Annual and semiannual variations in the ionospheric F2-layer. I. Modelling

Abstract

Abstract. Annual, seasonal and semiannual variations of F2-layer electron density (NmF2) and height (hmF2) have been compared with the coupled thermosphere± ionosphere±plasmasphere computational model (CTIP), for geomagnetically quiet conditions. Compared with results from ionosonde data from midlatitudes, CTIP reproduces quite well many observed features of NmF2, such as the dominant winter maxima at high midlatitudes in longitude sectors near the magnetic poles, the equinox maxima in sectors remote from the magnetic poles and at lower latitudes generally, and the form of the month-to-month variations at latitudes between about 60°N and 50°S. CTIP also reproduces the seasonal behaviour of NmF2 at midnight and the summer±winter changes of hmF2. Some features of the F2-layer, not reproduced by the present version of CTIP, are attributed to processes not included in the modelling. Examples are the increased prevalence of the winter maxima of noon NmF2 at higher solar activity, which may be a consequence of the increase of F2-layer loss rate in summer by vibrationally excited molecular nitrogen, and the semiannual variation in hmF2, which may be due to tidal eects. An unexpected feature of the computed distributions of NmF2 is an east±west hemisphere dierence, which seems to be linked to the geomagnetic ®eld con®guration. Physical discussion is reserved to the companion paper by Rishbeth et al.

Anomalous variations of <I>Nm</I>F2 over the Argentine Islands: a statistical study

“…Millward et al, 1996;Zou et al, 2000;Rishbeth et al, 2000;Tao Yu et al, 2000). On the other hand, Zou et al (2000) compared the coupled thermosphere-ionosphere-plasmasphere model (CTIP) results with ionosonde data from mid-latitudes for geomagnetically quiet conditions.…”

“…Millward et al, 1996;Zou et al, 2000;Rishbeth et al, 2000;Tao Yu et al, 2000). On the other hand, Zou et al (2000) compared the coupled thermosphere-ionosphere-plasmasphere model (CTIP) results with ionosonde data from mid-latitudes for geomagnetically quiet conditions. Observed variations of the mid-latitude winter anomaly of NmF2 at solar maximum and the fact of the matter that the winter anomaly of NmF2 is stronger at solar maximum than at solar minimum are not successfully explained by the CTIP model (see pages 927 and 942 of Zou et al, 2000).…”

“…On the other hand, Zou et al (2000) compared the coupled thermosphere-ionosphere-plasmasphere model (CTIP) results with ionosonde data from mid-latitudes for geomagnetically quiet conditions. Observed variations of the mid-latitude winter anomaly of NmF2 at solar maximum and the fact of the matter that the winter anomaly of NmF2 is stronger at solar maximum than at solar minimum are not successfully explained by the CTIP model (see pages 927 and 942 of Zou et al, 2000). Zou et al (2000) concluded that these disagreements may be a consequence of the increase of F2-layer loss rate in summer in comparison with that in winter by vibrationally excited N 2 which is not included in the CTIP model.…”

“…An odd number of foF2 values under investigation leads us to determine foF2(med) as the middle value. The average of the Torr, 1973, andZou et al, 2000). Table 3 shows the arithmetical mean, <foF2(med)>, of the median values of foF2 at 16:00 UT (11:43 SLT) for January, June, July, and December calculated from the Argentine Island ionosonde foF2 data for low, moderate, and high solar activity during the 1957-1959 and 1962-1995 time periods.…”

“…Croom et al, 1960;King, 1961;Torr and Torr, 1973;Millward et al, 1996;Zou et al, 2000;Rishbeth et al, 2000;Tao Yu et al, 2000;Pavlova, 2005, 2008a, b). The winter/summer variations in the foF2 monthly noon medians were studied by Torr and Torr (1973) using the data of 140 ionosondes in 1958, 1964, and 1969.…”