Publication Date:
2015-12-03
Description:
Simultaneous observations of F2 layer stratification and spread F at post-midnight (00:00 LT-05:00 LT) were carried out on 22, 23 and 28 November 2013, using ionosondes distributed over a northern equatorial anomaly region at three specific locations, i.e., Puer (PUR,22.7°N, 101.05°E, dip latitude 12.9°N), Chiang Mai (CMU, 18.8°N, 98.9°E, dip latitude 9.04°N), and Chumphon (CPN, 10.7°N, 99.4°E, dip latitude 0.93°N) . The results show that both the PUR and CMU stations observed the F2 layer stratification at post-midnight in the northern hemisphere, frequently accompanied with gravity waves (the periods~30-100 min). It is reported that F2 layer stratification at post-midnight can be observed in the northern hemisphere for the first time. It is suggested that the thermospheric neutral wind triggered by gravity waves strongly contribute to the altitude dependence of the combined vertical plasma velocity, which consequently poses significant impacts on the occurrence of the low-latitude F2 layer stratification at post-midnight. In addition, the spread F other than F2 layer stratification was observed at the CPN station located at the geomagnetic equator, suggesting that smaller geomagnetic inclination tend to inhibit the post-midnight F2 layer stratification in the equatorial region. Furthermore, on 23 November 2013 a good correlation was identified between the F2 layer stratification at PUR and the spread F at both CMU and CPN, possibly due to that the large-scale gravity waves originating at middle latitudes contribute to the nighttime spread F observed in the low-latitude and equatorial regions.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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