Mid-latitude ionospheric irregularities persisting into late morning during the magnetic storm on 19 March 2001

Post-sunrise intense ionospheric irregularities at low to mid-latitudes are reported for the first time. A method based on spaced-receiver technique is proposed to estimate the apparent drift velocity of the irregularities by using the correlation of the slant total electron content (TEC) from 3 GPS receivers. The irregularities were detected at 23 similar to 45 degrees N by the GPS Earth Observation Network (GEONET) of Japan from similar to 0455 LT to similar to 1051 LT on 21 March 2001 during the recovery phase of the magnetic storm. At the corresponding time spread F was observed with 3 ionosondes located meridionally at Okinawa (127.8 degrees E, 26.3 degrees N; 20.7 degrees N magnetic latitude), Kokubunji (139.5 degrees E, 35.7 degrees N; 30.0 degrees N magnetic latitude) and Wakkanai (141.7 degrees E, 45.4 degrees N; 40.5 degrees N magnetic latitude), while an intense negative ionospheric storm was processing and propagating from mid to lower latitudes. The irregularities were seen as plasma bubbles by the Defense Meteorological Satellite Program (DMSP) in-situ measurements. Westward drift with the speed of similar to 100 m/s was estimated by spaced receivers from GEONET and confirmed by DMSP during the evolution of the irregularities. The plasma bubbles at mid-latitude sustained similar to 1.5 hour after sunrise, and at the lower latitudes they survived more than 4 hours after sunrise. The observations suggested that the irregularities were generated by an eastward electric field associated with the disturbance dynamo, and the long time existence of the irregularities after sunrise seemed to be related to the daytime intense negative ionospheric storm on 21 March.