remote influences on the tropical atlantic climate system
DESCRIPTION
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; …) - PowerPoint PPT PresentationTRANSCRIPT
Remote Influences on the
Tropical Atlantic Climate System
R. SaravananNational 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?
NCAR Community Climate Model (CCM3)
• Atmospheric General Circulation Model
• T42 horizontal resolution (2.8 degrees lat/lon)
• 18 vertical levels
• Prescribed SST boundary condition
CCM3 integrations (5x45 years)
• GOGA (Global Ocean - Global Atmosphere)
• TOGA (Tropical Ocean – Global Atmosphere)
• TAGA (Tropical Atlantic – Global Atmosphere)
• TOGA - TAGA
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?
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”