Title
The influence of coastal upwelling front on the diurnal cycle of summer rainfall at thenorthern South China SeaMembers
Rui Shi1, Qinbo Cai1, Lingyu Dong1, Xinyu Guo2, & Dongxiao Wang1
Affiliations
1. State Key Laboratory of Tropical Oceanography, South China Sea Institute ofOceanology, Chinese Academy of Sciences, 164 West Xingang Road, Guangzhou
510301, China
2. Center for Marine Environmental Studies, Ehime University, 2-5 Bunkyo-cho,
Matsuyama 790-8577, Japan
Aim
Combining the recent research progress from the ongoing projects founded by National
Natural Science Foundation of China (NSFC, 2017-2020) and JSPS KAKENHI (2017-2020),
make further understanding into the fine structure of coastal upwelling front and its impacts
on the local weather at the northern South China Sea
Procedure
1. Analysis the annual variability of coastal upwelling front and its impact on the diurnal
cycle of summer rainfall at Hainan Island in the northern South China Sea.
2. Revisit the historical hydrological observation results of coastal fronts at the study area.
Result
The modulation of coastal rainfall at Hainan by large-scale circulation and coastal upwellingis studied using observations and numerical modeling. Tropical Rainfall Measuring Mission
data show that the monthly mean rainfall off southern Hainan was considerably higher inAugust 2010 than in August 2011. The main cause of this difference is an intensification ofoffshore rainfall from midnight to early morning. Compared with the multiyear (2000-2017)average field, reanalysis data shows that there is an apparent increase in atmospherichumidity in August 2010. During this time, a moderate El Niño was decaying and a new La
Niña event was developing, so a significant adjustment of the large-scale circulation wasobserved in the western Pacific. The resulting anomalous onshore wind depresses thedevelopment of upwelling, leading to a relatively warm SST off the south coast of Hainan,
which in turn enhances the land–sea thermal contrast and land breeze at night. Decreases
in upwelling intensity and asymmetric intensification of nocturnal and daytime offshore
rainfall are confirmed not only in the summer of 2010 but also in the summer of 2003.
Numerical simulations using the Weather Research and Forecasting model verify that theenhanced land breeze ultimately leads to pronounced coastal rainfall off southern Hainan atnight. The results indicate that localized surface convergence associated with the sea and1 / 3

land breezes may be more important than the atmospheric humidity and convective
instability in modulating the diurnal cycle of rainfall for tropical islands.
(a)

(b)

(c)

(d)

(e)

South China Sea

Figure 1 (a) Monthly Oceanic Niño Index (ONI) from NOAA (color shading) and upwelling
index UI∆SST (gray dashed line) from 2000 to 2017; (b) upwelling index UI∆SST (graydashed line), SST near coast (blue line), and SST of open ocean (magenta line) from 2000
to 2017; (c) anomalies in total nocturnal rainfall (0200–0800 LST) for August from 2000 to2017; (d) as the same in (c) but for daytime rainfall (1400–2000 LST). UI∆SST is theupwelling index which is defined as the difference of SST between the area near thecoastline and 100 km away from coastline. UI∆SST and total rainfall are calculated for theregion shown in (e). Anomalies are calculated as the monthly mean minus the multiyear
average from 2000 to 2017.

Publication
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1.

Rui Shi, Qinbo Cai, Lingyu Dong, Xinyu Guo, & Dongxiao Wang, 2019. Response of thediurnal cycle of summer rainfall to large-scale circulation and coastal upwelling at
Hainan, South China, Journal of Geophysical Research: Atmospheres. (accepted, DOI:
10.1029/2018JD029528).

Perspectives in future
During my visiting, except for working on above article, I also worked on data analysis for anobservation carried out in the Seto Inland Sea several years ago. I almost fixed the outline ofa paper on this analysis. I will keep working on the observed different response of
atmospheric boundary layer to the tidal front in summer and autumn at Seto Inland Sea, andpublish the research article.

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