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Peter Hitchcock and Theodore G. Shepherd

of local and linear radiative damping in the middle atmosphere . J. Atmos. Sci. , 67 , 2070 – 2085 . Hitchcock , P. , T. G. Shepherd , and G. L. Manney , 2013 : Statistical characterization of Arctic polar-night jet oscillation events . J. Climate , in press . Holton , J. R. , 1983 : The influence of gravity wave breaking on the general circulation of the middle atmosphere . J. Atmos. Sci. , 40 , 2497 – 2507 . Holton , J. R. , and C. Mass , 1976 : Stratospheric

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A. Hannachi and W. Iqbal

of Marshall and Molteni (1993) was considered by Kondrashov et al. (2004) . They run the model for 54 000 winter days and identified four clusters within the three-dimensional EOF space of the 500-hPa streamfunction using mixture modeling and k -means clustering. The obtained regimes represent both phases of the NAO and the Arctic Oscillation (AO). 3. Methodology a. Flow tendencies and low-dimensional PDFs An appropriate way to analyze large-scale flow characteristics is to examine the

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Masakazu Taguchi

warming (SSW), as shown in Matsuno's (1971) theoretical model, in which he assumed impulsive initiation of a planetary wave forcing in the troposphere. On the other hand, downward influence from the stratosphere to the troposphere has recently received increased attention in attempting to understand the troposphere–stratosphere (T–S) dynamical coupling. Some observational studies have presented evidence of the downward influence in the context of the Arctic Oscillation (AO), or the NH annular mode

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M. Mester and J. G. Esler

1. Introduction Elliptical diagnostics were introduced as a method to determine compact and fundamental information about the state of the Arctic and Antarctic stratospheric polar vortices by Waugh (1997) . The basic idea is to take an available chemical [e.g., nitrous oxide (N 2 O)] or dynamical (e.g., isentropic potential vorticity) tracer field on a given level in the stratosphere, and make a “best fit” of a piecewise constant function with an elliptical boundary to this field, with the aim

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Lon L. Hood and Boris E. Soukharev

it is not statistically significant. This, combined with the strong positive and significant Aleutian response, yields a pattern that resembles that of the Arctic Oscillation (AO). The North Atlantic Oscillation (NAO) index, defined as the difference in SLP between Lisbon, Portugal, and Reykjavik, Iceland, is also positive, as seen in the figure, though not formally significant. We emphasize that this response pattern is not repeated rhythmically every solar cycle. It is only the mean response

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J. S. Theon, W. Nordberg, L. B. Katchen, and J. J. Horvath

acoustic grenade technique were made over Barrow, Alaska (71N), during the arctic winter night and during the summer. Thewinter mesosphere temperatures were generally warmer than at any other location and season and werevariable from day to day. Temperatures oscillated with height in wavelike fashion at magnitudes up to30-40C between 70 and 90 kin. These wavelike structures were found to exist also in the winter mesosphereat Churchill (59N) and Wallops Island (38N). However, the magnitude of the

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Edwin K. Schneider, Lennart Bengtsson, and Zeng-Zhen Hu

level pressure (SLP) trend and that of the Arctic Oscillation (AO) “annular mode,” which is the primary mode of high-frequency extratropical sea level pressure variability given by empirical orthogonal function (EOF) decomposition, and which is closely related to the North Atlantic Oscillation (NAO) pattern in the Atlantic region. However, there are regions where the trend/AO resemblance is not strong, particularly the Pacific–North America (PNA) sector. Thompson et al. (2000) divide the trend

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Timothy DelSole

differs between the two measures and certain details such as the location of maxima depend on the number of EOFs. The leading T 2 optimal persistence pattern for the 26 EOF basis set is shown in Fig. 3 ; this pattern also is the second T 1 optimal. This pattern bears some similarity to the “Arctic oscillation” of Thompson and Wallace (1998) ; for example, it is of single sign in midlatitudes and of opposite sign over the polar regions, and has a strong loading over the southern tip of Greenland

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Lucien Froidevaux, Joe W. Waters, William G. Read, Lee S. Elson, Dennis A. Flower, and Robert F. Jarnot

-biennial oscillation (QBO), with a strong semiannual signalabove 20 hPa. Ozone values near 50 hPa exhibit an equatorial low from October 1991 to June 1992, after whichthe low ozone pattern splits into two subtropical lows (possibly in connection with residual circulation changestied to the QBO) and returns to an equatorial low in September 1993. The ozone hole development at highsouthern latitudes is apparent in MLS column data integrated down to 100 hPa, with a pattern generally consistentwith Nimbus-7 Total

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Michael E. Schlesinger and Yale Mintz

stratosphere, although there aresome deficiencies. In particular, the simulated temperatures are too cold in the lower and middle stratosphere in the polar regions, the sea level pressure is too high in the Arctic and in the Antarctic circumpolartrough, and the flow field in the middle-latitude troposphere does not show the observed wavenumber 3. Despite these shortcomings, the model has simulated the observed high correlation of synopticand time-averaged total ozone with the tropospheric height field

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