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Mathias W. Rotach
,
Georg Wohlfahrt
,
Armin Hansel
,
Matthias Reif
,
Johannes Wagner
, and
Alexander Gohm

Among the processes contributing to the global CO2 budget, net uptake by the land surface bears the largest uncertainty. Therefore, the land sink is often estimated as the residual from the other terms that are known with greater certainty. On average over the last decades, the difference between modeled land surface uptake and this residual is negative, thus suggesting that the different modeling approaches miss an important part in land–atmosphere exchange. Based on experience with atmospheric modeling at high resolution, it is argued that this discrepancy is likely due to missed mesoscale (thermally or dynamically forced) circulations in complex terrain. Noting that more than 50% of the land surface qualifies as complex terrain, the contribution of mesoscale circulations is hypothesized to alleviate at least partly the uncertainty in the modeled land surface uptake. While atmospheric models at coarse resolution (e.g., for numerical weather prediction; also climate simulations) use a parameterization to account for momentum exchange due to subgrid-scale topography, no such additional exchange is presently taken into account for energy or mass. It is thus suggested that a corresponding parameterization should be developed in order to reduce the uncertainties in the global carbon budget.

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Thomas Karl
,
Alexander Gohm
,
Mathias W. Rotach
,
Helen C. Ward
,
Martin Graus
,
Alexander Cede
,
Georg Wohlfahrt
,
Albin Hammerle
,
Maren Haid
,
Martin Tiefengraber
,
Christian Lamprecht
,
Johannes Vergeiner
,
Axel Kreuter
,
Jochen Wagner
, and
Michael Staudinger
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Thomas Karl
,
Alexander Gohm
,
Mathias W. Rotach
,
Helen C. Ward
,
Martin Graus
,
Alexander Cede
,
Georg Wohlfahrt
,
Albin Hammerle
,
Maren Haid
,
Martin Tiefengraber
,
Christian Lamprecht
,
Johannes Vergeiner
,
Axel Kreuter
,
Jochen Wagner
, and
Michael Staudinger

Abstract

The Innsbruck Atmospheric Observatory (IAO) aims to investigate atmospheric chemistry, micrometeorology, and mountain meteorology in a synergistic fashion within an urban setting. A new measurement supersite has been established in order to study processes affecting the exchange of momentum, energy, trace gases, and aerosols in an Alpine urban environment. Various long-term continuous measurements are augmented by frequent focused research campaigns with state-of-the-art instrumentation, linking different classes of data and addressing significant gaps in scientific data availability for urban environments. Current activities seek to address research objectives related to the urban heat island, trace gas emissions, the influence of foehn on air quality, and the atmospheric distribution of trace gases and aerosols in a mountainous city. We present initial results from long-term operations and first highlights from two intensive operational phases, showing that 1) the exchange of greenhouse gas emissions is dominated by anthropogenic activities and is driven by location-specific venting of street canyon air; 2) foehn events significantly perturb the photostationary state indicative for an extensive and rapid airmass exchange of the valley atmosphere; 3) the temporal distribution of pollutants is often decoupled from their emissions and primarily modulated by mountain boundary layer dynamics; 4) we can detect a large number of volatile chemical products in the urban atmosphere, which can be used to fingerprint anthropogenic emission sources; and 5) the first urban carbonyl sulfide (COS) flux measurements point toward anthropogenic emission sources.

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Sara H. Knox
,
Robert B. Jackson
,
Benjamin Poulter
,
Gavin McNicol
,
Etienne Fluet-Chouinard
,
Zhen Zhang
,
Gustaf Hugelius
,
Philippe Bousquet
,
Josep G. Canadell
,
Marielle Saunois
,
Dario Papale
,
Housen Chu
,
Trevor F. Keenan
,
Dennis Baldocchi
,
Margaret S. Torn
,
Ivan Mammarella
,
Carlo Trotta
,
Mika Aurela
,
Gil Bohrer
,
David I. Campbell
,
Alessandro Cescatti
,
Samuel Chamberlain
,
Jiquan Chen
,
Weinan Chen
,
Sigrid Dengel
,
Ankur R. Desai
,
Eugenie Euskirchen
,
Thomas Friborg
,
Daniele Gasbarra
,
Ignacio Goded
,
Mathias Goeckede
,
Martin Heimann
,
Manuel Helbig
,
Takashi Hirano
,
David Y. Hollinger
,
Hiroki Iwata
,
Minseok Kang
,
Janina Klatt
,
Ken W. Krauss
,
Lars Kutzbach
,
Annalea Lohila
,
Bhaskar Mitra
,
Timothy H. Morin
,
Mats B. Nilsson
,
Shuli Niu
,
Asko Noormets
,
Walter C. Oechel
,
Matthias Peichl
,
Olli Peltola
,
Michele L. Reba
,
Andrew D. Richardson
,
Benjamin R. K. Runkle
,
Youngryel Ryu
,
Torsten Sachs
,
Karina V. R. Schäfer
,
Hans Peter Schmid
,
Narasinha Shurpali
,
Oliver Sonnentag
,
Angela C. I. Tang
,
Masahito Ueyama
,
Rodrigo Vargas
,
Timo Vesala
,
Eric J. Ward
,
Lisamarie Windham-Myers
,
Georg Wohlfahrt
, and
Donatella Zona

Abstract

This paper describes the formation of, and initial results for, a new FLUXNET coordination network for ecosystem-scale methane (CH4) measurements at 60 sites globally, organized by the Global Carbon Project in partnership with other initiatives and regional flux tower networks. The objectives of the effort are presented along with an overview of the coverage of eddy covariance (EC) CH4 flux measurements globally, initial results comparing CH4 fluxes across the sites, and future research directions and needs. Annual estimates of net CH4 fluxes across sites ranged from −0.2 ± 0.02 g C m–2 yr–1 for an upland forest site to 114.9 ± 13.4 g C m–2 yr–1 for an estuarine freshwater marsh, with fluxes exceeding 40 g C m–2 yr–1 at multiple sites. Average annual soil and air temperatures were found to be the strongest predictor of annual CH4 flux across wetland sites globally. Water table position was positively correlated with annual CH4 emissions, although only for wetland sites that were not consistently inundated throughout the year. The ratio of annual CH4 fluxes to ecosystem respiration increased significantly with mean site temperature. Uncertainties in annual CH4 estimates due to gap-filling and random errors were on average ±1.6 g C m–2 yr–1 at 95% confidence, with the relative error decreasing exponentially with increasing flux magnitude across sites. Through the analysis and synthesis of a growing EC CH4 flux database, the controls on ecosystem CH4 fluxes can be better understood, used to inform and validate Earth system models, and reconcile differences between land surface model- and atmospheric-based estimates of CH4 emissions.

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