CMIT study of CR2060 and 2068 comparing L1 and MAS solar wind drivers

Abstract

While it is widely known that coronal mass ejections and their related solar wind features are significant drivers of activity with geospace it is less known that corotating interaction regions (CIRs) and the high speed stream (HSS) periods that precede them are also drivers of activity within geospace. The most recent extended and weak solar minimum interval has brought renewed attention to the space weather impacts of CIR+HSS periods since the highly structured and relatively stable coronal hole features on the Sun resulted in numerous CIR+HSS periods. In this paper we examine two Carrington Rotations (CRs) using the Coupled Magnetosphere Ionosphere Thermosphere (CMIT) model. CR2060 lasted from August 14, 2007 to September 11, 2007 and contained three CIR+HSS periods. CR2068, also known as the Whole Heliosphere Interval (WHI), began on March 20, 2008 and lasted until April 16, 2008 and contained two CIR+HSS periods. For each CR simulations driven by both L1 solar wind observations from the OMNI data set and L1 conditions extracted from CORHEL heliospheric simulations were conducted. The heliospheric simulation results capture the velocity and density structures seen in the solar wind well for CR2060 and only get one of the CIR+HSS periods in CR2068. In each CR the heliospheric simulations produce a much weaker IMF and have less temporal variability in all parameters. We compare the results of the CMIT simulations for each CR to observations of the cross polar cap potential (CPCP), hemispheric power (HP), and SYMH index including the computation of RMS and cross correlation error metrics. We examine the response of the thermospheric density during these intervals by utilizing data from the CHAMP satellite. In the magnetosphere we use magnetic field data from the GOES spacecraft to asses the different simulations ability to describe the distribution and intensity the ULF wave power. Our results show that the L1 driven simulations under-estimates the SYMH index and HP and over-estimates the CPCP. We believe that over estimation of the CPCP is directly linked to the low HP highlighting the need for an improved precipitation model within CMIT. The ULF power in the L1 simulations compares well with the observations, especially for the compressional component important in radiation belt energization processes. In all cases, the CMIT simulations driven by the heliospheric simulation results produce dramatically inferior predictions highlighting the importance of having good IMF predictions in heliospheric model results and possibly indicating the importance of having fluctuations in the solar wind.