ENSO and its impact on eastern/southern African climate:the large-scale view

Alessandra Giannini (IRI)alesall@iri.columbia.edu

Outline:

ENSO theoryENSO monitoringENSO impact on eastern/southern AfricaThe dynamics of the ENSO teleconnection

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

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-periodiclinear, stochastically forced

and their consequence for predictability

ENSO monitoring

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

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

ENSO impact

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 oceanslocal 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

El Nino – central equatorial Pacificglobal warming – global tropical oceans(e.g. Neelin et al., GRL 2003)

atmosphericadjustment:net surfaceheat fluxes

What role for theland surface??

(e.g. Chiang and Lintner, J. Climate 2005)

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

NCEP-NCARReanalysis

200 hPa height

NCEP-NCARReanalysissfc temp

Kaplan SSTa

Indeje, M et al., 2000. “ENSO signals in East African rainfall seasons”. Int. J. Climatology, 20, 19-46

Year (0) of a warm ENSO Year (1) of a warm ENSO

Reason, CJC and D Jagadheesha, 2005. “A model investigation of recent ENSO impacts over

southern Africa”. Meteorol. Atmos. Phys., 89, 181-205

January-March 1992 v. January-March 1998

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.