Horizontal drift in the ionosphere over Delhi

.Toumalof Atmospheric andTerrestrial

Physics,

1960, Vol. 19, pp. 172 to 183. Pcrgamon PressLtd. Printedin Northern Ireland

Horizontal drift in the ionosphere over Delhi S. N. MITRA, K. K. VIJ and Y. DASGUPTA Reseatch Department, All India Radio, Now Delhi

Abstract- Some results obtained at Delhi on the measurement of ionospheric drift by spaced receiver technique are described. Most probable velocities of reflections from the P- and E-layers for different The diurnal variations of the magnitude and direction of the drift seasons are indicated by histograms. v&&y have been plotted graphically. Harmonic analyses of the east-west and north-south components of the drift velocity have been worked out. No predominant periodicitg in any of the components was observed. It is interesting to note that the most probabie direction of the drift velocity is towards the south, and the northward component is almost completely inhibited. During magnetic storms, however, the northward component increases and its variation appears to be well correlated with the variation of the “K” index. 1.

IXTROD~OTI~X

of the drift system at ionospheric heights dates back to lYS4 when the Berlin astronomer, measured the height and velocity of the horizontal drift from the motion of noctilucent clouds. Similar investigations, in later years, were rather sporadic, due mainly to iimitations imposed by optical visibility and infrequent and unpredictable occurrence, at ionospheric height:;: of luminous night clouds and long enduring meteor t,rails. Systematic invest,igations of the horizontal drift system in the ionosphere could be commenced when, following a suggestion by J. A. Ratcliffe, the spaced receiver technique had been developed by one of the authors (S. N. Mitra) in 1947 at the Cavendish Laboratory. Since then, this method has been used to investigate horizontal drift in the ionosphere in many countries, notably Great’ Britain, Germany, U.S.A., Norway, New Zealand and India. Although considerable data on the horizontal drift system in the ionosphere have been collected, some of the basic questions have not so far been satisfactorily answered. For example, what causes the horizontal drift in the ionosphere? Is it dependent upon any other solar or geophysical ~lleiiorner~on? Is it possible to know for certain the location and vertical gradient (if any) of such’horizontal drift? How does the earth’s magnetic field influence motion of the charged particles constituting the ionosphere ? Considerable theoretical analysis and experimental work are required to be carried out before the drift system in the ionosphere is eomplet8ely understood. Such an opportunity has been afforded by the International Geophysical Year in which the investigation of ionospheric drift has formed a part of its programme. Systematic measurements of ionospheric drift were commenced at the Research Department of All India Radio, New Delhi (2@ 35’ N, 77’ 5’ E) in January 1958 as a part of its programlne of ionospheric investigations for the International Geophysical Year. The present paper deals with some of the analyses of data collected from April 1968 to March 1959. THE

discovery

OTTO JESSE

(1884),

172

Pig. 1. A typical drift record on reflection from the normal E-layer 0930 IST, 2.5 MC/S).

I----

‘---------Fig. 2. A typical

(i March 1960.

--*-------------~ drift record on reflection from the F-layer 6.5 MC/S).

(19 Jlarcll

IDqX, WOO IAT.

172

Horizontaldrift in the ionosphere over Delhi 2. EXPERIMENTAL ARRANGEMENT

The experimental set-up is essentially the same as developed earlier by one of the authors (MITRA, 1949). Three receivers are placed at the corners of a rightangled triangle, the two sides being 100 m. One pair is situated in the north-south The receiving aerials are horizontal and the other in the east-west direction. dipoles accurately aligned to be parallel to one another. A pulsed transmitter located at one of the receiving points radiates pulses (100 psec) in the frequency range 0.5-20.0 MC/S. The received echoes are fed to three recording oscilloscopes whose intensities are modulated by electronic gates which are made to “select” The traces on the recording oscilloscopes these echoes in a monitor oscilloscope. correspond to the amplitudes of the three desired echoes at the three spaced receivers. The fading of all the three echoes is simultaneously recorded on a 35 mm film moving at the rate of 6 in/min. Time marks at intervals of 15 set are provided on the film by momentarily closing the camera lens. The fading records at the three spaced receivers are usually taken for a period of lo-15 min. These are later analysed in the conventional manner and the magnitude and the direction of the drift velocity determined. The schedule of observation was as follows: During Regular World Days and Special World Intervals, observations were made once every hour. On other days, round-the-clock hourly observations were taken every third day. Observations once every 3 hr were made on the other days. The wave frequencies selected were 2.5 and 6.5 MC/S. The ionospheric characteristics are known from routine ionospheric measurements taken at the same place. The type of records obtained is shown in Figs. 1 and 2. Since the determination of drift velocity from the fading curves depends upon the fading of the received echoes, some of the observations could not be utilized when the fading was either very slow or extremely rapid. The wave frequency of 6.5 MC/S gives reflection mostly from the F-region; occasionally from E, when it is of the intense type. The effect of “magneto-ionic fading” is eliminated as the receiving aerials are aligned accurately to be parallel to one another. Moreover, for the period concerned, the critical frequency of the FZ-layer during the day was very high; reflection on 6.5 MC/S was mostly the ordinary ray, the extraordinary being highly absorbed. The analysis of records described in the following sections pertains to the study of any regular variations in the magnitude and phase of the drift velocity. Observations during Regular World Days, Special World Intervals and other disturbed days will be reported later. 3. MAGNITUDE OF THE DRIFT VELOCITY 3.1. Combined results

The magnitudes of the east-west (E-W) and north-south (N-S) components of the true drift velocity have been computed from the fading records. The resultant drift velocity has also been calculated. These velocities have been grouped statistically and histograms plotted for determining the most frequent occurrence. Figs. 3, 4 and 5 show the histograms of the magnitudes of the resultant drift velocity and its E-W and N-S components respectively. These results are for the 173

S. N. MITRA, K. K. VIJ and P. DASGUPTA

100

I-----80

20

0

20

40

1 60

Fig. 3. Histogram

showing

100

80

the distribution

Veloaty,

Fig. 4. Histogram

of the E-W

woclty,

120

140

16

m/w

Velocity,

m

of t,he magnitude

of the drift

/see

component of the drift velocity.

m/set

Fig. 5. Histogram of the N-S component. of the drift velocity.

velocity.

Horizontal

drift in the ionosphere over Delhi

fading records on echoes from the F-layer. The most frequent value of the resultant drift velocity is 85 m/set. Velocities less than 30 m/see and greater than 160 m/see have not usually been observed. The most frequent value for the E-W component (Fig. 4) is 65 m/set and that for the N-S component (Fig. 5) is the same. These histograms are, however, not so well defined as that of the resultant drift velocity.

18 5

si6 b

P” 2

0

20

40

60

80

Velocity,

Fig. 6. Histogram

100

120

140

m/set

of the E-region

drift velocity.

Fig. 6 shows the histogram for the E-region drift velocity. The fading records utilized for this histogram were on echoes from the E-layer or from E,. The most frequent drift velocity is 55 m/see. The number of observations is rather limited. The magnitudes of the drift velocity have also been grouped for summer 20 rl

‘0

Velocity,

Fig. 7. Histogram

m/set

of drift velocity during summer.

(May, June, July, August), equinox (September, October, March, April) and winter (November, December, January, February). Figs. 7, 8 and 9 indicate these histograms respectively. In summer the most frequent magnitude of the drift velocity is 75 m/set, in equinox 85 m/set and in winter also 85 m/set. This indicates that the velocity is somewhat higher in equinox and winter than in 175

8. X.

MITEA,

K. K.

171~

and

P.

DASGUPTA

We have not considered such histograms at different hours of the summer. day due to the limited number of observations. The diurnal variation of the magnitude of the drift velocity has also been worked out. Fig. 10 indicates the overall diurnal variation during the period April 1958 to March 1959. The maxima and minima of the magnitude are not -

nI

1 5G

70

Velocity,

90

m/see

Fig. 8. Histogram of drift velocity during equinox.

very well defined although the former appears to occur around 0100 and 1600 IST (GMT + 54j hr) and the latter at about 0700 and 1900 IST. The N-S and E-W components of the drift velocity have similarly been calculated and their overall diurnal variations are shown in Figs. 11 and 12. A significant feature in Fig. 11 is that almost all the time the N-S component is southwards as if a northward

10

30

50

,!G

70

130

!5O

17

Veiocrty. m/ser. Fig. 0. Hist,ogram of drift velocity during winter.

velocity is truly inhibited. The minima are at 0400 and 1900 IST and the maximum around 1300 IST. The values of the northward component are small on the very few occasions it is present. We shall show later that the situation changes considerably during a magnetic storm when the northward component suddenly becomes strong. The E-W component (Fig. 12) indicates both easterly and 176

Horizontal

drift in the ionosphere

IST

Time. Fig. 10. Diurnal

variation

over Delhi

of (overall)

drift velocity.

April 195%March

12

I7

1959.

0 :: z E

--IO -20

s .!? B

-30

P

-40 -50 -60

-80

0,

02

03

04

05

06

07

08

09

II

IO

Tme, Fig. 11. Diurnal

01

02

03

04

05

variation

06

07

08

13

14

15

of N-S component.

09

IO

16

18

19

2,

1, I2

13

14

15

April 1958-March

16

17

18

19

Tim? _ IST

Fig. 12. Diurnal

20

22

23

IS7

variation

177

of E-W

compomnt.

20

21

1959.

22

23

24

S. S. MITRA, K. K. VIJ and P. DASGUPTA SO E

P

400

-4o-

w -8OI

i -ac

04

I 06

I 08

0

02

Pig.

13. Diurnal variation

I 12

I 10

Time,

of E-W

/ I8

20

,\A 22

I 24

IST

during summer.

IST

of E--W and N-S components

westerly values; t,he former between rest of the time. 3.2. Diurnal

I6

and N-S components

Tme,

Fig. 14. Dinmel variation

14

during equinox.

1900 and 0900 TST and the latter during the

and seasonal variations

The E-W and N-S components of the drift velocity have been grouped for different seasons and Figs. 13, 14 and 15 show the diurnal variation of these 178

Horizontal

drift in the ionosphere over Delhi

Time, Fig. 15. Diurnal variation

of E-W

IST and N-S

components

during winter.

components for summer, equinox and winter, respectively. No regular periodicity, semi-diurnal or otherwise, is apparent from the figures. Nevertheless, harmonic analysis has been carried out to detect any predominant periodicity in the variation of the drift components. This analysis is given below: Summer JT,_, = -12.6 + 31.2 sin (4 + 65.3”) + 24 sin (~c#J+ 158.7”) + 9.3 sin (3+ + 45’) + 21 sin (44 + 129’) + 11.5 sin (54 + 304”) 16.9 sin (64 + 54’) + 12 sin (7#~ + 40.6”) + 23.4 sin (84 + 206’) G 25 sin (94 + 145.8“) + 5.6 sin (104 $ 161’) + 11.1 sin (114 + 51’) jTs_s =

12.8 cos 124. - 15.6 + 18.2 sin (C#I + 221.5”)

+

12.7 sin (24 t_ 304.6”)

+ 20.8 sin (34 + 286’) + 16.4 sin (44 + 24.3’) + 15.2 sin (54 + 280’) + 8 sin (64 + 41.4’) + 10.4 sin (74 f 296”) + 3.8 sin (84 + 281’) +

13.1 sin (94 +

-

7.2 cos 124.

188.7’)

+

13.4 sin (lO$

+

16.5’)

+

16.2 sin (114

+ 329”)

Equinox = -3.1 + 20.6 sin (C#I j- 11.5”) + 27.5 sin (24 + 14.7”) + 18 sin (34 + 336”) + 10.8 sin (44 + 147’) + 14.8 sin (54 + 194’) + 10.3 sin (64 + 6S”) i_ 4.5 sin (74 + 198”) + 18.3 sin (84 + 133”) + 3.7 sin (94 + 58’) + 24.2 sin (lo+ + 236”) + 4.9 sin (ll$ + 135”) + 0.9 sin (124 + 270”). T’s_s = - 44.4 + O-5 sin C#+ 11.2 sin (2$ + 207”) + 19.2 sin (34 + 233’) + 10.7 sin (44 + 121.3”) + 17.5 sin (54 + 148.7”) + 2.8 sin (64 + 216*a”) + 6 sin (74 + 90”) + 8.45 sin (84 + 74.8”) + 2.2 sin (9$ + 90”) + 19.2 sin (lo+ + 286’) + 11.1 sin (ll$ + 198.5’) + 1.4 sin (12$ + 270”).

V,_,-

179

S. N,

MITR.A,

K. K. VIJ and P. DXJGUPT-L

vx_w. = -1.6 +

+ 31 sin (#I _I- 89”) + 7.4 sin (24 + j?S5*7’) + 7.5 sin (34 + 164.3”) 19.5 sin (44 + 259’) + 9.6 sin (54 + 164.2”) + 13.6 sin (64 + 12S.S’)

+

16.5 sin (74 +

+ 20.5 sin (lo+ Vx_s =

-34.2

89”)

13.2 sin (84 + 47.2’)

+

+ 71.5”)

+

11.1 sin (114

+

+ 20.2 sin 4 + 12.4 sin (24 + 84”)

+ 20.7 sin (44 +

152’)

+

+

74.6’)

+

+

+- 2.4 sin (124

+ 90”).

14.5 sin (34 + 38.6”)

12.2 sin (54 + 169.6”) t_ 7.9 sin (64 + 202.4”)

+ 4.2 sin 74 + 3-S sin (84 + 340.4’) + 4.1 sin (104

10 sin (94 + 345’)

+

154.S”)

+ 5.1 sin (94 + 128.6”)

10.2 sin (114

+

109.3’)

+

l-6 sin (124

f

90’).

It is surprising that regular periodicities have been observed at Waltair (RAO and RAO, 1958). We find, on the contrary, that diurnal variations of the drift components are very irregular.

Time. IST Fig. 16. Diurnal variation of phase of the drift, velocity.

April 195%March 1959.

4. DIRECTION OF DRIFT MOTION

We have next enquired into the phase of the drift velocity. Fig. 16 shows the diurnal variation of the mean phase in degrees east of north for all observations during the period April 1958 to March 1959. The direction of the drift mot,ion is mostly confined between 90” and 270” E of N; in other words it is towards eastsouth-west. Here also, the northward direction is almost always absent excepting for 1 hr during the day at 1800 IST. The situation is more clearly expla’ined in Fig. I7 which shows a polar histogram of the phase. The most probable direction is towards south, and most of the observations are confined within SSE and SSW through S. Fig. 1S shows the diurnal variation of the phase during summer, equinox and winter seasons. It is significant that the variation of t’he direction at different hours of the day is almost similar during the three seasons and the phase mostly confined between 120’ and 240” E of N. This confirms that the southward component is most predominant in all the seasons. 5. CORRELATIONWITH MAGNETIC STORI\IS We have seen that the diurnal variation of both the magnitude and direction of the drift vector does not show any semi-diurnal oscillation as would be expected from a consideration of the effect of solar and lunar gravitational tides upon a Since the motion of ionospheric regions uniformly rotating neutral air-mass. 1SO

Horizontal

drift in the ionosphere over Delhi

Fig. 15. Polar histogram

of the direction of the drift velocity.

360 300 2 240 L;j 180

60.

Oi

02

07 04

05

06

Oi' 08

09

IO II 12 13

Time, Fig.

18. Diurnal variation

14

15

16

87

IS 19 20

PI

IST of phase in different seasons.

181

22

23 24

S. N. MITRA,

K. K. VIJ and P. DASGUPTA

essentially constitutes movement of charged particles, the earth’s magnetic field In a recent paper we (MITR~ and will exercise some influence on the drift velocity. \‘IJ, 1960) have considered in detail the relationship between K-figures and drift velocity. The quiet day variation of the E-W and N-S components is not correlated with K. The magnitude of the resultant drift velocity does not noticeably increase as K increases. The situation, however, becomes interesting during a magnetic storm as can be seen from Fig. 19. The K-figures for 8, 9, 10 and 11 January 1959

in6-

5K 0

*_e Mogreflc storms.c H=19,7, z =46 I I 05 10 15 20 01 06 05 18 23 04 09 14 19 0 IOI 59 9159 Fig. 19. Variation of E-W and K-8 components on a magnetically disturbed da>-. 1 10

have been plotted together with the E-W and N-S components at different hours of the day. A moderate magnetic storm of sudden commencement type started on 9 January 1959 at 2028 IST and ended at 1530 IST on 11 January. The range of horizontal intensity (H) went up to 191 y and that of the vertical field (2) was 46 y (Kodaikanal Observatory data). The E-W and N-S components both exhibited large fluctuations in synchronism with the magnetic storm. The maximum values of the E-W and N-S components were 173 (westward) and 90 (northward) m/set. A significant point to note is that as the magnetic storm started on the 9 January, the northward component increased and remained high for several hours till the storm subsided. Again on 11 January, when the K-figure increased the northward component also became high. In other words, the magnetic storm seems to increase the northward component of the drift velocity while this component is mostly absent on quiet days. An analysis of several other drift records during magnetic storms has confirmed this observation. Fig. 20 shows a typical drift record during a magnetic storm. The fading becomes much more rapid than that on a quiet day indicative of turbulence in the ionosphere during the progress of a magnetic storm. 182

Horizontal drift in the ionosphere over Delhi 6. SUMMARY Some of the results obtained at Delhi on the measurement of ionospheric drift by spaced receiver technique are described in the paper. The most probable velocity of the drift on reflections from the F-region is 85 m/see. The values in equinox and winter seasons appear to be somewhat higher than that in summer. The diurnal variation of the magnitude of the drift velocity and its components does not show any apparent semi-diurnal periodicity. The variations through 24 hr of the E-W and N-S components have been subjected to harmonic analysis and values up to the twelfth harmonic worked out. No predominant periodicity in any The most probable direction is towards south of the components was observed. and maximum number of observations is confined between 120” and 240” E of N. of the drift A magnetic storm, however, increases the northward component velocity; the K-figure and the magnitude of the northward component vary in the same manner so long as the storm lasts. The analyses presented in t’he paper refer to the drift records obtained on reflections from the F-region. The data collected during the IGY and the IGC are being analysed and the results will be published in due course. AcknouJedgements-The work described in this paper forms a part of the Indian programme for IGY extended through IGC conducted by the Research Department of All India Radio and is supported by financial grants from the Council of Scientific and Industrial Research. Two of us (K. K. V. and P. D.) are grateful to the C.S.I.K. for the award of a Research Assistantship. The paper is published by permission of the Chief Engineer, All India Radio, New Delhi. Our thanks are due to Mr. 11. SINHA4 for help in the observations. REFERENCES JESSE 0. hfITRA s. s. MITRA 12~0

and ~~~~ K. K. R. and Rao E. U.

S. N. 13.

1884 1949 1960 1958

183

Met. Z. 1, 127. Proc. InbstnElect. Engm III, 96, 441 J. Instn Telecom. Engrs 6, 90. S&we. Lord. 181,161”.