Sunday, November 13, 2011

Humidity and Convection

Much of the DYNAMO field work is focused on characterizing the convection using radars and infrared satellite data. Closely linked to the convection, is knowledge of the humidity field. Small fluctuations in the overall moisture are enough to support deep clouds, and the vertical distribution of the water vapor is speculated to influence if shallow convection can transition into deep convection or not. One achievement and legacy of DYNAMO will be a high-quality sounding dataset at 3 and 4 hour time resolution - not at all easy to pull off and perhaps even unprecedented. My contribution to DYNAMO represents another stab at characterizing the water vapor. Next to the S-PolKa radar there’s a scanning microwave radiometer, shown below. It looks rather cute compared to its much larger and active scanning cousin. The radiometer is sort of a cousin to the radar, in that the two instruments use some of the same frequencies but whereas the radar is active (transmitter and receiver), the radiometer is passive - it’s basically just the radar receiver. The radiometer is responsive to the amount of the atmospheric water vapor and liquid water (through water’s microwave absorption and emission, which is also what a microwave oven depends on). This radiometer is even capable (we think) of providing some insight into the vertical structure of the water vapor, more crudely than the soundings, but more continuously - so that we should be able to document changes in atmospheric water vapor occurring on the order of minutes. The radiometer also spends some of its time scanning in the same direction as the radar. With that data we hope to put together three-dimensional pictures of the humidity and cloud fields, and help answer questions such as: do clouds thrive when they move into more humid environments - and dissipate if the environments are drier? what comes first - clouds or moisture? do clouds humidify their environment ? or does the atmosphere already have to be moist to be able to support clouds?

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