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GEOPHYSICAL RESEARCH LETTERS, VOL. 32, L20804, doi:10.1029/2005GL022927, 2005

Why is the North Atlantic block more frequent and long-lived during the negative NAO phase?

Dehai Luo

Laboratory of Physical Oceanography, College of Physical and Environmental Oceanography, Ocean University of China, Qingdao, China


Abstract

The cause of why the North Atlantic (NA) blocks are more frequent and long-lived during the negative phase of the North Atlantic Oscillation (NAO) than the positive phase is theoretically explored using the envelope soliton block-eddy interaction model. It is shown that the negative NAO phase can enhance the planetary-scale split-jet (diffluent) flow prior to block onset, but the positive phase tends to weaken such a flow. Through the interaction with upstream synoptic-scale waves, the enhanced diffluence in the background flow during the negative phase of NAO allows the isolated block to form more easily and live longer. Thus, it appears that the negative NAO phase can provide a favourable environment for the frequent occurrence of the NA block and its persistence.

Received 8 March 2005; accepted 19 September 2005; published 21 October 2005.

Index Terms: 1610 Global Change: Atmosphere (0315, 0325); 1620 Global Change: Climate dynamics (0429, 3309); 3305 Atmospheric Processes: Climate change and variability (1616, 1635, 3309, 4215, 4513).

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Citation: Luo, D. (2005), Why is the North Atlantic block more frequent and long-lived during the negative NAO phase?, Geophys. Res. Lett., 32, L20804, doi:10.1029/2005GL022927.