阿拉伯海淡水输运量的季节变化特征研究
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摘要
本文利用简单海洋模式同化再分析产品等资料,阐述了阿拉伯海与赤道西印度洋,阿拉伯海与阿曼湾之间淡水输运量的季节变化特征,揭示了阿拉伯海淡水输运量的基本平衡和季节变化特征。结果表明,阿拉伯海得到的淡水输运量(包括来自赤道西印度洋、河流)和失去的淡水输运量(包括降水量减蒸发量、向阿曼湾输运)基本相当。阿拉伯海通过海气交换失去的淡水(降水量减蒸发量)主要由来自赤道西印度洋(包括孟加拉湾)的淡水输运来补偿,赤道西印度洋向阿拉伯海的淡水输运对维持阿拉伯海的盐度基本平衡起到至关重要的作用。阿拉伯海的淡水输运量在1-6月和12月为负值,失去淡水;7-11月为正值,9月最大,得到淡水。阿拉伯海的净淡水输运量的季节变化特征表现为单峰现象。阿拉伯海与赤道西印度洋(9°N断面)的淡水输运量主要出现在表层至约200 m层,多年平均约为0.1×106 m3/s,向阿拉伯海输运。从10月至翌年3月,来自孟加拉湾的低盐水向阿拉伯海输运,该输运主要出现在印度半岛西南端近海约60 m层以浅区域。夏季和秋季,出现在索马里半岛东部海域的涡旋(大回旋)引起的输运(涡旋的西部低盐水向北输运,东部高盐水向南输运),不仅输运量是一年当中最大的,而且影响的深度可达约300 m。该输运从6月开始形成,8-9月最强,11月迅速减弱。阿拉伯海与阿曼湾的淡水输运量较小,其垂直分布呈现3层结构,表层至10 m层,高盐水向阿拉伯海输运;15～170 m层,低盐水向阿曼湾输运;175～400 m层,高盐水向阿拉伯海输运。阿曼湾湾口断面多年平均淡水输运量约为0.39×104 m3/s,向阿曼湾输运。
Simple Ocean Data Assimilation reanalysis and other data were used to explore seasonal variation characteristics of freshwater transport between the Arabian Sea(AS) and the Equatorial Western Indian Ocean(EWIO),and the Gulf of Oman(GOO).Freshwater budget in the AS is characterized by a basic balance and its seasonal variation is also present.Our results indicate that the amount of input freshwater from the EWIO and river discharge is roughly equal to the amount of freshwater output to GOO and lost caused by the evaporation overwhelming the precipitation(P–E).The lost freshwater via air-sea exchange(i.e.P–E) is compensated by freshwater flux from the EWIO and the Bay of Bengal(BOB),which plays a key role in maintaining the basic balance of salinity over the AS.Net freshwater flux in the AS is negative(i.e.lost freshwater) from January to June together with December,and positive(i.e.receive freshwater) during July and November with a maximum positive value in September.The seasonal variation characteristics of net freshwater flux in the AS shows a single remarkable peak.Along the 9°N section,freshwater exchange between the EWIO and the AS primarily occurs from the surface to 200 m depth,with a multi-year averaged net flux into the AS of about 0.1×10~6 m~3/s.From October to next March,the BOB low-salinity water extends into the AS at above 60 m depth through the southwest of the Indian peninsula.In summer and autumn,the transport associated with the Great Whirl located at the east of Somali Peninsula,is characterized by low(high) salinity water in the west(east) of the whirl transported northward(southward) into the AS(equatorial Indian Ocean).This transport during these two seasons is largest in a year with its influence can extend downward to about 300 m depth,which forms in June,then peaks in August and September,and finally decays rapidly in November.Water exchange between the AS and the GOO is relatively weak,and has a sandwich-like three-layer structure in vertical direction:high salinity water intrudes from GOO into the AS in the upper 10 m layer and in the bottom layer between 175 m and 400 m depth;whereas in the middle layer(i.e.15 m to 170 m depth) low salinity water is transported from the AS to the GOO.On multi-year average,a net freshwater transport of about 0.39×10~4 m~3/s is further estimated into the GOO from the AS across the section along the GOO mouth.
Simple Ocean Data Assimilation reanalysis and other data were used to explore seasonal variation characteristics of freshwater transport between the Arabian Sea(AS) and the Equatorial Western Indian Ocean(EWIO),and the Gulf of Oman(GOO).Freshwater budget in the AS is characterized by a basic balance and its seasonal variation is also present.Our results indicate that the amount of input freshwater from the EWIO and river discharge is roughly equal to the amount of freshwater output to GOO and lost caused by the evaporation overwhelming the precipitation(P–E).The lost freshwater via air-sea exchange(i.e.P–E) is compensated by freshwater flux from the EWIO and the Bay of Bengal(BOB),which plays a key role in maintaining the basic balance of salinity over the AS.Net freshwater flux in the AS is negative(i.e.lost freshwater) from January to June together with December,and positive(i.e.receive freshwater) during July and November with a maximum positive value in September.The seasonal variation characteristics of net freshwater flux in the AS shows a single remarkable peak.Along the 9°N section,freshwater exchange between the EWIO and the AS primarily occurs from the surface to 200 m depth,with a multi-year averaged net flux into the AS of about 0.1×10~6 m~3/s.From October to next March,the BOB low-salinity water extends into the AS at above 60 m depth through the southwest of the Indian peninsula.In summer and autumn,the transport associated with the Great Whirl located at the east of Somali Peninsula,is characterized by low(high) salinity water in the west(east) of the whirl transported northward(southward) into the AS(equatorial Indian Ocean).This transport during these two seasons is largest in a year with its influence can extend downward to about 300 m depth,which forms in June,then peaks in August and September,and finally decays rapidly in November.Water exchange between the AS and the GOO is relatively weak,and has a sandwich-like three-layer structure in vertical direction:high salinity water intrudes from GOO into the AS in the upper 10 m layer and in the bottom layer between 175 m and 400 m depth;whereas in the middle layer(i.e.15 m to 170 m depth) low salinity water is transported from the AS to the GOO.On multi-year average,a net freshwater transport of about 0.39×10~4 m~3/s is further estimated into the GOO from the AS across the section along the GOO mouth.
引文
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[13]Bower A S,Hunt H D,Price J F.Character and dynamics of the Red Sea and Persian Gulf outflows[J].Journal of Geophysical Research:Oceans,2000,105(C3):6387-6414.
[14]Stramma L,Brandt P,Schott F,et al.Winter and summer monsoon water mass,heat and freshwater transport changes in the Arabian Sea near 8°N[J].Deep Sea Research Part II:Topical Studies in Oceanography,2002,49(7/8):1173-1195.
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[16]Fang Guohong,Susanto R D,Wirasantosa S,et al.Volume,heat,and freshwater transports from the South China Sea to Indonesian seas in the boreal winter of 2007-2008[J].Journal of Geophysical Research Oceans,2010,115(C12):C12020.
[17]Schott F,Quadfasel D R.Variability of the somali current system during the onset of the Southwest Monsoon,1979[J].Journal of Physical Oceanography,1982,12(12):1343-1357.
[2]Schott F A,McCreary J P.The monsoon circulation of the Indian Ocean[J].Progress in Oceanography,2001,51(1):1-123.
[3]Schott F A,Xie S P,McCreary Jr J P.Indian Ocean circulation and climate variability[J].Reviews of Geophysics,2009,47(1):RG1002.
[4]Jensen T G.Arabian Sea and Bay of Bengal exchange of salt and tracers in an ocean model[J].Geophysical Research Letters,2001,28(20):3967-3970.
[5]Jensen T G.Cross-equatorial pathways of salt and tracers from the northern Indian Ocean:modelling results[J].Deep Sea Research Part II:Topical Studies in Oceanography,2003,50(12/13):2111-2127.
[6]Han W Q,McCreary Jr J P.Modeling salinity distributions in the Indian Ocean[J].Journal of Geophysical Research:Oceans,2001,106(C1):859-877.
[7]Rao R R,Sivakumar R.Seasonal variability of sea surface salinity and salt budget of the mixed layer of the north Indian Ocean[J].Journal of Geophysical Research:Oceans,2003,108(C1):9-1.
[8]张玉红,徐海明,杜岩,等.阿拉伯海东南海域盐度收支的季节变化[J].热带海洋学报,2009,28(5):66-74.Zhang Yuhong,Xu Haiming,Du Yan,et al.Seasonal variability of salinity budget in the southeastern Arabian Sea[J].Journal of Tropical Oceanography,2009,28(5):66-74.
[9]宣莉莉,邱云,许金电,等.孟加拉湾与赤道东印度洋水交换的季节变化特征[J].热带海洋学报,2015,34(6):26-34.Xuan Lili,Qiu Yun,Xu Jindian,et al.Seasonal variation of the water exchange between the Bay of Bengal and the equatorial eastern Indian Ocean[J].Journal of Tropical Oceanography,2015,34(6):26-34.
[10]Sengupta D,Bharath Raj G N,Shenoi S S C.Surface freshwater from Bay of Bengal runoff and Indonesian throughflow in the tropical Indian Ocean[J].Geophysical Research Letters,2006,33(22):L22609.
[11]张玉红,杜岩,徐海明.赤道印度洋中部断面东西水交换的季节变化及其区域差异[J].海洋学报,2012,34(2):30-38.Zhang Yuhong,Du Yan,Xu Haiming.Seasonal variability of the west-east water mass exchange on the section of central equatorial Indian Ocean and its regional difference[J].Haiyang Xuebao,2012,34(2):30-38.
[12]D'Addezio J M,Subrahmanyam B,Nyadjro E S,et al.Seasonal variability of salinity and salt transport in the northern Indian Ocean[J].Journal of Physical Oceanography,2015,45(7):1947-1966.
[13]Bower A S,Hunt H D,Price J F.Character and dynamics of the Red Sea and Persian Gulf outflows[J].Journal of Geophysical Research:Oceans,2000,105(C3):6387-6414.
[14]Stramma L,Brandt P,Schott F,et al.Winter and summer monsoon water mass,heat and freshwater transport changes in the Arabian Sea near 8°N[J].Deep Sea Research Part II:Topical Studies in Oceanography,2002,49(7/8):1173-1195.
[15]Johns W E,Yao F,Olson D B,et al.Observations of seasonal exchange through the Straits of Hormuz and the inferred heat and freshwater budgets of the Persian Gulf[J].Journal of Geophysical Research:Oceans,2003,108(C12):3391.
[16]Fang Guohong,Susanto R D,Wirasantosa S,et al.Volume,heat,and freshwater transports from the South China Sea to Indonesian seas in the boreal winter of 2007-2008[J].Journal of Geophysical Research Oceans,2010,115(C12):C12020.
[17]Schott F,Quadfasel D R.Variability of the somali current system during the onset of the Southwest Monsoon,1979[J].Journal of Physical Oceanography,1982,12(12):1343-1357.