In:
Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 18, No. 3 ( 2018-02-07), p. 1819-1833
Abstract:
Abstract. The gravitational
separation of major atmospheric components, in addition to the age of air,
would provide additional useful information about stratospheric circulation.
However, observations of the age of air and gravitational separation are
still geographically sparse, especially in the tropics. In order to address
this issue, air samples were collected over Biak, Indonesia in February 2015
using four large plastic balloons, each loaded with two compact cryogenic
samplers. With a vertical resolution of better than 2 km, air samples from
seven different altitudes were analyzed for CO2 and SF6 mole
fractions, δ15N of N2, δ18O of O2, and δ(Ar∕N2) to examine the vertically dependent age and
gravitational separation of air in the tropical tropopause layer (TTL) and
the equatorial stratosphere. By comparing their measured mole fractions with
aircraft observations in the upper tropical troposphere, we have found that
CO2 and SF6 ages increase gradually with increasing altitude from
the TTL to 22 km, and then rapidly from there up to 29 km. The CO2 and
SF6 ages agree well with each other in the TTL and in the lower
stratosphere, but show a significant difference above 24 km. The average
values of δ15N of N2, δ18O of O2, and δ(Ar∕N2) all show a small but distinct upward decrease due to the
gravitational separation effect. Simulations with a two-dimensional
atmospheric transport model indicate that the gravitational separation effect
decreases as tropical upwelling is enhanced. From the model calculations with
enhanced eddy mixing, it is also found that the upward increase in air age is
magnified by horizontal mixing. These model simulations also show that the
gravitational separation effect remains relatively constant in the lower
stratosphere. The results of this study strongly suggest that the
gravitational separation, combined with the age of air, can be used to
diagnose air transport processes in the stratosphere.
Type of Medium:
Online Resource
ISSN:
1680-7324
DOI:
10.5194/acp-18-1819-2018
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2018
detail.hit.zdb_id:
2092549-9
detail.hit.zdb_id:
2069847-1
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