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The Influence of the North Atlantic Ocean on the Mean Temperature of Ireland
17 August 2015

The Influence of the North Atlantic Ocean on the Mean Temperature of Ireland

Researchers at Met Éireann have been involved in a collaborative study with the National Oceanography Centre in Southampton on the influence of the North Atlantic Ocean on the mean temperature of Ireland.

The influence of the moving North Atlantic Ocean on the climate of Ireland is more subtle than it first appears. Temperatures in Ireland are warmer than North American Atlantic and Pacific maritime climates at similar latitudes because heat carried in the Atlantic overturning circulation is released to the atmosphere over the North Atlantic.

Our study investigated variations in Irish climate using long-term station-based time series of temperature and precipitation. The Atlantic multidecadal oscillation (AMO) (http://www.cgd.ucar.edu/cas/catalog/climind/AMO.html) which relates to the North Atlantic sea surface temperatures, explains over 90% of the pronounced decadal variation in annual land temperatures and summer precipitation. The correlation between the 20-year running mean of the AMO anomaly (i.e. AMO differences relative to the mean AMO) and 20-year running mean of annual average land temperature anomalies (temperature differences relative to the mean temperature) over Ireland is shown in figure 1(a). This clearly shows that the AMO and mean annual land temperatures over Ireland are in phase i.e. when decadal averages are considered mean temperatures over Ireland are warmer when the North Atlantic ocean is warmer than average. Mean summer rainfall over Ireland is also correlated to the AMO, with drier summers on average when the AMO is in a negative phase.

Understanding the impact of these ocean variations when interpreting long climate records, particularly in the context of a changing climate, is crucial.

Figure 1. (a) 20-year running mean of the Atlantic Multidecadal oscillation (AMO) anomalies in red compared to 20-year running mean of annual average land temperature anomalies over Ireland in green. The year-to-year variations in the temperature anomaly are shown in blue and highlight the fact that even within a warm/cold AMO phase, colder/warmer than average years are possible. The y-axis shows the anomaly in degrees (b) 20-year running mean of the AMO anomalies compared to the 20-year means of average summer precipitation over Ireland.

This research was recently published in Weather: http://onlinelibrary.wiley.com/doi/10.1002/wea.2543/abstract

 
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