Anomalous variations of NmF2 over the Argentine Islands: a statistical study

• Published in: Annales Geophysicae
• Main Authors: Pavlov, A. V., Pavlova, N. M.
• Format: Text
• Language: English
• Published: 2018
• Subjects: Argentine; Argentine Islands
• Online Access: https://doi.org/10.5194/angeo-27-1363-2009; https://angeo.copernicus.org/articles/27/1363/2009/

We present a statistical study of variations in the F2-layer peak electron density, Nm F2, and altitude, hm F2, over the Argentine Islands ionosonde. The critical frequencies, fo F2, and, fo E, of the F2 and E-layers, and the propagation factor, M (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 Nm F2 and hm F2. The probabilities to observe maximum and minimum values of Nm F2 and hm F2 in a diurnal variation of the electron density are calculated. Our study shows that the main part of the maximum diurnal values of Nm F2 is observed in a time sector close to midnight in November, December, January, and February exhibiting the anomalous diurnal variations of Nm F2. Another anomalous feature of the diurnal variations of Nm F2 exhibited during November, December, and January when the minimum diurnal value of Nm F2 is mainly located close to the noon sector. These anomalous diurnal variations of Nm F2 are found to be during both geomagnetically quiet and disturbed conditions. Anomalous features are not found in the diurnal variations of hm F2. The statistical study of the Nm F2 winter anomaly phenomena over the Argentine Islands ionosonde was carried out. The variations in a maximum daytime value, R , of a ratio of a geomagnetically quiet daytime winter Nm F2 to a geomagnetically quiet daytime summer Nm F2 taken at a given UT and for approximately the same level of solar activity were studied. The conditional probability of the occurrence of R in an interval of R , the most frequent value of R , the mean expected value of R , 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 R and the occurrence frequency of the F2-region winter anomaly increase with increasing solar activity.