Interplanetary and Geomagnetic Consequences of Interacting CMEs of 13-14 June 2012
SSolar PhysicsDOI: 10.1007/ ••••• - ••• - ••• - •••• - • Interplanetary and Geomagnetic Consequences ofInteracting CMEs of 13 – 14 June 2012
Nandita Srivastava · Wageesh Mishra · D. Chakrabarty c (cid:13) Springer ••••
Abstract
We report on the kinematics of two interacting CMEs observed on 13and 14 June 2012. Both CMEs originated from the same active region NOAA11504. After their launches which were separated by several hours, they wereobserved to interact at a distance of 100 R (cid:12) from the Sun. The interaction ledto a moderate geomagnetic storm at the Earth with D st index of approximately,-86 nT. The kinematics of the two CMEs is estimated using data from the SunEarth Connection Coronal and Heliospheric Investigation (SECCHI) onboardthe
Solar Terrestrial Relations Observatory (STEREO). Assuming a head-oncollision scenario, we find that the collision is inelastic in nature. Further, thesignatures of their interaction are examined using the in situ observations ob-tained by
Wind and the
Advance Composition Explorer (ACE) spacecraft. It isalso found that this interaction event led to the strongest sudden storm com-mencement (SSC) ( ≈
150 nT) of the present Solar Cycle 24. The SSC was of longduration, approximately 20 hours. The role of interacting CMEs in enhancingthe geoeffectiveness is examined.
Keywords:
Coronal mass ejections, STEREO, Heliospheric Imagers Udaipur Solar Observatory, Physical Research Laboratory,Udaipur, India -313001email: [email protected] CAS Key Laboratory of Geospace Environment,Department of Geophysics and Planetary Sciences,University of Science and Technology of China, Hefei, Chinaemail: [email protected] Space and Atmospheric Sciences Division, PhysicalResearch Laboratory, Ahmedabad-380009, Indiaemail: [email protected]
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1. Introduction
After the launch of twin
Solar TErrestrial Relations Observatory spacecraft(STEREO: Kaiser et al.
Sun Earth Connection Coronaland Heliospheric Investigation (SECCHI: Howard et al. et al. , 2009; Harrison et al. , 2012; Liu et al. , 2013; M¨ostl et al. ,2015; Vemareddy and Mishra, 2015). These observations have also revealed directevidence of CME–CME interaction when they are launched in close successionin the same direction (Harrison et al. , 2012; Lugaz et al. , 2012; Shen et al. , 2012;Mishra, Srivastava, and Chakrabarty, 2015). In fact, CME interactions are nowcommonly observed, in particular, around solar maximum when the occurrenceof CMEs is larger in number. A number of studies pertaining to understandingof the individual cases of interacting CMEs have been reported highlighting thenature of the interaction and/or collision and their signatures for example byHarrison et al. et al. et al. et al. et al. et al. , 2012; Shen et al. ,2012; Mishra and Srivastava, 2014; Mishra, Srivastava, and Chakrabarty, 2015;Mishra, Wang, and Srivastava, 2016). Further, using in situ observations, itmay also be possible to answer the question, under what conditions, interactingCMEs lead to a merged or a separate structure. One of the important questions iswhether the interaction of CMEs leads to enhanced geoeffectiveness as indicatedby Farrugia et al. (2006). If so, what are the distinct signatures of the same?Interaction of CMEs also has bearing on the prediction of space weather as thekinematics of CMEs change after interaction. For this purpose one also needsto understand the pre- and post-interaction kinematics which can influence theresulting geoeffectiveness.In this study, we present the evolution, propagation and interaction of twoCMEs launched on 13 and 14 June 2012 as they travelled in the inner heliosphereand reached the Earth. The observations reveal that the launch times of theCMEs were separated by about 24 hr. The observations also reveal that theCMEs of 13 and 14 June were directed towards the Earth and their initialspeed values indicate their probable interaction as they propagated out in theheliosphere. In this regard, the event provides an excellent opportunity for usto understand the interaction process in details. To achieve this objective, wehave estimated the 3D kinematics of the two CMEs using STEREO/SECCHIobservations, and the distance from the Sun at which they interacted. We havealso calculated the true mass of the interacting CMEs and their momentum toreveal the type of collision, and estimated momentum and energy transfer duringthe collision phase. Taking into account the propagation characteristics, the typeof collision and energy transfer properties of the two CMEs during the interactionwere estimated. We also examined the in situ data of the tracked CME features.The geomagnetic consequence of the interacting CMEs are very distinct andhave been studied in detail. The results and conclusions are presented in thefinal section.
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2. Observations
For the CME–CME interaction event of 13 – 14 June 2012, we analyzed datafrom the SECCHI suite (Howard et al. , 2008) onboard NASA’s twin STEREO (Aand B) mission. The SECCHI package includes the
Extreme Ultraviolet Imager (EUVI), two coronagraphs (COR1 and COR2), and two Heliospheric Imagers(HI1 and HI2)(Eyles et al. R (cid:12) , of COR1 is 1.5–4 R (cid:12) and of COR2, is 2.5–15 R (cid:12) . TheFOVs of the EUVI and CORs are centered on the Sun. On the other hand, HI1and HI2 have their optical axis aligned in the ecliptic plane and are off-centeredfrom the Sun at solar elongation of 14 ◦ and 53 . ◦ , respectively. The field ofview of HI1 and HI2 is 20 ◦ and 70 ◦ , respectively. Thus using SECCHI/STEREOinstrument data, a CME can be tracked from 0.4 to 88 . ◦ elongation. For quickexamination, we also used the coronagraph observations by the Large Angle andSpectrometric Coronagraphs (LASCO: Brueckner et al., 1995) onboard the Solarand Heliospheric Observatory (SOHO). During 13 – 14 June 2012, STEREO Aand B were 117 ◦ westward and 118 ◦ eastward from the Sun–Earth line at adistance of 0.96 AU and 1.0 AU from the Sun, respectively. The in situ propertiesof interacting CMEs were studied using the OMNI database which includes datarecorded by instruments on board Wind (Lepping et al. , 1995; Ogilvie et al. ,1995) and
Advance and Composition Explorer (ACE) spacecraft (Stone et al. ,1998).
A partial halo CME (CME1) at 13:25 UT with a projected speed of 630 km s − was recorded by LASCO coronagraphs on 13 June 2012. On the next day, i.e. − at 14:12 UT. The two CMEsare shown in Figure 1. As CME1 had a slower speed than CME2 and bothseemed to propagate in the earthward direction, the observations suggest theprobability of their interaction in the heliosphere. Both CMEs originated fromthe same active region, i.e. from NOAA AR 11504. CME1 was associated withan M1.2 flare which occurred at around S16 E18 location on 13 June 2012 andCME2 was associated with an M1.0 flare in the same active region and occurredon 14 June. The separation angle of the STEREO spacecraft during 13–14 June2012 was large, i.e. ◦ , therefore, in order to estimate the 3D kinematics ofthe CMEs, the Graduated Cylindrical Shell (GCS model: Thernisien, Howard,and Vourlidas, 2006) was used for 3D reconstruction of the CMEs. This modelrepresents the large scale flux rope structure of CMEs. It consists of a tubularsection which forms the main body of the structure attached to two cones thatform the legs of the CME. The resulting shape resembles that of a hollow crois-sant. For the present case, we have applied the GCS forward fitting model tothe contemporaneous images of the CMEs obtained from the SECCHI/COR2-B,SOHO/LASCO-C3, and SECCHI/COR2-A coronagraphs as shown in the imagesoverlaid with the fitted GCS wireframed contour (Figure 2). From the fitting of SOLA: sola_ti_nandita-dec13.tex; 22 December 2017; 19:38; p. 3 rivastava et al. the GCS model, we estimate the propagation direction of CME1 along E15 S30at 10.9 R (cid:12) . The propagation direction for the following CME2 was along E02S25 at 13.5 R (cid:12) . In addition to the propagation direction, the best visual GCSfitting gives a half angle of 22 . ◦ , a tilt angle of 70 ◦ , and an aspect ratio of 0.55for CME1. The half angle, tilt angle and aspect ratio for CME2 is 30 ◦ , 70 ◦ , 0.6,respectively. At around 11 R (cid:12) , the 3D speed of CME1 is estimated as 560 km s − and for CME2 as 900 km s − . The directions and speeds of the CMEs suggestthat they possibly collide during their heliospheric evolution. Using SECCHI/HIobservations, we determined the distance from the Sun at which the interactiontook place and also the nature of collision. We also attempted to identify distinctCME structures in the in situ data taken at L1 point and used them to estimatethe arrival time of the interacting CMEs. The CMEs of 13–14 June 2012 were well observed also in the HI-A and HI-Bfield of views of STEREO also. For the tracking of CME features, a minimumbackground image was created from a sequence of HI images. We constructedthe time-elongation maps, conventionally called J-maps, (Sheeley et al. , 2008;Davies et al. , 2009) using the running difference images of HI-1 and HI-2. Thedetails of the procedure to construct the J-maps and to derive the distancefrom the measured elongation angles have been described in Mishra, Srivastava,and Chakrabarty (2015); Mishra, Wang, and Srivastava (2016). These J-mapsreveal the kinematic evolution of these CMEs and are shown in Figure 3. Thepositively inclined bright features in the J-maps correspond to the enhanceddensity structure of the CMEs. The J-maps for 13–14 June events indicate thatenhanced brightness features came in close contact with each other and appearto merge around 25 ◦ elongation. Both features were tracked further up to 35 ◦ elongation.On the basis of earlier studies regarding the relative performance of the re-construction methods (Lugaz, 2010; Liu et al. , 2013; Mishra, Srivastava, andDavies, 2014), we applied the stereoscopic self-similar expansion (SSSE) (Davies et al. , 2013) method to the J-maps of the interacting CMEs in the present study.The SSSE method is expected to yield better results as the CMEs were observedin HI field of view of both STEREO-A and B. To implement the SSSE method,we require an appropriate value of the cross-sectional angular half width ( λ ) ofthe CMEs as an input. Earlier studies have also revealed that use of differentvalues of λ with the SSSE method give different estimates of the kinematicsof CMEs (Liu et al. , 2013; Mishra, Srivastava, and Davies, 2014). It has beenobserved that for CMEs that are Earth-directed when STEREO spacecraft arebehind the Sun, the SSSE method should be implemented with a value of λ as 90 ◦ (Liu et al. , 2013, 2014; Mishra, Srivastava, and Singh, 2015; Vemareddyand Mishra, 2015). In our case, the CMEs are Earth-directed and therefore theSSSE method is implemented with a value of λ as suggested in earlier studies.The estimated kinematics by implementing the SSSE method on the derivedtime-elongation profiles of these CMEs is shown in Figure 4 and has been usedto understand the collision phase of CMEs. As described in an earlier article SOLA: sola_ti_nandita-dec13.tex; 22 December 2017; 19:38; p. 4 nterplanetary and Geomagnetic Consequences of Interacting CMEs (Mishra, Srivastava, and Chakrabarty 2015), we define the collision phase as theinterval during which the two CMEs come in close contact with each other andshow opposite trends of acceleration relative to one another until they attainan approximately equal speed or their trend of acceleration is reversed. Thecollision of the two interacting CMEs occurred between 8:40 UT to 15:50 UTin a 7.2 hr span on 15 June 2012. At the beginning of the collision, the trackedfeature of CME1 was at around 105 R (cid:12) and that of CME2 at around 100 R (cid:12) .During the collision, they traveled a distance of around 25 R (cid:12) before reaching anapproximately equal speed. The collision led to an acceleration of the precedingCME1 from 590 km s − to 680 km s − and a deceleration of the following CME2from 865 km s − to 680 km s − . To estimate the momentum exchange during the collision of the CMEs, it isrequired to estimate the true masses of the two CMEs. Assuming that the CMEobserved in white-light is due to Thomson scattered photospheric light fromthe electrons in the CME (Minnaert, 1930; Billings, 1966; Howard and Tappin,2009), the recorded scattered intensity can then be converted into the number ofelectrons, and hence the mass of a CME can be estimated, assuming a completelyionized corona with a composition of 90% hydrogen and 10% helium. In earlierstudies (Munro et al. , 1979; Poland et al. , 1981; Vourlidas et al. , 2000), the massof a CME was calculated assuming the CME location in the observer’s plane ofsky. We use the method of Colaninno and Vourlidas (2009) which is based onthe Thomson scattering theory, to estimate the true propagation direction andtrue mass of both CMEs. For this purpose we used the simultaneous image pairof SECCHI/COR2 and estimated the masses of CME1 and CME2 to be 8.4 × kg and 9.2 × kg, respectively. The mass ratio of the interacting CMEsis approximately 1.1.Although, we have estimated the true mass, this also involves uncertainties.A straightforward uncertainty arises due to the assumption that the mass of aCME is concentrated on the plane-of-sky. However, a CME is a three dimensionalstructure with a significant depth along the line-of-sight. It has been reportedearlier that such an assumption leads to underestimation of the CME mass by15% (Vourlidas et al. , 2000). We made several independent mass measurementsfor this event and found that the values are within 20% of the measured ones.Further, the role of the uncertainty in the mass estimation has been studied tounderstand the variation in the coefficient of restitution which has been foundto be negligible in deciding the nature of the collision (Shen et al. , 2012; Mishra,Wang, and Srivastava, 2016). This is expected as our approach constrains the mo-mentum conservation while modifying the observed post-collision speeds (Mishraand Srivastava, 2014). Therefore, in this study we did not assess the effect ofuncertainties in the mass. Significant momentum exchange takes place during theinteraction, with an increase in the momentum of the preceding and decreasein the momentum of the following CME. In the present case, the momentum ofCME1 increased by 57% and that of CME2 decreased by 24% after the collision. SOLA: sola_ti_nandita-dec13.tex; 22 December 2017; 19:38; p. 5 rivastava et al.
For our analysis we consider that after crossing the FOV of the COR2 corona-graph, during the collision of CME1 and CME2, their estimated true masses ( M and M ) remained constant. Using the estimated kinematics before and after thecollision (Figure 4) and their true masses, the coefficient of restitution has beencalculated. The observed velocity of CME1 and CME2 before the collision isestimated as ( u , u ) = (590, 865) km s − and the observed velocity of CME1and CME2 after the collision is ( v , v ) = (680, 680) km s − . To understand thenature of the collision of the two CMEs, we estimate the coefficient of restitu-tion ( e ) of the colliding CME1 and CME2 following the formulations describedin Mishra and Srivastava (2014); Mishra, Srivastava, and Singh (2015). Thecoefficient of restitution measures the bounciness of the collision and is definedas the ratio of their relative velocity of separation to their relative velocity ofapproach. In this particular case, the coefficient of restitution ( e ) is estimated tobe 0 . i.e. the collision is perfectly inelastic in nature. Consequently the kineticenergy of the system after the collision is found to be lower than that before thecollision. In situ
Properties and Time of Arrival of the InteractingCMEs of 13 – 14 June 2012
We analyzed the in situ data associated with the 13-14 June, interacting CMEsusing the OMNI database to identify interplanetary signatures of different fea-tures of the CMEs. Figure 5 shows the magnetic field and plasma measurementsduring 00:00 UT on 16 June to 00:00 UT on 18 June. The arrival of a forwardshock (labeled S1) marked by a sudden enhancement in speed, temperature,and density is observed at 08:42 UT on June 16. This is followed by an ICMEstructure (ICME1) for approximately 12 hrs. The second shock S2 is markedby a sharp and huge increase in density indicating a pile-up or compression ofthe plasma as the shock passes through the cloud. S2 was observed at 21:40UT on 16 June. Based on the signatures of ICMEs that are expected to beobserved in in situ observations (Zurbuchen and Richardson, 2006), the regionbounded between approximately 21:40 UT on 16 June and 21:00 UT on 17 Juneis identified as the second ICME structure (ICME2).During the passage of ICME1, the magnetic field was quite strong ( ≈
10 nT),while plasma β < β <
1, temperature is also low ( ≈ K) and the density high.These signatures are suggestive of the passage of a magnetic cloud as definedby Burlaga et al. (1981). It is further observed that the temperature does notshow any distinct variation during the interaction of the two CMEs contraryto our previous studies (Mishra and Srivastava, 2014; Mishra, Srivastava, andChakrabarty, 2015) where the interaction of the CMEs was represented by ahigh temperature region associated with the first CME, which is higher thanusually found for a normal isolated CME (Zurbuchen and Richardson, 2006).
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Thus, examining the in situ observations, we can mark the arrival of twodistinctly different regions as far as the CME–CME interaction is concerned inthe present case. The first part appears to be the arrival of the first CME markedby the increase of the plasma parameters at 8:42 UT on 16 June but steady forsome time. Then the second CME at 21:40 UT on 16 June probably piercesthrough the first one creating a small region where the density falls off veryrapidly. The two peaks in SYM-H (Iyemori, 1990) at 22:40 UT on 16 June andat 01:05 UT on 17 June interspersed by a dip probably correspond to the arrivalof the faster CME in which a rarefied region is embedded. The estimated speedsof two shocks marked as S1 and S2 were 450 and 485 km s − , respectively. Theproton temperature ratio Tp down /Tp up was approximately 0.04 for the secondshock as compared to 1.26 for the first shock.
4. Geomagnetic Consequences of the Interacting CMEs of13 – 14 June 2012
The CMEs on 13 – 14 June 2012 were quite normal CMEs in terms of theirinitial speeds. They resulted in a single moderate ( D st ≈ -86 nT) and long lastinggeomagnetic storm. However, the magnitude of the sudden storm commencement(SSC) was exceptionally high ( ≈
150 nT) at 21:40 UT on 16 June. This callsour attention to study the impact of the interaction of the two CMEs on theterrestrial magnetosphere-ionosphere system in detail.
As mentioned above, the resulting geomagnetic storm is important because of itsintense magnitude, particularly of the associated SSC. Generally the time of theSSC denotes the arrival of the interplanetary shock and its strength. Previousstudies based on a statistical analysis have shown that the occurrence rate ofSSCs is less than 5% for amplitudes larger than 50 nT and less than 1% foramplitudes larger than 100 nT (Araki, 2014). Further, generally large amplitudeSSCs tend to occur during the declining phase of the solar activity, however,the present case is an exception as it occurred during the ascending phase ofSolar Cycle 24. The SYM-H index rose from 39 nT to 150 nT, during 16 June2012, 20:20 UT to 20:47 UT, the rise time being 27 minutes. This puts theobserved SSC as the strongest observed in Solar Cycle 24 and also as one ofthe most intense events if one considers the past events examined by Araki etal. (2014). Further, SSCs with amplitude larger than 100 nT are extremely rare(less than 1%) and the rise time is usually 3 to 4 min (Maeda et al. , 1962). In thisregard, the amplitude of this SSC is very large and the rise time is unusuallylong. The present case due to its large variation with time, strongly suggeststhe strengthening of the shock which occurred due to the interaction of the twosuccessive CMEs. This is unique for three reasons. First, is its long duration(more than 20 hr); second, its high peak magnitude ( ≈
150 nT); and third, itoccurred in three distinct steps with a small rise to start with and two peakswith a sharp fall in between. It is also interesting to point out that during this
SOLA: sola_ti_nandita-dec13.tex; 22 December 2017; 19:38; p. 7 rivastava et al. time the y-component of interplanetary electric field (IEFy) was negative, whichmeans that the z-component of the interplanetary magnetic field (IMF), B z , wasnorthward during this interval, thereby implying that its time of occurrence isprior to the main phase of the storm and hence confirms that the feature is anSSC.Also, in an attempt to understand the role of interacting CMEs for the uniqueSSC event, we observed that solar wind density increased three times from 20to 60 cm − and the velocity from 300 to 550 km s − during this interval, whichcorresponds to distinct steps manifested in SYM-H values. This further suggeststhat solar wind ram pressure related shocks have contributed significantly to theSSC.The IP shock properties as derived from Wind data and catalogued at http://ipshocks.fi/ reveal that for the second shock (S2), the value of θ , i.e. theangle between the shock normal and the magnetic field lines upstream is 60 ◦ as compared to 15 ◦ , for the first shock (S1). Here, the values of θ indicate thatshock S1 is quasi-parallel ( θ < ◦ ) and therefore should be associated withextended foreshock regions, whereas the shock transitions are typically moregradual; the jumps in the solar wind plasma parameters and in the magneticfield magnitude are less significant than at quasi-perpendicular shocks (Burgess et al. , 2005; Kruparova et al. , 2013), where θ > ◦ . As may be noted from Figure 5, the main phase of the geomagnetic storm lastedfor more than 16 hr and the recovery phase was also quite long (approximately 72hr).
In situ observations indicate the arrival of two shocks and a merged structurefor the two events. In particular, the OMNI in situ data reveal a weak shock at09:03 UT with a small ICME followed by a stronger shock at 19:34 UT and aprolonged ICME. It is also noted that the intensity of the geomagnetic storm, D st reached a peak value of ≈ -86 nT at 14:00 UT and maintained the moderatelevel of −
50 nT for 14 hr. The event suggests a resemblance with that describedby Lugaz and Farrugia (2014), wherein they reported a long-duration isolatedevent that resulted from the merging of two CMEs with peak D st reaching ≈
150 nT and remaining at moderate values (below 50 nT) for 55 hr. It may alsobe noted that we do not observe any signature of a distinct interaction region in in-situ data for 13 – 14 June event, as was reported in the case of 9–10 November2012 interacting CMEs (Mishra, Srivastava, and Chakrabarty, 2015).
5. Summary and Conclusion:
Although the interacting CMEs of 13 – 14 June 2012 appear to be quite normalin terms of speeds and associated flares and the resulting geomagnetic storm isalso moderate with D st attaining ≈ -86 nT value, the interaction event is quiteunique in terms of its geomagnetic consequence. The two CMEs interacted at adistance of 100 R (cid:12) from the Sun and reached the Earth as a merged structure.The arrival of the CMEs is marked by an enhanced SSC with a peak of 150 SOLA: sola_ti_nandita-dec13.tex; 22 December 2017; 19:38; p. 8 nterplanetary and Geomagnetic Consequences of Interacting CMEs nT. The magnitude of this SSC is the highest recorded in Solar Cycle 24. Theduration of the rise time of this SSC is also unusually high, of the order ofseveral hours due to the strengthening of the shock owing to the interactionof the CMEs. The merged structure led to a single step moderate storm whoseduration was unusually long, both for the main phase ( ≈
16 hr) and the recoveryphase ( ≈
72 hr). Contrary to the present knowledge that the strong SSCs occurduring the descending phase of the solar cycle, the CMEs of 13 – 14 June 2012are remarkable as their interaction led to the strongest SSC in the ascendingphase of Solar Cycle 24.
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Acknowledgments
We acknowledge the UK Solar System Data Centre for providing theprocessed level-2 STEREO/HI data. The in situ measurements of solar wind data from ACEand Wind spacecraft were obtained from NASA CDAweb ( http://cdaweb.gsfc.nasa.gov/ ). W.M. is supported by the Chinese Academy of Sciences (CAS) President’s International Fellow-ship Initiative (PIFI) grant No. 2015PE015.
Disclosure of Potential Conflicts of Interest:
The authors declare thatthey have no conflicts of interest.
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Figure 1.
The two interacting coronal mass ejections of 13 and 14 June 2012 observed aspartial halos by COR2-B coronagraph in the left and right panels, respectively.
Figure 2.
The GCS wired model overlaid on the contemporaneous images observed for thetwo CMEs, upper panel (CME1) around 16:54 UT on 13 June and lower panel (CME2) around15:39 UT on 14 June. For both CMEs the fitting of the model is done for the three imagesrecorded by COR2-B (left), LASCO-C3 (middle), COR2-A (right) images.
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Spacecraft A: Ecliptic E l onga t i on ( o ) STEREO HI-1 and HI-2
Spacecraft B: Ecliptic E l onga t i on ( o ) STEREO HI-1 and HI-2
Figure 3.
Time-elongation maps (J-maps) using the COR2 and HI observations ofSTEREO/SECCHI spacecraft during interval of 13 – 14 June 2012 is shown. The featurescorresponding to leading edges of CME1 and CME2 are tracked and overplotted on the J-maps.
SOLA: sola_ti_nandita-dec13.tex; 22 December 2017; 19:38; p. 12 nterplanetary and Geomagnetic Consequences of Interacting CMEs D i s t an c e ( R O • ) CME1CME2 SSSE ( λ ~ 90 ° ) -20-10010 D i r e c t i on ( ° ) Sun-Earth line
14 Jun00:00 14 Jun12:00 15 Jun00:00 15 Jun12:00 16 Jun00:0004008001200 S peed ( k m s - ) Date (UT)
Figure 4.
The plots show the distance and speed estimated for different tracked features ofthe two CMEs.
SOLA: sola_ti_nandita-dec13.tex; 22 December 2017; 19:38; p. 13 rivastava et al. B ( n T ) -25025 B z ( n T ) N p ( c m - ) T p ( K ) V p ( k m s - ) β
16 Jun00:00 16 Jun12:00 17 Jun00:00 17 Jun12:00 18 Jun00:00-80080160 S y m - H ( n T ) Date (UT)
S1 S2ICME1 ICME2
Figure 5.
From top to bottom, total magnetic field magnitude, z-component of magnetic field,proton density, proton temperature, proton speed, plasma beta ( β ), and SYM-H, is shown forthe time interval of 00:00 UT on 16 June to 00:00 UT on 18 June. From the left, the first,second, and third vertical (dashed) lines mark the arrival of shock (S1) associated with CME1,shock (S2) associated with CME2, and the trailing boundary of ICME2, respectively. SOLA: sola_ti_nandita-dec13.tex; 22 December 2017; 19:38; p. 14 nterplanetary and Geomagnetic Consequences of Interacting CMEs
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