Anomalous variations of <I>Nm</I>F2 over the Argentine Islands: a statistical study
We present a statistical study of variations in the F2-layer peak electron density, <I>Nm</I>F2, and altitude, <I>hm</I>F2, over the Argentine Islands ionosonde. The critical frequencies, <I>fo</I>F2, and, <I>fo</I>E, of the F2 and E-layers, and the...
| Main Authors: | , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2009-04-01
|
| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/27/1363/2009/angeo-27-1363-2009.pdf |
| Summary: | We present a statistical study of variations in the
F2-layer peak electron density, <I>Nm</I>F2, and altitude, <I>hm</I>F2, over the Argentine
Islands ionosonde. The critical frequencies, <I>fo</I>F2, and, <I>fo</I>E, of the F2 and
E-layers, and the propagation factor, <I>M</I>(3000)F2, measured by the ionosonde during
the 1957–1959 and 1962–1995 time periods were used in the statistical
analysis to determine the values of <I>Nm</I>F2 and <I>hm</I>F2. The probabilities to observe
maximum and minimum values of <I>Nm</I>F2 and <I>hm</I>F2 in a diurnal variation of the
electron density are calculated. Our study shows that the main part of the
maximum diurnal values of <I>Nm</I>F2 is observed in a time sector close to midnight
in November, December, January, and February exhibiting the anomalous
diurnal variations of <I>Nm</I>F2. Another anomalous feature of the diurnal
variations of <I>Nm</I>F2 exhibited during November, December, and January when the
minimum diurnal value of <I>Nm</I>F2 is mainly located close to the noon sector.
These anomalous diurnal variations of <I>Nm</I>F2 are found to be during both
geomagnetically quiet and disturbed conditions. Anomalous features are not
found in the diurnal variations of <I>hm</I>F2. The statistical study of the <I>Nm</I>F2
winter anomaly phenomena over the Argentine Islands ionosonde was carried
out. The variations in a maximum daytime value, <I>R</I>, of a ratio of a
geomagnetically quiet daytime winter <I>Nm</I>F2 to a geomagnetically quiet daytime
summer <I>Nm</I>F2 taken at a given UT and for approximately the same level of
solar activity were studied. The conditional probability of the occurrence
of <I>R</I> in an interval of <I>R</I>, the most frequent value of <I>R</I>, the mean expected
value of <I>R</I>, and the conditional probability to observe the F2-region winter
anomaly during a daytime period were calculated for low, moderate, and high
solar activity. The calculations show that the mean expected value of <I>R</I> and
the occurrence frequency of the F2-region winter anomaly increase with
increasing solar activity. |
|---|---|
| ISSN: | 0992-7689 1432-0576 |