EISCAT Svalbard radar-derived atmospheric tidal features in the lower thermosphere as compared with the numerical modeling ATM2

The EISCAT Svalbard radar (ESR) has obtained neutral wind field data down to 90 km altitude in two period runs in August 1998. This has been rendered possible by successful elimination of ground clutter echoes by the ESR staff. Features of the obtained tidal components are then comparatively studied with the ATM2 (Atmospheric Tidal Modeling Version 2) steady tidal model which assumes climatological background zonal flow. It is found that the results are fairly consistent with theoretical predictions that the diurnal component is almost evanescent with some indication of propagating characteristics, and that the semi-diurnal one is dominated by short vertical wavelength higher order mode prevalent at higher latitudes. The ter-diurnal component is also not in contradiction with non-linear interaction theory. Convincing delineation of these behaviors, however, awaits further study on the zonal wave number characteristics of relevant waves by longitudinal network collaborations

24/7 Solar Minimum Polar Cap and Auroral Ion Temperature Observations

During the International Polar Year (IPY) two Incoherent Scatter Radars (ISRs) achieved close to 24/7 continuous observations. This presentation describes their data sets and specifically how they can provide the International Reference Ionosphere (IRI) a fiduciary E- and F-region ionosphere description for solar minimum conditions in both the auroral and polar cap regions. The ionospheric description being electron density, ion temperature and electron temperature profiles from as low as 90 km extending to several scale heights above the F-layer peak. The auroral location is Poker Flat in Alaska at 65.1 N latitude, 212.5 E longitude where the NSF s new Poker Flat Incoherent Scatter Radar (PFISR) is located. This location during solar minimum conditions is in the auroral region for most of the day but is at midlatitudes, equator ward of the cusp, for about 4-8 h per day dependent upon geomagnetic activity. In contrast the polar location is Svalbard, at 78.2 N latitude, 16.0 E longitude where the EISCAT Svalbard Radar (ESR) is located. For most of the day the ESR is in the Northern Polar Cap with a noon sector passage often through the dayside cusp. Of unique relevance to IRI is that these extended observations have enabled the ionospheric morphology to be distinguished between quiet and disturbed geomagnetic conditions. During the IPY year, 1 March 2007 - 29 February 2008, about 50 solar wind Corotating Interaction Regions (CIRs) impacted geospace. Each CIR has a two to five day geomagnetic disturbance that is observed in the ESR and PFISR observations. Hence, this data set also enables the quiet-background ionospheric climatology to be established as a function of season and local time. These two separate climatologies for the ion temperature at an altitude of 300 km are presented and compared with IRI ion temperatures. The IRI ion temperatures are about 200-300 K hotter than the observed values. However, the MSIS neutral temperature at 300 km compares favorably with the quiet-background in temperature, both in magnitude and climatology

Ionospheric local model and climatology from long-term databases of multiple incoherent scatter radars

Empirical ionospheric local models have beendeveloped from long-term data sets of seven incoherentscatter radars spanning invariant latitudes from 25 to 75 inAmerican, European and Asian longitudes at Svalbard,Tromsø, Sondrestrom, Millstone Hill, St. Santin, Areciboand Shigaraki. These models, as important complements toglobal models, represent electron density, ion and electrontemperatures, and ion drifts in the E and F regions, giving acomprehensive quantitative description of ionosphericproperties. A case study of annual ionospheric variationsin electron density and ion temperature is presented basedon some of these models. Clear latitudinal, longitudinal, andaltitude dependency of annual and semiannual componentsare found