Presentation on theme: "Remote Influences on the Tropical Atlantic Climate System R. Saravanan National Center for Atmospheric Research (Collaborators: Alessandra Giannini, NCAR;"— Presentation transcript:
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)
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?
MAM 200 hPa wind regression vs. (NINO3, NTA) (Saravanan & Chang, 2000)
MAM Precipitation regression vs. (NINO3, NTA) (Saravanan & Chang, 2000)
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
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?
MAM Surface pressure regression vs. (NINO3, NTA) (Saravanan & Chang, 2000)
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”
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