Ionospheric and geomagnetic conditions during periods of degraded GPS position accuracy: 2. RTK events during disturbed and quiet geomagnetic conditions

The paper analyzes the ionospheric conditions associated with strong RTK events observed during the strong geomagnetic storm on 31 March 2001 and on 16 January 2000, a day with very low geomagnetic activity. The analysis is based on ionograms obtained from ground-based ionosondes stations at Chilton (UK), Juliusruh (Germany), and Dourbes (Belgium). The storm onset on 31 March 2001 occurs at 0058UT followed by decreasing the F layer ionization and sharp increase of its height. At sunrise, a layer, classified as F0.5, tears off the normal F layer and start descending as the time develops. It merges the normal E layer about 2 h later. The second RTK event on that day, with larger intensities, occurs in association of a series of substorms in the afternoon hours. Then ionograms clearly show the presence of side reflections, interpreted as large-scale traveling ionospheric disturbances (LSTIDs). In the quiet period 16–19 January 2000, strong RTK events are observed to appear in the morning hours and disappear in afternoon. The behavior of the bottomside ionosphere on 16 January 2000 is analyzed in details. The E layer traces first appear on ionograms at height of 150 km instead of 100 km, as it usually happens. This layer, classified as E2 layer, is accompanied in most of the cases examined with a “c” type Es layer, as they both descent to the height of the normal E layer within 2–3 h. The appearing of morning RTK events during winter months is suggested to reflect phenomena known in the literature as tidal ion layers and solar terminator associated processes.