lee cyclogenesis in the (western) mediterranean

Lee cyclogenesis in the (western) Mediterranean

Kristian Horvath, DHMZ

[email protected]

5 June 2012 Cyclone week 2012 2

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/~horvathInternational conference on Alpine meteorology, Chambery, France, 2007


Contents

• A classification of cyclone activity in the Mediterranean

• Numerical analysis of MAP IOP 15 Genoa lee cyclogenesis

• Conclusions


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


Where do we find the highest number of cyclones in the Mediterranean?

ALPS

Pyrenees

Atlas Mnt.

Dinaric Alps

ApenninesBalkan Mnt..

Turkish Mnt.


Classification: ERA-40 (~125 km)

Trigo et al., 1999

Selection criteria:MSLP minimum


Classification: ERA-40 (~125 km)

Trigo et al., 1999


Classification: HIRLAM (~60 km)

Campins et al., 2006Higher-resolution data:Increased number of cyclonesNew cyclogenetic areasObjective classifications are highly sensitive to criteria applied (factor of ~10, Gill et al., 2002)

SUMMER WINTER


Classification: HIRLAM (~60 km)

Campins et al., 2006

SHALLOW DEEP

Shallow summer cyclones (thermal lows) & deep winter cyclones

Thermal lows are frequent, however, are these cyclones ?


Are thermal lows cyclones ?

Yes No


Are thermal lows cyclones ?

Thermal lows are pressure lows which are:1. stationary 2. non-frontal 3. with weak and diffuse cyclonic circulation


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)


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)


Classification: Type A – Genoa cyclone

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

DJF MAM JJA SON TOTALA-I 14 6 7 8 35A-II 4 2 0 4 10


Classification: Type B – Adriatic cyclone and Type AB – “Twin” (“eyeglass”) cyclone

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

DJF MAM JJA SON TOTALB 10 6 11 7 34

AB 3 2 1 2 8


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 173. ICTP Conf., Trieste, Italy DHMZ 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


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)

SmithSperanzaEgger


Lee cyclogenesis: Introduction: Potential vorticity approach

• Potential vorticity (PV)

• “PV thinking”– Conservation of PV– Invertibility principle

• Application to understanding of lee cyclogenesis

)(1

fq

Review by Hoskins et al., 1985)


Potential vorticity and waver-vapour analysis


Potential vorticity and waver-vapour analysis

Wave-vapor imagery can be used also to detect discrepancies between the observations and the numerical model results !

Large moisture gradient


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?


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 !


Sensitivity to initial-analysis dynamical uncertainties: PV error statistics

• phase (displ.) and amplitude (intensity) errors at 300 hPa

Extreme errorsclose to 150 km

Average errorsclose to 50 km


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


Sensitivity to initial-analysis dynamical uncertainties: MAP IOP 15: Synoptic overview


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


Sensitivity to initial-analysis dynamical uncertainties: MAP IOP 15: Modifications of initial conditions

7E

+p17S7W

7N -p1


Sensitivity to initial-analysis dynamical uncertainties: MAP IOP 15: Results: MSLP

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

985

990

995

10001005

1010

1015

1020

1025

6 6,5 7 7,5 8 8,5 9

day

MS

LP

[h

Pa

]con

7E

7N

7S

7W

-p1

+p1


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)



• The spread of tracks in the initial phase due to changes of the background flow (non-)linearity

Cyclone centre Cyclone centre

Strengthened PVWeakened PV



• The spread of tracks in the mature phase due to differing upper-level dynamics (“cut-off”)

7E

+p17S7W

7N -p1


Sensitivity to initial-analysis dynamical uncertainties: MAP IOP 15: Results: Bora

• Macroscale and mesoscale chains of events


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?

0

5

10

15

20

25

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35

7,25 7,5 7,75 8 8,25 8,5 8,75 9

dayw

ind

sp

eed

[m

/s]

986

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1002

1006

1010

1014

1018

1022

1026

1030

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LP

[h

Pa

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con 7E 7N 7S 7W -p1 +p1


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

500

600

700

800

900

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0 2 4 6 8

12 UTC 08 Nov, l [1000/m]

p [

hP

a]

con

7E

7N

7S

7W

-p1

+p1

500

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03 UTC 8 Nov, l [1000/m]

p [

hP

a]


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.


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


THANK YOU !

lee cyclogenesis in the (western) mediterranean

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