The very cold conditions in Arctic winter 2010/2011 led to the first Northern Hemisphere ozone hole. MLS on Aura and MIPAS on Envisat monitored the development of the ozone hole over all the winter. The animation below shows all relevant species involved in ozone depletion at the lower stratosphere from 15 November 2010 to 30 April 2011. The ozone hole starts to develop in late February 2011. The white lines provide the vortex boundary, while the black circle in the ClO animation shows the area of polar night. The animation has been produced by the MLS/Aura team of NASA's Jet Propulsion Laboratory. Click on the image to start the animation (150 MB).