The empirical model of the winter ionosphere including the ionization trough in the Northern and Southern hemispheres is presented. The model is based
on the topside sounding data of the Intercosmos-19 satellite (about 2500 passes in both hemispheres)
and in situ electron density Ne measurements onboard the low-orbiting CHAMP satellite (about 15 000 passes)
for high and low solar activity, accordingly.
The radio-occultation observations data obtained in the experiments of GRACE, CHAMP and COSMIC/FORMOSAT were partially used.
The IRI model was also applied for correction, thus, the data of ground-based stations were indirectly taken into account.
The model is applicable to the quiet geomagnetic conditions (Kp = 2), all hours of local time (00 - 24 LT), a
ll winter months (November-February in the Northern hemisphere and May-August in the Southern hemisphere),
and different levels of solar activity (F10.7=70-250).
Model covers the geographical latitudes from 40o to 85o. Model describes at first the dependence of trough minimum position
on the LT and UT, and longitude. These dependencies are different in the Northern and Southern hemispheres and at low and high solar activity.
The model describes not only the trough minimum position but its shape too, i.e. the foF2 distribution in the trough region including its minimum,
equatorial and polar walls.
The model input parameters are the longitude, latitude, LT, UT and F10.7. The model allows to calculate on-line the foF2distribution
for any LT and UT in Cartesian and polar coordinate system, minimum trough positions, latitudinal and longitudinal foF2 profiles and foF2 at any place.
The accuracy of the model is 2o in latitude, and 0.2-0.3 MHz in foF2. In the future the model will be extended to the equinoctial conditions.
The model can be used in fact in the interval Kp=0-4 taking in to account the trough position shift according to
relation Δ=Δ(LT, Kp=2)-α(2-Kp).
The approximate value of coefficient
can be obtained from the plot below. The accuracy of the model certainly decreases at the edges of the range Kp = 0-4.
The constructed model more adequately reproduces longitudinal and latitudinal variations of foF2 than the international model of the ionosphere IRI-2016.
The model was tested according to the ground based sounding data and satellite radio-occultation measurements.
The author would like to give thanks to sponsors and operators of the CHAMP mission; Deutsches GeoForschungs Zentrum (GFZ) Potsdam and German Aerospace Center (DLR).
The authors are also grateful to sponsors and operators of the FORMOSAT-3/COSMIC mission; Taiwan's National Science Council and National Space Organization (NSPO),
the US National Science Foundation (NSF), National Aeronautics and Space Administration (NASA),
National Oceanic and Atmospheric Administration (NOAA) and the University Corporation for Atmospheric Research (UCAR).
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