Abstract. The diurnal cycles of precipitation over the northern
coast of West Java have been studied using the Tropical Rainfall Measuring
Mission (TRMM) Real Time Multi-satellite Precipitation Analyses (TMPA-RT)
products with records spanning from 2000 to 2016, with emphasis on the
occurrences of early morning precipitation peaks. Diurnal precipitation over
the study area during November to March is basically characterized by
precipitation peaks that occur in the afternoon to evening time
(15:00–21:00 LT), but secondary peaks in the night to morning time (01:00–07:00 LT) are also pronounced in January and February. The harmonic analysis method
was then applied to data of January and February to objectively determine
the diurnal phase and classify the timing of precipitation for each day into
three categories, i.e. afternoon-to-evening precipitation (AEP), early
morning precipitation (EMP), and late morning precipitation (LMP) with peaks
that occur in the time windows of 13:00–24:00, 01:00–04:00, and
05:00–12:00 LT, respectively. In terms of frequency of occurrence, AEP,
EMP, and LMP constitute 55 %, 18.9 %, and 26.1 % of total samples
of precipitation events. In spite of the smallest percentage, EMP events are
characterized by seaward (as well as landward) propagation, flat phase
distribution, and large mean amplitudes. The propagating characteristics of
EMP are more prominent, with indications of stronger connectivity between
precipitation systems over land and ocean, when data are composited by
taking the 99th percentile values in each grid to represent extreme
precipitation events. The flat phase distribution of EMP events suggests
that the timing of coastal precipitation is not necessarily locked to the
phase of land–sea breezes, thus allowing precipitation to occur more
randomly. Furthermore, the role of the South China Sea cold tongue (SCS-CT) and
cross-equatorial northerly surge (CENS) as influencing factors for the
occurrences of the EMP event have also been investigated. In agreement with
previous studies, we confirmed that the SCS-CT generally prevails in January
and February, and morning precipitation events over the northern coast of
West Java mainly occurred when there was more enhanced sea surface
temperature (SST) cooling in the South China Sea. Additionally, we found
that CENS is the most differential factor with regard to the phase of
coastal precipitation. In this case, CENS is positively correlated with
SCS-CT and, when associated with EMP events, concurrent enhancement of CENS
and SCS-CT is connected to a narrow channelling of strong surface northerly
wind anomalies just offshore of Indochina and the Malay Peninsula.
Diurnal Rainfall Propagation Relate to Cold Surge-Cold Tongue Interaction over The Northern Coast of West Java
