Polar Stratospheric CloudsPolar Stratospheric Clouds -Properties and Climate Impacts -Properties and Climate Impacts

Haibin LiHaibin Li

OutlineOutline Why these clouds?Why these clouds? Properties of PSCsProperties of PSCs Definition; Occurrence; Type; CharacteristicsDefinition; Occurrence; Type; Characteristics

Measurements of PSCsMeasurements of PSCs

Methods, exampleMethods, example

Climate ImpactsClimate Impacts

Ozone depletion with PSCs; mechanismOzone depletion with PSCs; mechanism

Why??Why??

Relationship with ozone depletionRelationship with ozone depletion

Understand the past climate (Sloan Understand the past climate (Sloan et alet al., ., 1998)1998)

They are beautiful… “mother of pearl”They are beautiful… “mother of pearl”

http://www.sundog.clara.co.uk/atoptics/nacr1.htmhttp://www.sundog.clara.co.uk/atoptics/nacr1.htm

http://alphais.inep.ksc.ru/knet_in/sky.htmhttp://alphais.inep.ksc.ru/knet_in/sky.htm

http://www.nilu.no/projects/theseo2000/images/general/psc8.jpghttp://www.nilu.no/projects/theseo2000/images/general/psc8.jpg

Properties of PSCsProperties of PSCs Definition:Definition:

High altitude clouds that form in the stratosphere above Antarctica High altitude clouds that form in the stratosphere above Antarctica

during the Southern Hemisphere winter. Their presence seems to during the Southern Hemisphere winter. Their presence seems to initiate the ozone loss experienced during the ensuing Southern initiate the ozone loss experienced during the ensuing Southern Hemisphere spring. (Hemisphere spring. (http://earthobservatory.nasa.gov/Library/glossary.php3http://earthobservatory.nasa.gov/Library/glossary.php3))

Large, diffuse, ice-particle clouds that form in the stratosphere usually Large, diffuse, ice-particle clouds that form in the stratosphere usually over polar regions.(over polar regions.(http://www.grida.no/climate/ipcc/aviation/158.htmhttp://www.grida.no/climate/ipcc/aviation/158.htm))

Formation:Formation: During the polar night (i.e. winter) a strong circumpolar wind develops During the polar night (i.e. winter) a strong circumpolar wind develops

in the middle to lower stratosphere. This creates a vortex, which in the middle to lower stratosphere. This creates a vortex, which isolates the air above the poles. Due to a lack of sunlight the air inside isolates the air above the poles. Due to a lack of sunlight the air inside the vortex cools and once the temperature falls below about 195K the the vortex cools and once the temperature falls below about 195K the probability of PSC formation increases very rapidly. probability of PSC formation increases very rapidly.

Temperature decided TypeTemperature decided Type

TypeType TemperatureTemperature Particle SizeParticle Size CompositionComposition

Type IaType Ia < 195 K< 195 K ~ 1 ~ 1 μμmm characterized by NAT (HNO3.3H2O) crystalscharacterized by NAT (HNO3.3H2O) crystals(depolarizing solid)(depolarizing solid)

Type IbType Ibnitric acid/water/sulphuric acidnitric acid/water/sulphuric acid Supercooled Supercooled

ternary solution (STS)(nondepolarizing ternary solution (STS)(nondepolarizing liquid)liquid)

Type IIType II ~ 188 K~ 188 K ~ 10 ~ 10 μμmm Small Ice CrystalsSmall Ice Crystals

PSCs Type and physical properties

( Crutzen, 1986; Hofmann, 1989;Voigt et al., 2000;Toon et al., 1995)

Measurements of PSCsMeasurements of PSCs

Measuring Methods:Measuring Methods: ground-based and aircraft LIDAR systems (Stein ground-based and aircraft LIDAR systems (Stein et alet al., 1999)., 1999) in-situin-situ balloons-borne and aircraft instruments measuring particle balloons-borne and aircraft instruments measuring particle

sizes and densities through sampling and backscatter laser devices sizes and densities through sampling and backscatter laser devices ( Voigt ( Voigt et alet al., 2000; Kivi ., 2000; Kivi et al.,et al., 2001) 2001)

Satellite observations of absorption, emission and scattering of light Satellite observations of absorption, emission and scattering of light by PSC particles (Foschi by PSC particles (Foschi et al.,et al., 2002) 2002)

Interested in: Interested in: Particle size; surface area; volume; frequency of PSC events; Particle size; surface area; volume; frequency of PSC events;

different PSC types; the relation between the PSC occurrence and different PSC types; the relation between the PSC occurrence and the environmental atmospheric conditions. the environmental atmospheric conditions.

Example of PSC Measurements

X-axis :the backscatter ratio R (red line), the depolarization*20 (thin line), and the color ratio from two wavelength measurements.  A: Early stage: few highly aspherical particles; B: mid winter: strong PSC layer of spherical particles; C: late winter: decaying PSC signals;

http://www.awi-potsdam.de/www-pot/atmo/psc/psc.html#Lidar_Measurements_of_PSCs

Climate Impacts:Ozone depletion and PSCsClimate Impacts:Ozone depletion and PSCs

PhenomenonPhenomenon

MechanismsMechanisms PSCs act as catalysts converting chlorine from the inert "reservoir" PSCs act as catalysts converting chlorine from the inert "reservoir"

species to active species by heterogeneous chemical reactions on species to active species by heterogeneous chemical reactions on their surface.their surface.

Details…Details…

HNO3·3H2O HCl ClONO2

HCl ClONO2

ClONO2

ClHCl-Cl HNO3

Vaporize

HNO3

Cl-Cl

Cl-Cl Cl* *Cl

Net: 2O3→3O2

ClONO2+HCl → Cl2+HNO3ICE

Hv ≤450 nm

O3 + Cl → ClO + O2

O3+hv(≤ 1140nm)→O2+O

ClO + O → Cl + O2

Future Stuff ???Future Stuff ???Chlorine activation chemistry is sensitive to the chemical position and the sizes of PSC particles but PSC properties have never been adequately quantified, either observationally or theoretically.

So far, size distributions are among the best known PSC properties(light scattering or parameterized lidar measurements).

PSC chemical compositions are still very poor known --- the best guesses are based on equilibrium thermodynamic models ( Carslaw, 1995).

How to understand them more realistically?

More advanced&consistent satellite observation + improved models simulation.