Atmospheric processes governing the Northern Hemisphere annular mode/North Atlantic Oscillation

2003 ◽  
pp. 81-112 ◽  
Author(s):  
David W. J. Thompson ◽  
Sukyoung Lee ◽  
Mark P. Baldwin
Keyword(s):  
North Atlantic Oscillation ◽  
Northern Hemisphere ◽  
North Atlantic ◽  
Annular Mode ◽  
Atmospheric Processes ◽  
Northern Hemisphere Annular Mode

scholarly journals Autumn Sea Ice Cover, Winter Northern Hemisphere Annular Mode, and Winter Precipitation in Eurasia

2012 ◽  
Vol 26 (11) ◽  
pp. 3968-3981 ◽  
Author(s):  
Fei Li ◽  
Huijun Wang
Keyword(s):  
Sea Ice ◽  
Surface Temperature ◽  
Northern Hemisphere ◽  
Ice Cover ◽  
Winter Precipitation ◽  
The Arctic ◽  
Northern Eurasia ◽  
Laptev Sea ◽  
Annular Mode ◽  
Northern Hemisphere Annular Mode

Abstract This paper examines the impacts of the previous autumn sea ice cover (SIC) on the winter Northern Hemisphere annular mode (NAM) and winter precipitation in Eurasia. The coherent variations among the Kara–Laptev autumn SIC, winter NAM, and Eurasian winter precipitation appear after the year 1982, which may prove useful for seasonal prediction of winter precipitation. From a physical point of view, the Kara–Laptev SIC and sea surface temperature (SST) anomalies develop in autumn and remain in winter. Given that winter NAM is characterized by an Arctic–midlatitude seesaw centered over the Barents Sea and Kara–Laptev Seas, it is closely linked to the Arctic forcing that corresponds to the Kara–Laptev sea ice increase (reduction) and the associated surface temperature cooling (warming). Moreover, based on both model simulations and observations, the diminishing Kara–Laptev sea ice does induce positive sea level pressure (SLP) anomalies over high-latitude Eurasia in winter, which is accompanied by a significant surface warming in northern Eurasia and cooling south of the Mediterranean. This surface air temperature (SAT) anomaly pattern facilitates increases of specific humidity in northern Eurasia with a major ridge extending southward along the East Asian coast. As a result, the anomalous Eurasian winter precipitation has a more zonal band structure.

scholarly journals The Long- and Short-Lived North Atlantic Oscillation Events in a Simplified Atmospheric Model

2019 ◽  
Vol 76 (9) ◽  
pp. 2673-2700 ◽  
Author(s):  
Jie Song
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Early Stage ◽  
Atmospheric Model ◽  
Boreal Winter ◽  
Geophysical Fluid Dynamics Laboratory ◽  
The North ◽  
Northern Hemisphere Annular Mode ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Abstract This study investigates the North Atlantic Oscillation (NAO) events with relatively long and short lifetimes based on an 8000-day perpetual-boreal-winter [December–February (DJF)] run result of the idealized Geophysical Fluid Dynamics Laboratory (GFDL) dynamical core atmospheric model. We identify the so-called long- and short-lived positive and negative NAO events from the 8000-day model output. The composite 300-hPa geopotential height anomalies show that the spatial patterns of the composite long-lived NAO events closely resemble the Northern Hemisphere annular mode (NAM) because the NAO dipole is accompanied with a statistically significant North Pacific meridional dipole (NPMD) at similar latitudes as that of the NAO dipole. The composite short-lived NAO events exhibit the locally confined canonical NAO. Twelve sets of modified initial-value experiments indicate that an absence (a presence) of the NPMD-type perturbations at the early stage of the long (short)-lived NAO events will decrease (increase) their intensities and naturally shorten (lengthen) their lifetimes. Thus, the preceding NPMD is an early factor that is conducive to the emergence of the long-lived NAO events in the model. We argue that through directly modulating the synoptic eddy forcing over the North Atlantic region, the preceding NPMD can gradually arouse the NAO-like circulation anomalies on the following days. That is the reason why the preceding NPMD can modulate the intensities and lifetimes of the NAO events.

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