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The seasonal variations of greenhouse gases at about 11 km altitude were analyzed from monthly air samples collected aboard a commercial airliner flying between Europe and Japan from April 2012 to March 2014. Compared to lower latitudes, the upper troposphere between 50 and 70°N showed higher CH4 and SF6 and an earlier seasonal phase of CO2. However, N2O values were similar to those in the subtropics. CH4, N2O, and SF6 in the lower stratosphere with potential temperature of up to 50 K above the tropopause showed seasonal variations with maxima in November/December and minima in April/May. At potential temperatures of 37.5–50 K above the tropopause, SF6 age was estimated to be about 22 months in May and 9 months in November. This strong seasonal variation is explained by the subsidence of high-stratospheric air in spring and the effective flushing of the lowermost stratospheric air with tropospheric air in autumn.

In this study we reexamine nearly four decades of in situ balloon-based stratospheric observations of SF6 and CO2 with an idealized model and reanalysis products. We use new techniques to account for the spatial and temporal inhomogeneity of the sparse balloon profiles and to calculate stratospheric mean ages of air more consistently from the observations with the idealized model. By doing so we are able to more clearly show and account for the variability of mean age of air throughout the bulk of the depth of the stratosphere. From an idealized model guided by the observations, we identify variability in the mean age due to the seasonal cycle of stratospheric transport, the quasi-biennial oscillation in tropical zonal winds, major volcanic eruptions, and linear trends that vary significantly with altitude. We calculate a negative mean age trend in the lowest 5 km of the stratosphere that agrees within uncertainties with a trend calculated from a set of chemistry climate model mean ages in this layer. The mean age trends reverse sign in the middle and upper stratosphere and are in agreement with a previous positive trend estimate using the same observational data set, although we have substantially reduced the uncertainty on the trend. Our analysis shows that a long time series of in situ profile measurements of trace gases such as SF6 and CO2 can be a unique and useful indicator of stratospheric circulation variability on a range of time scales and an important contributor to help validate the stratospheric portion of global chemistry climate models. However, with only SF6 and CO2 measurements, the competing effects on mean age between mean circulation and mixing (tropical entrainment) are not uniquely separable.

We have carried out monthly flask sampling using aircraft, in the altitude range of 0-7 km, over the boreal wetlands in Surgut (61°N, 73°E; since 1993) and a pine forest near Novosibirsk (55°N, 83°E; since 1997), both located in the West Siberian Lowland (WSL). The temporal variation of methane (CH4) concentrations at all altitudes at both sites exhibited an increasing trend with stagnation during 2000-2006 as observed globally from ground-based networks. In addition to a winter maximum as seen at other remote sites in northern mid to high latitudes, another seasonal maximum was also observed in summer, particularly in the lower altitudes over the WSL, which could be attributed to emissions from the wetlands. Our measurements suggest that the vertical gradient at Surgut has been decreasing; the mean CH4 difference between 5.5 km and 1.0 km changed from 64±5 ppb during 1995-1999 to 37±3 ppb during 2009-2013 (mean ± standard error). No clear decline in the CH4 vertical gradient appeared at Novosibirsk. Simulations using an atmospheric chemistry-transport model captured the observed decrease in the vertical CH4 gradient at Surgut when CH4 emissions from Europe decreased but increased from the regions south of Siberia, e.g., East and South Asia. At Novosibirsk, the influence of the European emissions was relatively small. Our results also suggest that the regional emissions around the WSL did not change significantly over the period of our observations.

Stratospheric and upper tropospheric air samples were collected during 1994–2004 over Sanriku, Japan and in 1997 over Kiruna, Sweden. Using these archived air samples, we determined the triple oxygen-isotope composition of stratospheric CO2 and the N2O mixing ratio. The maximum Δ17OCO2 value of +12.2‰, resembling that observed previously in the mesosphere at 60 km height, was found in the middle stratosphere over Kiruna at 25.6 km height, suggesting that upper stratospheric and mesospheric air descended to the middle stratosphere through strong downward advection. A least-squares regression analysis of our observations on a δ18OCO2−δ17OCO2 plot (r2>0.95) shows a slope of 1.63±pm0.10, which is similar to the reported value of 1.71±0.06, thereby confirming the linearity of three isotope correlation with the slope of 1.6–1.7 in the mid-latitude lower and middle stratosphere. The slope decrease with increasing altitude and a curvy trend in three-isotope correlation reported from previous studies were not statistically significant. Using negative linear correlations of Δ17OCO2 and δ18OCO2 with the N2O mixing ratio, we quantified triple oxygen-isotope fluxes of CO2 to the troposphere as +48‰ GtC/yr (Δ17OCO2) and +38‰ GtC/yr (δ18OCO2) with ~30% uncertainty. Comparing recent model results and observations, underestimation of the three isotope slope and the maximum Δ17OCO2 value in the model were clarified, suggesting a smaller O2 photolysis contribution than that of the model. Simultaneous observations of δ18OCO2, δ17OCO2, and N2O mixing ratios can elucidate triple oxygen isotopes in CO2 and clarify complex interactions among physical, chemical, and photochemical processes occurring in the middle atmosphere.

Systematic collections of stratospheric air samples have been conducted over Japan since 1985 using a balloon-borne cryogenic sampler. The collection of stratospheric air samples was also carried out twice over Scandinavia and once over Antarctica. Vertical profiles of CO 2 concentration thus obtained over these locations were quite similar to each other; CO 2 concentration decreased with increasing altitude in the lower stratosphere and reached an almost constant value in the mid-stratosphere. δ 13 C of stratospheric CO 2 observed over these locations enriched with increasing altitude. A negative correlation between δ 13 C and CO 2 concentration with Δδ 13 C/ΔCO 2 of −0.02‰ ppmv −1 was found in the lower stratosphere. Although CO 2 concentration was almost constant in the mid-stratosphere, the δ 13 C enrichment was observed in succession. δ 18 O of stratospheric CO 2 also enriched with increasing altitude. The enrichment was significant; δ 18 O was almost 0‰ at the tropopause and reached a maximum value of about 11‰ at a layer with N 2 O concentration of about 10 ppbv. A compact relation between δ 18 O and N 2 O concentration was consistently observed for these locations. Stratosperic CO 2 over Japan showed a secular increase with an average rate of 1.4 ppmv yr −1 for the period 1985–2000. The secular increase was not constant with time, and temporal stagnation of the CO 2 increase was observed in 1997. DOI: 10.1034/j.1600-0889.2003.00059.x

[1] The atmospheric N2O variations between the Earth's surface and the lower stratosphere, simulated by an atmospheric general circulation model–based chemistry transport model (ACTM), are compared with aircraft and satellite observations. We validate the newly developed ACTM simulations of N2O for loss rate and transport in the stratosphere using satellite observations from the Aura Microwave Limb Sounder (Aura-MLS), with optimized surface fluxes for reproducing N2O trends observed at the surface stations. Observations in the upper troposphere/lower stratosphere (UT/LS) obtained by the Japan AirLines commercial flights commuting between Narita (36°N), Japan, and Sydney (34°S), Australia, have been used to study the role of stratosphere-troposphere exchange (STE) on N2O variability near the tropopause. Low N2O concentration events in the UT region are shown to be captured statistically significantly by the ACTM simulation. This is attributed to successful reproduction of stratospheric air intrusion events and N2O vertical/horizontal gradients in the lower stratosphere. The meteorological fields and N2O concentrations reproduced in the ACTM are used to illustrate the mechanisms of STE and subsequent downward propagation of N2O-depleted stratospheric air in the troposphere. Aircraft observations of N2O vertical profile over Surgut (West Siberia, Russia; 61°N), Sendai-Fukuoka (Japan; 34°N–38°N), and Cape Grim (Tasmania, Australia; 41°S) have been used to estimate the relative contribution of surface fluxes, transport seasonality in the troposphere, and STE to N2O seasonal cycles at different altitude levels. Stratospheric N2O tracers are incorporated in the ACTM for quantitative estimation of the stratospheric influence on tropospheric N2O. The results suggest strong latitude dependency of the stratospheric contribution to the tropospheric N2O seasonal cycle. The periods of seasonal minimum in the upper troposphere, which are spring over Japan and summer over Surgut, are in good agreement between the ACTM and observation and indicate a different propagation path of the stratospheric signal between the two sites in the Northern Hemisphere. The stratospheric tracer simulations, when utilized with the observed seasonal cycle, also provide qualitative information on the seasonal variation in surface fluxes of N2O.

The long-term changes of the stratospheric mixing ratio of CH4 over the period of 1978-2003 are derived from balloon-borne data of H-2, CH4 and N2O. The data were obtained by collecting whole air samples and subsequent gas chromatographic analyses. To eliminate the short-term variability attributed to dynamical processes, the N2O mixing ratio is used as a proxy for altitude. A correlation analysis for the individual years is applied and the CH4 mixing ratios are interpolated to four different levels of N2O, corresponding to altitudes of approximately 17, 23, 26 and 30 km at midlatitudes. For the investigated period of 1978 to 2003 we find increases at the four levels of 207 +/- 32 ppb, 159 +/- 21 ppb, 140 +/- 34 ppb and 111 +/- 60 ppb, respectively. The CH4 trend has slowed down in recent years and is best fitted by a second-order polynomial. The increase of CH4 can account for only 25-34% of the increase in stratospheric H2O of 1%/yr over the last decades as derived from previous studies. The simultaneously measured time series of stratospheric H-2 mixing ratios shows that the contribution of stratospheric H-2 to the H2O trend in the period 1988-2003 is minor.

[1] Vertical profiles of nitrous oxide and methane at high latitudes (57–72°N; 64–89°S) were observed by the Improved Limb Atmospheric Spectrometer (ILAS) solar occultation sensor aboard Advanced Earth Observing Satellite. These measurements were made continuously from November 1996 through June 1997 with some additional periods in September–October 1996. A validation study of the nitrous oxide and methane data processed with the Version 5.20 ILAS retrieval algorithm is presented in this paper. Comparisons are made with (1) nitrous oxide and methane obtained by the ILAS validation balloon campaigns at Kiruna, Sweden, and at Fairbanks, Alaska, in the Arctic; (2) nitrous oxide and methane by the Photochemistry of Ozone Loss in the Arctic Region in Summer aircraft campaign in the Arctic; (3) nitrous oxide by the ground-based spectroscopic measurements and by the aircraft-based remote sensing measurements in the Arctic; and (4) methane by satellite measurements of the Version 19 Halogen Occultation Experiment in the Arctic and Antarctic. Comparisons of ILAS nitrous oxide and methane with Upper Atmosphere Research Satellite Reference Atmosphere data are also made. The results of the comparisons and additional ILAS internal consistency analyses are as follows: (1) the uncertainty of ILAS nitrous oxide is better than 10% over 10–30 km in altitude, and is larger than 50% over 30–40 km, which is comparable to the expected total errors of the ILAS measurements; (2) the uncertainty of ILAS methane is better than 10% over 10–50 km, except for 15–30 km in winter with positive biases exceeding 20%, which is smaller than or comparable to the expected total errors of the ILAS measurements (the quality of ILAS methane in the polar lower stratosphere is better in summer than in winter). In summary, the characteristics of ILAS measurements, i.e., high sampling frequency in polar latitudes with high vertical resolution, along with the good quality of ILAS Version 5.20 nitrous oxide for 10–40 km and the good quality of ILAS Version 5.20 methane for 10–50 km except for 15–30 km in winter, make the ILAS nitrous oxide and methane data set valuable for scientific study of various polar stratospheric phenomena.

[1] Measurements of CFC-12 were made by the Improved Limb Atmospheric Spectrometer (ILAS) between 57°N and 72°N in the Northern Hemisphere and between 64°S and 89°S in the Southern Hemisphere. ILAS was launched on 17 August 1996 on board the Advanced Earth Observing Satellite (ADEOS). The ILAS validation balloon campaigns were carried out from Kiruna, Sweden (68°N, 21°E), in February and March 1997 and from Fairbanks, Alaska (65°N, 148°W), in April and May 1997. During these validation balloon campaigns, CFC-12 was measured with the in situ instruments ASTRID, BONBON, and SAKURA and the remote sensing spectrometers MIPAS-B, FIRS-2, and MkIV. ILAS version 6.0 CFC-12 profiles obtained at the nearest location to the validation balloon measurement are compared with these validation balloon measurements. The quality of ILAS CFC-12 data processed with the version 6.0 algorithm improved significantly compared to previous versions. Low relative differences between ILAS CFC-12 and the correlative measurements of about 10% were found between 13 and 20 km. The comparison of vertical profiles shows that ILAS CFC-12 data are useful below about 20–22 km inside the vortex and below about 25 km outside the vortex. However, at greater altitudes the relative percentage difference increases very strongly with increasing altitude. Further, correlations of CFC-12 with N2O show a good agreement with the correlative measurements for N2O values of N2O > 150 ppbv. In summary, ILAS CFC-12 data are now suitable for scientific studies in the lower stratosphere.

We present observations of CH 4 concentrations from the lower to upper troposphere (LT and UT) over Japan during 1988–2010 based on aircraft measurements from the Tohoku University (TU). The analysis is aided by simulation results using an atmospheric chemistry transport model (i.e. ACTM). Tropospheric CH 4 over Japan shows interannual and seasonal variations that are dependent on altitudes, primarily reflecting differences in air mass origins at different altitudes. The long-term trend and interannual variation of CH 4 in the LT are consistent with previous reports of measurements at surface baseline stations in the northern hemisphere. However, those in the UT show slightly different features from those in the LT. In the UT, CH 4 concentrations show a seasonal maximum in August due to efficient transport of air masses influenced by continental CH 4 sources, while LT CH 4 reaches its seasonal minimum during summer due to enhanced chemical loss. Vertical profiles of the CH 4 concentrations also vary with season, reflecting the seasonal cycles at the respective altitudes. In summer, transport of CH 4 -rich air from Asian regions elevates UT CH 4 levels, forming a uniform vertical profile above the mid-troposphere. On the other hand, CH 4 decreases nearly monotonically with altitude in winter–spring. The ACTM simulations with different emission scenarios reproduce general features of the tropospheric CH 4 variations over Japan. Tagged tracer simulations using the ACTM indicate substantial contributions of CH 4 sources in South Asia and East Asia to the summertime high CH 4 values observed in the UT. This suggests that our observations over Japan are highly sensitive to CH 4 emission signals particularly from Asia. Keywords: methane, aircraft observation, long-term variation, seasonality, vertical profile, Asian outflow, atmospheric chemistry transport model (Published: 22 May 2014) Citation: Tellus B 2014, 66 , 23837, http://dx.doi.org/10.3402/tellusb.v66.23837 To access the supplementary material to this article, please see Supplementary files under Article Tools online.

Systematic measurements of the atmospheric O 2 /N 2 ratio have been made using aircraft and ground-based stations in Japan since 1999. The observed seasonal cycles of the O 2 /N 2 ratio and atmospheric potential oxygen (APO) vary almost in opposite phase to that of the CO 2 concentration at all altitudes, and their amplitudes and phases are generally reduced and delayed, respectively, with increasing altitude. Simulations of APO using two atmospheric transport models reproduce general features of the observed seasonal cycle, but both models fail to reproduce the phase at an altitude ranging from 8 km to the tropopause. By analysing the observed secular trends of APO and CO 2 concentration, and assuming a global net oceanic O 2 outgassing of 0.2±0.5 GtC yr −1 , we estimate global average terrestrial biospheric and oceanic CO 2 uptake for the period 2000–2010 to be 1.0±0.8 and 2.5±0.7 GtC yr −1 , respectively. Keywords: O 2 /N 2 ratio over Japan, Atmospheric Potential Oxygen (APO), Simulation of APO in the free troposphere, Terrestrial biospheric CO 2 uptake, Oceanic CO 2 uptake (Published: 5 July 2012) Citation: Tellus B 2012, 64 , 18964, http://dx.doi.org/10.3402/tellusb.v64i0.18964