Plasma Bubble Observations over Alcantara, Brazil During the Guara Campaign, Using a High Frequency Capacitance Probe

A Black Brant X rocket launched during the Guara campaign conducted from Alcantara, Brazil, carried a High Frequency Capacitance Probe (HFC) in addition to various other plasma diagnostic experiments. The main objective of the experiments was to study the equatorial ionosphere during the presence of high altitude plasma bubbles. On 14-th October, 1994 when the rocket was launched at 1955hrs (LT) a network of ground instruments operated during the campaign clearly indicated the presence of plasma bubbles extending to altitudes over 900km. The HFC experiment performed well throughout the flight giving useful data in the height range of about 167km upto the rocket apogee of 956.6km during the upleg and from the apogee down to the E-region altitudes during the downleg. Large amplitude plasma irregularities were observed in the height regions of 310km to 610km during the upleg and 575km to 315km during the downleg. Small amplitude plasma irregularities were observed in the height regions of 600km to 820km during the upleg and 725km to 575km during the downleg. A comparison of these results with the plasma density profiles obtained by a Plasma Frequency probe on board clearly showed that the regions of plasma bubbles are associated with medium scale plasma density irregularities.