[1] Magnetically active times, e.g., Kp > 5, are notoriously difficult to predict, precisely the times when such predictions are crucial to the space weather users. Taking advantage of the routinely available solar wind measurements at Langrangian point (L1) and nowcast Kps, Kp forecast models based on neural networks were developed with the focus on improving the forecast for active times. To satisfy different needs and operational constraints, three models were developed: (1) a model that inputs nowcast Kp and solar wind parameters and predicts Kp 1 hour ahead; (2) a model with the same input as model 1 and predicts Kp 4 hour ahead; and (3) a model that inputs only solar wind parameters and predicts Kp 1 hour ahead (the exact prediction lead time depends on the solar wind speed and the location of the solar wind monitor). Extensive evaluations of these models and other major operational Kp forecast models show that while the new models can predict Kps more accurately for all activities, the most dramatic improvements occur for moderate and active times. Information dynamics analysis of Kp suggests that geospace is more dominated by internal dynamics near solar minimum than near solar maximum, when it is more directly driven by external inputs, namely solar wind and interplanetary magnetic field (IMF).

Observations of solar wind proton temperatures indicate that the solar wind is heated as it moves outward toward the orbit of Earth. This heating, which may be the result of electron heat conduction and perhaps MHD waves, has proven difficult to quantify and hence is often neglected in MHD models of the solar wind. An alternate approach to finding explicit heating terms for the MHD energy equation is to use a polytropic approximation. This paper discusses the properties of the polytropic approximation and its application to the solar wind plasma. By using data from the Helios 1 spacecraft, an empirical value for the polytropic index of the free-streaming solar wind is determined. Various corrections to the data are made to account for velocity gradients, nonuniformity in radial sampling, and stream interaction regions. The polytropic index, as derived from proton data, is found to be independent of speed state, within statistical error, and has an average value of 1.46. If magnetic pressure is included, the polytropic index has an average value of 1.58.

Data from Helios 1 are examined to find an experimental fit for the T(V) relationship at 1 AU. The data show a distinct change in the proton temperature‐velocity slope at V ∼ 500 km s−1. For V > 500 km s−1, T = (0.77±0.021)V ‐ (265±12.5), while for V < 500 km s−1, T1/2 = (0.031 ± 0.002)V ‐ (4.39±0.08) or T1/3 = (0.0106±0.001)V ‐ (0.278±0.03). These results are compared to the results of Burlaga and Ogilvie (1973) and show excellent agreement in the V < 500 km s−1 range. In addition, the secular variation of T(V) is examined, and it is found that the above functional forms still provide a good fit for a 2‐year interval approaching solar minimum and a 2‐year interval approaching solar maximum.

Between the hours of 6–10 UT on May 24, 2000, the IMAGE extreme ultraviolet (EUV) instrument observed a shoulder‐shaped bulge in the morning sector plasmapause [Burch et al., 2001a, 2001b]. Simulation results of the data‐driven Magnetospheric Specification Model (MSM) have reproduced the formation (during 4:00–5:15 UT) and subsequent evolution of the shoulder. In the model, the shoulder is created by a dusk‐to‐dawn overshielding electric field, triggered by two sudden, strong northward (Nwd) turnings of the IMF. Overshielding causes antisunward flow of pre‐dawn plasma, producing an asymmetric bulge that rotates eastward.

We have constructed a mathematical model of the magnetosphere in which a large‐scale uniform electric field, representing plasma flow from the tail, is superimposed on the geomagnetic field. In addition, the model includes a corotation electric field and an electric field resulting from the conductivity of the plasmasphere. Drift paths of charged particles with various energies are traced out in the equatorial plane, assuming that these particles may enter the magnetosphere through the tail. It is found that an electric field of 0.3 mv/m (across the tail) forms a forbidden zone for thermal particles that is approximately the size and shape of the plasmasphere. The electric field model is also found to provide a qualitative explanation for such varied phenomena as asymmetric ring currents, field‐aligned currents in the magnetosphere, and the existence of an abrupt inner termination to the plasma sheet. The presence of return flow of plasma near the magnetopause resulting from a viscous interaction with magnetosheath plasma is discussed, and it is argued that the return flow does not affect the electric field picture except very near the boundary.