Mechanisms of ENSO-forcing of hemispherically symmetric precipitation variability

LDEO Publication: 
Publication Type  Journal Article
Year of Publication  2005
Authors  Seager, R.; Harnik, N.; Robinson, W. A.; Kushnir, Y.; Ting, M.; Huang, H. P.; Velez, J.
Journal Title  Quarterly Journal of the Royal Meteorological Society
Volume  131
Issue  608
Pages  1501-1527
Journal Date  Apr
ISBN Number  0035-9009
Accession Number  ISI:000230262500010
LDEO Publication Number  6708
Key Words  enso; precipitation; symmetry; nino-southern-oscillation; sea-surface temperatures; el-nino; hadley circulation; subtropical anticyclones; drought; climate; cycle; reanalysis; equator

The patterns of precipitation anomalies forced by the El Nino-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 tropical ly-forced changes in the subtropical jets. During El Niho 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 Nino 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 Ann, 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.


Part B942DGTimes Cited:12Cited References Count:47

URL  <Go to ISI>://000230262500010
DOI  Doi 10.1256/Qj.04.96