Wijaya Mardiansyah

Spatio-temporal variations of sea surface temperature in the Banda Sea during the period of 2002-2008

Spatial and temporal variations of sea surface (SST) in the Banda Sea are studied for the period of June 2002 – May 2008. An empirical orthogonal function (EOF) analysis has been applied to an optimum interpolation SST (OISST) having spatial resolution of 0.25° and temporal resolution of 1 day. The results revealed that the four EOF modes account for 53.1% of the total SST variance. The first EOF mode, which accounts for 33.2% of the total variance, revealed the east-west SST pattern in the Banda Sea. This indicates 180° out of phase temporal variability between the eastern and the western parts of the Banda Sea. The second and the fourth modes explain 9.6% and 4.6% of the total variance respectively. Both two modes show the southeast-northwest spatial pattern. Meanwhile, the third mode accounting for 5.4% of the total variance indicates that the high SST variation is concentrated in the central Banda Sea. In addition, the corresponding principal component time series of the first mode revealed robust sea...

How strong was the 2015/2016 El Niño event?

On the interannual timescale, the Indonesian climate is strongly influenced by a coupled ocean-atmosphere modes in the tropical Pacific Ocean. During a warm phase (El Nino event), negative sea surface temperature anomalies (SSTA) in the western tropical Pacific lead to suppress convection activities causing reduce precipitation over the maritime continent. The situation is reverse during the cold season(La Nina event). In this study, the evolution of 2015/2016 El Nino event is evaluated based on the collected data by the Tropical Atmosphere Ocean/Triangle Trans-Ocean Buoy Network (TAO/TRITON) buoys. The results show that the evolution of the event has started in boreal spring (April – May 2015). It came to thepeak in boreal fall/winter (October – December 2015). The event lasted until boreal spring before it terminated in April/May 2016. In addition, the intensity of the event is classified as a strong event, and it is one of the strongest El Nino events during the last three decades.

Simulated Interannual Modulation of Intraseasonal Kelvin Waves in the Equatorial Indian Ocean

Outputs from a high-resolution ocean general circulation model (OGCM) for the period of 1990-2003 indicate an interannual modulation of intraseasonal Kelvin waves along the equatorial Indian Ocean. During normal conditions without IOD event, the first mode explains about 30-40% of the total variance in the western (60-65oE) and central (75-80oE) basin, while the second mode contributes up to 45% to the total variance in the central basin around the longitude of 82oE. In contrast, during the 1997/98 IOD event, the fourth mode caused about 40% of the total variance in the central and eastern basin. During the 1994 IOD event, the contribution from the fourth baroclinic mode in the eastern basin caused 45% of the total variance. In the central basin, the second and the fourth baroclinic mode caused almost the same variance (~40%). The variations in the characteristics of the intraseasonal Kelvin waves are related to variations in the vertical stratification. During the IOD event, the pycnocline in the eastern basin was raised by about 50 m and the stratification at the upper level is strengthened, while it is weakened at lower levels. These changes lead to an increase in the contribution of higher-order baroclinic modes.

VARIASI TEMPORAL ARUS WYRTKI DI SAMUDERA HINDIA DAN HUBUNGANNYA DENGAN FENOMENA INDIAN OCEAN DIPOLE

Interaksi laut dan atmosfer baik secara lokal, regional maupun global sangat mempengaruhi variasi temporal arus Wyrtki yang terjadi pada arus permukaan ekuator Samudera Hindia yang bergerak ke arah timur. Kajian ini difokuskan pada variasi musiman dan variasi antar-tahunan (interannual) yang dihubungkan dengan fenomena Indian Ocean Dipole (IOD). Analisis dilakukan dengan menggunakan data Ocean Surface Current Analysis-Real time (OSCAR) Project. Hasil penelitian menunjukkan bahwa arus Wyrtki musim peralihan II (Oktober – November) lebih kuat dan berlangsung lebih lama jika dibandingkan dengan arus Wyrtki musim peralihan I. Arus Wyrtki musim peralihan II membentang di sepanjang ekuator dari bujur 50oBT hingga sisi timur Samudera Hindia. Sementara itu, arus Wyrtki musim peralihan I terkonsentrasi di sisi timur Samudera Hindia. Dalam skala antar-tahunan, arus Wyrtki musim peralihan II termodulasi oleh fenomena IOD. Pada kejadian IOD positif, arus Wyrtki musim peralihan II mengalami pelemahan atau bahkan berbalik arah, sementara pada kejadian IOD negatif arus Wyrtki musim peralihan II mengalami peningkatan intensitas. Pola dan amplitudo arus Wyrtki sangat dipengaruhi oleh pola dan amplitudo angin baratan di atas ekuator Samudera Hindia. Angin baratan pada musim peralihan II lebih kuat dan berlangsung lebih lama dibandingkan dengan angin baratan musim peralihan I. Lebih lanjut lagi, ketika terjadi IOD positif di ekuator Samudera Hindia terdapat angin timuran selama musim peralihan II, sedangkan pada saat IOD negatif angin baratan mengalami peningkatan intensitas