|
|
 |
|
|
Ann. Geophys., 24, 2841-2849, 2006
www.ann-geophys.net/24/2841/2006/
© European Geosciences Union 2006
Comparison of long-term Moscow and Danish NLC observations: statistical results
P. Dalin1, S. Kirkwood1, H. Andersen2, O. Hansen2, N. Pertsev3, and V. Romejko4
1Swedish Institute of Space Physics, Box 812, SE-981 28 Kiruna, Sweden
2The Danish Association for NLC research, Lyngvej 36, Kølvrå, 7470 Karup J., Denmark
3A. M. Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences, Pyzhevskiy per., 3, Moscow, 119017, Russia
4The Moscow Association for NLC research, Moscow, Russia
Abstract. Noctilucent clouds (NLC) are the highest clouds in the Earth's atmosphere,
observed close to the mesopause at 80–90 km altitudes. Systematic NLC
observations conducted in Moscow for the period of 1962–2005 and in Denmark
for 1983–2005 are compared and statistical results both for seasonally
summarized NLC parameters and for individual NLC appearances are described.
Careful attention is paid to the weather conditions during each season of
observations. This turns out to be a very important factor both for the NLC
case study and for long-term data set analysis. Time series of seasonal
values show moderate similarity (taking into account the weather conditions)
but, at the same time, the comparison of individual cases of NLC occurrence
reveals substantial differences. There are positive trends in the Moscow and
Danish normalized NLC brightness as well as nearly zero trend in the Moscow
normalized NLC occurrence frequency but these long-term changes are not
statistically significant. The quasi-ten-year cycle in NLC parameters is
about 1 year shorter than the solar cycle during the same period. The
characteristic scale of NLC fields is estimated for the first time and it is
found to be less than 800 km.
Full Article in PDF (1039 KB) |
|
|
