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1 t (s6 ~lj t') \ >""\., ~hysia Indian Jurnal f 11adi&Sp8Ce V~3.February 1994,pp. ~::4().,I\' :!",,,. 'I\.J \ '0f"'~ r't t <,), >~.'c;. ~~ \,!2!!!m'!!.y~atin6fhriznt~~cb' in the ~()wert.~2qq~~herever.. ' ' 9adanki ( N, E)', _'frw.""..,.~.,.~ 0, Mr'fSasi ( Space Physics Labratry, Vikrarn Sar~bhai Space Centre, Trivandrum ).r",~.,An experiment was cnducted with the Indian MST radar Lin ST mde) at Gadanki (13.47 N, E) in March 1992 t study the diurnal nnnugratmg ti<lalvariatin in the lwer trpsphere. The results btained are presented in this paper and they d nt indicate any evidence fr the presence f the diurnal nnmigrating tides in the lwer trpsphere ver Gadanki. 1 Intrductin The majr surces f slar. atmsqheric tidel are heating due t absrptin f slar ra<haa'n by water vapur in the trpsphere and zne in the stratsphere and messphere and eddy heat transfer in the planetary bundary layer (PBL). When these heat surces d nt have any lngitudinal variatin, atmspheric tides are hmgeneus in lngitude and prpagate westward with the sun. These tides are called migrating tides. When these heat surces have significant ingitudinal variatin the tides excited by them d nt necessarily prpagate westward with the sun and are called nnmigrating tides. A few bservatinal studies f the nnmigrating tides have been made by different grups in the past. Fr example, Wallace and Tadd1, using radisnde data fund that diurnal wind scillatins are largely affected by tpgraphy and are characterized by a vertical wavelength shrter than 10 km. Fuka et a[.2 detected a diurnal scillatin with amplitudes ranging frm 1 t 5 m/s and vertical wavelength less than 10 km in the lwer stratsphere by the Jicamarca VHF radar Arecib UHF radar bservatins have detected a similar diurnal scillatin in the 1030 km height range3. In rcket wind data at Trivandrum (8SN), evidence f diurnal wind scillatin with vertical wavelengths f 510 km can be seen in the lwer stratsphere4 Vertical wavelength f the diurnal migrating tides in this height regin is 28 km. Recent theretical studies by Tsuda and Kat05 indicate that these bserved tidal features may be explained in terms f the diurnal nnmigrating tides generated by differential heating due t landsea distributin. Their study5 als shws that the expected amplitudes f the nnmigrating diurnal tides are f the rder f 12 m/s as against the migrating tidal amplitude f 0.1 m/s in the trpical trpsphere and vertical wavelength f 25 km. In rder t study the tidal (nnmigrating) variatin in winds in the trpical lwer trpsphere, an experiment was cnducted with the Indian MST radar (in ST mde) at Gadanki (13.47"N, E), Tirupati, in Mar :'he details f the radar may be fund elsewhere6 The experiment cnsisted f bserving the Dppler spectra in the suth, west, nrth and east directins. Frm the linefsight cmpnent f the wind alng the fur directins btained frm the Dppler spectra, hrizntal and vertical cmpnents f the winds are derived. In this paper, results btained frm this wind data in the height range 3.56 km are presented. 2 Experiment The experiment was cnducted n tw days, namely, 14 and 21 Mar Dppler data were recrded using the MST radar parameter specificatins given in Table 1. Dppler data (spectra), btained by the radar parameter specificatins given in Table 1, were recrded every 1 h n 14 and 21 Mar Thus, the hurly data were btained fr tw diurnal cycles, ne n 14 Mar and the ther n 21 Mar Data analysis The methd f extracting the wind infrmatin frm the Dppler data is described as fllws. First the Dppler spectra crrespnding t each scan cycle in each range bin fr each beam were gruped tgether t frm a set f 10 spectra (fr each hur). Then an incherent averaging was perfrmed using 6 spectra lying arund the medi

2 SASI: DIURNAL VAItIATION OF HORIZONTAL WlNDSJN WWER 'lroposjihere 37 Table 1 MST radar parameters used fr the diurnal experiment n 14 and 21 Mar N. f range bins : 129 N. f FFr pints : 128 N. f cherent integratims : 128 IPP Pulse width N. f beams N. f scan cycles : 1000 fjs ; 16 fjs (cded) : 5 (zenith, east, west, nrth and suth) :10 an spectrum. This incherently averaged spectrum was used t btain (manually) the mean Dppler values crrespnding t each beam in each range bin. Then the mean Dppler values were cnverted t mean winds in each range bin. Nw frm the linefsight winds in the suth and nrth beam directins, meridinal and vertical cmpnents f the wind are derived fr each hur. A similar prcedure was used t btain the znal and vertical cmpnents f the winds fr each hur using the west and east beam data. Thus, the znal and meridinal winds were btained fr every hur and these hurly values f winds were harmnicanalysed t btain the diurnal (24h) and semidiurnal (12h) wind cmpnents at different height levels. 4 Results and discussin The results are presented fr six heights, viz., 3.55,3.97,4.53,4.96, 5.52 and 5.94 km. The upper height level was limited t 5.94 km, because, at heights abve this level, SIN rati was very pr which made it difficult t btain the mean 4 2 III 2 'Ẹ. II) a ~ 2 ~ winds at thse heights at every ne hur. III 0 At many f the heights, the vertical winds b E tained were having values m/s. These ver : tical winds were nt cnsidered fr the study f ~ diurnal variatins. Only the znal and meridinal ~ 0 cmpnents were cnsidered fr the present ~ study. Figures 1 and 2 shw the diurnal variatin f the znal winds at 4 levels and meridinal winds at 6 levels n 14 Mar in the height range 3.56 km, respectively. The znal winds are shwn nly at 4 levels because f deteriratin f SIN rati at higher levels. The bservatins started at 0900 hrs 1ST n 14 Mar and lasted till 0800 hrs 1ST n 15 Mar Figures 1 and 2 shw that dminant time variatin f bth the cmpnents is dminated by 24h perid, thugh shrter perids are als present. On 14 Mar the meridinal cmpnent shws a larger diurnal amplitude than the znal cmpnent. Si km TIME, hrs 1ST Fig. 1 Diurnal variatin f znal winds at 3.55, 3.97, 4.53 and 4.96 Ian heights at Gadanki (13.47"N, 79.18"E) n 14 Mar (The bserved wind values are represented by triangles.) 5.94 km 4.96 km O TIME, hrs 1ST Fig. 2 Same as in Fig. 1, but fr meridinal winds

3 I I 38 INDIAN J RADIO & SPACE PHYS, FEBRUARY 1994 O k m km / 141 I,III I 6 2 I tf) ~ / 'I. km \I).... ~ 2 E. 14 I\~ 4.53 I k m km.~ 3.97 km km O TIME, hrs 1ST Fig. 3 Same as in Fig. 1 except fr znal winds n 21 Mar TI ME, hrs 1ST Fig. 4 Same as in Fig. 1 except fr meridinal winds n 21 Mar milar hurly plts f the znal and meridinal cmpnents fr the secnd day (21 Mar. 1992) f the experiment are shwn in Figs 3 and 4, respectively. In cntrast t the first day (14 Mar. 1992), the znal cmpnent shwed a larger diurnal variatin than the,meridinal cmpnent. The 24 hurly values f the wind cmpnents n bth the days were subjected t. harmnic analysis in rder t estimate the dminating harmnic cmpnents. The analysis shws that the 24h and 12h cmpnents are the dminant nes. The results f the harmnic analysis f the hurly values f the znal and meridinal winds n 14 and 21 Mar are given in Tables 2 and 3, respectively. The steady cmpnent n 14 Mar is nrtheasterly, whereas it is mainly easterly n 21 Mar The amplitudes f the 24h scillatins, in general, are greater than thse f the 12h scillatins. On 14 Mar the amplitude f the diurnal wind is larger fr the meridinal cmpnent as cmpared t that fr the znal cmpnent. The meridinal cmpnent shws a maximum diurnal amplitude f 4.6 mls at 4.5 km, whereas znal cmpnent shws a maximum value f 1.7 mls at the same height. On the secnd day (21 Mar. 1992), the situatin is reversed. Diurnal amplitude f the znal wind shws a maximum amplitude f 4.3 mls at 6 km altitude, whereas that f the meridinal wind shws a maximum value f 1.7 mls at 4.5 km. On bth the days the larger diurnal amplitude values tend t ccur at a higher'level. On 14 Mar. 1992, upward phase prpagatin f the 24h znal cmpnent with a vertical wavelength f 12 km and dwnward phase prpagatin f the meridinal cmpnent with a vertical wavelength f 16 km can be seen in a limited height range (Table 2). On 21 Mar als similar upward and dwnward phase prpagatin fr the tw cmpnents in a limited height range can be seen but with shrter vertical wavelengths j 8 km fr the znal cmpnent and 6 km fr the meridignal cmpnent (Table 3). On 14

4 m/s m/s nents n 14 Mar m/s * ZnaIwind SASI: DIURNAL ' ;8 4.6 Amp Steady 24h. 12h Phase m/s VARIATION Znal Amp. OF Phase m/s HORIZONTAL Meridinal..cmpnent. wind WINDS IN LOWER"rROPOSPHERE 39 Steady Height Height Table 3 Amplitudes and phases f the 24 and 12h peridic cmpnents n 21 Mar Mar the meridinal cmpnent leads the znal cmpnent by apprximately 69 h as can be seen frm Table 2. A similar phase relatinship betwee(l the tw cmpnents is bserved n the secnd day (21 Mar. 1992) als, except at 3.55 and 4.96 km heights (Table 3). It may be nted. that the phases f the diurnal cmpnents n the tw days differ frm each ther cnsiderably (bth fr znal and meridinal winds) at individual height levels. Theretically expected amplitudes and vertical wavelengths in the trpical lwer trpsphere are 12 m/s and 25 km, respectively, fr the diurnal nnmigrating tides and m/s and 2530 km, respectively, fr diurnal migrating tides5 The present bservatins shw much larger amplitudes. Further, an upward phase prpagatin is bserved fr znal wind, whereas it is dwnward prpagatin fr the meridinal wind. Hence, what is bserved as 24h scillatin f the winds in the lwer trpsphere ver Gadanki cannt be attributed t tidal rigin. The reginal rgraphic fearures may have t be taken int accunt t understand the rigin f the bserved diurnal features. Data ver a lnger perid and cvering a larger altitude range wuld help in understanding the bserved diurnal scillatins. Acknwledgements The Indian MST radar facility is being established jintly by the Cuncil f Scientific and Industrial Research (CSIR), Defence Research and Develpment Organisatin (DRDO), Departments f Electrnics (DOE), Envirnment (DOEn); Science and Technlgy (DST) and Space (DOS).()f the Gvernment f India with the Department f Space as the ndal agency. The authr gratefully acknwledges the very fruitful and helpful discussin he had with Dr B V Krishna Murthy, Space Physics Labratry, Vikram Sarabhai Space Centre, during the preparatin f the manuscript f this paper.

5 . 40.,INDIAN J RADIO & SPACE PHYS, FEBRUARY 1994 References I Wallace J M & Tadd R F. Man Weather Rev (USA), 102 (']974) Fuka S, Kat S, Yki S, Harper R M, Wdman R F & Grdn W E, J Almas Terr Phys ( UK), 40 (1978) Fuka S, Sat T, Yamasaki N, Harper R M & Kat S, J Atmas.'lei( USA), 37 (1980) Sasi M N & Krishna Murthy B V, J Gemagn & Gee/eetr (Japan), 45 ( 1993), in press. 5 Tsuda T & Kat S, J Met Sc Jpn (Japan), 67 ( 1(89) Sarkar B K & Agarwal A, Hand Bk fr MAP, edited by C H Liu & Belva Edwards (SCOSTEP Secretariat, University f Illinis. Illinis USA) Vl. 28, p. 503.

Interference is when two (or more) sets of waves meet and combine to produce a new pattern.

Interference is when two (or more) sets of waves meet and combine to produce a new pattern. Interference Interference is when tw (r mre) sets f waves meet and cmbine t prduce a new pattern. This pattern can vary depending n the riginal wave directin, wavelength, amplitude, etc. The tw mst extreme