****************************************************************************************************************

第 109 回 大気海洋物理系 B 棟コロキウム のおしらせ

日　時：2001年 4月 23日(月) 午後 16:30 〜 18:30
場　所：地球環境科学研究科 Ｃ棟 Ｃ１０４

発表者：Thoppil Prasad Gouri (気候モデリング講座 D3)
題　目：Seasonal spreading of the Arabian Sea high-salinity water mass (ASHSW): A model study

****************************************************************************************************************

Seasonal spreading of the Arabian Sea high-salinity water mass (ASHSW): A model study (Thoppil Prasad Gouri) 発表要旨 :

  
 The Arabian Sea is unique in many ways. First, it is land-locked in the 
 north. Second, it is driven by strong and distinct monsoon winds, which 
 reverses in an annual cycle. The strong seasonally reversing surface 
 forcing over the Arabian Sea forces a seasonally reversing circulation in 
 the upper ocean. These seasonally reversing currents play a significant 
 role in exchanging the water masses between Arabian Sea and Bay of Bengal 
 and within these basins. 
  
 In the northern Arabian Sea, excess evaporation over precipitation during a 
 relatively calm period of the winter monsoon is known to be responsible for 
 the convective formation of the Arabian Sea high-salinity water mass 
 (ASHSW)  (Kumar and Prasad, 1999; Prasad and Ikeda, 2001). It subducts in 
 the region north of 20N and spreads equatorward along sigma_t = 24 
 isopycnal surface. In the equatorial region, it can be found as a well 
 defined subsurface salinity maximum at about 100 m. 
  
 Using a level 2 three-dimensional turbulent closure model, we address two 
 issues; one is to examine the seasonal variability in the distribution of 
 ASHSW, and the other is to determine the important oceanic processes that 
 affect the upper ocean salt balance in the Arabian Sea. 
  
 We have found seasonal variability in the distribution of the ASHSW, and it 
 is strongly dependent on monsoonal circulation. During the summer monsoon, 
 the northward flowing Somali Current advects low salinity water from south 
 that mixes with the ASHSW in the western Arabian Sea. At this time, the 
 high salinity water spreads southward along the eastern side of the basin. 
 During winter monsoon, the westward flowing north equatorial current (NEC) 
 carries fresher water from the Bay of Bengal that mixes with the ASHSW 
 south of 10N, thereby maintaining salt balance in the Arabian Sea. The 
 importance of three-dimensional processes (particularly horizontal salt 
 advection) in the Arabian Sea salt balance is confirmed by comparing the 
 salinity variability with that simulated by a one-dimensional model. 
 Estimation of the upper ocean salt budget in the Arabian Sea shows a rough 
 balance between the horizontal advection and time change in salt. 
  

-----
連絡先