Identification of sting-jet extratropical cyclones in ERA-Interim Oscar Martinez-Alvarado Suzanne Gray Department of Meteorology University of Reading EGU General Assembly May 2010 Vienna, Austria

Sting Jets Jet descending from mid- troposphere from the tip of the hooked cloud head Located in the frontal fracture region Mesoscale (~100 km) region of strong surface winds (that can reach more than 100 km/h) occurring in rapidly deepening extratropical cyclones Transient (~ few hours), possibly composed of multiple circulations 2 Sting-jet cyclones in ERA-Interim– Contact: Shapiro-Keyser cyclogenesis Stage III Adapted from Clark et al. (2005)

Sting Jets Case-studies Mechanisms hypothesized to be important: –Evaporative cooling of cloudy air, and –The release of conditional symmetric instability (CSI) Global frequency and distribution are unknown 3 Great Storm15/16 October 1987UK Browning 2004; Clark et al Anna25/26 February 2002 UK Martinez-Alvarado et al Jeanette27 October 2002UK Parton et al Oili07-11 February 2006 UK, Germany Weidle and Wernli 2008 Gudrun07/08 January 2007UK, N. Europe Baker 2009 Sting-jet cyclones in ERA-Interim– Contact:

There are just a handful of well-documented case studies on sting jets (Browning 2004, Clark et al. 2005, Parton et al. 2009, Baker 2009). These are valuable for all the detailed insight they provide into the structure and dynamics of sting jets. However, they cannot answer the question of how frequently sting jets occur. Another unanswered question is what other regions (apart from the UK and N. Europe) are likely to experience sting jets. The need for a climatology of sting jets 4 Sting-jet cyclones in ERA-Interim– Contact:

5 Unstable slantwise convective circulations in an otherwise inertially and gravitationally stable atmosphere Downdraught SCAPE (DSCAPE) is the potential energy available to parcel to descend in slanted downdraughts CSI and Downdraught SCAPE  e * increasing M g increasing Sting-jet cyclones in ERA-Interim– Contact:

Storm Anna: Synoptic situation 6 Synoptic situation at 0700 UTC on 26 February The bold grey line represents the edge of the cloud head. The red circle marks the position of the sting jet at each time. Sting-jet cyclones in ERA-Interim– Contact:

Storm Anna: Downdraught SCAPE 7 Downdraught SCAPE (DSCAPE, in J/kg) at (A) 0100 UTC and (B) 0300 UTC on 26 February The bold dark line represents the edge of the cloud head; the grey lines are lines of constant wet-bulb potential temperature (in K). The red circle marks the position of the sting jet at each time. AB Sting-jet cyclones in ERA-Interim– Contact:

Minimum DSCAPE descending from the mid-troposphere –DSCAPE > 200 J kg -1 Search restricted to upper levels –p start < 650 hPa Moisture needed to precipitate over unstable areas with large DSCAPE –RH > 80 % Location within a fractured cold front Threshold values appear to be robust for a number of cases A climatology of sting jets 8 Sting-jet cyclones in ERA-Interim– Contact:

ERA-Interim is the new ECMWF reanalysis covering the period 1989-present Resolution: ~0.7° This work looks at fields on pressure levels Domain limited to 30°N - 70°N, 70°W - 30°E (North Atlantic and Europe) 50 most intense cyclones during the first ten years in the reanalysis ( ). Thanks to Jen Catto for kindly providing these cyclone tracks. Only winter months (DJF) A climatology of sting jets using ERA-Interim 9 Sting-jet cyclones in ERA-Interim– Contact:

10 Sting Jet Cyclones in ERA-Interim: Track 39 Mid-tropospheric CSI regions near (red circles) or far from (green circles) cyclone. Grey: wet-bulb potential temperature at 600 hPa. Blue: RH at 550 hPa. RH at 550 hPa  w at 600 hPa Instability region Sting-jet cyclones in ERA-Interim– Contact:

Sting Jet Cyclones in ERA-Interim: Track Mid-tropospheric CSI regions near (red circles) or far from (green circles) cyclone. Grey: wet-bulb potential temperature at 600 hPa. Blue: RH at 550 hPa. Sting-jet cyclones in ERA-Interim– Contact:

From the 50 most intense cyclones: ~29 show CSI in the vicinity of the cyclone centre ~8 show the potential to develop sting jets. ~16 cyclones show instability regions associated with the warm conveyor belt 12 Sting Jet Cyclones in ERA-Interim: Preliminary results Dec 1989 Dec 1991Jan 1992 Jan 1993Dec 1995Feb 1996Feb 1997 Sting-jet cyclones in ERA-Interim– Contact:

Limitations and possible ways forward A missing link: surface observations (how much surface damage have sting jets actually caused?) The small number of cases found in these years in ERA-Interim will allow us to look into them in detail (in mesoscale simulations) Ongoing work is to extend the period of analysis to the full ERA-Interim period, and to the rest of the extra- tropical region. 13 Sting-jet cyclones in ERA-Interim– Contact:

Conclusions Mid-tropospheric regions of CSI have been shown to be very well spatially correlated with descending sting jets in mesoscale simulations of 3 sting jet storms (and are not present in a storm without a sting jet). A DSCAPE-based method to detect sting jet precursors has been developed and has started to give results. This method is being currently applied to the ECMWF reanalysis ERA-Interim. In the first 10 years of the dataset 8 out of 50 most intense cyclones show signs of mid-tropospheric CSI. The occurrence of sting jets in these cyclones is still awaiting verification. 14 Sting-jet cyclones in ERA-Interim– Contact:

Other sting-jet presentations in EGU 2010 Sting jets in severe northern European wind storms: a case study of Windstorm Gudrun Laura Baker, Suzanne Gray, and Peter Clark NH1.7/AS4.10 Extreme events induced by extreme weather and climate change: Evaluation and forecasting of disaster risk and proactive planning Room 3 / Mon, 03 May, 9:00–09:15 Idealised simulations of sting jet cyclones Laura Baker, Suzanne Gray, and Peter Clark AS1.1Dynamical Meteorology (General Session) Halls X/Y / Thu, 06 May, 08:00–19:30 XY13 15 Sting-jet cyclones in ERA-Interim– Contact:

References 1.Baker, L., 2009: Sting jets in severe northern European wind storms. Weather, 64 (6), Browning, K. A., 2004: The sting at the end of the tail: Damaging winds associated with extratropical cyclones. Q. J. R. Meteorol. Soc., 130, Clark, P. A., K. A. Browning and C. Wang, 2005: The sting jet at the end of the tail: Model diagnostics of fine-scale three-dimensional structure of the cloud head, Q. J. R. Meteorol. Soc., 131, Martinez-Alvarado, O., F. Weidle and S. L. Gray, 2010: Robust characteristics of sting jets as simulated by two mesoscale models, Re- submitted to Mon. Wea. Rev.. 5.Parton, G. A., G. Vaughan, E. G. Norton, K. A. Browning and P. A. Clark, 2009: Wind profiler observations of a sting jet. Q. J. R. Meteorol. Soc., 135 (640), Schultz, D. A. and P. N. Schumacher, 1999: The use and misuse of conditional symmetric instability. Mon. Wea. Rev., 127, Sting-jet cyclones in ERA-Interim– Contact: