1 / 42

Sting Jets in severe Northern European Windstorms

Sting Jets in severe Northern European Windstorms. Suzanne Gray, Oscar Martinez-Alvarado, Laura Baker (Univ. of Reading), Peter Clark (collaborator, Met Office). June 2009. Outline. Review Severe Northern European windstorms. Currently identified sting jet cases Climatological importance

macon
Download Presentation

Sting Jets in severe Northern European Windstorms

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Sting Jets in severe Northern European Windstorms Suzanne Gray, Oscar Martinez-Alvarado, Laura Baker (Univ. of Reading), Peter Clark (collaborator, Met Office) June 2009

  2. Outline • Review • Severe Northern European windstorms. • Currently identified sting jet cases • Climatological importance • Mechanisms • A brief guide to conditional symmetric instability • Synthesis • Project aims and tools • New sting jet cases • Potential cases • Observations • Synoptic and mesoscale evolution • Mechanisms for sting jet development • Ongoing work • Towards a climatology of sting jet cyclones • Idealised modelling • Conclusions

  3. Outline • Review • Severe Northern European windstorms. • Currently identified sting jet cases • Climatological importance • Mechanisms • A brief guide to conditional symmetric instability • Synthesis • Project aims and tools • New sting jet cases • Potential cases • Observations • Synoptic and mesoscale evolution • Mechanisms for sting jet development • Ongoing work • Towards a climatology of sting jet cyclones • Idealised modelling • Conclusions

  4. Review – severe Northern European windstorms Browning (2004) Conceptual model of cyclone (undergoing transition from stage III to IV of Shapiro-Keyser evolution) showing principal air streams: • Warm conveyor-belt (W1, W2) • Cold conveyor-belt (CCB) • Dry intrusion

  5. Review – severe Northern European windstorms Shapiro and Keyser (1990) Insurance losses for extreme windstorms are significant: e.g. 3.4 billion Euro for the Christmas 1999 storms Lothar and Martin Some of the most damaging winds in extratropical cyclones are found in the dry slot of cyclones evolving according to the Shapiro-Keyser conceptual model. A recent series of papers has attributed these winds to a coherent mesoscale feature – a sting jet

  6. Review – existing cases : October 1987 storm, observations Mesoanalysis IR imagery Browning (2004)

  7. Review – existing cases : October 1987 storm, modelling Clark et al. (2005) Model system-relative 825hPa windspeed at 0300 UTC Pseudo-IR at 0300 UTC and system-relative track of the maximum descending trajectory.

  8. Review - existing cases :Windstorm Jeanette, observations Windspeed from MST radar IR satellite imagery Parton et al. (2009)

  9. Review - existing cases:Windstorm Jeanette, modelling MST radar wind fields overlaid by operational UM fields. Sting jet present in model fields due to assimilation of MST data. Enhanced UM synthesis showing sting jet, CCB, and dry intrusion. Parton et al. (2009)

  10. Review - climatological importance 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) Extracted from PhD thesis by Parton

  11. Review - mechanisms: evaporative cooling • Browning (1994) suggested that evaporation associated with slantwise convection could enhance the surface winds by • Intensifying the slantwise circulations and so amplifying the latent heat sources and sinks on the mesoscale • Reducing the static stability in the dry slot (where there is potential instability so leading to upright convection) and/or closer to the cloud head so leading to turbulent momentum transfer. Clark et al. (2005)

  12. Review – mechanisms: Conditional symmetric instability (CSI) • Browning (2004) noted that the multiple slantwise circulations inferred from banded cloud tops near the tip of the cloud head in the Oct. 87 storm are suggestive of CSI release. • Parton et al. (2009) found that the sting jet in windstorm Jeanette started at the tip of the region of CSI in the cloud head. Browning(2004) Parton et al. (2009)

  13. Review – a brief guide to CSI:theory • CSI is the due to the combination of inertial and conditional instability (gravitational instability) for air parcels displaced along a slantwise path. • It will only be released if the atmosphere is inertially stable to horizontal displacements and conditionally stable to vertical displacements. Morcrette (2004)

  14. Review – a brief guide to CSI:prevalence • Single and multi-banded clouds in frontal zones. • Trailing precipitation regions of mesoscale convective systems. • Hurricane eyewalls • Cloud heads in extratropical cyclones. Schultz and Schumacher (1999)

  15. Review – a brief guide to CSI:Diagnosis • SCAPE (slantwise convective available potential energy): large values of SCAPE indicate that CSI is present. • DSCAPE (downdraught SCAPE): large values indicate that CSI could be released by a descending air parcel. • MPV (moist potential vorticity): negative MPV in the absence of gravitational and inertial instability indicates regions of CSI. Schultz and Schumacher (1999)

  16. Review – synthesis: 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

  17. Review – synthesis: conceptual model Sting jet is a transient mesoscale feature that occurs during the process of frontal fracture Based primarily on one case study (October ’87 storm) Clark et al. (2005)

  18. Outline • Review • Severe Northern European windstorms. • Currently identified sting jet cases • Climatological importance • Mechanisms • A brief guide to conditional symmetric instability • Synthesis • Project aims and tools • New sting jet cases • Potential cases • Observations • Synoptic and mesoscale evolution • Mechanisms for sting jet development • Ongoing work • Towards a climatology of sting jet cyclones • Idealised modelling • Conclusions

  19. 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

  20. Project tools • (UK) Met Office operational numerical weather forecast model (Unified Model), used in case study and idealised modes • Case study configuration: limited area (North Atlantic European domain), 0.11o horizontal gridboxes, enhanced vertical resoution (76 levels), full physics, initial conditions from Met Office or ECMWF analyses. • Observational validation from satellite, radar (MST radar, Chilbolton radar, wind profilers) and surface station observations (radiosonde ascents). • Trajectory analysis and diagnostic tools for CSI • Climatological data from re-analyses datasets such as ERA-40.

  21. Outline • Review • Severe Northern European windstorms. • Currently identified sting jet cases • Climatological importance • Mechanisms • A brief guide to conditional symmetric instability • Synthesis • Project aims and tools • New sting jet cases • Potential cases • Observations • Synoptic and mesoscale evolution • Mechanisms for sting jet development • Ongoing work • Towards a climatology of sting jet cyclones • Idealised modelling • Conclusions

  22. New cases - potential cases Gudrun/Erwin 7th-9th January 2005 26th February 2002 Tilo: 7th/8th January 2007 11th January 2005 Kyrill 18th/19th January 2007 Klaus 23rd January 2009 .....

  23. New cases – observations:satellite A storm on 26th February 2002 Gudrun, 7th to 9th January 2005 IR satellite imagery (Shapiro-Keyser stage III)

  24. New cases – observations:Gudrun wind gusts • Gudrun/Erwin was a powerful windstorm that exhibited strong surface winds and gusts of over 40ms-1, and caused significant damage as it passed over land in the UK and Northern Europe.

  25. New cases – observations:26th February storm, wind gusts 0518 UTC 0300 0500 0700 0200 0700 0400 0800 0400 This storm passed over the UK during 25th to 26th February 2002 and was associated with strong winds over northern England and Wales, with wind gusts of over 40ms-1 recorded Observed surface wind gusts

  26. New cases – synoptic and mesoscale evolution Gudrun 04 UTC 8th January 07 UTC 26th February 2002 Top of boundary layer Earth-relative winds and midlevel relative humidity

  27. New cases – synopticand mesoscale evolution Gudrun 04 UTC 8th January 07 UTC 26th February 2002 Top of boundary layer system-relative winds and qw

  28. New cases – synopticand mesoscale evolution 07 UTC 26th February 2002 Gudrun 04 UTC 8th January UL Jet UL Jet CCB? CCB Sting Jet WCB WCB Sting Jet

  29. New cases – synopticand mesoscale evolution Back trajectories Gudrun 26th February 2002 Pressure evolution RH evolution

  30. New cases – synopticand mesoscale evolution 26th February 2002 Conceptual picture Browning (2004) Modelled ascending and descending sting jet branches.

  31. New cases – mechanisms: role of evaporational cooling Gudrun 26th February 2002 q evolution qw evolution

  32. New cases – mechanisms: role of CSI (SCAPE) Gudrun 18 UTC 7th January 22 UTC 25th February 2002 SCAPE (lifting from low-levels) prior to descent of sting jet with midlevel RH (cloud head) and low-level qw

  33. New cases – mechanisms: role of CSI (DSCAPE) Gudrun 23 UTC 7th January 04 UTC 26th February 2002 DSCAPE (DSCAPE maxima in sting jet region falling from level of sting jet trajectories) at onset of descent of sting jet with midlevel RH (cloud head) and low-level qw

  34. New cases – mechanisms: role of CSI (MPV) Gudrun 23 UTC 7th January 04 UTC 26th February 2002 MPV (at level of sting jet trajectories) at onset of descent of sting jet with midlevel RH (cloud head) and low-level qw

  35. New cases – mechanisms: role of CSI (MPV) Gudrun 7th/8th January 26th February 2002 MPV evolution

  36. New cases – mechanisms: role of CSI (MPV) Moist PV along trajectories 26th February 2002 Sting jet Pressure (hPa) Ascending branch PVU

  37. New cases – mechanisms : role of CSI (MPV) Moist PV along trajectories 26th February 2002 Pressure (hPa) PVU

  38. Outline • Review • Severe Northern European windstorms. • Currently identified sting jet cases • Climatological importance • Mechanisms • A brief guide to conditional symmetric instability • Synthesis • Project aims and tools • New sting jet cases • Potential cases • Observations • Synoptic and mesoscale evolution • Mechanisms for sting jet development • Ongoing work • Towards a climatology of sting jet cyclones • Idealised modelling • Conclusions

  39. Ongoing work – towards a sting jet climatology DSCAPE Sting jet DCAPE 26th February 2002 Global model (0.4o) Limited area model (0.11o)

  40. Ongoing work – idealised modelling: theory Polar jet stream Subtropical jet stream LC2 cyclonic shear cyclone: Norwegian frontal cyclone Shapiro et al. (1999) LC1 nonshear cyclone: Shapiro-Keyser frontal cyclone LC3 anticyclonic shear cyclone

  41. Ongoing work – idealised modelling: application qwat 850 mb Day 7 of baroclinic lifecycle 1 Surface pressure deviation from 1000 mb Limited area UM simulations: east-west periodic domain, wave-number 6 perturbations

  42. Conclusions • New sting jet cases have been presented that are consistent with the conceptual model developed from the two cases already published. • The new cases show some evidence of evaporational cooling occurring along the sting jet. • A detailed analysis of the role of CSI release has demonstrated its importance in generating slantwise descending motions from cloud level. This is a modification to the conceptual model of the sting jet as the slantwise descending branch of a circulation arising from the release of CSI by the ascending branch. • Ongoing work is examining potential diagnostics to develop a climatology of sting jet cases and sting jets in idealised baroclinic lifecycles.

More Related