Survey of Meteor Signal Rates Observed Over a VHF Forward-Scatter Link Between Waltair & Dehra Dun

Indian Journal of Radio & Space Physics Vol. 12, April 1983, pp. 50-52

Survey of Meteor Signal Rates Observed over a VHF Forward-scatter Link between Waltair & Dehra Dun

M SRIRAMA RAO, S RAJA RATNAM & D A V KRISHNA RAO* Department of Physics, Andhra University, Waltair 530003 and E BHAGIRATHA RAO Defence Electronics and Research Laboratory, Hyderabad 500005 Received 6 May 1982; rerised receired 4 January 1983

Diurnal and day-to-day variation in meteor signal rates observed for a period of one year over a VHF forward-scatter link between Waltair and Dehra Dun (a distance of 1533 km) at 48.2 MHz are presented. The diurnal variations of meteor rates are discussed and the results are compared with the meteor wind radar observations at Waltair.

1 Introduction details of the experimental set-up have been published It is well understood that the ionization produced by elsewhere 7. The method of analysis of the forward- the passage of a meteor into earth's atmosphere serves scatter meteor records has already been published in as a radio target and it thus makes a new method an earlier paper by Rao et al.6 possible for studying both the astronomical properties of meteors and the physical conditions in the 3 Diurnal Variation of Meteor Rates atmosphere. The scattering of radio waves by meteor The meteor signal rates for the corresponding hour trails' has been studied extensively in the past, in each month have been averaged and the average originally for the back-scatter case, by McKinley and diurnal variation in the hourly meteor rates for all the Millman", Lovell? and Manning:'. Later, it has been 12 individual months are shown in Fig.l. Error bars extended to forward-scatter techniques using continuous wave transmission with relatively small radiated power'v". An extensive study of radio meteors using forward-scatter system has been carried out by a number of workers". In this paper, the results of the analysis of continuous recording of meteor echoes observed on a forward-scatter link experiment conducted between Waltair and Dehra Dun during the period Dee, 1974-Nov. 1975 are presented.

2 Experimental Set -up The CW transmissions at 48.2 MHz and 200 W power from Dehra Dun are received at Waltair at a distance of 1533 km by way of meteor forward-scatter. Six-element Yagi antennas with 10 dB gain are used both at the transmitting and receiving ends and directed towards the meteoric region at a height of 100 km above the ground midway between the two stations. The meteor echoes are recorded continuously at WaItair using a Brush recorder during the second half of every hour and round the clock. The complete

TIME, hrs lMT

"Present address: Naval Science and Technological Laboratory, Fig. I Monthly mean diurnal variation of meteor signal rates Vigyana Nagar, Visakhapatnam 530006 from January to December

50 RAO et al: METEOR SIGNAL RATES ON FORWARD-SCATTER LINK BETWEEN WALTAIR & DEHRA DUN were calculated from the total number of meteor 4 Day-to-day Variation of Daily Mean Hourly echoes contributing to each data point and represented Meteor Rates in Fig.l. The most common feature observed in all The daily mean hourly meteor rates for the period these curves is that they exhibit a maximum activity Dec. 1974 - Nov. 1975 are obtained by averaging all the around 0600 hrs LMT and a minimum around 1800 hourly values in each day. This day-to-day variation of hrs LMT. The early morning peak and evening dip in daily mean hourly meteor rates of the whole day for the meteor activity are due to well known "Apex effect" above period is shown in Fig.2. The curve showing the (Ref.8) assuming an isotropic distribution of sporadic day-to-day variation of meteoric activity suffers great meteor radiants. Similar results have also been increases at irregular intervals due to the occurrence of obtained by many others?'!", However, following the major and minor meteor showers. In particular, the latitudinal dependence of meteor rates reported by increased activity is prominently seen during the active Whipple II and Lo veJI2 , the observed crest at early periods of meteor showers presented in Table I. morning hours and trough at evening hours coincide Although these meteor showers are highly active, with the expected diurnal variation of meteor activity owing to their short lived activity their contribution to for Waltair, a low latitude station. Besides the above the total number of meteors entering the earth's characteristic features in diurnal variation curves, a atmosphere during the year is considerably less than sharp fall in meteor activity at around 0800 hrs L M T the contribution from the sporadic meteors. is also noticed in most of the cases. This less meteor activity may be due to the rapid increase in absorption l1 Table I . Major Meteor Showers with Date of Peak at D-region height . The unsteady conditions in the Activity ionosphere around this time (0800-1000 hrs), resulting in rapid layer movements may also be a cause for the Name of the shower Date of peak decreased activity. The same facts have also been 1974 activity noticed in the diurnal variation curves established by Geminids 12 Dec. I3 1 meteor wind radar measurements at Waltair . ". The 1975 diurnal variation gets also markedly affected by any Quadrantids 3 Jan. meteor shower". During the months September to Lyrids 20 Apr. December the 0600 hrs peak is shifted towards earlier Ela Aquarids 4 May hours probably due to non-isotropic distribution of Ariet ids 4 June Zeta Perscids 7 June sporadic meteor radiants. During the same months Beta Taurids 29 July another peak is also observed which coincides with the Capricorn ids 25 July time of upper transit of the major meteor showers like Iota Aquarids 3 Aug. Orionids, Leonids and Geminids indicating a large Perseids 14 Aug. influence of these meteor showers on the diurnal Kappa Cygnids. 20 Aug. Orion ids 20 Oct. activity. Taurids 2 Nov. Leonids 17 Nov.

= :::;:+ •• ...•.. :,"," •. ~g +-0 g :: ZN .•, 0" -~..,. N N 0 2~ N .,. ~ "'ON.. - ...... •. 0" + •• + ~ -" GIN"- ZN ]!O ][0 ~~ oct, 00 2 ... .; ii, :> .• ",," eo •• •• :;I ~:00 a", ]00 "'•... z:; ;:!I :~ '--' j ~ a: ~ I ~ ~ ~ :100 :z:~ z ••• uo •...][ ][ 100

I,J 40 )', ,'0 ~O )\ ~ ';0 iI ~ 1'0 )1. lo io ~O it it ~ ~6 l. i'o "Ii ;1 ~.Jo 11 ~ ~ ~ Ma 10 l ~o;. I DEC.74 I J••••. ~ I FE8.~ I ·MAR.» I APR.75 I MAY 7S I ~ "S I J\V 15 I AU5.7S I UP.1S I DCT. 1S ~ NOV. n f MONTH

Fig. 2 Day-to-day values of mean hourly meteor signal rates of whole day for the period Dec. 1974-Nov. 1975

51 INDIAN J RADIO & SPACE PHYS, VOL. 12, APRIL 1983

On the basis of meteor activity, Leonid is by far the References strongest shower followed by Geminid and I McKinley D W R & Millman P M. Proc Inst Radio Eng Quadrantid showers. The day time showers are iAustraliav: 37 (1949) 364. Arietids, Zeta Perseids, Beta Taurids and 2 Lovell A C B. Meteor Astronomy (Clarendon Press. Oxford). 1954. Capricorn ids. Normally meteor showers last from 3 Manning L A. Proc Inst Radio Eng tAustraliar. 2 (1954)82. several days to several weeks, depending on the individual shower". Meteor shower activity is 4 Allen E W. Proc Inst Radio Eng tAustroliar. 36 (1948) 346. 5 Forsyth P A & Vogan E L. Can] Phys (Canada). 33 (1955) 176. superimposed over the sporadic background. So the rate increase, depending on the shower activity, may 6 Rao B R. Srirama Rao M. Raja Ratnam S. Krishna Rao D A V & Bhagiratha Rao E.lndian] Radio & Space Phvs, 4(1975) not always be particularly marked. The meteor rate for 99. individual shower and the date of peak activity during 7 Bhagiratha Rao E. Srirama Rao M. Raja Ratnam S & Krishna a shower can vary from year to year 15. Fourteen well Rao D A V. ] Inst Electron & Telecommun Eng i lndia), 22 marked shower peaks and their dates of peak activity (1977) 427. are presented in Table 1.They are consistent with those 8 McKinley D W R. Meteor Science and Engineering (McGraw Hill Co .. New York). 1971.

already presented by MCKinlel. 9 Forsyth P A. Vogan E L. Hansen D R & Hines C O. Proc 111.1'1 Acknowledgement Radio Eng t Australiai. 45(1957) 1642. The authors are grateful to the Rand D 10 Vogan E L & Campbell L L. Call] Phvsi Canadat, 35(1957) 1176. Organisation, Ministry of Defence, Government of II Whipple R L. Astrophvs ] (USA). 59 (1954) 201. India, for the sanction of Grant-in-aid Project on the 12 Baldwin J P & Kaiser T R. Puhl.No.29. Deutsche Ak ademic der study of "Meteor Forward-Scatter Propagation Wisscnschaften Zu Berlin. GeomagnetismInstitute, Potsdam, Characteristics". They are also thankful to the staff of 1962. 145. 13 Devara pes. Ahmed M r.Srirama Rao M & Ramachandra Rao Defence Electronics and Applications Laboratory at B. Indian ] Radio & Space Phvs, 7 (1978) 192. Dehra Dun for maintaining the transmissions. One of 14 Devara pes. Ahmed M 1& Srirama Rao M. Indian] Radio & the authors (DA VKR) is thankful to the University Space Phvs. 8 (1979) X5. Grants Commission, New Delhi, for awarding him a 15 Goldsbrough P E & Elleyett C D. ] Geophys Res(USA), 81 (1976) junior research fellowship. 6135.