Mechanisms of ENSO-forcing of hemispherically symmetric precipitation variability

Rich Seager, N. Harnik, W. A. Robinson, Y. Kushnir, M. Ting, Huei-Ping Huang, J. Velez

Research output: Contribution to journalArticle

127 Citations (Scopus)

Abstract

The patterns of precipitation anomalies forced by the El Niño-Southern Oscillation during northern hemisphere winter and spring are remarkably hemispherically symmetric and, in the midlatitudes, have a prominent zonally symmetric component. Observations of global precipitation variability and the moisture budget within atmospheric reanalyses are examined to argue that the zonally symmetric component is caused by interactions between transient eddies and tropically-forced changes in the subtropical jets. During El Niño events the jets strengthen in each hemisphere and shift equatorward. Changes in the subtropical jet influence the transient-eddy momentum fluxes and the eddy-driven mean meridional circulation. During El Niño events, eddy-driven ascent in the midlatitudes of each hemisphere is accompanied by low-level convergence and brings increased precipitation. These changes in the transient-eddy and stationary-eddy moisture fluxes almost exactly cancel each other and, in sum, do not contribute to the zonal-mean precipitation anomalies. Propagation of anomalous stationary waves disrupts the zonal symmetry. Flow around the deeper Aleutian Low and the eastward extension of the Pacific jet stream supply the moisture for increased precipitation over the eastern North Pacific and the western seaboard of the United States, while transient-eddy moisture convergence supplies the moisture for increased precipitation over the southern United States. In each case, increased precipitation is fundamentally caused by anomalous ascent forced by anomalous heat and vorticity fluxes.

Original languageEnglish (US)
Pages (from-to)1501-1527
Number of pages27
JournalQuarterly Journal of the Royal Meteorological Society
Volume131
Issue number608
DOIs
StatePublished - Apr 2005
Externally publishedYes

Fingerprint

El Nino-Southern Oscillation
eddy
moisture
anomaly
moisture flux
jet stream
Southern Oscillation
standing wave
meridional circulation
vorticity
symmetry
momentum
Northern Hemisphere
winter

Keywords

  • ENSO
  • Precipitation
  • Symmetry

ASJC Scopus subject areas

  • Atmospheric Science

Cite this

Mechanisms of ENSO-forcing of hemispherically symmetric precipitation variability. / Seager, Rich; Harnik, N.; Robinson, W. A.; Kushnir, Y.; Ting, M.; Huang, Huei-Ping; Velez, J.

In: Quarterly Journal of the Royal Meteorological Society, Vol. 131, No. 608, 04.2005, p. 1501-1527.

Research output: Contribution to journalArticle

Seager, Rich ; Harnik, N. ; Robinson, W. A. ; Kushnir, Y. ; Ting, M. ; Huang, Huei-Ping ; Velez, J. / Mechanisms of ENSO-forcing of hemispherically symmetric precipitation variability. In: Quarterly Journal of the Royal Meteorological Society. 2005 ; Vol. 131, No. 608. pp. 1501-1527.
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