Modelling the response of the thermosphere and ionosphere to geomagnetic storms: Effects of a mid-latitude heat source

The UCL-Sheffield coupled thermosphere/ionosphere model has been used to assess the consequences of a heat source from ring current ion precipitation during a geomagnetic storm. Such a source might in principle cause the thermospheric upwelling needed to produce significant changes in the neutral molecular/atomic ratio, and thus in F2 layer electron density, it having been shown that auroral sources probably cannot produce such changes at mid-latitudes. Some alternative explanations of the F2 layer depletions are considered and largely discounted. The computations show that an O+ source of around 4 mW/m2, as has been detected by satellites, could appreciably change the molecular/atomic ratio, notably in the early morning sector. The response qualitatively agrees with a number of satellite observations of composition and airglow, and with observations of NmF2. If increased in duration and intensity, the source may be able to account for the negative storm phenomena.