altostratus betydelse and definition

Exempel på altostratus

• Often, when an altostratus cloud thickens and descends into lower altitudes, it will become nimbostratus.

• This cloud typically forms from altostratus in the middle altitude range, but it tends to thicken into the low altitude range during precipitation.

• The variety "undulatus" (having a wavy undulating base) can occur with any clouds of the species stratiformis or lenticularis, and with altostratus.

• Altostratus and nimbostratus clouds always have this physical appearance without significant variation or deviation and, therefore, do not need to be subdivided into species.

• They also can occur under altostratus cloud preceding a warm or occluded front, when cumulus usually lose vertical development as the sun's heat decreases.

• The altostratus velum cloud appears dark in comparison to its parent cloud, and can persist even after the cumulonimbus has disintegrated.

• A further thickening of the altostratus is often accompanied by virga and the arrival of precipitation is imminent.

• However, only two are seen with altostratus and stratus nebulosus whose uniform structures prevent the formation of a perlucidus variety.