View all of the Arctic Hemisphere daily maps of total ozone for April 1991. Satellite instruments monitor the ozone layer, and we use their data to create the images that depict the amount of ozone.
Click any map image to bring up a new page with a high-resolution map.
The data for this month are from the TOMS instrument on the NASA/NOAA Nimbus-7 satellite.
Missing areas (bad orbits and polar night) are filled using assimilated ozone data from the Modern-Era Retrospective analysis for Research and Applications (MERRA) assimilation, produced by the Goddard Earth Observing System Data Assimilation System (GEOS DAS). MERRA uses a version of the GEOS model with the Gridpoint Statistical Interpolation (GSI) atmospheric analysis developed jointly with NOAA/NCEP/EMC.
A week begins with Sunday. Fainter images are shown in the previous and following months. Missing days are indicated with a plain gray globe.
Monthly averages (1979–current)