BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Talks.cam//talks.cam.ac.uk//
X-WR-CALNAME:Talks.cam
BEGIN:VEVENT
SUMMARY:The Atlantic\; strong but subservient in the meridional overturnin
 g circulation - Agatha de Boer\, UEA
DTSTART:20071009T100000Z
DTEND:20071009T110000Z
UID:TALK7879@talks.cam.ac.uk
CONTACT:Deb Shoosmith
DESCRIPTION:North Atlantic (NA) deep water formation and the resulting Atl
 antic meridional overturning cell is generally regarded as the primary fea
 ture of the global overturning circulation and believed to be a result of 
 the geometry of the continents. Here\, instead\, we view the overturning a
 s a global energy-driven system and investigate the robustness of NA domin
 ance within this framework. Using an idealized-geometry ocean general circ
 ulation model coupled to an energy moisture balance model\, we test the ef
 fect of various climatic forcing mechanisms on the strength and structure 
 of the overturning circulation. Without winds or a high vertical diffusivi
 ty\, the ocean does not support deep convection. A supply of mechanical en
 ergy through winds or mixing (purposefully included or due to numerical di
 ffusion) starts the deep water formation. Once deep convection and overtur
 ning set in\, the distribution of convection centers is \ndetermined by th
 e relative strength of the thermal and haline buoyancy forcing. In the mos
 t thermally dominant state (i.e.\, negligible salinity gradients)\, strong
  convection is shared among the NA\, North Pacific (NP) and Southern Ocean
  (SO) while near the haline limit\, convection is restricted to the NA. Th
 e effect of a more vigorous hydrological cycle is to produce stronger sali
 nity gradients\, favoring the haline state of NA dominance. In contrast\, 
 a higher mean ocean temperature will increase the importance of temperatur
 e gradients because the thermal expansion coefficient is higher in a warm 
 ocean\, leading to the thermally dominated state. An increase in SO winds 
 or global winds tends to neutralize the salinity gradients\, also pushing 
 the ocean to the thermal state. The NA overturning does not respond direct
 ly to changes in its own local forcing but rather responds indirectly to t
 he changes that occur in the SO and NP.
LOCATION:British Antarctic Survey
END:VEVENT
END:VCALENDAR