ALBERT

Description: 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 (MPA-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 characterised by precipitation peaks that occur in the afternoon to evening time (15:00–21:00 LT) but secondary peaks in night to morning time (01:00–07:00 LT) are also pronounced in January and February. Harmonic analysis method was then applied on 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 LT, 01:00–04:00 LT, and 05:00–12:00 LT, respectively. In terms of frequency of occurrence, AEP, EMP, and LMP constitute 55 %, 26.1 %, and 18.9 % of total samples of precipitation events. In spite of the smallest percentage, EMP events are characterised 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 South China Sea Cold Tongue (SCS-CT) and Cross Equatorial Northerly Surge (CENS) as influencing factors for the occurrences of 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 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 the Indochina and Malay Peninsula.

Description: 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.

Description: For the first time, the processes controlling the variations of mixed layer temperature (MLT) and salinity (MLS) in the Banda Sea are quantified using data from a single Argo float in combination with satellite and reanalysis outputs from August 2017 to August 2019. This augments previous studies that utilized ocean model data only. We document the presence of a barrier layer and quantify the roles of air-sea heat and mass exchanges, horizontal advection, and vertical entrainment in the seasonal variability of MLT and MLS. We find that heat gains and losses at the air-sea interface are the main contributor to the warming and cooling of the MLT. Seasonal changes in MLS are driven by advection of low salinity water rather than freshwater fluxes from precipitation and evaporation. This is particularly the case during the late northwest and monsoon transition period from February to April when low salinity is advected eastward from the Java Sea into the Banda Sea.

Description: Over one hundred years of vigorous progress in tropical cyclone (TC) research, the genesis of the cyclone (hereafter, tropical cyclogenesis) is remarkable as a doubtful subject. Furthermore, predicting tropical cyclogenesis, particularly in the lesser latitude, remains a significant challenge. Therefore, understanding the complex interactions in developing tropical cyclogenesis over the region is vital to improving tropical cyclogenesis forecasting. Hence, the Indonesia Maritime Continent is a tropical cyclone-free region due to decreasing the Coriolis effect. However, Seroja TC hit Flores (8.6° S, 120° E), east Nusa Tenggara, Indonesia, on 4 April 2021, and was recorded as the first TC that occurred over the mainland, which brought a catastrophic disaster in the region. This study investigated the tropical cyclogenesis of Seroja by using observational and numerical studies. The results indicate that a marine heatwave and double vortices were favorable conditions that produced preconditions for developing tropical cyclogenesis over the Maluku Sea. Thus, tropical cyclogenesis is formed by the breakdown of the intertropical convergence zone (ITCZ) associated with synoptic-scale wave train driven under the interaction of the Madden Julian oscillation (MJO) and equatorial Rossby waves. Moreover, our finding suggested that an extensive background cyclonic vorticity under the cold pool mechanisms is responsible for maintaining tropical cyclogenesis into a persistent Seroja TC.