scholarly journals Abiotic and biogeochemical signals derived from the seasonal cycles of tropospheric nitrous oxide

2010 ◽  
Vol 10 (11) ◽  
pp. 25803-25839
Author(s):  
C. D. Nevison ◽  
E. Dlugokencky ◽  
G. Dutton ◽  
J. W. Elkins ◽  
P. Fraser ◽  
...  
Keyword(s):  
Nitrous Oxide ◽  
Interannual Variability ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Seasonal Cycle ◽  
Coastal Upwelling ◽  
Seasonal Cycles ◽  
Mixing Ratios ◽  
Stratospheric Temperature ◽  
Deep Ocean Water

Abstract. Seasonal cycles in the mixing ratios of tropospheric nitrous oxide (N2O) are derived by detrending long-term measurements made at sites across four global surface monitoring networks. These cycles are examined for physical and biogeochemical signals. The detrended monthly data display large interannual variability, which at some sites challenges the concept of a "mean" seasonal cycle. The interannual variability in the seasonal cycle is not always correlated among networks that share common sites. In the Northern Hemisphere, correlations between detrended N2O seasonal minima and polar winter lower stratospheric temperature provide compelling evidence for a stratospheric influence, which varies in strength from year to year and can explain much of the interannual variability in the surface seasonal cycle. Even at sites where a strong, competing, regional N2O source exists, such as from coastal upwelling at Trinidad Head, California, the stratospheric influence must be understood in order to interpret the biogeochemical signal in monthly mean data. In the Southern Hemisphere, detrended surface N2O monthly means are correlated with polar lower stratospheric temperature in months preceding the N2O minimum, suggesting a coherent stratospheric influence in that hemisphere as well. A decomposition of the N2O seasonal cycle in the extratropical Southern Hemisphere suggests that ventilation of deep ocean water (microbially enriched in N2O) and the stratospheric influx make similar contributions in phasing, and may be difficult to disentangle. In addition, there is a thermal signal in N2O due to seasonal ingassing and outgassing of cooling and warming surface waters that is out of phase and thus competes with the stratospheric and ventilation signals. All the seasonal signals discussed above are subtle and are generally better quantified in high-frequency in situ data than in data from weekly flask samples, especially in the Northern Hemisphere. The importance of abiotic influences (thermal, stratospheric influx, and tropospheric transport) on N2O seasonal cycles suggests that, at many sites, surface N2O mixing ratio data by themselves are unlikely to provide information about seasonality in surface sources (e.g., for atmospheric inversions), but may be more powerful if combined with complementary data such as CFC-12 mixing ratios or N2O isotopes.

scholarly journals Exploring causes of interannual variability in the seasonal cycles of tropospheric nitrous oxide

2011 ◽  
Vol 11 (8) ◽  
pp. 3713-3730 ◽  
Author(s):  
C. D. Nevison ◽  
E. Dlugokencky ◽  
G. Dutton ◽  
J. W. Elkins ◽  
P. Fraser ◽  
...  
Keyword(s):  
Nitrous Oxide ◽  
Interannual Variability ◽  
Empirical Evidence ◽  
Southern Hemisphere ◽  
Seasonal Cycle ◽  
Coastal Upwelling ◽  
Transport Model ◽  
Seasonal Cycles ◽  
Stratospheric Temperature

Abstract. Seasonal cycles in the mixing ratios of tropospheric nitrous oxide (N2O) are derived by detrending long-term measurements made at sites across four global surface monitoring networks. The detrended monthly data display large interannual variability, which at some sites challenges the concept of a "mean" seasonal cycle. In the Northern Hemisphere, correlations between polar winter lower stratospheric temperature and detrended N2O data, around the month of the seasonal minimum, provide empirical evidence for a stratospheric influence, which varies in strength from year to year and can explain much of the interannual variability in the surface seasonal cycle. Even at sites where a strong, competing, regional N2O source exists, such as from coastal upwelling at Trinidad Head, California, the stratospheric influence must be understood to interpret the biogeochemical signal in monthly mean data. In the Southern Hemisphere, detrended surface N2O monthly means are correlated with polar spring lower stratospheric temperature in months preceding the N2O minimum, providing empirical evidence for a coherent stratospheric influence in that hemisphere as well, in contrast to some recent atmospheric chemical transport model (ACTM) results. Correlations between the phasing of the surface N2O seasonal cycle in both hemispheres and both polar lower stratospheric temperature and polar vortex break-up date provide additional support for a stratospheric influence. The correlations discussed above are generally more evident in high-frequency in situ data than in data from weekly flask samples. Furthermore, the interannual variability in the N2O seasonal cycle is not always correlated among in situ and flask networks that share common sites, nor do the mean seasonal amplitudes always agree. The importance of abiotic influences such as the stratospheric influx and tropospheric transport on N2O seasonal cycles suggests that, at sites remote from local sources, surface N2O mixing ratio data by themselves are unlikely to provide information about seasonality in surface sources, e.g., for atmospheric inversions, unless the ACTMs employed in the inversions accurately account for these influences. An additional abioitc influence is the seasonal ingassing and outgassing of cooling and warming surface waters, which creates a thermal signal in tropospheric N2O that is of particular importance in the extratropical Southern Hemisphere, where it competes with the biological ocean source signal.

scholarly journals Interannual variability of precipitable water

1996 ◽  
Vol 14 (4) ◽  
pp. 464-467 ◽  
Author(s):  
R. P. Kane
Keyword(s):  
Interannual Variability ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Precipitable Water ◽  
Radiosonde Data ◽  
High Latitudes ◽  
Zonal Winds ◽  
Low Latitudes ◽  
Linear Trends

Abstract. The 12-month running means of the surface-to-500 mb precipitable water obtained from analysis of radiosonde data at seven selected locations showed three types of variability viz: (1) quasi-biennial oscillations; these were different in nature at different latitudes and also different from the QBO of the stratospheric tropical zonal winds; (2) decadal effects; these were prominent at middle and high latitudes and (3) linear trends; these were prominent at low latitudes, up trends in the Northern Hemisphere and downtrends in the Southern Hemisphere.

scholarly journals Simulations of Global Hurricane Climatology, Interannual Variability, and Response to Global Warming Using a 50-km Resolution GCM

2009 ◽  
Vol 22 (24) ◽  
pp. 6653-6678 ◽  
Author(s):  
Ming Zhao ◽  
Isaac M. Held ◽  
Shian-Jiann Lin ◽  
Gabriel A. Vecchi
Keyword(s):  
Global Warming ◽  
Interannual Variability ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Vertical Shear ◽  
Shallow Convection ◽  
Coupled Models ◽  
Lower Boundary Condition ◽  
Atlantic Hurricane ◽  
Sst Anomalies

Abstract A global atmospheric model with roughly 50-km horizontal grid spacing is used to simulate the interannual variability of tropical cyclones using observed sea surface temperatures (SSTs) as the lower boundary condition. The model’s convective parameterization is based on a closure for shallow convection, with much of the deep convection allowed to occur on resolved scales. Four realizations of the period 1981–2005 are generated. The correlation of yearly Atlantic hurricane counts with observations is greater than 0.8 when the model is averaged over the four realizations, supporting the view that the random part of this annual Atlantic hurricane frequency (the part not predictable given the SSTs) is relatively small (<2 hurricanes per year). Correlations with observations are lower in the east, west, and South Pacific (roughly 0.6, 0.5, and 0.3, respectively) and insignificant in the Indian Ocean. The model trends in Northern Hemisphere basin-wide frequency are consistent with the observed trends in the International Best Track Archive for Climate Stewardship (IBTrACS) database. The model generates an upward trend of hurricane frequency in the Atlantic and downward trends in the east and west Pacific over this time frame. The model produces a negative trend in the Southern Hemisphere that is larger than that in the IBTrACS. The same model is used to simulate the response to the SST anomalies generated by coupled models in the World Climate Research Program Coupled Model Intercomparison Project 3 (CMIP3) archive, using the late-twenty-first century in the A1B scenario. Results are presented for SST anomalies computed by averaging over 18 CMIP3 models and from individual realizations from 3 models. A modest reduction of global and Southern Hemisphere tropical cyclone frequency is obtained in each case, but the results in individual Northern Hemisphere basins differ among the models. The vertical shear in the Atlantic Main Development Region (MDR) and the difference between the MDR SST and the tropical mean SST are well correlated with the model’s Atlantic storm frequency, both for interannual variability and for the intermodel spread in global warming projections.

scholarly journals Sixty years of radiocarbon dioxide measurements at Wellington, New Zealand 1954–2014

2016 ◽  
Author(s):  
Jocelyn C. Turnbull ◽  
Sara E. Mikaloff Fletcher ◽  
India Ansell ◽  
Gordon Brailsford ◽  
Rowena Moss ◽  
...  
Keyword(s):  
New Zealand ◽  
Southern Ocean ◽  
Co2 Emissions ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Seasonal Cycle ◽  
Fossil Fuel ◽  
Anthropogenic Sources ◽  
Deep Waters ◽  
Cape Grim

Abstract. We present 60 years of Δ14CO2 measurements from Wellington, New Zealand (41° S, 175° E). The record has been extended and fully revised. New measurements have been used to evaluate the existing record and to replace original measurements where warranted. This is the earliest atmospheric Δ14CO2 record and records the rise of the 14C "bomb spike", the subsequent decline in Δ14CO2 as bomb 14C moved throughout the carbon cycle and increasing fossil fuel CO2 emissions further decreased atmospheric Δ14CO2. The initially large seasonal cycle in the 1960s reduces in amplitude and eventually reverses in phase, resulting in a small seasonal cycle of about 2 ‰ in the 2000s. The seasonal cycle at Wellington is dominated by the seasonality of cross-tropopause transport, and differs slightly from that at Cape Grim, Australia, which is influenced by anthropogenic sources in winter. Δ14CO2 at Cape Grim and Wellington show very similar trends, with significant differences only during periods of known measurement uncertainty. In contrast, Northern Hemisphere clean air sites show a higher and earlier bomb 14C peak, consistent with a 1.4-year interhemispheric exchange time. From the 1970s until the early 2000s, the Northern and Southern Hemisphere Δ14CO2 were quite similar, apparently due to the balance of 14C-free fossil fuel CO2 emissions in the north and 14C-depleted ocean upwelling in the south. The Southern Hemisphere sites show a consistent and marked elevation above the Northern Hemisphere sites since the early 2000s, which is most likely due to reduced upwelling of 14C-depleted and carbon-rich deep waters in the Southern Ocean. This developing Δ14CO2 interhemispheric gradient is consistent with recent studies that indicate a reinvigorated Southern Ocean carbon sink since the mid-2000s, and suggests that upwelling of deep waters plays an important role in this change.

scholarly journals Global reconstruction reduces the uncertainty of oceanic nitrous oxide emissions and reveals a vigorous seasonal cycle

2020 ◽  
Vol 117 (22) ◽  
pp. 11954-11960 ◽  
Author(s):  
Simon Yang ◽  
Bonnie X. Chang ◽  
Mark J. Warner ◽  
Thomas S. Weber ◽  
Annie M. Bourbonnais ◽  
...  
Keyword(s):  
Nitrous Oxide ◽  
Seasonal Cycle ◽  
Coastal Upwelling ◽  
Learning Algorithm ◽  
Southern Oscillation ◽  
Latitudinal Gradients ◽  
Nitrous Oxide Emissions ◽  
Boreal Summer ◽  
Intergovernmental Panel ◽  
Tropical Ocean

Assessment of the global budget of the greenhouse gas nitrous oxide (N2O) is limited by poor knowledge of the oceanicN2O flux to the atmosphere, of which the magnitude, spatial distribution, and temporal variability remain highly uncertain. Here, we reconstruct climatologicalN2O emissions from the ocean by training a supervised learning algorithm with over 158,000N2O measurements from the surface ocean—the largest synthesis to date. The reconstruction captures observed latitudinal gradients and coastal hot spots ofN2O flux and reveals a vigorous global seasonal cycle. We estimate an annual meanN2O flux of 4.2 ± 1.0 Tg N⋅y−1, 64% of which occurs in the tropics, and 20% in coastal upwelling systems that occupy less than 3% of the ocean area. ThisN2O flux ranges from a low of 3.3 ± 1.3 Tg N⋅y−1in the boreal spring to a high of 5.5 ± 2.0 Tg N⋅y−1in the boreal summer. Much of the seasonal variations in globalN2O emissions can be traced to seasonal upwelling in the tropical ocean and winter mixing in the Southern Ocean. The dominant contribution to seasonality by productive, low-oxygen tropical upwelling systems (>75%) suggests a sensitivity of the globalN2O flux to El Niño–Southern Oscillation and anthropogenic stratification of the low latitude ocean. This ocean flux estimate is consistent with the range adopted by the Intergovernmental Panel on Climate Change, but reduces its uncertainty by more than fivefold, enabling more precise determination of other terms in the atmosphericN2O budget.

scholarly journals Global marine plankton functional type biomass distributions: coccolithophores

2012 ◽  
Vol 5 (2) ◽  
pp. 491-520 ◽  
Author(s):  
C. J. O'Brien ◽  
J. A. Peloquin ◽  
M. Vogt ◽  
M. Heinle ◽  
N. Gruber ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Seasonal Cycle ◽  
Marine Phytoplankton ◽  
The North ◽  
Carbon Biomass ◽  
Time Period ◽  
The Pacific ◽  
Individual Contributions ◽  
June July

Abstract. Coccolithophores are calcifying marine phytoplankton of the class Prymnesiophyceae. They are considered to play an import role in the global carbon cycle through the production and export of organic carbon and calcite. We have compiled observations of global coccolithophore abundance from several existing databases as well as individual contributions of published and unpublished datasets. We estimate carbon biomass using standardised conversion methods and provide estimates of uncertainty associated with these values. The database contains 58 384 individual observations at various taxonomic levels. This corresponds to 12 391 observations of total coccolithophore abundance and biomass. The data span a time period of 1929–2008, with observations from all ocean basins and all seasons, and at depths ranging from the surface to 500 m. Highest biomass values are reported in the North Atlantic, with a maximum of 501.7 μg C l−1. Lower values are reported for the Pacific (maximum of 79.4 μg C l−1) and Indian Ocean (up to 178.3 μg C l−1). Coccolithophores are reported across all latitudes in the Northern Hemisphere, from the Equator to 89° N, although biomass values fall below 3 μg C l−1 north of 70° N. In the Southern Hemisphere, biomass values fall rapidly south of 50° S, with only a single non-zero observation south of 60° S. Biomass values show a clear seasonal cycle in the Northern Hemisphere, reaching a maximum in the summer months (June–July). In the Southern Hemisphere the seasonal cycle is less evident, possibly due to a greater proportion of low-latitude data. The original and gridded datasets can be downloaded from Pangaea (http://doi.pangaea.de/10.1594/PANGAEA.785092).

Atmospheric short-chain-chlorinated paraffins in Melbourne, Australia – first extensive Southern Hemisphere observations

2017 ◽  
Vol 14 (2) ◽  
pp. 106 ◽  
Author(s):  
Robert W. Gillett ◽  
Ian E. Galbally ◽  
Melita D. Keywood ◽  
Jennifer C. Powell ◽  
Gavin Stevenson ◽  
...  
Keyword(s):  
Temperature Dependence ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Seasonal Cycle ◽  
Metal Cutting ◽  
Short Chain ◽  
Ambient Atmosphere ◽  
Industrial Chemicals ◽  
Chlorinated Paraffins ◽  
Atmospheric Concentrations

Environmental contextThis study presents the first comprehensive set of ambient atmospheric concentrations of short-chain-chlorinated paraffins in the Southern Hemisphere. The data show a seasonal cycle with a summer maximum and a winter minimum. The seasonal cycle is consistent with temperature dependence of the vapour pressure of the short-chain-chlorinated paraffins resulting in partitioning between the atmosphere and other reservoirs with a secondary modulation by soil moisture. AbstractThe first extensive measurements of short-chain chlorinated paraffins (SCCPs) in the atmosphere of the Southern Hemisphere are presented. The analytical and sampling methodologies used in this Australian study were verified by systematic testing along with two inter-comparisons with Northern Hemisphere laboratories with established SCCP programs. In the ambient atmosphere of Melbourne, Australia, in 2013–14, there was a clear seasonal cycle in SCCP monthly averaged concentrations, these ranging from 28.4ng m–3 in summer to 1.8ng m–3 in winter. Air temperature was the factor most closely related to the seasonal cycle in SCCPs in Melbourne. The average SCCP concentrations observed indoors were less than those observed outdoors. Atmospheric concentrations of SCCPs in Melbourne are more than two orders of magnitude higher than concentrations in the background atmosphere. Surprisingly, the SCCP concentrations in Melbourne are similar to those observed in cities in Japan, South Korea and the United Kingdom, and less than those observed in China. Direct transport of SCCPs in the atmosphere from the Northern Hemisphere emissions to Melbourne is ruled out. Instead elevated concentrations in the Melbourne air-shed are most likely a result of the long-term import of SCCPs as industrial chemicals and within manufactured materials from the Northern Hemisphere so that the use of SCCPs in Melbourne and their consequent release to the environment has produced environmental reservoirs of SCCPs in Melbourne that are comparable with those in some Northern Hemisphere cities. The increase in SCCP concentrations from winter to summer is consistent with the temperature dependence of partitioning of SCCPs between the atmosphere and other reservoirs. Insufficient information exists on SCCP use and its presence in soils and sediments in Australia to indicate whether the atmospheric presence of SCCPs in Melbourne is a legacy issue due to its import and use as a metal cutting agent in past decades or due to ongoing imports of manufactured materials containing SCCPs today.

scholarly journals TransCom N<sub>2</sub>O model inter-comparison – Part 1: Assessing the influence of transport and surface fluxes on tropospheric N<sub>2</sub>O variability

2014 ◽  
Vol 14 (2) ◽  
pp. 2307-2362 ◽  
Author(s):  
R. L. Thompson ◽  
P. K. Patra ◽  
K. Ishijima ◽  
E. Saikawa ◽  
M. Corazza ◽  
...  
Keyword(s):  
Northern Hemisphere ◽  
Seasonal Cycle ◽  
Large Scale ◽  
Atmospheric Transport ◽  
Lower Troposphere ◽  
Vertical Gradient ◽  
Surface Fluxes ◽  
Meridional Transport ◽  
Mixing Ratios

Abstract. We present a comparison of chemistry-transport models (TransCom-N2O) to examine the importance of atmospheric transport and surface fluxes on the variability of N2O mixing ratios in the troposphere. Six different models and two model variants participated in the inter-comparison and simulations were made for the period 2006 to 2009. In addition to N2O, simulations of CFC-12 and SF6 were made by a subset of four of the models to provide information on the models proficiency in stratosphere-troposphere exchange (STE) and meridional transport, respectively. The same prior emissions were used by all models to restrict differences among models to transport and chemistry alone. Four different N2O flux scenarios totalling between 14 and 17 Tg N yr−1 (for 2005) globally were also compared. The modelled N2O mixing ratios were assessed against observations from in-situ stations, discrete air sampling networks, and aircraft. All models adequately captured the large-scale patterns of N2O and the vertical gradient from the troposphere to the stratosphere and most models also adequately captured the N2O tropospheric growth rate. However, all models underestimated the inter-hemispheric N2O gradient by at least 0.33 ppb (equivalent to 1.5 Tg N), which, even after accounting for an overestimate of emissions in the Southern Ocean of circa 1.0 Tg N, points to a likely underestimate of the Northern Hemisphere source by up to 0.5 Tg N and/or an overestimate of STE in the Northern Hemisphere. Comparison with aircraft data reveal that the models overestimate the amplitude of the N2O seasonal cycle at Hawaii (21° N, 158° W) below circa 6000 m, suggesting an overestimate of the importance of stratosphere to troposphere transport in the lower troposphere at this latitude. In the Northern Hemisphere, most of the models that provided CFC-12 simulations captured the phase of the CFC-12, seasonal cycle, indicating a reasonable representation of the timing of STE. However, for N2O all models simulated a too early minimum by 2 to 3 months owing to errors in the seasonal cycle in the prior soil emissions, which is still not adequately represented by terrestrial biosphere models. In the Southern Hemisphere, most models failed to capture the N2O and CFC-12 seasonality at Cape Grim, Tasmania, and all failed at the South Pole, whereas for SF6, all models could capture the seasonality at all sites, suggesting that there are large errors in modeled vertical transport in high southern latitudes.

scholarly journals Global upper-tropospheric formaldehyde: seasonal cycles observed by the ACE-FTS satellite instrument

2009 ◽  
Vol 9 (1) ◽  
pp. 1051-1095 ◽  
Author(s):  
G. Dufour ◽  
S. Szopa ◽  
M. P. Barkley ◽  
C. D. Boone ◽  
A. Perrin ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Biomass Burning ◽  
Growing Season ◽  
Global Scale ◽  
Tropospheric Chemistry ◽  
Data Set ◽  
Mixing Ratios ◽  
Good Reproduction ◽  
Summer Maximum

Abstract. Seasonally-resolved upper tropospheric profiles of formaldehyde (HCHO) observed by the ACE Fourier transform spectrometer (ACE-FTS) on a near-global scale are presented for the time period from March 2004 to November 2006. Large upper tropospheric HCHO mixing ratios (>150 pptv) are observed during the growing season of the terrestrial biosphere in the Northern Hemisphere and during the biomass burning season in the Southern Hemisphere. The total errors estimated for the retrieved mixing ratios range from 30 to 40% in the upper troposphere and increase in the lower stratosphere. The sampled HCHO concentrations are in satisfactory agreement with previous aircraft and satellite observations with a negative bias (<25%) within observation errors. An overview of the seasonal cycle of the upper tropospheric HCHO is given for different latitudes. A maximum is observed during summer, i.e. during the growing season, in the northern mid- and high latitudes. The influence of biomass burning is visible in HCHO upper tropospheric concentrations during the September-to-October period in the southern tropics and subtropics. Comparisons with two state-of-the-art models (GEOS-Chem and LMDz-INCA) show that the models fail to reproduce the seasonal variations observed in the southern tropics and subtropics but they capture well the variations observed in the Northern Hemisphere (correlation >0.9). Both models underestimate the summer maximum over Europe and Russia and differences in the emissions used for North America result in a good reproduction of the summer maximum by GEOS-Chem but in an underestimate by LMDz-INCA. Globally, GEOS-Chem reproduces well the observations on average over one year but has some difficulties in reproducing the spatial variability of the observations. LMDz-INCA shows significant bias in the Southern Hemisphere, likely related to an underestimation of methane, but better reproduces the temporal and spatial variations. The differences between the models underline the large uncertainties that remain in the emissions of HCHO precursors. Observations of the HCHO upper tropospheric profile provided by the ACE-FTS represent a unique data set for investigating and improving our current understanding of the formaldehyde budget and upper tropospheric chemistry.

scholarly journals An intercomparison of total column-averaged nitrous oxide between ground-based FTIR TCCON and NDACC measurements at seven sites and comparisons with the GEOS-Chem model

2019 ◽  
Vol 12 (2) ◽  
pp. 1393-1408 ◽  
Author(s):  
Minqiang Zhou ◽  
Bavo Langerock ◽  
Kelley C. Wells ◽  
Dylan B. Millet ◽  
Corinne Vigouroux ◽  
...  
Keyword(s):  
Nitrous Oxide ◽  
Southern Hemisphere ◽  
Near Infrared ◽  
A Priori ◽  
Polar Vortex ◽  
Inversion Method ◽  
Seasonal Cycles ◽  
A Posteriori ◽  
Model Simulations ◽  
N2o Fluxes

Abstract. Nitrous oxide (N2O) is an important greenhouse gas and it can also generate nitric oxide, which depletes ozone in the stratosphere. It is a common target species of ground-based Fourier transform infrared (FTIR) near-infrared (TCCON) and mid-infrared (NDACC) measurements. Both TCCON and NDACC networks provide a long-term global distribution of atmospheric N2O mole fraction. In this study, the dry-air column-averaged mole fractions of N2O (XN2O) from the TCCON and NDACC measurements are compared against each other at seven sites around the world (Ny-Ålesund, Sodankylä, Bremen, Izaña, Réunion, Wollongong, Lauder) in the time period of 2007–2017. The mean differences in XN2O between TCCON and NDACC (NDACC–TCCON) at these sites are between −3.32 and 1.37 ppb (−1.1 %–0.5 %) with standard deviations between 1.69 and 5.01 ppb (0.5 %–1.6 %), which are within the uncertainties of the two datasets. The NDACC N2O retrieval has good sensitivity throughout the troposphere and stratosphere, while the TCCON retrieval underestimates a deviation from the a priori in the troposphere and overestimates it in the stratosphere. As a result, the TCCON XN2O measurement is strongly affected by its a priori profile. Trends and seasonal cycles of XN2O are derived from the TCCON and NDACC measurements and the nearby surface flask sample measurements and compared with the results from GEOS-Chem model a priori and a posteriori simulations. The trends and seasonal cycles from FTIR measurement at Ny-Ålesund and Sodankylä are strongly affected by the polar winter and the polar vortex. The a posteriori N2O fluxes in the model are optimized based on surface N2O measurements with a 4D-Var inversion method. The XN2O trends from the GEOS-Chem a posteriori simulation (0.97±0.02 (1σ) ppb yr−1) are close to those from the NDACC (0.93±0.04 ppb yr−1) and the surface flask sample measurements (0.93±0.02 ppb yr−1). The XN2O trend from the TCCON measurements is slightly lower (0.81±0.04 ppb yr−1) due to the underestimation of the trend in TCCON a priori simulation. The XN2O trends from the GEOS-Chem a priori simulation are about 1.25 ppb yr−1, and our study confirms that the N2O fluxes from the a priori inventories are overestimated. The seasonal cycles of XN2O from the FTIR measurements and the model simulations are close to each other in the Northern Hemisphere with a maximum in August–October and a minimum in February–April. However, in the Southern Hemisphere, the modeled XN2O values show a minimum in February–April while the FTIR XN2O retrievals show different patterns. By comparing the partial column-averaged N2O from the model and NDACC for three vertical ranges (surface–8, 8–17, 17–50 km), we find that the discrepancy in the XN2O seasonal cycle between the model simulations and the FTIR measurements in the Southern Hemisphere is mainly due to their stratospheric differences.

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