Energy transfer across magnetopause under dawn-dusk IMFs

A parametric study on the energy transfer of the solar wind across the magnetopause entering the magnetosphere is conducted using a global magnetohydrodynamic numerical simulation. The characteristics of the mechanical and electromagnetic energy distribution under the dawn-dusk interplanetary magnetic fields (IMFs) are investigated by analyzing magnetic reconnection and viscous effect, and compared with the radial and north-south IMFs. It is shown that (1) the interactions at the magnetopause and the transfer of energy across this boundary move in relation to the IMF orientation. (2) For the duskward IMF, the mechanical energy flow clearly enters the equatorial and low-latitude regions on the dayside, and the electromagnetic energy flow has a small inflow on the equatorial and low latitudes of the dayside. A significant energy inflow appears on the dawn side in the northern hemisphere and the dusk side in the southern hemisphere near the polar cusp. (3) The energy distribution characteristics across the magnetopause under dawn-dusk IMFs are mirror symmetric about the [Formula: see text] plane. (4) For a magnetic field of 5 nT, the electromagnetic energy input under the dawn-dusk IMFs is twice as large as the mechanical energy and the electromagnetic energy under the radial IMF, which is five times as large as the electromagnetic energy during the pure northward IMF, but only half as large as the electromagnetic energy under the pure southward IMF. The mechanical energy input under dawn-dusk IMFs has the same magnitude as that under radial and north-south IMFs. The magnitude of the energy transfer rate for the dawn IMF and dusk IMF (about 3.5%) is between 1.71% for the northward IMF and 4.95% for the southward IMF, but higher than 2.22% for the radial IMF. The Akasofu-type energy-coupling formula, [Formula: see text], underestimates the energy input from the solar wind under [Formula: see text] dominated IMF.

Dayside Transient Phenomena and Their Impact on the Magnetosphere and Ionosphere

Dayside transients, such as hot flow anomalies, foreshock bubbles, magnetosheath jets, flux transfer events, and surface waves, are frequently observed upstream from the bow shock, in the magnetosheath, and at the magnetopause. They play a significant role in the solar wind-magnetosphere-ionosphere coupling. Foreshock transient phenomena, associated with variations in the solar wind dynamic pressure, deform the magnetopause, and in turn generates field-aligned currents (FACs) connected to the auroral ionosphere. Solar wind dynamic pressure variations and transient phenomena at the dayside magnetopause drive magnetospheric ultra low frequency (ULF) waves, which can play an important role in the dynamics of Earth's radiation belts. These transient phenomena and their geoeffects have been investigated using coordinated in-situ spacecraft observations, spacecraft-borne imagers, ground-based observations, and numerical simulations. Cluster, THEMIS, Geotail, and MMS multi-mission observations allow us to track the motion and time evolution of transient phenomena at different spatial and temporal scales in detail, whereas ground-based experiments can observe the ionospheric projections of transient magnetopause phenomena such as waves on the magnetopause driven by hot flow anomalies or flux transfer events produced by bursty reconnection across their full longitudinal and latitudinal extent. Magnetohydrodynamics (MHD), hybrid, and particle-in-cell (PIC) simulations are powerful tools to simulate the dayside transient phenomena. This paper provides a comprehensive review of the present understanding of dayside transient phenomena at Earth and other planets, their geoeffects, and outstanding questions.

Solar wind entry into the high-latitude terrestrial magnetosphere during geomagnetically quiet times

An understanding of the transport of solar wind plasma into and throughout the terrestrial magnetosphere is crucial to space science and space weather. For non-active periods, there is little agreement on where and how plasma entry into the magnetosphere might occur. Moreover, behaviour in the high-latitude region behind the magnetospheric cusps, for example, the lobes, is poorly understood, partly because of lack of coverage by previous space missions. Here, using Cluster multi-spacecraft data, we report an unexpected discovery of regions of solar wind entry into the Earth's high-latitude magnetosphere tailward of the cusps. From statistical observational facts and simulation analysis we suggest that these regions are most likely produced by magnetic reconnection at the high-latitude magnetopause, although other processes, such as impulsive penetration, may not be ruled out entirely. We find that the degree of entry can be significant for solar wind transport into the magnetosphere during such quiet times.