Ionospheric variability at low latitude station: Hainan, China

Abstract

In this paper, the ionospheric characteristic parameters obtained from ionograms recorded by the DPS-4 digisonde at Hainan(19.4°N, 109.0°E), China are used to analyze the diurnal and seasonal behavior of the ionospheric variability at low latitude. Data used for the present study are hourly interval resolution data of the F2 layer critical frequency foF2, the F2 layer peak height hmF2, the thickness parameter BO and the shape parameter B1. Time period coverage of the data used for the present study is from March 2002 to June 2003. The monthly inter-quartiles (Δ IntQT) and monthly ranges (Δ Range) as well as their percentage ratios to the monthly medians (Δ IntQT (%), Δ Range (%)) are used as quantitative measurements of the variability of the ionospheric parameters in the present study. Seasonal averages of these quantities are also obtained for summer, winter and equinox. Our study showed that: (1) for the foF2 parameter, the variability is much lower during daytime hours than during nighttime hours, with the maximum variability occurring at pre-sunrise hours — in terms of percentage inter-quartile values. The seasonal averages of Δ IntQT (%) are less than 15% by day and fluctuate between 12% and 40% at night; (2) for the hmF2 parameters, the variability has a minimum value at hours after sunrise and sunset, whereas it has a maximum value at about 4:OOLT. The seasonal averages of Δ IntQT (%) fluctuate between 6.9% and 19.2%, with a slightly lower value at equinox than in the other two seasons; (3) for the B0 parameter, for the winter and equinox seasons, the variability has a minimum value at hours after sunrise and sunset, whereas it has maximum values at about 02:00-03:OOLT and post-noon hours; for the summer season, the occurrence time of the maximum and minimum shifts to later compared with those observed in the other two seasons. The seasonal averages of Δ IntQT (%) range between 21% and 46.2% for winter and between 18.2% and 37.6% for the other two seasons; (4) for the BI parameter, in terms of the absolute monthly inter-quartiles and monthly ranges, except for the hours near 06:00–07:OOLT when the variability reaches a maximum value, it changes within a very limited extent. In terms of the percentage 'ratios to the monthly medians, the variability of B1 is higher during daytime than during nighttime. The seasonal averages of Δ IntQT (%) change between 11.6% and 33.2%, showing in general slightly higher values in the solstices (23.4–32.9%) than at equinox (15.0–23.1%) in the time period between 02LT and 15LT.