The Structure of O3/H2O Mixing Relationships in the Tropopause Transition Layer at Middle and High Latitudes of the Northern Hemisphere

Abstract

AbstractUsing HALOE O3 and H2O vertical profiles in 40°N~50°N of the Northern Hemisphere, considering chemical lifetime and transport temporal constant of O3 and H2O, the structure and seasonal characteristic of O3/H2O mixing relationships between 300 K to 390 K near the tropopause and the lowest stratosphere have been constructed in the isentropic coordinates. The results are as follows: (1) The slope of O3 mixing ratios profile has a spatial sudden change between 320~380 K isentropic surfaces of the tropopause translation layer, while the slope of H2O mixing ratios profile exhibits a spatial gradual change. The source region of O3 is stratosphere but H2O is troposphere near tropopause. So on the two sides of 320~380 K isentropic surfaces, mixing ratios of O3 and H2O show distinctly different vertical gradient. (2) In the vicinity of the tropopause where O3/H2O relationships reach best least square fitting, the troposphere and stratospheric branch of the non‐regular “L” relationship show seasonal and intra‐seasonal changes with a negative slope in tropospheric branch, but positive and negative slopes alter with seasons in stratospheric branch. At the same time, based on the “L” corner, the characteristic of chemopause with seasons can be confirmed. (3) The O3/H2O mixing relationship indicates that the transition layer is formed by stratospheric mixing with tropospheric air masses from different regions, and the mixing line of the transition layer is not constant. The transition layer mixing is equivalent in January, April 2003 and in January 2005, about 30 K isentropic thickness, that is between 320~350 K isentropic surfaces. Mixing height increases in November 2005, and the H2O coming into the stratosphere is less than in January 2003 and 2005, with about 30 K isentropic thickness, between 330~360 K isentropic surfaces. The change of mixing isentropic thickness is small in different seasons, but mixing height changes with seasons. The stratospheric branch of O3/H2O mixing relationship obviously changes with seasons, for which the significant reason is the lowest stratospheric air dehydration in January.