A Daily Determination of B Z Using the Russell‐McPherron Effect to Forecast Geomagnetic Activity

Since the middle of the last decade, UCSD has incorporated magnetic field data in its Institute for Space-Earth Environmental Research interplanetary scintillation tomographic analysis. These data are extrapolated upward from the solar surface using the Current Sheet Source Surface model (Zhao & Hoeksema, 1995, https://doi.org/10.1029/94JA02266) to provide predictions of the interplanetary field in RTN coordinates. Over the years this technique has become ever more sophisticated, and allows different types of magnetogram data (SOLIS, Global Oscillation Network Group, etc.,) to be incorporated in the field extrapolations. At Earth, these fields can be displayed in a variety of ways, including Geocentric Solar Magnetospheric (GSM) B-x, B-y, and B-z coordinates. Displayed daily, the Current Sheet Source Surface model-derived GSM B-z shows a significant positive correlation with the low-resolution (few day variation) in situ measurements of the B-z field. The nano-Tesla variations of B-z maximize in spring and fall as Russell and McPherron (1973, https://doi.org/10.1029/JA078i001p00092) have shown. More significantly, we find that the daily variations are correlated with geomagnetic Kp and Dst index variations, and that a decrease from positive to negative B-z has a high correlation with minor-to-moderate geomagnetic storm activity, as defined by NOAA Space Weather Prediction Center planetary Kp values. Here we provide an 11-year study of the predicted B-z field, from the extrapolation of the Global Oscillation Network Group-magnetograms. We provide a skill-score analysis of the technique's geomagnetic storm prediction capability, which allows forecasts of moderate enhanced geomagnetic storm activity. UCSD and the Korean Space Weather Center currently operate a website that predicts this low-resolution GSM B-z field component variation several days in advance.