Electron temperature variations in developing plasma bubbles – rocket observations from Brazil Original Research Article

In situ measurements of the height variation of the ionospheric electron density and electron temperature were made on 18th December, 1995 at 2117 h (LT) from the equatorial station Alcantara (2.31°S; 44.4°W) in Brazil, with a rocket-borne Langmuir probe. The main objective of the measurement was to study the height variation of the ionospheric electron density and electron temperature under ionospheric conditions favourable for the development of plasma bubbles. The rocket reached an apogee altitude of 557 km covering a horizontal range of 589 km. The upleg electron density profile showed the presence of a clearly defined base for the F-region around 300 km, while the downleg profile showed the presence of several plasma bubbles in this height region as well as in the upper F-region. Electron temperature was estimated by applying a sweep potential varying from −1.5 to +2.5 V in about 2.5 s, to the Langmuir probe. During the rocket upleg the base of the F-region showed abnormally large electron temperatures reaching more than 3000 K just below the F-peak at 300 km. The maximum electron temperature observed above the F-peak was only about 750 K close to the rocket apogee. During the downleg relatively larger temperatures were observed inside the plasma bubbles, especially at the top side of the bubbles. Bottom side of the bubbles were associated with relatively lower electron temperatures. The region below the base of the F-region seems to be associated with very large electron temperatures just before the development of plasma bubbles. Once the bubbles develop and start rising up the electron temperature falls down except inside the plasma bubbles. Rising bubbles seem to have larger electron temperatures inside especially on their top sides. Bubble regions are associated with relatively larger electron temperatures in comparison with the regions outside the bubbles. Possible reasons for the higher electron temperature observed inside a plasma bubble could be larger particle precipitation often observed close to the South Atlantic Magnetic Anomaly region, heating by photoelectrons or the operation of various plasma instability mechanisms that can result in the transfer of wave energy into the kinetic energy of electrons.