PROBLEMS OF GEOCOSMOS

Proceedings of the 7th International Conference "Problems of Geocosmos" (St. Petersburg, Russia, 26-30 May 2008)
The events were selected for the cold period (October-March), because in this half of the year the
maximum intensity of cyclonic activity is observed. The superposed epoch analysis was used to calculate the
mean pressure deviations from the undisturbed level, which was obtained by averaging the GPH data over 10
days before the event onset. The day of the event onset was considered as the zero day.
The mean variations in geopotential heights of the isobaric surface 1000 hPa during Forbush decreases
under consideration are presented in Fig.1. The white lines indicate the areas, where the statistical significance of
the deviations is above 0,95 and 0,99 according to the Student t-criterion. As it seen from the figure, a slow
pressure growth takes place near the south-eastern coasts of Greenland on the first days (0/+1 days) after the
Forbush decrease onset. Then, the area of the increasing pressure extends in the north-eastern direction and
reaches its maximum on the +3/+4 days after the Forbush decrease beginning, covering all Scandinavia, the north
of European part of Russia and the Arctic Ocean coasts. The deviations from the undisturbed level in this region
amount to ∼ 60-70 gp.m.
Latitude, deg.
80
60
40
20
80
60
40
20
80
60
40
20
80
60
40
20
-50 0
-1 day
50
0.95
0.99
-50 0
0 day
50
-50 0
1 day
50
-50 0
2 day
50
0.95
0.99
0.99
0.95
0.99
0.95
40
20
0
-20
-40
40
20
0
-20
-40
40
20
0
-20
-40
40
20
0
-20
-40
80
60
40
20
80
60
40
20
80
60
40
20
80
60
40
20
Longitude, deg.
0.95
0.99
0.99
0.95
0.95
0.99
-50 0 50
3 day
0.95
0.95
0.99
0.99
-50 0
4 day
50
0.95
0.99
-50 0
5 day
50
0.99
-50 0
6 day
50
Fig. 1 Mean variations in geopotential heights (in gp.m) of the isobaric level 1000 hPa in the
course of GCR Forbush decreases for 48 events (1980-2006, cold half of year). White lines
show the areas where the effects are significant at 0,95 and 0,99 confidence level. Black and
blue lines show the climatic position of the Arctic and Polar fronts in January, respectively
[Khromov and Petrosyants, 1994].
Variations in geopotential heights of the isobaric levels 1000, 850, 700, 500, 300 and 200 hPa on the +4
day after the Forbush decrease onset, which is the day of the greatest pressure increase, are shown in Fig.2. White
lines show the areas where the effects are significant at 0,95 and 0,99 confidence level according to the Student tcriterion.
We can see a noticeable pressure growth at all the isobaric levels, but the most significant effects take
place near the Earth’s surface. The effect weakens with the increase of the altitude.
The data in Fig. 2 show also the climatic position of the main atmospheric fronts at middle latitudes in
January according to Khromov and Petrociants (1994). Atmospheric fronts are rather narrow transition bands
between air masses with different thermal characteristics which are formed over different kinds of surface. The
8
0.95
0.95
0.99
0.99
40
20
0
-20
-40
40
20
0
-20
-40
40
20
0
-20
-40
40
20
0
-20
-40