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Gravitational Separation in the Stratosphere – a New Indicator of Open Access Atmospheric Circulation Biogeosciences Biogeosciences Discussions S EGU Journal Logos (RGB) Open Access Open Access Open Access Advances in Annales Nonlinear Processes Geosciences Geophysicae in Geophysics Open Access Open Access Natural Hazards Natural Hazards and Earth System and Earth System Sciences Sciences Discussions Open Access Open Access Atmos. Chem. Phys., 13, 8787–8796, 2013 Atmospheric Atmospheric www.atmos-chem-phys.net/13/8787/2013/ doi:10.5194/acp-13-8787-2013 Chemistry Chemistry © Author(s) 2013. CC Attribution 3.0 License. and Physics and Physics Discussions Open Access Open Access Atmospheric Atmospheric Measurement Measurement Techniques Techniques Discussions Open Access Gravitational separation in the stratosphere – a new indicator of Open Access atmospheric circulation Biogeosciences Biogeosciences Discussions S. Ishidoya1, S. Sugawara2, S. Morimoto3, S. Aoki4, T. Nakazawa4, H. Honda5, and S. Murayama1 1National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8569, Japan Open Access 2Miyagi University of Education, Sendai 980-0845, Japan Open Access 3National Institute of Polar Research, Tokyo 190-8518, Japan Climate 4 Climate Center for Atmospheric and Oceanic Studies, Tohoku University, Sendai 980-8578, Japan of the Past 5Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA),of the Past Sagamihara 252-5210, Japan Discussions Open Access Correspondence to: S. Ishidoya ([email protected]) Open Access Earth System Earth System Received: 30 December 2012 – Published in Atmos. Chem. Phys. Discuss.: 20 February 2013 Dynamics Revised: 23 July 2013 – Accepted: 23 July 2013 – Published: 3 September 2013 Dynamics Discussions Abstract. As a basic understanding of the dynamics of the at- spheric components occurs in the atmosphere above the tur- Open Access Open Access mospheric circulation, it has been believed that gravitational bopause (about 100 km) (LewisGeoscientific and Prinn, 1984; Jacobs, Geoscientific separation of atmospheric components is observable only in 1999). On the other hand,Instrumentation we have suggestedfrom our mea- Instrumentation the atmosphere above the turbopause. However, we found, surements of the stable isotopicMethods ratios of and major atmospheric 15 18 Methods and from our high-precision measurements of not only the iso- components (δ( N) of NData2 and δ Systems( O) of O2) (Ishidoya et Data Systems topic ratios of N2,O2 and Ar but also the mole fraction of al., 2006, 2008a, b) that gravitational separation exists even Ar, that gravitational separation occurs even in the strato- in the stratosphere. However, in our earlier studies, we were Discussions Open Access Open Access sphere below the turbopause; their observed vertical profiles not able to exclude the possibility that some other factors af- Geoscientific are in good agreement with those expected theoretically from fected our measurement results.Geoscientific Model Development molecular mass differences. The O2/N2 ratio observed in the In this paper,Model we present Development new concrete evidence for the middle stratosphere, corrected for gravitational separation, existence of gravitational separation in the stratosphere. We Discussions showed the same mean air age as estimated from the CO2 also show a significant effect of gravitational separation on Open Access mole fraction. Simulations with a 2-dimensional model of the O2/N2 ratio (δ(O2/N2)) measured in theOpen Access stratosphere. the middle atmosphere indicated that a relationship between Furthermore, we proposeHydrology to use gravitational and separation as Hydrology and gravitational separation and the age of air in the stratosphere a new indicator to detectEarth a change System in the Brewer–Dobson Earth System would be significantly affected if the Brewer–Dobson circu- Circulation (BDC) (Brewer, 1949) in the stratosphere. At- lation was enhanced due to global warming. Therefore, grav- mospheric general circulation modelsSciences have shown that the Sciences itational separation is usable as a new indicator of changes in mean age of stratospheric air decreases as the BDC is en- Discussions Open Access the atmospheric circulation in the stratosphere. hanced under global warming (Austin and Li, 2006;Open Access Li et al., 2008), but a significant change of the air age has not been Ocean Science observed so far (EngelOcean et al., 2009). Science Since the gravitational separation occurs physically due to gravity, its effect is ex- Discussions 1 Introduction pected to become more pronounced as the stratospheric air is slowly transported poleward after it enters the tropical strato- Open Access The gravity of the earth prevents the atmosphere from dis- sphere from the troposphere. Therefore, in thisOpen Access conceptual sipating into space. It is also known that the gravity causes framework, by measuring gravitational separation, it would Solid Earth atmospheric molecules to separate depending on their mo- be possible to obtain informationSolid about Earth changes in the strato- lar masses, which is called “gravitational separation”. It spheric circulation. To confirm this supposition, we simulate Discussions is widely recognized that gravitational separation of atmo- Open Access Open Access Published by Copernicus Publications on behalf of the European Geosciences Union. The Cryosphere The Cryosphere Discussions 8788 S. Ishidoya et al.: Gravitational separation in the stratosphere stratospheric gravitational separation using a 2-dimensional and model of the middle atmosphere (SOCRATES) (Huang et al. 40 36 n Ar /n Ar sample 1998; Park et al., 1999; Khosravi et al., 2002), and then ex- δ 40Ar = − 1. (1e) 40 36 amine the relationship between gravitational separation and n Ar /n Ar reference the stratospheric circulation. Here, n means the amount of each substance, and “refer- ence” is dried natural air filled in a high-pressure cylinder 2 Stratospheric air collection and sample analyses in the suburban areas of Sendai (38◦ N, 140◦ E, 150 m a.s.l.), Japan, in November 1998 as a primary standard of our mea- The collection of stratospheric air has been carried out using surements (Ishidoya et al., 2003). We have also prepared 6 a balloon-borne cryogenic air sampler over Sanriku (39◦ N, working standard air by a similar procedure, and the working 142◦ E) and Taiki (43◦ N, 143◦ E), Japan, since 1985 (e.g., standards showed no systematic trend in the δ(15N), δ(18O) Nakazawa et al., 1995; Aoki et al., 2003). Our air sampler and δ(O2/N2) with respect to the primary standard since 1999 consists of 12 stainless-steel sample containers, a liquid he- (Ishidoya et al., 2012). To detect gravitational separation in 15 18 lium dewar, a receiver, a transmitter, a control unit and batter- the stratosphere, we measured the δ( N) of N2, δ( O) of ies; all these components are housed in a water- and pressure- O2 and δ(O2/N2) of the air samples collected over Sanriku proof aluminum chamber (Honda, 1990; Honda et al., 1996). on 31 May 1999, 28 August 2000, 30 May 2001, 4 Septem- The volume of each sample container is about 760 mL, and ber 2002, 6 September 2004, 3 June 2006 and 4 June 2007, its inner wall is electropolished. A motor-driven metal-to- as well as of those collected over Taiki on 22 August 2010, metal seal valve is attached to each sample container. The using a mass spectrometer (Finnigan MAT-252) (Ishidoya et 15 18 other end of the motor-driven valve is connected to a sam- al., 2003). δ( N) of N2 and δ( O) of O2 were also mea- ple intake, located 3.5 m below the bottom of the aluminum sured for the samples collected over Sanriku on 8 June 1995. chamber, through a manifold and a stainless-steel bellows Furthermore, the air samples collected over Sanriku on 4 15 18 tube with an inner diameter of 15 mm reinforced with mesh. June 2007 were analyzed for δ( N) of N2, δ( O) of O2, 40 Before sampling, all the sample containers were evacuated δ(O2/N2), δ(Ar/N2) and δ( Ar) using a new mass spectrom- by heating and then cooled by filling the dewar with liquid eter (Thermo Scientific DELTA-V). It is noted that the δ(15N) He. Then, the cryogenic air sampler was connected to a large and δ(18O) values measured by using the MAT-252 are con- balloon, launched from the balloon center at Sanriku or Taiki firmed to agree with those measured by DELTA-V within early in the morning and recovered from the Pacific Ocean the measurement precision, as seen in Fig. 1 discussed be- around noon. Air samples were collected in the containers at low. The measurement precision (external reproducibility) 15 18 assigned altitudes by opening and closing the motor-driven of MAT-252 for δ(O2/N2), δ( N) and δ( O) of the strato- valves using a telecommand system. The flow rates of sam- spheric air samples was estimated to be ± 30–40, ± 12 and ple air at the respective altitudes were 50–100 L min−1 at am- ± 26 per meg (± 1σ), respectively, by repeatedly introducing bient pressures, and typical amounts of air samples collected the same air sample into the mass spectrometer (Ishidoya et were about 25 L at standard temperature (0 ◦C) and pressure al., 2006). On the other hand, DELTA-V showed a precision 15 18 (1013.25 hPa). of ± 5, ± 7, ± 35 and ± 22 per meg for δ( N) of N2, δ( O) 15 18 40 In this study, δ( N) of N2, δ( O) of O2, δ(O2/N2), of O2, δ(Ar/N2) and δ( Ar), respectively. 40 δ(Ar/N2) and δ( Ar) are reported in per meg (one per meg is equal to 1 × 10−6), 3 Results and discussion n15N14N/n14N14N 15 sample δ N = − 1, (1a) 3.1 Vertical profiles of the isotopic ratios of N2,O2 and n15 14 /n14 14 N N N N reference Ar, and the Ar/N2 ratio Figure 1 shows the vertical profiles of the isotopic ratios of n18O16O/n16O16O 18 sample N2,O2, and Ar, and the Ar/N2 ratio over Sanriku on 4 July δ O = − 1, (1b) 18 n18O16O/n16O16O 2007.
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