Dynamic effects of aurora-generated gravity waves on the mid-latitude ionosphere

Abstract

This paper gives a brief review of aurora-generated large-scale traveling ionospheric disturbances, and presents results of numerical simulations of one such event. Numerous observations and several theoretical studies have shown that large-scale gravity waves are generated in the high-latitude thermosphere during geomagnetic disturbances. Traveling to middle and low latitudes within the thermosphere, these waves interact with the ionosphere to produce large-scale traveling ionospheric disturbances. Relatively large amplitude waves generated by the Joule heating due to high-latitude ionospheric electric currents can propagate many thousands of kilometers at speeds of 300–1000 m/s, with periods of 30 min to several hours and horizontal wavelengths of thousands of kilometers. They affect the ionosphere not only by imparting vertical motion to the ionization, but also by altering the chemical reaction rates and heat transfer rates. Numerical simulations of the event of 18 September 1974 show that a Joule heat source of 2–4 × 10 15 J can generate gravity waves capable of reproducing the observed ionospheric disturbances at the Millstone Hill and Arecibo incoherent scatter observatories.