Analysis of H_2O and CH_4 Distribution Characteristics in the Middle Atmosphere Using HALOE Data

The HALOE observational data from December 1991 to May 2004 are used to analyze the vertical and horizontal distributions of H2O and CH4 in the middle atmosphere,especially in the upper stratosphere and mesosphere.For a more convenient comparison,the objective analyses are made on the HALOE data and 5°×5° grid data are obtained(covering 70°S70°N,180°W 180°E).The vertical profiles of H2O and CH4 mixing ratio at various latitudes and longitudes as well as in the different years are given,and the latitude-altitude cross section and longitude-altitude cross section of the H2O and CH4 mixing ratio are also presented in this paper.The results show that the H2O mixing ratio decreases from the upper troposphere to the tropopause quickly and reaches a minimum near the tropopause(the minimum is called as "hygropause");and then it increases with height in the lower-middle stratosphere,while it is disturbed significantly in the upper stratosphere and lower mesosphere;it decreases with altitude again and reaches another minimum near the mesopause;the profiles of H2O mixing ratio for the different latitudes,various longitudes and in the different years are similar,except that some difference is exist in mixing ratio amount and the altitudes of the hygropause of different latitudes are not the same.The characteristic of vertical distribution of CH4 shows that it always decreases with height in the middle atmosphere.The profiles for the different latitudes,various longitudes and in the different years are similar,but the mixing ratio values are somewhat different.The meridional distribution shows that the low value zone of H2O mixing ratio bulges upward in the tropical low-middle stratosphere,the H2O mixing ratio increases from low latitudes to high latitudes.In contrast,the high value zone of the CH4 mixing ratio bulges upward in the same place,the CH4 mixing ratio decreases from low latitude to high latitude.Relatively strong horizontal gradients are seen in the subtropical lower stratosphere near 20°N30°N and 20°S30°S. Both the H2O and CH4 mixing ratio contours change into double-peaked pattern in the upper stratosphere in JJA,but they remain a single peak in DJF.Approximately opposite patterns appear in DJF and JJA both for H2O and CH4 in the lower-middle mesosphere: the high values of both H2O and CH4 mixing ratio occur in north high latitude in JJA,while the high values in DJF occur in south high latitude.The minimum of H2O and CH4 mixing ratio in DJF is over arctic in the middle-upper mesosphere,however they are near Antarctic in JJA.Longitudinal gradients of the two trace gas as near 30°N in JJA are all small in the lower-middle stratosphere,but they are large in the upper troposphere and mesosphere.