Changes In Interplanetary Magnetic Field Research Articles

Energetic Dynamics of the Inner Magnetosphere in Contact with Fast Solar Wind Currents: Case of the Period 1964-2009

The Earth’s magnetosphere is a magnetic shield that protects Earth from high-energy particles and is subject to a series of internal processes caused by jets of the solar wind (SW) that destabilize it. These disturbances affect health as well as technology and become more extreme when SW is more accelerated. Thus, to better understand the impact of high-speed solar wind (HSSW) invasion on the dynamics of the magnetospheric system, a statistical study of HSSW populations was conducted for even (20 and 22) and odd (21 and 23) solar cycles. The regression analysis using the solar-derived fields from all solar cycles, indicates three states of the inner magnetosphere: 1) the 00:00UT-15:00UT period marked by a magnetic reconnection on the day side of the Earth closest to the Sun with the interplanetary magnetic field (IMF) facing South; 2) the 15:00UT-21:00UT period where IMF changes from South to North and remains there until 21:00UT; and 3) the 21:00UT-24:00UT period where there is a reconnection on the night side with stretched field lines. Observations made at different phases of solar activity lead us to suggest that the magnetospheric electric field (EM) and the Bz component of IMF (IMF-Bz) are strongly correlated not only at a particular time scale, but at different time scales. We believe that the daily fluctuations of the electrical and magnetic effects of magnetospheric origin currents play a very important role in the dayside magnetic reconnection rate. Moreover, examination of the cycles with different parities shows important amplitudes of the solar causes for the even cycles compared to the odd solar cycles. Therefore, even solar cycles have a strong influence on our socio-economic system compared to odd cycles.

Multi‐Instrument Observations of Ion‐Neutral Coupling in the Dayside Cusp

AbstractUsing data from the Scanning Doppler Imager, the Super Dual Auroral Radar Network, the EISCAT Svalbard Radar, and an auroral all‐sky imager, we examine an instance of region neutral winds which have been influenced by the presence of poleward moving auroral forms near the dayside cusp region. We observe a reduction in the time taken for the ion drag force to reorientate the neutrals into the direction of the convective plasma (on the order of minutes), compared to before the auroral activity began. Additionally, because the ionosphere near the cusp is influenced much more readily by changes in the solar wind via dayside reconnection, we observe the neutrals responding to an interplanetary magnetic field change within minutes of it occurring. This has implications on the rate that energy is deposited into the ionosphere via Joule heating, which we show to become dampened by the neutral winds.

The Induced Magnetosphere of Mars: Asymmetrical Topology of the Magnetic Field Lines

AbstractAn asymmetrical pileup of the interplanetary magnetic field leads to an additional draping of the field lines in the opposite direction to the motional electric field. Such a draping and the associated magnetic field forces push the ionosphere plasma in the transverse direction opening a passage for an ion trail which contains dense and slowly moving plasma. We found that wrapping of the field lines around Mars starts in the hemisphere pointing in the direction of the motional electric field and propagates to the opposite hemisphere where the cross‐flow component of the draped interplanetary magnetic field changes sign in a broad area accompanied by the formation of loops of closed field lines. Reconnection near Mars accompanied by the generation of plasma vortices imposes serious constraints on the ion dynamics and their escape through the tail. The existence of all these features is confirmed by hybrid simulations.

Transient Oscillations Near the Dayside Open‐Closed Boundary: Evidence of Magnetopause Surface Mode?

AbstractGeomagnetic pulsations in Pc5‐6 band (~3–20 min) are persistent feature of ULF activity at dayside high latitudes. Magnetopause surface eigenmodes may be suggested as potential mechanism of these pulsations. One might expect the ground response of these modes to be near ionospheric projection of the open‐closed field line boundary (OCB). Using data from instruments located at Svalbard we study transient geomagnetic response to impulsive “intrusion” of magnetosheath plasma into the dayside magnetosphere. These intrusions are triggered by modest changes of interplanetary magnetic field to southward, and observed as sudden shifts of equatorward red aurora boundary to lower latitudes and green line emission intensification. Each auroral disturbance is accompanied by burst of ~1.7–2.0‐mHz geomagnetic pulsations. Near‐cusp latitudinal structure of ULF pulsations is compared with instant location of equatorward boundary of the red aurora, assumed to be a proxy of the OCB. Optical OCB latitude has been identified using data from the meridian scanning photometer. The latitudinal maximum of the transient geomagnetic response tends to be located near disturbed OCB proxy, within the error ~1°–2° of the photometer and magnetometer methods. Recorded transient pulsations may be associated with the ground image of the magnetopause surface mode harmonic. Theoretical consideration indicates that after an initial excitation, surface large‐scale mode converts into localized Alfvén oscillations and thus can exist for limited time only. Therefore, MHD surface modes in realistic inhomogeneous plasma cannot be considered in isolation, but as a combined system of modes with discrete and continuous spectra with irreversible transformation between them.

Spatially Resolved Neutral Wind Response Times During High Geomagnetic Activity Above Svalbard

AbstractIt has previously been shown that in the high‐latitude thermosphere, sudden changes in plasma velocity (such as those due to changes in interplanetary magnetic field) are not immediately propagated into the neutral gas via the ion‐drag force. This is due to the neutral particles (O, O2, and N2) constituting the bulk mass of the thermospheric altitude range and thus holding on to residual inertia from a previous level of geomagnetic forcing. This means that consistent forcing (or dragging) from the ionospheric plasma is required, over a period of time, long enough for the neutrals to reach an equilibrium with regard to ion drag. Furthermore, mesoscale variations in the plasma convection morphology, solar pressure gradients, and other forces indicate that the thermosphere‐ionosphere coupling mechanism will also vary in strength across small spatial scales. Using data from the Super Dual Auroral Radar Network and a Scanning Doppler Imager, a geomagnetically active event was identified, which showed plasma flows clearly imparting momentum to the neutrals. A cross‐correlation analysis determined that the average time for the neutral winds to accelerate fully into the direction of ion drag was 75 min, but crucially, this time varied by up to 30 min (between 67 and 97 min) within a 1,000‐km field of view at an altitude of around 250 km. It is clear from this that the mesoscale structure of both the plasma and neutrals has a significant effect on ion‐neutral coupling strength and thus energy transfer in the thermosphere.

Segmentation of SED by Boundary Flows Associated With Westward Drifting Partial Ring current

AbstractThe segmentation mechanism of polar cap patches is agreed to be related to temporal changes of interplanetary magnetic field or transient reconnection. In this letter, using Global Ionosphere Thermosphere Model driven by two‐way coupled Block‐Adaptive‐Tree‐Solarwind‐Roe‐Upwind‐Scheme and Rice Convection Model, a new segmentation mechanism is proposed. This mechanism works as follows: A strong boundary flow between the Region 1 and Region 2 field‐aligned currents develops, while a shielding process develops in the inner magnetosphere. As the partial ring current drifts westward, the peak of the boundary flow also moves westward. This strong boundary flow raises the ion temperature through enhanced frictional heating, enhances the chemical recombination reaction rate, and reduces the electron density. When this boundary flow crosses the storm‐enhanced density (SED) plume, the plume will be segmented into patches. No external interplanetary magnetic field variations or transient reconnections are required in this mechanism.

Cooperatives Roles of Dynamics and Topology in Generating the Magnetosphere‐Ionosphere Disturbances: Case of the Theta Aurora

AbstractTo understand the magnetosphere‐ionosphere (M‐I) disturbances, it is necessary to know the change in the null‐separator structure along with the development of convection. The present paper explains this proposition by taking the case of the theta aurora that occurs after the switch of interplanetary magnetic field By and reveals auroral development inside the polar cap. The interplanetary magnetic field change is followed by the reformation of the null‐separator structure to cause a convection transient and a successive deformation of separatrices inside the magnetosphere, where separatrices separate the space into different volumes that include different types of magnetic field lines, and intersections of separatrices form separators that connect nulls. By the reconnection on the separator, energy inflow occurs from the solar wind to the magnetosphere. Convection driven by this energy transports nulls. In the case of theta aurora, two new nulls on the dayside coexist with two old nulls carried toward the tail by convection. Each set of nulls generates two open‐closed boundaries (separatrices) bounded by separators. Thus, open‐closed boundaries are divide into four parts. Separatrices generated by different sets partially become side by side near the nightside stem limes. The theta aurora is generated at the area corresponding to the low‐latitude side with respect to both of two boundaries. Thus, the occurrence of the theta aurora is a natural consequence of a transition in the null‐separator structure. The present example indicates that the global structure of the magnetosphere is almost decided from the skeleton of nulls.

Variability of Geomagnetic Field with Interplanetary Magnetic Field at Low, Mid and High Latitudes

The fluctuations in the Interplanetary Magnetic Field significantly affect the state of geomagnetic field particularly during the Coronal Mass Ejection (CME) events. In the present investigation we have studied the influence of Interplanetary Magnetic Field changes on the geomagnetic field components at high, low and mid latitudes. To carry out this investigation we have selected three stations viz. Alibag (18.6°N, 72.7°E), Beijing MT (40.3°N, 116.2°E) and Casey (66.2°S, 110.5°E) one each in the low, mid and high latitude regions. Then we selected geomagnetic storm events of three types namely weak (-50≤Dst≤-20), moderate (100≤Dst≤-50) and intense (Dst≤-100nT). In each storm category 10 events were considered. From our study we conclude that geomagnetic field components are significantly affected by the changes in the IMF at all the three latitudinal regions during all the storm events. At the same time we also found that the magnitude of change in geomagnetic field components is highest at the high latitudes during all types of storm events while at low and mid latitude stations the magnitude of effect is approximately the same.

Deriving Global Convection Maps From SuperDARN Measurements

AbstractA new statistical modeling technique for determining the global ionospheric convection is described. The principal component regression (PCR)‐based technique is based on Super Dual Auroral Radar Network (SuperDARN) observations and is an advanced version of the PCR technique that Waters et al. (, https//:doi.org.10.1002/2015JA021596) used for the SuperMAG data. While SuperMAG ground magnetic field perturbations are vector measurements, SuperDARN provides line‐of‐sight measurements of the ionospheric convection flow. Each line‐of‐sight flow has a known azimuth (or direction), which must be converted into the actual vector flow. However, the component perpendicular to the azimuth direction is unknown. Our method uses historical data from the SuperDARN database and PCR to determine a fill‐in model convection distribution for any given universal time. The fill‐in data process is driven by a list of state descriptors (magnetic indices and the solar zenith angle). The final solution is then derived from a spherical cap harmonic fit to the SuperDARN measurements and the fill‐in model. When compared with the standard SuperDARN fill‐in model, we find that our fill‐in model provides improved solutions, and the final solutions are in better agreement with the SuperDARN measurements. Our solutions are far less dynamic than the standard SuperDARN solutions, which we interpret as being due to a lack of magnetosphere‐ionosphere inertia and communication delays in the standard SuperDARN technique while it is inherently included in our approach. Rather, we argue that the magnetosphere‐ionosphere system has inertia that prevents the global convection from changing abruptly in response to an interplanetary magnetic field change.

On fast and slow Earth’s magnetospheric dynamics during geomagnetic storms: a stochastic Langevin approach

The Earth’s magnetosphere responds to the external changes of interplanetary magnetic field and solar wind conditions showing a multiscale dynamics, manifesting in the occurrence of fluctuations over a very wide range of timescales. Here, using an approach based on a Langevin/Fokker-Planck description we investigate the nature of the fast (short-) and slow (long-timescale) fluctuations of SYM-H index during geomagnetic storms. The results point towards a different origin of the fast (τ < 200 min) and slow (τ > 200 min) fluctuations, which are characterized by state functions of different nature. In detail, the state function associated with the slow dynamics shows the evidence of the occurrence of first-order-like topological phase transition during the different phases of a geomagnetic storm, while the fast dynamics seems to be characterized by a quasi-invariant quadratic state function. A modeling in terms of stochastic Langevin equation is discussed and the relevance of our results in the framework of Space Weather studies is outlined.

RISR‐N observations of the IMF By influence on reverse convection during extreme northward IMF

AbstractPrevious studies have demonstrated that the high‐latitude ionospheric convection is strongly influenced by the interplanetary magnetic field (IMF) direction. However, the temporal details of how the convection transitions from one state to another are still not understood completely. In this study, we analyze an interval on 12 September 2014 which provided a rare opportunity to examine dynamic variations in the dayside convection throat as the IMF transitioned from strong By+ to strong Bz+. Between 18:00 and 20:00 UT the northward face of the Resolute Bay Incoherent Scatter Radar (RISR‐N) rotated through the noon sector and directly measured strengthening reverse convection flows in the dayside throat region that peaked at ∼2800 m/s. Near‐simultaneous measurements from DMSP satellites confirm the magnitude of the reverse convection and its proximity to the cusp. Time series comparison of the RISR‐N north‐south flows with the IMF Bz component shows a remarkably high correlation, suggestive of strong linear coupling, with no sign of velocity saturation. Likewise, the east‐west flow variations were highly correlated with the changes in IMF By. However, time‐lagged correlation analysis reveals that the IMF By influence acted on a time scale 10 min shorter than that of the Bz component. As a consequence, the manner in which the convection transitioned from the strong By+ condition to the strong Bz+ condition is inconsistent with either the antiparallel or component reconnection models. Instead, we suggest that these particular observations are consistent with two separate reconnection sites on the magnetopause driven independently by the IMF By and Bz components.

Role of IMF By in the prompt electric field disturbances over equatorial ionosphere during a space weather event

AbstractOn 7 January 2005 (Ap=40) prompt penetration electric field perturbations of opposite polarities were observed over Thumba and Jicamarca on a few occasions during 13:45–16:30 UT. However, the electric field was found to be eastward during 14:45–15:30 UT over both Thumba and Jicamarca contrary to the general expectation wherein opposite polarities are expected at nearly antipodal points. On closer scrutiny, three important observational features are noticed during 14:10–15:15 UT. First, during 14:10–14:45 UT, despite increasing southward interplanetary magnetic field (IMF) Bz condition, the already westward electric field over Thumba weakened (less westward) while the eastward electric field over Jicamarca intensified (more eastward). Second, the electric field not only became anomalously eastward over Thumba but also got intensified further during 14:45–15:00 UT similar to Jicamarca. Third, during 15:00–15:15 UT, despite IMF Bz remaining steadily southward, the eastward electric field continued to intensify over Thumba but weakened over Jicamarca. It is suggested that the changes in IMF By component under southward IMF Bz condition are responsible for skewing the ionospheric equipotential patterns over the dip equator in such a way that Thumba came into the same DP2 cell as that of Jicamarca leading to anomalous electric field variations. Magnetic field measurements along the Indian and Jicamarca longitude sectors and changes in high‐latitude ionospheric convection patterns provide credence to this proposition. Thus, the present investigation shows that the variations in IMF By are fundamentally important to understand the prompt penetration effects over low latitudes.

Investigation of triggering of poleward moving auroral forms using satellite‐imager coordinated observations

AbstractPoleward moving auroral forms (PMAFs) are thought to be an ionospheric signature of dayside magnetic reconnection. While PMAFs are more likely to occur when the interplanetary magnetic field (IMF) is southward, how often PMAFs are triggered by changes in solar wind parameters is still an open question. To address this issue, we used one of the Automatic Geophysical Observatories all‐sky imagers in Antarctica and the Time History of Events and Macroscale Interactions during Substorms (THEMIS) B and C satellites, which can give solar wind measurements much closer to the subsolar bow shock than by Wind or ACE, to examine if PMAFs occurred in association with IMF orientation changes. We identified 60 PMAFs in conjunction with THEMIS B and C during 2008, 2009, and 2011 and 70% of events show reduction of Bz before PMAF onset indicating that IMF southward turning plays an important role in triggering a majority of PMAFs. In contrast, the magnitude of the IMF Bz reduction in OMNI data was smaller and the reduction occurred in a slightly smaller percentage of events (40–60%). This suggests that solar wind structures that missed the L1 point or evolution of solar wind between the L1 point and THEMIS may be important for identifying IMF changes responsible for transient dayside reconnection. Additionally, 17 PMAFs that did not have substantial IMF southward turnings are correlated well with foreshock events, indicating that foreshock phenomena may also play a role in triggering PMAFs.

Kelvin‐Helmholtz wave at the subsolar magnetopause boundary layer under radial IMF

AbstractWe present the first observation of the Kelvin‐Helmholtz (KH) rolled‐up vortex at the dayside magnetopause layers under a radial interplanetary magnetic field (IMF). The study uses measurements of four Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes aligned along the YGSE axis about 10 RE upstream of the Earth and located in different regions of the near‐Earth environment. THEMIS C and A serve as monitors of the quiet solar wind and fluctuating magnetosheath conditions, respectively, and THEMIS D and E observe the magnetopause and low‐latitude boundary layer (LLBL) crossings. The analysis shows the following: (1) a radial IMF changes to the southward pointing magnetosheath magnetic field; (2) dayside reconnection forms the thin but dense LLBL; (3) a large velocity shear at the LLBL inner edge excites a train of KH waves; and (4) in spite of a short path from the subsolar point (≈5 RE), one of the KH waves exhibits all features of a fully developed rolled‐up vortex.

Statistical features of the global polarity reversal of the Venusian induced magnetosphere in response to the polarity change in interplanetary magnetic field

AbstractIn this study we present the first statistical analysis on the effects of heliospheric current sheet crossings on the induced magnetosphere of Venus. These events are of particular interest because they lead to the reconfiguration of the induced magnetosphere with opposite polarity. We use a statistical approach based on 117 orbit pairs, and we study the spatial distribution of the heavy ion flux measurements in the plasma environment of Venus. The average and median heavy ion flux measurements are compared before and after the polarity reversal events. The results show that after the events the average and median heavy ion fluxes in the magnetotail are reduced by the factors of 0.75 ± 0.09 and 0.52, respectively. We find that even if a passage of a current sheet is a short time scale event lasting about 10 min, its effect on the near‐Venus plasma environment lasts for a few hours. We conclude that the observations show similarities to the previous comet studies and the polarity reversal of the induced magnetosphere might be accompanied with dayside reconnection and magnetic disconnection of the plasma tail from the planetary ionosphere.

Seasonal and solar cycle variations in the ionospheric convection reversal boundary location inferred from monthly SuperDARN data sets

Abstract. Multi-year (1995–2013) velocity data collected by the Super Dual Auroral Network (SuperDARN) HF radars are considered to investigate seasonal and solar cycle variations of the convection reversal boundary (CRB) location for interplanetary magnetic field (IMF) Bz < 0. By considering monthly data sets we show that the CRB is at higher latitudes in summer between 1995 and 2007. The poleward shifts are on the order of 2–5°. After 2007, the seasonal effect weakens, and the highest latitudes for the CRB start to occur during the winter time. We show that the CRB latitudes decrease with an increase of the IMF transverse component at a rate of (1–2°)/2 nT. Because of this effect, on average, the CRB latitudes are lower during high solar activity periods with stronger IMFs. We also confirm the effect of the CRB dawn-dusk shifts related to the IMF changes in the IMF By sign.

Search of predictors of geoeffective heliospheric events by means of muon hodoscope URAGAN

The flux of charged primary cosmic rays (PCR) is modulated by changes of interplanetary magnetic field which depend on various heliospheric processes. After interaction of PCR with nuclei of atoms of the Earth's atmosphere, these modulations are transferred to a flux of secondary muons. Muon hodoscope URAGAN allows to trace changes not only of intensity of the muon flux, but also its angular distribution in a wide range of zenith angles (0-80°). Some results of searching of predictors of geoeffective heliospheric events by means of muon hodoscope URAGAN are presented.

Toward more reliable long‐term indices of geomagnetic activity: Correcting a new inhomogeneity problem in early geomagnetic data

AbstractFor the time before the space era, our knowledge of the centennial evolution of solar wind (SW) and interplanetary magnetic field (IMF) is based on proxies derived from geomagnetic indices. The reliability of these proxies is dependent on the homogeneity of magnetic field data. In this paper, we study the interhourly (IHV) and interdiurnal (IDV1d) variability indices calculated from the data of two British observatories, Eskdalemuir and Lerwick, and compare them to the corresponding indices of the German Niemegk observatory. We find an excess of about 14 ± 4% (5.8 ± 2%) and 27 ± 10% (15 ± 6%) in the IHV (IDV1d) in the indices of Eskdalemuir and Lerwick in 1935–1969. The timing of this excess accurately coincides with instrument changes made in these observatories, strongly supporting the interpretation that the excess is indeed caused by instrument related inhomogeneities in the data of Eskdalemuir and Lerwick. We show that the detected excess notably modifies the long‐term trend of geomagnetic activity and the centennial evolution of IMF strength and solar wind speed estimated using these indices. We note that the detected inhomogeneity problem may not be limited to the data of the two studied observatories but may be quite common to long series of geomagnetic measurements. These results question the reliability of the present measures of the centennial change in solar wind speed and IMF.

Probabilistic forecasting analysis of geomagnetic indices for southward IMF events

Geomagnetic disturbances that drive space weather impacts such as ground-induced currents and radiation belt enhancements are usually driven by strong southward interplanetary magnetic field (IMF) intervals. However, current heliospheric models either do not predict or provide low-accuracy forecasts of IMF Bz. Here we examine the probability distribution function of geomagnetic activity indices for southward IMF intervals. We analyze the in situ plasma and magnetic field measurements long-duration large-amplitude southward IMF intervals (called Bs events). The statistical profiles of other solar wind and IMF parameters show significant differences during the periods 1 day before the Bs events for different solar wind transients (such as interplanetary coronal mass ejections and stream interaction regions). As is well known, we find that the solar wind speed is positively correlated with geomagnetic indices and that strong southward IMF is the key in storm triggering but not necessarily for substorms. We find that the solar wind density weakly affects geomagnetic field activity, but the response depends on the type of solar wind transient that includes the strong Bs events. We also find that magnetospheric ultralow-frequency waves are induced by both strong southward IMF and solar wind dynamic pressure disturbances. We suggest that strong Bs events could be predicted from the preceding characteristics of solar wind and IMF changes and that probabilistic forecasting of geomagnetic activity occurrence is potentially useful in space weather forecasting. We present preliminary analysis to demonstrate the out-of-sample ability to predict IMF Bs events with in situ solar wind data.

Distinguishing between pulsed and continuous reconnection at the dayside magnetopause.

Magnetic reconnection has been established as the dominant mechanism by which magnetic fields in different regions change topology to create open magnetic field lines that allow energy and momentum to flow into the magnetosphere. One of the persistent problems of magnetic reconnection is the question of whether the process is continuous or intermittent and what input condition(s) might favor one type of reconnection over the other. Observations from imagers that record FUV emissions caused by precipitating cusp ions demonstrate the global nature of magnetic reconnection. Those images show continuous ionospheric emissions even during changing interplanetary magnetic field conditions. On the other hand, in situ observations from polar‐orbiting satellites show distinctive cusp structures in flux distributions of precipitating ions, which are interpreted as the telltale signature of intermittent reconnection. This study uses a modification of the low‐velocity cutoff method, which was previously successfully used to determine the location of the reconnection site, to calculate for the cusp ion distributions the “time since reconnection occurred.” The “time since reconnection” is used to determine the “reconnection time” for the cusp magnetic field lines where these distributions have been observed. The profile of the reconnection time, either continuous or stepped, is a direct measurement of the nature of magnetic reconnection at the reconnection site. This paper will discuss a continuous and pulsed reconnection event from the Polar spacecraft to illustrate the methodology.