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Electron density profiles in the equatorial F-region during evening hours
Adv. Space Res. Vol. 7, No. 6, pp. (6)69—(6)71, 1987 Printed in Great Britain. All rights reserved.
0273—1177/87 $0.00 + .50 Copyright © COSPAR
ELECTRON DENSITY PROFILES IN THE EQUATORIAL F-REGION DURING EVENING HOURS S. P. Gupta Physical Research Laboratory, Ahmedabad — 380 009, India
ABSTRACT 0
Two RH—560 rockets were launched from Indian rocket range,SHAR (dip=11 N) during evening hours on different days. The rockets were launched about fifteen minutes before the Onset of spread—F.The F region profiles were smooth. The results can be included in I.R.I. as these are the only profiles for night time conditions over low latitude without the spread—F pre s en t. INTRODUCTION The electron density profiles in the equatorial ionosphere during night time is highly distorted due to the presence of equatorial spread—F /1,2,3/. The rocket borne in—situ measurements carried out so far from eciuatorfal latitudes were mostly during spread—F conditions.The profiles of night tine F region over low latitudes which have been available so far can not he included in the International Reference Ionosphere Model because these profiles are not smooth. In order to measure the night time profiles over low latitudes in the absence of spread F,two rocket flights were carried out from Indian rocket range,SHAR (dip 11°N,lat.14°N,long.80°!).Oneflight, ASV—26, was launched on 16th February 1982 at 1909 hrs. 1ST, while flight ASV—30 was launched on 1st March 1982 at 1905 hrs. IST.The local time is 10 minute behind IST.The rockets reached the apogee heights five minutes after the launch. The electron density was measured by Langmuir Probe. The ionosonde at SHAR was operational during flight time during both these days. The lonosonde was kept operational two hours before the flight and upto two hours after the flight. During the flight of ASA—26 the ionosonde data showed F layer reflection from 2.5 MHz (f !iin.F) to 14 MHz (N Max.F) at 1916 hrs. IST.,the virtual height being 400 km at 2.5 MHz and about 650 km at 14 MHz.The virtual height at the minimum frequency during night time can be considered as real height.So the base of the F layer was at 400 km.In second flight ASV—30,the lonosonde data showed F layer reflection from 2.5 MHz (f Min.F) to 10 MHz (N Max.F) at 1915 hrs. IST.The virtual height was about 425 km at 2.5 MHz and was about 700 km at 10 MHz. RESULTS The rockets were launched before the Onset of spread—F.The rocket ASV—26 reached an altitude of 364 ktn,while the rocket ASV—30 attained an altitude of 365 km.Fig.1 shows the electron density profile obtained during evening hours before the onset of spread—F.Sfnce the rockets did not reach the base of F layer, we could not calibrate the probe current to get the electron density data from ionosonde data.Therefore the calibration factor which had been used in earlier flights /4/ have been used.We have plotted only the ascent profiles for the two flights. The main features of the descent profiles within the F region are more or less same. The following features are seen in the electron density profiles: 1. The electron density profile in F region between 160 km and 365 km is quite smooth on both the evenings . However in flight ASv—26 irregularities with amplitude less than 20 per cent were observed in the altitude region between 240 and 2R0 km.Their scale size is about one km.We will not discuss their features here. 2. In both the profiles, sporadic H layers have been observed in the region between 90 km and 120 km. (6)69
(6)70
3.
4.
5. 6.
S. P. Gupta
In one of the flights, ASV—26 , a layer of ionisation was seen at 287 km with a thickness of 2 km and the electron density in the layer is 50 % higher than the ambient electron density.No such layer is seen in the second flight. In both the electron density prifiles,a valley is seen in the region between 170 km and 280 km. The density within this valley Is nearly constant. 3 For ASV—26 the electron density is about 4X10 4electrons per cc, while for ASV—30 the electron density is about 10 electrons per cc in the valley region. The electron density profiles do not exhibit appreciable density gradient even above 300 km. The vertical drift in the E region was upward during the two flights 380 SR AR INDIA
360
—FLIGHTASV3O MAR. 1982 .1905 HRS.IST
340
_———
FLIGHT ASV26 16 FEB.1982,1909 HR$ 1ST ASCENT DATA
320
300
r
280
C
~260 ~
240
~22O 200 180 60 40
20. 00 80
~—t” 0’
ELECTRON DENSITY /
Fig.
1
I
lO~
02
cm
Electron density profiles during evening hours over low magnetic latitudes.
DISCUSSIONS
For International Reference Ionosphere the valley region between 170 and 280 km is very important. The electron density has been observed to he nearly constant within this region. Therefore the profiles of ASV—26 and ASV—30 can form the part of the international reference ionosphere over low latitude for the night time conditions. The F region profiles measured earlier by other workers over low latitudes are highly irregular.Rut our measurements show nearly smooth F region electron density profiles during evening hours. ACKNOWLEDGEMENTS The author is thankful to Prof. Satya Prakash for useful scientific discussions.The project was supported by Dept. of Space,Covt.of India.
Profiles in Equatorial F-Region
(6)71
REFERENCES 1.
2.
3. 4.
F.A.Morse, B.C.Edgar, H.C.Koons, C.J.Rice, W.J.Heikkila,J.B.Hofmann, B.A.Tinsley, J.A.Winningham, A.B.Christensen, R.F.Woodman ,J.Pomalaza and N.R.Teixeira,J.Geophys.Res. 82,578 (1977). M.C.Kelley, G.Haerendel, H.Kappler, A.Valenzuela, B.B.Balsley, D.A.Carter, W.L.Ecklund, C.W.Carlson, B.Hansler and R.Torhet, Geophys.Res.Lett. 3,2148(1977). S.Prakash, S.Pal, R.Pandey and B.H.Subbaraya, Adv.Space Res.2,10, 195 (1983). S.Prakash and S.Pal, Adv.Space Res.5, 7, 39 (1985).
0273—1177/87 $0.00 + .50 Copyright © COSPAR
ELECTRON DENSITY PROFILES IN THE EQUATORIAL F-REGION DURING EVENING HOURS S. P. Gupta Physical Research Laboratory, Ahmedabad — 380 009, India
ABSTRACT 0
Two RH—560 rockets were launched from Indian rocket range,SHAR (dip=11 N) during evening hours on different days. The rockets were launched about fifteen minutes before the Onset of spread—F.The F region profiles were smooth. The results can be included in I.R.I. as these are the only profiles for night time conditions over low latitude without the spread—F pre s en t. INTRODUCTION The electron density profiles in the equatorial ionosphere during night time is highly distorted due to the presence of equatorial spread—F /1,2,3/. The rocket borne in—situ measurements carried out so far from eciuatorfal latitudes were mostly during spread—F conditions.The profiles of night tine F region over low latitudes which have been available so far can not he included in the International Reference Ionosphere Model because these profiles are not smooth. In order to measure the night time profiles over low latitudes in the absence of spread F,two rocket flights were carried out from Indian rocket range,SHAR (dip 11°N,lat.14°N,long.80°!).Oneflight, ASV—26, was launched on 16th February 1982 at 1909 hrs. 1ST, while flight ASV—30 was launched on 1st March 1982 at 1905 hrs. IST.The local time is 10 minute behind IST.The rockets reached the apogee heights five minutes after the launch. The electron density was measured by Langmuir Probe. The ionosonde at SHAR was operational during flight time during both these days. The lonosonde was kept operational two hours before the flight and upto two hours after the flight. During the flight of ASA—26 the ionosonde data showed F layer reflection from 2.5 MHz (f !iin.F) to 14 MHz (N Max.F) at 1916 hrs. IST.,the virtual height being 400 km at 2.5 MHz and about 650 km at 14 MHz.The virtual height at the minimum frequency during night time can be considered as real height.So the base of the F layer was at 400 km.In second flight ASV—30,the lonosonde data showed F layer reflection from 2.5 MHz (f Min.F) to 10 MHz (N Max.F) at 1915 hrs. IST.The virtual height was about 425 km at 2.5 MHz and was about 700 km at 10 MHz. RESULTS The rockets were launched before the Onset of spread—F.The rocket ASV—26 reached an altitude of 364 ktn,while the rocket ASV—30 attained an altitude of 365 km.Fig.1 shows the electron density profile obtained during evening hours before the onset of spread—F.Sfnce the rockets did not reach the base of F layer, we could not calibrate the probe current to get the electron density data from ionosonde data.Therefore the calibration factor which had been used in earlier flights /4/ have been used.We have plotted only the ascent profiles for the two flights. The main features of the descent profiles within the F region are more or less same. The following features are seen in the electron density profiles: 1. The electron density profile in F region between 160 km and 365 km is quite smooth on both the evenings . However in flight ASv—26 irregularities with amplitude less than 20 per cent were observed in the altitude region between 240 and 2R0 km.Their scale size is about one km.We will not discuss their features here. 2. In both the profiles, sporadic H layers have been observed in the region between 90 km and 120 km. (6)69
(6)70
3.
4.
5. 6.
S. P. Gupta
In one of the flights, ASV—26 , a layer of ionisation was seen at 287 km with a thickness of 2 km and the electron density in the layer is 50 % higher than the ambient electron density.No such layer is seen in the second flight. In both the electron density prifiles,a valley is seen in the region between 170 km and 280 km. The density within this valley Is nearly constant. 3 For ASV—26 the electron density is about 4X10 4electrons per cc, while for ASV—30 the electron density is about 10 electrons per cc in the valley region. The electron density profiles do not exhibit appreciable density gradient even above 300 km. The vertical drift in the E region was upward during the two flights 380 SR AR INDIA
360
—FLIGHTASV3O MAR. 1982 .1905 HRS.IST
340
_———
FLIGHT ASV26 16 FEB.1982,1909 HR$ 1ST ASCENT DATA
320
300
r
280
C
~260 ~
240
~22O 200 180 60 40
20. 00 80
~—t” 0’
ELECTRON DENSITY /
Fig.
1
I
lO~
02
cm
Electron density profiles during evening hours over low magnetic latitudes.
DISCUSSIONS
For International Reference Ionosphere the valley region between 170 and 280 km is very important. The electron density has been observed to he nearly constant within this region. Therefore the profiles of ASV—26 and ASV—30 can form the part of the international reference ionosphere over low latitude for the night time conditions. The F region profiles measured earlier by other workers over low latitudes are highly irregular.Rut our measurements show nearly smooth F region electron density profiles during evening hours. ACKNOWLEDGEMENTS The author is thankful to Prof. Satya Prakash for useful scientific discussions.The project was supported by Dept. of Space,Covt.of India.
Profiles in Equatorial F-Region
(6)71
REFERENCES 1.
2.
3. 4.
F.A.Morse, B.C.Edgar, H.C.Koons, C.J.Rice, W.J.Heikkila,J.B.Hofmann, B.A.Tinsley, J.A.Winningham, A.B.Christensen, R.F.Woodman ,J.Pomalaza and N.R.Teixeira,J.Geophys.Res. 82,578 (1977). M.C.Kelley, G.Haerendel, H.Kappler, A.Valenzuela, B.B.Balsley, D.A.Carter, W.L.Ecklund, C.W.Carlson, B.Hansler and R.Torhet, Geophys.Res.Lett. 3,2148(1977). S.Prakash, S.Pal, R.Pandey and B.H.Subbaraya, Adv.Space Res.2,10, 195 (1983). S.Prakash and S.Pal, Adv.Space Res.5, 7, 39 (1985).