Ocean Observing and Climate
OVAC Theme 2 - Surface Fluxes and Changes in the Ocean
Impact of the North Atlantic Oscillation (NAO) on Air-Sea Freshwater Flux and Wind Stress. The figure shows the spatial patterns of freshwater exchange and wind stress forcing associated with the NAO as determined from NCEP/NCAR reanalysis fields for 1949-1997. Contours represent the difference in sea level pressure (units mb) between positive and negative states of the NAO. They show the familiar dipole in pressure between the Azores and Iceland which is characteristic of the NAO. The impact of the NAO on the wind stress is shown by the arrowed field which reveals stronger wind stress forcing of the ocean in the mid-latitude belt from 50-65 °N. The NAO also modifies the freshwater exchange (evaporation-precipitation) between the ocean and the atmosphere which is shown by the coloured field (red colours: stronger net evaporation, blue: stronger net precipitation).
Ocean-atmosphere exchanges of heat, freshwater and momentum are key components of the coupled climate system. Significant variability has been observed in the large scale exchange patterns for each of these components at interannual to interdecadal timescales, with the potential for significant impacts on the ocean circulation. However, much uncertainty remains regarding the mechanisms by which anomalous surface exchanges lead to modification of the ocean by the atmosphere, and vice versa. The main aim of the Surface Fluxes and Changes in the Ocean cross-cutting team is to identify and understand these mechanisms. The research associated with this aim has three principal objectives:
- Development and analysis of new fields of the net ocean-atmosphere freshwater flux and the investigation of the impact of freshwater anomalies on the ocean.
- Analysis of variability in surface heat flux and wind stress forcing fields, and in the ocean response.
- Development of new corrections for biases in ship meteorological observations, new flux parameterisations, and new instrumentation for measuring fluxes.
Progress towards achieving these objectives is being made using a variety of approaches including the analysis of measurements made at sea and from satellites together with studies that involve sophisticated computer models of the oceanic and atmospheric circulation. The focus of the research is the North Atlantic but processes by which variability in the surface forcing modifies the ocean circulation are also being investigated in several other ocean basins. Selected examples of the research that we are carrying out are presented in web pages linked from the key on the left.
Links to OVAC Theme 2 Research
Rainfall Variability Atlantic Freshwater SST Anomalies Flux Parameterisations
