Polar Stratospheric Clouds (PSC) Patrick Shaw SIO 209 May 15, 2009

Polar Stratospheric Clouds(PSC)

Patrick ShawSIO 209

May 15, 2009

Zondlo et al., 2000

Cirrus in general

• Cover 30% of earth’s surface at all times• Upper troposphere generally has low T, high

RH and enough CCN to form large coverage of ice crystal clouds

• Diversity of formation regions makes for variety of unique particle size, density and morphology

• Optically thin allows most in sun, traps IR out

PSC’s in particular• Form at poles because of extremely low T in

winter• Reaction site where reservoir chlorine

compounds are converted into ozone-destroying chlorine radicals

• Type 1 – ice + liquid nitric acid and water mixtures formed at ~195 K

• Type 2- less common, water-ice crystals at < 187K

PSC classification

Zondlo et al., 2000

http://www.atm.ch.cam.ac.uk/tour/psc.html

http://www.atm.ch.cam.ac.uk/tour/psc.html

Sudden Sudden creation of creation of Type 1Type 1

http://www.atm.ch.cam.ac.uk/tour/psc.html

Sudden Sudden creation of creation of Type 2Type 2

Chemistry

ClO + NO2 + M -> ClONO2 + M

As clouds grow, they attain enough mass to deposit out and remove nitrogen compounds with them. This increases the ClO in the net equation, and promotes ozone destruction once sunlight is available to catalyze active Cl compounds.

Denoxification occurs on PSC drops, resulting (…) in the net reaction:

http://www.atm.ch.cam.ac.uk

Measuring Ozone

(toms.nasa.gsfc.com)

Antarctic vs. Arctic

• Antarctic has stronger polar vortex lowest stratosphere T during winter, prone to PSC formation and ozone depletion

• Arctic has weaker polar vortex, but standing lee waves may still process enough air to deplete N. Hemisphere ozone layer

• If GHG-induced climate change makes stratosphere colder, as predicted, more PSC may form, and N. Hemisphere ‘mini’ ozone hole may grow

Can infer vortex strength, and thus effect of PSC, from Total Ozone Mapping Spectrometer data:

(toms.nasa.gsfc.com)

From http://www.jpl.nasa.gov/releases/2004/108.cfm