Kelvin-Helmholtz Instability associated with reconnection and Ultra Low Frequency Waves at the ground

The Kelvin-Helmholtz instability (KHI) and its effects related to the transfer of energy and mass from the solar wind into the magnetic environment of the Earth remain an important focus of magnetospheric physics. One such effect is the generation of Pc4-Pc5 ultra low frequency (ULF) waves at the ground. On July 3, 2007 at ∼0500 magnetic local time the Cluster space mission encountered Pc4 frequency Kelvin-Helmholtz waves (KHWs). Typically, KHI is thought to occur during the northward polarity of the interplanetary magnetic field and at low latitudes, however, the event occurred during a period of the southward polarity  according to the OMNI data and THEMIS observations at the subsolar point and at the high latitude magnetopause. Several of the KHI vortices were associated with magnetic field reconnection. Global magnetohydrodynamic simulation of the event confirmed the generation of KHWs at the magnetopause. The observed KHWs associated with reconnection coincided with recorded ULF waves at the ground whose properties suggest that they were driven by those waves.