Overview of the Event
On May 4, 1998 the velocity and density of the solar wind were high and the interplanetary magnetic field at times strong and southward. The 1997-068 HEO spacecraft appears to have encountered the magnetopause at a distance of 3.7 RE at a SZA of 66o at 0545 UT. The POLAR spacecraft crossed the dayside magnetopause at 0541:21 UT well inside geosynchronous orbit, at 5.3 RE and a solar zenith angle of 19o. After this crossing, POLAR spent much of the rest of its outbound orbit in the magnetosheath and for brief periods crossed into the solar wind at distances from 7.3 RE and a solar zenith angle of 32o to a distance of 8.5 RE and a solar zenith angle of 45o. This corresponds to subsolar distances of only 6.8 to 7.5 RE for the shock. These observations are important not solely because they are POLAR's only observations to date of the subsolar magnetopause and the bow shock. The first magnetopause crossing is a spectacular example of a rotational discontinuity with a field change of 500 nT in the north-south direction with no change in magnitude on either side of the current layer but a depressed field strength within it. The normal component across the current sheet is about 50 nT pointing inward as expected for POLAR's northern hemisphere location. The six bow shock crossings are all examples of supercritical shocks. The 3-axis electric field experiment on board provides the opportunity to test assumptions about the electric field across the bow shock for the first time.
Configuration of ISTP Spacecraft
On May 4 both WIND and ACE were close to the forward libration point about 220 Re upstream. As shown in Figure 1 WIND was close to Earth-sun line as projected on the ecliptic plane but about 27 RE above it as shown in the view from the sun given in Figure 2. Thus both spacecraft should be of equal quality for providing measurements of the input to the magnetosphere. The circles in Figure 2 show the approximate radii of the magnetosphere for undisturbed conditions and the most highly compressed conditions on this day.
Closer to the magnetosphere Interball 1 was upstream of the average location of the bow shock as shown in Figure 3. Geotail and Imp 8 were in the region that would usually be the afternoon post dusk magnetosheath and Polar was in the dayside magnetosphere. The view from the sun in Figure 4 shows that Polar was crossing the dayside equatorial region moving to higher latitudes. Geotail was above the GSM equator and Interball 1 and Imp 8 significantly below the GSM equator. No data were available from IMP 8 during the most interesting periods of this event. Geotail remained in the solar wind until 1130 UT at which point it entered the magnetosheath.
Inside the magnetopause the GOES 8 and 9 spacecraft at synchronous orbit were on the nightside of the Earth during the most active period of activity as shown in Figure 5.
Data Plots
The ISTP project has established a web page containing solar and in situ observations of the May 1998 period
Selected plots from that page include solar wind and IMF
data from ACE;
POLAR imagery from VIS
and UVI; energetic
particle spectrograms from the LANL geosynchronous spacecraft; a movie showing
the predicted distortion of the
magnetosphere and
measurements by NOAA satellites. Sample ground based magnetograms from the
CPMN are shown in Figure 6a, b, c, and
d. Gang Lu has provided a plot showing the Kp index, the AU, AL and AE indices and the Dst index.
Also provided are plots of the potential drop, Joule heating and auroral energy flux in the northern hemisphere.
Publications
C. T. Russell, G. Le, P. Chi, X.-W. Zhou, J.-H. Shue, S. M. Petrinec, P. Song, F. R. Fenrich and J. G. Luhmann, The Extreme compression of the magnetosphere on May 4, 1998, as observed by the Polar spacecraft, Adv. Space Res., in press, 1999.
J. Chen and T. A. Fritz, May 4, 1998 storm: Observations of energetic ion composition by POLAR, Geophys. Res. Lett, 26, 2921-2924, 1999.
S.-W. Chang, J. D. Scudder, J. F. Fennell, R. Friedel, R. P. Lepping, C. T. Russell, K. J. Trattner, S. A. Fuselier, W. K. Peterson, and H. E. Spence
Energetic magnetosheath ions connected to the Earth's bow shock: Possible source of CEP's, J. Geophys. Res., submitted 1999.
Fall 1999 AGU Meeting abstracts
C. J. Farrugia, et al., Unprecedented Power to the Magnetosphere: May 4, 1998
C. J. Farrugia, et al., Large-scale Geomagnetic Disturbances during May 4, 1998
J. Aarons, M. Mendillo, and B. Lin, The Great Magnetic Storm of May 1998 and Its
Effect On Phase Fluctuations in the Auroral and Equatorial Regions, Ionospheric Effects
Symposium, May, 1999.
| C. T. Russell (ctrussel@igpp.ucla.edu) | Overview |
| C. Farrugia (farrugia@monet.sr.unh.edu) | Power input |
| J. Shue (shuej1@oval.jhuapl.edu) | Size and Shape of Magnetosphere |
| C. Goodrich (ccg@astro.umd.edu) | Simulations of May 1-5 |
| J. Berchem (jberchem@igpp.ucla.edu) | Simulations of May 4 |
| P. Anderson (phillip.c.anderson@aero.org) | DMSP/Pixie Xrays |
| J. Wygant (wygant@belka.space.umn.edu) | Magnetopause structure |
| J. Scudder (jack-scudder@uiowa.edu) | Walen Relationship |
| P. Song (psong@engin.umich.edu) | Tide particles |
| K. Trattner (trattner@mail.spasci.com) | Timas particles |
| J. Chen (chen@buasta.bu.edu) | Cammice particles |
| J. Scudder (jack-scudder@uiowa.edu) | Hydra particles |
| A. Hull (ahull@ssl.berkeley.edu) | Bow shock structure |
| S. Petrinec (petrinec@mail.spasci.com) | Bow shock location |
| C. Farrugia (farrugia@monet.sr.unh.edu) | Inner magnetospheric observations |
| Gang Lu (ganglu@hao.ucar.edu) | Global ionospheric response |
| J. Fennell (Joseph.F.Fennell@aero.org) | Ring Current |
| X. W. Zhou, et al. | The Extreme Compression of the Magnetosphere of May 4, 1998 |
| J. R. Wygant, et al. | Observations of Intense Electric Field Structures at the May 4, 1998 Magnetopause Crossings |
| J. U. Kozyra, et al. | POLAR Magnetosheath Observations on May 4, 1998 |
| J. D. Scudder, et al. | The Generalized Walen Tests Throughout the May 4, 1998 Magnetopause Traverses |
| Jiasheng Chen, et al. | May 4, 1998 Storm: Multiple Spacecraft Observations |
| S.-W. Chang, et al. | Observations of Energetic Ions in the Magnetosbeath on May 4, 1998 |
| Jih-Hong Shue, et al. | Dependence of the Magnetopause Erosion on Southward IMF |
| C. Cocheci, et al. | Interplanetary Features of May 2-7, 1998, and Aspects of Their Effects on the Magnetosphere |
| J. F. Fennell, et al. | Multisatellite Observations of the Energetic Electron Response to the May 1998 Magnetic Storm |
| J. F. Fennell, et al. | Multiple Satellite Study of the May 1998 Magnetic Storm: Ring Current Response |
| 08:30 | C. T. Russell | Event overview: Solar wind conditions and spacecraft configuration |
| 08:40 | C. Farrugia | Power input into the magnetosphere on May 4, 1998 |
| 08:50 | S. Petrinec | Size and shape of the magnetosphere/X ray observations |
| 09:00 | P. Song/J. H. Shue | Size and shape of the magnetosphere |
| 09:10 | Y-S Su | Magnetopause crossings by the LANL geosynchronous satellites |
| 09:20 | J. Wygant | Magnetopause observations: E field |
| 09:30 | C.T. Russell | Magnetopause observations: B field |
| 9:40 | J. D. Scudder | Walen Relation |
| 9:50 | P. Song | Polar magnetosheath observations |
| 10:00 | K. Trattner | TIMAS Observations |
| 10:10 | J. D. Scudder/Chang | Magnetosheath particles |
| 10:20 | T. Fritz | CEPPAD observations |
| 10:30 | J. Newbury | Bow shock crossings: B field |
| 10:45 | F. Mozer | Bow shock crossings: E. field |
| 11:00 | J. D. Scudder/A. Hull | Plasma observations |
| 11:15 | J. Berchem/M. Abdalla | Simulations |
| Noon | Summary | |
| 12:30 | Lunch |
