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Zentralanstalt für Meteorologie und Geodynamik BASIC INVESTIGATION OF SYMMETRIC INSTABILITY DURING CONVECTIVE INITITATION IN THE ALPINE REGION Thomas Krennert,

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Presentation on theme: "Zentralanstalt für Meteorologie und Geodynamik BASIC INVESTIGATION OF SYMMETRIC INSTABILITY DURING CONVECTIVE INITITATION IN THE ALPINE REGION Thomas Krennert,"— Presentation transcript:

1 Zentralanstalt für Meteorologie und Geodynamik BASIC INVESTIGATION OF SYMMETRIC INSTABILITY DURING CONVECTIVE INITITATION IN THE ALPINE REGION Thomas Krennert, Central Institute of Meteorology and Geodynamics, Vienna, Austria Forecasting

2 CWGWORKSHOP PRAGUE 2012 THOMAS KRENNERT SYMMETRIC 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

3 CWGWORKSHOP PRAGUE 2012 THOMAS KRENNERT SYMMETRIC 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.

4 CWGWORKSHOP PRAGUE 2012 THOMAS KRENNERT SYMMETRIC 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

5 CWGWORKSHOP PRAGUE 2012 THOMAS KRENNERT SYMMETRIC 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

6 CWGWORKSHOP PRAGUE 2012 THOMAS KRENNERT SYMMETRIC INSTABILITIES DURING CONVECTIVE INITIATION CASE STUDY: 28 July 2005, 1100 UTC, MSG RGB Image composite IR 8.7µ (red)/ WV 7.3µ(green) / WV 6.2µ(blue)

7 CWGWORKSHOP PRAGUE 2012 THOMAS KRENNERT SYMMETRIC INSTABILITIES DURING CONVECTIVE INITIATION CASE STUDY: 28 July 2005, 1100 UTC, MSG RGB Image loop

8 CWGWORKSHOP PRAGUE 2012 THOMAS KRENNERT SYMMETRIC INSTABILITIES DURING CONVECTIVE INITIATION 28 July 2005, 1200 UTC, Eqivalent (Moist) Potential Vorticity, EPV [ |-5| (blue) – |-30| (red) K*m 2 /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

9 CWGWORKSHOP PRAGUE 2012 THOMAS KRENNERT SYMMETRIC 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

10 CWGWORKSHOP PRAGUE 2012 THOMAS KRENNERT SYMMETRIC 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) INDICATIONS FOR SI: NUE

11 CWGWORKSHOP PRAGUE 2012 THOMAS KRENNERT SYMMETRIC INSTABILITIES DURING CONVECTIVE INITIATION PROPERTIES 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

12 CWGWORKSHOP PRAGUE 2012 THOMAS KRENNERT SYMMETRIC INSTABILITIES DURING CONVECTIVE INITIATION Indications of release of convective-symmetric instability along upper level moisture gradients Further 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


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