Solar cycle dependence of solar wind energy coupling to the thermosphere

Abstract

Solutions to the differential equations describing the behavior of driven-dissipative systems are compared with measured exospheric temperatures (T∞) and provisional Dst indices acquired during 38 magnetic storms between mid-2002 and 2008. The only storm selection criterion was the availability of solar wind and interplanetary magnetic field data to compute driving electric fields εVS. Globally averaged T ∞ was inferred from measurements by accelerometers on the GRACE satellites. Statistical regression analyses indicate that the coupling coefficients for T∞, Dst, and their ratio are well represented as functions of 81 day averaged F10.7a. Using Dst as the driver, this functional relationship yielded reasonable estimates of the evolution of T ∞ during the Halloween 2003 magnetic storm. Linear relations between T∞ and the total energy of the thermosphere (E th) and between Dst and the energy of the ring current (E RC) allow estimates of the storm time energy partitioning. Empirical estimates of the energy coupling coefficients for the thermosphere (αE) and ring current (αERC) span the ranges 1.5-0.2 and 0.5-0.2 TW/mV/m, respectively. Outside of extreme solar minimum conditions, main phase increases in Eth exceed those of E RC.. Copyright © 2011 by the American Geophysical Union.