June 23, 2010
Today, Haviland started a data run in the morning because there were a lot of plane contrails in the sky, and she wanted to view one with the LIDAR. However, the research student hike was also today at 1:30pm GMT, so she only got 80 minutes of observation with contrails. As it happened, none of the contrails passed directly over the LIDAR, so that section of the run had only clear sky data. The hike ended at 6:00pm GMT, so Haviland started up EARL again. At this time, the sky had several clouds, and Haviland had to put the cloud mask over the primary mirror to prevent over-saturation.
The clouds in the afternoon, between 6:00pm GMT and 8:00pm GMT when Haviland shut down EARL for the evening, show up on the Range Corrected Backscatter graph as being around 2 kilometers high. Two of them were about a kilometer thick. They had no measurable depolarization signal because (A) they were too low to the ground and were likely made primarly of water molecules rather than ice, and (B) the air quality for this day had low pollution.
Usually with clear skies data, the boundary layer hardly shows up as rising any. There is a bit of a rise, but it is gradual and not very noticeable because--on a clear, clear day--the heating up of aerosols is not too noticeable.
However, look at the morning time from 12:00pm GMT until 1:18pm GMT, when EARL was stopped early. This is only a couple of hours after sunrise, and it seems like streams of the atmosphere scatter back more light than streams directly under or above. From 0 to 2 kilometers, these streams are easily visible. The day was not overly windy, only about 3 mile/hour winds according to the METAR data, but that is not more windy than other days with data taken that did not produce this stream-effect. Haviland noted at 1:18pm GMT that the boundary layer was looking very odd; it had an odd spiking downward at 300 meters. This corresponds with that very low turquoise trail near 1:10pm GMT until shutdown. We should keep an eye on this, on windy days and odd spikes in the boundary layer, to see what the correlation is.
The other distinct possibility is that these are plane contrails from low-flying planes... but that does not make sense of the 300-meter backscatter, since planes should probably not be flying that low nearby. An interesting question to ask, though, would be: how long do low plane contrails last in the sky?
Usually with clear skies data, the boundary layer hardly shows up as rising any. There is a bit of a rise, but it is gradual and not very noticeable because--on a clear, clear day--the heating up of aerosols is not too noticeable.
However, look at the morning time from 12:00pm GMT until 1:18pm GMT, when EARL was stopped early. This is only a couple of hours after sunrise, and it seems like streams of the atmosphere scatter back more light than streams directly under or above. From 0 to 2 kilometers, these streams are easily visible. The day was not overly windy, only about 3 mile/hour winds according to the METAR data, but that is not more windy than other days with data taken that did not produce this stream-effect. Haviland noted at 1:18pm GMT that the boundary layer was looking very odd; it had an odd spiking downward at 300 meters. This corresponds with that very low turquoise trail near 1:10pm GMT until shutdown. We should keep an eye on this, on windy days and odd spikes in the boundary layer, to see what the correlation is.
The other distinct possibility is that these are plane contrails from low-flying planes... but that does not make sense of the 300-meter backscatter, since planes should probably not be flying that low nearby. An interesting question to ask, though, would be: how long do low plane contrails last in the sky?
The depolarization signals today were close to nil. The least noisy part of the graph where a consistent and reliable signal can be obtained--i.e., the main blue part--has nothing out of the ordinary. The area under where the clouds are is a brighter blue than the rest of the signal, which indicates slightly more backscatter and also suggests a slightly higher amount of aerosols in the mixing layer below the clouds. An eye should be kept on this bright vs. dark blue, especially since every day tends to have this blue, non-noisy depolarization signal.