Semianalytical estimation of energy deposition in the ionosphere by monochromatic Alfvén waves

For the first time we derive an analytical expression for energy deposition by propagating monochromatic Alfven waves in the collisional ionosphere-thermosphere (IT). Based on empirical models of IT parameters, we show an approximately 10% increase in efficiency of energy deposition at high latitudes and about 150 km altitude by Alfven waves at 5Hz as compared to static fields of the same magnitude. We analyze the dependence of the wave energy deposition on geomagnetic activity through a Global Ionosphere-Thermosphere Model (GITM) simulation of IT conditions during the 13-14 October 2016 geomagnetic storm. The peak Alfven wave contribution occurs in the E layer and lower part of the F layer. Wave-induced heating is shown to increase in the daytime and postdusk high-latitude F layer during the storm due to increased wave-modified conductivity. We estimate that the Alfven wave contribution to the IT energy budget can reach about 30% of the value of static Joule heating during a strong storm and that the actual percentage increase is dependent on latitude and altitude. This effect carries important implications for ionospheric dynamics, especially for density enhancement in the daytime cusp, heating in the vicinity of auroral arcs and ion outflow.