A Mid-Latitude Space Weather Hazard Driven Directly by the Magnetosphere
Journal of Atmospheric and Solar-Terrestrial Physics
This study revisits and attempts to quantify the effects of high-latitude electric field penetration on the mid-latitude ionosphere. These penetration electric fields (PEFs) are strongest during geomagnetically dynamic and disturbed conditions. The consequences of PEFs arise principally from the induced vertical drift of the F-layer from the eastward electric field component. Both positive and negative storm phases are associated with the PEF. Although no readily available description of the PEF exists, observational and modeling results are combined to provide a crude model. The largest uncertainty arises from a lack of knowledge of whether PEFs are always short lived (less than 1 h) or are a persisting feature of disturbed conditions. According to simulations with the Utah State University time dependent ionospheric model (TDIM), under Kp=3 conditions the PEF readily generates a factor of 2 increase in the pre-midnight ionosphere F-layer density (positive storm phase). For Kp=5 conditions this positive phase is further enhanced to produce almost an order of magnitude increase in F-region density. Negative storm phases, F-layer density decreases, are also present in the pre-dawn and pre-noon sectors. The pre-dawn negative storm phase can reach a factor of 10 for Kp=5 conditions while the pre-noon depletions are a few 10s of percent. These large density changes have operational impact on systems using coordinate registration based upon Global Positioning Satellite (GPS) measurements. GPS satellite-to-ground radio paths pass through the ionosphere at different angles relative to the zenith and hence have different propagation corrections dependent upon the paths total ionospheric electron content. Factors of 2 change in electron density corresponds to tens of centimeters to meters correction errors in coordinate registration position finding. Corrections this large are a potentially insurmountable obstacle for the GPS based wide area augmentation system (WAAS) designed to provide the airline industry over the USA position accuracy of only a few centimeters. Examples of mid-latitude ray tracing at 5 and 9 MHz are used to demonstrate the frequency sensitivity and coordinate registration dependence upon these factors of 2 ionospheric density changes. Operational systems such as the over-the-horizon (OTH) radar is very sensitive to such dependences and hence upon the mid-latitude PEF.
Sojka, J. J., M. David, and R. W. Schunk, A mid-latitude space weather hazard driven directly by the magnetosphere, J. Atmos. Solar-Terr. Phys., 64, 687-695, 2002.