Long-Term Trends in foF2: A Comparison of Various Methods

JAN LASTOVICKA; ANDREI V. MIKHAILOV; THOMAS ULICH; JURGEN BREMER; ANA G. ELIAS; NIEVES ORTIZ DE ADLER; ALBERTO J. FOPPIANO; V. JARA; RODRIGO ABARCA DEL RIO; ELIAS OVALLE

New Orleans, Louisiana

Congreso; AGU 2005 Joint Assembly; 2005

AGU, American Geophysical Union

Results of various authors on long-term trends in foF2, i.e. in the maximum electron density in the ionosphere, and their interpretation do not reveal a consistent pattern. Therefore a joint analysis of one carefully selected data set was performed by five teams, which used different approaches to trend determination. High-quality data of station Juliusruh (54.6N, 13.4E) for noon (average from 10-14 UT) with a small number of gaps were used. The data covered the period of two solar cycles from minimum to minimum (1976-1996). Data gaps were filled in by interpolation using Juliusruh measurements at other times and measurements of neighbor stations. Juliusruh is relatively sensitive to geomagnetic activity as an almost subauroral station, which might play some role in interpretation of trend results. Various methods provide results, which differ to some extent. Even when one co-author applies various modifications of his method,the results differ. Another source of differences are various ways of removal (or at least large suppression) of effects of solar (and geomagnetic) activity. Also interpretation is not unique - co-authors consider either the long-term change in geomagnetic activity, or greenhouse effect to be predominantly responsible for trends. Nevertheless, there is some output from the joint analysis. All trends are either negative or insignificant. Data corrections with sunspot number (R), F10.7 adjusted to the Sun-Earth distance, and observed F10.7 result in somewhat different trends; the observed F10.7 appears to be the best correcting factor. The Juliusruh dip angle increased over the period 1976-1996 from 68.6 to 68.8 deg, but the possible impact of that increase is negligibly small and it would make the trend more positive. The paper will present results in more detail.