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:
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–
–
–
–
•
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?
Balkan Mnt..
Turkish 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)
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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 ?
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Campins et al., 2006
9
Are thermal lows cyclones  ?
Yes
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No
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Are thermal lows cyclones ?
Thermal lows are pressure lows which are:
1. stationary
2. non-frontal
3. 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
A-I
A-II
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DJF
14
4
Type A-II - discontinuous
MAM
6
2
JJA
7
0
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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
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DJF
10
3
MAM
6
2
“Twin” cyclone (Type AB)
JJA
11
1
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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
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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
5 June 2012
Cyclone
week
2012Italy
3. ICTP
Conf.,
Trieste,
DHMZ
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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
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Speranza
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Smith
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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
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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 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 !
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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 > 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
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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 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
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Sensitivity to initial-analysis dynamical uncertainties:
MAP IOP 15: Modifications of initial conditions
7E
7N
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7W
7S
-p1
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+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
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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
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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
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Sensitivity to initial-analysis dynamical uncertainties:
MAP IOP 15: Results: Bora
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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
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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
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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
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7
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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 ± 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
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THANK YOU !
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