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Conditional symmetric instability and the development of sting jets

European Meteorological Society Annual Meeting 29 September – 03 October 2008 Amsterdam, The Netherlands. Conditional symmetric instability and the development of sting jets. Oscar Martinez-Alvarado (O.MartinezAlvarado@reading.ac.uk) Sue Gray Laura Baker Department of Meteorology

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Conditional symmetric instability and the development of sting jets

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  1. European Meteorological Society Annual Meeting 29 September – 03 October 2008 Amsterdam, The Netherlands Conditional symmetric instability and the development of sting jets Oscar Martinez-Alvarado (O.MartinezAlvarado@reading.ac.uk) Sue Gray Laura Baker Department of Meteorology University of Reading

  2. Extratropical cyclones:Shapiro-Keyser model CCB CCB CCB CCB WCB WCB WCB WCB I II III IV • Extratropical cyclones carry with them the potential of causing catastrophic damage to both life and property. • Regions of strong winds at low levels • Warm conveyor belt (WCB) • Cold conveyor belt (CCB) CSI and Sting Jets – Contact: O.MartinezAlvarado@reading.ac.uk

  3. Sting Jets CCB • Able to generate highly damaging winds of more than 100 km/h • Mesoscale (~100 km) region of strong surface winds occurring in rapidly deepening extratropical cyclones • Transient (~ few hours), possibly composed of multiple circulations • Occur at the tip of the hooked cloud head WCB III CSI and Sting Jets – Contact: O.MartinezAlvarado@reading.ac.uk

  4. Sting Jets • Mechanisms hypothesized to be important: • Evaporative cooling of cloudy air, and • The release of conditional symmetric instability(CSI) • Vertical transport of mass and momentum through boundary layer needed to yield surface wind gusts CSI and Sting Jets – Contact: O.MartinezAlvarado@reading.ac.uk

  5. Conditionalsymmetric instability • A combination of gravitational and inertial instabilities in a moist atmosphere • Leads to slantwise convective circulations • Diagnosed by (Schultz and Schumacher, 1999) • Mg – q*e relationship • Negative geostrophic moist potential vorticity (MPVg) • Slantwise convective available potential energy (SCAPE) Mg increasing qe* increasing CSI and Sting Jets – Contact: O.MartinezAlvarado@reading.ac.uk

  6. Objective • To determine the importance of conditional symmetric instability as a mechanism leading to sting jets CSI and Sting Jets – Contact: O.MartinezAlvarado@reading.ac.uk

  7. Case study: A storm in February 2002 • Case Identified from climatology study over 7 years of MST radar data (Parton, 2007) 0300 0500 0700 0200 0700 0400 0800 0400 Source: Met Office website CSI and Sting Jets – Contact: O.MartinezAlvarado@reading.ac.uk

  8. Numerical simulation • UK Met Office Unified Model version 6.1 • 0.11˚ (equivalent to 12 km) horizontal resolution • Enhanced vertical resolution (76 levels) • Initial time: 1200 UT on 25/02/2002 • Initial conditions from ECMWF operational analysis data interpolated to the model resolution CSI and Sting Jets – Contact: O.MartinezAlvarado@reading.ac.uk

  9. Searching for sting jets • Wind strength > 35 m/s • Relative humidity > 80 % • Vertical velocity < -0.05 m/s • Lagrangian backward trajectories CSI and Sting Jets – Contact: O.MartinezAlvarado@reading.ac.uk

  10. A sting jet in thestorm in February 2002 m/s Wind strength at the top of the boundary layer CSI and Sting Jets – Contact: O.MartinezAlvarado@reading.ac.uk

  11. A sting jet in the storm in February 2002 m/s Model-derived surface wind gusts CSI and Sting Jets – Contact: O.MartinezAlvarado@reading.ac.uk

  12. Sting Jets and CSI:Conceptual picture Ascending Browning (2004) Descending CSI and Sting Jets – Contact: O.MartinezAlvarado@reading.ac.uk

  13. Sting Jets and CSI Moist PV along trajectories Sting jet Pressure (hPa) Ascending branch PVU CSI and Sting Jets – Contact: O.MartinezAlvarado@reading.ac.uk

  14. Sting Jets and CSI Moist PV along trajectories Pressure (hPa) PVU CSI and Sting Jets – Contact: O.MartinezAlvarado@reading.ac.uk

  15. Sting Jets and CSI Cloud contour SCAPE J/kg CAPE contours Frontal zone Ascending air CSI and Sting Jets – Contact: O.MartinezAlvarado@reading.ac.uk

  16. Sting Jets and CSI SCAPE J/kg CSI and Sting Jets – Contact: O.MartinezAlvarado@reading.ac.uk

  17. Conclusions • A sting jet was identified in the case study • It is likely this was responsible for part of the strong gusts recorded at the surface • The presence of CSI around the region of occurrence has been verified using two alternative methods • Positive SCAPE • Regions of negative moist PV • Non-zero CAPE is also present in the same regions • Circulations are possibly due to the release of a combination of moist gravitational and moist symmetric instabilities CSI and Sting Jets – Contact: O.MartinezAlvarado@reading.ac.uk

  18. References • Browning, K. A., 2004: The sting at the end of the tail: Damaging winds associated with extratropical cyclones. Q. J. R. Meteorol. Soc., 130, 375-399. • Parton, G. A., 2007: Observation and interpretation of strong winds in the mid-troposphere. PhD thesis, University of Manchester. • Schultz, D. A. and P. N. Schumacher, 1999: The use and misuse of conditional symmetric instability. Mon. Wea. Rev., 127, 2709-2732. CSI and Sting Jets – Contact: O.MartinezAlvarado@reading.ac.uk

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