zentralanstalt für meteorologie und geodynamik basic investigation of symmetric instability during...
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Zentralanstalt für Meteorologie und Geodynamik
BASIC INVESTIGATION OF SYMMETRIC INSTABILITY DURING CONVECTIVE INITITATION IN THE ALPINE REGION
Thomas Krennert, [email protected], Central Institute of Meteorology and Geodynamics, Vienna, Austria
Forecasting
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THOMAS KRENNERTSYMMETRIC INSTABILITIES DURING CONVECTIVE INITIATION
During the warm season
Estimation: about 40% of all convective events in the eastern Alpine region can be related to air mass convection (pulse convection)
Widespread gravitational (conditional) instability (500 < CAPE < 2500 J/kg)
Sufficient moisture for initial shallow convection over mountainous regions
Due to entrainment, CIN, lack of sufficient availability of ingredients,further development from shallow convective cells towards DMC
would often be disabled
INTRODUCTION
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THOMAS KRENNERTSYMMETRIC INSTABILITIES DURING CONVECTIVE INITIATION
indicators of the existence of symmetric instabilities in the area prone to deep moist convection:
negative Equivalent Potential Vorticity EPV (MPV – moist potential) Symmetric Convective Available Potential Energy SCAPE
upper level moisture gradients mark zones with increasing vertical shear and deformation.
Discuss with case study of the 28 July 2005
INTRODUCTION CONTD.
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THOMAS KRENNERTSYMMETRIC INSTABILITIES DURING CONVECTIVE INITIATION
Schultz and Schumacher (1999), Fantini et al. (2011): convection can possess characteristics of slantwise convection,
gravitational convection, or both Coexistence of: CSI/PSI, CI/PI, adequate moisture / lift
Hoskins (1974), Mc Cann (1995): Mg – θ relationship for dry symmetric instability is equivalent to
geostrophic potential vorticity PVg
Limitations: identifying regions with PVg / EPVg might also indicate PI / CI and
gravitational convection
REVIEW: CHARACTERISTICS 1
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THOMAS KRENNERTSYMMETRIC INSTABILITIES DURING CONVECTIVE INITIATION
Santurette, Georgiev, 2005 moisture gradients mark zones of increased wind speed unidirectional wind shear gradient of equivalent potential temperature
Xu, 1986a “Upscale development” most likely occurrence : outside of frontal regions,
absence of synoptic-scale air mass boundaries
Jascourt et al. (1988): nature and organization of convection can be modulated
by the symmetric stability
REVIEW: CHARACTERISTICS 2
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THOMAS KRENNERTSYMMETRIC INSTABILITIES DURING CONVECTIVE INITIATIONCASE STUDY: 28 July 2005, 1100 UTC, MSG RGB Image composite
IR 8.7µ (red)/ WV 7.3µ(green) / WV 6.2µ(blue)
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THOMAS KRENNERTSYMMETRIC INSTABILITIES DURING CONVECTIVE INITIATIONCASE STUDY: 28 July 2005, 1100 UTC, MSG RGB Image loop
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THOMAS KRENNERTSYMMETRIC INSTABILITIES DURING CONVECTIVE INITIATION
28 July 2005, 1200 UTC, Eqivalent (Moist) Potential Vorticity, EPV [ |-5| (blue) – |-30| (red) 10-6 K*m2/kg*sec, increment 0,3] , 850 – 500 hPa, WRF-model
Negative EPV indicates areas of symmetric instability SI (Schultz, Knox, 2007)
Saturated buoyant air parcel reaches a zone of distinct negative EPVg A possible release of SI slantwise supports convective lift (cms-1) Provides sufficient lift for the air parcel to reach LFC?
INDICATIONS FOR SI: EPV
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THOMAS KRENNERTSYMMETRIC INSTABILITIES DURING CONVECTIVE INITIATION
28 July 2005, 1200 UTC, Symmetric Available Potential Energy,
SCAPE [500 (blue) – 3000 (red) J/kg, increment 30] , above 950 hPa,
WRF-model
SCAPE indicates the potential for symmetric instability (calculated after Dixon, 2000)
INDICATIONS FOR SI: SCAPE
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THOMAS KRENNERTSYMMETRIC INSTABILITIES DURING CONVECTIVE INITIATION
Emanuel, 1994:“Horizontal gradients of conservative field quantities (such as: EPV, Θe) are strengthened by the geostrophic wind field when deformation terms are dominant”
-> Derivation of a geostrophic wind-vector-gradient matrix (“NUE”) Divergence (D), Stretching (E), Shear (F) and Relative Vorticity (ξ)
Only the negative values of the NUE – parameter indicate strengthening of the MPV – gradient.
In combination with the WV gradients a zone for favourable DMC onset can be highlighted (easily applied operationally)
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INDICATIONS FOR SI: NUE
http://www.nwcsaf.org/HD/files/vsadoc/vsa_report_tk.pdf
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THOMAS KRENNERTSYMMETRIC INSTABILITIES DURING CONVECTIVE INITIATIONPROPERTIES OF NUE: CASE STUDY
28 July 2005, 1200 UTC, Geostrophic Wind-Vector-Gradient Matrix (“NUE”), zonal vertical cross section,
negative values represent the increase of the gradient of EPV in case of ξ < 0
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THOMAS KRENNERTSYMMETRIC INSTABILITIES DURING CONVECTIVE INITIATION
Indications of release of convective-symmetric instability alongupper level moisture gradients
Further investigations @ ZAMG: Significant differences between NWP LAM model and reality during the
forecasting process Sufficient representation of SI in NWP model? Investigate presence of UL WV gradients and / or SI for pulse convection Experiments with LAMs, i.e. ALARO (Austria) Rethinking parameterization / assimilation ?
To be continued…
FUTURE PLANS