ENSO and its impact on eastern/southern African climate: the large-scale view Alessandra Giannini (IRI) alesall@iri.columbia.edu

Outline: ENSO theory ENSO monitoring ENSO impact on eastern/southern Africa The dynamics of the ENSO teleconnection

ENSO theory - a coupled ocean/atmosphere system Bjerknes (1969), reviewed in Neelin et al., “ENSO theory”, in J. Geophys. Res. (1998) http://www.cpc.noaa.gov/products/analysis_monitoring/impacts/warm_impacts.shtml

ENSO theory - a coupled ocean/atmosphere system Delayed Oscillator theory: Schopf, PF and MJ Suarez, 1988. “Vacillations in a coupled ocean-atmosphere model”, J. Atmos. Sci., 45, 549-566 Battisti, DS and AC Hirst, 1989. “Interannual variability in the tropical atmosphere/ocean system: influence of the basic state, ocean geometry and nonlinearity” J. Atmos. Sci., 46, 1687-1712 all reviewed in Neelin et al., 1998. “ENSO theory”, J Geophys Res, 103(C7), 14261-14290 2 characterizations of the ENSO system: non-linear, quasi-periodic linear, stochastically forced and their consequence for predictability

ENSO monitoring http://iridl.ldeo.columbia.edu/maproom/.ENSO

ENSO impact http://www.cpc.noaa.gov/products/analysis_monitoring/impacts/warm_impacts.shtml

ENSO impact Ropelewski and Halpert, 1987. “Global and regional precipitation patterns associated with the El Nino-Southern Oscillation”, Mon Wea Rev, 115, 1606-1626

The ENSO teleconnection: Chiang, JCH and AH Sobel, 2002. “Tropical tropospheric temperature variations caused by ENSO and their influence on the remote tropical climate”, J. Climate, 15, 2616-2631 - atmospheric anomalies, i.e. the “atmospheric bridge”: global (e.g. tropospheric temperature, 200hPa height...) and regional (e.g. near-surface winds, precipitation...) - delayed response of the remote oceans local thermodynamic response, response to ENSO-related anomalies in near-surface winds...

Goddard, L and NE Graham, 1999. “Importance of the Indian Ocean for simulating rainfall anomalies over eastern and southern Africa”, J Geophys Res, 104, 19099-19116

atmospheric adjustment: net surface heat fluxes El Nino – central equatorial Pacific global warming – global tropical oceans (e.g. Neelin et al., GRL 2003) What role for the land surface?? (e.g. Chiang and Lintner, J. Climate 2005)

Chiang and Sobel, J Climate 2002 (Yulaeva and Wallace , J Climate 1994)

NCEP-NCAR Reanalysis 200 hPa height sfc temp Kaplan SSTa

Year (0) of a warm ENSO Year (1) of a warm ENSO Indeje, M et al., 2000. “ENSO signals in East African rainfall seasons”. Int. J. Climatology, 20, 19-46

January-March 1992 v. January-March 1998 Reason, CJC and D Jagadheesha, 2005. “A model investigation of recent ENSO impacts over southern Africa”. Meteorol. Atmos. Phys., 89, 181-205

Conclusions: we have sensible theories for how the coupled ocean-atmosphere ENSO system works, and for its impact on the global climate these theories can guide our expectations related to prediction of ENSO and its general impacts, BUT knowledge of the regional climate system, and understanding of its interaction with global climate anomalies is critical to predict regional impacts.