The mid-latitude field-aligned disturbances and their effect on differential GPS and VLBI

For the first time we propose a method for detecting the mid-latitude field-aligned disturbances (FADs) prolated on the magnetic field. The method is based on GPS detection of isolated ionosphere disturbances and analysis of the angle between the “GPS satellite-receiver” line-of-sight and the local magnetic field vector, for which maximum (minimum) of aperiodic variation of the total electron content (TEC) is registered.The method possibilities are shown by example of recording abnormal mid-latitude isolated disturbances over California during the 5 October 2001 magnetic storm recovery phase. If the plasma FADs with a positive deviation relative to the background TEC were caused by the extension of a plasma blobs at the magnetic equator, then this would imply that the plasma blobs reached an altitude of 5890 km in the apex of magnetic field line. When crossing FADs, the TEC gradients may reach quite great values (up to 10 TECU/1000 km). Such gradients determine large short-term range errors in single-frequency (differential) GPS systems and refraction errors in radioastronomical interferometers when the line-of-sight passes next to the magnetic zenith.