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  • Author or Editor: Richard D. Rosen x
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John R. Anderson
and
Richard D. Rosen

Abstract

Quasi-periodic variations in the relative angular momentum of the atmosphere on time scales of around 40–50 days have been observed by Langley et al. (1981). A description of the two-dimensional (latitude-height) structure of the winds responsible for these changes is constructed here from five years of NMC twice-daily global analyses. Using cross-spectral and amplitude-phase eigenvector techniques, we find these variations are associated with wavelike motions in the tropical upper troposphere that propagate and downward in phase within the tropics. A coherently connected midlatitude Northern Hemisphere component is also present whose phase is essentially independent of height. We believe the tropical component to be the zonally averaged part of the motions described by Madden and Julian (1971, 1972). The Northern Hemisphere midlatitude component may be a direct response to the tropical motions or both motions may be the common response to an as yet unidentified tropical forcing.

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Rui M. Ponte
and
Richard D. Rosen

Abstract

Atmospheric angular momentum (AAM) reached extremely high values during the large 1982–83 El Niño event. The mechanisms responsible for the anomalously high AAM are examined using mountain torque (τ m ) and friction torque (τ f ) time series computed from the National Centers for Environmental Prediction–National Center for Atmospheric Research reanalyses. AAM anomalies, defined with respect to a 29-yr climatology (1968–96), are mostly positive from mid-1982 onward, but notably they double in amplitude over a 2-week period in early 1983. Analysis of the torque series reveals that this sharp AAM increase is mostly related to anomalies in τ m , primarily associated with American and Eurasian orography. After reaching its peak value in January, AAM anomalies decay slowly to near-normal values over the next three months, with anomalies in τ f , especially over the subtropical North Pacific, playing a dominant role in this downturn. The relevant anomalies in τ m and τ f are discussed in relation to rapid synoptic-scale variability and longer-term, large-scale anomalous patterns in surface pressure and winds that characterized this El Niño event.

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David A. Salstein
,
Richard D. Rosen
, and
Jose P. Peixoto

Abstract

The variability of annually averaged water vapor and water vapor transport fields over the Northern Hemisphere during the fifteen year period 1958–1973 is studied by means of empirical orthogonal function (EOF) analysis. Examined are vertically integrated values of the moisture quantities at a set of 91 stations chosen to cover the hemisphere as uniformly as possible. Analyses of the zonal and meridional transports are performed separately, but in addition a version of the EOF analysis is performed in which the two are treated as components of a single vector. All resulting modes are examined in light of statistical significance criteria established through a form of Monte Carlo testing.

The first mode in moisture variability appears to be highly significant, and it is dominated by opposite behavior in the held over Africa and over the western equatorial Pacific. Its time series reflects a sharp change in regime during the period studied. The significant mode of variability in the zonal transport field mirrors that of water vapor content, whereas the first two modes of meridional transport variability point to the Afro-Indian region as being important in explaining changes in the zonal mean Hadley cell during the period.

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