Library Dissertation Showcase

Assessing the seasonal causes of Greenland blocking and the subsequent impacts on UK temperature, UK regional precipitation, and the North Atlantic Oscillation

  • Year of Publication:
  • 2022

Greenland Blocking is becoming an increasingly researched area because of its large impacts upon UK temperature, precipitation, and the North Atlantic Oscillation. Greenland Blocking is defined as the influx of greater than usual temperatures over the Greenland region, resulting in the formation of high pressure and is measured by the Greenland blocking index. Both its causes and impacts are often debated and are largely only investigated individually at the seasonal scale. Therefore, by normalizing and detrending data of Sea ice, Sea surface temperatures and climate indices and subsequently using a multi-linear analysis this study commenced by investigating the causes of the Greenland blocking index. It was found that Sea ice data within the winter was the main driver of the Greenland blocking index through positive feedbacks and ocean-atmospheric heat releases. Whereas, in summer due to a reduction in sea ice and a weakened NAO both sea surface temperature data and climate indices had an increasing impact on causing the Greenland blocking index through atmospheric and oceanic circulations to polar regions.

In addition to the investigation of the causes, the study also looked to assess daily impacts of Greenland blocking events. To analyses immediate impacts on UK weather, six Greenland blocking events were chosen based on known extreme climatic events. Data ten days prior and following the event was then collected from the Greenland blocking index, central England temperature, the north Atlantic oscillation and region precipitation of Central England, Northeast England, Northwest England, Southeast England, Southwest England, South Scotland, East Scotland, North Scotland, and Northern Ireland. The UK weather datasets and north Atlantic oscillation were correlated against the Greenland blocking index. Alongside this GIF image files of geopotential heights at 500mb, air temperature at 850mb, vector winds at 850mb and specific humidity at 300mb were also produced. From this analysis it was found that the Greenland blocking index consistently forced the north Atlantic oscillation into a negative phase, forcing the jet stream to become weaker, more meandering and move further south. Across all events, temperature saw a significant decrease often as a result of the influx of cold Arctic or Siberian winds.

Furthermore, precipitation in winter months saw a reversal of normal conditions with wetter conditions in the East and drier conditions in the West. Whereas summer saw an overall increase in precipitation. However, during 2018 alongside the Greenland blocking event, the stratospheric polar vortex was disrupted resulting in a strong storm to propagate into the UK from the East. The storm brought with it extreme cold and large snowfall across the UK contradicting the individual Greenland blocking event of 2010. Therefore, Greenland blocking events by themselves simply reverse conditions of normal seasons, however coupled with disruptions to climate indices, severe weather events such as extreme cold storms and droughts could form over the UK.

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