Sains Malaysiana 44(2)(2015): 167–173

Impacts of 2009 Typhoons on Seawater Properties and Top Layer Ocean’s Structure

in the Northwest Pacific Ocean

(Kesan Ribut Taufan pada Tahun 2009 kepada Sifat-Sifat Air Laut dan Struktur Permukaan

Laut di Barat Laut Lautan Pasifik)

DAYANG SITI MARYAM MOHD HANAN*, THAN AUNG & EJRIA SALEH

Borneo Marine Research Institute, Universiti Malaysia Sabah, Jalan UMS, 88400 Kota Kinabalu, Sabah, Malaysia

Received: 26 February 2013/Accepted: 4 August 2014

ABSTRACT

Passing over the ocean surface, typhoon absorbs heat from the sea water as it needs the heat as its 'fuel'. The process is via evaporation of water. Subsequently, the sea surface temperature (SST) in that area will significantly decrease. Due to strong typhoon wind water is evaporated from the surface layer of the ocean, the amount of water mass in that area is lost, but the same amount of salt will remain, causing sea surface salinity (SSS) to increase. Strong winds induced by typhoons will also cause turbulence in the water, causing entrainment, where cold deeper water is brought up to the surface layer of the ocean, which will consequently increase its SSS and change the isothermal layer and mixed layer depth (MLD). Here, isothermal layer means the ocean layer where temperature is almost constant and MLD is the depth where salinity is almost constant. This paper focuses on the effect of typhoons on SST, SSS, isothermal layer and MLD by taking 15 typhoons in the Northwest Pacific throughout 2009 typhoon season (typhoons Lupit and Ketsana are used as examples in results) into consideration. Temperature and salinity data from selected Array of Regional Geostrophic Oceanography (ARGO) floats close to the individual typhoon’s track are used in this study. The results showed that SST decreased up to 2.97°C; SSS increased up to 0.44 pss and majority of the typhoons showed deepening of isothermal layer (between 39.8 m and 4.6 m) and MLD (between 69.6 and 4.6 m) after the passage of typhoons. Passing of each individual typhoon also removed significant amount of heat energy from the affected area. The highest amount of heat of 841 MJ m^-2 to the lowest of 30 MJ m^-2 was calculated during the study period. For comparison purpose, an equivalent amount of electrical energy in kWh is also calculated using the amount of heat removed by the typhoons.

Keywords: Isothermal layer; MLD; SSS; SST; typhoon; western North Pacific Ocean

ABSTRAK

Semasa merentasi permukaan lautan, taufan menyerap haba daripada air laut kerana ia perlu kepanasan sebagai bahan 'bakar'. Proses ini dilakukan melalui penyejatan air. Oleh itu, suhu permukaan laut (SST) di kawasan berkenaan akan menurun. Apabila air tersejat daripada lapisan permukaan laut akibat daripada laluan taufan, jumlah jisim air di kawasan berkenaan akan berkurang, tetapi jumlah garam akan kekal sama, menyebabkan kemasinan permukaan laut (SSS) meningkat. Angin kencang dicetuskan oleh taufan juga akan menyebabkan pergolakan dalam air di kawasan itu yang menyebabkan percampuran dengan air sejuk dibawa dari kawasan lebih dalam ke lapisan permukaan lautan yang meningkatkan SSTnya dan juga mengubah lapisan suhu dan lapisan campur kedalaman (MLD). Kertas ini memfokuskan kepada kesan taufan terhadap SST, SSS, lapisan suhu dan MLD dengan mengambil 15 taufan di Barat Laut Lautan Pasifik sepanjang 2009 (taufan Lupit and Ketsana digunakan sebagai contoh dalam keputusan) untuk kajian. Data suhu dan kemasinan daripada tatasusunan oseanografi geostropik serantau (ARGO) terapung paling hampir dengan trek taufan masing-masing digunakan dalam kajian ini. Keputusan menunjukkan bahawa SST menurun sehingga 2.97°C; SSS meningkat sehingga 0.44 pss dan majoriti taufan menunjukkan pendalaman lapisan suhu (antara 39.8 dan 4.6 m) dan MLD (antara 69.6 dan 4.6 m) selepas laluan taufan. Laluan setiap taufan juga menyingkirkan jumlah kepanasan yang ketara dari kawasan terlibat. Nilai kepanasan tertinggi ialah 841 MJ m^-2 dan yang terendah ialah 30 MJ m^-2 semasa tempoh kajian. Bagi tujuan perbandingan, nilai setara tenaga elektrik dalam kWh juga dikira menggunakan amaun kepanasan yang disingkirkan oleh taufan.

Kata kunci: Barat Laut Lautan Pasifik; lapisan suhu; MLD; SSS; SST; taufan

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*Corresponding author; email: dayang.siti.maryam@gmail.com