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ISTP Sun-Earth Connections Event Banner

October 22nd, 1999

      POLAR Auroral Movies

      Movies made from Polar images on Friday, 22 October 1999 of the auroral storm that occurred over the United States.

      Ionospheric Convection Movies


      Observations of Solar Wind Conditions

      Solar Observations

      October 22, 1999 Event Summary

      A solar wind interplanetary compound stream hits the Earth's magnetosphere in the morning of October 22, 1999, and a display of intense aurora at midlatitude over continental USA was observed by the POLAR cameras (VIS, and UVI), while observers across the mid-west sections of North America reported the unusual sighting of aurora as far south as Kansas. These disturbances noticed in America and elsewhere produced the strongest magnetic storm of the year.

      Preliminary time line

      LASCO and EIT observed a partial halo CME beginning late UT on 1999/10/17, and continuing into 1999/10/18. The event was first visible in C2 at 00:06 UT on 1999/10/18, as a bright arcade over NE limb. Fainter extensions were visible along the east limb and over the south pole. The event extended over about 210 degrees, from PA 0 (N pole) to PA 210 (SW limb). Measurements at PA 45 (NE limb) show a gradual acceleration of 17 m/s^2 throughout the field of view, with a final measured speed of 450 km/s at 13 solar radii.

      EIT observed a filament activation and eruption, with an accompanying wave event, on the SE portion of the disk, beginning at 23:12 UT on 1999/10/17.

      WAVES/WIND and Culgoora/Australia detected type II radio burst enhancements in the 10 MHz frequency range from 2327 to 2336 on October 17.

      At 0145 UT on October 21 an IP shock reaches Earth compressing the magnetosphere but causing minor 'unsettled' conditions to the geomagnetic environment because it was followed by more than 12 hours of an almost uninterrumpted northward interplanetary field, with well above average (~ 20 nT ejecta magnetic field) solar wind speed of > 400 km/s, and a mean density of approximately 12 AMU/cm^3 (ACE/MAG and SWEPAM, and WIND/MFI and SWE NRT observations). Near 21 UT on October 21, the plasma conditions remain the same but the interplanetary magnetic field turns sharply South and starts large amplitude oscillations which last until almost the end of the day when the velocity of the solar wind and the magnitude of the ejecta's magnetic field sharply increase to above 500 km/s and well above 20 nT respectively.

      The geomagnetic disturbances reached maximum near 0700 UT when the ejecta magnetic field near Earth reached above 30 nT while almost completely oriented southward and disturbed storm time index (Dst) reached - 231 nT. Followed by abrupt rise on the solar wind speed up to above 700 km/s announcing the arrival of a high speed stream which continued to affect the Earth vicinity for several more days.

      During the more disturbed conditions several ISTP spacecraft were ideally located to study the solar wind-magnetospheric-ionospheric coupling, with GEOTAIL for example able to record very unusual radio emissions down-stream of the Earth, in the magnetotail region (private communication Dr. Roger Anderson).

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