Digital Commons Network^™

Estimating Tropical Forest Structure Using A Terrestrial Lidar, Michael W. Palace, Franklin B. Sullivan, Mark Ducey, Christina Herrick

Earth Sciences

Forest structure comprises numerous quantifiable biometric components and characteristics, which include tree geometry and stand architecture. These structural components are important in the understanding of the past and future trajectories of these biomes. Tropical forests are often considered the most structurally complex and yet least understood of forested ecosystems. New technologies have provided novel avenues for quantifying biometric properties of forested ecosystems, one of which is LIght Detection And Ranging (lidar). This sensor can be deployed on satellite, aircraft, unmanned aerial vehicles, and terrestrial platforms. In this study we examined the efficacy of a terrestrial lidar scanner (TLS) system in …

Can Continental Bogs With Stand The Pressure Due To Climate Change?, Nigel T. Roulet, E R. Humphreys, Jianghua Wu, Steve Frolking, Julie Talbot, P M. Lafleur, Tim Moore

Earth Sciences

Not all peatlands are alike. Theoretical and process based models suggest that ombrogenic, oligotrophic peatlands can withstand the pressures due to climate change because of the feedbacks among ecosystem production, decomposition and water storage. Although there have been many inductive explanations inferring from paleo-records, there is a lack of deductive empirical tests of the models predictions of these systems’ stability and there are few records of the changes in the net ecosystem carbon balance (NECB) of peatlands that are long enough to examine the dynamics of the NECB in relation to climate variability. Continuous measurements of all the components of …

Spectral Aerosol Extinction (Spex): A New Instrument For In Situ Ambient Aerosol Extinction Measurements Across The Uv/Visible Wavelength Range, C. E. Jordan, B E. Anderson, A J. Beyersdorf, C A. Corr, Jack E. Dibb, Margaret E. Greenslade, R F. Martin, R H. Moore, Eric Scheuer, M A. Shook, Kenn L. Thornhill, D Troop, Luke D. Ziemba, E L. Winstead

Earth Sciences

We introduce a new instrument for the measurement of in situ ambient aerosol extinction over the 300– 700 nm wavelength range, the spectral aerosol extinction (SpEx) instrument. This measurement capability is envisioned to complement existing in situ instrumentation, allowing for simultaneous measurement of the evolution of aerosol optical, chemical, and physical characteristics in the ambient environment. In this work, a detailed description of the instrument is provided along with characterization tests performed in the laboratory. Measured spectra of NO2 and polystyrene latex spheres (PSLs) agreed well with theoretical calculations. Good agreement was also found with simultaneous aerosol extinction measurements at …

Neither Dust Nor Black Carbon Causing Apparent Albedo Decline In Greenland's Dry Snow Zone: Implications For Modis C5 Surface Reflectance, Chris Polashenski, Jack E. Dibb, Mark G. Flanner, Justin Y. Chen, Zoe R. Courville, Alexandra M. Lai, James J. Schauer, Martin M. Shafer, Mike Bergin

Earth Sciences

Remote sensing observations suggest Greenland ice sheet (GrIS) albedo has declined since 2001, even in the dry snow zone. We seek to explain the apparent dry snow albedo decline. We analyze samples representing 2012–2014 snowfall across NW Greenland for black carbon and dust light-absorbing impurities (LAI) and model their impacts on snow albedo. Albedo reductions due to LAI are small, averaging 0.003, with episodic enhancements resulting in reductions of 0.01–0.02. No significant increase in black carbon or dust concentrations relative to recent decades is found. Enhanced deposition of LAI is not, therefore, causing significant dry snow albedo reduction or driving …

Brown Carbon Aerosol In The North American Continental Troposphere: Sources, Abundance, And Radiative Forcing, J. Liu, Eric Scheuer, Jack E. Dibb, G S. Diskin, L D. Ziemba, K L. Thornhill, B E. Anderson, A Whisthaler, T Mikoviny, J J. Devi, M Bergin, A E. Perring, M Z. Markovic, J P. Schwarz, P Campuzano-Jost, D A. Day, J L. Jimenez, R J. Weber

Earth Sciences

Chemical components of organic aerosol (OA) selectively absorb light at short wavelengths. In this study, the prevalence, sources, and optical importance of this so called brown carbon (BrC) aerosol component are investigated throughout the North American continental tropospheric column during a summer of extensive biomass burning. Spectrophotometric absorption measurements on extracts of bulk aerosol samples collected from an aircraft over the central USA were analyzed to directly quantify BrC abundance. BrC was found to be prevalent throughout the 1 to 12 km altitude measurement range, with dramatic enhancements in biomass-burning plumes. BrC to black carbon (BC) ratios, under background tropospheric …

Modeling Impacts Of Changes In Temperature And Water Table On C Gas Fluxes In An Alaskan Peatland, Jia Deng, Changsheng Li, Steve Frolking

Earth Sciences

Northern peatlands have accumulated a large amount of organic carbon (C) in their thick peat profile. Climate change and associated variations in soil environments are expected to have significant impacts on the C balance of these ecosystems, but the magnitude is still highly uncertain. Verifying and understanding the influences of changes in environmental factors on C gas fluxes in biogeochemical models are essential for forecasting feedbacks between C gas fluxes and climate change. In this study, we applied a biogeochemical model, DeNitrification-DeComposition (DNDC), to assess impacts of air temperature (T_A) and water table (WT) on C gas fluxes …

The Polarcat Model Intercomparison Project (Polmip): Overview And Evaluation With Observations, L K. Emmons, S R. Arnold, S A. Monks, V Huijnen, S Tilmes, K S. Law, J L. Thomas, J C. Raut, I Bouarar, S Turquety, Y Long, B Duncan, S Steenrod, S Strode, J Flemming, J Mao, J Langner, A M. Thompson, D Tarasick, E C. Apel, D R. Blake, Robert C. Cohen, Jack E. Dibb, Glenn Diskin, A Fried, S R. Hall, L Gregory Huey, Andrew Weinheimer, Armin Wisthaler, Tomas Mikoviny, J Nowak, Jeff Peischl, J M. Roberts, Thomas B. Ryerson, C Warneke, D Helmig

Earth Sciences

A model intercomparison activity was inspired by the large suite of observations of atmospheric composition made during the International Polar Year (2008) in the Arctic. Nine global and two regional chemical transport models participated in this intercomparison and performed simulations for 2008 using a common emissions inventory to assess the differences in model chemistry and transport schemes. This paper summarizes the models and compares their simulations of ozone and its precursors and presents an evaluation of the simulations using a variety of surface, balloon, aircraft and satellite observations. Each type of measurement has some limitations in spatial or temporal coverage …

Revealing Important Nocturnal And Day-To-Day Variations In Fire Smoke Emissions Through A Multiplatform Inversion, Pablo E. Saide, David A. Peterson, Arlindo Da Silva, Bruce Anderson, Luke D. Ziemba, Glenn Diskin, Glen Sachse, Jonathan Hair, Carolyn Butler, Marta Fenn, Jose L. Jimenez, Pedro Campuzano-Jost, Anne E. Perring, Joshua P. Schwarz, Milos Z. Markovic, Phil Russell, Jens Redemann, Yohei Shinozuka, David G. Streets, Fang Yan, Jack E. Dibb, Robert Yokelson, O Brian Toon, Edward Hyer, Gregory R. Carmichael

Earth Sciences

We couple airborne, ground-based, and satellite observations; conduct regional simulations; and develop and apply an inversion technique to constrain hourly smoke emissions from the Rim Fire, the third largest observed in California, USA. Emissions constrained with multiplatform data show notable nocturnal enhancements (sometimes over a factor of 20), correlate better with daily burned area data, and are a factor of 2-4 higher than a priori estimates, highlighting the need for improved characterization of diurnal profiles and day-to-day variability when modeling extreme fires. Constraining only with satellite data results in smaller enhancements mainly due to missing retrievals near the emissions source, …

Evolution Of Brown Carbon In Wildfire Plumes, Haviland Forrister, Jiumeng Liu, Jack E. Dibb, Eric Scheuer, Luke D. Ziemba, Kenn L. Thornhill, Bruce Anderson, Glenn Diskin, Anne E. Perring, Joshua P. Schwarz, Pedro Campuzano-Jost, Douglas A. Day, Brett B. Palm, Jose L. Jimenez, Athanasios Nenes, Rodney J. Weber

Earth Sciences

Particulate brown carbon (BrC) in the atmosphere absorbs light at subvisible wavelengths and has poorly constrained but potentially large climate forcing impacts. BrC from biomass burning has virtually unknown lifecycle and atmospheric stability. Here, BrC emitted from intense wildfires was measured in plumes transported over 2 days from two main fires, during the 2013 NASA SEAC4RS mission. Concurrent measurements of organic aerosol (OA) and black carbon (BC) mass concentration, BC coating thickness, absorption Ångström exponent, and OA oxidation state reveal that the initial BrC emitted from the fires was largely unstable. Using back trajectories to estimate the transport time indicates …

Simulating Ice Core 10be On The Glacial–Interglacial Timescale, C Elsasser, D Wagenbach, I Levin, A Stanzick, Mark J. Christl, A Wallner, S Kipfstuhl, I K. Seietstad, H Wershofen, Jack E. Dibb

Earth Sciences

¹⁰Be ice core measurements are an important tool for paleoclimate research, e.g., allowing for the reconstruction of past solar activity or changes in the geomagnetic dipole field. However, especially on multi-millennial timescales, the share of production and climate-induced variations of respective ¹⁰Be ice core records is still up for debate. Here we present the first quantitative climatological model of the ¹⁰Be ice concentration up to the glacial–interglacial timescale. The model approach is composed of (i) a coarse resolution global atmospheric transport model and (ii) a local ¹⁰Be air–firn transfer model. Extensive global-scale observational data of short-lived …

Arctic Air Pollution: New Insights From Polarcat-Ipy, Katherine S. Law, Andreas Stohl, Patricia K. Quinn, Charles A. Brock, John F. Burkhart, Jean-Daniel Paris, Gerard Ancellet, Hanwant B. Singh, Anke Roiger, Hans Schlager, Jack E. Dibb, Daniel J. Jacob, S R. Arnold, Jacques Pelon, Jennie L. Thomas

Earth Sciences

Given the rapid nature of climate change occurring in the Arctic and the difficulty climate models have in quantitatively reproducing observed changes such as sea ice loss, it is important to improve understanding of the processes leading to climate change in this region, including the role of short-lived climate pollutants such as aerosols and ozone. It has long been known that pollution produced from emissions at midlatitudes can be transported to the Arctic, resulting in a winter/spring aerosol maximum known as Arctic haze. However, many uncertainties remain about the composition and origin of Arctic pollution throughout the troposphere; for example, …

Assessing Effects Of Permafrost Thaw On C Fluxes Based On Multiyear Modeling Across A Permafrost Thaw Gradient At Stordalen, Sweden, Jia Deng, C Li, Steve Frolking, Y Zhang, K Backstrand, P Crill

Earth Sciences

Northern peatlands in permafrost regions contain a large amount of organic carbon (C) in the soil. Climate warming and associated permafrost degradation are expected to have significant impacts on the C balance of these ecosystems, but the magnitude is uncertain. We incorporated a permafrost model, Northern Ecosystem Soil Temperature (NEST), into a biogeochemical model, DeNitrificationDeComposition (DNDC), to model C dynamics in highlatitude peatland ecosystems. The enhanced model was applied to assess effects of permafrost thaw on C fluxes of a subarctic peatland at Stordalen, Sweden. DNDC simulated soil freeze–thaw dynamics, net ecosystem exchange of CO2 (NEE), and CH4 fluxes across …

Water: Macro-Scale Process-Based Modeling Of Water, Steve Frolking, Richard B. Lammers, Danielle S. Grogan

Earth Sciences

No abstract provided.

Atmospheric Oxidation Chemistry And Ozone Production: Results From Sharp 2009 In Houston, Texas, Katherine A. Duderstadt, Jack E. Dibb, Charles H. Jackman, Cora E. Randall, Stanley C. Solomon, Michael J. Mills, Nathan A. Schwadron, Harlan E. Spence

Earth Sciences

This study considers whether spikes in nitrate in snow sampled at Summit, Greenland, from August 2000 to August 2002 are related to solar proton events. After identifying tropospheric sources of nitrate on the basis of correlations with sulfate, ammonium, sodium, and calcium, we use the three-dimensional global Whole Atmosphere Community Climate Model (WACCM) to examine unaccounted for nitrate spikes. Model calculations confirm that solar proton events significantly impact HOx, NOx, and O3 levels in the mesosphere and stratosphere during the weeks and months following the major 9 November 2000 solar proton event. However, solar proton event (SPE)-enhanced NOy calculated within …

Nitrate Deposition To Surface Snow At Summit, Greenland, Following The 9 November 2000 Solar Proton Event, Katherine A. Duderstadt, Jack E. Dibb, Charles H. Jackman, Cora E. Randall, Stanley C. Solomon, Michael J. Mills, Nathan A. Schwadron, Harlan E. Spence

Earth Sciences

Abstract

This study considers whether spikes in nitrate in snow sampled at Summit, Greenland, from August 2000 to August 2002 are related to solar proton events. After identifying tropospheric sources of nitrate on the basis of correlations with sulfate, ammonium, sodium, and calcium, we use the three-dimensional global Whole Atmosphere Community Climate Model (WACCM) to examine unaccounted for nitrate spikes. Model calculations confirm that solar proton events significantly impact HO_x, NO_x, and O₃ levels in the mesosphere and stratosphere during the weeks and months following the major 9 November 2000 solar proton event. However, solar …

Intercomparison Of Field Measurements Of Nitrous Acid (Hono) During The Sharp Campaign, J R. Pinto, Jack E. Dibb, B H. Lee, B Rappengluck, E C. Wood, M Levy, R Y. Zhang, Barry Lefer, Xinrong Ren, J Stutz, C Tsai, L Ackermann, J Golovko, S C. Herndon, M Oakes, Q Y. Meng, J W. Munger, M Zahniser, J Zheng

Earth Sciences

Because of the importance of HONO as a radical reservoir, consistent and accurate measurements of its concentration are needed. As part of SHARP (Study of Houston Atmospheric Radical Precursors), time series of HONO were obtained by six different measurement techniques on the roof of the Moody Tower at the University of Houston. Techniques used were long path differential optical absorption spectroscopy (DOAS), stripping coil-visible absorption photometry (SC-AP), long path absorption photometry (LOPAP® ), mist chamber/ion chromatography (MC-IC), quantum cascade-tunable infrared laser differential absorption spectroscopy (QC-TILDAS), and ion drift-chemical ionization mass spectrometry (ID-CIMS). Various combinations of techniques were in operation from …

Brown Carbon In The Continental Troposphere, Jiumeng Liu, Eric Scheuer, Jack E. Dibb, Luke D. Ziemba, Kenn L. Thornhill, Bruce Anderson, Armin Wisthaler, Tomas Mikoviny, J J. Devi, Mike Bergin, Rodney J. Weber

Earth Sciences

No abstract provided.

Mercury Speciation At A Coastal Site In The Northern Gulf Of Mexico: Results From The Grand Bay Intensive Studies In Summer 2010 And Spring 2011, Xinrong Ren, Winston T. Luke, Paul Kelley, Mark Cohen, Fong Ngan, Richard Artz, Jake Walker, Steve Brooks, Christopher Moore, Phil Swartzendruber, Dieter Bauer, James Remeika, Anthony Hynes, Jack E. Dibb, John Rolison, Nishanth Krishnamurthy, William M. Landing, Arsineh Hecobian, Jeffery Shook, L Gregory Huey

Earth Sciences

During two intensive studies in summer 2010 and spring 2011, measurements of mercury species including gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and particulate-bound mercury (PBM), trace chemical species including O₃, SO₂, CO, NO, NO_Y, and black carbon, and meteorological parameters were made at an Atmospheric Mercury Network (AMNet) site at the Grand Bay National Estuarine Research Reserve (NERR) in Moss Point, Mississippi. Surface measurements indicate that the mean mercury concentrations were 1.42 ± 0.12 ng∙m⁻³ for GEM, 5.4 ± 10.2 pg∙m⁻³ for GOM, and 3.1 ± 1.9 pg∙m⁻³ for …

Mapping Crop Cycles In China Using Modis-Evi Time Series, Le Li, Mark A. Friedl, Qinchuan Xin, Josh M. Gray, Yaozhong Pan, Steve Frolking

Earth Sciences

As the Earth’s population continues to grow and demand for food increases, the need for improved and timely information related to the properties and dynamics of global agricultural systems is becoming increasingly important. Global land cover maps derived from satellite data provide indispensable information regarding the geographic distribution and areal extent of global croplands. However, land use information, such as cropping intensity (defined here as the number of cropping cycles per year), is not routinely available over large areas because mapping this information from remote sensing is challenging. In this study, we present a simple but efficient algorithm for automated …

Size And Frequency Of Natural Forest Disturbances And Amazon Carbon Balance, Fernando D.B. Espirito-Santo, Manuel Gloor, Michael Keller, Yadvinder Malhi, Sassan Saatchi, Bruce Nelson, Raimundo C. Oliveira Jr, Cleuton Pereira, Jon Lloyd, Steve Frolking, Michael W. Palace, Yosio E. Shimabukuro, Valdete Duarte, Abel Monteagudo Mendoza, Gabriela Lopez-Gonzalez, Tim R. Baker, Ted Feldpausch, Roel J.W. Brienen, Gregory P. Asner, Doreen S. Boyd, Oliver L. Phillips

Earth Sciences

Forest inventory studies in the Amazon indicate a large terrestrial carbon sink. However, field plots may fail to represent forest mortality processes at landscape-scales of tropical forests. Here we characterize the frequency distribution of disturbance events in natural forests from 0.01 ha to 2,651 ha size throughout Amazonia using a novel combination of forest inventory, airborne lidar and satellite remote sensing data. We find that small-scale mortality events are responsible for aboveground biomass losses of B1.28 Pg C y 1 over the entire Amazon region. We also find that intermediate-scale disturbances account for losses of B0.01 Pg C y 1 …

Representation Of Multiple Cropping Systems In Land Use Data Sets, K Waha, A Bondeau, Steve Frolking, F T. Portmann, S Siebert

Earth Sciences

No abstract provided.

Ice Cores From The St. Elias Mountains, Yukon, Canada: Their Significance For Climate, Atmospheric Composition And Volcanism In The North Pacific Region, Christian Zdanowicz, David Fisher, Jocelyne Bourgeois, Mike Demuth, James Zheng, Paul A. Mayewski, K Kreutz, Erich Osterberg, Kaplan Yalcin, Cameron P. Wake, Eric J. Steig, Duane Froese, Kumiko Goto-Azuma

Earth Sciences

A major achievement in research supported by the Kluane Lake Research Station was the recovery, in 2001 –02, of a suite of cores from the icefields of the central St. Elias Mountains, Yukon, by teams of researchers from Canada, the United States, and Japan. This project led to the development of parallel, long (103 – 104 year) ice-core records of climate and atmospheric change over an altitudinal range of more than 2 km, from the Eclipse Icefield (3017 m) to the ice-covered plateau of Mt. Logan (5340 m). These efforts built on earlier work recovering single ice cores in this …

Glaciers And Small Ice Caps In The Macro-Scale Hydrological Cycle: An Assessment Of Present Conditions And Future Changes, Richard B. Lammers, R Hock, Alexander Prusevich, A Bliss, V Radic, Stanley Glidden, Danielle S. Grogan, Steve Frolking

Earth Sciences

Glacier and small ice cap melt water contributions to the global hydrologic cycle are an important component of human water supply and for sea level rise. This melt water is used in many arid and semi-arid parts of the world for direct human consumption as well as indirect consumption by irrigation for crops, serving as frozen reservoirs of water that supplement runoff during warm and dry periods of summer when it is needed the most. Additionally, this melt water reaching the oceans represents a direct input to sea level rise and therefore accurate estimates of this contribution have profound economic …

Adaptability Of Irrigation To A Changing Monsoon In India: How Far Can We Go?, E Zaveri, Danielle S. Grogan, K Fisher-Vanden, Steve Frolking, D H. Wrenn

Earth Sciences

Agriculture and the monsoon are inextricably linked in India. A large part of the steady rise in agricultural production since the onset of the Green Revolution in the 1960’s has been attributed to irrigation. Irrigation is used to supplement and buffer crops against precipitation shocks, but water availability for such use is itself sensitive to the erratic, seasonal and spatially heterogeneous nature of the monsoon. Most attention in the literature is given to crop yields (Guiteras, 2009; Fishman, 2012; Auffhammer et al, 2011) and their ability to withstand precipitation shocks, in the presence of irrigation (Fishman, 2012). However, there remains …

Effect Of Carex Rostrata On Seasonal And Interannual Variability In Peatland Methane Emissions, Genevieve L. Noyce, Ruth Varner, Jill L. Bubier, Steve Frolking

Earth Sciences

Peatlands are a large natural source of atmospheric methane (CH₄), and the sedge Carex rostrata plays a critical role in the production, oxidation, and transport of CH₄ in these systems. This 4 year clipping experiment examined the changes in CH₄ emissions from a temperate peatland after removing all aboveground C. rostrata biomass. Methane fluxes, dissolved CH₄, and environmental variables were measured during spring, summer, and fall from 2008 to 2011. Clipping and removing the C. rostrata leaves and stems caused an immediate decrease in CH₄ emissions that persisted over 4 years of this …

In Situ Permafrost Thaw Due To Climate Change Drives Holistic Microbial Community Shifts With Implications For Methane Cycling, R Monday, C K. Mccalley, S B. Hodgkins, Virginia Rich, Steve Frolking, S R. Saleska, Andrew Barnes, J Chanton, P Crill

Earth Sciences

Thawing permafrost is a potentially significant source of radiative forcing feedback due to increased emissions of methane, a biogenic greenhouse gas (GHG). This study investigated changes in the microbial community along a permafrost thaw gradient at Stordalen Mire, Sweden using 16S rRNA gene amplicon and metagenomic methods. In situ measurements of geochemical parameters, including CH4 and C isotopes, enabled linkage of community dynamics to significant shifts in C balance. The thaw gradient ranged from intact at a palsa (low productivity and GHG emissions), through partially thawed in a bog (high productivity, low GHG emissions) to a completely thawed fen (high …

Beyond Peak Reservoir Storage? A Global Estimate Of Declining Water Storage Capacity In Large Reservoirs, Dominik Wisser, Steve Frolking, Stephen Hagen, Marc F. P. Bierkens

Earth Sciences

Water storage is an important way to cope with temporal variation in water supply and demand. The storage capacity and the lifetime of water storage reservoirs can be significantly reduced by the inflow of sediments. A global, spatially explicit assessment of reservoir storage loss in conjunction with vulnerability to storage loss has not been done. We estimated the loss in reservoir capacity for a global data set of large reservoirs from 1901 to 2010, using modeled sediment flux data. We use spatially explicit population data sets as a proxy for storage demand and calculate storage capacity for all river basins …

Nitrogen Cycling, Forest Canopy Reflectance, And Emergent Properties Of Ecosystems, Scott V. Ollinger, Peter B. Reich, Steve Frolking, Lucie Lepine, David Y. Hollinger, Andrew D. Richardson

Earth Sciences

No abstract provided.

Snow Spectral Albedo At Summit, Greenland: Measurements And Numerical Simulations Based On Physical And Chemical Properties Of The Snowpack, Carlo Carmagnola, Florent Domine, Marie Dumont, Patrick Wright, B Strellis, M Bergin, Jack E. Dibb, G Picard, Q Libois, L Arnaud, S Morin

Earth Sciences

The broadband albedo of surface snow is determined both by the near-surface profile of the physical and chemical properties of the snowpack and by the spectral and angular characteristics of the incident solar radiation. Simultaneous measurements of the physical and chemical properties of snow were carried out at Summit Camp, Greenland (72°36´ N, 38°25´ W, 3210 m a.s.l.) in May and June 2011, along with spectral albedo measurements. One of the main objectives of the field campaign was to test our ability to predict snow spectral albedo by comparing the measured albedo to the albedo calculated with a radiative transfer …

The Preservation Of Atmospheric Nitrate In Snow At Summit, Greenland, Dorothy L. Fibiger, Meredith G. Hastings, Jack E. Dibb, L Gregory Huey

Earth Sciences

There is great interest in using nitrate NO3 isotopic composition in ice cores to track the history of precursor nitrogen oxides (NOx = NO + NO2) in the atmosphere. Nitrate NO3 however can be lost from the snow by surface processes, such as photolysis back to NOx upon exposure to sunlight, making it difficult to interpret records of NO3 as a tracer of atmospheric NOx loading. In a campaign consisting of two field seasons (May–June) at Summit, Greenland, high temporal frequency surface snow samples were collected and analyzed for the oxygen isotopic composition of NO3. The strong, linear relationship observed …