The origins of the interplanetary southward B z which cause the 10 major (Dst • --100 nT) magnetic storms detected during the 500 days of study (August 16, 1978, to December 28, 1979 of the Gonzalez and Tsurutani (1987) work are examined in detail. A full complement of ISEE 3 plasma and field data, an ll-station AE index and the near-equatorial Dst index, are used in this analysis. It is found that the origins of the interplanetary southward B.. events are quite varied. If it is defined that the B z event which leads to Dst • --100 nT is "the cause" of the storm, then one of the storm intensifications is caused by shock compression of preexisting southward interplanetary magnetic fields, four (or five) are related to driver gas magnetic fields, one (or two) are caused by shocked kinky heliospheric current sheets, two (or three) by turbulence or waves behind interplanetary shocks, and one possibly by draped fields associated with a noncompressive density enhancement event (without a shock or a high-speed stream). In simplistic terms, four (or five) storms are caused by driver gas fields, four by shocked (sheath) fields, and one possibly by high-intensity draped fields. In actuality, many of the interplanetary southward B z and corresponding magnetic storm (Dst) structures are more complex than stated above. At least four of the interplanetary events have both major sheath and driver gas southward B z events. In two storms, sheath southward Bz features led to Dst reaching levels of --90 nT prior to driver gas southward B z features; the following driver gas fields then caused Dst to exceed our storm criteria of _< -100 nT. In two other cases, sheath B.. features led to magnetic storm onsets (Dst • --100 nT); the following driver gas southward B z features cause further storm intensifications. The above magnetic storms therefore displayed two-stage development characteristics. The results of this study indicate the equal importance of both sheath fields or draped fields and driver gas fields for the generation of major geomagnetic storms. Because of the importance of the sheath fields the intensity and duration of geomagnetic storms cannot be predicted by solar observations of active regions alone. Tang et al. (1988) will address this topic in detail. Paper number 7A9404. 0148-0227/88/007 A-9404 $05.00 when oriented in the vertical direction, have large southward (then northward) field components (or vice versa). The criteria of a "cloud" are a radial dimension of .-•0.25 AU at 1 AU, high, > 10 nT, field magnitudes, and magnetic field directional changes by a rotation in a plane. Klein and Burlaga note that this field geometry is consistent with a magnetic loop or bubble [see Burlaga and Behannon, 1982] but cannot be uniquely determined because of the limitation of singlespacecraft measurements. In a sense the above classification is unfortunately too broad for the purpose of this present study.As examples, kinky heliospheric current sheets [Smith, 1981;Akasofu, 1981;Tsurutani et al., 1984 that are present in the co...
[1] Forecasting the time of arrival at Earth of interplanetary shocks following solar metric type II activity is an important first step in the establishment of an operational space weather prediction system. The quality of the forecasts is of utmost importance. The performances of the shock time of arrival (STOA) and interplanetary shock propagation models (ISPM) were previously evaluated by Smith et al. Each model predicts shock arrival time (SAT) at the Earth using real-time metric type II radio frequency drifts and coincident X-ray and optical data for input and L1 satellite observations for verification. Our evaluation of input parameters to the models showed that the accuracy of the solar metric type II radio burst observations as a measure of the initial shock velocity was compromised for those events at greater than 20°solar longitude from central meridian. The HAF model also calculates the interplanetary shock propagation imbedded in a realistic solar wind structure through which the shocks travel and interact. Standard meteorological forecast metrics are used. A variety of statistical comparisons among the three models show them to be practically equivalent in forecasting SAT. Although the HAF kinematic model performance compares favorably with ISPM and STOA, it appears to be no better at predicting SAT than ISPM or STOA. HAFv.2 takes the inhomogeneous, ambient solar wind structure into account and thereby provides a means of sorting event-driven shock arrivals from corotating interaction region (CIR) passage.
For many years, researchers have utilized definitions of the substorm phenomenon that are not consistent among one another, and this has created great difficulties in comparing the results reported in the literature by the various researchers. In August 1978, nine magnetospheric physicists active in the field of substorm research met in Victoria, British Columbia, Canada, to attempt to reach a consensus on an acceptable definition for a magnetospheric substorm. This paper reports the agreements reached at the Victoria workshop and presents an operational definition of the magnetospheric substorm and a critique of the various signatures by which researchers can identify the time sequence and spatial extent of the substorm.
indices. Our present estimates give t•e following relationshi•s: Uj • 2.3 times 10 v ß AE, U A • 0.6 times 10 8 ß AE and U I = 2.9 times 108 ß AE; Uj -3.0 times 108 ß AL U -0.8 times 108 ß AL, and U I -3.8 times 10 • -AAL. Injection Rate
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