September 1999 Space Weather Month Campaign: What's New and What's Next

Janet Kozyra, Space Physics Research Lab, University of Michigan, Ann Arbor, MI 48109-2143 <jukozyra@engin.umich.edu>, and David Webb, AFRL/USBS, 29 Randolph Road, Hanscom AFB, MA 01731-3010 <webb@plh.af.mil>

What is September 1999 Space Weather Month?

Space Weather Month is a month-long campaign interval during September 1999, conceived and coordinated under the auspices of SCOSTEP's S-RAMP program.

• Purpose:
  • to study space weather events from their initiation on the sun to their impacts at the Earth
  • to investigate the effects on space-based and ground-based worldwide assets
  • to assess the accuracy of forecasting techniques.
• Special features of the campaign include:
  • broad international cooperation,
  • complete as possible coverage of the event through worldwide coordinated space and ground-based observations (including maximized coverage by the ISTP program, the Oersted satellite and other spacecraft),
  • enhanced forecasts by ISES,
  • three scheduled Incoherent Scatter Radar world days (15-17 September 1999),
  • encouraged involvement of the user communities, and participation of the forecasting community.
• A campaign web site was set up at http://aoss.engin.umich.edu/intl_space_weather/sramp/ to
  • handle the coordination of activities,
  • post lists of participants,
  • display links to campaign data, forecasts, prediction sites, real-time displays and archives.
• Information to date indicates that there were some 100 scientists from more than 15 countries among the participants in the observational phase of the campaign.
• Campaign Status: post-event analysis phase.

What Happened during Space Weather Month?

Summary of Interplanetary Sources of Activity:

• A recurrence pattern of high speed streams was used by John Foster to select 15-17 September as the ISR world day's interval within the Space Weather Month campaign. Figure 1 shows the recurrent appearances over 3 solar rotations of of a high speed stream on July 22, August 18 and finally on September 16 during the selected ISR world days interval.
• However, the first campaign magnetic activity arrived several days earlier than expected, on September 12 . Another recurrent high speed stream was introduced during Carrington rotation #1952 and subsequently reappeared on September 12 bringing with it several moderate magnetic storms.
• Later in the month, a major magnetic storm was driven by an interplanetary magnetic cloud event.

Summary of Magnetic Storm Activity

Figure 2 is a summary of all magnetic storm events (numbered 1-5) with minimum Dst values less than -50 nT (moderate to major storm events) within the core campaign interval (September 6 - 25). The embedded ISR world days interval is also indicated. Within the core campaign interval, 4 moderate and 1 major magnetic storms occurred.

Geoeffective Solar Wind Events:

There were roughly three periods of shocks, ejecta and southward interplanetary magnetic fields that triggered magnetic storms during the core campaign interval. Dates and times in this preliminary report of solar wind features are taken from WIND observations, whereas ACE observations are given in the figures. As a result times at which ACE observed the features may differ slightly from those quoted in the text for the WIND spacecraft.

• 12-14 September 1999 Storms (Figure 3)
  • An interplanetary shock (Sept 12, 0315 UT) arrived just prior to a sector boundary crossing (Sept 12, 0800 UT) with strong density and pressure enhancements.
  • No obvious ejecta signatures are seen in the data during this time interval.
  • The interplanetary magnetic field (IMF) is enhanced but highly fluctuating with long southward intervals. These intervals of intermittent southward IMF Bz extend into the early part of September 14, triggering the magnetic storm activity on September 12-14 (labeled as Storms 1 and 2 in Figure 2).
  • There are no obvious solar events that can be associated with these geoeffective solar wind signatures.
  • Both the sector boundary and the following high-speed stream drive the magnetic storms. The presence of the shock and enhanced IMF indicates solar ejecta may also be present.
• 15-16 September 1999 Storms (Figure 4)
  • The second geoeffective interval in the solar wind, shown in Figure 4, contains two forward interplanetary shocks (IP shocks) on September 15, one at 0710 UT and the other at 19:40 UT.
  • The shock at 0710 UT is followed closely by a small interplanetary 'probable' magnetic cloud (IMC), extending from ~0900 - 1730 UT, with south to north magnetic field rotation and maximum IMF ~ 15 nT.
  • The strong southward magnetic field early in the cloud event triggers a moderate magnetic storm with minimum Dst ~-53 nT labeled Storm 3 in Figure 2.
  • The second shock at 1940 UT is not followed by obvious solar ejecta. However, there is a period of sustained southward IMF Bz triggering the magnetic storm activity on September 16, identified as Storm 4 (min Dst ~-67 nT) in Figure 2.
  • There were two partial halo coronal mass ejections (CME) observed by the SOHO LASCO coronagraphs on September 13 that are the possible sources for the two shock events on September 15. However, the required travel times to Earth are a bit shorter than would be considered usual.
    • The first halo CME event occurred on September 13 at 0930 UT with a projected speed of 730 km/s. This halo event was associated with an X-ray class >C5 flare erupting from solar active region #8699 near sun center. The estimated travel time to the onset of the interplanetary shock signature at Earth is 49 hours with a required speed of 850 km/s; the travel time to the peak of the magnetic storm is 50 hours.
    • The second solar halo CME event was triggered on September 13 at 1731 UT with a projected speed of 410 km/s. This event was associated with a class C3 flare from solar active region #8693. Travel time between this CME event and the interplanetary shock event at Earth is 51 hours with a required speed of 817 km/s; between the CME event and the storm peak is 64 hours with a required speed of 650 km/s. The later is a more reasonable time delay.
• 22-23 September 1999 Storms (Figure 5)
  • A forward shock at 1130 UT on Sept 22 is followed by a large 'probable' IMC with south to north field rotation. The IMC extends from 2000 UT on Sept 22 to 0700 UT on Sept 23 with maximum IMF >25 nT.
  • There is a reverse shock on Sept 23 at 0920 UT. Reverse shocks were always considered to be rare inside of 1 AU, but are now being seen more frequently by the sensitive WIND magnetic field experiment.
  • The signature of a sector boundary crossing is visible in the WIND data (not shown) on Sept 22 at 1300 UT appearing well before the arrival of the 'probable' IMC and followed by a high-speed stream.
  • The strong IMF Bs early in the IMC drives a major magnetic storm with minimum Dst ~-164 nT on Sept 23 at 0000UT identified as Storm 5 in Figure 2.
  • The solar source of this event was a faint, but complete halo CME on Sept 20 at 0606 UT with projected speed of 450 km/s. The travel time between the CME onset and the onset of the IMC at Earth is 63 hours with required travel speed of 660 km/s.
  • SOHO EIT images show a filament eruption with bright arcade loops and dimming, and a possible coronal wave on Sept 20 at ~0500 UT. A small C2.5 X-ray flare is associated with this event. Figure 6 displays a sequence of EIT 195 Å images showing the bright arcade loops and dimming regions associated with the filament eruption (indicated by an arrow in each image) in the southern polar crown area crossing the central meridian. The filament itself is usually not visible in the 195Å images.
  • The full halo CME, itself, was captured by the SOHO LASCO coronagraph and is pictured in Figure 7. (LASCO C2 Movie - 536K MPG)

What is Happening Now?

A number of important efforts in the forecast, research and user communities were undertaken during the campaign. A variety of archives containing data, predictions and model outputs are already in existence for this period and more are coming on-line all the time.

Data Archive

• A master table of data sets, model outputs, temporal coverage and contact information is under construction for the September 1999 campaign period and will be provided to the community on the Space Weather Month campaign web pages.
• The purpose of the table is to support collaborative analysis efforts throughout the international community.

Request for Contributions

• More contributions are requested.
• Please send information about data products and URLs (if appropriate) for the September 1999 interval to Janet Kozyra <jukozyra@engin.umich.edu>.

What is Next?

First Workshop in Boulder, Colorado

• To be held during Space Weather Week, 1-5 May 2000 in Boulder. This venue has been selected to enable groups interested in space weather impacts on technology, as well as researchers and forecasters, to participate in the analysis.
• Dual purpose of the workshop:
  • To provide an initial exchange of ideas and information which will kick-off the analysis phase of the campaign
  • To pave the way for an electronically-aided worldwide analysis effort in collaboration with the NSF's Space Physics and Aeronomy Research Collaboratory (SPARC)

First S-RAMP Workshop in Sapporo, Japan

• During the week of 2-6 October 2000 in Sapporo, Japan
• More information about the S-RAMP Space Weather Month post-event analysis effort will be distributed as it becomes available both through the email list of campaign participants and through community newsletters.