Publication Date:
2019-01-02
Description:
Interminimum changes of June noontime monthly median foF1 were analyzed for European and
Japanese ionosonde stations over the period of five (Moscow six) solar cycles. The magnitude of these
changes is different at different stations and depends on the solar minima considered. In particular, both
European and Japanese stations manifest a pronounced foF1 change between 1996/1997 and 2008/2009
solar minima, the latter being the deepest one. For the first time, the total EUV solar flux with λ ≤ 1,050 Å has
been retrieved for the 1946–2015 period using observed June monthly median foF1. The deep solar
minimum in 2008/2009 was the lowest one among the last six solar cycles comparing the retrieved EUV. The
change from 1996/1997 to 2008/2009 in the retrieved EUV is ~2.0%, and this is much less than the difference
of ~10–12% being discussed in the literature. A 10% interminimum change in the total EUV flux results in
neutral temperature and gas density, which are larger in 2008 than in 1996, and this contradicts the satellite
drag neutral gas density observations. The mechanism of foF1 interminimum changes is based on an interplay
between molecular (NO+ and O2
+) and O+ ions. The main contribution (〉72%) to the interminimum NmF1
change provides [M+] ions via the total ion production rate variation, the rest is provided via O+ ions. The
absence (or inversed) difference in foF1 between 1996 and 2008 minima implies that neutral temperature and
density are larger in 2008 than in 1996, and this contradicts the satellite drag observations.
Description:
Published
Description:
768-780
Description:
2A. Fisica dell'alta atmosfera
Description:
JCR Journal
Keywords:
Long term trend in the ionosphere
;
Thermosphere
;
01.02. Ionosphere
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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