Khera, M K

Raina, B N

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ChcrBuhov Tadiation due. to th^passage of an oscillatory etc. 5 01rciRponsible for this anomaly. The intensity of radiation from (1) and (3) per milt frequency interval depends on space coordinates (/,=) and so it fluctuates sj)iiiially. A  similar phenomenon is also obtained by the variation of a. The equa­tion (2) signifies that by sim])ly adjusting, a the output of radiation can be aceeler- ai'cd or 7'ctardcd. Thus the conducting boundaiy acts as a promoter and plaj'^ s an important role in the graduaiion of cneigy loss which is technically important for concentration of radiation.The author expresses his sincere thanks t.o Dr. II M. Khnn of City College, fliiloul-ia for his kind helji in i>i‘oparing this noteR bt ’e r e n o e sBftlHZfl N. L . in.56 P h y s  R ev  104(G), 1220Klmt> R. M 1970 J a p a n e s e  J o m n a l  o f  A p jt  Phi/» 9, 120.J . P h y s . 47, 501-GOt (197.3)Preliminary results on the conductivity of air under a thunder cloudIVl K  K h ERA a n d  B  N . llATNAGulmarq Jle-sfiarch Obacrvalory, Gulmarg {Kashmir).{Received 30 June 1972, revised 30 September 1972)There is a considerable interest in the pioblem of electrical conductivity of air mider a thunder cloud befiause the data available so far arc very sketchy and ( onflieting (Chalmers 1967a). Preliminary results of an investigation of conducti­vity under a thunder cloud carried out on June 9, 1972 at the Gulmarg Research Ol)sorvatory (lit 2700 metres m s.l , 34 TN, 74 4“E) are iiresented here and the oliservations recorded seem to be interesting.Polar conductivities (A.,, A_) wore measured at the height of one metre above ihc ground alternately by a Gerdien type of cylindrical condenser. The Gerdicn chamber used was constructed having the same dimensions as the one described hy Hatakeyama et al (1958) A number of improvements made and described by (hmii (1965) in his conductivity apparatus were also incorporated in the design of our Gerdien chamber, except those which were not considered very essential, ns the instrument Avas originally designed to operate in dry weather conditions, The electrometer used was the one described by Vanderschmidt (1960) and was dii’cotly coupled^to the Gerdien tube, The output of the electrometer was fed502 M . K . K h era  and B . N . R ainato an Angus Strip Chart Recorder. Complete details of the condiu;11 Vi ty apparatus are to bo given elsewhere. The instrument is in use at tiu- Observat firy for more than a year with satisfactory results.Potential gradient was measured by using passive antenna system devised }»y (Vozier (1963). The antenna used was a 20 metres aluminium wire (diameter,I mrn) stretched pai-allel to the le\'-ol ground at the height of one metre Tlio details of tho held installation of the antenna and its associated circuitry wcie kept the .same as tho.se described by Crozior (1963), Tliis type of sensor being suitable for fair-weather had an operating range of —100 volts to -1-250 volts. Meteorological data were available from the meteorological station operating at the observatoryA thunder cloud started developing around 1230 hrs on the southern side and it gradually spiead over the station Positive eonductivity showed contiiiuom downward trend from 1230 hrs onward. As the thunder cloud approached tin; .station the positive conductivity decreased more rapidly and became zero when the cloud was overhead. During the period of two hmns when the cloud was over the station (altitude; 1800 metros approx.) negative potential gradient was observed Occasional lightning flashes occuring within the cloud produced ab­normal hut momentary changes in conductivity The average negative conducti­vity during the above period was 1 9 x1 0 “ ^^ mho/m which was higher than tlii' normal v'-alue of about 1 4 X 10“ *^ iiiho/m usually observed during this period at Oulmai'g With the slow recoding of the cloud towards w^ cst the potential gradient' vdiieli was greater than —100 V/m gradually reversed its polarity and became ]>(>sii.ive (>250V/ni) During the next 38 minutes the average positive and negative polar conductivities increased to values of 2.4x10“ '  ^ mho/m and 2 2x 10“ ^^^ mho/m respectively and showed greater agitation. With the potential gradient atlainmg more or less normal fair-weather value around 1650 hrs (about 80 YIm for Giilmarg for this hour) the negative conductivity fell to a value of 0 7 X 10'^' mho/m l^he measurements were stopped around 1710 hi's bccau.se ol' drizzling The drizzle seemed to have brought down some positive charge to the ground The sign of the charge was ascertained from the actual conductivity record (not .shovm in figure 1). The wind speed throughout the whole period vas between 2-4 m/see and the wind which was coming from south in the begiiiing cojTcsponded to the dii-ectjon of the movement of the thunder cloud The measure­ments wor e started again ati 1930 hrs after the drizzle stooped and were continued till 2100 hr.s. During this period the wind speed was between 6-7 m/sec and it kept on changing direction Figure! shows the variation of positive and negative conduct ivities for the period 1130 hr.s-1707 hrs; 1930 hrs—2100 hrs and those of the potential gradient between 1937 hrs to 2100 hrs. The vahies plotted represent- averag(‘is over i‘u.eh of 4-mmute interval The values of potential gradient' prior to 1937 hr.s are also indicated wdrenovor possible as no continuous recordP relim in a ry results on the conductivity o f  i 503■4- ? *-\ . 3C - .r : r :/ '?  ..g■ \ ■1/*NT>  1 :8K*Js1J§1z <1 i//1S/>\i3\<Jt "/.................  .S-21oOh.1E ^ r504: M . K . K hera and B . N . B ain aavailable. From iho actual record of conductivities (using ion filter) one could easily oonchrdo that when the positive ctmductivity was zero large positive ions wore also absojil Therefore the complete disappearance of positive charge (near the ground) from the station would appear to be unusual and may not be easily under­stood in terms of the earlier work of Chalmers (]9b7b). The higher values of conductivity observed (between 1612 hrs and 1650 hrs) could bo attributed partly1.0 freshly injected negative ions from the lightning flashes and partly to the arrival of air masses from the cloud at the station., Further work in this direction is in progressHefisbenoesChulmors .T A. 1907a A tm o s p h e r ic  JClectrtcity, 2nd Ifld. Pergantion I’roHs, p. 439.C'halinors J. A. 1907b A tm o s p h e r ic  JC lectncity, 2nd Ed Eergamon I’ross, p 2fi9-00 Urozior W D. 1903 J .  O eo p h y s . R e s  68i 6173 (junn H. 1966 R e v  o f  S e t . In s tr  36, 694HataUoyama H, Kobayashi J, Kitaoka T. & Uc’hikawa Iv 196S R e c e n t  A d v a n c e s  'in A tn w s p h n  tvE lv iti Peigumon Press, p 121Vandersohmidl G. F 1960 R e v  S e i. I its tr . 39, 1004tn d ia n  J . P h y s . 47, 504-607 (1973)Basic aluminum sulphate : An X-ray diffraction studyD. P. SiNHA, U Pka-sad* and a  K  HoyUniversity Deparbnenl of Physics, Patna University, Patna-^{^ Received 23 June 1972, revised 24 October and 8 December 1972)Composition of basic aluminium sulphate varies depending on its mode of pre­paration. In literature and while going through the ASTM cards one come.s across at least seveuieen basic aluminium sulphates differing in their chemical compositions and structures.Ill the present work basic aluminium sulphate was prepared in the following way. Melloncla’odl Analar solution (O.IM) of aluminium sulphate was refluxed in a round bottom flask at about 70“C for several hours (Milligan 1966). The resulting hydrolysed material Avas washed several times with distilled waler to got the sample free from the associated anions The sample was dried at room temperature and the powder was placed in a capillary tube of low absorbing glass having wall thickness of 0.01mm and diameter 0 5mm. The X-ray powder♦ProHont adilroHS : Badio-assay Laboratory, Univorsity of lllmois, Modical Centros, Uhiottgo. 111. 00012, USA,

Preliminary Results on the Conductivity of Air Under a Thunder Cloud

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Preliminary Results on the Conductivity of Air Under a Thunder Cloud

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