On Sunday afternoon, Jan. 18th, UTC, a moderately strong solar flare and Coronal Mass Ejection erupted on the directly Earth-facing portion of the sun. The flare was an X class (X-ray flare) that sent the CME in our direction, but not a particularly strong flare. Originally predicted to affect Earth well into the day (in UTC) on the 20th, it ended up being rather fast moving and stronger than the typical CME.
Arriving earlier than expected, a CME struck Earth's magnetic field on Jan. 19th (1930 UT). The impact sparked a severe G4-class geomagnetic storm. The timing of the impact favored Europe, where widespread auroras are now being reported. It remains to be seen whether the storm will persist long enough for a similar display in North America.
The CME that struck Earth today crossed the sun-Earth divide in only ~25 hours. That's fast. For comparison, most CMEs take 3 or 4 days to get here. The high speed of this CME (~1660 km/s) places it in the top few percent of all CMEs observed in the past 30 years.
The NOAA Space Weather Prediction Center posted this summary of planetary K-index (Kp) values as the last update for Jan. 19:
The two red "towers" Kp at 8.33 and then 8.67 (or 8-1/3 and 8-2/3) are obvious signs of CME impacts. The two yellow boxes at the top right labelled S2 and G2 are Solar Radiation Storm and Geomagnetic storm cautions.
S2 (Moderate) Solar Radiation Storm ImpactsBiological: Passengers and crew in high-flying aircraft at high latitudes may be exposed to elevated radiation risk.
Satellite operations: Infrequent single-event upsets possible.
Other systems: Small effects on HF propagation through the polar regions and navigation at polar cap locations possibly affected.
G2 (Moderate) Geomagnetic Storm ImpactsPower systems: High-latitude power systems may experience voltage alarms, long-duration storms may cause transformer damage.
Spacecraft operations: Corrective actions to orientation may be required by ground control; possible changes in drag affect orbit predictions.
Other systems: HF radio propagation can fade at higher latitudes, and aurora has been seen as low as New York and Idaho (typically 55° geomagnetic lat.).
At the top level of the website with that Planetary K index graphic, lies this one:
Across the top of the graphic under SPACE WEATHER CONDITIONS it shows that earlier today S4 and G4 conditions were observed. I was doing some paperwork in the shack today, closer to 5PM or 2200 UTC, and the G4 condition was displayed. Note that the prediction for the next 24 hours at the right edge of this graphic also includes severe G4 storms. I have to add my usual summary: if you think plain old NOAA weather forecasts for your city are bad, they're generations of progress better than solar-terrestrial storm forecasts.
The usual thing people ask about is if auroras will be visible. The aurora forecasters seem more inclined to be cautious than plain old weather forecasters. They say tonight will be more active than last night and more active than tomorrow night, but they don't say something specific like they'll be visible from northern Illinois but not southern Indiana, for example. This plot, from the NOAA SWPC, was generated 0223 UTC, and I happen to typing at 0226 UTC. It's hard to get a much fresher forecast than that. That thin red line is marked as the view line, meaning that from around that line, the auroras might be visible as color on the horizon.
Here is what Wikipedia says about classes of solar flares. They are classed by the amount of soft x-ray radiation but I think they have other kinds of radiation including charged particles that do not travel at the speed of light
ReplyDeleteThe modern classification system for solar flares uses the letters A, B, C, M, or X, according to the peak flux in watts per square metre (W/m2) of soft X-rays with wavelengths 0.1 to 0.8 nanometres (1 to 8 ångströms), as measured by GOES satellites in geosynchronous orbit. [citation needed]