Ionospheric climatology and weather in the Australian ‐ Japanese sector during the SUNDIAL/ATLAS 1 campaign

Abstract

The SUNDIAL/ATLAS 1 campaign took place during a period of high solar flux and moderate magnetic activity. For most days during the campaign, the ionosphere over Australia and Japan was undisturbed. The International Reference Ionosphere (IRI), used with a suitable equivalent sunspot number, provided a good climatological description of the Australian and Japanese observations. The measured hmF2 was employed in the Field Line Interhemispheric Plasma (FLIP) model to determine equivalent neutral winds and O+/H+ fluxes and accurately reproduced the measured hmF2. With these winds, the daytime nmF2 was well reproduced in most cases, although the measured nmF2 tended to peak before noon while the model nmF2 peaked 2–3 hours later at some locations. At night, the model nmF2 was typically lower than the measurements. The difference between the modeled and measured nighttime nmF2 worsened as the latitude decreased, suggesting that the problem is not principally due to inadequate plasmaspheric fluxes. While changes in nmF2 due to wind changes are modeled closely in some cases, generally the smaller day‐to‐day changes in nmF2 were not matched well by either the IRI or FLIP. The equivalent winds calculated from hmF2 in FLIP were similar in amplitude to the winds from the HWM90 model, but there were large differences in the phases. The two sets of winds show a similar decrease in amplitude with decreasing latitude. There appears to be a large longitudinal variation in the wind behavior in the Australian sector. While the winds in eastern Australia show similar diurnal variations with daytime poleward winds and nighttime equatorward winds, the west coast winds were poleward most of the time. The differences in poleward winds are reflected in the much smaller changes in hmF2 in the west. The calculated O+ fluxes to and from the plasmasphere are generally larger than the H+ fluxes for these solar maximum conditions. They show structure related to the neutral winds and hmF2. The O+ flux variations are similar at most stations with upward fluxes during the day and very large downward O+ fluxes at sunset followed by a rapid decay to small fluxes for most of the night. The calculated H+ flux behavior is more complex with the west coast station (Mundaring) showing a classical, strong diurnal variation, upward during the day and downward at night. On the other hand, the calculated H+ fluxes are upward most of the time at Hobart on the east coast.