Fadli Syamsudin

Dynamics of the South Java Current in the Indo‐Australian Basin

A year-long deployment of a mooring in the South Java Current (SJC) of Indonesia provides a fascinating insight into this poorly understood, semi-annually reversing boundary current. A striking three-week period of south- eastward flow begins in mid-May 1997. An analytical model directly account for changes in velocity at this time due to the passage of a westerly wind-forced, downwelling Kelvin wave from the equatorial western Indian Ocean. The entire water column is warmed, with a fresh cap overlying salty water, consistent with the Indian Ocean source. Following the wave passage, the SJC is north-westward, and the prevailing south- easterly monsoon winds lead to upwelling of cold, salty water. In early August, the SJC abruptly returns to south-eastward flow, and remains so until November 1997 in the face of steady south-easterly local winds. The anomalous flow direction and cooler water are related to an upwelling Kelvin wave, forced b y unseasonal prolonged easterly wind anomalies in the equatorial Indian Ocean. After a small reversal of flow in November 1997, the SJC is south-eastward, as expected during the north-east monsoon. A trend toward increasing salinities in the record is attributed to the increased input of salty Indian Ocean water, enhanced evaporation, and a lack of freshwater advection due to the regionally reduced precipitation during the 1997-98 E1 Nifo.

Diurnal Cycle of Precipitation Observed in the Western Coastal Area of Sumatra Island: Offshore Preconditioning by Gravity Waves

AbstractThis study analyzes data obtained by intensive observation during a pilot field campaign of the Years of the Maritime Continent Project (Pre-YMC) to investigate the diurnal cycle of precipitation in the western coastal area of Sumatra Island. The diurnal cycle during the campaign period (November–December 2015) is found to have a number of similarities with statistical behavior of the diurnal cycle as revealed by previous studies, such as afternoon precipitation over land, nighttime offshore migration of the precipitation zone, and dependency on Madden–Julian oscillation (MJO) phase. Composite analyses of radiosonde soundings from the Research Vessel (R/V) Mirai, deployed about 50 km off the coast, demonstrate that the lower free troposphere starts cooling in late afternoon (a couple of hours earlier than the cooling in the boundary layer), making the lower troposphere more unstable just before precipitation starts to increase. As the nighttime offshore precipitation tends to be more vigorous on d...

Intraseasonal coastal upwelling signal along the southern coast of Java observed using Indonesian tidal station data

Sea level variations along the coasts of Sumatra and Java were investigated to determine the coastal upwelling signal that is linked to local sea surface temperature (SST) variability. We used Indonesian tidal station data together with satellite SST data and atmospheric reanalysis data. The sea level variations along the southern coast of Java have a significant coherence with remote wind, local wind, and local SST variations, with an intraseasonal time scale of 20–50 days. Assuming that a coastal upwelling signal would appear as a sea level drop (SLD), we focused on intraseasonal-scale SLD events in the data. Significant upwelling signals are frequently observed during both the boreal summer and winter. To evaluate the impact of the coastal upwelling on local SST, we examined statistical relationships between sea level and SST variations. The results demonstrated that events that occurred during April–August were associated with local SST cooling. The horizontal distribution of the SST cooling was analogous with annual mean SST, suggesting the importance of intraseasonal-scale coastal upwelling in forming the climatic conditions of the southeastern tropical Indian Ocean.

Meridional march of diurnal rainfall over Jakarta, Indonesia, observed with a C-band Doppler radar: an overview of the HARIMAU2010 campaign

AbstractThis paper presents an overview of the HARIMAU2010 campaign focusing on convective activity with the diurnal rainfall meridional march (DRMM) over Jakarta, which is located on the northern coast of Jawa Island of the Indonesian maritime continent (IMC), based on 1-month intensive observations by a C-band Doppler radar and multi-point atmospheric sounding array conducted during 16 January–14 February 2010. The campaign period corresponded to a phase after large-scale Madden–Julian oscillation (MJO) active convections passed over Jakarta (MJO inactive phase). The cross-equatorial northerly surge (CENS) intruded into the Jawa Sea with a cold tongue (CT) of sea surface temperature (SST) in the beginning of the period (CENS active period: 16–26 January), and then, it started to retreat (transition period: 27 January–05 February); afterward, only a few signs of it were apparent (CENS inactive period: 06–14 February). The observational results showed that (1) rainfall over Jakarta has the nature of DRMM during the MJO inactive phase at least, (2) the DRMM is likely driven primarily by “land-breeze”-like local meridional circulation, and (3) the meridional spatiotemporal variation of rainfall over Jakarta is thus controlled by activities of both the CENS and CT over the Jawa Sea.

Diurnal cycle over a coastal area of the Maritime Continent as derived by special networked soundings over Jakarta during HARIMAU2010

AbstractThis study investigates the nature and mechanisms of the diurnal precipitation system over a coastal area of the Maritime Continent (MC) by utilizing the data from a field campaign, HARIMAU2010. During the 1-month campaign, diurnal cycles over Jakarta were well identified by special networked soundings and a C-band radar. Radar and satellites captured the convective-type heavy rains that appeared in the afternoon over the array, which were followed by stratiform-type precipitation during the night. Thermodynamic budget analyses were also performed using sounding data. The period-averaged vertical profiles of Q1 and Q2 indicate that diurnal precipitation acted as deep convection in the diabatic heating and drying. The diurnal composite of the obtained parameters revealed key processes such as (1) just before the onset of the afternoon convective rain, the lower troposphere was moistened by subarray-scale processes; (2) moistening of the troposphere continued during the convective heavy precipitation; (3) the stratiform rains during the night were partly maintained by consuming the pre-existing hydrometeor aloft; and (4) in the early morning, the clouds redeveloped over the ocean to produce precipitation as well as hydrometeor aloft. The possible physical processes promoting lower-tropospheric moistening before onset of the convective rain are also discussed.

DAMPAK PEMANASAN PULAU PERKOTAAN (URBAN HEAT ISLAND) PADA PENINGKATAN TREN CURAH HUJAN EKSTREM DAN AEROSOL DI MEGAPOLITAN JAKARTA SEJAK TAHUN 1986

Dampak pemanasan pulau perkotaan (urban heat island (UHI)) pada curah hujan ekstrem dan aerosol telah dikaji dalam penelitian ini menggunakan data curah hujan harian dan konsentrasi aerosol bulanan (NO 2 , SO 2 , dan SPM) di stasiun Badan Meteorologi Klimatologi dan Geofisika (BMKG) pada megapolitan Jakarta dan wilayah pegunungan Bogor dan Citeko dari 1986-2012. Analisis harmonik dilakukan untuk menghilangkan pengaruh musiman pada hasil tren data curah hujan dan selanjutnya signifikansi tren tersebut diuji dengan metoda statistik Mann-Kendall. Hasil penelitian menunjukkan dampak pemanasan pulau perkotaan (UHI) telah terjadi secara nyata dengan tren peningkatan curah hujan ekstrem dari indikator total hari hujan 40, 50 dan 100 mm/tahun dan konsentrasi aerosol di wilayah megapolitan Jakarta dan sekitarnya dengan laju tren masing-masing sebesar 0.17 hari/tahun, 0.17 hari/tahun, dan 0.04 hari/tahun, dan 3.7e-004 ppm/tahun (NO 2 ) dan 0.148 ppm/tahun (SO 2 ). Namun sebaliknya terjadi tren penurunan di wilayah pegunungan Bogor dan Citeko. Hasil penelitian ini menunjukkan ada indikasi peningkatan UHI menyebabkan kenaikan konsentrasi aerosol di megapolitan Jakarta dan kondisi ini menjadi trigger peningkatan curah hujan ekstrem yang berdampak pada intensitas banjir yang semakin meningkat sejak tahun 1986. Kata kunci: Pemanasan pulau perkotaan, curah hujan ekstrem, aerosol, tren

Profiling measurement of internal tide in the Bali Strait by reciprocal sound transmission

A reciprocal sound transmission experiment was carried out from 10 to 12 June 2015 along one-crossed-strait line in the Bali Strait with strong tidal current to measure the vertical section structures of range-averaged current and temperature at a 3 minutes interval. The five-layer structures of those parameters in the vertical sections were reconstructed by the regularized of travel time data for 2 rays. The hourly mean current showed a generation of nonlinear internal tide with amplitudes of (1.0—1.5)m/s and period of 6 hours, superimposed on semi-diurnal internal tide with amplitudes, decreasing from the upper to lower layer. The hourly mean temperature was characterized by variation with amplitude of (1.0-1.5) and period of 6 and 8 hours. Current variation revealed an out of phase relation between the upper and lower layer while temperature varied in phase for all five layers. The 2-day average current formed a stratified structure, varying from -0.6 to -0.1m/s and from 23.8 to 28, respectively. The f...

Applicability and feasibility studies of coastal acoustic tomography for long-term monitoring of the Indonesian throughflow transport variability

We have been trying to monitor the Indonesian Throughflow (ITF), especially to understand how prominent tides and tidal mixing along the ITF main pathways in the Makassar and Lombok straits could transform the Pacific waters into Indian Oceans in the shorter scale and how the ITF variability in longer time scales affect the climate regimes over the region, using a modern and innovative technology of Coastal Acoustic Tomography (CAT). The first trial will be done in the Lombok sill where two 5-kHz CATs and three tide gauge sensors are put in the sill of depth range 200-300 m, lying between Lombok and Nusa Penida islands in the southern Lombok strait by the end of July 2016. The experimental design is a real-time land-cable CAT system, equipped with a 3G mobile antenna for telemetering CAT data to our Maritime Continent Center of Excellence (MCCOE) monitoring center in Jakarta every 10 minutes interval. Results are expected to verify CAT aplicability and feasibility as a cost effective oceanographic instrum...

Recent progress in coastal acoustic tomography

Coastal acoustic tomography (CAT) which was proposed by Hiroshima University in 1990s as a shallow-sea application of ocean acoustic tomography (OAT) is developed as a mirror-type CAT (MCAT) for measuring deep strait throughflows in Indonesian archipelago seas in real time. MCAT system is composed of a land station (M0) connected to a 100 m submarine cable edged by a 5 kHz subsurface transceiver and triangular-arrayed bottom-moored stations (M1, M2, and M3). Reciprocal data are first obtained among three station pairs (M1M2, M2M3, and M3M1). Data received at M1 from M2 and M3 are transferred to the land station (M0) by the first mirror reflection, resulting in travel time summations (t21 + t10, t31 + t10) (t21: travel time from M2 to M1). Data obtained at the offshore stations M2 and M3 are transferred to the nearshore station M1 by the first mirror reflection, resulting in travel time summations (t12 + t21, t13 + t31, t23 + t31, and t32 + t21). All the first mirror data at M1 are also transferred to M0 b...