Manifestation of field-angled ionosphere plasma disturbances at mid-latitude

  1. Institute of Solar-Terrestrial Physics SB RAS

Using technique of magnetic zenith scanning by GPS rays it was shown that registered 5th October 2001
(during recovery phase of 3 October 2001 magnetic storm) unusual northward ionosphere irregularities above
California are manifestation of field-angled plasma disturbances (FAD). FAD are characterized by positive de-
viation of total electron content (TEC) value up to 4 TECU (1016 el/m2 ) what is 10-20 % against background
TEC. Corresponding TEC variations are isolated impulses with duration of 20 min. FAD corresponds flat
“feathers” with longitudinal size equal to 800 km and cross size more than 100 km in the horizontal plane.
Field-angled plasma disturbances was registered at 40 − 50◦ geomagnetic latitudes what corresponds to apex
altitude of about 5000 km. This features allow us to colligate FAD with ionosphere bubbles, generated in the
equatorial ionosphere. But bubbles are usually characterized by depletion of TEC. We estimate influence of
such irregularities on differential GPS because FAD gradients determine substantial short-term range errors
in single-frequency differential GPS systems when the visual line passes next to the magnetic zenith. Similar
problems may arise when up-to-date very long base interferometers operate, for example, LOFAR or SKA.