Fig. 15

A latitude–longitude color composite map of 1.74-, 2.26- and 2.32-µm nightside images obtained from the IR2 camera on April 25 showing an unusual sharp boundary in the intensity (left). A latitude–longitude grid (30° spacing) is overlaid with the equator along the middle of the image. On the right are plots of radiance and the local contrast at three wavelengths along 24°N latitude, from − 75° to − 50° longitude (marked on the color composite) that cuts across the “mushroom” feature and the sharp boundary that occurs at about − 56° longitude. The contrast is defined here as the difference in radiance at the two neighboring pixels of a given pixel divided by the average of their two pixels. Such sharp boundaries are seen on Earth only in water vapor channels, thereby showing the dry and moist air masses (Fig. 16)