Ma usam, (1986). 31. I. 11-26 55 1.5 09 .3 13: 55 1.553 .2 1: 5 51.5 15.1 Pred iction of a monsoon depression w ith a regional primitive equation model S. S. SI NGH lndiun institute of Tropical Meteorology, Pune and M ASATO S UGI Electronic Computation Cell Ir e. JMA , Tokyo, Japan (Receil'ed 7 M arclr /984) . " T< :- "3"'T ,i" '" "''f'''' qit,"" "' '1'" " '('I """,)q lfrfinl ei" f.mi fr.qr "'" I" 'I 'It)"" .. 'l.""""" R>:" WI ....q 'ITl>u oro"),,, "'m 'It I 'I11IR " ....'" llTif""'"" JI>:r """"" """'" "" """ I """ :m. ""''r'''''''''''"' "" ..-.rit 'lft! ""I ""i ,i'>'i .:t ""lr... m !IV< ir .:'t I <mt""" Wrfu if "'ffl" if, ffl:T'l.:t '"'Jffi >if .:t I J openuional limited UfC" model is applied to a predic tion expc rtmcut over the tropical belt. In the experiment. time varying lateral boundary is provided by a global model forecast . The balanced initial field is obtained by normal mode initialization . The mnintennnce awl movement of " monsoon depreeslon ;100 associated rainfall area arc pred icted wel l. The development of the depression in the eurly stuge is also predicted. I. Introduction Synoptic, climatological and statistical methods are generally used for the prediction of meteorological phenomena over the tropical belt. A few research anti experimental numerical models have been developed ( Krishnarnurti et al, 1976; Das and Bedi 1978) and applied for the ease studies of Indian summer monsoon. Ideally speaking, a global model with high resolu- tion in honzontat and vertical is very much desirable fur the tropical prediction. However, clue 10 co rnpu ta- tionul and physical constraints, a higher resolution Iimil ed area model is considered quite adeq uate for the pred iction of synoptic scale disturbances. The app lication of limited area model poses a serious pro- blem in specification of lateral boundary conditions. An artiticiul imposition of boundary conditions excites the external gravity waves and reflec ts backward in the domain of integration. It has been recognised by many workers .. Price and Mae Pherson 1973; Williamsnn and Browning 1974; Chen and Miyakoda 1974; Davies 1976) that Ihe time varying boundary conditions circumvent to a large extent the prob lem posed by a limited area prediction model in the speci- fica lion of lateral bou ndary con di tio ns. Basically. there arc two approaches. In one approach. the fore- «1St with large doma in is made and the boundary (11) - datu to the limited mea mod el is provided. This is known as one way interaction. In the second approach. both model s arc dynami cally coupled and form a single dy na mical system. This is known as two way interactions. Ano ther prob lem of tropical modelling which re- quires special treatment is the initialization. A great deal or research over past few years in the field of initiali zati on has shown that the no rma l mode initia- lization technique is quite effective in lower latitudes. The nor ma l moue initialization is based on the idea of expanding initial datil into normal modes or free oscillations or lineal versio ns o r the mod el. Th e model amplitude thoughr to be unrealistically large is set to zero or considerably reduced. In the present ex peri me n t with regkmul primitive equation model, we have applied the time va ryi ng boundary co nditions with one way interaction to spc- dfy the lateral boundary conditions. For obtaining the initial balance of meteorological helds, the normal mode initialization is adopted. With these two so phis- tications, the regional model is applied to two synop- tic situations for 48-hou r forecast. The paper presents briefly the descriptions of the model. computational sche me a nd Ihe physical processes incorporat ed in the model. Furt her mo re, the resc lts or init iali zat ion
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