Severe thunderstorm over Istanbul

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On 27 July 2017 a severe thunderstorm with hail and high winds raged over the Istanbul area in Turkey.

Severe thunderstorm over Istanbul
Date & Time
27 July 2017 00:00–18:00 UTC
Meteosat-8, 9 & 10
Airmass RGB, High Resolution Visible (HRV), Infrared Channel, Water Vapour

By HansPeter Roesli (Switzerland), Jose Prieto (EUMETSAT) and Erdem Erdi (TSMS)

It was reported that at least two people died and dozens injured when the storm hit. Numerous roofs, trees, vehicles and even an airplane were also badly damaged.

Figure 2
Figure 2: Met-8 HRV overlaid with IR10.8 temperature, 27 July, 15:00 UTC Download animation, 14:00–17:00 UTC (MP4, 731 KB)

At synoptic scale the storm was linked to a relatively deep eastward travelling trough and a sharpening temperature gradient along the Dardanelles, as shown by the image sequence of Meteosat-8 Airmass RGBs with tropical tuning, 27 July 00:00 UTC–18:00 UTC (MP4, 4 MB).

At a mesoscale level other factors, such as land-sea contrast, may have favoured the development of a supercell-like feature from about 15:00 UTC onward — see Figure 2 and the animation of HRV reflectivity overlaid with a multi-coloured hue of IR10.8 temperature, both channels from Meteosat-8.

The thunderstorm being positioned at 41.2 °N/29.1 °E allowed it to be seen from different viewing angles and parallaxes by both Meteosat-10 at 0° and Meteosat-8 at 41.5 °E longitudes, e.g. using the HRV channel.

A sequence of the two-panel images, from 14:00–17:00 UTC (MP4, 2 MB) gives the evolution observed from the two observation points. Due to the parallaxes resulting from the oblique view of both satellites the highest cloud towers are shifted north-northeastward (Meteosat-10) and north-northwestward (Meteosat-8) by some 10km or more.

It is obvious that the 15-minute temporal resolution was too coarse to follow the evolution in detail. Meteosat-9 imagery at 5-minute intervals between 14:00 UTC and 17:00 UTC {MP4, 3 MB) reveals the generation of gravity waves, as a possible result of interaction of the convective system with the Bosporus, in particular after they start at around 15:15 UTC, together with a major growth of overshooting cloud tops. Note: Jumps in colour inside the animation are due to enhancement at low sun elevation.

Figure 3
Figure 3: Meteosat-9 HRV/IR Rapid Scan, 27 July 16:25 UTC

The animation of negative temperature difference of WV6.2–IR10.8 overlaid over the HRV band (MP4, 2 MB) brings out these overshooting tops in false colours, the most prominent ones with differences close to -1 K being tinted in blue colours.

Figure 3 gives more details for the rapid scan at 16:25 UTC, when the overshooting was the most robust. The left panels show the temperatures from IR10.8 and WV6.2–IR10.8, the right panels show the same frames overlaid in semi-transparency over the HRV band.

A massive overshooting top of the size of several pixels stands out in blue (black arrow, bottom left). As expected the coldest temperatures (black arrow, top left), marking the tropopause temperature, are found just adjacent to the overshooting top. The overshooting top is slightly warmer due to its penetration into the stratosphere. As already mentioned above, due to the parallax the cloud top is shifted off the coast by more than 10 km.

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