Polar stratospheric clouds were observed over Antarctica some time ago. How might they have formed,and what happens if some of these clouds break down due to heat in the presence of sunlight?

(N/A) In winter,special clouds called polar stratospheric clouds form over Antarctica. These clouds provide a surface for the hydrolysis of chlorine nitrate to form hypochlorous acid,and they also react with hydrogen chloride to produce chlorine molecules.
$ClONO_{2(g)} + H_2O_{(g)} \rightarrow HOCl_{(g)} + HNO_{3(g)}$
$ClONO_{2(g)} + HCl_{(g)} \rightarrow Cl_{2(g)} + HNO_{3(g)}$
When sunlight returns to Antarctica in the spring,the heat from the sun causes these clouds to break down. The sunlight then triggers the photolysis of $HOCl$ and $Cl_2$:
$HOCl_{(g)} \xrightarrow{hv} \cdot OH_{(g)} + Cl^{\bullet}_{(g)}$
$Cl_{2(g)} \xrightarrow{hv} 2Cl^{\bullet}_{(g)}$
Thus,chlorine free radicals are generated,which initiate the chain reaction for ozone depletion.