Solar wind variations and geomagnetic storms: A study of individual storms based on high time resolution ISEE 3 data

Interplanetary conditions (VBs V²Bs ε) are derived from ISEE 3 and IMP 8 field and plasma data for the two Coordinated Data Analysis Workshop (CDAW 6) intervals of study and are compared with various aspects of geomagnetic activity (AE, UT, derived Joule heating, electric potential, westward, eastward and total electrojet currents). The March 22 (day 81), 1979, interval contains two distinct periods of geomagnetic activity, both highly correlated with interplanetary features. The start of the first active interval is caused by a southward turning of the interplanetary magnetic field (IMF) associated with the passage of a heliospheric current sheet. The start of the second interval is related to a second IMF southward turning. The geomagnetic activity intensifies when the second crossing of the current sheet, and a ram pressure increase of 4 to 6, impinges on the magnetosphere. Because the interplanetary parameters VBs, V²Bs and ε decrease across the discontinuity, it is concluded that either additional energy is injected into the magnetosphere from the conversion of ram energy into magnetospheric substorm energy or some feature associated with current sheet crossing “triggers” the release of previously stored magnetosphere/magnetotail energy. It is not possible at this time to distinguish between these two possibilities. For day 81, VBs, V²Bs and ε were highly correlated with AL, AE, westward and equivalent currents with coefficients ranging from ∼0.75 to 0.90. The interplanetary parameters were significantly less correlated with geomagnetic activity in the second interval (days 90–91, 1979), with all correlation coefficients being less than 0.6. Several possible explanations for the latter result are (1) the scale of Alfvénic fluctuations was small in comparison to the size of the magnetosphere and the “upstream” spacecraft did not get an accurate indication of the solar wind impinging on the magnetosphere, or (2) during some periods of high and continuous activity, substorms are due to internal magnetospheric processes and occur randomly, independent of the interplanetary drivers.

Section: Intercomparison Of Events and Discussionmentioning

confidence: 99%

Coupling between the solar wind and the magnetosphere: CDAW 6

Tsurutani¹,

Slavin²,

Kamide³

et al. 1985

“…The weakest wave intensities occur during intense northward fields. It is possible that this relationship is actually stronger, but is decreased due to intrinsic wave variability within an event, a feature discussed previously.Because southward directed interplanetary (or magnetosheath) fields have been shown to be well correlated with the occurrence of geomagnetic activity[Arnoldy, 1971;Tsurutani and Meng, 1972;Murayama et al, 1980;Baker et al, 1983;Tsurutani et al, 1984;Akasofu et al, 1985;Gonzalez and Tsurutani, 1987] and because of the above results, one…”

mentioning

confidence: 94%

A statistical study of ELF‐VLF plasma waves at the magnetopause

Tsurutani¹,

Brinca²,

Smith³

et al. 1989

A statistical study of the broadband ELF‐VLF plasma waves at the magnetopause has been performed using ISEE 1 plasma wave data. It is found that enhanced wave intensities are detected at 85% of all magnetopause crossings. Although wave amplitudes are highly variable from event to event and even within an event (particularly during high‐intensity events), the wave spectra averaged over many passes are remarkably similar at dawn, noon, and dusk local hours. Thus to first order, the average wave intensity and spectral shape are independent of local time. At select frequencies, the intensities are 10−8, 10−13, and 3 × 10−17 V2/m2 Hz at 101, 103, and 105 Hz and 3 × 10−4 and 5 × 10−8 nT2/Hz at 101 and 102 Hz, respectively. The average wave intensity is independent of latitude, magnetosheath field strength, and magnetopause position. The only parameter found to be correlated with wave intensity is the magnitude of the Z component of the magnetosheath magnetic field. The broadband wave intensities increase with increasing negative Bz. These observational results put strong constraints on any proposed generation mechanism for the broadband magnetopause boundary layer waves. Reasonable mechanisms should be able to explain the lack of local time, latitude, and interplanetary parameter dependences. The dependence of IMF Bz and possible correlation with magnetic reconnection should be a principal feature in the model. These observations support the conjecture that cross‐field diffusion of magnetosheath plasma by wave particle interaction with these waves (Tsurutani and Thorne, 1982) is the steady state source of the low‐latitude boundary layer, and that pitch angle scattering and the consequential particle precipitation into the ionosphere is the mechanism for the dayside aurora. For cyclotron resonant interaction with E>100 eV electrons during southward IMF Bz events, a total precipitation rate of 1.0 to 1.2 ergs/cm2 s is determined.

“…Changes in the interplanetary magnetic field (IMF) are well known to be important in regulating geomagnetic activity. In particular, the variation of the north‐south component of the IMF ( B z ), when rendered in the geocentric solar‐magnetospheric (GSM) coordinate system, plays a crucial role in determining the amount of solar wind energy that is transferred to the magnetosphere [ Arnoldy , 1971; Tsurutani and Meng , 1972; Russell and McPherron , 1981; Akasofu , 1981; Akasofu et al , 1985; Farrugia et al , 1993]. This paper concentrates only on strong geomagnetic activity, geomagnetic storms.…”

Section: Introductionmentioning

confidence: 99%

Effects of magnetic clouds on the occurrence of geomagnetic storms: The first 4 years of Wind

Wu¹

2002

101

[1] We investigate geomagnetic activity associated with magnetic clouds as well as some aspects of the clouds' magnetic field structure (e.g., magnetic field distributions of the clouds). Thirty-four magnetic cloud events observed by Wind over the years 1995-1998 are investigated in this study. Magnetic clouds are a principal source of strong, long-lasting, interplanetary, negative B z fields (in solar magnetospheric coordinates) and hence are a major source of geomagnetic activity (Dst < À50 nT). The region just upstream of a cloud may be a significant source of southward fields instead of, or as well as, the cloud itself. We call this upstream region a ''sheath'' if it is bounded by a shock (or a pressure pulse) and the cloud. This study helps to identify the major sources (regions of southward B z following shock passages or within the magnetic clouds) that are most dominant in the generation of geomagnetic storms. It is found that a geomagnetic storm can be induced by (1) a sheath, (2) the leading (i.e., front part) region of a cloud, (3) the trailing part of a cloud, and (4) both sheath and cloud regions. (Because of this complexity a storm with a multistep main phase can occur.) The related occurrence percentages of storms were 17.6% (six events), 44.1% (15 events), 5.9% (two events), and 20.6% (seven events), and the averaged storm intensities (minimum Dst) were À60, À85, À92, and À58 nT, respectively. For the remaining four events (11.8%), there were no storms. The occurrence timing of storm intensity is highly correlated with the occurrence timing of minimum B z (maximum VBs or ) for a magnetic cloud with the field rotating from southward to northward.