LLJ) streams provided sufficient water vapor. Meanwhile, the transport of low-level warm and humid airflow kept the low level of the rainstorm area under the control of high energy and high humidity for a long time, and the strong convergent upward motion provided favorable dynamic conditions. A surface convergence line was formed under the influence of a warm and moist airflow from the ocean and a southward cold airflow along the Lianhua Mountain. The difference was that the low-level wind speed in the rainfall area was stronger and the strengthening was more obvious, and the intensity of the mesoscale kinetic energy front was stronger in Process 1. In Process 2, the large value of water vapor flux was more northerly, and the unstable atmospheric stratification in the rainfall area was maintained for a longer period of time. The height range of the large value area of vertical motion was wider. The radar echo of Process 1 was a strong mono echo moving northward to the surface convergence line of the SSCZ. Subsequently, it developed rapidly and moved less, and was accompanied by a meso-γ-scale vortex. In Process 2, the radar echo was a linear strong echo that was triggered continuously near the long-maintained surface convergence line and thus the "train effect" was developed. [ABSTRACT FROM AUTHOR]

The evolution of three mesoscale convective systems (MCS), i. e., MCS-A, MCS-B, MCS-C, experienced multiple division and reorganization, resulting in a heavy rainfall in the warm sector ahead of fronts in Southern China on 27 March 2020, which sustained for more than 15 hours. The synoptic background, organization modes and initiation conditions of MCS are analyzed by using surface automatic meteorological stations data, Doppler weather radar data, ERA-Interim reanalysis data and mesoscale CMAGD model data. The results are shown as follows. (1) Favorable configuration and stable circulation systems, including a 500 hPa upper-level trough, a 200 hPa westerly jet and a frontal trough are important reasons for long-term maintenance of the warm-sector heavy rainfall. The low-level jet provides conditional instability and convective available potential energy for the generation and development of convection. (2) The convection in key region 1 from Hezhou to Huaiji was triggered on the ground with the decrease of the level of free convection and the reduction of CIN energy. The interaction between wind speed convergence at the height of 1500 m and a cool pool in key region 2 80 km away from key region 1 resulted in the convection. (3) MCS-A and MCS-B are modulated into forward and backward propagation in key region 1, while MCS-C is modulated into backward propagation in key region 2. The convective cells of all three MCSs form echo "train band effects". In addition, both MCS-B and MCS-C form several short and parallel convective rainbands in a nearly N-S direction triggering eastward "train band effects". MCS-A and MCS-B split again into short and parallel convective rainbands in a nearly NE-SW direction triggering southeastward "train band effects". (4) The warm and humid southwesterly flow on the left side of the meso - β - scale secondary circulation is lifted, releasing latent heat and triggering convection. The interaction of the cold outflow resulting from the drag effect of heavy precipitation formed a downdraft below 850 hPa and a warm inflow on the west side near the surface was conductive to new convection, which was the development mechanism of the backward propagation. (5) Forward propagation was caused by the convergence between the cold pool outflow, which was formed on the ground after the genesis of upstream MCSs, and the warm moist flow. [ABSTRACT FROM AUTHOR]