Coherent HF radars.

One of the many ways of studying the ionosphere is through the use of radars. The coherent HF (high frequency) radar antennas shown in the picture are located in Iceland and were built by the University of Leicester. The radars we use reflect radio waves from periodic structures in the ionosphere (see diagram below). Coherent HF radars use radio frequencies around 10 MHz which will scatter from unevenness in the electron density, which we call field aligned irregularities (they are parallel to the magnetic field), in the ionosphere. The radars in the SuperDARN network, of which the CUTLASS radars run by RSPPG are the easternmost pair in the northern hemisphere, scan through 16 different beam directions giving a large field-of-view.

Various properties of the ionospheric plasma in the field-of-view of the radars can be determined from the received signal. These include the power of the received signal and the velocity in the line-of-sight direction of the radar beam. When combined with velocity data from other beams, or even better overlapping data from the other radars of the SuperDARN network, a picture of the global plasma convection can be built up. One way of looking at this data is by using the potential map model . This combines a model of the plasma flows and the data from the SuperDARN radars and you will be using it this afternoon in task 2.