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1 Met Office FitzRoy Road, Exeter, Devon, EX1 3PB, UK Email: [email protected]
Synoptic pressure patterns associated with wind-borne transport into the UK of the vector for Bluetongue, the biting midge CulicoidesLaura Burgin1 and Marie Ekström2
Weather and the Culicoides midge
2 CSIRO Land and Water, Black Mountain, GPO Box 1666 Canberra ACT 2601, Australia Email: [email protected]
Acknowledgements: colleagues at the Met Office, the University of Exeter and the Institute for Animal Health are gratefully acknowledged for their contributions to this work, particularly Paul Agnew, John Gloster, Matthew Hort and Anthony Wilson. Funding for this research is providedby Defra contract SE4204.
Map-pattern classification and the occurrence of midge days
Relative frequency (%)PP DJF MAM JJA SON YEAR1 0.0 2.9 0.0 3.7 2.22 0.0 62.9 65.1 65.4 64.83 0.0 8.6 11.1 3.7 7.34 0.0 5.7 3.2 12.3 7.85 0.0 20.0 20.6 14.8 17.9N 0 35 63 81 179
Conclusions
Midge days and meteorological data
Aim
Map-pattern classification of synoptic weather types deduced from principal component and cluster analysis and surface winds described by wind roses at Langdon Bay, Kent, UK (green = 1-5ms-1, yellow = 5-10ms-1, red = >10ms-1, number in centre = <1ms-1).
1 2
3 4
5
• An automated eigenvector-based map-pattern classification based on principal component of high-pass filtered daily 00Z MSLP patterns in combination with a k-means clustering technique was used to identify the significant modes of atmospheric circulation across the study area.
• Wind roses from Langdon Bay were plotted to analyse surface winds occurring in areas thought to be at risk on each date in each cluster.
• This study provides new insight into the relationship between synoptic circulation patterns and surface winds suitable for incursions of potentially infected midges into the UK: an NAO gradient and a blocking high synoptic situation were found to characterise MSLP during midge days and surface wind observations generally verified the geostrophic winds indicated by these patterns.
• This relationship could now be used for seasonal and decadal predictions of risk of midge-borne disease incursions into the UK. Example of NAME output used to specify a ‘midge day’.
• Pattern 2 shows a pressure gradient associated with the North Atlantic Oscillation (NAO), which accounts for 64.8% of all midge days and was the most common pattern overall. Surface observations show low to moderate S, SW and W winds were predominant at these times.
• Pattern 5, a blocking anticyclone, occurred fairly infrequently but was still associated with 17.9% of midge incursions. Surface observations showed low to moderate E, SE and S winds were mainly present.
• This study aims to understand how large scale synoptic conditions over north-west Europe relate to surface winds during times of midge incursions from infected areas of the near-continent to the UK.
• This relationship will subsequently be used to predict the risk of the spread of Culicoides-borne viruses at seasonal and decadal timescales, where accurate wind forecast data is not available.
Two patterns (see Table 1) were found to characterise the synoptic situation present on most midge days:
Table 1. Seasonal and annual relative frequency distribution of midge days associated with each pressure pattern
• A ‘midge’ dispersion model has been developed within the UK Met Office’s Numerical Atmospheric-dispersion Modelling Environment (NAME) to identify days when midges are likely to be transported to the UK i.e. a ‘midge day’.
• The number of ‘midge particles’ released into the model is based on several meteorological thresholds derived from experiments carried out at the Institute for Animal Health, Pirbright. The model was run every evening in the midge season, April to November, for 2005-2007.
• Mean sea level pressure (MSLP) data at 00Z from the Unified Model was used to determine the patterns of circulation which are present during each overnight midge incursion event.
• Hourly measurements of temperature, wind speed and direction at Langdon Bay, UK and Ostend, Belgium were used to assess the surface climate associated with the circulation patterns.
• Spread of the viruses by the midge is strongly linked to meteorological conditions as temperature, precipitation, wind speed and direction have a significant impact on midge flight.
• Despite having poor flight capabilities, midges can be carried for long distances on the wind and have therefore been implicated in the spread of disease into areas several hundreds of kilometres away.
• Large scale pressure systems have previously been linked to patterns of midge-borne disease spread e.g. AHS outbreaks in South Africa have been linked to the El Niño/Southern Oscillation.
• The spread of Culicoides-borne diseases into Europe is likely to increase with climate change.
Culicoides, the vector for BT and AHS (Courtesy of Chris Sanders, Institute for Animal Health).
• The biting midge Culicoides is the principal vector for several viruses causing economically important animal diseases including Bluetongue (BT), and African Horse Sickness (AHS). Since 2006 northern Europe has been in the midst of an extensive epidemic of BT which has cost the European economy hundreds of millions of pounds due to death, sickness and movement restrictions of livestock.
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