ionospheric heating due to solar flares as measured by sross-c2 satellite
TRANSCRIPT
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Advances in Space Research 48 (2011) 12–18
Ionospheric heating due to solar flares as measured bySROSS-C2 satellite
D.K. Sharma a,⇑, M.S. Khurana a, Jagdish Rai b
a Department of Physics, Manav Rachna College of Engineering, Faridabad 121001, Indiab Department of Physics, Indian Institute of Technology, Roorkee 247667, India
Received 16 August 2010; received in revised form 9 February 2011; accepted 10 February 2011Available online 13 February 2011
Abstract
The data on thermal fluctuations of the topside ionosphere have been measured by Retarding Potential Analyser (RPA) payloadaboard the SROSS-C2 satellite over the Indian region for half of the solar cycle (1995–2000). The data on solar flare has been obtainedfrom National Geophysical Data Center (NGDC) Boulder, Colorado (USA) and other solar indices (solar radio flux and sunspot num-ber) were download from NGDC website. The ionospheric electron and ion temperatures show a consistent enhancement during thesolar flares. The enhancement in the electron temperature is 28–92% and for ion temperature it is 18–39% compared to the normal day’saverage temperature. The enhancement of ionospheric temperatures due to solar flares is correlated with the variation of sunspot andsolar radio flux (F10.7cm). All the events studied in the present paper fall in the category of subflare with almost same intensity. Theionospheric electron and ion temperatures enhancement have been compared with the IRI model values.� 2011 COSPAR. Published by Elsevier Ltd. All rights reserved.
Keywords: Ionospheric temperature; Satellite observations; Solar flare; Sunspot number; Radio flux
1. Introduction
The ionospheric electron and ion temperatures showdiurnal, seasonal, latitudinal, longitudinal and altitudinalvariation and also variation during the 11-year solar cycle(Mahajan et al., 1983; Oyama et al., 1996; Richards, 2001;Sharma et al., 2003, 2005). Some other phenomena occur-ring above the ionosphere such as solar flare, solar wind,coronal mass ejection etc. and below the ionosphere suchas seismic activity, volcanic eruptions, thunderstorms andlightning/sprites also play an important role in changingthe ionospheric temperatures in F2 region (Rai et al.,1972; Schunk and Sojka, 1996; Sharma et al., 2004a,b,2006, 2010). These changes in ionospheric temperaturesmay affect the radio communication, navigation, explora-tion of near earth space; electronic systems in satellitesand spacecrafts (Kazimirovsky et al., 2003). Therefore,
0273-1177/$36.00 � 2011 COSPAR. Published by Elsevier Ltd. All rights rese
doi:10.1016/j.asr.2011.02.007
⇑ Corresponding author. Tel.: +91 129 4198513; fax: +91 129 4198111.E-mail address: [email protected] (D.K. Sharma).
understanding, monitoring and forecasting the changes inionospheric temperatures due to solar flare has alsobecome an important problem of the present day.
In the low and mid latitude ionosphere, solar activity isthe main source of energy and is related to ionospherictemperatures (Suhasini et al., 2001). The effect of solar flareon total electron content (TEC) has been studied by vari-ous workers (Hanssen and Emslie, 1988; Anastasiadis,1999; Charikov, 2000; Kudryashev and Avakyan, 2000;Afraimovich, 2000; Avakyan, 2001; Afraimovich et al.,2001a,b; Mannucci et al., 2005; Tsurutani et al., 2005,2008) using GPS and satellite data. Afraimovich (2000)and Afraimovich et al. (2000, 2001a,b) have developed anovel technology of global detection of ionospheric effectsfrom solar flares and presented data from the GPS mea-surements of global response of ionosphere to powerfulimpulsive flares of 29 July 1999 and 28 December 1999.They found that fluctuations of TEC are coherent for allstations on the dayside of the Earth. The time profile ofTEC responses is similar to the time profile of hard X-
rved.
D.K. Sharma et al. / Advances in Space Research 48 (2011) 12–18 13
ray emission variations during flares, in the energy range25–35 keV, if the relaxation time of electron density distur-bances in the ionosphere of the order of 50–100 s is intro-duced. No such effect on the nightside of the Earth hasbeen detected yet. Leonovich et al. (2002) have also pro-posed a method for estimating the TEC in different iono-spheric regions due to solar flare. They have used thedata from the international network of two frequencymulti-channel receivers of the navigation GPS system.They found that about 75% of the TEC increase corre-sponds to the ionospheric region lying below 300 km andabout 25% to regions lying above 300 km. Tsurutaniet al. (2005) have studied the October 28, 29, November4, 2003 and Bastille Day flares and their ionospheric effects.They found that the October 28, 2003 event was by far themost intense flare of the four events when measured inEUV wavelengths. The extreme EUV solar flare caused asudden, intense, long lasting dayside ionospheric TECincrease. The duration of the enhanced TEC due to theflare was �3 h, much longer than the EUV flare duration.
The effect of solar flares on the ionospheric F region hasalso been studied (Mendillo et al., 1974; Mitra, 1974) byVHF radio beacon experiment on geo-stationary satelliteand the TEC enhancement was noticed. Global observa-tion of the flares of August 7, 1972 using 17 stations inNorth America, Europe and Africa (Mendillo et al.,1974) revealed that the TEC was increased by 15–30% dur-ing the solar flares. Some events of solar flares have alsobeen studied by Kanellakos et al. (1962) to see the effecton E and F region ionosphere and it has been found thatthe electron density was enhanced at these heights. Thomeand Wagner (1971) theoretically studied the effect of solarflares on electron density and found that the electron den-sity is enhanced in E and F regions of the ionosphere.Tsugawa et al. (2007) have studied the effect of solar activ-ity on summer–winter hemispheric asymmetry in TEC andobserved sudden increase in the TEC due to solar flares.
In the present paper the ionospheric electron and iontemperature satellite data has been analyzed to study thetemperature anomalies due to solar flare in the F2 regionof the ionosphere. Only the data which was in coincidencewith the solar flare events was selected for the presentstudy. The recorded average electron and ion temperaturesduring flare events have been compared with the averagenormal day’s temperature for the same time interval andhave also been compared to estimated values by the Inter-national Reference Ionosphere (IRI-95).
2. Data source, selection and analysis
The ionospheric ion and electron temperature data weremeasured with the help of RPA payload aboard IndianSROSS-C2 satellite. The SROSS-C2 satellite was launchedon May 04, 1994 to study the ionospheric composition andionospheric temperature anomalies. It was launched withthe help of ASLV-D4 rocket in the orbit 625 � 425 km alti-tude with the inclination 46� to the equatorial plane. The
satellite functioned well for 7 years and on July 12, 2001returned to earth’s atmosphere. It covered geographic lati-tude belt of 31�S to 34�N and the longitude range from40�E to 100�E. A detailed description of the RPA payloadhas been given by Garg and Das (1995).
For the present study only 5 events of solar flare wereselected which are free from thunderstorm and seismicactivities. A few (3–4) cases were found in our availablesatellite database where the dayside solar flare occurredbut those cases were in coincidence with the thunderstormand seismic activity and hence were not considered.Authors have already observed correlation between theionospheric temperatures and thunderstorms and seismicactivity (Sharma et al., 2004a,b, 2006). Therefore, it wasimportant to rule out solar flare events coinciding withthunderstorms and seismic activity from our data base.For verification of thunderstorms we have used the datafrom India Meteorological Department (IMD), Pune(India). The IMD covers the area almost bounded by40�E to 100�E only. Further, the SROSS-C2 satelliterecordings were also confined to the region 31�S to 34�Nin latitude and 40�E to 100�E in longitude. For the verifica-tion of seismic activity the data was downloaded fromNational Earthquake Information Centre (NEIC) website.The International Reference Ionosphere (IRI-95) modeldata for the same period was downloaded from the Internetand used for the purpose of comparison. In the subsequentpart of the paper the IRI-95 model will be referred to asIRI model.
It is a difficult task to study the ionospheric temperatureusing the satellite data during solar flares because veryrarely passes of satellite matches with the occurrence ofsolar flares at the meteorological data stations. We haveanalyzed the data for ten meteorological stations duringthe period 1995–2000 over India. However, only five eventsof solar flares were identified which matched with the elec-tron and ion temperature data recorded by satellite. Thesesolar flare events correspond to two at Panji (15.30�N,73.55�E), two at Pune (18.31�N, 73.55�E) and one eventat Bhopal (23.16�N, 77.36�E). Data for electron and iontemperatures were analyzed for these locations at the alti-tude range 425–625 km. Care has been taken to select thesatellite data, which is free form diurnal, seasonal, latitudi-nal, longitudinal and altitudinal effects by selecting theappropriate data window at fixed location with 5� variationin longitude and latitude.
The satellite with the velocity of 7.8 km/s crosses theselected location within about 70 s (the ionospheric dis-tance of a window of 5� in latitude and longitude). Suchpasses are rare and therefore only the temperature mea-sured by the satellite can be compared with the averagetemperature and the consideration of hourly variation isnot possible. To compute the normal days temperaturefor the flare duration, the electron and ion temperaturedata for normal days were selected for the same time inter-val (3 h prior to start of flare event and 3 h after the end offlare event) for a month, which includes for about 15 days
0
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16.67-17.03 hrs (LT)
Fig. 1. Variation of electron and ion temperatures during the solar flareevent on May 19, 1995 over Panji (15.30�N, 73.55�E) along with thesunspot number and radio flux (F10.7cm).
14 D.K. Sharma et al. / Advances in Space Research 48 (2011) 12–18
before the solar flares and for about 15 days after the event.Thus, the possibility of diurnal and seasonal effect has beenruled out. The enhancement in temperature during eventwas calculated by taking average value of normal days tem-perature and average value of flare day temperatures. Themaximum possible data points available for the study dura-tion have been used. The solar flare events selected for pres-ent study are also free from thunderstorm and seismicactivities, which have been verified.
All the five events studied in the present paper are mag-netically quiet events. The flare events fall in the categoryof subflare. The area covered by a great flare may be aslarge as 109 km2 and area smaller than about 3 � 108 km2
is known as subflare (Hanssen and Emslie, 1988). Theevents studied had nearly same area and brilliancy is fainton a three level scale. The intensity of a subflare is approx-imately 5 sfu (solar flux unit).
3. Result and discussion
During the study period from January 1995 to Decem-ber 2000, a total of five solar flare events were identifiedon the dayside of earth, which correspond to the locationsat Panji (15.30�N, 73.55�E), Pune (18.31�N, 73.55�E) andBhopal (23.16�N, 77.36�E) over India. These stations werechosen on the basis of maximum passes of SROSS-C2satellite and also having the IMD stations. Figs. 1–5 showthe variations in ionospheric electron and ion temperaturesduring the solar flare and normal days along with therespective sunspot number and radio flux. The time dura-tion of the flare has also been mentioned in the figures.The electron and ion temperature panels also have errorbars for the reference temperature.
Two solar flare events were identified over the meteoro-logical station Panji (30�N, 73.55�E) on May 19, 1995 andJuly 10, 1996. The variation of electron and ion tempera-ture for the above events has been shown in Figs. 1 and2, respectively. The sunspot number and radio flux(F10.7cm) for the event day have also been presented inthe same figure. It was found that the electron and ion tem-perature was enhanced compared to the normal days tem-perature. This enhancement was 28–45% for electrontemperature and 20–40% for ion temperature over the nor-mal days temperature. During both the event days, the sun-spot number was 35 and 20, respectively, while the monthlyaverage numbers were 15 and 7, respectively. The radio flux(F10.7cm) on the same days was 86 and 80, while themonthly average values were 76 and 71, respectively. Wemay say that during both the flare events the sunspot num-ber and radio flux were also high in comparison to monthlymean values.
Similarly, two solar flare events were identified overIMD Pune (18.31�N, 73.55�E) on June 5, 1995 and Decem-ber 28, 1998. It was found that the ionospheric electron andion temperatures were enhanced during both the flareevents. This enhancement was more prominent for electrontemperature in comparison to the enhancement of ion tem-
perature. This enhancement was 48–78% for electron tem-perature and 32–38% for ion temperature over the normaldays temperature. During both the event days, the sunspotnumber was 30 and 121, respectively, while the monthlyaverage numbers were 15 and 82, respectively. The radioflux (F10.7cm) during the event days was 82 and 184 com-
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Fig. 2. Variation of electron and ion temperatures during the solar flareevent on July 10, 1996 over Panji (15.30�N, 73.55�E) along with thesunspot number and radio flux (F10.7cm).
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Fig. 3. Variation of electron and ion temperatures during the solar flareevent on June 5, 1995 over Pune (18.31�N, 73.55�E) along with the sunspotnumber and radio flux (F10.7cm).
D.K. Sharma et al. / Advances in Space Research 48 (2011) 12–18 15
pared to the monthly average of 76 and 150, respectively.The variation of ionospheric electron and ion temperatureduring both the solar flare events along with the sunspotnumber and radio flux for the aforesaid events have beenshown in Figs 3 and 4, respectively. In the event of Decem-ber 28, 1998, the electron temperature enhancement isanomalous as compared to other events. It is showing grad-ual enhancement.
Fig. 5 shows the variation of electron and ion tempera-ture during the solar flare event on November 9, 1998 overmeteorological station Bhopal (23.16�N, 77.36�E). Thesunspot number and radio flux (F10.7cm) for the eventday have also been presented in the same figure. It was
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Fig. 4. Variation of electron and ion temperatures during the solar flareevent on December 28, 1998 over Pune (18.31�N, 73.55�E) along with thesunspot number and radio flux (F10.7cm).
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pot N
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adio
Flu
x 10
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Local Time, hrs
Days
Fig. 5. Variation of electron and ion temperatures during the solar flareevent on November 9, 1998 over Bhopal (23.16�N, 77.36�E) along with thesunspot number and radio flux (F10.7cm).
16 D.K. Sharma et al. / Advances in Space Research 48 (2011) 12–18
found that the electron and ion temperature was enhancedin comparison to the normal day’s temperature. Thisenhancement in electron temperature was 92% whereas incase of ion temperature it was 18% compared to the normalday’s temperature. Anomalously on the flare day the sun-spot number was found to be 71 whereas the monthly aver-age was 74. The value of the radio flux (F10.7cm) was 162
while the average radio flux was 140 during the samemonth.
The temperature enhancements have been comparedwith the daily satellite temperature measurements for15 days before and after the events. All temperature datarecorded by SROSS-C2 satellite are within the error limitof ±50 K for the temperature range of 500–5000 K. There-
Table 1aAverage electron temperature during solar flare and normal days as measured by SROSS-C2 satellite and IRI-95.
S.no.
Date of event Time and duration of solarflares (LT in hours)
Time of maximumbrightness (LT in hours)
Study location Average electron temperature (K)
Duringnormal days
During solarflares day
IRI-95
1 19 May 1995 16.67–17.03 16.67 15.30�N, 73.55�E 1897 2419 17262 5 June 1995 8.90–10.03 8.95 18.31�N, 73.55�E 1613 2367 13763 10 July 1996 10.67–11.27 10.72 15.30�N, 73.55�E 1382 2005 12684 9 November
19985.60–6.17 5.72 23.16�N, 77.36�E 1795 3446 2053
5 28 December1998
9.04–9.83 9.14 18.31�N, 73.55�E 1485 2637 1534
Table 1bAverage ion temperature during solar flare and normal days as measured by SROSS-C2 satellite and IRI-95.
S.no.
Date ofevent
Time and duration of solarflares (LT in hours)
Time of maximum brightness(LT in hours)
Study location Average ion temperature (K)
Duringnormal days
During solarflares day
IRI-95
1 19 May1995
16.67–17.03 16.67 15.30�N, 73.55�E 1050 1262 1159
2 5 June1995
8.90–10.03 8.95 18.31�N, 73.55�E 950 1311 1022
3 10 July1996
10.67–11.27 10.72 15.30�N, 73.55�E 1175 1630 1135
4 9 Nov.1998
5.60–6.17 5.72 23.16�N, 77.36�E 1005 1188 1021
5 28 Dec.1998
9.04–9.83 9.14 18.31�N, 73.55�E 1233 1630 1351
D.K. Sharma et al. / Advances in Space Research 48 (2011) 12–18 17
fore, the variation in the electron and ion temperaturesmeasured by SROSS-C2 satellite during the flare time canbe interpreted as the ionospheric temperature response tothe solar flares. These enhancements have been found onthe dayside of the earth’s ionosphere. To see the effect ofsolar flares on nightside earth’s ionosphere we have alsostudied two events, one at Chennai (13.04�N, 80.17�E)and other at Panji (15.30� N, 73.55� E) in India. At Chen-nai the SROSS-C2 data was available for the solar flareevent of February 2, 1997 (18:57:41–21:20:41 LT) and atPanji for May 4, 1998 (21:44:12–22:24:12 LT). The localtime for both the solar flares over India was night hours.The temperature variation recorded for these events fallwithin the error limit of the normal temperatures. Henceit may be concluded that the solar flares do not showsany measurable effect on the ionospheric temperature onthe night side earth’s ionosphere. Afraimovich et al.(2001b) also concluded that the solar flares do not haveany effect on the night side earth’s ionosphere. Theenhancement in ionospheric temperature is mainly due tohigh energy X-rays and ultraviolet radiation produced dur-ing the solar flares (Donnelly, 1976; Charikov, 2000;Kocharov et al., 2000). These high-energy radiations reachthe earth’s ionosphere and heat the plasma.
The average electron and ion temperatures during solarflares, normal days and values estimated by IRI model for
all five events have been shown in Tables 1a and 1b respec-tively. The table also shows the time and duration of theflare and also the time of the maximum brightness andlocation of solar flares. The values estimated by IRI arelower to the events values.
4. Conclusions
The ionospheric temperatures recorded by the SROSS-C2 satellite during 1995–2000 have been analysed to seethe effect of solar flares. In all five subflare events recordedduring different local time are matching with the SROSS-C2satellite’s passes time. The study reveals that the electronand ion temperatures show a consistent enhancement dur-ing the solar flares. The ionospheric temperature responseto the solar flares is correlated with the local time electronand ion temperature behaviour. The electron temperatureis more sensitive in comparison to the ion temperature.The estimated enhancement for the average electron tem-perature is 28–92% whereas for ion temperature it is 18–39% compared to the normal day’s average temperature.The effect of solar flare on the nightside ionospheric temper-atures has not been detected in the altitude range 425–625 km. All the flare events studied in the present paperhad the same intensity therefore the study of temperatureenhancement relationship with the magnitude of intensity
18 D.K. Sharma et al. / Advances in Space Research 48 (2011) 12–18
of solar flares is beyond the scope of present paper. Duringthe day of flare event the sunspot number was higher thanthe monthly average value in most of the events. However,on the flare day the radio flux (F10.7cm) was much morehigher than the monthly average value.
Acknowledgements
Two of the authors are thankful to Prof. Naveen Prak-ash, Director-Principal, Manav Rachna College of Engi-neering (MRCE), Faridabad for providing the necessaryfacilities. The authors are also thankful to NGDC, Boul-der, Colorado, USA for providing the data of solar flaresand IMD, Pune, India for providing the necessary data.
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