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14-16 July 2000

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      July 14, 2000


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An explosion on the Sun this morning has already smacked Earth's magnetosphere with the most intense blast of solar particles ever detected by the Solar and Heliospheric Observatory (SOHO) and the Advanced Composition Explorer Spacecraft (ACE). The particles were produced by an intense solar flare and by an accompanying explosion of solar plasma, known as a coronal mass ejection.

The wave of solar particles - known as a solar energetic particle event (SEP) - is already four times more intense than any other event detected since the great SEP event of October 1989, the peak of the last solar maximum. At mid-afternoon today, the storm of particles from the Sun was still intensifying. Large solar particle events have in the past been associated with failures and disruptions of satellite electronics (known as single event upsets, or SEUs).

The solar flare -- one of the brightest ever seen by SOHO - originated near the center of the solar disk, and its brightness peaked at 10:24 UT (6:24 a.m. Eastern Daylight Time). It has been categorized as an X-class flare, a classification reserved for the most powerful flares. Flares accelerate subatomic particles in the solar atmosphere out into space, and those particles produce bright spots and streaks in SOHO images when they impact the spacecraft's instruments. This flare produced a particle deluge so intense that the image from SOHO was temporarily lost in a blizzard of specks. It has also saturated many of the particle detectors on NASA's ACE and Wind spacecraft.

The flare was accompanied by an Earth-directed coronal mass ejection (CME) that left the Sun at approximately 1775 kilometers per second (about 4 million miles an hour). An interplanetary shock wave, rippling through the solar wind in front of the storm, was estimated to be moving at 1300 to 1600 km/s (2.9 to 3.6 million miles an hour). The arrival at Earth of this massive electrified gas cloud may cause vivid auroral (northern and southern lights) displays Saturday or Sunday, depending on the direction of the storm and the orientation of its magnetic field.

At 3 p.m. Eastern time on July 14, the NOAA Space Environment Center declared that a G2 geomagnetic storm was already in progress, and that solar radiation storms and radio blackouts had already begun. NOAA space weather forecasters predicted that "the CME will impact the Earth's magnetic field on Saturday afternoon and will cause a geomagnetic storm that is expected to reach category G3 (strong) to G4 (severe) levels. The radiation and geomagnetic storms are expected to produce adverse effects on spacecraft operations, power systems, high-frequency radio communications, and low-frequency navigation signals. In addition, the geomagnetic storm is expected to produce aurora displays that will be visible over much of the U.S."

NASA's ACE, Polar, IMAGE, and Wind satellites will monitor the solar storm as it passes Earth. CMEs typically disturb Earth's magnetic field, distorting its shape like a jellyfish buffeted by a strong current. This interaction energizes the electrically charged particles naturally trapped in Earth's magnetosphere, causing the eerie auroral displays. The Polar spacecraft provides a large scale, global view of this activity from its unique orbit over Earth's poles.

From Nicky Fox (ISTP Science & Operations Coordinator)

SOHO/EIT observed a flare at 10:12 UT, 2000/07/14, near the disk center and GOES reported an X5.7 class flare event from this same area starting at 10:03 UT. LASCO and EIT observed a full halo CME at 10:54 UT. The event was first visible as a bright front extending all around the sun's disk, forming a full halo. The measured speed averaged 1775 km/sec. This HALO CME was (probably) associated with the X5.7 flare. The flare was also accompanied by a very strong energetic proton storm - clearly visible in the SOHO images.

Shortly after 10 UT, the GOES proton detector picked up an unusually steep rise in the proton flux. We regularly see a slight increase in energies greater than 10 MeV particles - typically as high as 10 particles/s/sr - associated with halo events and flares, however in this case particles with energies greater than 100 MeV arrived promptly and the fluxes jumped to ~400 part/s/sr. The fluxes of the lower energy (>10 MeV) continued to rise and peeked on Saturday (7/15) around 10 UT at flux levels above 10,000 part/s/sr - I am guessing at this time since the fluxes were off the scale between 3-18 UT. After 18 UT, the fluxes in all energies have continued to steadily decline.

This high rate of particles in the interplanetary medium are likely to have caused spacecraft anomalies such as the loss of the WIND sun sync, ACE/SWEPAM and GOES electron instrument 'mis-readings'

Murray Dryer gave a model-based prediction that the shock would arrive within 24-28 hours from the start of the event.

At ~14:10 UT on Saturday 7/15, the SOHO/CELIAS instrument detected a clear jump in speed (initially to ~800 km/s and then an increase to ~900 km/s about an hour later). The ACE/MAG also show a very clear increase in the interplanetary magnetic field - to ~40nT. Approximately 25 minutes later, the event arrived at Earth. The POLAR/VIS instrument detected a brightening of the dayside aurora at ~14:38 UT. The ejecta arrived around 19 UT (at ACE) - so about 24 minutes later at Earth - the IMF jumped to an unbelievable 60 nT, dropping down to 40 nT over the course of 8 hours. The IMF remained southward for about 10 hours, finally turning northward shortly before 5 UT. The aurora continued to be extremely active throughout the day with particularly spectacular displays around 00:43 UT (7/16).

NOAA reported the Kp index at a value of 9 - for 9 hours. The ground based magnetometer chains in Canada (ISTP/CANOPUS) and Scandinavia (IMAGE) both detected magnetic fluctuations of about 1000 nT and the Dst minima (from Kyoto) was ?277 nT. The quick look AE indices (also from Kyoto) were over -2000 nT. The GOES onboard magnetometer indicated a possibility that it was located outside the geostationary orbit in the solar wind for ~5 hours at 19-24 UT, 7/15.

For comparison, the storm which occurred on April 6, 2000, when the aurora were visible in the Carolinas had a Dst of -321 nT, but an AE over only just over -1000 nT. Since it is the reconnection in the tail which drives the aurora and also the AE index, this shows that despite a larger storm index, the auroral activity should have been better in this current case. If only the event had hit just 2 hours later and there had not been a full moon - we should have seen aurora in Washington DC.

From Kevin Schenk (SOHO/LASCO & EIT)

LASCO and EIT observed a full halo CME today, 2000/07/14. The event was first visible in C2 at 10:54 UT, as a bright front extending all around the occulting disk. The measured speed averaged through 4 points in both the C2 and the C3 field before saturation from particles was 1775 km/sec at PA 262 (SW limb). This speed may not be accurate due to limitations of the level of the Proton event in view.

EIT observed a flare from AR9077 with wave at 10:12 UT near disk center at location [N16.8;E0.21]. GOES reports an X5.7 class flare event from this same area starting at 10:03 UT. This HALO CME was problably associated with this flare.

From Joe Gurman(SOHO/EIT)

There was an X5.7 flare from AR 9077 near central meridian today, with peak soft X-ray emission at ~ 10:24 UT. Connected with this event there is a clear EIT wave, and, I suspect, a halo CME, though the latter may be difficult to detect, since there is a very strong solar energetic particle (SEP) event connected with the flare/CME in progress, producing a near whiteout of LASCO images. We should be able to see a halo in C3 later if not in C2 in the first couple of hours after the event.

In any case, the EIT movie is _quite_ impressive, and this one, though mainly in the northern hemisphere, is headed straight toward a planet near you. No guarantee of geoeffectiveness, obviously, since we don't know the direction of B_z.

From Mike Kaiser(WIND/WAVES)

More asthetically pleasing type II bursts there have been! This guy is so broadband and strong that it doesn't lend itself well to a nice dynamic spectral display (see gif file on Web site -- best I could do on short notice -- note the intensity scale 0-30 dB on the high frequency receiver -- most of our events are 0-3 or 0-6 dB). Specifically, WAVES observed a series of extremely intense type III-like bursts starting at about 10:30 on July 14. Also starting at about that same time are a bunch of intermittent bright spots superimposed on a relatively featureless and weak background that fills a goodly part of the receiver band and rapidly drifts to lower frequencies. This broadband emission is observed continuously until the arrival of the shock at about 14:30 on July 15. Speed would be hard to determine in our usual way (i.e. fitting Saito density law curves through a fundamental-harmonic pair) because of the 'diffusiveness'. Furthermore, we'll likely have a difficult time determining the direction of arrival from the spin modulation, because the Wind spacecraft lost its sun sensor for a couple of days when the prompt particles hit. This event looked 'prettier' as seen by our Cassini instrument at 4 A.U. and 120 degrees west of Earth.

On a more mundane note, WAVES also detected a second type II on July 14 between 14:00 and 14:10 in the frequency range from 6 to 2 MHz. This was at the time of the M flare. Lots of individual type III burst activity reported in the daily event reports, but not metric type IIs.

From Patrick McIntosh(HELIOSYNOPTICS, Boulder, CO)

High activity period extended by strong active region now at SE limb

An important activity complex rotating into view at s15 east limb will add Significant flare and cme activity to the three flare sources now on the Solar disk. A large cme at s15 early today corresponds to the location of Returning regions 9058/9064. Coronal structure along the entire east limb Has been very complex for the past two days.

Late today a broad system of high loops developed near s15 with bright Emission in fexv at the top of the loops. The loops reached their peak Intensity near 1650 ut at the time of an m2 long-duration xray flare that Had a gradual rise. This event indicates a flare source at least a full day Behind the limb. The brightest part of the flare which produced the loops Was probably occulted by the limb and, therefore, the flare was much more Intense than m2.

This region may be more important than region 9077 (n17 e15) which produced Two class x events in the past two days.

Region 9077 continues to evolve new and complex sunspot structures, Intensifying the high magnetic-field gradient within its delta Configuration. The sunspot umbrae are linear and curved as in past Proton-flare sunspot groups. A low-intensity proton event is in progress From flares in this region. Additional major xray events are expected here. Proton fluence will increase during the next week as this region rotates Toward a position with direct connection to the earth's location.

A strong delta configuration also persists in region 9070 at n10 w65 where An m5 flare occurred today. Spot growth is continuing near the delta. A Class m5 to x2 event may occur before this region rotates over the west Limb. Significant proton fluence would occur with such an event.

The chain of four bipolar regions now crossing the sw limb includes a weak Delta configuration and complex surrounding fields that could generate a Major xray event. This activity complex is weakening, however.


GEOPHYSICAL ACTIVITY FORECAST: Due to the expected arrival of an earth-directed full halo CME from the x5/3b event, the geomagnetic field is expected to see an increase during the latter half of the first day. Major to severe storm levels are possible after the storm onset through the second day of the period. By late on the third day of the period activity should start to decrease to active to minor storm conditions.

From Daniel Berdichevsky (ISTP/SPOF)

There is an extremely powerful interplanetary shock that may have originated close to the Sun's Equator. Very preliminary estimates of the shock speed using metric Type II radio bursts puts its speed at 1300-1600 km/s.

These conditions are observed after a fast forward interplanetary shock passed Earth at approximately 1539UT, July 14, 2000.

It is highly possibly that extraordinarily hazardous radiation conditions at high altitude may be encountered now and will persist until after the passage of an extremely powerful interplanetary shock.

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Last Updated: 08/04/00