Occlusion, warm air over cold

FTLComm - Tisdale - January 29, 1999

Sunrise this morning was extraordinary, I dashed outside to catch these glimpses of the tuned up sky. The image below was the first the sequence and the one above about the middle, while the one at the right was the last before the sun slipped above the overcast layer and the bottom surface of the clouds returned to bland.

This phenomena shown in these pictures is called an "Occlusion". As you can see there appears to be a diagonal line or wedge of light below the cloud formation. This is not an optical illusion but rather it is actually what is happening. Cold air as you know is substantially heavier then warm air and the air mass sitting on top of us this morning was -14 which though not really cold is substantially colder then the air to the South. A large low pressure area is located to the

West and South of us pumping warm (+5 to +10) air up to us and it encounters the cold air lying on the surface. It sweeps up over the cold air and as it does the water it carries is turned to fog (cloud) as it is carried aloft and chilled. If the air mass is large enough and the differential in temperature great enough precipitation will form at the edges of the systems.

So this morning's beautiful sunrise is actually warm air riding along over the cooler air below forming the wedge of light along the horizon. For aviators the conditions this morning are a bit dangerous because that water vapour becomes super chilled and aircraft flying through it will experience moderate icing.

The reflection of this morning's sunrise is shown at left.


*FTLComm - Tisdale - January 29, 1999*
Sunrise this morning was extraordinary, I dashed outside to catch these glimpses of the tuned up sky. The image below was the first the sequence and the one above about the middle, while the one at the right was the last before the sun slipped above the overcast layer and the bottom surface of the clouds returned to bland. This phenomena shown in these pictures is called an "Occlusion". As you can see there appears to be a diagonal line or wedge of light below the cloud formation. This is not an optical illusion but rather it is actually what is happening. Cold air as you know is substantially heavier then warm air and the air mass sitting on top of us this morning was -14 which though not really cold is substantially colder then the air to the South. A large low pressure area is located to the

	West and South of us pumping warm (+5 to +10) air up to us and it encounters the cold air lying on the surface. It sweeps up over the cold air and as it does the water it carries is turned to fog (cloud) as it is carried aloft and chilled. If the air mass is large enough and the differential in temperature great enough precipitation will form at the edges of the systems. So this morning's beautiful sunrise is actually warm air riding along over the cooler air below forming the wedge of light along the horizon. For aviators the conditions this morning are a bit dangerous because that water vapour becomes super chilled and aircraft flying through it will experience moderate icing. The reflection of this morning's sunrise is shown at left.