Predicting the location of polar cusp in the Lyon-Fedder-Mobarry global magnetosphere simulation

Abstract

In this paper we compare observations of the high-latitude cusp from DMSP data to simulations conducted using the Lyon-Fedder-Mobarry (LFM) global magnetosphere simulation. The LFM simulation is run for the 31 August 2005 to 02 September 2005 moderate storm, from which the solar wind data exhibits a wide range of conditions that enable a statistical representation of the cusp to be obtained. The location of the cusp is identified using traditional magnetic depression and plasma density enhancement at high altitude. A new diagnostic using the parallel ion number flux is also tested for cusp identification. The correlation of the cusp latitude and various solar wind interplanetary magnetic field (IMF) coupling functions is explored using the three different cusp identification methods. The analysis shows (1) the three methods give approximately the same location and size of the simulated cusp at high altitude and (2) the variations of the simulated cusp are remarkably consistent with the observed statistical variations of the low-altitude cusp. In agreement with observations, a higher correlation is obtained using other solar wind coupling functions such as the Kan-Lee electric field. The magnetic local time (MLT) position of the simulated cusp is found to depend upon the IMF B y component, with a lower linear correlation. The width of the simulated cusp in both latitude and MLT is also examined. The size of the cusp is found to increase with the solar wind dynamic pressure with saturation seen when the dynamic pressure is greater than 3 nPa. Key Points Parallel ion number flux is used in the simulation for cusp identification The simulated cusp variations are consistent with observations The size of the cusp saturates when solar wind pressure > 3 nPa ©2013. American Geophysical Union. All Rights Reserved.