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The July 23, 2012 CME was an extremely fast backside event, reaching ∼1 AU (STEREO-A) within 20 h as compared to ∼3–6 days for typical CME events. Here, we present results from a simulation study of the CME and its driven shock using a combined kinematic and magnetohydrodynamic (MHD) simulation model, H3DMHD. In general, the model results match well with in situ measurements in the arrival time of the CME-driven shock and the total magnetic field strength, assuming an initial CME speed of 3100 km/s. Based on extrapolation of an empirical model, the fast CME and its large magnetic field (| B |∼120 nT) are capable of producing an extremely large geomagnetic storm ( Dst ∼−545 nT), comparable to the well-known Halloween storm in 2003, if the CME had made a direct impact to the Earth. We investigated the effect of the adiabatic index ( γ ). It is found that the shock tends to arrive slightly later for a smaller γ value, and γ =5/3 provides the best agreement for the shock arrival time. We also demonstrate that the strength (the Mach number) of the CME-driven fast-mode shock is not the largest at the “nose” of the CME. This is mainly due to the manifestation of fast-mode wave speed upstream of the shock.

We use a one-dimensional, time-dependent adaptive grid MHD code to study the evolution of shocks (both slow and fast shocks) from the surface of the Sun through the heliosphere. In order to achieve the goal, we track a specific solar event's plasma and magnetic field output as it propagates into interplanetary space with a possible geoeffective consequence. We have chosen the famous event of the October/November (“Halloween 2003”) epoch which produced two of the largest geomagnetic storms during solar cycle 23, followed by the arrivals of the shocks at Earth. These two geomagnetic storms are associated with two of these flares (X17/4B and X10/2B). Accordingly, four separate pressure pulses, at the appropriate times and with different strengths and duration, determined via a trial and error procedure, are introduced on the Sun to mimic the four flares. The results show that the simulated solar wind velocity temporal profiles successfully matched the observations at L1. The propagation speed of shock waves near the Sun also matched with the CME observations of SOHO/LASCO. The major objective, to demonstrate the detailed nature of interacting shocks and some of their products after origination from closely spaced solar events, is achieved. The evolution of both slow and fast shocks is also discussed in detail.

A user-friendly, real-time, observation-driven system for forecasting solar wind and interplanetary magnetic field conditions is described. The forecast system presently uses the Hakamada–Akasofu–Fry (version 2) kinematic solar wind model to predict, in real-time, solar wind conditions in the heliosphere, including at the location of Mars, and beyond. Properly characterizing and predicting this region of the space environment are essential steps towards improving the accuracy of “downstream” space weather models used to forecast the space radiation environment and geomagnetic activity. Representative modeling results are presented and the conclusion is made that uncertainty in determining the physical parameters needed for model inputs from real-time solar observations is the biggest factor limiting the accuracy of solar wind models used for space weather analysis and prediction. Future directions include extending the forecast system via a hybrid approach to include 3D MHD modeling.

The ionospheric total electron content (TEC) in the equatorial anomaly region is studied by analyzing dual-frequency signals from the global position system (GPS) acquired from a meridional chain of 9 observational sites clustered around Taiwan (21.9°–26.2°N, 118.4°–121.6°). This relatively dense GPS chain provides a powerful tool for studying ionospheric TEC in the northern hemispheric equatorial anomaly region with an unprecedented spatial resolution. Specifically, we studied seasonal and geomagnetic effects on the equatorial ionospheric anomaly during the solar minimum period between September 1996 and August 1997. We found that the surveyed data indicated semiannual variations in the magnitude of TEC, Ic, at the anomaly, with maxima in the equinoxes, similar to the semiannual variation of geomagnetic activity. The values of Ic were found to maximize in April, 1997 and minimize in July, 1997. Statistical studies indicate that the monthly values of Ic do not correlate with the planetary Kp magnetic index (r=0.41) but correlate well with the Dst geomagnetic activity index (r=0.72). This suggests that variations of TEC are mainly driven by a low-latitude forcing for the surveyed period. The most likely time for Ic to occur was 1400 local time (∼30%) at 20°N geographic latitude (∼37%).