26 November 2012
Gravity Waves Are Not Something You Only Hear About On Doctor Who
Posted by Dan Satterfield
We had a nice display of gravity waves over the Mid Atlantic on Saturday. You have likely seen this type of cloud pattern in the sky many times and the view from the Aqua satellite as it passed over Virginia on Saturday shows it well. In many waves this is the atmospheric equivalent of throwing a rock in a pond. Instead of a series of waves emanating from the spot the rock entered we have cloud waves as the winds blow over the Appalachians.
Sometimes the wavelength between the clouds makes it difficult to see from the ground but the view from space is clear. This past Saturday was one of those days when it was clear there were waves of clouds, but you could see it easier in some areas than others. You can tell for sure when you look at a satellite image. Clouds form as air rises and cools.
If the air cools enough then the dew-point temperature is reached and the humidity is 100% (if not more). The cloud dissipates as the air sinks down to the next trough but reforms again as it rises back at the top of the next wave downstream. Sometimes a large mountain can produce lenticular clouds that form hundreds of miles downstream as well.
Greetings. What would explain the “sandwich” of different air masses with different moisture content? I can understand the cloud formation if one had dry air overlaid by moist air, and as both air masses pass over the Appalachian mountains, they would be deformed (so to speak) and a gravity wave would start propagating from there, rising and cooling moist air at the crest of the wave, lowering and warming moist air in the trough of the wave. Thanks a lot.