Space Weather alert
Evidence for an Earth directed solar cloud
posted: Feb 15, 2011
The Sun was extremely active the last days. Early February 15, the Space Weather Forecast Centre of Belgium witnessed extreme space weather. Fast Alerts were sent to the space weather community.

2011/02/15, at 02:41UT - The GOES X-ray flare detection email-alert from the SIDC/RWC states:

A class X2.3 solar X-ray flare occurred on 2011/02/15 with peak time 01:56UT.

2011/02/15, at 07:07UT - The forecaster on duty sent out a PRESTO-alert:

NOAA AR 1158 has produced an X2.3 flare peaking at 01:56 UT, associated with an Earth directed CME. Furthermore, an M2.2 flare (from the same AR) peaking at 17:26 UT on February 14 had also an associated Earth directed CME. They are expected to arrive to the Earth around February 17.


Some facts about this space weather event

  • A flare started at 01:48UT, peaked at 01:56UT and ended at 02:58UT. These times are measured by GOES in the X-ray radiation.
  • LYRA onboard PROBA2 captured the flash-flare in its time series. You see a clear sudden increase in 2 bandpasses. With LYRA you can determine the strength of the flare in a particular wavelength in a quantitative manner. GOES determines the strength of flares in X-ray radiation. According to GOES, it is an X2.3 flare. If you want a bigger image, click on it. It's the right one.
  • SWAP onboard PROBA2 captured the flash-flare in the image on the left. With SWAP you can determine the flaring site on the solar disk.
    See the SWAP movie.
    If you want a bigger image, click on it.
  • In the difference movie of SWAP, we see two events. One short event limited in size occured before 01:00UT. The second event is a large EUV wave. The EUV wave is initiated at 01:50UT. The wave is circular and covers a large part of the solar disk as is shown in the 3 pictures below. An EUV wave is an on disk signature for an associated CME.
    In the SWAP difference movie it becomes even more clear.
    By the way, a difference image is an image which you obtain by substracting two images. This method of substracting shows the differences. If nothing has changed in a pixel, that pixel stays gray.
  • The CME is seen by STEREO A and B with the COR2 coronograph. The CME is already in the field of view of the STEREO A/HI1 coronograph. A rough estimate of the speed of the plasma cloud based on the beacon data is 1000 km/s. This cloud is fast.
This is an image of the solar corona, taken by the SECCHI outer coronograph (COR2) on the STEREO behind observatory on February 15, 2011 at 03:24:57 UT. This image was produced from the STEREO space weather beacon telemetry. This is an image of the solar corona, taken by the SECCHI inner Heliospheric Imager (HI-1) on the STEREO Ahead observatory on February 15, 2011 at 07:18:01 UT. This image was produced from the STEREO space weather beacon telemetry.
  • Today, the coronograph images of LASCO onboard of SOHO were analysed. We see the cloud as a halo around the Sun. The Sun is presented as a white circle. The cloud is strong and heading Earth.
    Check the movie by clicking the image
  • The proton flux has slightly increased a few hours after the actual flare. The protons are heading the plasma cloud. The trailing plasma cloud pushes and accelerates the protons. Protons are charged energetic particles with relativistic speeds. They arrive at Earth after 20 min up to a few hours after they left the Sun. A proton storm can damage satellites and the instruments onboard. Protons can 'fall' on Earth near the poles. Airplanes on polar flights, its crew and its passengers are vunerable. The proton increase was not dramatic and did not reach the storm threshold which is denoted by the dashed line in the figure which you can enlarge by clicking.
  • The previous X-flare occurred on 2006/12/14. This is slightly more then 4 years ago. It was an X1.5 flare. We can definitely say that we passed solar minimum.


Some facts about flares
  • A flare is a brutal release of solar energy in the form of radiation. A flare is localised on the solar disk and limited in time. It takes the light 8 minutes to arrive at Earth.
  • During a flare, the X-ray, UV and EUV radiation flux increases dramatic. A flare is seen as a flash in solar EUV-movies. Flares are difficult to see in visible light, the increase in the visible wavelengths is usually limited.
  • Flares are put in a category according to their intensity in X-ray radiation, ranking from small to extremely large and energetic: A, B, C, M, X, Y. This scale is logarithmic. This means that the increase from M to X is much larger compared to an increase from A to B.


Some facts about CME's - plasma clouds
  • A CME is a Coronal Mass Ejection. It is solar plasma that is ejected. The Sun looses energy in the form of moving mass, i.e. kinetic energy.
    A plasma cloud comes on top of the background solar wind. Compare it with a shock wave/tsunami running over a river or sea. It has speeds between 100 km/s up to 2000 km/s. A slow CME is often overtaken by the background solar wind. While a fast CME forms a shock travelling through the background solar wind.
  • The solar wind is a continuous stream of plasma leaving the Sun. This wind blows in all directions. Part of the wind blows over the Earth magnetic shield. The slow solar wind blows at speeds of 200-400 km/s. A fast solar wind blows at speeds up to 700-800 km/s. If the solar wind has a speed of 500 km/s, it takes the plasma blowing in the direction of Earth around 3 days and 11 hours to bridge the distance between the Sun and the Earth.
  • The solar wind is magnetized, plasma clouds also. When blowing over the Earth, this magnetized plasma can couple with the magnetic field of the Earth. In this way, energy is transported into the Earth outer system. This physical process causes magnetic storms. Magnetic storms disturb radio communication, disturb the signal to satellites and by this disturb navigation systems like GPS. Magnetic storms induce electric currents in electrical power plants and lines, in pipes. A nice visual side effect is aurora.


The Space Weather Prediction Centre of Belgium
The Royal Observatory of Belgium, ROB incoorporates the Regional Warning Center, RWC of Western-Europe. The RWC is a space weather prediction centre. A forecaster reports on a daily basis about the activity of the Sun, the conditions in space and the status of the Earth environment. This bulletin included also a forecast of the space weather. The forecaster alerts the community in case of extreme space weather. This alert is called 'PRESTO'. The RWC Belgium has also an automatic alerting system. It was for example triggered tonight (20110215) by the occurrence of an extreme flare.
In case of extreme space weather, like now, the complete forecast team assists the forecaster on duty. They have regular space weather briefings.

Which actions does the RWC have to undertake?
As a Space Weather Forecast Centre we will go through the data available to determine the speed of the plasma cloud and the magnetic configuration. According to the estimated speed, we can determine the arrival at Earth. By determining the magnetic configuration, we try to foresee the strength of the clash and the response of the Earth magnetic field on the impacting plasma cloud. With satellites in front of the Earth, we can check if the plasma has passed or not.
This information is important for companies involved in the satellite business. Many are!

Consequences mentioned in the press:
Solar Flare Suspends Parts of Radio Communications in Korea

Check also our involvement in the space mission STEREO



The RWC Belgium makes part of the Solar-Terrestrial Centre of Excellence. This institute involves all the science and applications from Sun, through space, to Earth present at the Belgian Institute for Space Aeronomy, the Royal Observatory of Belgium and the Royal Meteorological Institute.