Progress in trend studies: Highlights of the TREND2004 Workshop Original Research Article

TREND2004, the third IAGA/ICMA Workshop Long Term Changes and Trends in the Atmosphere, presented a lot of new information and in some way summarized progress over the last few years in the field of long-term trends in the atmosphere–ionosphere system with emphasis on the middle atmosphere and ionosphere. The paper briefly summarizes the results of the Workshop with focus on the mesosphere, ionosphere and thermosphere and presents some new findings. Progress in recent years was substantial in trends in thermospheric density, mesospheric and mesopause region temperature, and in the lower ionosphere (ionized component). On the other hand, principal contradictions remain in trends in the F2 region of the ionosphere, particularly in interpretation of the observed trends.