Search

his study assesses the performance of three high-resolution regional numerical models in predicting hourly rainfall over Hainan Island from April to October for the years from 2020 to 2022. The rainfall amount, frequency, intensity, duration, and diurnal cycle are examined through zoning evaluation. The results show that the China Meteorological Administration Guangdong Rapid Update Assimilation Numerical Forecast System (CMA-GD) tends to forecast a higher occurrence of light precipitation. It underestimates the late afternoon precipitation and the occurrence of shortduration events. The China Meteorological Administration Shanghai Numerical Forecast Model System (CMA-SH9) reproduces excessive precipitation at a higher frequency and intensity throughout the island. It overestimates rainfall during the late afternoon and midnight periods. The simulated most frequent peak times of rainfall in CMA-SH9 are 0–1 hour deviations from the observed data. The China Meteorological Administration Mesoscale Weather Numerical Forecasting System (CMA-MESO) displays a similar pattern to rainfall observations but fails to replicate reasonable structure and diurnal variation of frequency-intensity. It underestimates the occurrence of long-duration events and overestimates related rainfall amounts from midnight to early morning. Notably, significant discrepancies are observed in the predictions of the three models for areas with complex terrain, such as the central, southeastern, and southwestern regions of Hainan Island. [ABSTRACT FROM AUTHOR]

The sea-land breeze circulation (SLBC) occurs regularly at coastal locations and influences the local weather and climate significantly. In this study, based on the observed surface wind in 9 conventional meteorological stations of Hainan Island, the frequency of sea-land breeze (SLB) is studied to depict the diurnal and seasonal variations. The statistics indicated that there is a monthly average of 12.2 SLB days and an occurrence frequency of about 40%, with the maximum frequency (49%) in summer and the minimum frequency (29%) in autumn. SLB frequencies (41%) are comparable in winter and spring. A higher frequency of SLB is present in the southern and central mountains due to the enhancement effect of the mountain-valley breeze. Due to the synoptic wind the number of SLB days in the northern hilly area is less than in other areas. Moreover, the WRF model, adopted to simulate the SLBC over the island for all seasons, performs reasonably well reproducing the phenomenon, evolution and mechanism of SLBC. Chiefly affected by the difference of temperature between sea and land, the SLBC varies in coverage and intensity with the seasons and reaches the greatest intensity in summer. The typical depth is about 2.5 km for sea breeze circulation and about 1.5 km for land breeze circulation. A strong convergence zone with severe ascending motion appears on the line parallel to the major axis of the island, penetrating 60 to 100 km inland. This type of weak sea breeze convergence zone in winter is north-south oriented. The features of SLBC in spring are similar both to that in summer with southerly wind and to that in winter with easterly wind. The coverage and intensity of SLBC in autumn is the weakest and confined to the southwest edge of the central mountainous area. The land breeze is inherently very weak and easily affected by the topography and weather. The coverage and intensity of the land breeze convergence line is significantly less than those of the sea breeze. The orographic forcing of the central mountain exhibits significant impacts on low-level airflow. A windward land breeze front usually occurs along the coastline between the wee hours and the morning in summer, with an arc-shaped convergence zone about 10 to 30 km off shore. In winter the arc-shaped convergence zone is weak and appears only in the southeast coastal area. Landing on the flat regions of northern to western parts of the island and going inland from there, the sea breeze front at the leeward side meets with that at the windward side in the centre of the island when sea breeze fully develops, causing an intense convergence zone throughout the whole island. Consistent with prevailing winds in direction, the windward sea breeze and leeward land breeze develop quickly but are not distinguishable from background winds. [ABSTRACT FROM AUTHOR]