Vol. VII, Nr. 5 / 2008

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1 Abord ri conceptuale i metodologice RADAR SIGANATURE OF A COLD FRONT OVER WEST SIDE OF ROMANIA ELZA HAUER,CRISTIAN NICHITA,ADINA-ELIZA CROITORU ABSTRACT. - Radar siganature of a cold front over west side of Romania. For synoptic conditions we used maps from electronic archives of MetOffice and Karlsruhe Weather Center, Germany. The most part of radar images used in the study are recorded in Timi oara in the first elevation of the radar (0.5 degr.) and they are taken over OmniWx Trac. For a better understanding of the phenomena, the images were also processed into PUP. A cold front that came up in the morning of July 30, 2007 developed radar structures as WER, MEZO and BOW ECHO. Rotational phenomena have determined the emergence of funnel shaped clouds. The severe convection ingredients which are associated to the synoptic structure have early revealed the emergence of some special phenomena. Key words: radar, frontal instability, synoptic conditions, wind, Banat. 1. Introduction The work presents a frontal instability case study and the ways that their associated hazardous phenomena may be forecast using radar products The synoptic situation chosen is from August, 30, 2007, when a cold front came up and affected the Western part of the country. The structure is local scale developed and it is located about 15 km away from Timi oara city, Eastward. For synoptic conditions we used maps from electronic archives of MetOffice and Karlsruhe Weather Center, Germany. The analyzed radar images from the archive of Timisoara radar. The most part of images we used in this study are recorded in the first elevation of the radar (0.5 degr.) and they are taken over OmniWx Trac. For a better understanding of the phenomena, the images were also processed into PUP. Theoretical aspects are also presented, not in their mathematical details, but more in descriptive ones. 2. Synoptic conditions First hours of August, 30, at the sea level, were characterized by the presence of a very large anticyclonic area extended from West to Est over the 49

Riscuri i catastrofe Victor Sorocovschi European continent.

In altitude, at 500 hpa level, there was an extension of the subtropical high geopotential

2 Riscuri i catastrofe Victor Sorocovschi European continent. The extention of the Azore Anticyclon covered Western and Central Europe. In altitude, at 500 hpa level, there was an extension of the subtropical high geopotential field, with 584 damg in the central area, corresponding to the sea-level anticyclon (figure 1). a Figure 1. Distribution of the sea level pressure centers(a) and of the 500 hpa level geopotential(b) on August, 30, 2007, h b Figure 2. Infrared thermal ( μm) satellite image on August, 30, 2007, h UTC 50

3 Abord ri conceptuale i metodologice Associated warm advection determined the motion toward North-East of the low pressure centers generated near Scandinavian Peninsula (in the North- Eastern part of Atlantic Ocean). Between the Azores and Groenlanda Anticyclons a new weak Island cyclon developed. A Genoa Gulf developed cyclone (up to 500 hpa level) moved in the Western Mediteranean Basin. Easward, over the land, few weak cyclons connected by warm and cold fronts moved toward Romania s territory. Over Ceantral and Eastern Europe, a West circulation developed. The UTC satellite image shows the distribution of the atmospheric fronts from Eastern to Western Europe (figure 2). 3. Instability indexes used to identify convective situations For the convective situations forecast, both synoptic situation analyze and instability indexes are used. The values of indexes are determined using the sounding data or mathematically. The data presented below were generated using ALADIN model. Total Totals Index (TTI), K index (KI), and Cross Totals Index (CTI) are those which could identify a potential convective activity. Total Totals Index (TTI) represents the sum between the Vertical Totals (VT) and Cross Totals (CT): TTI = VT + CT where: TTI - Total Totals Index VT - Vertical Totals VT = T T 500 T 850 air temperature at 850 hpa level; T 500 air temperature at 500 hpa level; CT - Cross Totals CT = Td T 500 Td 850 dew point teperature at 850 hpa So that, TTI can be calculated using the following formula: TTI = (T T 500 ) + (Td T 500 ) Operational observations allowed to emphasize the values of this index connected to a convective situation occurring: TTI < 44 unlikely convection; TTI possible convection; TTI severe convection which can occur isolated; 51

4 Riscuri i catastrofe Victor Sorocovschi TTI general severe convection; TTI >56 extremely severe convection. where: K index (KI) usually is computed as it follows: KI = VT + (Td Tdd 700 ) KI K index; VT Vertical Totals: VT = T T 500 Td 850 dew point temperature at 850 hpa level; Tdd 700 difference between the air temperature and the dew point temperature at 700 hpa level; Tdd 700 = T 700 Td 700 The operational significance of KI values is: small potential for convection; moderate potential for convection convective potential; >40 high potential for convection. Cross Totals (CT) shows how much the floatability of an air particle is influenced by the less dense and less moist air below. Operational values of the index are presented below: <17 unlikely storms; scattered storms, isolated severe; scattered storms, locally severe; 30 many severe storms. Other important instability indexes as CAPE (convective available potential energy) and MOCOM could not be used because the analyzed situation is not a mass instability but a frontal instability 4. Radar monitoring of the synoptic situation Radar images recorded between h and showed values of 52 for TTI, for KI and 23 for CTI, which are specific to moderate convection (figure 3, figure 4, figure 5). Around h (2.30 UTC), in the Western part of Romania, first frontal evidences and associated phenomena such as squalls, lightning, hail occurred. In the same time, both eye witnesses and radar images indicated the presence of funnel shaped clouds. 52

Abord ri conceptuale i metodologice a b c Figure 3.

00 (a), 03.00 (b),06.00 (c) a b c Figure 4.

00 (a), 03.00 (b), 06.00 (c) a b c Figure 5.

00 (a), 03.00 (b), 06.00 (c) At 04.20, local time (02.

lightning warning followed, few minutes later, by a squall

Then frontal phenomena began in Arad and a precipitation

5 Abord ri conceptuale i metodologice a b c Figure 3. TTI index using ALADIN model on August, 30, 2007, h (a), (b),06.00 (c) a b c Figure 4. KI index using ALADIN model on August, 30, 2007, h (a), (b), (c) a b c Figure 5. CT index using ALADIN model on August, 30, 2007, h (a), (b), (c) At 04.20, local time (02.20 UTC) Weather Station Sânicolau Mare sent the first lightning warning followed, few minutes later, by a squall (19 m/s) warning. Then frontal phenomena began in Arad and a precipitation warning was sent by Arad Weather Station. Meso and TVS zones appeared on radar images and also 61 Kg/m 2 of VIL index associated with severe hail (figure 6). 53

Riscuri i catastrofe Victor Sorocovschi The Meso and TVS signals could be seen also in the next images recorded by Timisoara radar, at 05.07 and 05.13 local time (03.07 and 05.13 UTC).

6 Riscuri i catastrofe Victor Sorocovschi The Meso and TVS signals could be seen also in the next images recorded by Timisoara radar, at and local time (03.07 and UTC). The TVS signal was associated with a funnel cloud also confirmed by an eye witness. Figure 6. Radar Images on August, 30, 2007 h 05.01, local time(03.01 UTC) Moving eastward, the front affected also Timi oara city periphery areas and villages located in Lipova Hills where squalls occurred (figure 7). The frontal line is smooth with modulations of warm and cold sectors generated by upper draft inflow and downdraft outflow. Then frontal line moves towards Lugoj together with convection evidences. The main cold front in Banat is connected by a warm front to another cold front developed in Sebi area. Echo top is about m height, and the reflectivity was about 70 dbz. Both VIL and VIL density values were very high and they are corresponding to severe hail: VIL was 63 kg/m 2 and VIL density was 5.33 g/m 3 (figure 8). Just in front of the mountain area, the height of the minimum echo is above 13 km. At that moment and area the frontal and cloud systems had their maximum vertical development. In the same area the highest values of VIL density and VIL are recorded (7.23 g/m 3 and 56 kg/m 2 ) (figure 9). 54

7 Abord ri conceptuale i metodologice Figure 7. Radar Images on August, 30, 2007 h 05.19, local time,( 03.19, UTC) Figure 8. Radar Images on August, 30, 2007 h 05.44, local time (03.44, UTC) 55

02 UTC) In the selected area, a WER (Weak Echo Region) was identified using reflectivity and

8 Riscuri i catastrofe Victor Sorocovschi Figure 9. Radar Images on August, 30, 2007 h 06.02, local time, (04.02 UTC) In the selected area, a WER (Weak Echo Region) was identified using reflectivity and velocity field for more elevations and also Echo Tops products (figure 10). Figure 10. Radar image (0.5 deg) where WER was identified, on August, 30, 2007 h 05.13, local time, (03.13 UTC) 56

Abord ri conceptuale i metodologice WER is a weak echo region delimited by stronger echoes both horizontally and vertically.

It is also generated by a strong uplifted current with precipitations particles in the middle levels of the storm. The particles are not detectable by radar at this size.

Cross Section image through reflectivity field (a) and 3D image with projection of the uplifted current and reflectivity values (b) Radar images of 0.5, 3.4 and 6.0 degr.

9 Abord ri conceptuale i metodologice WER is a weak echo region delimited by stronger echoes both horizontally and vertically. It is usually located in low altitude, in the input area of the storm (figure 11). It is also generated by a strong uplifted current with precipitations particles in the middle levels of the storm. The particles are not detectable by radar at this size. This situation can not be detected by human eye. A Figure 11. The theoretical model of WER. Cross Section image through reflectivity field (a) and 3D image with projection of the uplifted current and reflectivity values (b) Radar images of 0.5, 3.4 and 6.0 degr. elevations show an increasing reflectivity from lower regions towards mountain areas with a Meso zone as developing center of the storm (figure 12). This is the reason that determined the hanging of the reflectivity field only at higher elevations and it is proved by the velocity field where, at 2.4 and 6.0 degr. elevations there is a specific cyclonic motion (fig. 13). There were also detected two little symbols of the TVS. b a 57

10 Riscuri i catastrofe Victor Sorocovschi b c Figure 12. Radar images at 0.5 (a), 3.4 (b) and 6.0 (c) degr. elevations at UTC- Base Reflectivity Due to short distance between the analyze area and profile coordinates and also the motion velocity, the image of the RCF50 Cross Section (Ref) was considered relevant, even if it was recorded 6 minutes in advance (figure 14). 58

Abord ri conceptuale i metodologice Figure 13.

elevations at 03.14 UTC- Base Velocity Figure 14.

14 UTC In the Echo Tops image, the minimum height

11 Abord ri conceptuale i metodologice Figure 13. Radar images at 2.4 and 6.0 degr. elevations at UTC- Base Velocity Figure 14. Echo Tops radar image at UTC In the Echo Tops image, the minimum height of the maximum echo is in the Meso area and that means that the upper draft is there. 59

12 Riscuri i catastrofe Victor Sorocovschi A B Figure 15. The influence of wind vertical shear on convective structure inclination: the highest values of ECHO TOPS are located in front of low elevations reflectivity Figure 16. Vertical Profile of wind using VAD Wind Profile Product One of the most important factor which determines the severity of a convective situation is the vertical wind shear (variation of the wind speed with altitude which can be or not associated with direction variation). It can be determined using hodographer or wind speed vertical profile (algorithm WAD 60

13 Abord ri conceptuale i metodologice wind profile). There is also a divergence between the upper draft inflow and the down draft outflow. When the upper draft flow interacts with the shear vector, a different distribution of low and high pressure centers occurs (figure 15). Due to the short distance from the analyzed are (less than 15 km), in this paper we consider that we can use wind profile from Timisoara location (figure 16). At UTC and in the following tens of minutes a strong vertical wind shear was evident. Only a direction shear was identified. The upper level shear is connected with the images of the wind velocity field of 2.4 and 6.0 degr. elevations. Conclusions Values of the instability parameters must be analyzed only correlated one by other and they offer rather the potential of severe weather than a very rigorous location of the area with maximum intensity of the associated phenomena. Due to the great variety of radar products and good knowledge on atmosphere dynamic, one can make a good forecast of the severe weather phenomena occurrence and evolution, both in their location and intensity. For the case study, when a cold front entered Romanian territory in the very early morning of July, 30, 2007 radar structures as WER, MEZO and BOW ECHO could have been identified. Rotational phenomena generated funnel clouds as eye witnesses said. Severe convection ingredients associated to the synoptic structure determined using radar images, allowed an easy forecast of the phenomena. REFERENCES 1. Bhatnaga, A. K., Rajesh Rao, P., Kalyanasundaram,S., Thampi, S. B., Suresh R., Gupta J. P. (2003), Doppler radar A detecting tool and measuring instrument in meteorology, in Current Science, Vol. 85, no. 3, pp Brooks, H. E., Doswell, C.A. III (1994), The Role of Midtropospheric Winds in the Evolution and Maintenance of Low-Level Mesocyclones, in Monthly Weather Review, Vol. 122, pp Doswell III, Ch., Brooks, H., Maddox, R. (1996), Flash Flood Forecasting: An Ingredients-Based Methodology, 560 volume 11, in Weather And Forecasting, NOAA/Environmental Research Laboratories, National Severe Storms Laboratory, Norman, Oklahoma, pp Hjelmfelt M. R. (2008), Microbursts and Macrobursts: Windstorms and Blowdowns, ob=miamiimageurl&_imagekey=b8k3r- 4PNFPR9-B-1&_cdi=44153&_us.pdf (accessed on May, 31, 2008). 5. Holobâc, I. H., Croitoru, Adina-Eliza (2005), Relations entre les quantités journalières des précipitations et les types de circulation atmosphérique au centre de 61

14 Riscuri i catastrofe Victor Sorocovschi la Roumanie, în Climat urbain, Ville et Architecture, Actes du Colloques, Dipartamento di Storia e Progetto dell teritorio e del paesaggio POLIS Facolta di Architettura, Universita degli Studi di Genova. Editori: Gerardo Brancuci, Genova, p Stumpf, G. J., Witt, A., E., Mitchell, D., Spencer, P. L., Johnson, J. T., Eilts, M. D., Thomas, K. W., Burgess, D. W. (1998), The National Severe Storms Laboratory Mesocyclone Detection Algorithm for the WSR-88D, in Weather And Forecasting, American Meteorological Society, no/volume 13, pp Wilson, J., W., Mueller, Cynthia (1993) Nowcasts of Thunderstorm Initiation and Evolution, in Weather And Forecasting, American Meteorological Society, no.8, pp ***, Conceptual Models of Mesoscale Convective Systems, The COMET Program (Cooperative Program for Operational Meteorology, Education and Training), (accessed on April, 7, 2008). 9. ***, Convective Storm Structure and Evolution, in Distance Learning Operations Course, Topic 7, Training course, www. (accessed on April, 7, 2008). 62

THE MESOSCALE CONVECTIVE SYSTEM FROM

RISCURI I CATASTROFE, NR.X, VOL.9, NR. 1/2011 THE MESOSCALE CONVECTIVE SYSTEM FROM 24.07.2010 ELZA HAUER, 1 C. NICHITA 1 ABSTRACT. The Mesoscale Convective System from 24.07.2010. A severe weather event