HR: 1340h
AN: A43B-1147    [Abstracts]
TI: Low Frequency Variability and the Eastern Mediterranean Teleconnection Pattern
AU: * Hatzaki, M
EM: marhat@phys.uoa.gr
AF: Department of Environmental Physics and Meteorology, Faculty of Physics, University of Athens, University Campus, Build Phys. V, Athens, 15784, Greece
AU: Flocas, H A
EM: efloca@phys.uoa.gr
AF: Department of Environmental Physics and Meteorology, Faculty of Physics, University of Athens, University Campus, Build Phys. V, Athens, 15784, Greece
AB: The long time series analysis of the atmospheric circulation has revealed large scale correlations between the flow at remote locations. These fluctuations belong in the low frequency range of timescale and referred to as teleconnections patterns. They are located in particular places and appear as preferred modes of low-frequency natural variability of the atmospheric circulation with fixed oscillating nodes and antinodes, called poles. These teleconnection patterns describe standing waves oscillating with time scales of a month or longer. It has been recognized that the large scale eddies and their feedback onto the mean flow, the propagation of Rossby waves in the midlatitudes and the stratosphere-troposphere interaction play an important role in understanding low frequency general circulation and variability. In previous studies, the Eastern Mediterranean Teleconnection pattern (EMP) was found with its two poles located in North-eastern Europe and Eastern Mediterranean, and it was predominantly identified at the upper troposphere during winter. An index was defined, based on the exact position of the two poles of the pattern, to represent the strength of the teleconnection pattern and to discriminate its positive and negative phase. The objective of this study is to investigate the large scale dynamics related to the development of EMP. For this purpose, datasets of daily geopotential height, temperature and horizontal wind components at several isobaric levels are employed, as obtained from the NCEP/NCAR and from the ECMWF centres, for the calculation of transient eddy kinetic energy, E-vectors, Rossby wave source and potential vorticity. It was found that the role of the eddy driven mid-latitude jet is important. It is likely that the subtropical jet is passive and that the transient eddies remove much more momentum in the negative phase, when the storm- track comes charging into Europe. Rossby wave propagation seems to determine the differing wave-guide aspects of the two EMP phases. In the negative phase, there is a significant southeastward Rossby wave propagation over Western Europe, while in the positive phase Rossby waves tend to move towards Scandinavia, consistent with the increased anticyclonic circulation over North Atlantic.
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 1620 Climate dynamics (0429, 3309)
DE: 3305 Climate change and variability (1616, 1635, 3309, 4215, 4513)
DE: 3309 Climatology (1616, 1620, 3305, 4215, 8408)
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting