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Lee cyclogenesis in the (western) Mediterranean

Lee cyclogenesis in the (western) Mediterranean. Kristian Horvath, DHMZ horvath @cirus.dhz.hr. Presenter. Kristian Horvath , DHMZ PhD in 2008 : U pper-level dynamics and lee cyclogenesis Postdoc 09/10 : dynam i cal downscaling @ DHMZ + Desert Research Institute, USA Areas of interest:

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Lee cyclogenesis in the (western) Mediterranean

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  1. Lee cyclogenesis in the (western) Mediterranean Kristian Horvath, DHMZ horvath@cirus.dhz.hr

  2. Presenter • Kristian Horvath, DHMZ • PhD in 2008: Upper-leveldynamics and lee cyclogenesis • Postdoc 09/10: dynamical downscaling @ DHMZ+Desert Research Institute, USA • Areas of interest: • Lee cyclogenesis and severe winds • Dynamical downscaling • Meteotsunamis • Data assimilation • Wind energy applications • http://radar.dhz.hr/~horvath International conference on Alpine meteorology, Chambery, France, 2007 Cyclone week 2012

  3. Contents • A classification of cyclone activity in the Mediterranean • Numerical analysis of MAP IOP 15 Genoa lee cyclogenesis • Conclusions Cyclone week 2012

  4. Classification: Introduction • Cyclonic activity over the Mediterranean strongly determines the weather and climate in the region • Extreme weather (severe winds, HPE) often associated with the cyclone existence in the Mediterranean • Existing classifications: • Synoptic: early subjective (even from 19th century) and objective • Mesoscale: still mostly subjective due to lack of mesoscale reanalysis Cyclone week 2012

  5. Where do we find the highest number of cyclones in the Mediterranean? ALPS Dinaric Alps Pyrenees Apennines Balkan Mnt.. Turkish Mnt. Atlas Mnt. Cyclone week 2012

  6. Classification: ERA-40 (~125 km) Selection criteria: MSLP minimum Trigo et al., 1999 Cyclone week 2012

  7. Classification: ERA-40 (~125 km) Trigo et al., 1999 Cyclone week 2012

  8. Classification: HIRLAM (~60 km) WINTER SUMMER Higher-resolution data: Increased number of cyclones New cyclogenetic areas Objective classifications are highly sensitive to criteria applied (factor of ~10, Gill et al., 2002) Campins et al., 2006 Cyclone week 2012

  9. Classification: HIRLAM (~60 km) DEEP SHALLOW Shallow summer cyclones (thermal lows)& deep winter cyclones Thermal lows are frequent, however, are these cyclones ? Campins et al., 2006 Cyclone week 2012

  10. Are thermal lows cyclones  ? Yes No Cyclone week 2012

  11. Are thermal lows cyclones ? • Thermal lows are pressure lows which are: • stationary • non-frontal • with weak and diffuse cyclonic circulation Cyclone week 2012

  12. Classification:meso-beta cyclones (20-200 km) • Synoptic classifications have contraints (e.g. effective model resolution is ~5dx) • For many areas in the Mediterranean, mesoscale classifications are essential • E.g., scales relevant for the Adriatic basin (~200 km) • Main challenges: • Mesoscale surface data nor high-resolution reanalysis (e.g. 10 km) not available • Scale and complex orography make objective algorithms extremely hard to design (e.g. mesolows are not cyclones) Cyclone week 2012

  13. Classification: Mesoscale methodology • ECMWF T511 long cut-off operational reanalysis (4 years, 6-hourly, ~40km) • Mesoscale objective analysis • 1. Cyclone criteria • MSLP minimum of 2 hPa • Closed circulation (streamlines) • 2. Definition of track types • Place of origin • Cyclone continuity over the Apennines (continuous or discontinuous) Cyclone week 2012

  14. Classification: Type A – Genoa cyclone • Type A-I - continuous Type A-II - discontinuous Cyclone week 2012

  15. Classification: Type B – Adriatic cyclone and Type AB – “Twin” (“eyeglass”) cyclone • Adriatic (Type A-I, A-II) cyclone “Twin” cyclone (Type AB) Cyclone week 2012

  16. Contents • A classification of cyclone activity in the Mediterranean • Numerical analysis of MAP IOP 15 Genoa lee cyclone • Conclusions Cyclone week 2012

  17. Sensitivity to initial-analysis dynamical uncertainties Alpine lee or Genoa cyclones are one of the most frequent cyclones in the mid-latitudes Genoa cyclone occurs in association with a pre-existing cyclone and synoptic upper-level trough in 2 phases (BT1978, BM1982): Rapid formation of a shallow cyclone due to frontal retardation Further less-rapid deepening due to baroclinic interaction with the upper-level trough and extraction of energy from the mean flow Cyclone week 2012 3. ICTP Conf., Trieste, Italy DHMZ 17

  18. Lee cyclogenesis: Introduction: Theories • Two main theories (linear, QG, Ro<<1): • Baroclinic lee wave (Smith 1984) • Orographic modification of baroclinic instability (SBTM 1985) • Numerical test: (excessive) violation of linearity and balanced dynamics in the first phase (Egger, 1988) Speranza Egger Smith Cyclone week 2012

  19. Lee cyclogenesis: Introduction: Potential vorticity approach Review by Hoskins et al., 1985) • Potential vorticity (PV) • “PV thinking” • Conservation of PV • Invertibility principle • Application to understanding of lee cyclogenesis Cyclone week 2012

  20. Potential vorticity and waver-vapour analysis Cyclone week 2012

  21. Potential vorticity and waver-vapour analysis Large moisture gradient Wave-vapor imagery can be used also to detect discrepancies between the observations and the numerical model results ! Cyclone week 2012

  22. Sensitivity to initial-analysis dynamical uncertainties • The key roles in formation of Genoa cyclones is due to the Alpine orography and the upper-level trough • The predictability depends mainly on the features of the upper-level trough • Q1: how to estimate the realistic initial-analysis dynamical uncertainties in the upper-levels? • Q2: what is the influence of these uncertainties to the development of Genoa lee cyclone? Cyclone week 2012

  23. Sensitivity to initial-analysis dynamical uncertainties: PV error statistics • Statistics of the Ertel’s PV (ErPV) • calculated through the differences in the ECMWF and NCEP reanalysis • 21 case of the deepest Mediterranean cyclones (1996-2006) • Statistics methodology • Phase/displacement error (km) evaluated on the basis of maximum correlation between mesoscale “cores” of the upper-level ErPV • Amplitude/intensity error ( f(ErPV), %) based on the ErPV fields with “subtracted” phase error • Since PV can be traced from the satellite imagery, the error statistics could be calculated by using satellite data ! Cyclone week 2012

  24. Sensitivity to initial-analysis dynamical uncertainties: PV error statistics • phase (displ.) and amplitude (intensity) errors at 300 hPa Extreme errors close to 150 km Average errors close to 50 km Cyclone week 2012

  25. Sensitivity to initial-analysis dynamical uncertainties: MAP IOP 15: Introduction • Deep and rapid Genoa lee cyclone 06-10 November 1999 (MAP IOP 15) • Extreme weather conditions: • Heavy rain in the northern Italy > 60 mm / 12 h • Gale winds in the northern Adriatic (10-min average > 25 ms-1, gusts > 40 ms-1) • MM5 mesoscale model at 2.5 km and 35 vertical levels driven with ECMWF T511 analysis • Parameterizations: Kain-Fritsch 2 CPS, MRF PBL, Reisner 2 microphysics Cyclone week 2012

  26. Sensitivity to initial-analysis dynamical uncertainties: MAP IOP 15: Synoptic overview Cyclone week 2012

  27. Sensitivity to initial-analysis dynamical uncertainties: MAP IOP 15: Modification of the initial conditions • Macroscale modifications of the upper-level dynamics only (PV error integrated over 500-100 hPa for PVU>1) • Choice made: 90th percentile to reflect the greatest possible dynamical initial-analysis errors • Phase – 157.5 km • Amplitude – 23 % • => application to the MAP IOP 15 upper-level trough: • Moving the trough to the E, W, N and S • Increase and decrease the trough intensity Cyclone week 2012

  28. Sensitivity to initial-analysis dynamical uncertainties: MAP IOP 15: Modifications of initial conditions 7E 7N -p1 Cyclone week 2012 7W 7S +p1

  29. Sensitivity to initial-analysis dynamical uncertainties: MAP IOP 15: Results: MSLP • The greatest spread of intensity (18 hPa) in the most intensive deepening phase Cyclone week 2012

  30. Sensitivity to initial-analysis dynamical uncertainties: MAP IOP 15: Results: cyclone tracks • Initial increase of the spread of cyclone tracks (~250 km) • The highest spread of tracks in mature phase (~750km) Cyclone week 2012

  31. Sensitivity to initial-analysis dynamical uncertainties: MAP IOP 15: Results: cyclone tracks Strengthened PV Weakened PV Cyclone centre Cyclone centre • The spread of tracks in the initial phase due to changes of the background flow (non-)linearity Cyclone week 2012

  32. Sensitivity to initial-analysis dynamical uncertainties: MAP IOP 15: Results: cyclone tracks • The spread of tracks in the mature phase due to differing upper-level dynamics (“cut-off”) 7E 7N -p1 Cyclone week 2012 7W 7S +p1

  33. Sensitivity to initial-analysis dynamical uncertainties: MAP IOP 15: Results: Bora • Macroscale and mesoscale chains of events Cyclone week 2012

  34. Sensitivity to initial-analysis dynamical uncertainties: MAP IOP 15: Results: Bora • Bora strength (± 30%) depends on the intensity and position of the cyclone • However, “details” strongly differ (-p1,7W) • Q: what is the influence of the initial-analysis uncertainties to the background flow impinging on the Dinaric Alps? Cyclone week 2012

  35. Sensitivity study: MAP IOP 15: Bora • Charactersitics of the background flow investigated through the analysis of: • Scorer parameter • variations in synoptically induced critical levels • Froude number • variations in flow regimes Cyclone week 2012

  36. Conclusions: Classification of Mediterranean cyclones • Main cyclogenetic areas in the Mediterranean are near the mountains such as the Alps, the Atlas, the Apennines, the Balkan mnts etc. • Two main types of cyclones in the Mediterranean: • Deep winter cyclones (mostly lee cyclones) • Shallow summer cyclones (mostly thermal lows) • Meso-beta cyclones hardly identified in global reanalysis may be equally frequent as the larger-scale cyclones • Special cyclone types do exist – e.g. discontinuous cyclones, twin cyclones, rotational twin cyclones etc. Cyclone week 2012

  37. Conclusions: numerical analysis of lee cyclogenesis • Large sensitivity of Genoa cyclone to upper-level trough details for: • Intensity: in the most rapid deepening phase (18 hPa) • Track: in the late mature phase (750 km) • The sensitivity of Bora wind strength to initial-analysis dynamical uncertainties equals ± 30% • The water vapour satellite imagery is useful for analysis of the upper-level dynamical processes (troughs, jet streaks) • Satellite products may provide the realistic potential vorticity error estimates important for everyday probabilistic NWP Cyclone week 2012

  38. THANK YOU ! Cyclone week 2012

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