July 1, 2010
Lauren turned EARL on at 2:30pm GMT. They were grey clouds out, and it was very cloudy and breezy. The temperature outside was surprisingly low, about 76 degrees Fahrenheit. There was very high humidity outside and, because of the clouds, very little sun interference. The bowtie cloud mask was placed on the primary mirror at the beginning of the run and, due to the saturation of the channels caused by the low-lying clouds, stayed on for the entirety of the run.
This cloudiness is quite visible on the Range Corrected Backscatter graph below. Look at all the dark red and orange at about 500 meters! From 2:30pm GMT until about 4:00pm GMT, there continued to be 500-meter clouds. At about 4:30pm GMT, there were some clouds at 2 kilometers. Then from about 5:00pm GMT until the end of the run, there were intermittent clouds at 1 kilometer, with the exception of a couple of clouds near 3 kilometers at 6:50pm GMT. Because of the excessive amount of clouds, it is difficult to say anything about humidity and the boundary layer.
This cloudiness is quite visible on the Range Corrected Backscatter graph below. Look at all the dark red and orange at about 500 meters! From 2:30pm GMT until about 4:00pm GMT, there continued to be 500-meter clouds. At about 4:30pm GMT, there were some clouds at 2 kilometers. Then from about 5:00pm GMT until the end of the run, there were intermittent clouds at 1 kilometer, with the exception of a couple of clouds near 3 kilometers at 6:50pm GMT. Because of the excessive amount of clouds, it is difficult to say anything about humidity and the boundary layer.
One very interesting feature about today's run, other than the excessive amount of clouds, is the higher depolarization signal coming from the 500-meter clouds that lasted from 2:30pm GMT until 4:00pm GMT. There is a slight, almost unnoteworthy, depolarization signal coming from the clouds later on; but the signal for the 500-meter clouds is very distinct. Usually, a depolarization signal corresponds to spiky molecules like ice, dust, pollen, soot, etc. However, ice only forms at high altitudes around 7 kilometers. This depolarization signal is coming from 500 meters!
So what could this signal be? The temperature was lower than usual today, but considering it has been in the 80s and 90s recently, that should not cause ice to form in clouds at low altitudes. The depolarization is probably due to some particulate matter in the clouds. What this particulate matter is specifically is unknown.