It has been demonstrated that there is a globally unified linear relationship between the interannual varia-tions of the fall-to-spring polar ozone accumulation and the winter-mean poleward eddy heat flux on the 100 hPa pressure surface. The foundation of this relationship is investigated using time-slice experiments on a chemistry-climate model with two levels of ozone-depleting substances (ODSs). The features of the transport field are interpreted by decomposing the horizontal ozone flux caused by the residual circulation into contributing processes including the eddy heat flux with the aid of the transformed Eulerian-mean momentum equation followed by rearrangement of terms. The linear relationship between the interannual variations of the fall-to-spring ozone buildup integrated poleward and above a reference point Pref on a meridional plane and the poleward eddy heat flux during the corresponding period at Pref is realized for each hemisphere implying that the interhemispheric unification should be treated with caution. This relationship is interpreted using the fact that the interannual variation of poleward ozone transport in the upper stratosphere is captured well by the vertical convergence of the constituent-based Eliassen-Palm (EP) flux (F similar to), which is defined as the product of the constitu-ent (ozone) mixing ratio and EP flux. The eddy momentum flux contributes to the meridional ozone transport in combina-tion with the eddy heat flux in the form of the divergence of F similar to, although it is not responsible for realizing the linear relationship. The dependence of the linearity on the location of Pref and ODS levels is discussed.

The ozonesonde observations in Hanoi, Vietnam, over 14 years since 2004, have confirmed an enhancement in lower tropospheric ozone concentration at about 3 km altitude in the spring season. We investigated the evolution of the ozone enhancement from analysis of meteorological data, backward trajectories, and model sensitivity experiments. In spring, air masses over Hanoi exhibit strong height dependence. At 3 km, the high‐ozone air masses originate from the land area to the west of Hanoi, while low‐ozone air masses below about 1.5 km are from the oceanic area to the east. Above 4 km, the air masses are mostly traced back to the farther west area. The chemical transport model simulations revealed that precursor emissions from biomass burning in the inland Indochina Peninsula have the largest contribution to the lower tropospheric ozone enhancement, which is transported upward and eastward and overhangs the clean air intrusion from the ocean to the east of Hanoi. At this height level, the polluted air has the horizontal extent of about 20° in longitude and latitude. The polluted air observed in Hanoi is transported further east and widely spread over the northern Pacific Ocean.

The ozonesonde observations in Hanoi, Vietnam, over fourteen years since 2004 have confirmed the enhancement in lower tropospheric ozone concentration at about 3 km altitude in the spring season. We investigated the evolution of the ozone enhancement from analysis of meteorological data, backward trajectories, and model sensitivity experiments. In spring, air masses over Hanoi exhibit strong height dependence. At 3km, the high-ozone air masses originate from the land area to the west of Hanoi, while low-ozone air masses below about 1.5 km are from the oceanic area to the east. Above 4 km, the air masses are mostly traced back to the farther west area. The chemical transport model simulations revealed that precursor emissions from biomass burning in the inland Indochina Peninsula have the largest contribution to the lower tropospheric ozone enhancement, which is transported upward and eastward and overhangs the clean air intrusion from the ocean to the east of Hanoi. At this height level, the polluted air has the horizontal extent of about 20 degrees in longitude and latitude. The polluted air observed in Hanoi is transported further east and widely spread over the northern Pacific Ocean.

Stratospheric profiles of the mean age of air estimated from cryogenic air samples acquired during a field campaign over Indonesia, the Coordinated Upper-Troposphere-to-Stratosphere Balloon Experiment in Biak, were investigated using the boundary impulse evolving response (BIER) method and Lagrangian backward trajectories, with the aid of an atmospheric general circulation model-based chemistry transport model (ACTM). The ACTM provides realistic meteorological fields at 1-hour intervals by nudging toward the European Centre for Medium- Range Weather Forecasts Reanalysis-Interim. Since the BIER method is capable of taking unresolved diffusive processes into account, while the Lagrangian method can distinguish the pathways the air parcels took before reaching the sample site, the application of the two methods to the common transport field simulated by the ACTM is useful in assessing the CO2- and SF6-derived mean ages. The reliability of the simulated transport field has been verified by the reproducibility of the observed CO2, SF6, and water vapor profiles using the Lagrangian method. The profile of CO2 age is reproduced reasonably well by the Lagrangian method with a small young bias being consistent with the termination of trajectories in finite length of time, whereas the BIER method overestimates the CO2 age above the altitude of 25 km, possibly due to high diffusivity in the transport model. In contrast, the SF6 age is only reproducible in the lower stratosphere, and far exceeds the estimates from the Lagrangian method above the altitude of 25 km. As air parcels of mesospheric origin are excluded in the Lagrangian age estimation, this discrepancy, together with the fact that the observed SF6 mole fractions are much lower than the trajectory-derived values in this height region, supports the idea that the stratospheric air samples are mixed with SF6-depleted mesospheric air, leading to overestimation of the mean age.

A three-dimensional simulation of gravitational separation, defined as the process of atmospheric molecule separation under gravity according to their molar masses, is performed for the first time in the upper troposphere and lower stratosphere. We analyze distributions of two isotopes with a small difference in molecular mass (13C16O2 (Mi=45) and 12C16O2 (Mi=44)) simulated by the National Institute for Environmental Studies (NIES) chemical transport model (TM) with a parameterization of molecular diffusion. The NIES model employs global reanalysis and an isentropic vertical coordinate and uses optimized CO2 fluxes. The applicability of the NIES TM to the modeling of gravitational separation is demonstrated by a comparison with measurements recorded by high-precision cryogenic balloon-borne samplers in the lower stratosphere. We investigate the processes affecting the seasonality of gravitational separation and examine the age of air derived from the tracer distributions modeled by the NIES TM. We find a strong relationship between age of air and gravitational separation for the main climatic zones. The advantages and limitations of using age of air and gravitational separation as indicators of the variability in the stratosphere circulation are discussed.

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.

Vertical profiles of carbon dioxide (CO2) mixing ratio in the equatorial eastern and western Pacific were measured by newly developed balloon-borne CO2 sondes in February 2012 (two soundings) and February-March 2015 (four soundings), respectively. The 1-10 km vertically averaged CO2 mixing ratios lie between the background surface values in the Northern Hemisphere (NH) and those in the Southern Hemisphere (SH) monitored at ground-based sites during these periods. A backward trajectory analysis, taking account of convective mixing processes using geostationary satellite cloud-image data, is applied to the measured CO2 profiles to estimate the origin of the observed air masses. Air masses originating in the SH show low CO2 mixing ratios that are similar to the background values in the SH. This relationship is confirmed by a positive correlation (similar to 0.6) between the CO2 mixing ratio and the latitude of air mass origin which is found from trajectory calculations. This result suggests that the CO2 distribution in the troposphere over the equatorial Pacific is controlled by monthly time scale, large-scale CO2 distribution and weekly time-scale atmospheric transport processes. Furthermore, this study shows that the combination of CO2 sonde measurements and trajectory analysis, taking account of convective mixing, is a useful tool in investigating CO2 transport processes.

Vertical profiles of nitrous oxide (N2O) and its isotopocules, isotopically substituted molecules, were obtained over the Equator at altitudes of 16–30 km. Whole air samples were collected using newly developed balloon-borne compact cryogenic samplers over the eastern equatorial Pacific in 2012 and Biak Island, Indonesia, in 2015. They were examined in the laboratory using gas chromatography and mass spectrometry. The mixing ratio and isotopocule ratios of N2O in the equatorial stratosphere showed a weaker vertical gradient than the previously reported profiles in the subtropical and mid-latitude and high-latitude stratosphere. From the relation between the mixing ratio and isotopocule ratios, further distinct characteristics were found over the Equator: (1) observed isotopocule fractionations (ε values) in the middle stratosphere (25–30 km or [N2O] < ca. 260 nmol mol−1) are almost equal to ε values reported from broadband photolysis experiments conducted in the laboratory; (2) ε values in the lower stratosphere (< ca. 25 km or [N2O] > ca. 260 nmol mol−1) are about half of the experimentally obtained values, being slightly larger than those observed in the mid-latitude and high-latitude lower stratosphere ([N2O] > ca. 170 nmol mol−1). These results from the deep tropics suggest the following. (i) The timescale for quasi-horizontal mixing between tropical and mid-latitude air in the tropical middle stratosphere is sufficiently slow relative to the tropical upwelling rate that isotope fractionation approaches the Rayleigh limit for N2O photolysis. (ii) The air in the tropical lower stratosphere is exchanged with extratropical air on a timescale that is shorter than that of photochemical decomposition of N2O. Previously observed ε values, which are invariably smaller than those of photolysis, can be explained qualitatively using a three-dimensional chemical transport model and using a simple model that assumes mixing of aged tropical air and extratropical air during residual circulation. Results show that isotopocule ratios are useful to examine the stratospheric transport scheme deduced from tracer–tracer relations.

The stratospheric response to climate forcing, such as an increase in greenhouse gases, is often unpredictable because of interactions between radiation, dynamics, and chemistry. Climate models are unsuccessful in simulating the realistic distribution of stratospheric water vapor. The long-term trend of the stratospheric age of air (AoA), a measure that characterizes the stratospheric turnover time, remains inconsistent between diagnoses in climate models and estimates from tracer observations. For these reasons, observations designed specifically to distinguish the effects of individual contributing processes are required. Here, we report on the Coordinated Upper-Troposphere-to-Stratosphere Balloon Experiment in Biak (CUBE/Biak), an observation campaign organized in Indonesia. Being inside the “tropical pipe” makes it possible to study the dehydration in the tropical tropopause layer and the gradual ascent in the stratosphere while minimizing the effects of multiple circulation pathways and wave mixing. Cryogenic sampling of minor constituents and major isotopes was conducted simultaneously with radiosonde observations of water vapor, ozone, aerosols, and cloud particles. The water vapor “tape recorder,” gravitational separation, and isotopocules are being studied in conjunction with tracers that are accumulated in the atmosphere as dynamical and chemical measures of elapsed time since stratospheric air entry. The observational estimates concerning the AoA and water vapor tape recorder are compared with those derived from trajectory calculations.

Size distributions and volatility of aerosols in the Tropical Tropopause Layer (TTL) over Tarawa (1.5 o S, 173.0 o E) were observed using balloon-borne dual optical particle counters (OPC) in January 2016. One OPC observed number concentration of ambient aerosols and another OPC observed aerosol size distribution denuded at 200 o C, in order to discuss volatility of aerosls. Unusual aerosol layer was found in the stratosphere from 18 to 22 km in altitude. The layer was divided into two sub-layers. Upper layer was characterized by smaller high volatile aerosol, and lower one by mixture with larger submicron un-volatile aerosol. The feature was similar to fresh volcanic aerosol layer, however we did not find any report of large volcanic eruption in 2015. We will discuss about origin of the layer.

In the atmosphere over the turbopause (about 100 km), the mole fraction of heavier molecules decreases with increasing altitude due to diffusive separation in Earth’s gravitational field. Recently, Ishidoya et al. (2013) reported such gravitational separation of the atmosphere is also found in the middle to lower stratosphere (about 15-35 km) over Japan from high precision measurements of the composition of the atmospheric major components. To investigate whether gravitational separation is also detectable over the equatorial region or not, we carried out collection of the stratospheric air using a balloon-borne cryogenic air sampler over Biak, Indonesia during February 22-28, 2015. For the observation, we used a Joule-Thomson minicooler, developed by Morimoto et al. (2009), as the cryogenic air sampler, and succeeded to collect 8 air samples at heights of 17-29 km. The collected air samples were analyzed for delta(Ar/N2), delta(O2/N 2), delta N of N2, delta O of O2 and delta Ar by using a mass spectrometer (Ishidoya and Murayama, 2014), and the measured values showed small but significant decrease with altitude probably due to gravitational separation. The amount of gravitational separation, evaluated as delta values for the mass number difference of 1 (e.g. delta for NN/NN), is found to be 11 per meg at the height of 29 km. Based on the observed gravitational separation and a 1-dimensional steady state eddy diffusion/molecular diffusion model, we estimated 1-dimensional vertical eddy diffusion coefficients (Kz) over the equatorial region. By using the average Kz from the surface to the middle stratosphere, we calculated a timescale of the vertical diffusion for a length scale from the surface to the middle stratosphere assuming simple Fickian diffusion. We found that the calculated timescale agrees with the elapsed time since the stratospheric air passed an upper boundary of the tropical tropopause layer (TTL), estimated from tape recorder signals of stratospheric water vapor (Mote et al., 1996), which is significantly smaller than the mean age of air estimated from CO2 concentration (CO2 age). This discrepancy may be due to insensitivity of gravitational separation to mixing processes in Brewer-Dobson circulation, of which variations change the mean age of air significantly. References Ishidoya, S. et al. (2013) Gravitational separation in the stratosphere –a new indicator of atmospheric circulation. Atmos. Chem. Phys., 13, 8787–8796, www.atmos-chem-phys.net/13/8787/2013/, doi:10.5194/acp-13-8787-2013. Ishidoya, S. & Murayama, S. (2014) Development of high precision continuous measuring system of the atmospheric O2/N2 and Ar/N2 ratios and its application to the observation in Tsukuba, Japan. Tellus B, 66, 22574, http://dx.doi.org/ 10.3402/tellusb.v66.22574. Morimoto et al. (2009) A new compact air sampler and its application in stratospheric greenhouse gas observation at Syowa station, Antarctia. J. Atmos. Oceanic and Technol., 26 10.1175/2009JTECHA1283.1. Mote, P. W. et al. (1996) An atmospheric tape recorder: The imprint of tropical tropopause temperatures on stratospheric water vapor. J. Geophys. Res., 101, 3989-4006. AAS11-12 Japan Geoscience Union Meeting 2016

The sudden decrease in stratospheric water vapor at around the year 2000 to 2001 is relatively well accepted in spite of the difficulty to quantify the long-term variations. This stepwise change is studied by examining the entry value of water to the stratosphere ([H2O]e) and some Lagrangian diagnostics of dehydration taking place in the tropical tropopause layer (TTL). The analysis is made using the backward kinematic trajectories initialized every ∼ 10 days from January 1997 to December 2002 at 400 K potential temperature surface in the tropics. The [H2O]e is estimated by the ensemble mean value of the water saturation mixing ratio (SMR) at the Lagrangian cold point (LCP) where SMR becomes minimum (SMRmin) in the TTL before reaching the 400 K surface. The drop in [H2O]e is identified to have occurred in September 2000. The horizontal projection of September trajectories, tightly trapped by anticyclonic circulation around the Tibetan high, shows eastward expansion since the year 2000. Associated changes are measured by three-dimensional bins, each having the dimension of 10° longitude by 10° latitude within the TTL. The probability distribution of LCPs shows an appreciable change exhibiting a composite pattern of two components: (i) the dipole structure consisting of the decrease over the Bay of Bengal and Malay Peninsula and the increase over the northern subtropical western Pacific and (ii) the patterns of the decrease over the equatorial western Pacific and the increase over the central Pacific that are almost symmetric with respect to the Equator. The SMRmin shows a general decrease in the tropics with some enhancement in the central Pacific. The expectation values, defined by the multiple of the probability of LCP events and the ensemble mean values of SMRmin, are calculated on each bin for both periods prior and posterior to the drop. These values are the spatial projection of [H2O]e on an individual bin. The results indicate that the drop is brought about by the decrease in water transport borne by the air parcels that have experienced the LCP over the Bay of Bengal and the western tropical Pacific. The former is related to the eastward expansion of the anticyclonic circulation around the weakened Tibetan high, while the latter would be linked to the eastward expansion of western tropical warm water to the central Pacific. This oceanic surface forcing may be responsible also for the modulation of dehydration efficiency in the successive northern winter. The drop in September 2000 and the sustained low values thereafter of [H2O]e are thus interpreted as being driven by the changes in thermal forcing from the continental and oceanic bottom boundaries.