Some observations of Melting Band in Radar Precipitation Echoes …metnet.imd.gov.in/mausamdocs/512216.pdf · radar observations at Poona have been summarised in two previous papers
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551' 577 : 621 '300'9 Some observations of Melting Band in Radar Precipitation Echoes at Poona B. K. GUPTA, AXXA )IAXI and S. P . ygXK ITESH\L\RAX .11et eorol OfJ icai QQice. Poona ( Rl'Ceivl<l II Na,v",ober 19.59 ) r. Introduction The melting hand is a phen omenon fre- quently observed in radar echoes from wide- spread steady preci pitut ion. It appea.r:-\ as. a narrow ban d of i nte nse echo in the vic inity of the O· C level. sepa rati ng a relatively ec ho obt ained from the snow above the melting region and n rapid ly fluctuat ing echo of often rat her greater intensi ty from the rain below. It has also been obse rve d in the dissipating stageR of thunderstorms. The appellrance of t.1 w melting band WUl'!. first exp la ined by Ryde ( 1946 ) to arise from til" coa lesce nce and meltin g of snowflakes near the O· C level. Aus tin and Bemis (1950) and Browne have modified Hyde's theory to include factors such ali t he ag,b rrega ti on of snowflakes near the melting regio n, ve rt ica l d raughts and variation of the radar pulse- length. Because of its great significance the melt ing ba nd has been th e subject of consider- able research during recent years, but obser- vations in tropical latitudes have been very meagre. )lelt ing band observations have been made at Poena both during the south west monsoon {June to September) and during thunder- storms in the months preceding the monsoon (March to )l ay) and following the monsoon (Dctober to Xovember], Some features of the radar observations at Poona have bee n summarised in two previous papers (Gupta, 1\I ani and Venkiteshwaran 1955, Gupta and Venk it esh waran 1958). The present paper deuls with the o bserva tio ns of the melting hand ill the radar precl) Ht ation echoes at I'oona ,hIring the years 195:1 -1 955, and an atte mpt is made to exami ne the s pf-'{'i al feat ure.. s, if any, a .. ssocinted with the occu r- rences of bands at Poena. 2. Equipment and Operational Procedure The equipment used was a search radar, type 71 7C, operating on 9·1 CIIl , installed Oil the roof of the Office, Poona. The peak power of t he transmitte r is approxi - mately ·10 KW , the pulse duration 1· 125 II- sees and it has five ranges of'·1, 10, 20 ,50 and 100 nan ti cal mi les, 'rith this radar, a preci- pitation rate of 0·02 inch per honr can he expected to he just detected at a range of 10,000 fr et (Day 1953), if it is assumed t hat the rain storm complete ly fills t he radar beam and has 8 size distributiou as given by L awa and Parsons (1943). Also drops of 1 mm diameter and a density of 100 drops per cubic metre would be just visible at the range of 10,000 feet; those of 0 ·5 nun diame ter would be just visible at the same range, if their density were lOC drops per cubic metre. The radar antenna which is a dipole-fed paraboloid, mounted in the manner first adopted hy Bowen and his collaborators (Day 1953) in Australia, i.e., the radar beam scans a path from horizon to horizon through the zenith. This res ults in 8 represe nta tion ill t he cat hode ray display unit, of a cro.., ...ect ion through the atmosphere about t he point of ehservation. In this met hod of scanni ng, the range and height arc maintained in true
