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We report new observations made on April 11 2000 over Jicamarca of daytime spread-F-like irregularities. These irregularities are extremely rare and were first reported by Woodman et al. [1985]. The main features of these new observations, which are similar to the previous ones, are that they were: (1) two orders of magnitude stronger than the incoherent scatter echoes at the F peak, (2) observed between 1400 and 1600 LT; (3) characterized by small Doppler shifts (|υd| < 1 m s−1); and (4) characterized by long correlation times, i.e., narrow spectral widths. The latter is interpreted as evidence that these irregularities are field aligned (very aspect sensitive in the north-south direction). On this occasion the irregularities occurred at higher altitudes than before, between 950 and 1450 km compared to 600–1000 km. The echoes in these recent observations were quite localized in the east-west direction (they were much stronger in the west beam than in the east beam). Furthermore, using interferometry we determined that the irregularities were in the form of blobs, aspect sensitive in the east-west (as well as north-south) direction with aspect angle widths as small as 0.2 degrees, particularly when the echoes were strong. |
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