© University of Reading 2007 www.reading.ac.uk

Sting Jets in severe Northern European WindstomsSuzanne Gray, Oscar Martinez-Alvarado, Laura Baker (Univ. of Reading), Peter Clark (collaborator, Met Office)

23 September 2008

• Battered northern Europe from Ireland to Russia on 7-9 January 2005, killing at least 17 people and severely disrupting sea, air and land transport

• Cut power to around 500,000 homes.

• Widespread property damage.

• Strong winds and floods caused widespread damage in UK.

• Forest damage in Sweden was the worst recorded in recent history

• Oil production hampered at three offshore fields.

Impacts: Windstorm Erwin/Gudrun

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Conceptual model

Clark et al. 2005

Sting jet is a transient mesoscale feature that occurs during the process of frontal fracture

Based primarily on one case study (October ’87 storm)

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Observational evidence

Browning 2004: October ’87 storm

Mesoanalysis IR imagery

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Climatological importance

Extracted from PhD thesis by Parton

Algorithm developed to extract mesoscale strong wind events from MST radar data – classified by structure and synoptic setting

9 potential sting jets passed over radar (in 7 years)

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Key features

• Mesoscale (~100 km) region of strong surface winds occurring in the most intense class of extratropical cyclones

• Occurs at the tip of the hooked cloud head• Distinct from warm and cold conveyor belt low level jets• Transient (~ few hours), possibly composed of multiple

circulations• Evaporative cooling of cloudy air and the release of

condition symmetric instability (a mixed gravitational/ inertial instability) hypothesized to be important

• Vertical transport of mass and momentum through boundary layer needed to yield surface wind gusts

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Project aims

• To determine the dominant mechanisms leading to sting jets

• To determine the environmental sensitivities of sting jets

• To develop diagnostics that can be used to predict the development of sting jets and the likelihood of the existence of a sting jet from synoptic-scale data

• To develop and analyse a climatology of sting jet events

• To explore the effect of climate change on sting jets

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Project tools

• Met Office numerical weather forecast model (Unified Model), used in case study and idealised modes

• Observational validation from satellite, radar (MST radar, Chilbolton radar, wind profilers) and surface station observations (radiosonde ascents).

• Climatological data from re-analyses datasets such as ERA-40.

• Trajectory analysis and diagnostic tools for CSI

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Project plan

Mechanisms

Diagnostics

Climatology

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Project plan

7 tasks, split between PDRA and PhD student

1. Detailed modelling of representative sting jets

2. Determination of the mechanisms leading to sting jets

3. Development of diagnostic parameters

4. Sting jet climatology

5. Configuration of a sting jet in an idealised model

6. Exploration of environmental parameter space of sting jets

7. Sting jets under future climate scenarios

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Example: 26 Feb 02 storm

Modelled boundary layer top winds

Modelled pseudo-IR satellite image

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Example: 26 Feb 02 storm

Observed surface wind gusts 12/15

Modelled surface wind gusts

Example: 26 Feb 02 storm

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Modelled ascending and descending sting jet branches.

Example: 26 Feb 02 storm

Conceptual pictureBrowning 2004

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Potential for collaboration with Willis

What we would like• To understand how storms are classified for insurance

risk and how windstorm models estimate risk• Climatological statistics (such as frequency and

distribution) of sting jets derived from insurance loss data

• Windspeed validation for specific events

What we can offer• Attributes of models that yield sting jets• Validated statistical data on sting jet storms• Attributes of storms that are likely to develop sting jets

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