1. Long-term trends of the critical frequency of the F2 layer at northern and southern high-latitude regions;Alfonsi;Phys. Chem Earth,2002
2. Bencze, P., et al., Long-term changes of hmF2 possible latitudinal and regional variations. in: Proceedings of the 2nd COST 251 Workshop Algorithms and Models for COST 251 Final Product, 30–31 March, 1998, Side Turkey, Rutherford Appleton Lab., UK, pp. 107–113, 1998.
3. Bremer, J., Some additional results of long-term trends in vertical-incidence ionosonde data. in: Paper presented at the COST 251 Meeting, Prague, September, 1996.
4. Trends in the ionospheric E and F regions over Europe;Bremer;Ann. Geophys.,1998
5. Trends in the thermosphere derived from global ionosonde observations;Bremer;Adv. Space Res.,2001