Analysis of convective indices over the northeastern Adriatic Karmen Babić, Gabrijela Poljak, Marko Kvakić, Maja Telišman Prtenjak Croatian-USA Workshop.

Analysis of convective indices over the northeastern Adriatic Karmen Babić, Gabrijela Poljak, Marko Kvakić, Maja Telišman Prtenjak

Croatian-USA Workshop on Mesometeorology18-20 June 2012, Ekopark Kraš Resort

Andrija Mohorovičić Geophysical Institute, Department of Geophysics, Faculty of Science, University of Zagreb

Introduction

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The northeastern Adriatic coast – a good example of a very complex coastline

Target of research regarding the sea/land breeze phenomenon

Specific features in the mesoscale wind field – the convergence zone

Previous studies of SB – primarily focused on the wind characteristics

The relationship between SB and Cb clouds was not investigated

Potential SB – Cb relationship

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• We focus on the summer months (from June to September), when the SB development is frequent (e.g., Prtenjak and Grisogono, 2007)

• Surface measurements for two meteorological stations - the Pula-Airport and Pazin (Fig) observed during a 10-year period (1997–2006)

Pula-Airport Number of SB days 563SB frequency 51%

Pazin Number of days with Cb clouds in Pazin 99Frequency of the daytime Cb during warm months 8.4%

Pula-Airport ∩ Pazin Number of days with SB and Cb clouds 51Frequency of the daytime Cb during SB events at the coast 9.1%

Station φ λ H (m) D (km) N MVPula-Airport

44° 54’ N 13° 55’ E 63 10 1097 V, T

Pazin 45° 14’ N 13° 56’ E 291 25 1220V, T, N,

P

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Corr coef= 0.81Corr coef= 0.78

Potential SB – Cb relationship

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Determination of potential SB-Cb relationship based only on the surface measurements of two measuring sites

What we still do not know:

What we know:

Simultaneously observed above Istria

The nature of SB- Cb interaction

NE Adriatic

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• NE Adriatic - the most convective area in Croatia more than 60% of convective days in the warm part of the years 2006-2009 (Mikuš et al. 2012)

Dominant large-scale weather types

82% of all days with convective activity

SW (46%) large-scale flow

NE (18%) large-scale flow

NW (18%) large-scale flow

non-gradient pressure field (21%) (NG)

the center of the cyclone (21%) (C)

the eastern front sector of the cyclone (20%)

the western back side of the cyclone (10%)

the front side of the trough (12%) (T)

Mean convective indices

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)(CAPE )(CIN )(LI )(RiB )(KI

Based on the dataset of convective days (2006-2009) for the NE Adriatic region – calculation of stability indices from the Udine (46.03°N, 13.18°E) radiosounding station

soundings within 100 km of the storm's event can satisfactory described deep moist convective conditions

Groenemeijer and van Delden (2007)

Numerical simulations

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• WRF-ARW mesoscale model simulations of

Three chosen cases

simultaneous occurrence of SB and daytime Cb above Istria

an interaction of SB with one of the dominant types of large-scale wind:NE, SW and NW above Istria

• Numerical sensitivity test NE large-scale wind without microphysics scheme (A0 case)

09 July 2006 - NE large-scale flow 08 August 2006 - NW large-scale flow

Satellite images in the combined (VIS + IR; channel CH139) channel received from Meteosat 8. The pink color represents the convective clouds.

Numerical simulations

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• Only partial similarities with average convective indices in Udine• The most prominent CAPE values - during the superposition of SW large-scale and the SB flow (accompanied by the relative small RiB (< 45))• As expected, the NW case has the largest RiB (> 60)

Convective available potential energy (CAPE)

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NE large-scale flow SW large-scale flow NW large-scale flow

Color: CAPE; arrows: 10 m wind field

Convective inhibition (CIN)

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NE large-scale flow SW large-scale flow NW large-scale flow

Color: CIN; arrows: 10 m wind field

Bulk Richardson Number (RiB)

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NE large-scale flow SW large-scale flow NW large-scale flow

Numerical sensitivity test

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CAPE RiB

Case

ACa

se A

0

Summary

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• Mean stability indices derived from the Udine radiosounding station– High mean values of CAPE and KI, negative LI values correspond to T and NG weather

types– Lower values of the same indices – for the C type due to its seasonal occurrance– NW / NE flow regime followed by the highest / lowest atmospheric instability

• Simulations of three chosen cases– Most prominant CAPE values during the superposition of SW large-scale and SB flow– The largest CIN values for the SW flow regime and the lowest for the NW flow regime– RiB values are the highest for NW and lowest for NE large-scale flow

• Possible reasons of disagreement – Distance of Udine radiosounding station from NE Adriatic– Seasonal character influences mean values of convective indices, while simulated cases

correspond to summer conditions

Thank you for your attention!

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