Open AccessThe Morphology of Northern Hemisphere Blocking
Author(s) -
Evangelos Tyrlis,
Brian J. Hoskins
Publication year - 2008
Publication title -
journal of the atmospheric sciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.853
H-Index - 173
eISSN - 1520-0469
pISSN - 0022-4928
DOI - 10.1175/2007jas2338.1
Subject(s) - rossby wave , northern hemisphere , jet stream , blocking (statistics) , climatology , anticyclone , tropopause , zonal and meridional , geology , atmospheric sciences , potential vorticity , storm , longitude , latitude , winter storm , cyclogenesis , jet (fluid) , environmental science , vorticity , stratosphere , meteorology , vortex , physics , cyclone (programming language) , geodesy , oceanography , mathematics , field programmable gate array , thermodynamics , statistics , computer science , computer hardware
The morphology of regional blocking in the Northern Hemisphere is discussed using the 40-yr ECMWF Re-Analysis (ERA-40) dataset and a measure of blocking based on the reversal at storm-track latitudes of meridional θ contrasts on a potential vorticity (PV) surface representative of the tropopause. The focus is on cyclonic and anticyclonic Rossby wave breaking that is inherent to the blocking development, and the extent to which this is determined by the climatological jet position and the ambient shears. More generally, the importance of the climatological planetary scale is discussed. The approach is mainly through composite behavior, but informed by consideration of many individual events. A diversity of behavior is found with longitude in both winter and summer, and there is a striking reversal of the sense of the wave breaking between the two seasons that is generally consistent with the difference in the jet locations. Preferred behaviors are found in various regions and seasons, and retrogression of blocking is discussed.