Geomagnetic control of the foF2 long-term trends

A. V. Mikhailov, D. Marin
2000 Annales Geophysicae  
Further development of the method proposed by Danilov and Mikhailov is presented. The method is applied to reveal the foF2 long-term trends on 30 Northern Hemisphere ionosonde stations. Most of them show signi®cant foF2 trends. A pronounced dependence of trend magnitude on geomagnetic (invariant) latitude is con®rmed. Periods of negative/positive foF2 trends corresponding to the periods of long-term increasing/ decreasing geomagnetic activity are revealed for the ®rst time. Pronounced diurnal
more » ... riations of the foF2 trend magnitude are found. Strong positive foF2 trends in the post-midnight-early-morning LT sector and strong negative trends during daytime hours are found on the sub-auroral stations for the period with increasing geomagnetic activity. On the contrary middle and lower latitude stations demonstrate negative trends in the earlymorning LT sector and small negative or positive trends during daytime hours for the same period. All the morphological features revealed of the foF2 trends may be explained in the framework of contemporary F2-region storm mechanisms. This newly proposed F2-layer geomagnetic storm concept casts serious doubts on the hypothesis relating the F2-layer parameter long-term trends to the thermosphere cooling due to the greenhouse eect.
doi:10.1007/s005850000232 fatcat:liehnmn7lnch3euhoevblcnrti