cgisackson
DSC_0058
Sonoran Desert Sunrise and Monsoon. Here the humid cloud layer has turned into ribbons of virga (rain that does not fall all the way to the hot ground). This view captures the visual phenomenon called virga, a sudden change in the brightness of the precipitation shaft below the cloud layer, is attributed to evaporation of raindrops. This is rain that does not reach the ground. The optical thickness of an evaporating rain shaft, however, decreases gradually from the cloud base to ground. Virga also results from snowflakes melting in descent. Horizontal optical-thickness decreases of more than ten can occur in the short distance over which a snowflake is transformed into a raindrop. The air currents at lower altitude are carrying the virga in a southward stream after a free descent to the airflow.
DSC_0058
Sonoran Desert Sunrise and Monsoon. Here the humid cloud layer has turned into ribbons of virga (rain that does not fall all the way to the hot ground). This view captures the visual phenomenon called virga, a sudden change in the brightness of the precipitation shaft below the cloud layer, is attributed to evaporation of raindrops. This is rain that does not reach the ground. The optical thickness of an evaporating rain shaft, however, decreases gradually from the cloud base to ground. Virga also results from snowflakes melting in descent. Horizontal optical-thickness decreases of more than ten can occur in the short distance over which a snowflake is transformed into a raindrop. The air currents at lower altitude are carrying the virga in a southward stream after a free descent to the airflow.