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Remote Influences on the Tropical Atlantic Climate System R. Saravanan National Center for Atmospheric Research (Collaborators: Alessandra Giannini, NCAR;

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Presentation on theme: "Remote Influences on the Tropical Atlantic Climate System R. Saravanan National Center for Atmospheric Research (Collaborators: Alessandra Giannini, NCAR;"— Presentation transcript:

1 Remote Influences on the Tropical Atlantic Climate System R. Saravanan National Center for Atmospheric Research (Collaborators: Alessandra Giannini, NCAR; Ping Chang & Marcelo Barreiro, Texas A&M)

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3 Sources and Mechanisms of Remote Influence ENSO (Covey & Hastenrath, 1978; …) –Midlatitude atmospheric bridge (Rossby wave propagation) Nobre & Shukla (1996), … –Tropical atmospheric bridge (Walker circulation) (…; Saravanan & Chang, 2000; Chiang et al, 2000; …) NAO –“Southern lobe” of the Atlantic SST tripole Grotzner et al (1998), Czaja et al (2002) South Atlantic? –Southern analogue of the NAO? –Influence on the Atlantic ENSO?

4 Sutton et al, 2000

5 SST, HFLX, Wind vs. NINO3, -NAO (Czaja et al, 2002)

6 NCAR Community Climate Model (CCM3) Atmospheric General Circulation Model T42 horizontal resolution (2.8 degrees lat/lon) 18 vertical levels Prescribed SST boundary condition

7 CCM3 integrations (5x45 years) GOGA (Global Ocean - Global Atmosphere) TOGA (Tropical Ocean – Global Atmosphere) TAGA (Tropical Atlantic – Global Atmosphere) TOGA - TAGA

8 SST standard deviation (timescales < 6 yrs)

9 SST – NINO3 correlation (MAM) (Saravanan & Chang, 2000)

10 SST – Nordeste Precip sq. correlation (MAM) (Saravanan & Chang, 2000)

11 MAM 200 hPa wind regression vs. (NINO3, NTA) (Saravanan & Chang, 2000)

12 MAM Precipitation regression vs. (NINO3, NTA) (Saravanan & Chang, 2000)

13 Conclusions ENSO clearly is a major influence on TAV –Upper level flow resembles large-scale Gill-type response to equatorial heat source –Surface flow does not! NAO is also a major influence

14 Open Questions What is the “horizontal propagation” mechanism for the ENSO influence on TAV? –Midlatitude Rossby wave propagation? –Walker cell mechanism? What is the “vertical” mechanism for inducing SST anomalies? –Windspeed changes and associated latent heat flux anomalies? –Tropospheric warming/changes in static stability? –Changes in cloudiness? –Latent heating vs. sensible heating vs. radiative heating? Are there interactions between the different remote influences? –“Preconditioning” of the response to ENSO Is there a role for the subtropical South Atlantic?

15 ENSO correlations (Klein et al, 1999)

16 NINO 3.4 index (Kaplan SST data set; base period )

17 SST index evolution (Dec Aug 1983) OBSMODEL

18 SST index evolution (Dec Aug 1989) OBSMODEL

19 NTA SST vs. NAO/NINO3 (Czaja et al, 2002)

20 SLP (JFM) vs. NINO3/NAO correlation (Czaja et al, 2002)

21 Tropical SST indices (Klein et al, 1999)

22 Tropical Atmospheric Bridge (Klein et al, 1999)

23 Enfield & Alfaro, 1999 (Fig. 2)

24 HFLX – N. Tropical Atlantic SST sq. correlation (MAM) (Saravanan & Chang, 2000)

25 MAM Surface pressure regression vs. (NINO3, NTA) (Saravanan & Chang, 2000)

26 Preconditioning role of Tropical Atlantic Variability (Giannini, Saravanan, and Chang, J. Climate, submitted) If there is no prior tropical Atlantic SST anomaly during the onset phase of ENSO –ENSO teleconnection follows the expected course –Warm event is correlated with a decreased in Nordeste rainfall and vice versa If there is a prior tropical Atlantic SST anomaly during the onset phase of ENSO –ENSO impact can be diminished, or even reversed, if the Atlantic anomaly is “discordant”

27 Concordant cases JJA0 SON0 DJF1 Warm Cold

28 Discordant cases JJA0 SON0 DJF1 Warm Cold

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