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Abstract. The Arecibo incoherent scatter radar facility was operated on February 26, 1998, and was used to observe the total solar eclipse that occurred over the Caribbean. A maximum of 87% obscuration was observed over Arecibo at 1430 LT (1830 UT). The radar was operated using an experimental technique, which uses a 300/•s single/multi-frequency pulse, to gather data from the altitude range 146-2412 km. The Sheffield University plasmasphere ionosphere model was used to interpret the measurements. The electron temperature was found to have decreased by 600 K at 400 km altitude, but the magnitude of the decrease becomes smaller with increasing altitude. This is shown to be the result of the lesser degree of obscuration of the solar disk at latitudes north of Arecibo. Conjugate point photoelectron heating effects are also shown to play a significant role in the electron energy balance during the eclipse. The H + ion temperature exhibited a response to the eclipse, with

Abstract.We compare total electron content measurements made using the Arecibo Incoherent Scatter Radar (ISR) with those made using the Global Positioning System (GPS). The ISR measurements have a limited range for these observations, up to 1500 km. We extend these profiles to GPS heights of 20,200 km with the aid of a numerical model. We use a GPS receiver on St. Croix, which has been calibrated using JPL's Global Ionospheric Mapping (GIM)technique. In addition, we also use the ISR to calibrate GPS measurements made at Isabela, PR and see how the calibration holds up on the next day. The GIM technique gives very good results on both a quiet night and a night with a severe ionospheric depletion. Normalizing the Isabela receiver to the ISR also gives good results and shows promise as a way to independently calibrate nearby GPS receivers in the future. Finally, we give evidence that the severe depletion observed by the ISR on the night of June 25/26, 1998 was associated with an elongated TEC depletion. The structure may be related to a disturbance originating in the southern hemisphere.

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