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Variation of ionospheric electron and ion temperatures during periods of minimum to maximum solar activity by the SROSS-C2 satellite over Indian low and equatorial latitudes
Available online at www.sciencedirect.com
Advances in Space Research 45 (2010) 294–302 www.elsevier.com/locate/asr
Review
Variation of ionospheric electron and ion temperatures during periods of minimum to maximum solar activity by the SROSS-C2 satellite over Indian low and equatorial latitudes P.K. Sharma a, P.P. Pathak a, D.K. Sharma b,*, Jagdish Rai c a
Department of Physics, Gurukula Kangri Vishwavidyalaya, Haridwar 249404, India Department of Applied Sciences & Humanities, MRCE, Faridabad 121001, India c Department of Physics, Indian Institute of Technology, Roorkee 247 667, India
b
Received 17 January 2009; received in revised form 30 July 2009; accepted 3 August 2009
Abstract To study the variation of ionospheric electron and ion temperatures with solar activity the data of electron and ion temperatures were recorded with the help of Retarding Potential Analyzer payload aboard Indian SROSS-C2 satellite at an average altitude of 500 km. The main focuses of the paper is to see the diurnal, seasonal and latitudinal variations of electron and ion temperatures during periods of minimum to maximum solar activity. The ionospheric temperatures in the topside show strong variations with altitude, latitude, season and solar activity. In present study, the temperature variations with latitude, season and solar activity have been studied at an average altitude 500 km. The peak at sunrise has been observed during all seasons, in both electron and ion temperatures. Further, the ionospheric temperatures vary with latitude in day time. The latitudinal variation is more pronounced for low solar activity than for high solar activity. Ó 2009 COSPAR. Published by Elsevier Ltd. All rights reserved. Keywords: Electron and ion temperatures; F2 region; Low latitude; Solar activity; Satellite observation
Contents 1. 2. 3.
Introduction . . . . . . . Results and discussion Conclusions. . . . . . . . References . . . . . . . .
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1. Introduction The solar activity has been studied for long by geophysicists and solar physicists with its conspicuous 11 year cycle. The change in ionospheric parameters may affect the radio communication, navigation, exploration of near Earth space electronic system in satellites and spacecraft. For measuring the ionospheric temperatures, the principal *
Corresponding author. Tel.: +91 129 4198513; fax: +91 129 4198111. E-mail address: dksphdes@rediffmail.com (D.K. Sharma).
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instruments are ground-based incoherent scatter radars and satellite in situ probes (Langmuir probe and Retarding Potential Analyzer). Temperature measurements with both techniques began in the early sixties and both techniques have been continuously improved and refined over the past decades. The changes in instrument design and data analysis, however, pose a problem for studies which investigate the long-term trends in parameters measured by these instruments. Namely, part of the changes seen may be due to improved accuracy rather than dependence on solar activity (Bilitza and Hoegy, 1990; Bilitza et al., 2007). Bili-
0273-1177/$36.00 Ó 2009 COSPAR. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.asr.2009.08.001
P.K. Sharma et al. / Advances in Space Research 45 (2010) 294–302
tza and Hoegy (1990) have studied that the ion temperature and its dependence on solar activity are determined by the close coupling with the neutrals and their temperatures at low altitudes and with electron at high altitudes. The ionospheric electron gas exhibits a rather complex thermal response pattern to changing solar activity. By using the satellite probe measurement from AE-C and DE-2 they found that the positive correlation between electron temperature and solar activity at high altitudes. Incoherent scatter measurements have shown that the response of electron temperature to changes in solar activity depends on season and is different for day and night (Bilitza and Hoegy, 1990). Measurement of ionospheric electron and ion temperatures give an insight into the energy balance of the ionosphere–thermosphere regime. Features of electron temperature have been studied using measurements from incoherent scatter radar (McClure, 1969, 1971; Mahajan, 1977; Oliver et al., 1991; Otsuka et al., 1998; Zhang and Holt, 2004; Lei et al., 2007), rocket probes (Oyama et al., 1980, 1996) and satellite based instruments (Brace et al., 1967; Sharma et al., 2003; Rich et al., 2003). Brace and Theis (1981) and Triskova et al. (1996) had empirical models of electron temperature in the ionosphere and lower plasmasphere. Schunk and Nagy (1978) have presented a review article on the electron temperature in F-region of ionosphere. Richards and Torr (1986) and Watanabe et al. (1995) theoretically studied the temperature variations in the ionosphere and plasmasphere. Su et al. (1995), Oyama et al. (1996) and Balan et al. (1996a,b) used Sheffield University Plasmasphere Ionosphere model, SUPIM to investigate the temperature measurements made by Hinotori and Exos D satellites. A Japanese ‘Hinotori’ satellite which had a nearly circular orbit at 600 km with an orbital inclination of 30° provided an ideal database for study of the temporal and spatial variations of the electron density and temperature in the topside ionosphere (Watanabe and Oyama, 1996; Oyama et al., 1985; Suhasini et al., 2001; Balan et al., 1997). But the Hinotori data are limited to a period of medium and high solar activity. Watanabe and Oyama (1996) studied the electron temperature observed by the Hinotori satellite in terms of local time, season, latitude magnetic inclination and the solar flux intensity for a 16 month period during 1981–1982. They found that the electron temperature shows a steep rise in the early morning, a decrease after that and again an increase at 18:00 h LT. Hanson et al. (1973) observed the electron and ion temperatures with the OGO-6 satellite near the magnetic equator above 500 km altitude. They showed that equatorial troughs of electron and ion temperatures occur in the topside ionosphere during nighttime. Plasma cooling was also measured by the ISS-b satellite at 1100 km altitude (Sagawa et al., 1981). From last decade ionospheric temperatures and composition anomalies over equatorial and low latitudes have been studied through the completion of many satellite missions like Atmospheric Explorer, Dynamic Explorer, ISIS,
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AEROS, TAIYO, etc. But the data base, to study these anomalies over the Indian region, is sparse. Another advantage of SROSS-C2 mission is that the orbit is just above the F-region electron density peak and the orbital ellipticity is much less. Many researchers (Bhuyan et al., 2002, 2004, 2006; Aggarwal et al., 2009) have also used the SROSS-C2 satellite data to study the behavior of ionospheric parameters. Bhuyan et al. (2004) studied the diurnal, seasonal and latitudinal variations of the ion temperature using the SROSS-C2 satellite data in the Indian zone equatorial and low latitude ionosphere at an average altitude 500 km. They found that the pre-sunrise enhancement in the ion temperature in between 4:00 and 6:00 LT and also found that an afternoon enhancement of lower amplitude is also observed in summer season. Aggarwal et al. (2009) have studies of electron and ion temperatures at 500 km altitude during the sunrise using the same satellite data set as that in the present study. They found that in winter the morning overshoot in electron temperature enhances to 4000 K is observed around 6:00 LT during low solar activity and it was slightly lower during higher solar activity. In summer, it is observed around 5:30 LT, but the rate of electron temperature enhancement is higher during moderate solar activity than low solar activity. During equinox, this phenomena is delayed and is observed around 6:00 LT during all three phases of solar activity. Present study is different from that of the study of other researcher (Bhuyan et al., 2002, 2004, 2006; Aggarwal et al., 2009) in various aspects using the same satellite data set. Aggarwal et al. (2009) chose the data only for sunrise period for the equatorial region from 10°S to 20°N. However, in the present study we have chosen the satellite data for whole Indian region (from 5°S to 20°N geomagnetic latitude and from 137°E to 168°E geomagnetic longitude) to study the variation of ionospheric electron and ion temperatures during minimum to maximum solar activity. This region was chosen on the basis of maximum passes of SROSS-C2 over India. Bhuyan et al. (2004, 2006) have chosen the same study region as that by Aggarwal et al. (2009) to study the diurnal, seasonal and latitudinal variations of electron and ion temperatures. Bhuyan et al. (2004) have also studied the latitudinal variation during day time for the year from 1994 to 1998. However, in the present study the latitudinal variation has also been studied during the quiet time (nighttime) along with the standard deviation for the year 1995 (solar minimum) to 2000 (solar maximum) for whole Indian region. The aim of the present study is to study the diurnal, seasonal and latitudinal variations of the ionospheric electron and ion temperatures during the low solar activity period (1995) to high solar activity (2000) using the data recorded by the SROSS-C2 satellite. The ionospheric electron and ion temperatures were measured with the help of Retarding Potential Analyzer (RPA) payload aboard the Stretched Rohini Series Satellite (SROSS-C2), which was launched by Indian Space Research Organization (ISRO) on May
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4, 1994 to study the ionospheric composition and temperature anomalies. The details and description of RPA payload aboard SROSS-C2 satellite are given by Garg and Das (1995) and Bhuyan et al. (2006). The satellite data have been selected over the Indian region from 5°S to 20°N geomagnetic latitude and from 137°E to 168°E geomagnetic longitude, which covers the maximum pass of the SROSS-C2 satellite over India. The measured electron and ion RPA data have been analyzed for three different seasons; summer (May, June, July and August), winter (November, December, January and February) and equinoxes (March, April, September and October) for the low solar activity period to high solar activity to study the diurnal, seasonal and latitudinal behavior of electron and ion temperatures. The maximum permissible error is ±50 K within the temperature range from 500 to 5000 K of the RPA measurements. 2. Results and discussion To study the diurnal, seasonal and latitudinal variations of electron and ion temperatures, the SROSS-C2 satellite data from low solar activity (1995) to high solar activity (2000) have been analyzed over Indian region. Figs. 1 and 2 show the diurnal variation of electron and ion temperature for half of the solar cycle, respectively. Fig. 1(a) 5000
Electron Temperature, K
4000
shows the electron temperature for the solar minimum year (1995) and found the electron temperature rises sharply at the time of sunrise and decreases as the day progress. A secondary enhancement has also been found at the time of sunset. The peak of evening enhancement is lower in magnitude than the sunrise peak. Similar enhancements have been found towards increasing the solar activity; the same have been represented in Fig. 1(b–f) for remaining years. The enhancement in the peak value of electron temperature during the time of sunrise is decreased as the solar activity increases. The diurnal variations of ion temperature have been represented in the Fig. 2(a–f) for the low solar activity period to high solar activity, respectively. The average solar activity (F10.7) has been mentioned in all the figures. The measured RPA data have been divided into three different seasons, viz. summer (May, June, July and August), winter (November, December, January and February) and equinoxes (Mach, April, September and October) for the solar minimum year to solar maximum for studying the seasonal effect on ionospheric electron and ion temperatures. However, we have chosen to present 2 year solar minimum year (1995) and solar maximum (2000) for three different seasons viz. summer, winter and equinox only to reduce the number of figures and improve the presentation quality. The left panel in Fig. 3(a–c) shows the diurnal variation of electron temperature for solar min5000
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Local Time, hrs Fig. 1. Dirunal variation of electron temperature for different years (a) 1995, (b) 1996, (c) 1997, (d) 1998, (e) 1999, (f) 2000, measured by SROSS-C2 satellite at an altitude 500 km.
P.K. Sharma et al. / Advances in Space Research 45 (2010) 294–302 2500
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Local Time, hrs Fig. 2. Dirunal variation of ion temperature for different years (a) 1995, (b) 1996, (c) 1997, (d) 1998, (e) 1999, (f) 2000, measured by SROSS-C2 satellite at an altitude 500 km.
imum year (1995) and right panel [Fig. 3(d–f)] for solar maximum year (2000) for three different seasons, respectively. Similarly, the ion temperature shown in Fig. 4(a–c) left panel for solar minimum and right panel in Fig. 4(d– f) solar maximum for aforesaid seasons, respectively. Fig. 3 shows the clear peak during the sunrise hours and also a diffuse peak corresponding to the secondary enhancement in electron temperature during the evening hours. However, for ion temperature, the sunrise peak and evening temperature enhancements (Fig. 4) are smaller than those for the electron temperature. Smoothing of the measured temperature variations have been done by computing hourly averages and calculating their standard deviations; these are presented in all figures for the electron and ion temperatures, respectively. It has been observed that the electron temperature rises sharply during the sunrise hours (5:30–6:30 LT), and a secondary enhancement has also been observed during the sunset hours (16:30–17:30 LT) for all seasons from solar minimum year to maximum. However, the ion temperature rises sharply during sunrise hours (6:30–7:30 LT), which is one hour late comparing to the electron temperature because it is much heavier than electron. The secondary enhancement is observed during the sunset as the same hour as that of electron temperature. A similar pre-sunrise ion temperature enhancement in the low and mid latitude ionosphere at 600 km has been reported by Chao et al. (2003).
During summer of solar minimum year (1995), the average electron temperature (Fig. 3a) at sunrise rises to over 3700 K from the nighttime average temperature of 850 K, whereas the evening temperature is enhanced to 2500 K during the secondary enhancement near sunset. Similar enhancements have also been observed during the winter and equinoxes seasons at the time of sunrise and sunset. In the winter, the average electron temperature (Fig. 3b) at sunrise rises to over 3500 K from the nighttime average temperature of 817 K, whereas the evening temperature rises to 1900 K during the secondary enhancement at sunset. During the equinoxes, the average electron temperature (Fig. 3c) at sunrise rises to over 4100 K from the nighttime average temperature of 830 K, whereas the evening temperature is enhanced to almost 2100 K during the secondary enhancement at the time of sunset. However, it was for solar maximum year (2000) in summer the average electron temperature (Fig. 3d) at sunrise less than 2900 K from the midnight average temperature 1050 K, whereas the evening temperature is enhanced to 1700 K during the secondary enhancement near sunset. In the winter, the average electron temperature (Fig. 3e) at sunrise rises to over 2950 K from the nighttime average temperature of 1080 K, whereas the evening temperature rises to 1577 K during the secondary enhancement at sunset. During the equinoxes, the average electron temperature (Fig. 3f) at sunrise rises to over 3300 K from the nighttime average tempera-
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Local Time, hrs Fig. 3. Left panel shows the diurnal variation of electron temperature for solar minimum (1995) and right panel for solar maximum (2000) for three different seasons: summer, winter and equinoxes, respectively.
ture of 1100 K, whereas the evening temperature is enhanced to almost 1680 K during the secondary enhancement at the time of sunset. The annual and seasonal average electron and ion temperatures during nighttime, maximum at sunrise and maximum at sunset for half of the solar cycle are shown in Tables 1a and 1b, respectively. The average ion temperature during summer of solar minimum year (1995) is shown in Fig. 4a at sunrise rises to 1350 K from the nighttime average temperature of 630 K, whereas the evening temperature is enhanced to 1500 K during the secondary enhancement near sunset. Similar enhancements have also been observed during the winter and equinoxes seasons at the time of sunrise and sunset. In the winter, the average ion temperature (Fig. 4b) at sunrise rises to over 1750 K from the nighttime average temperature of 700 K, whereas the evening temperature rises to 1100 K during the secondary enhancement at sunset. During the equinoxes, the average electron temperature (Fig. 4c) at sunrise rises to over 1513 K from the nighttime average temperature of 700 K, whereas the evening temperature is enhanced to almost 1200 K during the secondary enhancement at the time of sunset. However, it was for solar maximum year (2000) in summer the average ion temperature (Fig. 4d) at sunrise rises to over 1200 K from the midnight average temperature 930 K, whereas the evening temperature is enhanced to 1330 K during
the secondary enhancement near sunset. In the winter, the average ion temperature (Fig. 4e) at sunrise rises to over 1180 K from the nighttime average temperature of 970 K, whereas the evening temperature rises to 1200 K during the secondary enhancement at sunset. During the equinoxes, the average ion temperature (Fig. 4f) at sunrise rises to over 1150 K from the nighttime average temperature of 1000 K, whereas the evening temperature is enhanced to almost 1300 K during the secondary enhancement at the time of sunset. To study the latitudinal variation the data from the electron and ion RPAs have been analyzed for electron and ion temperatures for different orbits. Those orbits falling near to 12:00 noon and 24:00 midnight local time are considered for the study of latitudinal variation of electron and ion temperatures. The electron and ion temperatures data are analyzed over 1° bins in the geomagnetic latitude range from 5°S to 20°N, and plotted along with the standard deviation in Figs. 5 and 6. The latitudinal variations of the electron temperature near 500 km at 12:00 noon are shown in left panel of Fig. 5(a–c) for different seasons of the solar minimum year and right panel in Fig. 5(d–f) for solar maximum year. Similarly, for ion temperature variations are shown in Figs. 6, left panel for solar minimum year and the right panel for solar maximum year at 12:00 noon for all the above mentioned seasons. The electron
P.K. Sharma et al. / Advances in Space Research 45 (2010) 294–302 2500
Ion Temperature, K
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Local Time, hrs Fig. 4. Left panel shows the diurnal variation of ion temperature for solar minimum (1995) and right panel for solar maximum (2000) for three different seasons: summer, winter and equinoxes, respectively.
and ion temperature variations with latitude during nighttime are negligible, falling within the maximum error limit ±50 K of the measurements. However, there is a latitudinal variation in the electron daytime temperature. The maximum variation in electron temperature is observed during summer and the minimum during the equinoxes. It was further decreased toward increasing the solar activity. The latitudinal variations of electron temperature from 5°S to 20°N geomagnetic latitude over the Indian region show a positive correlation during low solar activity and decrease towards high solar activity. However, the latitudinal variations of ion temperature over the studied region are less than the corresponding variations in electron temperature. In the present work, we have not carried out any modeling study for theoretical calculation of the change in the iono-
spheric temperatures. The model calculations by Oyama et al. (1996) suggested that the possible mechanism for the ionospheric temperature enhancements is the downward drift of plasma, which varies with time of day, season and latitude. It has also been found that, during sunrise, the overshoot of the plasma downward drift velocity is a maximum, which explains the morning overshoot (Oyama et al., 1996). Brace et al. (1987) have studied the ionospheric electron temperature during high solar activity from 1981 to 1982 using the data of Dynamics Explorer-2 (DE-2) satellite data at altitude between 300 and 400 km. They found that during high solar activity the electron temperature strongly increased with latitude above about 40°. They also calculate that the day time electron temperature near the F2 peak is more responsive to short term variations in F10.7
Table 1a Annual average electron and ion temperatures during nighttime, maximum at sunrise and maximum at sunset from low solar activity to high solar activity. S. no.
1. 2. 3. 4. 5. 6.
Year
1995 1996 1997 1998 1999 2000
Electron temperature (K)
Ion temperature (K)
Avg. at Nighttime
Maximum at sunrise
Maximum at sunset
Avg. at Nighttime
Maximum at sunrise
Maximum at sunset
833 753 780 927 1014 1083
3812 3423 3326 3399 3178 3029
2171 1737 1637 2023 1648 1640
694 636 650 795 871 977
1524 1589 1470 1428 1200 1183
1226 1207 1164 1233 1244 1274
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Table 1b Seasonal average electron and ion temperatures during nighttime, maximum at sunrise and maximum at sunset from low solar activity to high solar activity. S. no.
Year
Seasons
1.
1995
Summer Winter Equinox
2.
1996
3.
Electron temperature (K) Avg. at Nighttime
Ion temperature (K)
Maximum at sunrise
Maximum at sunset
844 817 832
3742 3494 4131
2508 1922 2081
Summer Winter Equinox
702 781 733
3428 3381 3452
1997
Summer Winter Equinox
744 788 752
4.
1998
Summer Winter Equinox
5.
1999
6.
2000
Maximum at sunrise
Maximum at sunset
655 700 701
1344 1743 1513
1530 1065 1191
1988 1687 1541
613 646 617
1202 2133 1490
1499 1029 1136
3390 3025 3389
1951 1389 1563
607 637 635
1168 1497 1706
1594 932 1069
904 925 886
2859 3329 3886
2050 2057 1987
803 774 768
1089 1704 1272
1397 1078 1211
Summer Winter Equinox
975 1056 979
3262 3131 3113
1501 1745 1576
852 886 827
1090 1428 1245
1334 1216 1193
Summer Winter Equinox
1043 1084 1105
2882 2962 3300
1705 1577 1682
930 970 1007
1208 1183 1154
1337 1217 1300
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Geomagnetic Latitude, deg. Fig. 5. Left panel shows the latitudinal variation of electron temperature for solar minimum (1995) and right panel for solar maximum (2000) for three different seasons: summer, winter and equinoxes, respectively.
P.K. Sharma et al. / Advances in Space Research 45 (2010) 294–302 2500
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Geogmagnetic Latitude, deg. Fig. 6. Left panel shows the latitudinal variation of ion temperature for solar minimum (1995) and right panel for solar maximum (2000) for three different seasons: summer, winter and equinoxes, respectively.
than to any long-term changes that may occur between solar minimum to solar maximum. An empirical model of the electron and ion temperatures is presented in the altitude interval 50–4000 km as a function of time, space and solar flux by using observations of six satellites, five incoherent scatter stations and rocket measurements given by Kohnlein (1986). Mahajan and Pandey (1979) used electrostatics probe measurements of electron temperature from the ISIS-1 satellite for the equinox season of high solar activity years 1969 and 1970 are analyzed for the 1000 km altitude and compared the results with the Explorer-22 satellite measurements of electron temperature for the years 1965– 1967. They found that the large solar activity changes the latitudinal profiles of the electron temperature during both day and night. At low and mid latitudes, the electron temperature increases from about 2000 K to about 3500 K for the day time and from about 800 K to about 1700 K during the nighttime between low and high solar activity conditions. At high latitude there is an increase in electron temperature by about a factor of 2 from low to high solar activity period. Truhlik et al. (2009) have studied the latitudinal variation of the topside electron temperature at different levels of solar activity (low, medium and high). They have used a large database of most of the available satellite measurements in the topside ionosphere for studying the solar activity varia-
tions of the electron temperature at different latitudes, altitudes, local times and seasons. They found the small changes in electron temperature with solar activity. These changes in electron temperature were comparable in magnitude with seasonal changes but much smaller than the changes with altitude, latitude and from day to night. 3. Conclusions The diurnal, seasonal and latitudinal variations of electron and ion temperatures have been studied using data from the SROSS-C2 satellite during the low solar activity period to high solar activity over the low and equatorial latitude Indian region. This study shows that the electron and ion temperatures are lowest during the night and show variations during the daytime in all seasons. The daytime electron temperature shows at least two clear maximum values, with different magnitudes. The peak during sunrise is relatively sharp and larger, whereas the other peak during sunset is diffuse and smaller also. The enhancement in the peak value of electron and ion temperatures during the time of sunrise is decreased as the solar activity increases. A smaller variation in the ion temperature has also been observed. The electron temperature increases with increasing latitude during the daytime, whereas there are no latitudinal variations at night over the Indian region studied at 500 km altitude. The maximum variation in
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electron temperature is observed during summer and minimum during equinoxes. It was further decreased toward increasing the solar activity. However, the latitudinal variations of ion temperature over the studied region are less than the corresponding variations in electron temperature. The change in ionospheric temperatures may be related to diurnal, seasonal and latitudinal variations of the downward drift of plasma. References Aggarwal, Malini, Joshi, H.P., Iyer, K.N., Jivani, M.N. Studies of electron and ion temperatures at 500 km altitude during sunrise using Indian SROSS C2 satellite. Adv. Space Res. 43 (2), 273–281, 2009. Balan, N., Oyama, K.I., Bailey, G.J., Abe, T. Plasmasphere electron temperature studies using satellite observations and a theoretical model. J. Geophys. Res. 101, 15323–15330, 1996a. Balan, N., Oyama, K.I., Bailey, G.J., Abe, T. Plasmasphere electron temperature profiles and the effects of photoelectron trapping and an equatorial high altitude heat source. J. Geophys. Res. 101, 21689– 21696, 1996b. Balan, N., Oyama, K.I., Bailey, G.J., Fukao, S., Watanabe, S., Abdu, M.A. A plasma temperature anomaly in the equatorial topside ionosphere. J. Geophys. Res. 102, 7485–7492, 1997. Bhuyan, P.K., Chamua, M., Subrahmanyam, P., Garg, S.C. Diurnal, seasonal and latitudinal variations of electron temperature measured by the SROSS C2 satellite at 500 km altitude and comparison with the IRI. Ann. Geophys. 20 (6), 807–815, 2002. Bhuyan, P.K., Chamua, M., Subrahmanyam, P., Garg, S.C. Diurnal, seasonal and latitudinal variations of ion temperature measured by the SROSS C2 satellite in the Indian zone equatorial and low latitude ionosphere and comparison with the IRI. J. Atmos. Solar Terres. Phys. 66 (3–4), 301–312, 2004. Bhuyan, P.K., Chamua, M., Subrahmanyam, P., Garg, S.C. Effect of solar activity on diurnal and seasonal variations of electron temperature measured by the SROSS C2 over Indian low latitudes. Adv. Space Res. 37 (5), 885–891, 2006. Bilitza, D., Hoegy, W.R. Solar activity variation of ionospheric plasma temperatures. Adv. Space Res. 10, 81–90, 1990. Bilitza, D., Truhlik, V., Richards, P., Abe, T., Triskova, L. Solar cycle variations of mid-latitude electron density and temperature: satellite measurements and model calculations. Adv. Space Res. 39 (5), 779– 789, 2007. Brace, L.H., Reddy, B.M., Mayr, H.G. Global behavior of the ionosphere at 1000 kilometer altitudes. J. Geophys. Res. 72, 265– 283, 1967. Brace, L.H., Theis, R.F. Global empirical models of ionospheric temperature in the upper F region and Plasmasphere based on in situ measurements from the Atmospheric Explorer-C, ISIS-1 and ISIS-2 satellites. J. Atoms. Terres. Phys. 43, 1317–1343, 1981. Brace, L.H., Theis, R.F., Hoegy, W.R. Ionospheric electron temperature at solar maximum. Adv. Space Res. 7 (6), 99–106, 1987. Chao, C.K., Su, Y., Yeh, H.C. Pre-sunrise ion temperature enhancement observed at 600 km low and mid-latitude ionosphere. Geophys. Res. Lett. 30, 1187–1190, 2003. Garg, S.C., Das, U.N. Aeronomy experiment on SROSS-C2. J. Spacecraft Technol. 5, 11–15, 1995. Hanson, W.B., Nagy, A.F., Moffett, R.J. Ogo 6 measurements of super cooled plasma in the equatorial exosphere. J. Geophys. Res. 78, 751– 756, 1973. Kohnlein, W. A model of the electron and ion temperatures in the ionosphere. Planet. Space Sci. 34 (7), 609–630, 1986. Lei, J., Roble, R.G., Wang, W., Emery, B.A., Zhang, S.R. Electron temperature climatology at Millstone Hill and Arecibo. J. Geophys. Res. 112. A02302-1–A02302-11, 2007.
Mahajan, K.K. Models of electron temperature in the ionosphere Fregion using electron density height profiles. J. Atmos. Terres. Phys. 39, 637–639, 1977. Mahajan, K.K., Pandey, V.K. Solar-activity changes in the electrontemperature at 1000-km altitude from the Langmuir probe measurements on Isis-1 and Explorer-22 Satellites. J. Geophys. Res. 84, 5885– 5889, 1979. McClure, J.P. Diurnal variation of neutral and charged particle temperature in the equatorial F-region. J. Atmos. Solar Terres. Phys. 74, 279– 291, 1969. McClure, J.P. Thermospheric temperature variation inferred from incoherent scatter observations. J. Geophys. Res. 76, 3106–3115, 1971. Oliver, W.M., Takami, T., Fukao, S., Sato, T., Yamamoto, M., Thuda, T., Nakamura, T., Kato, S. Measurement of ionospheric and thermospheric temperatures and densities with the middle and upper atmosphere radar. J. Geophys. Res. 96, 17827–17838, 1991. Otsuka, Y., Kawamura, S., Balan, N., Fukao, S., Bailey, G.J. Plasma temperature variations in the ionosphere over the middle and upper atmosphere radar. J. Geophys. Res. 103, 20705–20713, 1998. Oyama, K.I., Hirao, K., Banks, P.M., Williumson, P.R. Is Te equal to Tn at the heights of 100–120 km? Planet. Space Sci. 28, 207–211, 1980. Oyama, K.I., Hirao, K., Yasuhara, F. Electron temperature probe on board Japan’s 9th scientific satellite OHZORA. J. Geomagn. Geoelectr. 37, 413–430, 1985. Oyama, K.I., Balan, N., Watanabe, S., Takahashi, T., Isoda, F., Bailey, G.J., Oya, H. Morning overshoot of Te enhanced by downward plasma drift in the equatorial topside ionosphere. J. Geomagn. Geoelectr. 22, 959–966, 1996. Rich, F.J., Sultan, P.J., Burke, W.J. The 27-day variations of plasma densities and temperatures in the topside ionosphere. J. Geophys. Res. 108, 1297–1305, 2003. Richards, P.G., Torr, D.G. Thermal coupling of conjugate ionosphere and the tilt of the earth’s magnetic field. J. Geophys. Res. 91, 9017–9025, 1986. Sagawa, E., Miyazaki, S., Mori, H. Night time electron temperature troughs in the equatorial topside ionosphere revealed from PRA experiments on the ISS-b satellite. J. Atmos. Solar Terres. Phys. 43, 1165–1173, 1981. Schunk, R.W., Nagy, A.F. Electron temperatures in F-region of ionosphere – theory and observations. Rev. Geophys. 16 (3), 355– 399, 1978. Sharma, D.K., Rai, J., Israil, M., Shalni, P., Subrahmanyam, P., Chopra, P., Garg, S.C. Sunrise effect on ionospheric temperature as measured by SROSS-C2 satellite. J. Ind. Geophys. Union 7, 117–123, 2003. Su, Y.Z., Oyama, K.I., Bailey, G.J., Takahashi, T., Watanabe, S. Comparison of satellite electron density and temperature measurements at low latitudes with a plasmasphere-ionosphere model. J. Geophys. Res. 100, 14591–14604, 1995. Suhasini, R., Raghavarov, R., Mayr, H.G., Hoegy, W.R., Wharton, L.E. Equatorial temperature anomaly during solar minimum. J. Geophys. Res. 106, 24777–24783, 2001. Triskova, L., Smilaver, J., Truhlik, V., Afonon, V.V. On the low latitude topside models: II. Electron temperature. Adv. Space Res. 18, 213–216, 1996. Truhlik, V., Bilitza, D., Triskova, L. Latitudinal variation of the topside electron temperature at different levels of solar activity. Adv. Space Res. 44 (6), 693–700, 2009. Watanabe, S., Oyama, K.I., Abdu, M.A. Computer simulation of electro´n and ion densities and temperaturas in the equitorial F-region and comparision with Hinotori results. J. Geophys. Res. 100, 14581–14590, 1995. Watanabe, S., Oyama, K.I. Effect of neutral wind on the electron temperature at a height of 600 km in the low latitude region. Ann. Geophys. 14, 290–296, 1996. Zhang, S.R., Holt, J.M. Ionospheric plasma temperatures during 1976– 2001 over Millstone Hill. Adv. Space Res. 33, 963–969, 2004.
Advances in Space Research 45 (2010) 294–302 www.elsevier.com/locate/asr
Review
Variation of ionospheric electron and ion temperatures during periods of minimum to maximum solar activity by the SROSS-C2 satellite over Indian low and equatorial latitudes P.K. Sharma a, P.P. Pathak a, D.K. Sharma b,*, Jagdish Rai c a
Department of Physics, Gurukula Kangri Vishwavidyalaya, Haridwar 249404, India Department of Applied Sciences & Humanities, MRCE, Faridabad 121001, India c Department of Physics, Indian Institute of Technology, Roorkee 247 667, India
b
Received 17 January 2009; received in revised form 30 July 2009; accepted 3 August 2009
Abstract To study the variation of ionospheric electron and ion temperatures with solar activity the data of electron and ion temperatures were recorded with the help of Retarding Potential Analyzer payload aboard Indian SROSS-C2 satellite at an average altitude of 500 km. The main focuses of the paper is to see the diurnal, seasonal and latitudinal variations of electron and ion temperatures during periods of minimum to maximum solar activity. The ionospheric temperatures in the topside show strong variations with altitude, latitude, season and solar activity. In present study, the temperature variations with latitude, season and solar activity have been studied at an average altitude 500 km. The peak at sunrise has been observed during all seasons, in both electron and ion temperatures. Further, the ionospheric temperatures vary with latitude in day time. The latitudinal variation is more pronounced for low solar activity than for high solar activity. Ó 2009 COSPAR. Published by Elsevier Ltd. All rights reserved. Keywords: Electron and ion temperatures; F2 region; Low latitude; Solar activity; Satellite observation
Contents 1. 2. 3.
Introduction . . . . . . . Results and discussion Conclusions. . . . . . . . References . . . . . . . .
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1. Introduction The solar activity has been studied for long by geophysicists and solar physicists with its conspicuous 11 year cycle. The change in ionospheric parameters may affect the radio communication, navigation, exploration of near Earth space electronic system in satellites and spacecraft. For measuring the ionospheric temperatures, the principal *
Corresponding author. Tel.: +91 129 4198513; fax: +91 129 4198111. E-mail address: dksphdes@rediffmail.com (D.K. Sharma).
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instruments are ground-based incoherent scatter radars and satellite in situ probes (Langmuir probe and Retarding Potential Analyzer). Temperature measurements with both techniques began in the early sixties and both techniques have been continuously improved and refined over the past decades. The changes in instrument design and data analysis, however, pose a problem for studies which investigate the long-term trends in parameters measured by these instruments. Namely, part of the changes seen may be due to improved accuracy rather than dependence on solar activity (Bilitza and Hoegy, 1990; Bilitza et al., 2007). Bili-
0273-1177/$36.00 Ó 2009 COSPAR. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.asr.2009.08.001
P.K. Sharma et al. / Advances in Space Research 45 (2010) 294–302
tza and Hoegy (1990) have studied that the ion temperature and its dependence on solar activity are determined by the close coupling with the neutrals and their temperatures at low altitudes and with electron at high altitudes. The ionospheric electron gas exhibits a rather complex thermal response pattern to changing solar activity. By using the satellite probe measurement from AE-C and DE-2 they found that the positive correlation between electron temperature and solar activity at high altitudes. Incoherent scatter measurements have shown that the response of electron temperature to changes in solar activity depends on season and is different for day and night (Bilitza and Hoegy, 1990). Measurement of ionospheric electron and ion temperatures give an insight into the energy balance of the ionosphere–thermosphere regime. Features of electron temperature have been studied using measurements from incoherent scatter radar (McClure, 1969, 1971; Mahajan, 1977; Oliver et al., 1991; Otsuka et al., 1998; Zhang and Holt, 2004; Lei et al., 2007), rocket probes (Oyama et al., 1980, 1996) and satellite based instruments (Brace et al., 1967; Sharma et al., 2003; Rich et al., 2003). Brace and Theis (1981) and Triskova et al. (1996) had empirical models of electron temperature in the ionosphere and lower plasmasphere. Schunk and Nagy (1978) have presented a review article on the electron temperature in F-region of ionosphere. Richards and Torr (1986) and Watanabe et al. (1995) theoretically studied the temperature variations in the ionosphere and plasmasphere. Su et al. (1995), Oyama et al. (1996) and Balan et al. (1996a,b) used Sheffield University Plasmasphere Ionosphere model, SUPIM to investigate the temperature measurements made by Hinotori and Exos D satellites. A Japanese ‘Hinotori’ satellite which had a nearly circular orbit at 600 km with an orbital inclination of 30° provided an ideal database for study of the temporal and spatial variations of the electron density and temperature in the topside ionosphere (Watanabe and Oyama, 1996; Oyama et al., 1985; Suhasini et al., 2001; Balan et al., 1997). But the Hinotori data are limited to a period of medium and high solar activity. Watanabe and Oyama (1996) studied the electron temperature observed by the Hinotori satellite in terms of local time, season, latitude magnetic inclination and the solar flux intensity for a 16 month period during 1981–1982. They found that the electron temperature shows a steep rise in the early morning, a decrease after that and again an increase at 18:00 h LT. Hanson et al. (1973) observed the electron and ion temperatures with the OGO-6 satellite near the magnetic equator above 500 km altitude. They showed that equatorial troughs of electron and ion temperatures occur in the topside ionosphere during nighttime. Plasma cooling was also measured by the ISS-b satellite at 1100 km altitude (Sagawa et al., 1981). From last decade ionospheric temperatures and composition anomalies over equatorial and low latitudes have been studied through the completion of many satellite missions like Atmospheric Explorer, Dynamic Explorer, ISIS,
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AEROS, TAIYO, etc. But the data base, to study these anomalies over the Indian region, is sparse. Another advantage of SROSS-C2 mission is that the orbit is just above the F-region electron density peak and the orbital ellipticity is much less. Many researchers (Bhuyan et al., 2002, 2004, 2006; Aggarwal et al., 2009) have also used the SROSS-C2 satellite data to study the behavior of ionospheric parameters. Bhuyan et al. (2004) studied the diurnal, seasonal and latitudinal variations of the ion temperature using the SROSS-C2 satellite data in the Indian zone equatorial and low latitude ionosphere at an average altitude 500 km. They found that the pre-sunrise enhancement in the ion temperature in between 4:00 and 6:00 LT and also found that an afternoon enhancement of lower amplitude is also observed in summer season. Aggarwal et al. (2009) have studies of electron and ion temperatures at 500 km altitude during the sunrise using the same satellite data set as that in the present study. They found that in winter the morning overshoot in electron temperature enhances to 4000 K is observed around 6:00 LT during low solar activity and it was slightly lower during higher solar activity. In summer, it is observed around 5:30 LT, but the rate of electron temperature enhancement is higher during moderate solar activity than low solar activity. During equinox, this phenomena is delayed and is observed around 6:00 LT during all three phases of solar activity. Present study is different from that of the study of other researcher (Bhuyan et al., 2002, 2004, 2006; Aggarwal et al., 2009) in various aspects using the same satellite data set. Aggarwal et al. (2009) chose the data only for sunrise period for the equatorial region from 10°S to 20°N. However, in the present study we have chosen the satellite data for whole Indian region (from 5°S to 20°N geomagnetic latitude and from 137°E to 168°E geomagnetic longitude) to study the variation of ionospheric electron and ion temperatures during minimum to maximum solar activity. This region was chosen on the basis of maximum passes of SROSS-C2 over India. Bhuyan et al. (2004, 2006) have chosen the same study region as that by Aggarwal et al. (2009) to study the diurnal, seasonal and latitudinal variations of electron and ion temperatures. Bhuyan et al. (2004) have also studied the latitudinal variation during day time for the year from 1994 to 1998. However, in the present study the latitudinal variation has also been studied during the quiet time (nighttime) along with the standard deviation for the year 1995 (solar minimum) to 2000 (solar maximum) for whole Indian region. The aim of the present study is to study the diurnal, seasonal and latitudinal variations of the ionospheric electron and ion temperatures during the low solar activity period (1995) to high solar activity (2000) using the data recorded by the SROSS-C2 satellite. The ionospheric electron and ion temperatures were measured with the help of Retarding Potential Analyzer (RPA) payload aboard the Stretched Rohini Series Satellite (SROSS-C2), which was launched by Indian Space Research Organization (ISRO) on May
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4, 1994 to study the ionospheric composition and temperature anomalies. The details and description of RPA payload aboard SROSS-C2 satellite are given by Garg and Das (1995) and Bhuyan et al. (2006). The satellite data have been selected over the Indian region from 5°S to 20°N geomagnetic latitude and from 137°E to 168°E geomagnetic longitude, which covers the maximum pass of the SROSS-C2 satellite over India. The measured electron and ion RPA data have been analyzed for three different seasons; summer (May, June, July and August), winter (November, December, January and February) and equinoxes (March, April, September and October) for the low solar activity period to high solar activity to study the diurnal, seasonal and latitudinal behavior of electron and ion temperatures. The maximum permissible error is ±50 K within the temperature range from 500 to 5000 K of the RPA measurements. 2. Results and discussion To study the diurnal, seasonal and latitudinal variations of electron and ion temperatures, the SROSS-C2 satellite data from low solar activity (1995) to high solar activity (2000) have been analyzed over Indian region. Figs. 1 and 2 show the diurnal variation of electron and ion temperature for half of the solar cycle, respectively. Fig. 1(a) 5000
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shows the electron temperature for the solar minimum year (1995) and found the electron temperature rises sharply at the time of sunrise and decreases as the day progress. A secondary enhancement has also been found at the time of sunset. The peak of evening enhancement is lower in magnitude than the sunrise peak. Similar enhancements have been found towards increasing the solar activity; the same have been represented in Fig. 1(b–f) for remaining years. The enhancement in the peak value of electron temperature during the time of sunrise is decreased as the solar activity increases. The diurnal variations of ion temperature have been represented in the Fig. 2(a–f) for the low solar activity period to high solar activity, respectively. The average solar activity (F10.7) has been mentioned in all the figures. The measured RPA data have been divided into three different seasons, viz. summer (May, June, July and August), winter (November, December, January and February) and equinoxes (Mach, April, September and October) for the solar minimum year to solar maximum for studying the seasonal effect on ionospheric electron and ion temperatures. However, we have chosen to present 2 year solar minimum year (1995) and solar maximum (2000) for three different seasons viz. summer, winter and equinox only to reduce the number of figures and improve the presentation quality. The left panel in Fig. 3(a–c) shows the diurnal variation of electron temperature for solar min5000
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imum year (1995) and right panel [Fig. 3(d–f)] for solar maximum year (2000) for three different seasons, respectively. Similarly, the ion temperature shown in Fig. 4(a–c) left panel for solar minimum and right panel in Fig. 4(d– f) solar maximum for aforesaid seasons, respectively. Fig. 3 shows the clear peak during the sunrise hours and also a diffuse peak corresponding to the secondary enhancement in electron temperature during the evening hours. However, for ion temperature, the sunrise peak and evening temperature enhancements (Fig. 4) are smaller than those for the electron temperature. Smoothing of the measured temperature variations have been done by computing hourly averages and calculating their standard deviations; these are presented in all figures for the electron and ion temperatures, respectively. It has been observed that the electron temperature rises sharply during the sunrise hours (5:30–6:30 LT), and a secondary enhancement has also been observed during the sunset hours (16:30–17:30 LT) for all seasons from solar minimum year to maximum. However, the ion temperature rises sharply during sunrise hours (6:30–7:30 LT), which is one hour late comparing to the electron temperature because it is much heavier than electron. The secondary enhancement is observed during the sunset as the same hour as that of electron temperature. A similar pre-sunrise ion temperature enhancement in the low and mid latitude ionosphere at 600 km has been reported by Chao et al. (2003).
During summer of solar minimum year (1995), the average electron temperature (Fig. 3a) at sunrise rises to over 3700 K from the nighttime average temperature of 850 K, whereas the evening temperature is enhanced to 2500 K during the secondary enhancement near sunset. Similar enhancements have also been observed during the winter and equinoxes seasons at the time of sunrise and sunset. In the winter, the average electron temperature (Fig. 3b) at sunrise rises to over 3500 K from the nighttime average temperature of 817 K, whereas the evening temperature rises to 1900 K during the secondary enhancement at sunset. During the equinoxes, the average electron temperature (Fig. 3c) at sunrise rises to over 4100 K from the nighttime average temperature of 830 K, whereas the evening temperature is enhanced to almost 2100 K during the secondary enhancement at the time of sunset. However, it was for solar maximum year (2000) in summer the average electron temperature (Fig. 3d) at sunrise less than 2900 K from the midnight average temperature 1050 K, whereas the evening temperature is enhanced to 1700 K during the secondary enhancement near sunset. In the winter, the average electron temperature (Fig. 3e) at sunrise rises to over 2950 K from the nighttime average temperature of 1080 K, whereas the evening temperature rises to 1577 K during the secondary enhancement at sunset. During the equinoxes, the average electron temperature (Fig. 3f) at sunrise rises to over 3300 K from the nighttime average tempera-
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ture of 1100 K, whereas the evening temperature is enhanced to almost 1680 K during the secondary enhancement at the time of sunset. The annual and seasonal average electron and ion temperatures during nighttime, maximum at sunrise and maximum at sunset for half of the solar cycle are shown in Tables 1a and 1b, respectively. The average ion temperature during summer of solar minimum year (1995) is shown in Fig. 4a at sunrise rises to 1350 K from the nighttime average temperature of 630 K, whereas the evening temperature is enhanced to 1500 K during the secondary enhancement near sunset. Similar enhancements have also been observed during the winter and equinoxes seasons at the time of sunrise and sunset. In the winter, the average ion temperature (Fig. 4b) at sunrise rises to over 1750 K from the nighttime average temperature of 700 K, whereas the evening temperature rises to 1100 K during the secondary enhancement at sunset. During the equinoxes, the average electron temperature (Fig. 4c) at sunrise rises to over 1513 K from the nighttime average temperature of 700 K, whereas the evening temperature is enhanced to almost 1200 K during the secondary enhancement at the time of sunset. However, it was for solar maximum year (2000) in summer the average ion temperature (Fig. 4d) at sunrise rises to over 1200 K from the midnight average temperature 930 K, whereas the evening temperature is enhanced to 1330 K during
the secondary enhancement near sunset. In the winter, the average ion temperature (Fig. 4e) at sunrise rises to over 1180 K from the nighttime average temperature of 970 K, whereas the evening temperature rises to 1200 K during the secondary enhancement at sunset. During the equinoxes, the average ion temperature (Fig. 4f) at sunrise rises to over 1150 K from the nighttime average temperature of 1000 K, whereas the evening temperature is enhanced to almost 1300 K during the secondary enhancement at the time of sunset. To study the latitudinal variation the data from the electron and ion RPAs have been analyzed for electron and ion temperatures for different orbits. Those orbits falling near to 12:00 noon and 24:00 midnight local time are considered for the study of latitudinal variation of electron and ion temperatures. The electron and ion temperatures data are analyzed over 1° bins in the geomagnetic latitude range from 5°S to 20°N, and plotted along with the standard deviation in Figs. 5 and 6. The latitudinal variations of the electron temperature near 500 km at 12:00 noon are shown in left panel of Fig. 5(a–c) for different seasons of the solar minimum year and right panel in Fig. 5(d–f) for solar maximum year. Similarly, for ion temperature variations are shown in Figs. 6, left panel for solar minimum year and the right panel for solar maximum year at 12:00 noon for all the above mentioned seasons. The electron
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24.00
Local Time, hrs Fig. 4. Left panel shows the diurnal variation of ion temperature for solar minimum (1995) and right panel for solar maximum (2000) for three different seasons: summer, winter and equinoxes, respectively.
and ion temperature variations with latitude during nighttime are negligible, falling within the maximum error limit ±50 K of the measurements. However, there is a latitudinal variation in the electron daytime temperature. The maximum variation in electron temperature is observed during summer and the minimum during the equinoxes. It was further decreased toward increasing the solar activity. The latitudinal variations of electron temperature from 5°S to 20°N geomagnetic latitude over the Indian region show a positive correlation during low solar activity and decrease towards high solar activity. However, the latitudinal variations of ion temperature over the studied region are less than the corresponding variations in electron temperature. In the present work, we have not carried out any modeling study for theoretical calculation of the change in the iono-
spheric temperatures. The model calculations by Oyama et al. (1996) suggested that the possible mechanism for the ionospheric temperature enhancements is the downward drift of plasma, which varies with time of day, season and latitude. It has also been found that, during sunrise, the overshoot of the plasma downward drift velocity is a maximum, which explains the morning overshoot (Oyama et al., 1996). Brace et al. (1987) have studied the ionospheric electron temperature during high solar activity from 1981 to 1982 using the data of Dynamics Explorer-2 (DE-2) satellite data at altitude between 300 and 400 km. They found that during high solar activity the electron temperature strongly increased with latitude above about 40°. They also calculate that the day time electron temperature near the F2 peak is more responsive to short term variations in F10.7
Table 1a Annual average electron and ion temperatures during nighttime, maximum at sunrise and maximum at sunset from low solar activity to high solar activity. S. no.
1. 2. 3. 4. 5. 6.
Year
1995 1996 1997 1998 1999 2000
Electron temperature (K)
Ion temperature (K)
Avg. at Nighttime
Maximum at sunrise
Maximum at sunset
Avg. at Nighttime
Maximum at sunrise
Maximum at sunset
833 753 780 927 1014 1083
3812 3423 3326 3399 3178 3029
2171 1737 1637 2023 1648 1640
694 636 650 795 871 977
1524 1589 1470 1428 1200 1183
1226 1207 1164 1233 1244 1274
300
P.K. Sharma et al. / Advances in Space Research 45 (2010) 294–302
Table 1b Seasonal average electron and ion temperatures during nighttime, maximum at sunrise and maximum at sunset from low solar activity to high solar activity. S. no.
Year
Seasons
1.
1995
Summer Winter Equinox
2.
1996
3.
Electron temperature (K) Avg. at Nighttime
Ion temperature (K)
Maximum at sunrise
Maximum at sunset
844 817 832
3742 3494 4131
2508 1922 2081
Summer Winter Equinox
702 781 733
3428 3381 3452
1997
Summer Winter Equinox
744 788 752
4.
1998
Summer Winter Equinox
5.
1999
6.
2000
Maximum at sunrise
Maximum at sunset
655 700 701
1344 1743 1513
1530 1065 1191
1988 1687 1541
613 646 617
1202 2133 1490
1499 1029 1136
3390 3025 3389
1951 1389 1563
607 637 635
1168 1497 1706
1594 932 1069
904 925 886
2859 3329 3886
2050 2057 1987
803 774 768
1089 1704 1272
1397 1078 1211
Summer Winter Equinox
975 1056 979
3262 3131 3113
1501 1745 1576
852 886 827
1090 1428 1245
1334 1216 1193
Summer Winter Equinox
1043 1084 1105
2882 2962 3300
1705 1577 1682
930 970 1007
1208 1183 1154
1337 1217 1300
4000
4000
(a)
3200
Electron Temperature, K
Avg. at Nighttime
F10.7~77
2400
2400
1600
1600
800
800
0
0
4000
4000
(b)
3200
(d)
3200
F10.7~77
(e)
3200
2400
2400
1600
1600
800
800
0
0
4000
F10.7~180
F10.7~175
4000
(c)
3200
F10.7~77
(f)
3200
2400
2400
1600
1600
800
800
F10.7~178
0
0 -5
0
5
10
15
20
-5
0
5
10
15
20
Geomagnetic Latitude, deg. Fig. 5. Left panel shows the latitudinal variation of electron temperature for solar minimum (1995) and right panel for solar maximum (2000) for three different seasons: summer, winter and equinoxes, respectively.
P.K. Sharma et al. / Advances in Space Research 45 (2010) 294–302 2500
2500
(a)
2000
F10.7~77
(d)
2000
1500
1500
1000
1000
500
500
0
0
2500
Ion Temperature, K
301
F10.7~180
2500
(b)
2000
F10.7~77
2000
1500
1500
1000
1000
500
500
0
0
(e)
F10.7~175
(f)
F10.7~178
2500
2500
(c)
2000
F10.7~77
2000
1500
1500
1000
1000
500
500
0 -5
0
5
10
15
20
0 -5
0
5
10
15
20
Geogmagnetic Latitude, deg. Fig. 6. Left panel shows the latitudinal variation of ion temperature for solar minimum (1995) and right panel for solar maximum (2000) for three different seasons: summer, winter and equinoxes, respectively.
than to any long-term changes that may occur between solar minimum to solar maximum. An empirical model of the electron and ion temperatures is presented in the altitude interval 50–4000 km as a function of time, space and solar flux by using observations of six satellites, five incoherent scatter stations and rocket measurements given by Kohnlein (1986). Mahajan and Pandey (1979) used electrostatics probe measurements of electron temperature from the ISIS-1 satellite for the equinox season of high solar activity years 1969 and 1970 are analyzed for the 1000 km altitude and compared the results with the Explorer-22 satellite measurements of electron temperature for the years 1965– 1967. They found that the large solar activity changes the latitudinal profiles of the electron temperature during both day and night. At low and mid latitudes, the electron temperature increases from about 2000 K to about 3500 K for the day time and from about 800 K to about 1700 K during the nighttime between low and high solar activity conditions. At high latitude there is an increase in electron temperature by about a factor of 2 from low to high solar activity period. Truhlik et al. (2009) have studied the latitudinal variation of the topside electron temperature at different levels of solar activity (low, medium and high). They have used a large database of most of the available satellite measurements in the topside ionosphere for studying the solar activity varia-
tions of the electron temperature at different latitudes, altitudes, local times and seasons. They found the small changes in electron temperature with solar activity. These changes in electron temperature were comparable in magnitude with seasonal changes but much smaller than the changes with altitude, latitude and from day to night. 3. Conclusions The diurnal, seasonal and latitudinal variations of electron and ion temperatures have been studied using data from the SROSS-C2 satellite during the low solar activity period to high solar activity over the low and equatorial latitude Indian region. This study shows that the electron and ion temperatures are lowest during the night and show variations during the daytime in all seasons. The daytime electron temperature shows at least two clear maximum values, with different magnitudes. The peak during sunrise is relatively sharp and larger, whereas the other peak during sunset is diffuse and smaller also. The enhancement in the peak value of electron and ion temperatures during the time of sunrise is decreased as the solar activity increases. A smaller variation in the ion temperature has also been observed. The electron temperature increases with increasing latitude during the daytime, whereas there are no latitudinal variations at night over the Indian region studied at 500 km altitude. The maximum variation in
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