The Big Solar Flare of April 2, 2001

Massive sunspot number 9393, shown in the image above as it rotates away from the Earth's view, had been winding up energy in it's complex magnetic field for many days when it finally let loose with a huge Class 20 X-ray  flare on April 2, of 2001. Many people had been watching this particular spot closely and a large flare was generally predicted to occur, but no one knew how big it might be.

Here on the Big Island in Hawaii I recorded the first portion of the flare at 144 MHz. During the event out power "glitched" out momentarily, killing the observatory computer. This is the first time such a power outage had occurred in the weeks the observatory had been in operation, so it leads me to wonder if the outage is in some way related to the flare itself.

The simple adding type interferometer in use shows quite nicely the galactic plane region as it passes overhead. The five element yagi antennas at end of each leg of the antenna were aimed about 11 degrees north of zenith to maximize their sensitivity to the powerful extra-galactic radio source, Cygnus A. The antennas were thus not pointed directly at the Sun, but close.  The recording was made on a P75 computer using Radio-SkyPipe software in Stand Alone Mode.

The chart above shows the last few minutes of the same observation. Note the size of the small humps (fringes) preceeding the flare event. The flare itself is preceeded by a short burst which is often seen just before a large event. I have seen this type of precursor event in VLF flare recordings also.  This flare was seen by Tom Ashcraft and the Windward Community College Radio Observatory on Oahu, Hawaii as a decametric radio absorption or fadeout event. This occurs due to the x-rays from the flare which quickly and heavily ionized the D layer of the ionosphere, making it absorb HF radio waves which would normally only be deflected by it.  The radio energy from the flare itself is thus sometimes not seen at frequencies below about 50 MHz, but the event can be detected at these frequency by the conspicuous absence of normally present signals from distant radio stations or from the cosmic background.

If have downloaded and installed Radio-SkyPipe, you can use it to analyze these charts in more detail

The full chart version of the chart in SkyPipe Format.

The last few minutes of the chart in SkyPipe Format.
Click here to see the X5 flare of April 6, 2001. 


updated 4/6/2001