In the south-west of Portugal, a rare phenomenon has recently occurred: a “was sightedroll cloud»(Or rolling cloud), or one cloudy training From the particular very long horizontal tubular shape. Strange cloudvisible for hundreds of bathers from different locations, including Cabo da Roca, was initially confused with the imminent arrival of a tsunami.
But what are these Roll Clouds and how are these Rolls? Specifically, the Rotal clouds They are formed when currents of cold and warm air interact with the edge of a dynamic weather system, such as a temporal system or a front. In the case of a temporal system characterized by a cumulonembo (a large storm cloud), where both hot ascending and cold currents are present, one descending, one cold air current it can expand horizontally once the soil is impacted, lifting hot air and wet (rarer due to the highest temperature) present in the lowest atmospheric layers. All this causes the condensation and the rapid cooling of the water vapor Content in the warm and humid air, thus giving rise to a roll cloud.
However, what really affects the “rolled” form is the so -called Wind Sheari.e. a variation of the speed and of the direction of windwhich induces the cloud a rotate Around your horizontal axis, acquiring this cylindrical form that distinguishes it. In some cases these clouds, which are part of the family of the “Arcus Cloud” (a type of low and horizontal clouds), can have one to have one thickness of 2 km and also a length of hundreds of kmalways remaining at low altitude (typically 100-200 meters from the ground).
While forming near thunderstorms, when the hot and humid currents are more likely to clash with cold air, the roll clouds do not generate in turn thunderstorms or rainfall. In itself, therefore, it is not a particularly atmospheric phenomenon dangerouseven if their presence can still anticipate a worsening of weather conditions.
However, these are phenomena particularly rare to be observed, especially in Italy and Europe in general. However, there are some regions of the world where roll clouds are more common: in Australiafor example, tend to form when the marine currents from the Gulf of Carpentaria collide with those of the Coral Sea.
The formation of this cloud in Portugal could be due to the high temperatures of the last few days, when several Portuguese cities have exceeded 40 ° C. The air, therefore, was more warm and wet compared to the usual and, going to clash with the cold oceanic currentsmay have favored the formation of highly developed and dynamic temporal systems, which in turn favor the formation of Roll Cloud.
