Supervisers: Ian Renfrew and Karen Heywood
The Irminger Sea has recently been re-discovered as an important site of open ocean convection, thus making a contribution to the overturning branch of the North Atlantic thermohaline circulation (the major density-driven circulation of the global ocean). Open ocean convection is forced by a pre-conditioning period of persistent ocean-atmosphere heat exchange within a cyclonic gyre and then triggered by intense periods of heat exchange, usually resulting from high-impact weather systems. In the case of the Irminger Sea it has been hypothesised that these triggering events are “tip jets” (Pickart et al. 2003), westerly high wind-speed jets that flow from the southern tip of Greenland. Although other intense weather systems in this area are likely to play a role in pre-conditioning and triggering ocean convection, for example, synoptic-scale cyclones, polar lows, reverse tip jets and barrier winds along the SE Greenland coast (Moore and Renfrew 2004).
This project will examine the effects of these high-impact weather systems on a highly-idealised mixed-layer ocean model (a 1 dimensional “water parcel” model) of the Irminger Sea and vicinity. A series of different atmospheric conditions derived from satellite observations, meteorological reanalyses and boundary-layer model output, will be used to force the ocean model. Model initialisation data will be taken from existing regional ocean model output, while validation data will be gathered from Argo floats and oceanographic cruise data. The project will address the hypothesis that barrier winds act to pre-condition, while tip jets act to trigger, open ocean convection in the Irminger Sea. A particular focus of the project will be on the winter of 2007, when it is anticipated that a major field programme will take place in the area.
Moore, G.W.K. and I.A. Renfrew, 2004: Tip jets and barrier winds: A QuikSCAT climatology of high wind speed events around Greenland, manuscript submitted to J. Climate.
Pickart, R. S. et al., 2003: Deep convection in the Irminger Sea forced by the Greenland tip jet. Nature, 424, 152-156.