TY - JOUR
T1 - Synoptic analysis of the Pacific-North American teleconnection pattern
AU - Franzke, Christian
AU - Feldstein, Steven B.
AU - Lee, Sukyoung
PY - 2011/1
Y1 - 2011/1
N2 - In this study, we use various diagnostic techniques to investigate the synoptic evolution of the Pacific-North American teleconnection pattern (PNA). National Center for Environment Prediction/National Center for Atmospheric Research reanalysis data are used. These data cover the years 1948-2008 for the months of November-March. It is found that the positive PNA is initiated by enhanced convection over the western tropical Pacific and weakened convection over the tropical Indian Ocean. The excitation of the negative PNA exhibits opposite features. For both phases, the response to tropical convection excites a small-amplitude PNA about 8-12 days prior to the pattern attaining its maximum amplitude. This is followed by slow, steady growth for about 5 days, after which driving by synoptic scale waves, via their eddy vorticity flux, together with stationary eddy advection lead to much more rapid growth and the establishment of the full PNA. For the positive PNA, the synoptic scale waves propagate eastward into the midlatitude northeastern Pacific, where they are observed to undergo cyclonic wave breaking. For the negative PNA, the synoptic scale waves first amplify over the midlatitude northeastern Pacific and then propagate equatorward into the Subtropics where they undergo anticyclonic wave breaking. Once established, for both phases, the PNA appears to be maintained through a positive feedback that involves a succession of wave breakings. These results suggest that preconditioning may play an important role in the formation of the PNA. For the positive PNA, in its early development, the strengthening and eastward extension of the subtropical jet result in an increase in the cyclonic shear and a decrease in the meridional potential vorticity gradient, features that are known to favour cyclonic wave breaking. For the negative PNA, opposite changes were observed for the background flow, which favour equatorward wave propagation and anticyclonic wave breaking. The role of optimal growth is also discussed. Our results also suggest that the PNA is potentially predictable 1-2 weeks in advance.
AB - In this study, we use various diagnostic techniques to investigate the synoptic evolution of the Pacific-North American teleconnection pattern (PNA). National Center for Environment Prediction/National Center for Atmospheric Research reanalysis data are used. These data cover the years 1948-2008 for the months of November-March. It is found that the positive PNA is initiated by enhanced convection over the western tropical Pacific and weakened convection over the tropical Indian Ocean. The excitation of the negative PNA exhibits opposite features. For both phases, the response to tropical convection excites a small-amplitude PNA about 8-12 days prior to the pattern attaining its maximum amplitude. This is followed by slow, steady growth for about 5 days, after which driving by synoptic scale waves, via their eddy vorticity flux, together with stationary eddy advection lead to much more rapid growth and the establishment of the full PNA. For the positive PNA, the synoptic scale waves propagate eastward into the midlatitude northeastern Pacific, where they are observed to undergo cyclonic wave breaking. For the negative PNA, the synoptic scale waves first amplify over the midlatitude northeastern Pacific and then propagate equatorward into the Subtropics where they undergo anticyclonic wave breaking. Once established, for both phases, the PNA appears to be maintained through a positive feedback that involves a succession of wave breakings. These results suggest that preconditioning may play an important role in the formation of the PNA. For the positive PNA, in its early development, the strengthening and eastward extension of the subtropical jet result in an increase in the cyclonic shear and a decrease in the meridional potential vorticity gradient, features that are known to favour cyclonic wave breaking. For the negative PNA, opposite changes were observed for the background flow, which favour equatorward wave propagation and anticyclonic wave breaking. The role of optimal growth is also discussed. Our results also suggest that the PNA is potentially predictable 1-2 weeks in advance.
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U2 - 10.1002/qj.768
DO - 10.1002/qj.768
M3 - Article
AN - SCOPUS:79952492553
SN - 0035-9009
VL - 137
SP - 329
EP - 346
JO - Quarterly Journal of the Royal Meteorological Society
JF - Quarterly Journal of the Royal Meteorological Society
IS - 655
ER -