Mesoscale Convective Systems in the Western Mediterranean Rigo, T.(1), and M. Berenguer (2)

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1 Mesoscale Convective Systems in the Western Mediterranean Rigo, T.(1), and M. Berenguer (2) (1) Servei Meteorologic de Catalunya, Barcelona (2) Centre of Applied Research in Hydrometeorology, Universitat Politècnica de Catalunya, BarcelonaTech

2 Presentation Index - Why is important to understand MCS behavior? - Starting point - Methodology - Results - Conclussions 2

3 Why is important to understand MCS behavior? One of the convective modes better organized 3

4 Why is important to understand MCS behavior? are the most convective precipitation structures associated with floods at mid-latitudes (e.g. Doswell et al., 1996; Gray and Marshall, 1998; Schiesser et al., 1995). are an important link between atmospheric convection and the larger-scale atmospheric circulation (Houze 2004). have important organization for hazardous weather forecasting and warning (Parker and Johnson 2000). commonly produce severe weather (Parker and Johnson 2004) behave as long-lived (>3 h), Parker and Johnson (2000) Electrical behavior depends on the type (Parker et al 2000) Precipitation Efficiency controlled by certain environmental factors (Market and Allen, 2003). 4

5 Starting point Preliminary analysis using single C-band weather radar Main conclusions: TS (39%), LS (18%), and NS (43%). MCS clusters (CLU) constituted 51%. Mean area of 25,000 km 2, Z max ~ 47 dbz, echotop ~ 12 km Maximum frequency at 12 UTC and early afternoon Displacement towards E-NE 5

000 km 2 Set used Discrete (57 cases) (1996-2000) 5 y Continuous (2012-2016) 5 y Corrections Doppler Advanced (EHIMI)

6 Starting point VERSION AEMET (Old) SMC (Current) Time resolution 10 6 Spatial res. 2x2 km 2 1x1 km 2 Total area (coverage) km km 2 Set used Discrete (57 cases) ( ) 5 y Continuous ( ) 5 y Corrections Doppler Advanced (EHIMI) Main differences: - Change on the spatial coverage (increasing) - Change in the spatial and time resolutions (improving) - Change in the reflectivity corrections (higher quality) - Only few cases vs. a whole period of analysis 6

7 Starting point Maybe change the title to... 7

8 Starting point... Or even better 8

9 Methodology

10 Methodology Identification ~ 438,000 imagery were analyzed regions with Z>12 dbz & Area>10,000 km 2 (maybe very restrictive) => 40,082 imagery with a possible MCS => ~11,000 discarded because low reliability of shape Stratiform/convective rainfall types discriminated by 35 dbz threshold At each time, some features were calculated: date, centroid position, total area, Zmax, Zmean, % of convective precipitation IMPORTANT: this is only spatial criteria time criteria is also needed 10

11 Methodology Tracking tracking considers distances between centroids of two consecutive images of less than 35 km this can produce interruptions of life cycles, in cases of merging/splitting 342 MCS were identified for the period of study ( ) AREA (>10,000 km2) + TIME (>3h) 11

12 Methodology Tracking: example of MCS 12

13 Goals

14 Goals Questions to answer: Q1: can we improve the information of the preliminary analysis? If yes, in which sense? Q2: which general and seasonal features have been observed? Q3: Can we associate with meteorological conditions? 14

15 Results

16 Results Identification: Hour of the day clear increase of number of observations from 12 UTC (max at 19 UTC) => daily cycle ± agrees with 2007 study 16

17 Results Tracking: Duration Most lasted for times between 4 and 8 hours (~55%) a significant number of cases with duration > 15 hours (~11%) Mean duration was 8.5 hours Probably, MCS lasted for more time (problem of coverage) in some cases 17

0 66.0 TOTAL (Dist) 262.2 412.3 655.7 1077.6 1875.6 Duration (h) 4.1 4.9 6.8 10.2 15.2 Agrees with 2007 Figure 3.

18 Results Tracking: Other parameters of interest (Quantiles) Area: km 2 Zmax: dbz Dist: km Parameter Q10 Q25 Q50 Q75 Q90 MEAN(Area) 15,300 18,300 22,600 28,600 40,800 MAX(Area) 21,300 25,700 32,600 46,200 65,600 MAX(Zmax) TOTAL (Dist) Duration (h) Agrees with 2007 Figure 3. For the subjective database ( ): (a) mean number of cyclones per year and possible cyclone tracks Campins et al

19 COLD COLD Results Identification: month of the year two seasons with a higher number of MCS, between cold and warm seasons CO-WA WA-CO CO-WA (March/April), ~26.5% of cases WARM WA-CO (September-November), ~27.4% of cases SST and land surface reach similar values 19

20 Results MCS evolution (life cycle): beginning CO-WA WA-CO dbz dbz 20

21 Results MCS evolution (life cycle): pre-maturity CO-WA WA-CO dbz dbz 21

22 Results MCS evolution (life cycle): maturity CO-WA WA-CO dbz dbz 22

23 Results MCS evolution (life cycle): dissipation CO-WA WA-CO dbz dbz 23

Results Comparison between CO-WA and WA-CO seasons Area: km 2 Zmax: dbz Dist: km Parameter Q10 Q25 Q50 Q75 Q90 MEAN(Area) 15865.6 17764.3 22880.2 28351.4 43334.7 MAX(Area) 20758.4 26420.7 32517.

24 Results Comparison between CO-WA and WA-CO seasons Area: km 2 Zmax: dbz Dist: km Parameter Q10 Q25 Q50 Q75 Q90 MEAN(Area) MAX(Area) MAX(Zmax) TOTAL (Dist) Duration (h) MEAN(Area) MAX(Area) MAX(Zmax) TOTAL (Dist) Duration (h)

25 Results Comparison between CO-WA and WA-CO seasons Both life cycles are similar, but Different trajectories: W to E (CO-WA) and SSW-NNE (WA-CO) Practically all parameters register larger values for MCS of WA-CO season => major number cases of floods during this stage (see Llasat et al. 2005) But... What happens with precipitation regimes? 25

26 Results Precipitation regimes The percentage of convective precipitation has a mean value of 25% in general for the whole set of MCS in the case of CO-WA MCSs not reaches the 20% On the contrary, is near 27% for the WA-CO MCSs => WA-CO present larger convective precipitating areas MCS set Q10 Q25 Q50 Q75 Q90 ALL CO-WA WA-CO

27 Results Precipitation regimes and electrical activity % conv. Prec. behavior strongly agrees with the relationship between TL and cumulated precipitation total QPE reaches similar values for both seasons, but TL acquires larger values during the WA-CO season the mean values of the rate NTL/QPE are 57.7 flashes/mm (CO- WA) and flashes/mm (WA-CO) 27

28 Conclusions Q1: can we improve the information of the preliminary analysis? If yes, in which sense? A1a: True: continuous database of radar imagery ( ) have allowed to found 342 MCS A1b: Two main periods with maxima of MCS observed, coinciding with the transition between Cold and Warm seasons (and vice versa) 28

29 Conclusions Q2: which general and seasonal features have been observed? the structure of MCS on both periods is similar, but important differences on respect the area, distance, duration or intensity autumn events (WA-CO) cases shown higher percentages of convective precipitation, as more number of total lightning, and also higher TL/QPE rate 29

30 Conclusions Q3: Can we associate with meteorological conditions? Trajectories with cyclone motion Major occurrence when SST similar to surface temperature More active MCS when SST>surface temperature 30

31 gencat.cat

Mesoscale Convective Systems in the Western Mediterranean Rigo, T.(1), and M. Berenguer (2)

Mesoscale Convective Systems in the Western Mediterranean Rigo, T.(1), and M. Berenguer (2) (1) Servei Meteorologic de Catalunya, Barcelona (2) Centre of Applied Research in Hydrometeorology, Universitat