Abstract
Abstract. An all-sky imager was installed in Asmara, Eritrea (15.4° N, 38.9° E, 7° N dip) and used to monitor the OI 630-nm nightglow. Nine months of data were studied between September 2001 and May 2002, a time including the recent maximum in the solar activity cycle. Equatorial plasma bubbles (EPBs) were recorded on 63% of nights with adequate viewing conditions. The station location within view of the equatorial ionization anomaly and with a magnetic declination near zero makes it an excellent test case for comparison with satellite studies of the seasonal variation of EPBs with longitude. The imager was accompanied by two Cornell GPS scintillation monitors, and the amplitude scintillation data are compared to the all-sky data. GPS scintillations indicate the beginning of EPBs, but die out sooner in the post-midnight period than the larger scale EPBs. Both phenomena exhibit clear occurrence maxima around the equinoxes. Ionospheric zonal drift speeds have been deduced from EPB and GPS scintillation pattern movement. Average near-midnight EPB drift speeds are between 100 and 120 m/s most months, with the GPS scintillation speeds being about the same. A winter drift speed maximum is evident in both EPB and GPS scintillation monthly means.
Highlights
The study of the equatorial spread F (ESF) phenomenon, great ionospheric turbulence events often detected at latitudes near the magnetic dip equator, has continued for decades and is currently quite intense
In the present study we report on observations of both Equatorial plasma bubbles (EPBs) and Global Positioning System (GPS) scintillations from Asmara, Eritrea (15.4◦ N, 39.8◦ E, 7◦ N dip) made possible by the availability of portable and reliable ground-based instrumentation
Observations of EPB and GPS scintillation occurrence and drift speed have been reported for a 9-month period during the recent maximum of solar activity from Asmara in northeast Africa
Summary
The study of the equatorial spread F (ESF) phenomenon, great ionospheric turbulence events often detected at latitudes near the magnetic dip equator, has continued for decades and is currently quite intense. Burke et al (2004) point out that the longitude region from 22.5◦ E to 52.5◦ E (where the magnetic declination is essentially zero) at equinox provides both a solar terminator parallel to the field and a minimal transequatorial wind to give maximum EPB occurrence at the equinoxes Asmara is in this longitude sector and provides a testing ground for these proposed influences. Since the occurrence of EPBs is longitude dependent, it is natural to inquire as to the variability of drift speeds with longitude This is again accomplished by providing observations from as many ground-based stations as possible, and here we offer Asmara data toward this goal. Our own efforts to do so indicated first that the problem is of sufficient complexity to be deferred to a later paper, and second that, even during this period, the great majority of nights are of low to moderate activity so that the storms only slightly affect the average occurrence statistics
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