Cirrus plume formation above thunderstorm anvils

By Jochen Kerkmann (EUMETSAT) and Ramon Vazquez (Aemet)

On 30 June several severe convective storms developed over Spain, in the Provinces of Granada, Jaen, Teruel, and over the Pyrenees. The most severe storm was observed in the Teruel Province (labelled '1' in the image below), having a clear supercell signatures for some time, and producing around 100 mm rain in some places (see PPI weather radar image at 15:50 UTC, source: INM, and 6-hourly accumulated rainfall, source: INM).

The animated HRV images show some typical features of severe convective storms for the Teruel storm:

• Strong low-level inflow (see 'feeder clouds' south of the storm).
• Marked high-level cirrus outflow.
• Strong overshooting of new convective towers.
• Above-anvil cirrus plume (like a stratospheric wave cloud).
• Continuous rebuilding of the storm on the right side (looking downstream).

Surprisingly, the event got little attention in the Spanish press because TV and newspapers were completely focused on the Spanish team in the European Championship. Also, the area is quite sparsely populated so that these phenomena may well remain unreported.

The Meteosat-8 HRV image below shows a second interesting storm labelled '2' over the Pyrenees. This storm started at around 15:10 UTC and was still very active when the Sun set behind the horizon. This storm developed a remarkable above-anvil Cirrus plume, which resembles the high-level plume-like cloud to the lee of an isolated mountain peak (see case study High level wave cloud spreading from Mt. Etna).

This would support the 'cloud top gravity wave breaking' theory explained in the paper from Pao Wang (2007). Thus, besides strong winds at high levels (with strong shear, i.e vicinity of jet streak), a pre-condition for the formation of well-developed above-anvil cirrus plumes could also be the fact that the convective storms remained quite stationary (so that they act as real obstacles to the high-level flow). This may be the reason why the Teruel storm, which slowly moved to the right, did not develop such a nice plume as the Pyrenees storm, which remained stationary over several hours.

For further reading, information about the multispectral properties of above-anvil cirrus plumes can be found in the paper from Levizzani and Setvak (1996).