High-latitude electromagnetic and particle energy flux during an event with sustained strongly northward IMF

Abstract

Abstract. We present a case study of a prolonged interval of strongly northward orientation of the interplanetary magnetic field on 16 July 2000, 16:00-19:00 UT to characterize the energy exchange between the magnetosphere and ionosphere for conditions associated with minimum solar windmagnetosphere coupling. With reconnection occurring tailward of the cusp under northward IMF conditions, the reconnection dynamo should be separated from the viscous dynamo, presumably driven by the Kelvin-Helmholtz (KH) instability. Thus, these conditions are also ideal for evaluating the contribution of a viscous interaction to the coupling process. We derive the two-dimensional distribution of the Poynting vector radial component in the northern sunlit polar ionosphere from magnetic field observations by the constellation of Iridium satellites together with drift meter and magnetometer observations from the Defense Meteorological Satellite Program (DMSP) F13 and F15 satellites. The electromagnetic energy flux is then compared with the particle energy flux obtained from auroral images taken by the far-ultraviolet (FUV) instrument on the Imager for Magnetopause to Aurora Global Exploration (IMAGE) spacecraft. The electromagnetic energy input to the ionosphere of 51 GW calculated from the Iridium/DMSP observations is eight times larger than the 6 GW due to particle precipitation all poleward of 78 • MLAT. This result indicates that the energy transport is significant, particularly as it is concentrated in a small region near the magnetic pole, even under conditions traditionally considered to be quiet and is dominated by the electromagnetic flux. We estimate the contributions of the high and mid-latitude dynamos to both the Birkeland currents and electric potentials finding that highlatitude reconnection accounts for 0.8 MA and 45 kV while we attribute <0.2 MA and ∼5 kV to an interaction at lower latitudes having the sense of a viscous interaction. Given that these conditions are ideal for the occurrence of the KH instability at the magnetopause and hence the viscous interaction, Correspondence to: H. Korth (haje.korth@jhuapl.edu) this result suggests that the viscous interaction is a small contributor to coupling solar wind energy to the magnetosphereionosphere system.

Magnetopause mapping to the ionosphere for northward IMF

“…(6) is 53.49 kV, in good agreement with Korth et al (2005). It is interesting to note that Korth et al (2005) found that the potential drop associated with viscous interaction is less than ∼5 kV, or about 9 times smaller than the potential drop caused by high-latitude reconnection. Figure 9 (right panel) shows the ionospheric electrostatic potential patterns in the southern polar cap calculated for case 1.…”

“…(7) gives 32 kV, a good agreement with the Siscoe et al (2001) MHD simulations results. We can check our result by comparing with the polar cap potential drop which was determined by Korth et al (2005). These authors presented a case study of a prolonged interval of strongly northward IMF on 16 July 2000.…”

“…Based on magnetic field observations by the constellation of Iridium satellites, together with the drift meter and magnetometer observations from DMSP F13 and F15 satellites, and on the FUV images taken by the IMAGE spacecraft, Korth et al (2005) estimated the electric potential drop as 45 kV. For the event interval (from 16:06 to 19:24 UT on 16 July 2000) the solar wind parameters were: B t =6.76 nT, n=0.8 cm −3 and V =740 km/s (Korth et al, 2005), the total potential drop in the northern polar cap calculated by Eq. (6) is 53.49 kV, in good agreement with Korth et al (2005).…”

“…For the event interval (from 16:06 to 19:24 UT on 16 July 2000) the solar wind parameters were: B t =6.76 nT, n=0.8 cm −3 and V =740 km/s (Korth et al, 2005), the total potential drop in the northern polar cap calculated by Eq. (6) is 53.49 kV, in good agreement with Korth et al (2005). It is interesting to note that Korth et al (2005) found that the potential drop associated with viscous interaction is less than ∼5 kV, or about 9 times smaller than the potential drop caused by high-latitude reconnection.…”

MESSENGER: Exploring Mercury’s Magnetosphere

“…Although this approach breaks down more than a few hours from dawn and dusk and under other circumstances (e.g., northward IMF) when fringing effects dominate the signatures, the magnetic signatures unambiguously indicate the presence of the currents even if one cannot confidently 'infer the current density distribution from the data (cf. Fung and Hoffman, 1992;Waters et al, 2001;Korth et al, 2005). In addition, particle data provide useful correlative observations of the current carriers, and the FIPS and EPS sensors which measure composition, velocity and density for both ions and electrons wjll, in principle, give a direct measurement of current.…”