Abstract
This study pertained to the relationship between critical frequency of F2 layer (foF2 ) and solar activity indices at three low latitude ionospheric stations during solar cycle 22 (1985-1996). The selected ionospheric stations lie in the latitudinal range of Pakistan: therefore, this investigation may also be useful to understand the impact of solar activity relevant to our region. The monthly median values of foF2 for Okinawa, (26.3ON, 127.8O E), Guangzhou, (23.10O N, 113.4O E) and Chongqing (29.50O N, 106.40O E) have been plotted against sunspot number (SNN) and solar radio flux (F10.7cm). The main purpose of this analysis was to compare the foF2 values at low latitude ionospheric stations. A comparison of different phases of solar activity with foF2 at the subject stations revealed almost similar patterns. The correlation coefficients between SSN and critical frequency of F2 layer (foF2 ) on hourly basis for all months were compared. These trends helped in understanding foF2 occupancy in the region of Pakistan during solar cycle 22. A strong dependence was observed between solar activity and foF2 during this period. Ikubanni et al. [14] have already investigated the trends of F2 layer critical frequency at a low latitude station, during solar cycle 22. This comparative study of foF2 was regarding Chongqing, Okinawa, and Guangzhou that have not been explored as yet. These studies emphasized the behavior of foF2 for all these stations and identified the latitude dependency of foF2 on solar activity. A better agreement was observed during the year of moderate solar activity (MSA). An International Reference Ionosphere (IRI) model has been used to reveal foF2 missing values
