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Gwendal Rivière and Marie Drouard

1. Introduction The Arctic Oscillation (AO), which refers to the leading empirical orthogonal function (EOF) of the Northern Hemisphere sea level pressure, has been the subject of numerous studies since the initial work of Thompson and Wallace (1998) . The leading EOF of the midtropospheric geopotential height brings strong resemblance with the AO and both variabilities are usually referred to as the tropospheric northern annular mode (NAM) ( Thompson and Wallace 2000 ; Quadrelli and Wallace

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Songmiao Fan, Daniel A. Knopf, Andrew J. Heymsfield, and Leo J. Donner

1. Introduction Mixed-phase clouds, comprising both ice and supercooled liquid water, are frequently observed in the Arctic ( Shupe et al. 2006 ; Verlinde et al. 2007 ; de Boer et al. 2011 ; Shupe 2011 ; Morrison et al. 2012 ). The thermodynamic phase partitioning in clouds is influenced locally by heterogeneous ice nucleation rates and the Wegener–Bergeron–Findeisen (WBF) process, which involves the growth of ice crystals via vapor deposition and evaporation of liquid water droplets (e

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Barry Saltzman, Alfonso Sutera, and Anthony R. Hansen

of auto-oscillatory climaticchange (Saltzman es a!., 1981) to represent high-inertia grounded and shelf sea ice forms, instead of thinnermarine ice forms, it is possible for the model to yield a much longer period of auto-oscillation, perhaps asmuch as 100 000 years (the dominant period of ice volume variations revealed by deep-sea ocean cores).The physical basis of the model can, in principle, be tested by future evidence regarding the long-termvariations of bulk ocean temperature and

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L. L. Hood and B. E. Soukharev

the Arctic Oscillation (AO) and the North Atlantic Oscillation (NAO) ( Zhou et al. 2001 ; Hurrell 1995 ; Graf et al. 1998 ). A trend toward more equatorward planetary wave fluxes has also been reported ( Kuroda and Kodera 1999 ; Ohhashi and Yamazaki 1999 ; Baldwin and Dunkerton 1999 ; Hartmann et al. 2000 ). Finally, the total wave flux entering the stratosphere has decreased, on average, during the last few decades ( Newman and Nash 2000 ; Randel et al. 2002 ). These observed trends are

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Richard W. Stewart and Martin I. Hoffert

-travelling thermal waves with astanding wave in eastern Siberia. Sudden warming in the Arctic was related to the poleward migration of theresultant thermal systems. In these events the arctic mean stratospheric temperature increased by about30-C in 8 days, but local increases were at least twice as great in the upper (1969-70 and 1970-71) or middle(1972-73) stratosphere. The polar vortex breakdown is illustrated with the aid of conventional 10-mbmap analyses and 2-mb data based on isobaric layer thicknesses

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Alexei Korolev and Paul R. Field

et al. (2004) suggested that observations of embedded liquid water regions with horizontal extents as short as 100 m may be the result of turbulent motions leading to the intermittent production of liquid water. Korolev and Isaac (2003) found that a cloud parcel undergoing vertical oscillations may be subject to an indefinitely long periodic evaporation and activation of liquid droplets in the presence of ice particles. After a certain amount of time, the average ice water content (IWC) and

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John Austin

12). This includes results from both two-dimensional and three-dimensional models but there is not yet an emerging consensus as to the likely change in future ozone. One of the main difficulties is that the temperature in the Arctic winter lower stratosphere is close to that required for heterogeneous chemical processes to operate and therefore small temperature reductions could trigger significant chemical change. Alongside the changes in ozone, changes in stratospheric temperature (e

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Dehai Luo, Tingting Gong, and Linhao Zhong

1. Introduction Recently it has been recognized that there is a possible link between the North Atlantic Oscillation (NAO) or Arctic Oscillation (AO), a dominant dipole mode in the Northern Hemisphere (NH), and the NH surface temperature, which has important implications in understanding the cause of global warming ( Hurrell 1995 , 1996 ; Thompson and Wallace 1998 ; Thompson et al. 2000 ). Thompson et al. (2000) noted that the observed positive trend in the NAO/AO index over the last three

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Yali Luo, Kuan-Man Xu, Hugh Morrison, and Greg McFarquhar

size distributions of hydrometeors more realistically and, thus, represent microphysical processes more accurately than one-moment schemes (e.g., Meyers et al. 1997 ; Morrison and Pinto 2006 ). Arctic clouds have been identified as playing a central role in the Arctic climate system. However, the role of clouds is even less well understood in the Arctic than in other geographic regions owing to sparse observations. Arctic field programs, such as the Surface Heat Budget of the Arctic (SHEBA

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Aditi Sheshadri, R. Alan Plumb, Erik A. Lindgren, and Daniela I. V. Domeisen

Grant PP00P2_170523 is gratefully acknowledged. We thank Rachel White for useful discussions; Kunal Mukherjee for assistance with the movies; and three anonymous reviewers for their constructive comments, which greatly improved the manuscript. REFERENCES Baldwin , M. P. , and T. J. Dunkerton , 1999 : Propagation of the Arctic Oscillation from the stratosphere to the troposphere . J. Geophys. Res. , 104 , 30 937 – 30 946 , . 10.1029/1999JD900445 Baldwin

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