Solar flare signature in the BDU riometer

There has been quite inspiring buzz in the media about the current "monster sunspot", and indeed, this giant AR2192 spot has sent multiple X-class solar flares towards us within the past few days. In addition to the widely reported HF-radio blackouts and GPS navigation disturbances, the energetic solar flares cause changes in the upper atmosphere/ionosphere due to increased photoionisation in the whole dayside hemisphere. SGO aims to quantify this ionisation by several ground-based measurement techniques, including riometers.

As mentioned in the earlier blog, we have just installed a new spectral riometer to Bahir Dar, Ethiopia and we were lucky to catch a few of these fresh solar flare events to the data, please have a look:

Received power (in arbitrary dB units) detected by the BDU spectral riometer (start, max and stop times of the solar flare event are marked as dashed lines).

One of the challenges in detecting the solar flare induced ionisation by riometry is that the Sun sends, not only the X-rays, but also bursts of radio emissions related to the flare events. As the riometer operates at the same radio frequencies, these emissions might mask totally the signature of the atmospheric response to the flare, i.e., reduction in the cosmic radio noise levels. 

In this case too, the increased levels of radio noise (red stuff) during the onset and offset phases of the flare are probably caused by the direct solar radio emissions. However, around the maximum time of the flare, there is a clear reduction in the radio noise, most likely caused by increased radio wave absorption in the ionosphere. We are particularly interested in the spectrum of this increased absorption (radio noise absorption at different frequencies) as it carries information on the ionisation profile in the atmosphere. 

This provides a very nice science case for collaboration between the SGO and BDU scientists and pretty awesome kick-off for this instrument, I'd say!

A few photos of the famous beauty & the beast:

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