Thursday, August 26, 2010

A little more about the science

We've had a truly beautiful day here today - the sky was clear and blue (although we do not see the sun here in McMurdo for a few more days because we face south and have some big obstructions to our north) and after lunch, we noticed an abundance of polar stratospheric clouds (PSCs) to the west.  People also know these as nacreous clouds or mother-of-pearl clouds.

PSCs are one of the key players in stratospheric ozone depletion. They are naturally occurring clouds residing 12-25 km (7 - 15 mi) above the surface and are composed of either pure water (if they are very cold, -85 oC/-121 oF) or a mixture of nitric acid and water (nitric acid trihydrate or NAT), around temperatures of -77 oC/-107 oF. PSCs provide a surface that catalyzes reactions between gas-phase molecules that would not otherwise react with one another. This, in turn, leads to conversion of chlorine-containing gases (derived from chlorofluorocarbons) into forms that react quickly with ozone. So, seeing PSCs means ozone depletion is occurring overhead. As you can tell from the picture below, it is also awe-inspiring, because they are beautiful.
Polar Stratospheric Clouds west of McMurdo - 27 Aug

For the PSC aficionado - this photo contains both Type 1 (NAT) and Type 2 (ice) PSCs. The Type 2s are the ones that are iridescent or brightly lit; the Type 1s are the hazy, grayish ones surrounding the Type 2s. You would not necessarily know that from the photo, but we were treated to the most gorgeous purple glow as the sun continued to set, confirming the presence of the NAT clouds throughout the sky.

Another piece of science being done here is the regular launching of ozone sondes - small balloons that carry a package to measure the profile of ozone from the surface to somewhere up in the ozone layer - 25 to 30 km, or wherever the balloon bursts. Terry Deshler's group from the University of Wyoming is doing this work, so I tagged along yesterday to photograph one of their launches. They'll be launching an ozone sonde about every 3 days to watch the progression of the ozone depletion over the next 6 to 8 weeks.

Inflating the ozonesonde balloon. Most of the
balloonis contained in that white bundle on the tarp.
Releasing the balloon - the person on the left is holding the sonde. He'll wait for the balloon to get overhead before letting go.

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