Ionospheric response to Strong Geomagnetic Storms during 2000-2005: An IMF clock angle perspective
Sumanjit Chakraborty, Sarbani Ray, Abhirup Datta, Ashik Paul
mmanuscript submitted to
Radio Science
Ionospheric response to Strong Geomagnetic Stormsduring 2000-2005: An IMF clock angle perspective
Sumanjit Chakraborty , Sarbani Ray , Abhirup Datta , , Ashik Paul Discipline of Astronomy, Astrophysics and Space Engineering, IIT Indore, Simrol, Indore 453552,Madhya Pradesh, India Center for Astrophysics and Space Astronomy, Department of Astrophysical and Planetary Science,University of Colorado, Boulder, CO 80309, USA Institute of Radio Physics and Electronics, University of Calcutta, Kolkata 700 009, West Bengal, India
Accepted for publication in Radio Science
Key Points: • Strong geomagnetic storms during 2000–2005 are selected in terms of Dst and IMF B z . • Global ion density plots are used to study the effects of PPEF. • Longitudes of ESF occurrence in response to PPEF are predicted from the timeof northward to southward transition of the IMF clock angle.
Corresponding author: Sumanjit Chakraborty, [email protected] –1– a r X i v : . [ phy s i c s . s p ace - ph ] A ug anuscript submitted to Radio Science
Abstract
This paper presents the equatorial ionospheric response to eleven strong-to-severe ge-omagnetic storms that occurred during the period 2000-2005, the declining phase of thesolar cycle 23. The analysis has been performed using the global ion density plots of De-fense Meteorological Satellite Program (DMSP). Observations show that for about 91%of the cases, post-sunset equatorial irregularities occurred within 3h from the time of north-ward to southward transition of the Interplanetary Magnetic Field (IMF) clock angle,thus bringing out the importance of the role played by IMF B y in the process of PromptPenetration of Electric Field (PPEF) in addition to the IMF B z . This is an improve-ment from the previously reported (Ray et al., 2015) 4h window of ESF generation fromthe southward IMF B z crossing -10 nT. The solar drivers of geomagnetic storms are the Coronal Mass Ejection (CME) andthe Co-rotating Interaction Region (CIR). CMEs pass across the Earth frequently withan average rate of two events per month, having variations throughout a given solar cy-cle (Richardson & Cane, 2010). The occurrence of CME-driven geomagnetic storms hav-ing stronger intensity tends to be high during the ascending and solar maximum phasesin a solar cycle. The other type, CIRs, are the drivers of weak-to-moderate geomagneticstorms that have a similar impact on the ionosphere comparable to a CME driven storm,and they mostly occur during the declining phase of a solar cycle (Borovsky & Denton,2006; Buresova et al., 2014; Y. D. Liu et al., 2014; Chakraborty et al., 2020). When thehigh speed solar wind streams, originating from a coronal hole, interact with the slowsolar winds, shocks along with compression and rarefaction regions are formed, causingrecurrent geomagnetic storm effects on the Earth (Richardson, 2018; Yermolaev et al.,2018).The solar wind emanating from the Sun carries a frozen-in Interplanetary MagneticField (IMF) that interacts with the Earth’s magnetosphere-ionosphere system. The IMFB field defined as: B = (cid:113) B y + B z (1)is a 2D vector (the y and z components designated as B y and B z respectively) of the so-lar wind IMF. The vertical plane, with respect to the ecliptic, is the B y − B z plane with B x being the corresponding x component (Sun-to-Earth line) of solar wind IMF. When B z is southward or has a negative orientation, the coupling to geomagnetic field is thestrongest, setting conditions favorable for geomagnetic storm activity. While IMF B givesthe magnitude, the orientation of this field is given by the IMF clock angle ( θ ) which isthe angle produced in the vertical plane from the vector addition of the B y and B z com-ponents of IMF and is defined as: tanθ = B y B z (2)where − ◦ ≤ θ ≤ ◦ (Grocott & Milan, 2014). The Interplanetary Electric Fieldof the solar wind enters the Earth’s ionosphere via magnetosphere under geomagneti-cally perturbed conditions due to the southward turning of the Interplanetary MagneticField’s (IMF B z ) north-south component (Fejer et al., 1990) passing across Earth for along time interval (Gonzalez et al., 1994). A sudden increase is observed in the dawn-to-dusk polar cap potential, which results from the change in region 1 current due to thepassage of IMF B z . An undershielding condition gets developed when the ionosphere adaptsitself from this prompt electric field from the outer magnetosphere. This happens be-cause the region 2 current, that shields the low-latitude ionosphere from electric fieldsat high latitudes, varies slowly in comparison to the region 1 current. As a result, en-try of this electric field from the high latitudes to the equatorial latitudes occur promptlyand hence are known as the Prompt Penetration Electric Field (PPEF) (Basu et al., 2010). –2–anuscript submitted to Radio Science
As time passes, an inertial field gets developed in the inner magnetosphere, that opposesthe PPEF and produces shielding. When there is a sudden northward turn of the IMF B z that cancels this penetrating electric field, the inertial field, which is oppositely di-rected to the incoming electric field becomes dominant in the ionosphere causing an over-shielding condition (Kikuchi et al., 1996). The electric field enhancements in the low-latitude ionosphere are related to magnetic activity and occur during the main phase ofmagnetic storms, revealing the fact that the interplanetary electric field continuously pen-etrates to the low-latitude ionosphere without shielding for many hours as long as thestrengthening of the magnetic activity is going on under storm conditions (Huang et al.,2005).In addition to PPEF, the electric field, which influences low-to-equatorial trans-portation of plasma during the disturbed conditions, comes from the neutral wind cir-culation changes at the sub-auroral thermosphere as a result of the deposition of enor-mous energy from the solar wind-magnetosphere and ionosphere coupling. This is knownas the Disturbance Dynamo Electric Field (DDEF), which opposes the PPEF and lastsupto few days after becoming active a few hours post-PPEF (Blanc & Richmond, 1980).Furthermore, the PPEF is directed eastward till 22:00 Local Time (LT), and turns west-ward after that and remains so till morning hours (Fejer et al., 2008a). During the day-time, eastward directed dynamo electric field of the E region gives rise to the E × B drift(where B is the magnetic fields that are nearly parallel to the Earth’s surface at equa-torial latitudes) in the vertical direction causing an upward lift of plasma in the F re-gion at the magnetic equator. As a consequence of forces due to pressure-gradient andgravity, these plasma move along the magnetic field lines. Thus the Equatorial Ioniza-tion Anomaly (EIA) is formed that has two crests around ± ◦ magnetic latitudes andtrough around the magnetic equator (Appleton, 1946).Ionosphere over the equatorial and low latitude regions present a dynamic feature,in addition to the EIA, known as the Equatorial Spread F (ESF) or irregularities of plasmathat are plasma structures having scale sizes ranging from a few meters to a few hun-dred kilometers (Abdu et al., 1981; Sales et al., 1996; Kil & Heelis, 1998; Li et al., 2012)and references therein. The dynamo electric fields and plasma densities decrease in theE region around local sunset and weaken the EIA. However, simultaneously the F layerdynamo is intensified. The ionospheric plasma is transported upward by the post-sunsetelectric field, which enhances the anomaly crests. The eastward PPEF gets enhanced aroundlocal sunset because of the gradient in day to night conductivity. The enhanced electricfield generates Rayleigh-Taylor instability of plasma. The instability causes the forma-tion of irregularities, which are large, plasma depleted structures known as the Equa-torial Plasma Bubbles (EPB) (Abdu et al., 1981; Kil & Heelis, 1998; Alfonsi et al., 2013)and references therein. These EPBs cause satellite signals to scintillate. In recent years,the study of PPEF has become a vital space weather issue as they are related to thesescintillations that cause catastrophic effects on the various Global Navigation SatelliteSystems (GNSS) such as GPS, GLONASS, etc. and Regional Navigation Satellite Sys-tems (RNSS) such as NavIC/IRNSS. Studies have been performed by several researcherswith the Defense Meteorological Satellite Program (DMSP) satellite in situ measurements.Basu et al. (2010) studied large geomagnetic storms of solar cycle 23 and showed thatwith the knowledge of the time duration of the main phase of storms, one would be ableto determine the dusk sector corresponding to the main phase and would be able to spec-ify the longitude interval over which the scintillations could be detected. Ray et al. (2015)have showed that in a longitude sector where the local time is dusk, ESF gets generatedwithin 4 hours of the southward turning of IMF B z .The equatorial ionospheric response to PPEF for the strong (G3 class, K p = 7) andsevere (G4 class, K p = 8), according to the National Oceanic and Atmospheric Admin-istration (NOAA) space weather scales, geomagnetic storms during the period from 2000-2005, which fall in the declining phase of solar cycle 23, using in situ DMSP global ion –3–anuscript submitted to Radio Science
Period Minimum Dst(nT) UT(HH:MM) DOY(DD)April 05-07, 2000 -292 01:00 098(07)August 11-13, 2000 -234 10:00 225(12)October 28-30, 2000 -126 04:00 303(29)March 19-21, 2001 -149 14:00 079(20)October 02-04, 2001 -166 15:00 276(03)April 17-19, 2002 -127 08:00 108(18)June 17-19, 2003 -141 10:00 169(18)August 17-19, 2003 -148 16:00 230(18)July 24-26, 2004 -136 17:00 205(25)August 29-31, 2004 -129 23:00 243(30)May 29-31, 2005 -113 14:00 150(30)
Table 1.
Minimum Dst values with the corresponding Day of Year and Date (DOY(DD)) ofminimum for the severe storms analyzed during 2000-2005. density measurements, have been studied in this work. This paper presents the ionosphericresponse to strong-to-severe geomagnetic storms during the declining phase of solar cy-cle 23 from an IMF clock angle perspective.
The storms in this paper are selected on the basis of the Disturbance storm time(Dst) index (nT) obtained from http://wdc.kugi.kyoto-u.ac.jp/dstdir/. The 1 minutehigh resolution interplanetary parameters: B y (nT) and B z (nT) component of the IMFrespectively, along with the SYM-H (nT) index are obtained from https://omniweb.gsfc.nasa.gov.The in situ total ion density measurements are obtained from https://cindispace.utdallas.edu/DMSPby the DMSP f12, f14, and f15 sun-synchronous, near-polar orbiting satellites, samplingwith a time interval of 4s at 840 km altitude with an orbital period of 101 minutes andcrossing the magnetic equator during the time span of 19:00-22:00 Magnetic Local Time(MLT). During the period from 2000-2005, eleven storms have been selected that satisfiedthe criteria of qualifying for a strong storm i.e., Dst ≤ -100 nT and IMF B z ≤ -10 nTfor at least 3 hours (Gonzalez & Tsurutani, 1987; Gonzalez et al., 1994). Table 1 showsa summary of the storm particulars (along with the time and day of Dst minimum), whereintwo storms (April 06, 2000 and August 12, 2000) showed minimum Dst values below -200 nT qualifying them to be falling under the severe storm category, rest falling underthe strong storm category (Loewe & Prolss, 1997). The storms of April 06, 2000 and May30, 2005 have been discussed in this paper. –4–anuscript submitted to Radio Science
Figure 1.
Variation of interplanetary parameters during April 05-07, 2000. Panels a to e showSYM-H followed by IMF B z , B y , B and the IMF clock angle respectively. On April 04, 2000, a CME event took place near the Sun’s western limb. The CMEshock hit the magnetosphere of Earth on April 6, 2000 (Huttunen et al., 2002). This stormhas been studied by several authors (Lee et al., 2002; Pulkkinen et al., 2003; L. Liu etal., 2004) and references therein. The event not only just resulted in the PPEF but alsothe DDEF and the travelling ionospheric disturbances (Rastogi & Chandra, 2016) andreferences therein. Figure 1 shows the variation of storm parameters during April 05-07, 2000. In Figure 1a, the SYM-H index has been plotted wherein the storm commencedat 16:45 UT on April 6, 2000. The SYM-H dropped to a minimum with a value of -320nT at 00:09 UT on April 07, 2000. In Figures 1b and 1c, the variations of IMF B z and B y , respectively, are shown. The IMF B z turned southward reaching below a value of-10 nT at 17:46 UT on April 06, 2000, reached a minimum of -33.0 nT at 23:12 UT andremained below -10 nT for a duration of 06:34 until 00:21 UT on April 07, 2000, thusindicating the storm to be of severe (G4) level according to the NOAA scales. Duringthe period when IMF B z turned southward, was minimum and turned northwards, thecorresponding IMF B y indicated values of -16.0 nT, 0.4 nT and -15.0 nT respectively.Furthermore, the variation of IMF B has been shown in Figure 1d wherein the value ofB had been 19.1 nT during B z turning southward, 33.0 nT when B z dropped to a min-imum value and 19.6 nT at B z turning northward. Figure 1e shows the variation of theIMF clock angle, θ in degrees. The clock angle had a sharp transition from northwardwith a value of 14.115 ◦ at 17:48 UT to southward with a value of -1.168 ◦ at 17:49 UTon April 6, 2000.The global effect of the enhanced PPEF at dusk on the equatorial ionosphere hasbeen observed by analyzing the in situ ion density measurements from successive DMSP –5–anuscript submitted to Radio Science transits crossing the equator between 19:00 and 22:00 MLT over the magnetic latitudes-30 ◦ to 30 ◦ . Figure 2 show the plots of the total ion density for the orbits of DMSP f12,f14, and f15 satellites with equator crossing times ranging from 17.21 UT to 23.36 UTwith corresponding MLTs ranging from 21.24 to 20.95 on April 6, 2000. Sudden outburstsof irregularities about the magnetic equator (indicated by black colored down arrows inthis figure) can be observed around 35.35 ◦ E at 18.30 UT (20.66 LT), 34.43 ◦ E at 18.92UT (21.21 LT), 09.40 ◦ E at 20.01 UT (20.64 LT) and 355.52 ◦ E at 20.67 UT (19.04 LT).Comparing the time of irregularity occurrence with the time of IMF B z crossing -10 nTduring the main phase of the storm, it is found that the irregularity occurred with a de-lay of 3.23h, Furthermore, the irregularity occurred with a delay of 0.49h from the IMFclock angle transition from northward to southward. –6–anuscript submitted to Radio Science
Figure 2.
Total Ion Density (cm −
3) variation as observed by the DMSP f12,f14 and f15 satel-lites on April 06, 2000 from post-sunset to pre-midnight UT. The black down arrows indicatepresence of irregularities during this period. –7–anuscript submitted to
Radio Science
Figure 3.
Variation of interplanetary parameters during May 29-31, 2005. panels a to e showSYM-H followed by IMF B z , B y , B and the IMF clock angle respectively. B z turnedsouthward, reaching below the value of -10 nT at 04:27 UT on May 30, 2005 in Figure3b while IMF B y showed -16.47 nT at that instant as observed in Figure 3c. IMF B z remained below -10 nT from 06:35 UT, with a value of -14.5 nT, to 15:34 UT with a valueof -14.7 nT, on May 30, 2005, which is for a duration of 08:59. During this period IMF B y recorded -5.9 nT and -3.5 nT respectively. From Figure 3d, the value of B was 19.7nT when B z first turned southward and remained below -10 nT while showing a valueof 15.2 nT at B z turning northward. Figure 3e shows the variation of the IMF clock an-gle. The clock angle had a sharp transition from northward with a value of 179.868 ◦ at03:56 UT to southward with a value of -179.313 ◦ at 03:57 UT on May 30, 2005.Figure 4 shows the variations in the total ion density for the orbits of the three DMSPsatellites with equator crossing times ranging from 09.26 UT to 17.80 UT on May 30,2005. The only outburst of irregularity about the magnetic equator (indicated by blackcolored down arrow in the figure) is observed around 172.59 ◦ E at 07.30 UT (18.81 LT)with the corresponding MLT 20.55. Comparing the time of irregularity occurrence withthe time of IMF B z , it is found that the irregularity occurred with a delay of 2.85h. Fur-thermore, the irregularity occurred with a delay of 3.37h from the IMF clock angle tran-sition from northward to southward. –8–anuscript submitted to Radio Science
Figure 4.
Total Ion Density (cm −
3) variation as observed by the DMSP f12,f14 and f15 satel-lites on May 30, 2005 from morning to post-sunset UT. Presence of irregularity is indicated byblack down arrow. –9–anuscript submitted to
Radio Science
Figure 5a shows the distribution of the time of transition of the IMF clock angle(red vertical bar) and the time of IMF B z crossing -10 nT (blue vertical bar) for all theeleven storms. Figure 5b shows the distribution of the delays of irregularity occurrencefrom the IMF clock angle transition (red vertical bar) and IMF B z crossing -10 nT (bluevertical bar). The delay between irregularity occurrence from the time of IMF B z cross-ing -10 nT is below 4h for all the storms, which is in accordance with that reported in(Ray et al., 2015). Additionally, it is observed that the delay between the IMF clock an-gle transition and the irregularity occurrence is below 3.5h for all the cases, which is animprovement over that reported by Ray et al. (2015). Furthermore, for 91% of the cases,irregularity occurred within 3.5h and 3h from the time of IMF B z –10–anuscript submitted to Radio Science
Figure 5. (a) Distribution of the time of transition of the IMF clock angle (in red) and timeof IMF B z crossing -10 nT (in blue); (b) Distribution of the delay of irregularity occurrence fromthe time of northward to southward transition of the IMF clock angle (in red) and the delay ofirregularity occurrence from the time of IMF B z crossing -10 nT (in blue) for all the storms.–11–anuscript submitted to Radio Science
Figure 6.
World map showing the geographic latitude and longitude of the irregularity oc-currence. The delay (in hours and designated as rectangles) between the time of northward tosouthward transition of the IMF clock angle and irregularity occurrence longitude (the cyan crossmarks) for all the storms during 2000-2005 are shown . –12–anuscript submitted to Radio Science
Study of the equatorial and low-latitude ionosphere, especially during geomagneticstorm time conditions, is useful to understand the dynamics and variability it presents,that would affect the navigation by satellite systems. In this paper, for eleven strong-to-severe geomagnetic storms during the declining phase of solar cycle 23 (2000-2005),it has been observed that for ∼
91% of the cases, post-sunset equatorial irregularitiesoccurred within 3.5h from the time of IMF B z crossing -10 nT and within 3h from thetime of northward to southward transition of the IMF clock angle. Ray et al. (2015) re-ported that within 4h of the southward IMF B z crossing -10 nT, irregularity would oc-cur in the dusk longitude sector. For predicting the storm time occurrence of ESF in re-sponse to PPEF, when undershielding condition prevails, the clock angle transition timeprovides better accuracy than the time of B z crossing -10 nT, as evident from this studybased on eleven strong-to-severe geomagnetic storms. This study also shows the impor-tance of taking the B y component of IMF into account, in addition to the B z compo-nent as IMF B y plays an important role in determining the PPEF polarity (Grocott &Milan, 2014; Chakrabarty et al., 2017). This paper, for the first time, shows that by hav-ing the knowledge of the time of sharp transition of the IMF clock angle, it would be pos-sible to predict the longitude sector that would be affected due to the ESF generation,thus an improvement, and hence a better forecast lead time, from the previously reported4h window of ESF generation from the southward IMF B z crossing -10 nT. Acknowledgments
SC acknowledges Space Applications Centre (SAC), ISRO for providing fellowship un-der project NGP-17. The authors acknowledge the Center for Space Physics, Universityof Texas at Dallas and the U.S. Air Force for the DMSP plasma data. Acknowledgementsgo to NASA Goddard Space Flight Center-Space Physics Data Facility (GSFC-SPDF)for the 1 minute high resolution omniweb data available at https://omniweb.gsfc.nasa.gov/form/omni min.html for the SYM-H index and the interplanetary parameters: IMF B y and B z . Further acknowledgements go to the World Data Center (WDC) at Kyoto Uni-versity for the Dst index data available at http://wdc.kugi.kyoto-u.ac.jp/. SR would liketo thank International Centre for Theoretical Physics (ICTP), Trieste for providing sup-port through Senior Associateship Program. –13–anuscript submitted to Radio Science
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