ABSTRAK Pengamatan laut bawah permukaan sampai kedalaman 1000m telah dilakukan selama Expedisi Indonesia PRIMA 2017 dengan meluncurkan instrumen Conductivity Temperature Depth (CTD). Terdapat tujuh stasiun CTD yang terletak di jalur ArusKatulistiwaSelatan (South Equatorial Current, SEC). Pengamatan atmosfer telah dilakukan dengan pelepasan balon radiosonde hingga ketinggian 17 km dan pengamatan meteorologisinoptiktiap jam di atas kapal. Makalah ini membahas analisis data kelautan bawah

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... (suhu dan salinitas)serta konvektifitas atmosfer yang diperoleh pada saat etape I expedisi menuju 12LS 85BT untuk menyelidiki kemungkinan terusan massa air Arus Lintas Indonesia(ARLINDO) di Samudra Hindia dan kaitannya dengan dinamika pusat tekanan rendah atmosfer di Samudera Hindia barat daya Sumetera. Analisis menunjukkan bahwa terdapat interaksi timbal balik laut-atmosfer pada saat berkembangnya daerah tekanan rendah di Samudera Hindia barat daya Sumatera yaitu keberadaan kolam air yang lebih panas (>28C) dari sekitarnya yang berasosiasi dengan pusat tekanan rendah atmosfer di atasnya. Kolam air hangat berasal dari massa air intrusif yang diduga berkaitan dengan penetrasi massa air ARLINDO di Samudera Hindia. ABSTRACT Sea sub-surface observations down to 1000m depth have been done during Expedition Indonesia PRIMA 2017 Indonesia by launching Conductivity Temperature Depth (CTD) instrument. There are seven CTD stations located on the South's Equatorial Current (SEC) pathway. Observations of the atmosphere have been done by releasing radiosonde balloons up to a height of 17 km and the hourly synoptic meteorological observation on board. This paper discusses the analysis of sub-surface marine data (temperature and salinity) as well as atmospheric convectivity obtained at the shiptime of Stage I of the Expedition towards 12°S 85°E to investigate the possibility of Indonesia Throughflow (ITF) water masses penetration in the Indian Ocean and its relation to the dynamics of the atmospheric low-pressure center in the Indian Oceas southwest of Sumatera. The analysis shows that there is an air-sea interaction at the time of the development of the low-pressure-area in the region, i.e. the presence of a warm pool region (> 28C) associated with a low-pressure atmospheric center. It is likely that the warm pool came from intrusive water masses suspected to be associated with ITF's water mass penetration in the Indian Ocean.