Fast news - fast news
On April 23, 17:00 Universal Time, a magnetic cloud coming from the sun reached the earth. The STCE alert system started ringing the entire night and longer.
For our PECASUS services for civil aviation, scientists and operators in Belgium and Finland were continuously in contact to give a correct interpretation of the data which was coming in.
An estimate of arrival
The picture below is the output of a simulation by EUHFORIA of the cloud propagation in the heliosphere. Left is a 'top' view of the sun (white dot) and the earth (blue dot). The black structure is the front of the magnetic cloud (purple) that reaches the earth. On the right is a side view of space. At the bottom, you see that the curve goes through the roof at the arrival.
It did arrive!
The satellite DSCOVR in a point 1 hour upstream of the earth, which means that it takes the solar wind 1 hour to reach the Earth, 'saw' the cloud passing and measured a jump on April 23, 17UT as seen in the top panel of the graph below. The cloud induced a severe geomagnetic storm on the planetary level (purple rectangles in the 6th panel)) and a moderate geomagnetic storm locally in Belgium (dark red rectangles in the 7th panel).
Impact on High Frequency Radio Communication
High Frequency (HF) radio waves used for radio communication were being absorbed in the polar region because of solar protons and precipitating electrons bombarding the Earth's atmosphere. The precipitating electrons enter the atmosphere in the auroral oval which expanded during this storm up to 60° latitude in the Northern hemisphere and up to 40° latitude in the Southern Hemisphere.
On top of this, a post storm depression was measured on the entire globe as can be seen in the picture below where several parts of the globe colour red. During a post storm depression, less frequencies of radio waves can be used to set up long distance HF radio contact.
Impact on Global Navigation Satellite Systems, GNSS
Simultaneously, global navigation satellite systems were also impacted. The signals sent out by the satellites were not well received anymore.
Alerting civil aviation
The first advisory on HF COM was sent at 17:06UT. It was the first of many.
