IMF Components Research Articles

Coronal mass ejection of 4 April 2000 and associated space weather effects

The effects of a Halo Coronal Mass Ejection (CME) erupted on 4 April 2000 are studied and reported here. The effect of such CME on the interplanetary medium (IPM) is sensed by the Interplanetary Scintillation (IPS) recorded at Rajkot. The Solar Observations of this CME and associated events, like Solar Energetic Particles (SEP) and flare, are presented. CME events with high speeds and negative magnetic field components have higher possibility of penetrating the earth's shield, viz. the magnetosphere. The 4 April 2000 CME with a high speed and southward component of IMF produced a big geomagnetic storm with D st reaching - 288 nT . Simultaneous ionospheric effects in F layer heights and auroral observations are reported. Such events are important in Space Weather Studies as these pose hazards to space operations including satellite communications and surveillance systems.

Structure of the high-altitude cusp formed by the horizontal IMF

The importance of a sign of the IMF B Z component for solar wind plasma entry into the magnetosphere was suggested about 40 years ago and later it was documented by experimental investigations. When IMF B Z is negative, subsolar reconnection fills the cusp with the magnetosheath plasma which partly precipitate to the ionosphere and partly is reflected and create a plasma mantle. During periods of a positive IMF B Z , the reconnection site moves tailward of the cusp. However, such situations are rather rare because B Z is often a minor IMF component. In spite of this, the structure of the cusp during periods of a small IMF B Z component is generally unknown; partly due to fully 3-D nature of interaction and partly due to a lack of experimental data. In the present paper, we are analyzing two-point observations of the cusp–magnetosheath boundary during a prolonged interval of dawnward pointing IMF. These observations are supported by an analysis of the precipitation patterns observed by the several spacecraft in different altitudes of the dayside auroral zone. An analysis shows that when the IMF B Y component is large enough the reconnection sites in both hemispheres move away from the local noon but in an opposite sense. Each of these sites is able to supply the precipitation in both hemispheres but the amount and parameters of precipitating particles are controlled by a magnetosheath speed above reconnection sites.

Magnetic storm cessation during sustained northward IMF

Times of sustained strong northward IMF can interrupt the magnetic storm development and lead to lower levels of geomagnetic activity for many hours. During 1997–2000 we have found two events of this kind observed on November 8, 1998 and October 13, 2000. In both cases, the storms started as usual after arrival of ejecta with a southward IMF component from the Sun to the Earth, but ceased after several hours due to the onset of sustained northward IMF leading to the faster recovery process. After the passage of this so-called positive domain, the storm development started again. The heliospheric magnetic field intensity remained enhanced and nearly constant. The solar origins of the geomagnetic storm interruptions have been investigated. Tentatively they may be related to strong nonlinear Alfvйn type solitary waves excited by non-stationary coronal current variations with a characteristic time-scale of about a day.

Three decades of bow shock observations by IMP 8 and model predictions

During almost three decades of operation, the IMP 8 satellite collected an extensive amount of both plasma and magnetic field measurements. The entire data set has been searched for all Earth's bow shock crossings observed by IMP 8. We have recorded total 11,455 single and multiple bow shock crossings and for 5870 of the crossings complete upstream interplanetary magnetic field and solar wind parameters, measured by the same spacecraft, were available allowing us to test empirical models predicting the bow shock position as a function of upstream parameters. The chosen models were F79, NS91, FR94, CL95, P95 and V01 (Planet. Space Sci. 27(9) (1979) 1151; J. Atmos. Terr. Phys. 53 (1991) 1049; J. Geophys. Res. 99(A9) (1994) 17,681; J. Geophys. Res. 100(A9) (1995) 17,173; J. Geophys. Res. 100(A5) (1995) 7907; Earth Planets Space 53 (2001) 1001). This study investigates these models’ accuracy not only for average upstream conditions but also for unusual conditions and as a result points out some deficiencies of these models. We demonstrate that most of the models underestimate bow shock distance for low Mach numbers and/or high magnitudes of IMF components.

RELATIONSHIPS OF THE SOLAR WIND PARAMETERS WITH THE MAGNETIC STORM MAGNITUDE AND THEIR ASSOCIATION WITH THE INTERPLANETARY SHOCK

It is investigated quantitative relations between the magnetic storm magnitude and the solar wind parameters such as the Interplanetary Magnetic Field (hereinafter, IMF) magnitude (B), the southward component of IMF (Bz), and the dynamic pressure during the main phase of the magnetic storm with focus on the role of the interplanetary shock (hereinafter, IPS) in order to build the space weather fore-casting model in the future capable to predict the occurrence of the magnetic storm and its magnitude quantitatively. Total 113 moderate and intense magnetic storms and 189 forward IPSs are selected for four years from 1998 to 2001. The results agree with the general consensus that solar wind parameter, especially, Bz component in the shocked gas region plays the most important role in generating storms (Tsurutani and Gonzales, 1997). However, we found that the correlations between the solar wind parameters and the magnetic storm magnitude are higher in case the storm happens after the IPS passing than in case the storm occurs without any IPS influence. The correlation coefficients of B and <TEX>$BZ_(min)$</TEX> are specially over 0.8 while the magnetic storms are driven by IPSs. Even though recently a Dst prediction model based on the real time solar wind data (Temerin and Li, 2002) is made, our correlation test results would be supplementary in estimating the prediction error of such kind of model and in improving the model by using the different fitting parameters in cases associated with IPS or not associated with IPS rather than single fitting parameter in the current model.

Sunspot cycle-dependent changes in the distribution of GSE latitudinal angles of IMF observed near 1 AU

[1] The solar cycle variations in the characteristics of the GSE latitudinal angles of the Interplanetary Magnetic Field (θGSE) observed near 1 AU have been studied for the period 1967–2000. It is observed that the statistical parameters mean, standard deviation, skewness and kurtosis vary with sunspot cycle. The θGSE distribution resembles the Gaussian curve during sunspot maximum and is clearly non-Gaussian during sunspot minimum. The width of the θGSE distribution is found to increase with sunspot activity, which is likely to depend on the occurrence of solar transients. Solar cycle variations in skewness are ordered by the solar polar magnetic field changes. This can be explained in terms of the dependence of the dominant polarity of the north-south component of IMF in the GSE system near 1 AU on the IMF sector polarity and the structure of the heliospheric current sheet.

Signatures of the Seismic Source in EMD-Based Characterization of the 1994 Northridge, California, Earthquake Recordings

In this article we use empirical mode decomposition (EMD) to charac- terize the 1994 Northridge, California, earthquake records and investigate the sig- natures carried over from the source rupture process. Comparison of the current study results with existing source inverse solutions that use traditional data processing suggests that the EMD-based characterization contains information that sheds light on aspects of the earthquake rupture process. We first summarize the fundamentals of the EMD and illustrate its features through the analysis of a hypothetical and a real record. Typically, the Northridge strong-motion records are decomposed into eight or nine intrinsic mode functions (IMF's), each of which emphasizes a different oscillation mode with different amplitude and frequency content. The first IMF has the highest-frequency content; frequency content decreases with an increase in IMF component. With the aid of a finite-fault inversion method, we then examine aspects of the source of the 1994 Northridge earthquake that are reflected in the second to fifth IMF components. This study shows that the second IMF is predominantly wave motion generated near the hypocenter, with high-frequency content that might be related to a large stress drop associated with the initiation of the earthquake. As one progresses from the second to the fifth IMF component, there is a general migration of the source region away from the hypocenter with associated longer-period signals as the rupture propagates. This study suggests that the different IMF components carry information on the earthquake rupture process that is expressed in their different frequency bands.

Study on Relationship between Southward IMF Events and Geomagnetic Storms

AbstractThe solar wind‐magnetosphere coupling is investigated in terms of forty‐three moderate and intense storms (Dst &lt;‐50 nT) and the associated southward IMF events during 1972 to 1982. The solar wind data is taken from spacecraft IMP‐8 and the geomagnetic storms are described by Dst and AE. The results show that: (1) There are 11 events (25.6% of the total 43 events) which closely follow a shock, 18 events (42%) which occur in the downstream of a shock, and the remainder 14 events bear no relation to the interplanetary shocks. Most of these events are accompanied with the increase of the magnetic field intensity and the dynamic pressure of the solar wind; (2) Only substorms exist when the interplanetary dawn‐to‐dusk electric field EI is less than 4 mV/m, but both of magnetic storms and substorms occur simultaneously if the EI is greater than 5 mV/m; (3) The ring current energization is related to the dynamic pressure (ρV 2), rather than the density or the velocity alone; (4) While the southward IMF component BZ is crucial, the relative strength of BX,BY to the BZ also play a certain role in the energy transfer from the solar wind to the magnetosphere. The energy coupling between the solar wind and the magnetosphere is enhanced if the relative strength is larger.

A coupled map as a model of the dynamics of the magnetotail current sheet

A magnetic field model of the magnetotail current sheet in the form of a coupled-map lattice (CML) is presented. It is continuously driven (“running”) and based on the MHD diffusion equation. Solar wind vB S data (solar wind speed multiplied by the southward component of IMF) are used for driving the model, and it is shown to exhibit perturbations (avalanches) with power-law scalings in their distributions of duration and size. Such distributions may indicate self-organized critical (SOC) behavior. Furthermore, it is shown that the power spectra of the model outputs are of bicolor power-law form with different slopes for high and low frequencies. Although the “running” model gives power-law distributions independent of the strength of the driver, it is argued that the model is in SOC state only when driven slowly. When the driver is strong the model acts more like an input–output system, and the power laws are possibly due to the statistics of the driver. This is supported by the fact that durations of southward turnings of IMF have also a power-law distribution. It is also shown that by driving the model very strongly we can reproduce AE data with correlation 0.74 by using large resistivity, and Dst with correlation 0.79 by using small resistivity.

Boundary-processing-technique in EMD method and Hilbert transform

By virtue of neural network, a series of signals is extended forward and backward, as a result, two additional maxima and two additional minima are obtained at both ends of the original data set, with which the EMD decomposition can be exactly achieved with cubic spline interpolation. Meanwhile, by using of neural network every IMF component can also be extended forward and backward, which effectively restrains the end effect, thus the veracious Hilbert spectra are achieved. Verifications of the sample signals and the actual surface elevation of sea waves show that the present extension method is relatively accurate.

Structure of the auroral precipitation region in the dawn sector: relationship to convection reversal boundaries and field-aligned currents

Abstract. Abstract. Simultaneous DMSP F7 and Viking satellite measurements of the dawnside high-latitude auroral energy electron and ion precipitation show that the region of the low and middle altitude auroral precipitation consists of three characteristic plasma regimes. The recommendation of the IAGA Working Group IIF/III4 at the IAGA Assembly in Boulder, July 1995 to decouple the nomenclature of ionospheric populations from magnetospheric population is used for their notation. The most equatorial regime is the Diffuse Auroral Zone (DAZ) of diffuse spatially unstructured precipitating electrons. It is generated by the plasma injection to the inner magnetosphere in the nightside and the subsequent drift plasma to the dawnside around the Earth. Precipitating particles have a hard spectrum with typical energies of electrons and ions of more than 3 keV. In the DAZ, the ion pitch-angle distribution is anisotropic, with the peak near 90°. The next part is the Auroral Oval (AO), a structured electron regime which closely resembles the poleward portion of the night-side auroral oval. The typical electron energy is several keV, and the ion energy is up to 10 keV. Ion distributions are pre-dominantly isotropic. In some cases, this plasma regime may be absent in the pre-noon sector. Poleward of the Auroral Oval, there is the Soft Small Scale Luminosity (SSSL) regime. It is caused by structured electron and ion precipitation with typical electron energy of about 0.3 keV and ion energy of about 1 keV. The connection of these low-altitude regimes with plasma domains of the distant magnetosphere is discussed. For mapping of the plasma regimes to the equatorial plane of the magnetosphere, the empirical model by Tsyganenko (1995) and the conceptual model by Alexeev et al. (1996) are used. The DAZ is mapped along the magnetic field lines to the Remnant Layer (RL), which is located in the outer radiation belt region; the zone of structured electrons and isotropic ion precipitation (AO) is mapped to the dawn periphery of the Central Plasma Sheet (CPS); the soft small scale structured precipitation (SSSL) is mapped to the outer magnetosphere close to the magnetopause, i.e. the Low Latitude Boundary Layer (LLBL). In the near-noon sector, earthward fluxes of soft electrons, which cause the Diffuse Red Aurora (DRA), are observed. The ion energies decrease with increasing latitude. The plasma spectra of the DRA regime are analogous to the spectra of the Plasma Mantle (PM). In the dawn sector, the large-scale field-aligned currents flow into the ionosphere at the SSSL latitudes (Region 1) and flow out at the AO or DAZ latitudes (Region 2). In the dawn and dusk sectors, the large-scale Region 1 and Region 2 FAC generation occurs in different plasma domains of the distant magnetosphere. The dawn and dusk FAC connection to the traditional Region 1 and Region 2 has only formal character, as FAC generating in various magnetospheric plasma domains integrate in the same region (Region 1 or Region 2). In the SSSL, there is anti-sunward convection; in the DAZ and the AO, there is the sunward convection. At PM latitudes, the convection is controlled by the azimuthal IMF component (By ). It is suggested to extend the notation of the plasma pattern boundaries, as proposed by Newell et al. (1996), for the nightside sector of the auroral oval to the dawn sector.Key words. Magnetospheric physics (current systems; magnetospheric configuration and dynamics; plasma convection)

Long term variability in solar wind velocity and IMF intensity and the relationship between solar wind parameters &amp; geomagnetic activity

A study is carried out on the mean monthly values of in situ observations of solar wind velocity (V) and the intensity of interplanetary magnetic field, B to elucidate their long term variations using the technique of singular spectrum analysis. It is shown that B exhibits a clear solar cycle signal with progressively deepening minimum and a well-defined longer period variation but V is marked by a ~9-yr cycle. Time variations in the amplitude of 16-month periodicity, observed sporadically in the velocity earlier by others are clearly brought out, as also the characteristic amplitude changes in a 42-month signal in velocity. It appears that time intervals which show certain significant fluctuations in B are marked by the absence of similar signal in V. aa index is next used as a proxy for solar wind velocity, after establishing a good correlation between Ap and observed V so that we could examine the evolution of different periodicities over 14 solar cycles. A significant trend with least value in 1900 and a near-linear rise up to 1960 is shown to be the main feature of the velocity change. The solar cycle component in V lags the solar activity peak by ~22 months. Streams emanating from coronal holes in the declining phase seem to be the most dominant contributor to the 11-year variation in velocity. The anomalous pattern of changes in V observed in cycle 20 is not present in any of the other 13 cycles. Statistical relationships between V, B and plasma density (N) with Ap are studied and it is shown that over three solar cycles (20, 21 and 22) the patterns are almost the same with a slight change observed in cycle 21. IMF B and Ap are linearly related over a wide range of Ap values from close to 0 up to about 60, whereas density/Ap relation appears insignificant. In case of V, an initial rapid rise in V causes moderate changes in Ap but for velocity in excess of 700 km/sec, the enhancement in geomagnetic activity is more rapid. From the statistical relation of several other solar wind/IMF parameters, their variability and combinations with Ap, one sees linear relation for solar wind electric field, n/s component of IMF and variability in the components of B. An estimate is made of the base level of the magnetosphere, corresponding to quiet levels of geomagnetic activity.

Magnetopause position dependence on the interplanetary magnetic field Bz-component. Analysis of the pressure balance equation

Analysis of the available data set, containing numerous intersections of the magnetopause by different satellites over more than 30 years, leads to the conclusion, that the form of the magnetopause should be approximated by a more complicated surface than those of the 2nd order (ellipsoid, paraboloid). The form of this surface is not only a fuction of pressure but also of the Bz IMF component. We used data on the change of the magnetopause form induced by variations of interplanetary medium parameters to analyze the local contribution of external sources to the geomagnetic field at the magnetopause as well as the variation of this contribution with changes in the magnetopause point location.

Equinoctial and solstitial averages of magnetospheric relativistic electrons: A strong semiannual modulation

Data from SAMPEX, POLAR, and other spacecraft shows that high energy electrons (E ≳ 1 MeV) vary in a highly coherent way throughout the entire outer radiation zone of the Earth (2.5 ≲ L ≲ 6.5). These data are used to perform long‐term analysis of the flux variations of E&gt;2 MeV electrons throughout the outer trapping zone. Averages are performed over 3‐month intervals centered on the spring and fall equinoxes and on the winter and summer solstices. Modulation is found such that equinoctial fluxes of electrons are nearly a factor of three larger than the solstitial fluxes based upon a superposed epoch analysis for 1992–1999. These semiannual modulations of relativistic electron fluxes are compared with concurrent solar wind data and are examined in terms of prior models of geomagnetic activity modulation. It is concluded that both southward IMF component merging (Russell‐McPherron) and Kelvin‐Helmholtz instability considerations (Boller‐Stolov) may play important roles.

A coupled‐map model for the magnetotail current sheet

A magnetic field model of the magnetotail current sheet in the form of a coupled‐map lattice (CML) is presented. It is a continuously driven and based on the MHD diffusion equation. Solar wind vBs data (solar wind speed multiplied by the southward component of IMF) are used for driving the model, and it is shown to exhibit perturbations (avalanches) with power‐law scalings in their distributions of duration and size. Such distributions may indicate self‐organized critical (SOC) behavior. Furthermore, it is shown that the power spectra of the model outputs are of bicolor power‐law form with different slopes for high and low frequencies. The model parameters determine the frequency of the break points of the spectra, and the slopes of their low and high frequency regimes.

Production and decay of excited quasiprojectiles in peripheral and semiperipheral35Cl+197Aureactions in Fermi energy domain

The peripheral and semiperipheral reactions in ${}^{35}\mathrm{Cl}{+}^{197}\mathrm{Au}$ have been studied at 30 and 43 MeV/nucleon. The nonequilibrium $\ensuremath{\alpha}$ and IMF components have been observed in the experiment. The fraction of nonequilibrium emission decreases with an increase in the atomic number of the projectilelike fragments but, for a given projectilelike fragment, it increases with the charge of the emitted particles. The characteristics of quasiprojectiles reconstructed from their decay products reveal several features reminiscent of damped reactions at lower bombarding energies. The atomic number and deflection angle of projectilelike fragments depend strongly on their kinetic energy or dissipated energy. At 30 MeV/nucleon, the experimental data can be explained by a deep inelastic transfer model. One-body dissipation is still the main mechanism for the energy and angular momentum dissipation. However, at 43 MeV/nucleon, deep inelastic transfer models can predict only the experimental tendency. Two-body dissipation plays a more important role at higher incident energies. The similarity observed in the decay product distributions, as a function of excitation energy, suggests that the excited quasiprojectiles formed in binary collisions might approach thermal equilibrium for both incident energies. The decay products have been analyzed with sequential-binary and simultaneous-disassembly statistical decay models. Both statistical models are able to provide good agreement with the experimental observables except for the mean kinetic energy of the products.

Energetic particle bursts and substorm activity observed by GEOTAIL at X = −32 RE

On February 9, 1995, the EPIC instrument on board the Japanese spacecraft GEOTAIL observed energetic electron and ion bursts in the near-magnetotail (X = −32 RE). The observations occurred during a period where the BZ component of IMF was turned southward 90 minutes prior to the bursts (WIND data located at X = 193 RE). The two bursts, were observed shortly after 0430 UT. and were separated by a short time interval (∼10 minutes).The energetic bursts were followed by intense substorm activity, which was recorded by GEOTAIL, as well as by ground magnetometers and geosynchronous satellites. The first interval of substorm activity started almost immediately with the first energetic electron burst and the second some 40 minutes after the second burst. During the first substorm GEOTAIL observed a strong tailward flow of ions, which lasted for almost 10 minutes and a flow reversal wasn't recorded by GEOTAIL. During the second activity, the BZ component of IMF turned positive 30 minutes before the onset (60-min time delay is already calculated), GEOTAIL observed a continuous tailward-dawnward flow followed by a short simultaneous earthward-tailward flow which was followed by a final flow reversal and earthward flow for the subsequent 10 minutes.Following Hones' model of substorms, we would expect the formation of a neutral line in the plasma sheet. Minutes after the substorm onset a structure of closed loops develops from reconnected plasma sheet field lines and flows tailward over GEOTAIL. At the beginning of the recovery phase at Earth, the substorm neutral line should have moved past GEOTAIL to a more tailward location, accounting for the northward turning of the field and the reversal of plasma flow at that time. The observations are especially interesting in view of the fact that although the northward turning was recorded by GEOTAIL, the plasma reversal was recorded more than an hour after the tailward flow of ions. During the interval between the tailward and earthward flows, the satellite recorded a new intensification in ion flow together with ground signatures of the intensification of the current wedge which indicates a second substorm activity.

Variations in the directions of north‐south component of IMF in the GSE System near Earth and Parker's Model

The monthly probability of occurence of southward IMF events in the GSE system in association with IMF sectors of away and toward polarity is shown to exhibit an annual variation following the heliographic latitude of earth if the IMF orientations are inferred to be in agreement with the Parker's model. Using this new idea we can infer deviations of IMF north‐south (Bz components) orientations observed near eath from that predicted by Parker's model of the solar wind. Analysis of relevant earth‐orbiting satellite observations of the interplanetary medium during the period 1973–80 does not reveal any systematic sunspot cycle and solar wind speed dependence for the inferred deviaitons of IMF from the Paker's model. However IMF north‐south orientations for the year 1974, a period of recurrent high speed solar wind stream activity, show a significant departure from the Parker's model.

Dependence of the North-South Component of IMF on the Solar Wind Acceleration

AbstractThe monthly probability of occurrence of southward component of IMF estimated independent of the sector polarity observed near earth is found to change with the magnitude of solar wind velocity. The above analysis is done for each month during two years around sunspot minima and maxima in cycle 21. The results will be interpreted in terms of association of southward Bz events with solar wind flows of distinct solar origin such as low and high speed solar wind.

Dependence of the north-south component of IMF on the solar wind acceleration

The monthly probability of occurrence of southward (Bz−) component of IMF estimated independent of the sector polarity observed near earth is found to change with the magnitude of solar wind velocity. The above analysis is done for each month during two years around sunspot minima and maxima in cycle 21. The results will be interpreted in terms of association of southwardBz events with solar wind flows of distinct solar origin such as low and high speed solar wind.