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Volume 18, issue 3 | Copyright
Atmos. Chem. Phys., 18, 1819-1833, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 07 Feb 2018

Research article | 07 Feb 2018

Age and gravitational separation of the stratospheric air over Indonesia

Satoshi Sugawara1, Shigeyuki Ishidoya2, Shuji Aoki3, Shinji Morimoto3, Takakiyo Nakazawa3, Sakae Toyoda4, Yoichi Inai3,5, Fumio Hasebe5, Chusaku Ikeda6, Hideyuki Honda6, Daisuke Goto7, and Fanny A. Putri8 Satoshi Sugawara et al.
  • 1Miyagi University of Education, Sendai 980-0845, Japan
  • 2National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8569, Japan
  • 3Center for Atmospheric and Oceanic Studies, Tohoku University, Sendai 980-8578, Japan
  • 4Department of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, Yokohama 226-8502, Japan
  • 5Faculty of Environmental Earth Science, Hokkaido University, Sapporo, 060-0810, Japan
  • 6Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara 252-5210, Japan
  • 7National Institute of Polar Research, Tokyo 190-8518, Japan
  • 8Indonesian National Institute of Aeronautics and Space (LAPAN), Bandung 40173, Indonesia

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 2km, 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 22km, and then rapidly from there up to 29km. The CO2 and SF6 ages agree well with each other in the TTL and in the lower stratosphere, but show a significant difference above 24km. 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.

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This is the first research that shows concrete evidence of gravitational separation in the tropical stratosphere. This implies that gravitational separation occurs within the entire stratosphere, which gives us new insight into atmospheric dynamics.
This is the first research that shows concrete evidence of gravitational separation in the...