© University of Reading 2007www.reading.ac.uk Sting Jets in severe Northern European Windstoms Suzanne 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 2/15

Conceptual model Clark et al Sting jet is a transient mesoscale feature that occurs during the process of frontal fracture Based primarily on one case study (October 87 storm) 3/15

Observational evidence Browning 2004: October 87 storm MesoanalysisIR imagery 4/15

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) 5/15

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 6/15

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 7/15

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 8/15

Project plan Mechanisms DiagnosticsClimatology 9/14

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 10/15

Example: 26 Feb 02 storm Modelled boundary layer top winds Modelled pseudo-IR satellite image 11/15

Example: 26 Feb 02 storm Observed surface wind gusts 12/15

Modelled surface wind gusts Example: 26 Feb 02 storm 13/15

Modelled ascending and descending sting jet branches. Example: 26 Feb 02 storm Conceptual picture Browning /15

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 15/15