Simultaneous Mesoscale Polar Cusp Field‐Aligned Currents Measured on Mid‐ and Low‐Altitude Satellites

Abstract

Using a conjunction of Cluster in the mid‐altitude dayside magnetosphere and Swarm in the low‐altitude ionosphere, we show, by employing multi‐spacecraft analysis, that matched, strong magnetic perturbations and the corresponding mesoscale field‐aligned current (FAC) structures are measured in the high latitude polar cusp region during the 7 October 2015 storm. Two pairs of opposite (positive/negative) FACs are observed by both Cluster and Swarm, which may relate to pulsed magnetic reconnection at the dayside magnetopause. Furthermore, the current intensity of these matched FACs decreases from high to low latitude, consistent with the time elapsed since reconnection. Corresponding geomagnetic disturbances are also observed by ground stations. Our observations provide direct evidence for the coupling of mesoscale FACs between the magnetosphere, ionosphere and ground in the polar cusp region, where the signatures are driven in this case by conditions suitable for inducing reconnection.

Global‐MHD Simulations Using MagPIE: Impact of Flux Transfer Events on the Ionosphere

“… The black dotted line in panel (a) corresponds to an observation by Dong et al. (2023). The black circles on the dotted curve represent the points where the data has been resampled at.…”

“…Figure 9a uses a part of the SWARM data first published in Dong et al. (2023). The SWARM data is publicly available at https://swarm-diss.eo.esa.int/ and the FAC data from two spacecrafts, Swarm A and C, named SW_OPER_FAC_TMS_2F has been used.…”

“…This FAC pair has a typical structure with a negative peak followed by a positive peak in the FAC magnitude. The black dotted curve in panel (a) of Figure 9 represents the FAC pair highlighted in panel (g) of Figure 2 in Dong et al (2023). In order to draw comparisons with the simulated signatures, we first resample the observed data at intervals of 10 s. The black circles on the dotted curve in panel (a) of Figure 9 represents the location where the resampled data points are located.…”

“…As evident by the location of the black dots in panel (a) of Figure 9, resampling at a 10 s cadence ensures that one of the data points lie on the positive peak and one at the negative peak of the observed data with at least one data point in between these two peaks. Now, as mentioned in Dong et al (2023), the plotted FAC pair is obtained after the subtraction of the CHAOS-6 magnetic model, that is, J ‖t = J ‖t(SWARM) − J ‖t(CHAOS6) . One can therefore easily derive that J ‖t − J ‖t−10s = J ‖t(SWARM) − J ‖t−10s(SWARM) .…”

“…Dong et al. (2023) report the speed of the FAC pair to be 0.8 km/s. Considering the height of SWARM to be 450 km during that time, the angular speed is calculated to be 1.1 × 10 −4 radians/second.…”