Lee%20cyclogenesis%20in%20the%20(western)%20Mediterranean

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Lee cyclogenesis in the (western) Mediterranean

• Kristian Horvath, DHMZ
• horvath_at_cirus.dhz.hr

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Presenter

• Kristian Horvath, DHMZ
• PhD in 2008 Upper-level dynamics and lee
  cyclogenesis
• Postdoc 09/10 dynamical downscaling _at_ 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
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Contents

• A classification of cyclone activity in the
  Mediterranean
• Numerical analysis of MAP IOP 15 Genoa lee
  cyclogenesis
• Conclusions

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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

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Where do we find the highest number of cyclones
in the Mediterranean?
ALPS
Dinaric Alps
Pyrenees
Apennines
Balkan Mnt..
Turkish Mnt.
Atlas Mnt.
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Classification ERA-40 (125 km)
Selection criteria MSLP minimum
Trigo et al., 1999
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Classification ERA-40 (125 km)
Trigo et al., 1999
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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
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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
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Are thermal lows cyclones ? ?
Yes
No
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Are thermal lows cyclones ?

• Thermal lows are pressure lows which are
• stationary
• non-frontal
• with weak and diffuse cyclonic circulation

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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)

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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)

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Classification Type A Genoa cyclone

• Type A-I - continuous Type A-II -
  discontinuous

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Classification Type B Adriatic cyclone and
Type AB Twin (eyeglass) cyclone

• Adriatic (Type A-I, A-II) cyclone Twin
  cyclone (Type AB)

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Contents

• A classification of cyclone activity in the
  Mediterranean
• Numerical analysis of MAP IOP 15 Genoa lee
  cyclone
• Conclusions

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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

3. ICTP Conf., Trieste, Italy
DHMZ 17
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Lee cyclogenesis Introduction Theories

• Two main theories (linear, QG, Roltlt1)
• 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)

Smith
Speranza
Egger
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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

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Potential vorticity and waver-vapour analysis
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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 !
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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?

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Sensitivity to initial-analysis dynamical
uncertainties PV error statistics

• Statistics of the Ertels 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 !

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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
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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 gt 60 mm / 12 h
• Gale winds in the northern Adriatic (10-min
  average gt 25 ms-1, gusts gt 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

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Sensitivity to initial-analysis dynamical
uncertainties MAP IOP 15 Synoptic overview
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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 PVUgt1)
• Choice made 90th percentile to reflect the
  greatest possible dynamical initial-analysis
  errors
• Phase 157.5 km
• Amplitude 23
• gt 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

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Sensitivity to initial-analysis dynamical
uncertainties MAP IOP 15 Modifications of
initial conditions
7E
7N
-p1
p1
7S
7W
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Sensitivity to initial-analysis dynamical
uncertainties MAP IOP 15 Results MSLP

• The greatest spread of intensity (18 hPa) in the
  most intensive deepening phase

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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)

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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

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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
p1
7S
7W
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Sensitivity to initial-analysis dynamical
uncertainties MAP IOP 15 Results Bora

• Macroscale and mesoscale chains of events

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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?

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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

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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.

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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
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• 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

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THANK YOU !