Gravitational separation of major atmospheric components observed in the stratosphere over Syowa Station, Antarctica, Kiruna, Sweden and Sanriku, Japan.

Abstract

To investigate the gravitational separation of atmospheric components in the stratosphere, air samples collected using an aircraft during the Arctic Airborne Measurement Program 2002 (AAMP02) were analyzed for the O_2 N_2 ratios (δ(O_2 N_2)), δ^N of N_2, δ^O of O_2 and Ar N_2 ratio (δ(Ar N_2)). The relationship between observed stratospheric δ^N of N_2, δ^O of O_2 and δ(Ar N_2) over the Svalbard Islands and Barrow showed mass-dependent fractionation of atmospheric components in the stratosphere, which suggested that gravitational separation could be observable in the lowermost stratosphere inside the polar vortex. By examining the rates of change in δ(O_2 Nv) and δ^C of CO_2 relative to the CO_2 concentration, such observed correlations were bound to be mainly attributable to upward propagation of their seasonal cycles produced in the troposphere and height-dependent air age as well as gravitational separation in the stratosphere. Air samples collected over Syowa Station, Antarctica, Kiruna, Sweden and Sanriku, Japan using balloon-borne cryogenic air samplers were analyzed for δ^N of Nv and δ^O of O_2. Strength of the gravitational separation was a function of latitude, showing the largest separation inside the polar vortex over Kiruna. It is suggested that information on increase of gravitational separation with height is useful in understanding the vertical transport of air masses in the stratosphere. By comparing the gravitational separations, mean age of air and N_2O concentration at two height intervals with N_2O concentrations > 125 ppb and < 45 ppb, the effect of descending air was found to be more significant over Kiruna than over Syowa Station and Sanriku. The variation in the gravitational separation with height is found to be weaker in the region with N_2O concentrations between 45 and 125 ppb than in other regions, which might suggest that vertical mixing of air occurred in this region.