Dayside Cusp Aurorae and Ionospheric Convection Under Radial Interplanetary Magnetic Fields

Abstract

The solar wind carries solar magnetic fields into the interplanetary space and forms the interplanetary magnetic field (IMF). In near-earth space, the IMF orientation is typically in the form of an Archimedean spiral. However, in the region where the solar wind velocity decreases gradually or follows an interplanetary coronal mass ejection, a satellite there can observe the direction of an IMF in alignment with (parallel or antiparallel to) the solar wind velocity, forming what is best known as the radial IMF. In the present study, we chose a radial IMF event with the duration >1.5 h from the criteria |B x |/B ≥ 0.9 (Pi et al., 2014), where B x is the component of the IMF in the direction of the Sun-Earth line and B is the total magnitude of the IMF.

Radial Interplanetary Magnetic Field‐Induced North‐South Asymmetry in the Solar Wind‐Magnetosphere‐Ionosphere Coupling: A Case Study

“…On the other hand, the northward-draped IMF lines in the magnetosheath cause magnetic reconnection on the nightside (tailward of the cusp) magnetopause in the Northern Hemisphere, which is called IMF B x -induced single lobe reconnection. We speculate that the sunward and anti-sunward components in the ionospheric plasma flows observed in the poleward and equatorward regions, respectively, from the main auroral oval near noon MLT in the Northern Hemisphere (Figure 6b) result from the high-latitude lobe and low-latitude dayside magnetopause reconnections under radial IMF conditions (Li et al, 2021). Moreover, ionospheric plasma flows that do not pass through the dayside auroral oval (Figures 6a and 6b) can be regarded as the ionospheric signature of single lobe reconnection (Imber et al, 2006), under the assumption that the open-closed boundary is located within the main auroral oval.…”

“…In addition, Figure 6b shows that plasma flows poleward (equatorward) of the main auroral oval near noon MLT have a sunward (anti‐sunward) component. These flow patterns imply the simultaneous signatures of the dayside magnetopause and lobe reconnections (Li et al., 2021). After the substorm onset time, however, the anti‐sunward plasma flows appear and traverse the dayside auroral oval as shown in Figure 6c.…”

“…Recently, Li et al. (2021) reported simultaneous observations of sunward and anti‐sunward convection near the footpoint of the northern cusp during an interval of almost purely earthward IMF. These observations support the picture of the dayside magnetopause and lobe reconnections under radial IMF conditions (Pi et al., 2017; Tang et al., 2013).…”

“…However, it has recently been shown that an auroral arc structure due to electron-only precipitation can occur in the polar cap under radial IMF dominant conditions as a result of accelerated polar rains driven by lobe reconnection with northward draped IMF lines (Park et al, 2021). Recently, Li et al (2021) reported simultaneous observations of sunward and anti-sunward convection near the footpoint of the northern cusp during an interval of almost purely earthward IMF. These observations support the picture of the dayside magnetopause and lobe reconnections under radial IMF conditions (Pi et al, 2017;Tang et al, 2013).…”

HMB Variations Measured by SuperDARN During the Extremely Radial IMFs: Is the Coupling Function Applicable in Radial IMF?

“…And small fluctuations of the IMF By and Bz in radial IMF cases may cause an unreasonable big change of the clock angle (see Figure 2 in Li et al. (2021)), then resulting in an incredible variation of ionospheric convection. So, we do not use the measurements of cross‐polar cap potential in this work.…”