Effects of CME and CIR induced geomagnetic storms on low-latitude ionization over Indian longitudes in terms of neutral dynamics
Sumanjit Chakraborty, Sarbani Ray, Dibyendu Sur, Abhirup Datta, Ashik Paul
EEffects of CME and CIR induced geomagnetic stormson low-latitude ionization over Indian longitudes interms of neutral dynamics
Sumanjit Chakraborty a, ∗ , Sarbani Ray c , Dibyendu Sur c , Abhirup Datta a,b ,Ashik Paul c a Discipline of Astronomy, Astrophysics and Space Engineering, IIT Indore, Simrol,Indore, 453552 b Center for Astrophysics and Space Astronomy, Department of Astrophysical andPlanetary Science, University of Colorado, Boulder, CO 80309, USA c Institute of Radio Physics and Electronics,University of Calcutta, Kolkata 700 009,West Bengal, India
Advances in Space Research Volume 65, Issue 1, 1 January 2020, Pages198-213
Abstract
This paper presents the response of the ionosphere during the intense geo-magnetic storms of October 12-20, 2016 and May 26-31, 2017 which occurredduring the declining phase of the solar cycle 24. Total Electron Content(TEC) from GPS measured at Indore, Calcutta and Siliguri having geomag-netic dips varying from 32.23 ◦ N, 32 ◦ N and 39.49 ◦ N respectively and at theInternational GNSS Service (IGS) stations at Lucknow (beyond anomalycrest), Hyderabad (between geomagnetic equator and northern crest of EIA)and Bangalore (near magnetic equator) in the Indian longitude zone havebeen used for the storms. Prominent peaks in diurnal maximum in excess ∗ Corresponding author.
Email addresses: [email protected] (Sumanjit Chakraborty), [email protected] (Sarbani Ray), [email protected] (Dibyendu Sur), [email protected] (Abhirup Datta), [email protected] (Ashik Paul)
Preprint submitted to Advances in Space Research June 15, 2020 a r X i v : . [ phy s i c s . s p ace - ph ] J un f 20-45 TECU over the quiet time values were observed during the October2016 storm at Lucknow, Indore, Hyderabad, Bangalore and 10-20 TECU forthe May 2017 storm at Siliguri, Indore, Calcutta and Hyderabad. The GUVIimages onboard TIMED spacecraft that measures the thermospheric O/N ratio, showed high values (O/N ratio of about 0.7) on October 16 when posi-tive storm effects were observed compared to the other days during the stormperiod. The observed features have been explained in terms of the O/N ra-tio increase in the equatorial thermosphere, CIR-induced High Speed SolarWind (HSSW) event for the October 2016 storm. The TEC enhancementhas also been explained in terms of the Auroral Electrojet (AE), neutral windvalues obtained from the Horizontal Wind Model (HWM14) and equatorialelectrojet strength from magnetometer data for both October 2016 and May2017 storms. These results are one of the first to be reported from the Indianlongitude sector on influence of CME- and CIR-driven geomagnetic stormson TEC during the declining phase of solar cycle 24. Keywords:
CME, CIR, HSSW, Ionospheric TEC, Geomagnetic storms,Neutral wind
1. Introduction
Ionospheric storms describe variations in the ionosphere due to geomag-netic disturbances. These storms occur due to the input of solar wind en-ergy, which is sudden, into the magnetosphere-ionosphere-thermosphere sys-tem. Generally, a geomagnetic storm occurs following a Coronal Mass Ejec-tion (CME) when the polarization of Interplanetary Magnetic Field (IMF)Bz changes from northward to southward, remain southward for several2ours (Gonzalez et al., 1994) and reconnects with the Earth’s magnetic field(Dungey, 1961). During the declining phase of the solar activity, anotherimportant phenomenon that causes geomagnetic storms is the coronal holes.Coronal holes emanate high speed solar wind ( > ∼ ◦ dip latitude and finally comes back towards the dipequator and vanishes by 24:00 LT (Rastogi, 1959; Anderson, 1973; Rishbeth,2000). The EIA is caused by two main plasma motions at the F region.Firstly, the motion that is perpendicular to the magnetic field of the Earth,generates plasma drift directed upwards caused by the zonal eastward(day-time)/westward(night-time) electric field produced by the E region dynamoand B. The second motion which is parallel to B, as a result, under theinfluence of ambipolar diffusion drift related to pressure and gravity gradi-ents, causes plasma to diffuse following the geomagnetic field lines (Kendalland Pickering, 1967). The day-to-day variability and dynamics of the EIAand consequently the Total Electron Content (TEC) are well known to belargely due to thermospheric winds and electric fields (Abdu et al., 1990).The storm time variability of EIA has been addressed by several workers(Nishida, 1968a,b; Blanc and Richmond, 1980; Kelley et al., 2003; Abduet al., 2006; Sastri, 1988).The enhanced eastward PPEF raises the dayside and evening ionosphereupward significantly causing huge increase in the ionospheric TEC (Maruyamaet al., 2004). During such periods, there is a poleward extension of the EIAwith its crest directing into the mid-latitudes (Abdu, 1997). During geomag-5etic storms, the thermosphere and ionospheric structures are affected by iondrag forcing and Joule heating (Astafyeva et al., 2015). This energy input athigh latitudes modifies the ionospheric F region electron density. Hence theelectric field changes globally as a result of these disturbances and producesan increase in the electron density which is well known as the positive stormeffect (Ngwira et al., 2012).Considerable amount of work on ionospheric TEC response to geomag-netic storms have been reported in literature. In recent years, (Astafyevaet al., 2015) studied the ionospheric response to the St. Patrick’s Day stormof March 16-21, 2015, which is the most intense (G4 class, Kp=8, severe,according to NOAA scales http://swpc/noaa.gov/noaa-scales-explanation)storm of solar cycle 24. They have observed dramatic TEC enhancements inand around the area of the eastern Pacific region. For the same storm, (Navaet al., 2016) using TEC measurements from the middle and low latitudes inthe Pacific, American, African and Asian longitude sectors showed positivestorm effects during the main phase of the storm depending on the longitudesector. During the recovery phase, sharp decrease in ionization lasting forseveral days has been observed at all longitude sectors. (Ray et al., 2017)have reported observations of amplitude, phase scintillations and TEC fromdifferent GPS stations of India during the storm of 17 March, 2015 and high-lighted its effects on the performance of GPS. A very interesting observationof severely depleted ionosphere on the day following the St.Patrick day stormof 2015 at high latitudes (north of 65 ◦ N) was reported by (Paul et al., 2018)using GPS TEC measurements over a network of stations extending fromthe equator to the polar regions along the African and European longitude6ector. The Indian subcontinent covers the low latitude zone in the South-Asian longitudes where the magnetic equator passes over the southern tip ofthe peninsula near Trivandrum (DasGupta et al., 2007).The paper presents the effect of the October 2016 storms that was bothCME and CIR-induced and May 2017 storm that was CME-induced over theIndian longitude sector. The stations have been carefully selected to revealchanges in the dynamism of the ionosphere in such an extremely variableionospheric region during geomagnetic disturbances. The paper also showsthe effect of HSSW on the ionospheric TEC at different locations in andaround the EIA in the Indian sector. The novelty of this work lies in thefact that impact of combined CME- and CIR-driven geomagnetic storms onionospheric Global Navigation Satellite System (GNSS) TEC over the Indiansubcontinent has not been extensively reported in literatures. Furthermore,the locations of the different observing stations ensure characterization ofstorm-induced effects on ionospheric TEC near the magnetic equator (Ban-galore) as well as around the northern crest of the EIA (Indore and Calcutta)and beyond (Lucknow and Siliguri).
2. Data and Methods
A multi-constellation and multi-frequency Global Navigation SatelliteSystem (GNSS) receiver is operational since May 2016 at the Discipline ofAstronomy, Astrophysics and Space Engineering, Indian Institute of Tech-nology Indore, Indore (22.52 ◦ N, 75.92 ◦ E geographic; magnetic dip 32.23 ◦ N)which is located in the EIA region of the Indian longitude sector. ThisGNSS receiver has the capability of tracking GPS, GLONASS, GALILEO7nd SBAS geostationary satellites at multiple frequencies (L1 1575.42MHz,L2 1227.6MHz, L5 1176.45MHz). The output includes the azimuth and ele-vation of the satellite, time (UTC) and calibrated TEC recorded at 1 minutesampling interval. Data has also been used from similar receivers operationalat the Institute of Radio Physics and Electronics, University of Calcutta,Calcutta (22.58 ◦ N, 88.38 ◦ E geographic; magnetic dip 32 ◦ N) and North Ben-gal University, Siliguri (26.72 ◦ N, 88.39 ◦ E geographic; magnetic dip 39.49 ◦ N).Ionospheric TEC data, available at a sampling interval of 1 min from the IGSstations at Lucknow (26.91 ◦ N, 80.95 ◦ E geographic; magnetic dip 39.75 ◦ N),Hyderabad (17.41 ◦ N, 78.55 ◦ E geographic; magnetic dip 21.69 ◦ N) and Ban-galore (13.02 ◦ N, 77.5 ◦ E geographic; magnetic dip 11.78 ◦ N), have also beenanalyzed available at (http://sopac.ucsd.edu/). Figure 1 shows the zone ofreception above an elevation angle of 50 ◦ for all the stations presented in thispaper along with the northern crest of EIA and the magnetic equator thatpasses over Tirunelveli (8.73 ◦ N, 77.70 ◦ E geographic; magnetic dip: 3.26 ◦ N).The present study emphasizes on TEC measurements obtained from a dis-tribution of stations located at Lucknow, beyond the northern crest of EIA,Indore (located near the crest of EIA), Hyderabad (located between geo-magnetic equator and northern crest of EIA) and Bangalore (located nearmagnetic equator) for the October 2016 storm. The stations used for the May2017 storm are Siliguri (located beyond the crest of EIA), Calcutta (locatednear the EIA crest), Indore and Hyderabad.In the analyses, Ionospheric Pierce Point (IPP) height of 350 km has beenused. The hourly Disturbance storm time (Dst) (nT) index has been obtainedfrom World Data Center for Geomagnetism, Kyoto (http://wdc.kugi.kyoto-8 igure 1: Locations of the stations Bangalore, Hyderabad, Indore, Calcutta, Siliguri andLucknow on a map of India. Zone of reception from these stations above an elevation of50 is shown by the different colored ellipses. The magnetic equator and the location of thenorthern crest of the equatorial ionization anomaly (EIA) are indicated in the map. at N column num-ber density level of 10 cm − (O/N ratio) (Lee et al., 2013). The GUVIO/N ratio has been derived from the measurements of OI 135.6 nm and N Lyman-Birge-Hopfield airglow emissions. The O/N ratio is widely used todescribe the effect of thermospheric neutral composition change on the iono-sphere. The global variation of O/N . Results and Discussions ∼ ◦ for the stations Lucknow, Indore, Hyderabad and Bangaloreduring October 12-20, 2016 plotted with reference to the average TEC forgeomagnetic quiet condition. The cut-off for elevation angle has been chosento be 50 ◦ so as to minimize the effects of sharp spatial gradients of ionization12 igure 2: Variation of the Dst index, Auroral Electrojet (AE), Interplanetary ElectricField (Ey), Solar Wind Speed (V) and IMF Bz during October 12-20, 2016. th , 20 th and 21 st , chosenbased on the lowest Sigma Kp values of the month (http://wdc.kugi.kyoto-u.ac.jp/kp/index.html), are plotted in red in this figure. During the recoveryphase of the storm i.e. during October 14-20, prominent peaks in diurnalmaximum in excess of 20-45 TECU over the quiet time values (that wouldintroduce range errors of 3.2-7.2 m on GPS L1 frequency) were observedfrom Lucknow on October 14, 16 and 17, from Indore on October 14 and16, from Hyderabad on October 14, 15, and 16 and Bangalore on October14 and 16 signifying a positive storm effect. This significant enhancementin TEC due to the CIR-induced storm agrees with the results published by(Buresova et al., 2014) where they report that even CIR-induced magneticstorms of weak to moderate intensity can have effects on the ionosphere in away similar to the effects caused due to the strong storms.Joule and particle heating of the polar upper atmosphere causes upwellingof the molecular species N and O and then pressure gradient force and iono-spheric convection extend the molecule rich gases equatorwards (Kil et al.,2011). The global wind circulation induced by heating of the polar upperatmosphere during storm period causes downwelling of the molecular gasesin the mid- and low latitudes, thereby reducing the O+ loss rate in the F re-gion in these latitudes and causing positive storm effect (Fuller-Rowell et al.,1994, 1996; Burns et al., 1995; Field et al., 1998).Figures 4, 5 show the global variation of thermospheric O/N ratio forthe storm periods of October 12-16 and October 17-20, 2016 respectively ata nearly constant local time of 16:00. It is observed that, over the Indian14 igure 3: TEC diurnal variation recorded at Lucknow, Indore, Hyderabad and Bangaloreas a function of Universal Time (UT) along with the average TEC for three geomagneticquiet days. igure 4: World map showing GUVI O/N ratio for the period October 12-16, 2016. longitude sector, the maximum thermospheric O/N ratio is observed onOctober 16. Plotting the Indian longitude sector separately in Figure 6, itis observed that O/N ratio values greater than 0.6 have been observed onOctober 14, 15 and 16. The maximum value ( ∼ ratio has beenobserved on October 16. On October 17, the O/N values were below 0.6over the whole subcontinent. On October 18 and 19, there were values ofO/N greater than 0.6. October 20 was quiet without any O/N increaseabove 0.6.The positive storm effect reported in the present paper observed in re-16 igure 5: World map showing GUVI O/N ratio for the period October 17-20, 2016. sponse to the CIR event of October 2016 storm from stations in the Indianlongitude sector show TEC enhancement with increase in O/N ratio on Oc-tober 16. The peak of AE ( ∼ ratio (Richmond and Roble, 1979; Balan et al., 2009). An enhancementof TEC near the equatorial region decreases the sharp latitudinal TEC gra-dient in the low latitudes. This causes negative ionospheric storm near EIA17 igure 6: Variation of O/N ratio over India for the period October 12-20, 2016. × B plasma drift. Any such influence onvertical plasma drift may cause change in ion-recombination rate and changein overall TEC (Rishbeth, 1997; Heelis, 2004). In the paper, the effects ofneutral wind on TEC are observed in geomagnetic disturbed conditions inlow latitude region.Figure 7a and b respectively shows the normalized meridional and zonalneutral wind plots, w.r.t. the quietest day (October 20, 2016) in this period.From Figure 7a, it can be observed that the meridional wind was negative atLucknow during 20-21 UT on October 13 and 16, 2016 that signifies south-ward directed wind which bring ionized particles from high latitudes to theIndian low latitudes suggesting a high value of TEC at Lucknow on October14 and 17, 2016. From Figure 7b, on October 13 and 16, 2016 around 2122UT, high values of zonal wind were observed from Lucknow, which signifiesenhancement of eastward zonal wind in early morning (LT = UT + 5.5) ofOctober 14 and 17, 2016. This eastward zonal wind shifts the ions eastwardwhich enhances eastward equatorial electrojet thus enhancing the net up-ward E × B drift. As a result, the upward movement of ions, signifying lesserrecombination, contribute towards enhancement of TEC on October 14 and17, 2016 at Lucknow. From Bangalore, sharp enhancement of eastward zonalwind is observed during 0-2 UT (LT =UT + 5) and a moderate enhance-ment is observed from Hyderabad justifying a TEC enhancement for thesetwo stations on October 14, 2016. From Indore, on October 13, 2016, at2123 UT, a negative enhancement of zonal wind is observed which signifies19he zonal wind that bring ions to westward direction at an altitude of 350km. Thus it adds component to westward equatorial electrojet at nighttimeand the net downward E × B drift is strengthened. Hence at Indore no ad-ditional enhancement in TEC is observed on October 14, 2016 compared tothe previous days.The equatorial electrojet strength that is related to the electric field, hasbeen computed by taking difference of the horizontal component, H (nT) ofEarth’s magnetic field at Alibag (10.51 ◦ N geomagnetic, a station away frommagnetic equator), from that at Dalat (2.23 ◦ N geomagnetic, a station nearto the magnetic equator). From Figure 8, it is observed that this differenceincreased from a value ∼ ∼ × B forceon the equatorial ionization and subsequent ionization distribution to theoff-equatorial regions. This is supported by enhanced TEC over the stationsas observed in Figure 3.Another important feature of the October 2016 storm was the presenceof CIR induced storm on October 16, in addition to the CME induced stormon October 13-14. The HSSW event observed on October 16 is characterizedby an abrupt rise of solar wind speed above 700 km/s and oscillatory natureof IMF Bz with a negative peak resulting in a peak Ey. This strengthensthe daytime eastward zonal electric field and causes an increase in TEC(Rodriguez-Zuluaga et al., 2016). The enhancement in TEC continued tillOctober 17 as long as the solar wind maintained high values above 700 km/s.Thus enhancement in TEC observed on October 16 was a consequence ofHSSW arising out of coronal holes and CIR in addition to the thermospheric20 igure 7: Normalized diurnal variations of (a) meridional neutral wind and (b) zonalneutral wind during October 1220, 2016 for the stations Lucknow (lck in red), Indore (idrin green), Hyderabad (hyd in blue) and Bangalore (blr in black). (For interpretation ofthe references to color in this figure legend, the reader is referred to the web version ofthis article.) igure 8: Electrojet strength during October 1220, 2016, taking the difference of horizontalcomponent of the Earth’s magnetic field (H in nT) of Alibag (station away from magneticequator) from that of Dalat (a station near magnetic equator). composition change as explained earlier. For October 17, the enhancementwas due to HSSW only as there were no significant changes in O/N on thatday.It should also be noted that the positive storm effect observed for theCME-induced storm on October 1314 was less significant than that observedduring the CIR-induced storm on October 1617. This is due to the fact thatthe onset of the storm at 23:00 UT on October 12 was not in the local (LT= UT + 05:30) morning to noon sector in which the ionization productionmechanism dominates and plasma accumulation due to mechanical effect ofneutral wind is greater than its chemical loss due to recombination (Prollset al., 1991; Balan et al., 2010; Ray et al., 2017).22 .2. Storm of May 26-31, 2017 ∼ -20 nT at 00:14 UT on May 28. Then again from 13:16 -14:24 UT on May 29, IMF Bz peaked to ∼ -14 nT at 13:33 UT. Figure 9dshows the corresponding Ey which maximized to 7.86 mV/m at 00:14 UT onMay 28 and 5.51 mV/m at 13:33 UT on May 29. Figure 9e plots the solarwind for the storm period. The speed remained below 500 km/s on most ofthe days except May 30 when it peaked to 554 km/s.Figure 10 shows the diurnal plots for the stations Siliguri, Indore, Cal-cutta, and Hyderabad during May 26-31, 2017 with respect to mean TEC forgeomagnetic quiet condition, plotted in red; the three geomagnetic quietestdays of the month being 3 rd , 25 th and 26 th . Here also cut-off for elevationangle has been chosen to be 50 ◦ . On May 27 and May 29, prominent peaks23 igure 9: Variation of the Dst index, Auroral Electrojet (AE), IMF Bz, InterplanetaryElectric Field (Ey) and Solar Wind Speed (V) during May 26-31, 2017. igure 10: Diurnal variation of TEC recorded at Siliguri, Indore, Calcutta and Hyderabadas a function of Universal Time (UT) along with the average TEC for three geomagneticquiet days for the period May 26-31, 2017. in diurnal maximum in excess of 10-20 TECU over quiet time values (thatwould introduce a range error of 1.6-3.2m at GPS L1 frequency), were ob-served from all the stations. Since the storm commenced at 16:00 UT onMay 27, after the diurnal maximum, the only enhancement in diurnal TECmaximum that occurred during the storm was on May 29. On May 28, adecrease in the diurnal maximum was observed from the pre-storm days ofMay 26 and 27. 25igure 11, which is similar to Figures 4 and 5 but for the storm of May26-31, 2017, shows the GUVI images for the storm days to show how thethermospheric O/N ratio varied globally at a nearly constant local timeof 16:00. Over the Indian longitude sector, the thermospheric O/N ratiois nearly similar for all the days. Concentrating on the Indian longitudesector (Figure 12), it is observed that the maximum value of O/N ratio hadbeen ( ∼ ∼ ratio on May 30 and 31, 2017. Henceno significant change in O/N ratio could be observed as compared to theOctober 2016 storm discussed earlier.Figure 13a and b shows the normalized meridional and zonal neutral windplots, respectively, w.r.t. the quietest day (May 26, 2017) in this period. InFigure 13a, it can be observed that the meridional wind was negative (south-ward) around 10-11 UT on May 28, 2017 over Indore. This southward windbrings ionized particles towards the lower latitudes of India and hence TECenhancement is observed over Indore on May 29, 2017. In Figure 13b, onMay 27, 2017 around 21-22 UT at Indore and around 22-23 UT at Hyder-abad, huge values of negative (westward) zonal wind is observed that signifiesthat wind is carrying ions westward. Thus it adds additional component towestward equatorial electrojet at nighttime and the net downward E × B driftis strengthened. Hence at Indore and Hyderabad there was no additional en-hancement in TEC on May 28, 2017. Thus neutral wind could be anotherfactor for TEC enhancement observed for some of the storm days.Additionally, it has been observed from Figure 14 that on May 28, thedifference of H-components between stations Dalat and Alibag decreased to26 igure 11: World map showing GUVI O/N2 ratio for the period May 26-31, 2017. igure 12: Variation of O/N2 ratio over India for the period May 26-31, 2017. ∼ ∼ × B force on equatorial ion-ization, thus reducing distribution of ionization at the off-equatorial regions.This supports the reason behind reduced TEC values as observed in Figure10. The TEC response during the main phase of this storm on May 28 andthe disturbance on May 29 observed from the Indian longitude shows thatthere is no significant enhancement during May 27-28. But a rise of TECin excess of 10-20 TECU was observed around the time of diurnal maximumon May 29. As AE remained above 600 nT for a duration of 5h on May28, 2017, TEC enhancement on May 29 may also be explained the AE valuein the form of DDEF. The difference in response for the two phases of this28 igure 13: Normalized diurnal variations of (a) meridional neutral wind and (b) zonalneutral wind during May 2631, 2017 for the stations Siliguri (slg in red), Indore (idr ingreen), Calcutta (ccu in blue) and Hyderabad (hyd in black). (For interpretation of thereferences to color in this figure legend, the reader is referred to the web version of thisarticle.) igure 14: Electrojet strength during May 2631, 2017, taking the difference of horizontalcomponent of the Earth’s magnetic field (H in nT) of Alibag (station away from magneticequator) from that of Dalat (a station near magnetic equator). storm may be attributed to the differences in their time of onset- first onein the local pre-midnight sector (21:30 LT) and the second one in the localdaytime sector (15:30 LT). Since O/N ratio did not show any appreciablechange during May 26-31 and there were no HSSW event during this period,their contribution to the positive storm effect observed during this periodcould be eliminated. The importance of the May 2017 storm lies in the factof its contrasting nature from the October 2016 storms. Although the stormof May 2017 had been more intense (i.e. lower Dst value) in comparison tothe October 2016 storms, dynamism of the latter had been greater due tothe unique presence of CME and HSSW.30 . Conclusions In the present paper, dramatic increase in low latitude TEC has beenobserved in response to the October 12-20, 2016 and May 26-31, 2017 stormsfrom the Indian subcontinent. The October 2016 event presents a unique caseof CME-induced storm (October 13-14) followed by a CIR-induced storm(October 16-17) during the declining phase of solar cycle 24. Drastic TECenhancement of 20-45 TECU in diurnal maximum was observed during theCIR-induced storm of October 2016 event due to Joule heating induced com-position change and CIR-induced HSSW event. The May 2017 storm presentsa contrasting case of October storms where no composition change or HSSWevents have been observed but TEC enhancement of 10-20 TECU in diurnalmaximum was observed. Additionally neutral wind values obtained from theHWM14 show positive TEC enhancement from different stations for boththe October 2016 and May 2017 storms. Thus even during low solar activity,geomagnetic storm induced electrodynamics at low latitudes is capable ofproducing TEC enhancements of about 20-45 TECU in excess of quiet timevalues. This translates to about 37m range error at GPS L1 frequency and isdetrimental for GNSS applications resulting in degradation of GNSS receiverperformance. To the best of our knowledge, such TEC enhancements, fromspatially distributed stations in the Indian longitude sector, due to compo-sition change and CIR event during a geomagnetic storm, occurring in thedeclining phase of the present solar cycle, has not been reported earlier.31 cknowledgments
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