Person: Wofsy, Steven
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Wofsy
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Steven
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Wofsy, Steven
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Publication Validation of TES Methane with HIPPO Aircraft Observations: Implications for Inverse Modeling of Methane Sources(Copernicus GmbH, 2012) Wecht, Kevin James; Jacob, Daniel; Wofsy, Steven; Kort, E. A.; Worden, J. R.; Kulawik, S. S.; Henze, D. K.; Kopacz, M.; Payne, V. H.We validate satellite methane observations from the Tropospheric Emission Spectrometer (TES) with 151 aircraft vertical profiles over the Pacific from the HIAPER Pole-to-Pole Observation (HIPPO) program. We find that a collocation window of ±750 km and ±24 h does not introduce significant error in comparing TES and aircraft profiles. We validate both the TES standard product (V004) and an experimental product with two pieces of information in the vertical (V005). We determine a V004 mean bias of 65.8 ppb and random instrument error of 43.3 ppb. For V005 we determine a mean bias of 42.3 ppb and random instrument error of 26.5 ppb in the upper troposphere, and mean biases (random instrument errors) in the lower troposphere of 28.8 (28.7) and 16.9 (28.9) ppb at high and low latitudes respectively. Even when V005 cannot retrieve two pieces of information it still performs better than V004. An observation system simulation experiment (OSSE) with the GEOS-Chem chemical transport model (CTM) and its adjoint shows that TES V004 has only limited value for constraining methane sources. Our successful validation of V005 encourages its production as a standard retrieval to replace V004.Publication Soil Respiration in a Northeastern US Temperate Forest: A 22-Year Synthesis(Ecological Society of America, 2013) Giasson, M.-A.; Ellison, Aaron; Bowden, R. D.; Crill, P. M.; Davidson, E. A.; Drake, J. E.; Frey, S. D.; Hadley, Julian; Lavine, M.; Melillo, J. M.; Munger, J. W.; Nadelhoffer, K. J.; Nicoll, L.; Ollinger, S. V.; Savage, K. E.; Steudler, P. A.; Tang, J.; Varner, R. K.; Wofsy, Steven; Foster, David; Finzi, A. C.To better understand how forest management, phenology, vegetation type, and actual and simulated climatic change affect seasonal and inter-annual variations in soil respiration (R\(_{s}\)), we analyzed more than 100,000 individual measurements of soil respiration from 23 studies conducted over 22 years at the Harvard Forest in Petersham, Massachusetts, USA. We also used 24 site-years of eddy-covariance measurements from two Harvard Forest sites to examine the relationship between soil and ecosystem respiration (R\(_{e}\)). R\(_{s}\) was highly variable at all spatial (respiration collar to forest stand) and temporal (minutes to years) scales of measurement. The response of R\(_{s}\) to experimental manipulations mimicking aspects of global change or aimed at partitioning R\(_{s}\) into component fluxes ranged from −70% to +52%. The response appears to arise from variations in substrate availability induced by changes in the size of soil C pools and of belowground C fluxes or in environmental conditions. In some cases (e.g., logging, warming), the effect of experimental manipulations on R\(_{s}\) was transient, but in other cases the time series were not long enough to rule out long-term changes in respiration rates. Inter-annual variations in weather and phenology induced variation among annual R\(_{s}\) estimates of a magnitude similar to that of other drivers of global change (i.e., invasive insects, forest management practices, N deposition). At both eddy-covariance sites, aboveground respiration dominated R\(_{e}\) early in the growing season, whereas belowground respiration dominated later. Unusual aboveground respiration patterns—high apparent rates of respiration during winter and very low rates in mid-to-late summer—at the Environmental Measurement Site suggest either bias in R\(_{s}\) and R\(_{e}\) estimates caused by differences in the spatial scale of processes influencing fluxes, or that additional research on the hard-to-measure fluxes (e.g., wintertime R\(_{s}\), unaccounted losses of CO\(_{2}\) from eddy covariance sites), daytime and nighttime canopy respiration and its impacts on estimates of R\(_{e}\), and independent measurements of flux partitioning (e.g., aboveground plant respiration, isotopic partitioning) may yield insight into the unusually high and low fluxes. Overall, however, this data-rich analysis identifies important seasonal and experimental variations in R\(_{s}\) and R\(_{e}\) and in the partitioning of R\(_{e}\) above- vs. belowground.Publication Methane emissions from natural gas infrastructure and use in the urban region of Boston, Massachusetts(Proceedings of the National Academy of Sciences, 2015) McKain, Kathryn; Down, Adrian; Raciti, Steve M.; Budney, John; Hutyra, Lucy R.; Floerchinger, Cody; Herndon, Scott C.; Nehrkorn, Thomas; Zahniser, Mark S.; Jackson, Robert B.; Phillips, Nathan; Wofsy, StevenMethane emissions from natural gas delivery and end use must be quantified to evaluate the environmental impacts of natural gas and to develop and assess the efficacy of emission reduction strategies. We report natural gas emission rates for 1 y in the urban region of Boston, using a comprehensive atmospheric measurement and modeling framework. Continuous methane observations from four stations are combined with a high-resolution transport model to quantify the regional average emission flux, 18.5 ± 3.7 (95% confidence interval) g CH4⋅m−2⋅y−1. Simultaneous observations of atmospheric ethane, compared with the ethane-to-methane ratio in the pipeline gas delivered to the region, demonstrate that natural gas accounted for ∼60–100% of methane emissions, depending on season. Using government statistics and geospatial data on natural gas use, we find the average fractional loss rate to the atmosphere from all downstream components of the natural gas system, including transmission, distribution, and end use, was 2.7 ± 0.6% in the Boston urban region, with little seasonal variability. This fraction is notably higher than the 1.1% implied by the most closely comparable emission inventory.Publication HIAPER Pole-to-Pole Observations (HIPPO): fine-grained, global-scale measurements of climatically important atmospheric gases and aerosols(The Royal Society, 2011) Wofsy, StevenThe HIAPER Pole-to-Pole Observations (HIPPO) programme has completed three of five planned aircraft transects spanning the Pacific from 85° N to 67° S, with vertical profiles every approximately 2.2° of latitude. Measurements include greenhouse gases, long-lived tracers, reactive species, O2/N2 ratio, black carbon (BC), aerosols and CO2 isotopes. Our goals are to address the problem of determining surface emissions, transport strength and patterns, and removal rates of atmospheric trace gases and aerosols at global scales and to provide strong tests of satellite data and global models. HIPPO data show dense pollution and BC at high altitudes over the Arctic, imprints of large N2O sources from tropical lands and convective storms, sources of pollution and biogenic CH4 in the Arctic, and summertime uptake of CO2 and sources for O2 at high southern latitudes. Global chemical signatures of atmospheric transport are imaged, showing remarkably sharp horizontal gradients at air mass boundaries, weak vertical gradients and inverted profiles (maxima aloft) in both hemispheres. These features challenge satellite algorithms, global models and inversion analyses to derive surface fluxes. HIPPO data can play a crucial role in identifying and resolving questions of global sources, sinks and transport of atmospheric gases and aerosols.Publication Calibration of the Total Carbon Column Observing Network Using Aircraft Profile Data(Copernicus GmbH, 2010) Wunch, D.; Toon, G. C.; Wennberg, P. O.; Wofsy, Steven; Stephens, B. B.; Fischer, M. L.; Uchino, O.; Abshire, J. B.; Bernath, P.; Biraud, S. C.; Blavier, J.-F. L.; Boone, C.; Bowman, K. P.; Browell, E. V.; Campos, T.; Connor, B. J.; Daube, Bruce; Deutscher, N. M.; Diao, M.; Elkins, J. W.; Gerbig, C.; Gottlieb, Elaine; Griffith, D. W. T.; Hurst, D. F.; Jiménez, R.; Keppel-Aleks, G.; Kort, E. A.; Macatangay, R.; Machida, T.; Matsueda, H.; Moore, F.; Morino, I.; Park, S.; Robinson, J.; Roehl, C. M.; Sawa, Y.; Sherlock, V.; Sweeney, C.; Tanaka, T.; Zondlo, M. A.The Total Carbon Column Observing Network (TCCON) produces precise measurements of the column average dry-air mole fractions of \(CO_2\), \(CO\), \(CH_4\), \(N_2O\) and \(H_2O\) at a variety of sites worldwide. These observations rely on spectroscopic parameters that are not known with sufficient accuracy to compute total columns that can be used in combination with in situ measurements. The TCCON must therefore be calibrated to World Meteorological Organization (WMO) in situ trace gas measurement scales. We present a calibration of TCCON data using WMO-scale instrumentation aboard aircraft that measured profiles over four TCCON stations during 2008 and 2009. These calibrations are compared with similar observations made in 2004 and 2006. The results indicate that a single, global calibration factor for each gas accurately captures the TCCON total column data within error.Publication Total Column \(CO_2\) Measurements at Darwin, Australia – Site Description and Calibration Against In Situ Aircraft Profiles(Copernicus GmbH, 2010) Deutscher, N. M.; Griffith, D. W. T.; Bryant, G. W.; Wennberg, P. O.; Toon, G. C.; Washenfelder, R. A.; Keppel-Aleks, G.; Wunch, D.; Yavin, Y.; Allen, Norton; Blavier, J.-F.; Jiménez, R.; Daube, Bruce; Bright, A. V.; Matross, D. M.; Wofsy, Steven; Park, S.An automated Fourier Transform Spectroscopic (FTS) solar observatory was established in Darwin, Australia in August 2005. The laboratory is part of the Total Carbon Column Observing Network, and measures atmospheric column abundances of \(CO_2\) and \(O_2\) and other gases. Measured \(CO_2\) columns were calibrated against integrated aircraft profiles obtained during the TWP-ICE campaign in January–February 2006, and show good agreement with calibrations for a similar instrument in Park Falls, Wisconsin. A clear-sky low airmass relative precision of 0.1% is demonstrated in the \(CO_2\) and \(O_2\) retrieved column-averaged volume mixing ratios. The 1% negative bias in the FTS \(X_{CO_2}\) relative to the World Meteorological Organization (WMO) calibrated in situ scale is within the uncertainties of the NIR spectroscopy and analysis.Publication Responses of terrestrial ecosystems and carbon budgets to current and future environmental variability(Proceedings of the National Academy of Sciences, 2010) Medvigy, D.; Wofsy, Steven; Munger, J.; Moorcroft, PaulWe assess the significance of high-frequency variability of environmental parameters (sunlight, precipitation, temperature) for the structure and function of terrestrial ecosystems under current and future climate. We examine the influence of hourly, daily, and monthly variance using the Ecosystem Demography model version 2 in conjunction with the long-term record of carbon fluxes measured at Harvard Forest. We find that fluctuations of sunlight and precipitation are strongly and nonlinearly coupled to ecosystem function, with effects that accumulate through annual and decadal timescales. Increasing variability in sunlight and precipitation leads to lower rates of carbon sequestration and favors broad-leaved deciduous trees over conifers. Temperature variability has only minor impacts by comparison. We also find that projected changes in sunlight and precipitation variability have important implications for carbon storage and ecosystem structure and composition. Based on Intergovernmental Panel on Climate Change model estimates for changes in high-frequency meteorological variability over the next 100 years, we expect that terrestrial ecosystems will be affected by changes in variability almost as much as by changes in mean climate. We conclude that terrestrial ecosystems are highly sensitive to high-frequency meteorological variability, and that accurate knowledge of the statistics of this variability is essential for realistic predictions of ecosystem structure and functioning.Publication Coupled weather research and forecasting–stochastic time-inverted lagrangian transport (WRF–STILT) model(Springer Nature, 2010) Nehrkorn, Thomas; Eluszkiewicz, Janusz; Wofsy, Steven; Lin, John C.; Gerbig, Christoph; Longo, Marcos; Freitas, SauloThis paper describes the coupling between a mesoscale numerical weather prediction model, the Weather Research and Forecasting (WRF) model, and a Lagrangian Particle Dispersion Model, the Stochastic Time-Inverted Lagrangian Transport (STILT) model. The primary motivation for developing this coupled model has been to reduce transport errors in continental-scale top–down estimates of terrestrial greenhouse gas fluxes. Examples of the model’s application are shown here for backward trajectory computations originating at CO2 measurement sites in North America. Owing to its unique features, including meteorological realism and large support base, good mass conservation properties, and a realistic treatment of convection within STILT, the WRF–STILT model offers an attractive tool for a wide range of applications, including inverse flux estimates, flight planning, satellite validation, emergency response and source attribution, air quality, and planetary exploration.Publication Vertical transport rates and concentrations of OH and Cl radicals in the Tropical Tropopause Layer from observations of CO2 and halocarbons: implications for distributions of long- and short-lived chemical species(Copernicus GmbH, 2010) Park, S.; Atlas, E. L.; Jiménez, R.; Daube, Bruce; Gottlieb, Elaine; Nan, J.; Jones, D. B. A.; Pfister, L.; Conway, T. J.; Bui, T. P.; Gao, R.-S.; Wofsy, StevenRates for large-scale vertical transport of air in the Tropical Tropopause Layer (TTL) were determined using high-resolution, in situ observations of CO2 concentrations in the tropical upper troposphere and lower stratosphere during the NASA Tropical Composition, Cloud and Climate Coupling (TC4) campaign in August 2007. Upward movement of trace gases in the deep tropics was notably slower in TC4 than during the Costa Rica AURA Validation Experiment (CR-AVE), in January 2006. Transport rates in the TTL were combined with in situ measurements of chlorinated and brominated organic compounds from whole air samples to determine chemical loss rates for reactive chemical species, providing empirical vertical profiles for 24-h mean concentrations of hydroxyl radicals (OH) and chlorine atoms in the TTL. The analysis shows that important short-lived species such as CHCl3, CH2Cl2, and CH2Br2 have longer chemical lifetimes than the time for transit of the TTL, implying that these species, which are not included in most models, could readily reach the stratosphere and make significant contributions of chlorine and/or bromine to stratospheric loading.Publication Global-scale black carbon profiles observed in the remote atmosphere and compared to models(Wiley-Blackwell, 2010) Schwarz, J. P.; Spackman, J. R.; Gao, R. S.; Watts, L. A.; Stier, P.; Schulz, M.; Davis, S. M.; Wofsy, Steven; Fahey, D. W.[1] Refractory black carbon (rBC) aerosol loadings and mass size distributions have been quantified during the HIPPO campaign above the remote Pacific from 80N to 67S. Over 100 vertical profiles of rBC loadings, extending from ∼0.3 to ∼14 km were obtained with a Single-Particle Soot Photometer (SP2) during a two-week period in January 2009. The dataset provides a striking, and previously unobtainable, pole-to-pole snapshot of rBC mass loadings. rBC vertical concentration profiles reveal significant dependences on latitude, while associated rBC mass size distributions were highly uniform. The vertical profiles averaged in five latitude zones were compared to an ensemble of AEROCOM model fields. The model ensemble spread in each zone was over an order of magnitude, while the model average over-predicted rBC concentrations overall by a factor five. The comparisons suggest that rBC removal in global models may need to be evaluated separately in different latitude regions and perhaps enhanced.