10 - metnet.imd.gov.inmetnet.imd.gov.in/mausamdocs/14712_F.pdf · MauMlnl. (1996), 47. I. :n ·3U...
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Mau Mlnl. (1996), 47. I. :n ·3U $51.461.2 : 551.553.21 (267 ) Upper ocean responses in the central western equatorial Indian Oce an during southwest monsoon season M. G. JOSEP H. P. V. I1AREESII KUMAR a nd P. MAO HUSOODANAN Naval Physical and Oceonogl'Gl'h ir Laboratory Thrikkak ara. Cocliin (Received /9 October /99•. Modified 2/ April /9 95) mt - Ullm. 1973 ""'" """ " fO<q "'l olt<llii' ''' a","" <rnl Ii'" if .am·llfroll <i: O· am: ,,'<IT GO' 'l' li\ oiTt ""''l.'' j; ""'" "'" ,,'{i . &It'" j; """ ,,'<IT llf.n 0ffi'II,j\' i\' t anti ffi ilia ) 'It <rem "" 10"" "" """, "'" 1 ""Ilmt\u <i: " if j; """"' !'R" <mil "'l 11: "'. j; """ .., 1ItlT , 'If "P I'" .m il ri '" if ('!" a ,<"a tla) "",,"Is'''''' om- nrn'i/ilfum "'" .., ("OTt it I! . ,010.5 ifa) "'" "'" i 1 f.rn;\ .'" i\' 11: 0ITt"0 "'" "'(0 """" if 'l'fr ' '<IT ,of "l<I '" 00. '''''"''' om- a <moil """"'" (""a """ j; 'I'" "'" """'" "'" i 1 """" " . ll"'a -j\a " .' 3 mt1 >.R!f!lfia a"'" (o:<allIa qmo ;!Ia) <i: "" Ola ma ,,'<IT "'{o j; m-""" 'IT<! "'l i 1 ''<IT ,.." '" ",r •• ",,;r-It ''''''' ..... IDp;f .... <rem ' IU 'lfuo; a",j 11: ""'"' "'" 11: 'l'Il'li ffi <i: ?R!'fa _ '" anti ffi il . "'0 >!I o 11: . ml /ilfum "'" (I, r..,;y i\' ju llI an ' ,,"0) ..... "ffiI am1\ i I for"". <miT <i: .' .21 i\' "'''''' " .. ","0 ","0 ,II <i: iffi'II nfu",, .... ,, '" ""'" arill»1Il 'l:l;T'm ii' 'If' "'" " '!" a .., a >!Ia . OI a >iro. ... "'{ a ,,<II ,,"0 llI" ll"' o ;!Io j; or. .... - """"' . it """ i I ",lb. """ ' '''';; '" ,,01\1> if .m:a 'lit nt i I ABSTRACT. L"PJ'(T OCt-Oll1 ell.' tn) respo n se u nde r th e pre- un set. o nse t and active rcghucs ofsouthwest (SW) monsoo na l forcing at n°N. ()(Jo E in IhI' Indian Oce an W3'i ana lysed. uliHsilli' tim e series data (01l('i. 1('.1 duri ng Indo-Sovi et Mon soon (ISMEX-73).Oceanic response und er th e pn>.ot u hl 'l d omin a- lio n of the wind stress momentum anti onset d omi n urion ofbuoynucy flux ([1,,1 was ap pare nt in shoa liua:1 warming and deepening/cooling (12 m/U.!i8C in 4 Jap ,1of'Mixed Laycr Depth (MlD). The increase was followed b)' au onset decrease in belo..... lay er th enuohufine/denshy l:r nJil'l1l ani' disappcaruucc o f Suh - lJ U l" flice Salin ity Maxi mum (SSMI, MlD and in h ral con lent U ICJ,ll O) W l 'le mon: co r- 10 l\ a nd Os ' U'r rwr OCI":ln Jurin¥ nClh-e 1"C8ime I11nnifl"slt'l1 in .Jl"l ' pening!cuoli ng elf) mIl 8C in 6 J11 )"S ) of MlD u nd('r do milHtOl Pflli..tu,; lilln ofturbulel11 kinl ,tk ent> rJ'y by slress e-XCl"pl (or Ihr con- \' l""'1 i n' ly d omin anl mixinwat the l:lI.. 'lIinniui and end . With redud ion in bl"lo .....-l a)"Cf thennohaline/J ensit), , nhlient and absence lI( SSM. Ihr ", 'olTelmi lllU bl'lwt"l 'n MLO. Ilg , Q s anJ HC Ul D be CHIUt' d ue to in cl\'ased aJ\'e"'1h>tflux during actin." regime. One o(mi.'t'J 10 )'l' r pnra mclel'S shO\w d L"'s son ah le 0eret"lUrnl. Key word, - InJi fll1 Oce an. $tnl1hWC5t lUunliOOll , Wind S ll\"S5, Il eal Mi., t"d la)'er, fl ral nlll tl' nt. Com'la tiun s, Simu lation. , I. Introduction In the north Indian Oc ea n. monsoo nal infl uen- ces are dominant in imp arti ng significan tc han ges in the thermohaline/density and c urren t fields of Ihe upper oce an . Con sequent ly. the upper ocea n variability differs with the intens ity a nd exte nt of the forcings by the southwest and northeast mon - soons in different are as. However. in the western nortb I ndian Oeoan and the Arabian Sea. southwest (SW) mo nsoon plays th e promin en t role in the transfer of mass. mome ntum a nd hea t thro ugh the a iNea interface. This. in turn effects the drastic cha nges in the u pper ocea n ther- mo haline a nd advective fie lds d uring May-Sep- tember. as has been observed earlie r. Studies on climatological scales (Me Phaden 1982. M olin ari 4 -618 IMD/ 95 (m '" al. 1986. She lye 1986. Rao .'1 al. 1(89) suggested 50 1075 % correlati o ns helween lhe s urfac e mixcd layer chi ua cterislk s and the verlical fluxes of energy and mas s throug h Ihe naviface in western Indian Ocean , nonh of equator. Some of these also indicated th at the correla tions incre ased by including lateral fluxes due 10 advection and effects of entrainment and wind stress convergence/divergence. Synoptic sca le verification of the se arg uments for Ihe Arilbh,n Sea a nd weste rn eq ualoria l InJian Ocean during soulhwest monsoon have bee n made by means of one dimens ional simulations. using time series data sets from MONSOO N-77 and MONEX-79. achieving various deg rees of agree- me n ls ancl di sag reements ( Rao 1986. Rao et al. 1990. Joseph I?I al. 1990. Sanil Kumar et al. 1991 ). Ho we ver. prese nce of signilicantzonal variability in the
Transcript of 10 - metnet.imd.gov.inmetnet.imd.gov.in/mausamdocs/14712_F.pdf · MauMlnl. (1996), 47. I. :n ·3U...
MauMlnl. (1996), 47. I. :n ·3U
$51.461.2 : 551.553.21 (267)
Upper ocean responses in the cent ral western equatorial Indian Oce anduring southwest monsoon season
M. G . JOSEP H. P. V. I1AR E ESII KUMAR a nd P. MAO HUSOODANANNaval Physical and Oceonogl'Gl'h ir Laboratory Thrikkak ara. Cocliin
(Received /9 October /99• . Modified 2/ April /995)
mt - """-~ ~ffif! Ullm. 1973(~-7.1 );j; ""'" """ " ~1Jiftla fO<q "'l olt<llii' ''' a","" <rnl ,~ . Ii'"~!TRPR if .am·llfroll~ <i: O· am: ,,'<IT GO' 'l' li\ oiTt~·ofR1l\ ""''l.'' j; ""'" "'" ,,'{i. &It'" j; """ ,,'<ITllf.n 0ffi'II,j\' i\'~!TRPR t anti ffi (~lX) ilia ) 'It~ <rem "" 10"""" ""","'" 1""Ilmt\u~ <i: " if~ j; """"' !'R" <mil "'l~ 11: "'. j; """ .., 1ItlT , 'If "PI'" .m~ il~ ri '" F~ if('!"a ,<"a tla) "",,"Is'''''' om- nrn'i/ilfum "'" .., ("OTt ~ it I! . ,010.5 ifa) "'" "'" i 1 f.rn;\ .'" i\' ~"''l.'' 11:
0ITt"0 "'" "'(0 ""~/"'R'?> """" if 'l'fr ' '<IT ,of"l<I '" 00. '''''"''' om- a<moil~~ """"'" (""a """ ~~o)j; 'I'" "'" """'" "'" i 1 """" " . q~o ll"'a -j\a ".' 3mt1 >.R!f!lfia a"'" (o:<allIa ~~o qmo ;!Ia) <i: "" Ola ma,,'<IT "'{o~o j; m-""" 'IT<! "'l i 1 ,~"" ''<IT ,.." '" ",r• • ",,;r-It ''''''' ..... IDp;f .... <rem ' IU~ 'lfuo;
a",j 11: ""'"' "'" 11: 'l'Il'li ffi <i: ?R!'fa _ '" anti ffi il ~r."'1 ~~o ."'0 >!Io 11: . ml/ilfum "'" (I, r..,;y i\' j u
llIan ' ,,"0) ....."ffiI am1\ i I for"". <miT <i: . '.21 i\'""~/"'''' "'''''' if~."r.< " .. ","0 ","0 ~~a ,II ?~
<i: iffi'II nfu",,....,, '" ""'" arill»1Il 'l:l;T'm ii' 'If' "'" " '!"a ..,a >!Ia . OIa >iro. ...~. "'{a ~o ,,<II ,,"0 llI"~~o ll"'o ;!Io j; or. ....- """"'. it """ i I ",lb. """ ''''';; '" ~ ,,01\1> 'JflI~ if .m:a ~_
'lit nt i I
ABSTRACT. L"PJ'(T OCt-Oll1 ell.' tn) respo nse u nde r the pre-un set. onset and active rcghucs o f south west(SW) monsoona l forcing at n°N. ()(Jo E in IhI' Ind ian Oce an W3'i ana lysed. uliHsilli' tim e series d ata (01l('i.1('.1duri ng Indo-Sovi et Monsoon E.'(perill1~nt.1973 (ISMEX-73). Oceanic response under th e pn>.otuhl'l dominalio n o f the wind stress mome ntum a nti onset domin urion ofbuoynucy flux ([1,,1 was apparent in shoa liua:1warming and deepenin g/cooling (12 m/U.!i8C in 4 Jap,1of'M ixed Laycr Depth (MlD). The pl"'-un~1 increasewas follo wed b)' au onset decrease in belo..... layer th enuohufine/d enshy l:rnJil'l1l ani' di sappcaruucc of Suh lJUl"flice Salin ity Maximum (SSMI, COfresponJin~l)', MlD and in h ral con le n t U ICJ,ll O) Wl'le mon: co rrelnh~'ll 10 l\ a nd Os ' U'r rwr OCI":ln rt"SPOI1~ Jurin¥ nClh-e 1"C8ime I11nnifl"slt'l1 in .Jl"l' pening!cuoli ng elf)mIl 8Cin 6 J11)"S ) of MlD u nd('r do milHtOl Pflli..tu,; lilln o f turb ulel11kin l,tk ent> rJ'y by ~inJ slress e-XCl"pl (or Ihr con\'l""'1 in'ly d ominanl mixinwat the l:lI..'lIinniui a nd end. With redud ion in bl"lo.....-la)"Cf thennoh aline/Jensit),, nhlie nt a nd absence lI( SSM. Ihr ",'olTelmi lllU bl'lwt"l'n MLO. Ilg, ~in&1 SI I~Ss. Qs a nJ HCUl D be CHIUt'in~illn iJic n.nt d ue to incl\'ased aJ\'e"'1h>tflux during a ct in." regime . One Jimen~ion(llllil11ulalion o( mi.'t'J 10)'l' rpnra mclel'S shO\wd L"'s son ah le 0eret"lUrnl.
Key word, - InJi fll1 Oce an. $tnl1hWC5t lUunliOOll, Wind Sll\"S5, Il eal 1111~ , Mi., t"d la)'er, fl ral nllltl' nt.Com'latiun s, Simulat ion .
,
I. Introduction
In the north Indian Oc ea n. monsoona l infl uences are do mina nt in imparti ng significan t changesin the thermo haline/density a nd current fields ofIhe upper oce an. Consequently. the uppe r ocea nvariability differs with the intens ity a nd extent ofthe forcings by the southwest a nd nort heast monsoons in different areas . Howeve r. in the westernnortb Indian Oeoan and the Arab ian Sea.sou thwest (SW) mo nsoon plays th e promin en t rolein the transfer of mass. momentum a nd hea tthrough the aiNea interface. This. in tu rn effectsthe drastic cha nges in the upper ocea n thermohaline a nd advective fields during M ay-September. as has been observed earlie r. Studies o nclim a tological scales (Me Phaden 1982. Molinari
4 -618 IMD/ 95(m
'" al. 1986. She lye 1986. Rao .'1 al. 1(89) suggested 501075% correlatio ns helween lhe surfac e mixcd layerchiuacterislk s a nd the verlical fluxes of energy andmass throug h Ihe naviface in western In di an Ocean,nonh of equator. Some of these a lso indicated thatthe correla tions increased by including la teralfluxes d ue 10 advec tio n and effects of entrainmentand wind stress convergence/dive rgence. Synopticsca le verification of these a rguments for IheArilbh,n Sea and weste rn eq ualoria l InJian Oceanduring soulhwes t monsoon have bee n made bymeans of one dimensiona l simula tions. usingtime series data sets from MONSOON-77 andMONEX-79. ac hieving various degrees of agreeme n ls ancl disagreeme nts (Rao 1986. Rao et al.1990. Joseph I?I al. 1990. Sa nil Kumar et al. 1991 ).However. presence ofsignilicantzonal variability in the
