CHANGES IN UPPER STRATOSPHERIC CH4 AND NO2 AS MEASURED BY HALOE AND IMPLICATIONS FOR CHANGES IN TRANSPORT

Measurements from HALOE indicate that there has been a significant dec rease in CH4 in the middle to upper stratosphere from 1991-1997. Two d imensional model calculations suggest that a decrease in the tropical upwelling is the most plausible explanation for the CH4 decrease. The changes in CH4 resulting from solar cycle variations or changes in tro pospheric CH4 and CFC emission rates are shown to be much smaller than the measured variations from similar to 35-45 km. The HALOE measureme nts of NO2 in the lower stratosphere near the equator also show an inc rease which is consistent with a reduction in the upward transport rat e. Above similar to 40 km the NO2 measurements appear to be consistent with the net effect of opposing solar and dynamical trends.