New measurements of equatorial spread-F: High-altitude irregularities and drifting bubbles

As a result of an unstable plasma stratification the nighttime equatorial ionosphere is subject to a variety of plasma instabilities known commonly as equatorial spread-F. In its fully developed form spread-F consists of large wedges of depleted plasma rising from the bottom of the ionospheric F-layer to altitudes of over 1000 km. Spacecraft flying through these depletion regions detect intermediate and large-scale structures in the electron density while small-scale irregularities are detected by coherent VHF and UHF backscatter radars. We present spread-F data from a high-altitude sounding rocket launched during the 1994 Guara rocket campaign in Alcantara, Brazil. We also present observations made with the Cornell 50 Mz radar interferometer (CUPRI) as part of the Guara campaign and compare the radar findings with simultaneous measurements of the total electron content (TEC) made with a Global Positioning System (GPS) receiver.; Numerical simulations and analytical results published in the literature suggest that for altitudes above {dollar}sim{dollar}600 km the ion-neutral collision frequency is small enough so that collisional effects in the plasma become negligible compared to ion inertia effects. We present plasma density and electric field spectra measured by the spread-F sounding rocket and compare them with predictions made by simulations. Results indicate that within spread-F density depletions below 820 km the characteristics of plasma irregularities are still dominated by collisional effects, despite indications that the ion-neutral collision frequency is small enough to allow inertial effects to dominate.; We also present DC electric field measurements performed with the rocket experiment, providing vertical profiles of the ionospheric electric field together with drift estimates based on these data. In addition we study TEC fluctuations measured with a GPS receiver. Data from the receiver are used to construct simple images of the ionosphere, showing TEC fluctuation structures drifting eastward through the nighttime ionosphere. We compare the GPS findings with CUPRI radar measurements and show a correlation with spread-F density depletions.