PROBLEMS OF GEOCOSMOS

Temperature gradient, °С/100 km
Proceedings of the 7th International Conference "Problems of Geocosmos" (St. Petersburg, Russia, 26-30 May 2008)
1.5
1.4
1.3
1.2
1.1
1
0.9
1.5
1.4
1.3
1.2
1.1
1
0.9
AFZ
λ = 40°W
temperature gradient
3-yr running averages
1950 1960 1970 1980 1990 2000 2010
AFZ
λ = 40°W
temperature gradient
11-yr running averages
1950 1960 1970 1980 1990 2000 2010
Years
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.8
1.7
1.6
1.5
1.4
1.3
1.2
AFZ
λ = 30°W
temperature gradient
3-yr running averages
1950 1960 1970 1980 1990 2000 2010
AFZ
λ = 30°W
temperature gradient
11-yr running averages
1950 1960 1970 1980 1990 2000 2010
Years
Fig.2. Time series of the maximum temperature gradient in the layer 1000-500 hPa near the south-eastern coasts of
Greenland (longitudes λ= 30° and 40°W) in the cold half of the year (October-March).
Normalized spectral density
8
6
4
2
AFZ
λ = 40°W
22 yrs
10 yrs
4 yrs
0
30 20 10 0
HFC, T cut-off = 3,7,11,17,19,23 yrs Period, years
12
8
4
0
AFZ
λ = 30°W
22 yrs
10 yrs
4 yrs
30 20 10 0
Period, years
Fig.3. Spectral density curves of the AFZ temperature gradients for the source time series (black lines) and their highfrequency
components with the different cut-off parameters (color lines).
of the temperature were used to calculate the charts of the temperature gradients in the layer 1000-500 hPa,
in order to find the maximum values of the magnitude of the gradients at different longitudes in the region of
the AFZ near Greenland for every month. The obtained values were averaged for the cold months (October-
March) which is the period of most intensive cyclogenesis at middle latitudes.
The time series of the temperature gradients in the Arctic frontal zone near the south-eastern coasts of
Greenland are presented in Fig.2, the long-term oscillations of the AFZ temperature contrasts are distinctly
seen. Having smoothed the data with 3-yr and 11-yr running averages, we can see the periodicities ∼10-11
and ~22 years which are close to the main cycles of solar activity. This allows the suggestion that the
temperature characteristics of the Arctic frontal zone are affected by solar activity and related phenomena. In
order to confirm a reliability of the observed periodicities, an analysis of the normalized spectral density
periodograms [Jenkins and Watts, 1969] was carried out both for the source time series and for their highfrequency
components according to the method by Dmitriyev et al. (1996). The results of the spectral
analysis confirmed (see Fig.3) that the harmonics with the periods ~10 and ~22 years are really the main
harmonics in the spectra of the AFZ temperature gradients with a rather stable position on the periodogram.
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