Simulation of atmospheric N<sub>2</sub>O with GEOS-Chem and its adjoint: evaluation of observational constraints
We describe a new 4D-Var inversion framework for nitrous oxide (N<sub>2</sub>O) based on the GEOS-Chem chemical transport model and its adjoint, and apply it in a series of observing system simulation experiments to assess how well N<sub>2</sub>O sources and sinks can be cons...
| Main Authors: | , , , , , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2015-10-01
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| Series: | Geoscientific Model Development |
| Online Access: | http://www.geosci-model-dev.net/8/3179/2015/gmd-8-3179-2015.pdf |
| _version_ | 1811265360525000704 |
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| author | K. C. Wells D. B. Millet N. Bousserez D. K. Henze S. Chaliyakunnel T. J. Griffis Y. Luan E. J. Dlugokencky R. G. Prinn S. O'Doherty R. F. Weiss G. S. Dutton J. W. Elkins P. B. Krummel R. Langenfelds L. P. Steele E. A. Kort S. C. Wofsy T. Umezawa |
| author_facet | K. C. Wells D. B. Millet N. Bousserez D. K. Henze S. Chaliyakunnel T. J. Griffis Y. Luan E. J. Dlugokencky R. G. Prinn S. O'Doherty R. F. Weiss G. S. Dutton J. W. Elkins P. B. Krummel R. Langenfelds L. P. Steele E. A. Kort S. C. Wofsy T. Umezawa |
| author_sort | K. C. Wells |
| collection | DOAJ |
| description | We describe a new 4D-Var inversion framework for nitrous oxide (N<sub>2</sub>O) based on the
GEOS-Chem chemical transport model and its adjoint, and apply it in a series
of observing system simulation experiments to assess how well N<sub>2</sub>O
sources and sinks can be constrained by the current global observing
network. The employed measurement ensemble includes approximately weekly and
quasi-continuous N<sub>2</sub>O measurements (hourly averages used) from several
long-term monitoring networks, N<sub>2</sub>O measurements collected from discrete
air samples onboard a commercial aircraft (Civil Aircraft for the Regular Investigation of the
atmosphere Based on an Instrument Container; CARIBIC), and quasi-continuous
measurements from the airborne HIAPER Pole-to-Pole Observations (HIPPO) campaigns. For a
2-year inversion, we find that the surface and HIPPO observations can
accurately resolve a uniform bias in emissions during the first year;
CARIBIC data provide a somewhat weaker constraint. Variable emission errors
are much more difficult to resolve given the long lifetime of N<sub>2</sub>O, and
major parts of the world lack significant constraints on the seasonal cycle
of fluxes. Current observations can largely correct a global bias in the
stratospheric sink of N<sub>2</sub>O if emissions are known, but do not provide
information on the temporal and spatial distribution of the sink. However,
for the more realistic scenario where source and sink are both uncertain, we
find that simultaneously optimizing both would require unrealistically small
errors in model transport. Regardless, a bias in the magnitude of the
N<sub>2</sub>O sink would not affect the a posteriori N<sub>2</sub>O emissions for the
2-year timescale used here, given realistic initial conditions, due to the
timescale required for stratosphere–troposphere exchange (STE). The same
does not apply to model errors in the rate of STE itself, which we show
exerts a larger influence on the tropospheric burden of N<sub>2</sub>O than does
the chemical loss rate over short (< 3 year) timescales. We use a
stochastic estimate of the inverse Hessian for the inversion to evaluate the
spatial resolution of emission constraints provided by the observations, and
find that significant, spatially explicit constraints can be achieved in
locations near and immediately upwind of surface measurements and the HIPPO
flight tracks; however, these are mostly confined to North America, Europe,
and Australia. None of the current observing networks are able to provide
significant spatial information on tropical N<sub>2</sub>O emissions. There,
averaging kernels (describing the sensitivity of the inversion to emissions
in each grid square) are highly smeared spatially and extend even to the
midlatitudes, so that tropical emissions risk being conflated with those
elsewhere. For global inversions, therefore, the current lack of constraints
on the tropics also places an important limit on our ability to understand
extratropical emissions. Based on the error reduction statistics from the
inverse Hessian, we characterize the atmospheric distribution of
unconstrained N<sub>2</sub>O, and identify regions in and downwind of South
America, central Africa, and Southeast Asia where new surface or profile
measurements would have the most value for reducing present uncertainty in
the global N<sub>2</sub>O budget. |
| first_indexed | 2024-04-12T20:21:09Z |
| format | Article |
| id | doaj.art-1854a77753d444308dfee58167c2288b |
| institution | Directory Open Access Journal |
| issn | 1991-959X 1991-9603 |
| language | English |
| last_indexed | 2024-04-12T20:21:09Z |
| publishDate | 2015-10-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Geoscientific Model Development |
| spelling | doaj.art-1854a77753d444308dfee58167c2288b2022-12-22T03:17:59ZengCopernicus PublicationsGeoscientific Model Development1991-959X1991-96032015-10-018103179319810.5194/gmd-8-3179-2015Simulation of atmospheric N<sub>2</sub>O with GEOS-Chem and its adjoint: evaluation of observational constraintsK. C. Wells0D. B. Millet1N. Bousserez2D. K. Henze3S. Chaliyakunnel4T. J. Griffis5Y. Luan6E. J. Dlugokencky7R. G. Prinn8S. O'Doherty9R. F. Weiss10G. S. Dutton11J. W. Elkins12P. B. Krummel13R. Langenfelds14L. P. Steele15E. A. Kort16S. C. Wofsy17T. Umezawa18Department of Soil, Water, and Climate, University of Minnesota, St. Paul, Minnesota, USADepartment of Soil, Water, and Climate, University of Minnesota, St. Paul, Minnesota, USADepartment of Mechanical Engineering, University of Colorado at Boulder, Boulder, Colorado, USADepartment of Mechanical Engineering, University of Colorado at Boulder, Boulder, Colorado, USADepartment of Soil, Water, and Climate, University of Minnesota, St. Paul, Minnesota, USADepartment of Soil, Water, and Climate, University of Minnesota, St. Paul, Minnesota, USADepartment of Soil, Water, and Climate, University of Minnesota, St. Paul, Minnesota, USAEarth System Research Laboratory, NOAA, Boulder, Colorado, USACenter for Global Change Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, USASchool of Chemistry, University of Bristol, Bristol, UKScripps Institute of Oceanography, University of California, San Diego, La Jolla, California, USAEarth System Research Laboratory, NOAA, Boulder, Colorado, USAEarth System Research Laboratory, NOAA, Boulder, Colorado, USACSIRO Oceans and Atmosphere Flagship, Aspendale, Victoria, AustraliaCSIRO Oceans and Atmosphere Flagship, Aspendale, Victoria, AustraliaCSIRO Oceans and Atmosphere Flagship, Aspendale, Victoria, AustraliaDepartment of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, Michigan, USASchool of Engineering and Applied Science and Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USACenter for Atmospheric and Oceanic Studies, Tohoku University, Sendai, JapanWe describe a new 4D-Var inversion framework for nitrous oxide (N<sub>2</sub>O) based on the GEOS-Chem chemical transport model and its adjoint, and apply it in a series of observing system simulation experiments to assess how well N<sub>2</sub>O sources and sinks can be constrained by the current global observing network. The employed measurement ensemble includes approximately weekly and quasi-continuous N<sub>2</sub>O measurements (hourly averages used) from several long-term monitoring networks, N<sub>2</sub>O measurements collected from discrete air samples onboard a commercial aircraft (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container; CARIBIC), and quasi-continuous measurements from the airborne HIAPER Pole-to-Pole Observations (HIPPO) campaigns. For a 2-year inversion, we find that the surface and HIPPO observations can accurately resolve a uniform bias in emissions during the first year; CARIBIC data provide a somewhat weaker constraint. Variable emission errors are much more difficult to resolve given the long lifetime of N<sub>2</sub>O, and major parts of the world lack significant constraints on the seasonal cycle of fluxes. Current observations can largely correct a global bias in the stratospheric sink of N<sub>2</sub>O if emissions are known, but do not provide information on the temporal and spatial distribution of the sink. However, for the more realistic scenario where source and sink are both uncertain, we find that simultaneously optimizing both would require unrealistically small errors in model transport. Regardless, a bias in the magnitude of the N<sub>2</sub>O sink would not affect the a posteriori N<sub>2</sub>O emissions for the 2-year timescale used here, given realistic initial conditions, due to the timescale required for stratosphere–troposphere exchange (STE). The same does not apply to model errors in the rate of STE itself, which we show exerts a larger influence on the tropospheric burden of N<sub>2</sub>O than does the chemical loss rate over short (< 3 year) timescales. We use a stochastic estimate of the inverse Hessian for the inversion to evaluate the spatial resolution of emission constraints provided by the observations, and find that significant, spatially explicit constraints can be achieved in locations near and immediately upwind of surface measurements and the HIPPO flight tracks; however, these are mostly confined to North America, Europe, and Australia. None of the current observing networks are able to provide significant spatial information on tropical N<sub>2</sub>O emissions. There, averaging kernels (describing the sensitivity of the inversion to emissions in each grid square) are highly smeared spatially and extend even to the midlatitudes, so that tropical emissions risk being conflated with those elsewhere. For global inversions, therefore, the current lack of constraints on the tropics also places an important limit on our ability to understand extratropical emissions. Based on the error reduction statistics from the inverse Hessian, we characterize the atmospheric distribution of unconstrained N<sub>2</sub>O, and identify regions in and downwind of South America, central Africa, and Southeast Asia where new surface or profile measurements would have the most value for reducing present uncertainty in the global N<sub>2</sub>O budget.http://www.geosci-model-dev.net/8/3179/2015/gmd-8-3179-2015.pdf |
| spellingShingle | K. C. Wells D. B. Millet N. Bousserez D. K. Henze S. Chaliyakunnel T. J. Griffis Y. Luan E. J. Dlugokencky R. G. Prinn S. O'Doherty R. F. Weiss G. S. Dutton J. W. Elkins P. B. Krummel R. Langenfelds L. P. Steele E. A. Kort S. C. Wofsy T. Umezawa Simulation of atmospheric N<sub>2</sub>O with GEOS-Chem and its adjoint: evaluation of observational constraints Geoscientific Model Development |
| title | Simulation of atmospheric N<sub>2</sub>O with GEOS-Chem and its adjoint: evaluation of observational constraints |
| title_full | Simulation of atmospheric N<sub>2</sub>O with GEOS-Chem and its adjoint: evaluation of observational constraints |
| title_fullStr | Simulation of atmospheric N<sub>2</sub>O with GEOS-Chem and its adjoint: evaluation of observational constraints |
| title_full_unstemmed | Simulation of atmospheric N<sub>2</sub>O with GEOS-Chem and its adjoint: evaluation of observational constraints |
| title_short | Simulation of atmospheric N<sub>2</sub>O with GEOS-Chem and its adjoint: evaluation of observational constraints |
| title_sort | simulation of atmospheric n sub 2 sub o with geos chem and its adjoint evaluation of observational constraints |
| url | http://www.geosci-model-dev.net/8/3179/2015/gmd-8-3179-2015.pdf |
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