Lee cyclogenesis in the (western) Mediterranean Kristian Horvath, DHMZ horvath@cirus.dhz.hr Presenter • • • • Kristian Horvath, DHMZ PhD in 2008: Upper-level dynamics 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 5 June 2012 Cyclone week 2012 2 Contents • A classification of cyclone activity in the Mediterranean • Numerical analysis of MAP IOP 15 Genoa lee cyclogenesis • Conclusions 5 June 2012 Cyclone week 2012 3 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 5 June 2012 Cyclone week 2012 4 Where do we find the highest number of cyclones in the Mediterranean? Balkan Mnt.. Turkish Mnt. 5 June 2012 Cyclone week 2012 5 Classification: ERA-40 (~125 km) Selection criteria: MSLP minimum Trigo et al., 1999 5 June 2012 Cyclone week 2012 6 Classification: ERA-40 (~125 km) Trigo et al., 1999 5 June 2012 Cyclone week 2012 7 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) 5 June 2012 Cyclone week 2012 Campins et al., 2006 8 Classification: HIRLAM (~60 km) DEEP SHALLOW Shallow summer cyclones (thermal lows) & deep winter cyclones Thermal lows are frequent, however, are these cyclones ? 5 June 2012 Cyclone week 2012 Campins et al., 2006 9 Are thermal lows cyclones ? Yes 5 June 2012 No Cyclone week 2012 10 Are thermal lows cyclones ? Thermal lows are pressure lows which are: 1. stationary 2. non-frontal 3. with weak and diffuse cyclonic circulation 5 June 2012 Cyclone week 2012 11 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) 5 June 2012 Cyclone week 2012 12 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) 5 June 2012 Cyclone week 2012 13 Classification: Type A – Genoa cyclone • Type A-I - continuous A-I A-II 5 June 2012 DJF 14 4 Type A-II - discontinuous MAM 6 2 JJA 7 0 Cyclone week 2012 SON 8 4 TOTAL 35 10 14 Classification: Type B – Adriatic cyclone and Type AB – “Twin” (“eyeglass”) cyclone • Adriatic (Type A-I, A-II) cyclone B AB 5 June 2012 DJF 10 3 MAM 6 2 “Twin” cyclone (Type AB) JJA 11 1 Cyclone week 2012 SON 7 2 TOTAL 34 8 15 Contents • A classification of cyclone activity in the Mediterranean • Numerical analysis of MAP IOP 15 Genoa lee cyclone • Conclusions 5 June 2012 Cyclone week 2012 16 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 5 June 2012 Cyclone week 2012Italy 3. ICTP Conf., Trieste, DHMZ 17 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) Egger 5 June 2012 Speranza Cyclone week 2012 Smith 18 Lee cyclogenesis: Introduction: Potential vorticity approach Review by Hoskins et al., 1985) • Potential vorticity (PV) q 1 ( f ) • “PV thinking” – Conservation of PV – Invertibility principle • Application to understanding of lee cyclogenesis 5 June 2012 Cyclone week 2012 19 Potential vorticity and waver-vapour analysis 5 June 2012 Cyclone week 2012 20 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 ! 5 June 2012 Cyclone week 2012 21 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? 5 June 2012 Cyclone week 2012 22 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 upperlevel 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 ! 5 June 2012 Cyclone week 2012 23 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 5 June 2012 Cyclone week 2012 24 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 5 June 2012 Cyclone week 2012 25 Sensitivity to initial-analysis dynamical uncertainties: MAP IOP 15: Synoptic overview 5 June 2012 Cyclone week 2012 26 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 5 June 2012 Cyclone week 2012 27 Sensitivity to initial-analysis dynamical uncertainties: MAP IOP 15: Modifications of initial conditions 7E 7N 5 June 2012 7W 7S -p1 Cyclone week 2012 +p1 28 MSLP [hPa] Sensitivity to initial-analysis dynamical uncertainties: MAP IOP 15: Results: MSLP 1025 1020 1015 1010 1005 1000 995 990 985 con 7E 7N 7S 7W -p1 +p1 6 6,5 7 7,5 8 8,5 9 day • The greatest spread of intensity (18 hPa) in the most intensive deepening phase 5 June 2012 Cyclone week 2012 29 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) 5 June 2012 Cyclone week 2012 30 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 5 June 2012 Cyclone week 2012 31 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 5 June 2012 7W 7N -p1 7SCyclone week 2012 +p1 32 Sensitivity to initial-analysis dynamical uncertainties: MAP IOP 15: Results: Bora • Macroscale and mesoscale chains of events 5 June 2012 Cyclone week 2012 33 Sensitivity to initial-analysis dynamical uncertainties: MAP IOP 15: Results: Bora 5 June 2012 con 7E 7N 7S 7W -p1 +p1 35 1030 1026 30 1022 1018 25 1014 20 1010 1006 15 1002 10 998 994 5 990 0 7,25 Cyclone week 2012 986 7,5 7,75 8 8,25 8,5 8,75 9 day 34 MSLP [hPa] wind speed [m/s] • 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? Sensitivity study: MAP IOP 15: Bora • Charactersitics of the background flow investigated through the analysis of: • Scorer parameter • Froude number – variations in synoptically induced critical levels 03 UTC 8 Nov, l [1000/m] 0 2 4 6 – variations in flow regimes 12 UTC 08 Nov, l [1000/m] 8 500 0 2 4 6 03UTC_h=1300m 8 12UTC_1300m 500 3,5 800 900 5 June 2012 1000 700 800 900 1000 con 7E 7N 7S 7W -p1 +p1 2,5 2 ĥ 700 EXP 1 con 2 -p1 3 +p1 4 7E 5 7N 6 7S 7 7W 3 600 p [hPa] p [hPa] 600 1,5 1 0,5 0 Cyclone week 20121 2 3 4 experiment 5 6 7 35 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. 5 June 2012 Cyclone week 2012 36 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 5 June 2012 Cyclone week 2012 37 THANK YOU ! 5 June 2012 Cyclone week 2012 38