The influence of sea- and land-breeze circulations on the diurnal variability in precipitation over a tropical island

Abstract

Abstract. This study examines the diurnal variation in precipitation over Hainan Island in the South China Sea using gauge observations from 1951 to 2012 and Climate Prediction Center MORPHing technique (CMORPH) satellite estimates from 2006 to 2015, as well as numerical simulations. The simulations are the first to use climatological mean initial and lateral boundary conditions to study the dynamic and thermodynamic processes (and the impacts of land-sea breeze circulations) that control the rainfall distribution and climatology. Precipitation is most significant from April to October and exhibits a strong diurnal cycle resulting from land-sea breeze circulations. More than 60 % of the total annual precipitation over the island is attributable to the diurnal cycle with a significant monthly variability. The CMORPH and gauge datasets agree well, except that the CMORPH data underestimate precipitation and have a 1 h peak delay. The diurnal cycle of the rainfall and the related landsea breeze circulations during May and June were well captured by convection-permitting numerical simulations with the Weather Research and Forecasting (WRF) model, which were initiated from a 10-year average ERA-Interim reanalysis. The simulations have a slight overestimation of rainfall amounts and a 1 h delay in peak rainfall time. The diurnal cycle of precipitation is driven by the occurrence of moist convection around noontime owing to low-level convergence associated with the sea-breeze circulations. The precipitation intensifies rapidly thereafter and peaks in the afternoon with the collisions of sea-breeze fronts from different sides of the island. Cold pools of the convective storms contribute to the inland propagation of the sea breeze. Generally, precipitation dissipates quickly in the evening due to the cooling and stabilization of the lower troposphere and decrease of boundary layer moisture. Interestingly, the rather high island orography is not a dominant factor in the diurnal variation in precipitation over the island.

Image Processing of Radar Mosaics for the Climatology of Convection Initiation in South China

“…The majority of CI events on the northern island were likely corresponding to the localized afternoon convection. Previous studies have demonstrated that the afternoon convection in the northern part of the island is closely associated with the activity of sea-breeze fronts (Zhu et al 2017). The collision of sea breezes from the west and east sides of the island is FIG.…”

“…13b). The thermal contrast may also drive sea-breeze circulation, triggering the afternoon convection in the central and northern areas of Hainan Island (Zhu et al 2017). In contrast, the early-morning peaks in CI and rainfall on windward coasts and in offshore areas were mainly due to the convergence of land breezes with onshore southerly monsoons or the effect of gravity waves (X.…”

Superenhancement of Precipitation at the Center of Tropical Islands

“…There is therefore only a weak or no superenhancement of precipitation on these islands. However, the convective precipitation continues to move inland at night, possibly driven by cold pools caused by convective downdrafts (Saito et al, ; Zhu et al, ).…”

Relative Roles of Low‐Level Wind Speed and Moisture in the Diurnal Cycle of Rainfall Over a Tropical Island Under Monsoonal Flows

“…In this study, we will focus on the rainfall diurnal cycle over a monsoonal tropical island (Hainan Island) during the East Asian summer monsoon season. Located in South China, Hainan Island is characterized by active convection and associated precipitation in the monsoon season (e.g., Bai et al, 2020; Zhu et al, 2017). In South China, the rainfall amount from April to June (also called Mei‐Yu or pre‐rainy season) typically accounts for more than 50% of the annual rainfall (Ding, 1992).…”