The North Atlantic Climate System Integrated Study (ACSIS) - 1 year extension

Lead Research Organisation: British Antarctic Survey
Department Name: Science Programmes


Major changes are occurring across the North Atlantic climate system: in oceanic and atmospheric temperatures and circulation, in sea ice thickness and extent, and in key atmospheric constituents such as ozone, methane and particles known as aerosols. Many observed changes are unprecedented in instrumental records. Changes in the North Atlantic directly affect the UK's climate, weather and air quality, with major economic impacts on agriculture, fisheries, water, energy, transport and health. The North Atlantic also has global importance, since changes here drive changes in climate, hazardous weather and air quality further afield, such as in North America, Africa, and Asia.

The ACSIS extension is a 1 year continuation of an ongoing 5-year strategic research programme called ACSIS: the North Atlantic Climate System Integrated Study.

ACSIS brings together and exploits a wide range of capabilities and expertise in the UK environmental science community. Its goal is to enhance the UK's capability to detect, attribute (i.e. explain the causes of) and predict changes in the North Atlantic Climate System. ACSIS is delivering new understanding of the North Atlantic climate system by integrating new and old observations of atmospheric physics and chemistry, of the ocean state and of Arctic ice, complemented by detailed data analysis and state-of-the-art computer simulations. Observations are obtained from diverse sources including NERC's observational sites in the North Atlantic, satellite remote sensing and the NCAS FAAM aeroplane. The computer modelling component is providing simulations of the atmosphere, ocean, and sea ice with unprecedented spatial detail.

The ACSIS extension will exploit advances made during the past 5 years to address specific new research questions which have arisen recently. It will investigate exciting evidence that changes in the climate of the North Atlantic/European region are much more predictable than was previously thought and will start to assess the impact of North Atlantic changes on the UK environment.


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Description 1) A persistent early winter equatorward bias in jet latitude still exists in the latest generation of climate models and leads to too-weak linkages between temporal (year-to-year) variability in the NA westerly jet and the NA sub-polar gyre. A potential cause of the early winter bias has been identified in terms of early winter biases meridional temperature gradient over the eastern part of North America.

2) There is a strong early-to-late winter contrast in the strength of multi-decadal atmospheric variability since the mid 19th century in reanalysis data. In late winter and through March the multi-decadal variability becomes more concentrated at the eastern part of the westerly jet.

3) An additional pathway that has the potential to bring improved skill for extended-range weather forecasts is uncovered by using an index that captures the variability of the early winter upper stratosphere. Evidence is provided to show that the upper stratosphere, a region conventionally regarded as inconsequential for weather forecasts, has a significant fingerprint on near surface weather in middle to late winter. See

4) Extreme polar vortex events known as sudden stratospheric warmings can influence surface winter weather conditions for up to two months, but the timing of SSWs is difficult to predict. By nudging the winds towards observations in different key regions, we found that the equatorial upper stratosphere plays an important role in determining the timing and spatial evolution of the SSWs. Our results suggest that better representation of the flow in this region is likely to improve predictability of extreme polar vortex events and hence their associated impacts at the surface. See and a recent paper accepted by QJ for detail.
Exploitation Route Improved seasonal to decadal predictions of the North Atlantic atmosphere-ice-ocean system.
Sectors Environment