PROBLEMS OF GEOCOSMOS

Proceedings of the 7th International Conference "Problems of Geocosmos" (St. Petersburg, Russia, 26-30 May 2008)
SOLAR ACTIVITY EFFECTS ON THE CHARACTERISTICS OF
FRONTAL ZONES IN THE NORTH ATLANTIC
S.V. Veretenenko, V.A. Dergachev, P.B. Dmitriyev
Ioffe Physico-Technical Institute RAS, St.Petersburg, 194021, Russia, e-mail: svetaveretenenko@mail.ru
1. Introduction
Abstract. Long-term changes of the characteristics of frontal zones, which are the regions of high
temperature contrasts influencing extratropical cyclone formation and development, were studied
in the North Atlantic, the ‘reanalysis’ data NCEP/NCAR being used. It was found that in the cold
half of the year (the period of most intensive cyclogenesis at middle latitudes) the oscillations of
the temperature gradients in the layer 1000-500 hPa near the south-eastern coasts of Greenland
(the Arctic frontal zone) reveal strong ∼10-yr and ∼22-yr periodicities. The detected effects
provide evidence of the influence of solar activity and related phenomena on the structure of the
thermo-baric field of the troposphere at middle and high latitudes resulting in the enhancement of
temperature contrasts in the frontal zones. In turn, the revealed changes of the frontal zone
characteristics may be a reason for long-period changes of cyclonic activity at middle latitudes.
It is known that the temperature field of the troposphere is highly inhomogeneous due to the difference of
thermal characteristics of air masses forming over different kinds of surface (e.g., over the warm ocean or the
cold land in winter). This difference results in the formation of the regions of high temperature contrasts near
the eastern coasts of continents, so called ‘frontal zones’. Cyclonic activity at middle latitude is closely
related to the frontal zones, since they determine the potential energy supply which may be transformed to
the kinetic energy of cyclones [Vorobjev, 1991]. The high temperature contrasts in the frontal zones and
related atmospheric fronts create favorable conditions for cold advection contributing to the intensification of
cyclonic vortices. Indeed, the effects of energetic Solar Proton Events on the cyclone development were
found in the region of the Arctic frontal zone near the south-eastern coasts of Greenland [Veretenenko and
Thejll, 2004, 2008]. In this work we study long-term variations of the temperature contrasts in the Arctic
frontal zone (AFZ) and compare them with solar activity and galactic cosmic ray (GCR) variations.
2. Analysis of experimental data and discussion
As experimental base of our investigation we used the NCEP/NCAR ‘reanalysis’ data [Kalnay et al., 1996]
on the geopotential heights of different pressure levels for the period 1958-2006 (http://www.cru.uea.ac.uk).
We calculated the mean monthly charts of the temperature in the layer 1000-500 hPa (Fig.1), using the
dependence of the temperature T in the layer between the pressure levels p1 and p2 on the difference of
geopotential heights of these levels Φ1 and Φ2 : Φ − Φ = . 4 ⋅T
⋅ lg( p p ) . The mean monthly charts
Latitude, deg.N
90
80
70
60
50
40
30
20
Arctic frontal zone
Polar frontal
zone
10
Layer 1000-500 hPa.
February 2003.
0
-80 -60 -40 -20 0 20 40 60 80
285
280
275
270
265
260
255
250
245
2
1
67 1 2
°K
°C/100 km
Longitude, deg.
Longitude, deg.
Fig.1. The Arctic and Polar frontal zones on the mean monthly charts of the temperature in the layer 1000-500 hPa (left
panel) and of the magnitude of the temperature gradient in this layer (right panel).
288
Latitude, deg.N
90
80
70
60
50
40
30
20
10
0
Arctic frontal zone
Polar frontal
zone
Layer 1000-500 hPa.
February 2003.
-80 -60 -40 -20 0 20 40 60 80
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2