These ClO maps from MLS show the large effect that a relatively small decrease in temperature can have on the amount of reactive chlorine in the lower stratosphere. Lower stratospheric temperatures remained low enough for polar stratospheric cloud (PSC) formation until the end of February in 1993, whereas in February 1992 they were too warm for PSCs. MLS ClO maps for February 15 in both 1992 and 1993, and temperature maps made from National Meteorological Center (NMC) data, are shown here. The data have been interpolated to the 465 K isentropic surface (about 20 km height). The color bar for ClO ranges from 0 to 2.25 ppbv, with red indicating 1 ppbv. Green/blue colors on the temperature map indicate temperatures are below 195 K (where PSCs can form). See Waters, et al. [1993] for more discussion of these data.
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