Special Features of Polar Meteorology During the winter polar night, sunlight does not reach the south pole a strong circumpolar wind develops in the middle to lower stratosphere, These strong winds are known as the polar vortex In the winter and early spring, the polar vortex is extremely stable, sealing off air in the vortex from that outside The exceptional stability of the vortex in Antarctic is the result of the almost symmetric distribution of ocean around antarctica The air within the polar vortex can get very cold Once the air temperature gets to below about -80C (193K) Polar Stratospheric Clouds (or pscs for short)are formed
Special Features of Polar Meteorology • During the winter polar night, sunlight does not reach the south pole. • A strong circumpolar wind develops in the middle to lower stratosphere; These strong winds are known as the 'polar vortex'. • In the winter and early spring, the polar vortex is extremely stable, sealing off air in the vortex from that outside. • The exceptional stability of the vortex in Antarctic is the result of the almost symmetric distribution of ocean around Antarctica. • The air within the polar vortex can get very cold. • Once the air temperature gets to below about -80C (193K), Polar Stratospheric Clouds (or PSCs for short) are formed
Polar vortex The polar vortex is a persistent large-scale cyclonic circulation pattern in the middle and upper troposphere and the stratosphere, centered generally in the polar regions of each hemisphere The polar vortex is not a surface pattern. It tends to be well expressed at upper levels of the atmosphere(> 5 km)
Polar vortex • The polar vortex is a persistent large-scale cyclonic circulation pattern in the middle and upper troposphere and the stratosphere, centered generally in the polar regions of each hemisphere. • The polar vortex is not a surface pattern. It tends to be well expressed at upper levels of the atmosphere (> 5 km)
Polar Stratospheric Clouds (Pscs) PSCs first form as nitric acid trihydrate(Hno3: 3H20) once temperature drops to 195K As the temperature gets colder, larger droplets of Water-ice with nitric acid dissolved in them can form PSCs occur at heights of 15-20km
Polar Stratospheric Clouds (PSCs) • PSCs first form as nitric acid trihydrate (HNO3.3H2O) once temperature drops to 195K. • As the temperature gets colder, larger droplets of water-ice with nitric acid dissolved in them can form. • PSCs occur at heights of 15-20km
Why do pscs occur at heights of 15-20 km? The long polar night produces temperature as low as 183 k(-90oC)at heights of 15 to 20 km The stratosphere contains a natural aerosol layer at altitudes of 12 to 30 km
Why do PSCs occur at heights of 15-20 km? • The long polar night produces temperature as low as 183 k (-90oC) at heights of 15 to 20 km. • The stratosphere contains a natural aerosol layer at altitudes of 12 to 30 km
PSCs promote the conversion of inorganic Cl and Cl reservoir species to active c Pathway 1: HCI(g>Cl2(g Absorption of gaseous HCl by PSCs occurs very efficientl y HC(g)→HCI(s) Heterogeneous reaction of gaseous ciono2 with Hcl on the pSc particles HCIS)+ CloNo2> HNO3(s)+ cl2 Where s denotes the psc surface Note: The gas phase reaction between HCl and CIONO2 is extremely slow
PSCs promote the conversion of inorganic Cl and Cl reservoir species to active Cl Pathway 1 : HCl(g) → Cl2 (g) • Absorption of gaseous HCl by PSCs occurs very efficiently HCl(g) → HCl(s) • Heterogeneous reaction of gaseous ClONO2 with HCl on the PSC particles HCl(s) + ClONO2 → HNO3 (s) + Cl2 where s denotes the PSC surface Note: The gas phase reaction between HCl and ClONO2 is extremely slow