Wednesday 27 March 2013

Active heating effect detected by the KAIRA riometer

Just a little update to our broad-band riometer studies (see previous posts on this topic here and here). 

We have manipulated the cosmic radio noise flux through the ionosphere! Buhahahaaa!

Ionospheric opacity for the radio waves depends on the electron temperature of the plasma, or more precisely, on the electron-neutral collision frequency. The electron temperature (and the collision frequency) can be increased artificially by using powerful radio-waves sent from the EISCAT Heating facility. Because the ionospheric opacity is altered, the effect should be visible, in principle, in the riometer data measuring the cosmic radio noise propagated through the heated region. This effect, however, is expected to be relatively small, especially if the riometer beam doesn't overlap the heated volume perfectly.

In our statistical study (Kero et al., 2007), we summed together all the IRIS riometer data during the heating experiments carried out between 1994-2004 in order to see this change, which turned out to be even smaller than expected theoretically. More recently, Senior et al., 2011 were able to measure the same effect within single experiments by using a high spatial resolution imaging riometer with more optimal geometry. Their effect was also found to be significantly smaller than expected by the theoretical model.

Obviously, we wanted to try this with our KAIRA riometer, and we did, please have a look:

In the figure above, the cosmic radio noise power ratio between heating on and off is plotted in dB as a function of frequency. This is done for two KAIRA beams, the red one pointing towards the heated volume and the blue pointing vertically. The effect is again very small (surprise!), but still clearly there, and not visible in the vertical reference beam. Good. This is the first broad-band riometer measurement of the active heating effect and hopefully it will provide the final answer on what the heck is wrong with our heating model!

Have a nice Easter!

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