Two severe MCSs on the same day over Hungary (29 June 2006)

by Mária Putsay, Ildikó Szenyán, André Simon, Ákos Horváth, Péter Németh and Kornél Kolláth (Hungarian Meteorological Service)

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On 29th June 2006 a Mesoscale Convective System (MCS) with a squall line swept across Hungary from the West to the East. The MCS had just left the country when another huge convective system developed over the Julian Alps and Dinaric Mountains, and soon arrived over Hungary from the South-West. The two MCSs caused heavy precipitation, hail and strong winds on the same day. Extreme weather conditions were experienced: at Lake Balaton more than 100 km/hour wind speed was measured; trees fell across roads and railways, and flash floods occurred on some creeks.

The synoptic situation of that day is shown here (PPT, 962 KB). The evolution of the MCSs can be followed on radar (03:00-23:45 UTC, AVI, 2377 KB) and in airmass RGB satellite (00:00-23:45 UTC, AVI, 2511 KB) animations.

The first MCS formed over the Alps the day before and reached the northwest boundary of Hungary in the early morning as a strong instability line. After 10:30 UTC an interesting asymmetric bow echo can be seen on the radar images. The northern part of the line curves more and more with time (see time sequence of radar images, PPT, 966 KB). The asymmetric bow shape of the squall line echo is due to the mid-level rear inflow jet and the Coriolis effect. The Coriolis effect significantly impacted the system evolution, since this MCS was a long living, huge system (see conceptual model, PPT, 169 KB).

Cloud top features like overshooting tops, gravity waves, and plumes are easily seen in the MODIS visible image (PPT, 1948 KB) and in some cases in the MSG HRV images (PPT, 1005 KB). The MSG IR10.8 channel satellite image shows the cloud top temperature structure. In some images one can observe cold rings and cold U shapes which are characteristic of severe systems (see example (08:15 UTC, JPG, 99 KB) and conceptual model (PPT, 709 KB)). Combining the HRV and IR10.8 channels we get the so-called HRV cloud composite image, a good tool for investigating convection (see example, PPT, 1686 KB).

To investigate the relative locations of the main updrafts and downdrafts (overshooting tops and highest radar Zmax values, PPT, 3753 KB), we marked the locations of the overshooting tops on the HRV images by circles, and overlaid them on a combined radar-satellite image. The shape of the line connecting the overshooting tops and the high radar reflectivities were similar and close to each other. They are shifted a little due to the effect of parallax.

Lightning activity was extremely high in the first MCS. 10-minute lightning data was also added to the simultaneous radar and satellite images (see time sequence of radar, satellite and lightning data, PPT, 7430 KB). The majority of flashes detected were close to the locations of the overshooting tops and the most intense precipitation.

The 3.9 micron reflectivity contains information about the average size of the cloud top ice crystals. This reflectivity can be calculated from the daytime IR3.9 channel data by subtracting the thermal radiation, or it can be approximated by the brightness temperature difference (BTD) of IR3.9-IR10.8. The storm RGB shows this difference in green. We visualised both the IR3.9refl and the storm RGB together with the HRV+radar and IR10.8 images. In the cloud top of the first MCS we see many small ice particles almost everywhere in the anvil (see time sequence, PPT, 3086 KB). These small ice particles are caused by cells with strong updrafts. In a strong updraft the small water particles at the cloud base reach the cloud top very quickly and have no time to interact or grow. The system was already quite old when it arrived over Hungary so we see many old, small ice crystals which were already widespread over the whole anvil. In some cases one can also see that the IR3.9-IR10.8 brightness temperature difference depends on the IR10.8 brightness temperature and not merely on the particle size. Investigating the much younger system over North Italy (see time sequence, PPT, 4850 KB), one can see near the overshooting top a concentrated, growing area of small ice particles. The second MCS was formed from this system and the cells developed over the Dinaric Mountains after 13:10 UTC.

The HRV cloud animation (12:15-17:15 UTC, AVI, 1659 KB) shows the dissipating phase of the first MCS. This MCS transformed to a MCV (Mesoscale Convective Vortex) due to the significant Coriolis effect. A MCV consists of mid-level convergent cyclonic flow and high-level divergent anticyclonic outflow within the anvil, which can be seen in the animation with some still active cells.

Meteosat-8 RGB Composite
Met-8, 29 June 2006, 13:00 UTC
RGB Composite WV6.2-WV7.3, IR9.7-IR10.8, WV6.2
Stereographic Projection
Full Resolution (JPG, 316 KB)
Animation (00:00-23:45 UTC, AVI, 2511 KB)

Meteosat-8 RGB Composite
Met-8, 29 June 2006, 14:45 UTC
RGB Composite HRV, HRV, IR10.8
Stereographic Projection
Full Resolution (JPG, 343 KB)
Animation (dissipation phase, 12:15-17:15 UTC, AVI, 1659 KB)

Meteosat-8 HRV Image
Met-8, 29 June 2006, 10:00 UTC
Channel 12 (HRV)
Stereographic Projection
Full Resolution (JPG, 137 KB)
Time Sequence (PPT, 1005 KB)
MODIS Image (09:25 UTC, PPT, 1948 KB)

Meteosat-8 IR (IR10.8) Image
Met-8, 29 June 2006, 08:15 UTC
Channel 09 (IR10.8, colour enhanced)
Stereographic Projection
Full Resolution (JPG, 99 KB)

Meteosat-8 RGB Composite
Met-8, 29 June 2006, 11:00 UTC
RGB Composite HRV, HRV, IR10.8
Radar (Zmax > 35dBz), Circles for overshooting tops
Stereographic Projection
Full Resolution (JPG, 165 KB)
Time Sequence (PPT, 3753 KB)

Meteosat-8 4-Panel Display
Met-8, 29 June 2006, 08:15 UTC
Upper left: HRV (range: 70% (black) - 100% (white))
Upper right: IR10.8 (colour enhanced)
Lower left: HRV (70-100%) and radar (Zmax>35dBz)
Lower right: RGB Composite, radar (Zmax>35dBz) and 10-minute lightning data
Stereographic Projection
Full Resolution (JPG, 315 KB)
Time Sequence (PPT, 7430 KB)

Meteosat-8 4-Panel Display
Met-8, 29 June 2006, 12:15 UTC
Upper left: HRV (70-100%) and radar (Zmax>35dBz)
Upper right: RGB Composite WV6.2-WV7.3, IR3.9-IR10.8, NIR1.6-VIS0.6
Lower left: IR10.8 (colour enhanced)
Lower right: IR3.9r (reflected component)
Stereographic Projection
Full Resolution (JPG, 274 KB)
Time Sequence (PPT, 4850 KB)

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