Abstract
AbstractA new method to retrieve hmF2 and vertical plasma drift W from foF1 and foF2 ionosonde observations has been proposed and applied at five European stations for June noontime conditions over the (1958–2017) period. Linear long‐term trends were estimated using the retrieved hmF2 and W variations. It has been shown that negative and statistically significant hmF2 trends manifest a pronounced latitudinal dependence: the largest (~2.7 km per decade) is at lower‐latitude station Rome, while the smallest (< 1 km per decade) is at high‐latitude station Sodankylä. It was shown that hmF2 trends are due to vertical plasma drifts that manifest similar latitudinal dependence: the largest (~1 m/s per decade) is at Rome and the smallest (~0.3 m/s per decade) is at Sodankylä. Vertical plasma drift converted to the meridional northward thermospheric wind manifests an average increase of (11.6 ± 3.0) m/s over the period of ~60 years. This may be related to a decrease in ion drag due to negative trends in the ionospheric F1 and F2 regions. An additional factor is a decrease in auroral heating related to long‐term decrease in solar and geomagnetic activity observed for June months over the analyzed period.
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