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  • Articles  (26)
  • Wiley  (26)
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  • Articles  (26)
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  • 1
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    Isentropic transport and the seasonal cycle amplitude of CO2 (2016)
    Wiley
    Details
    Publication Date: 2016-06-26
    Description: Carbon-concentration feedbacks and carbon-climate feedbacks constitute one of the largest sources of uncertainty in future climate. Since the beginning of the modern atmospheric CO 2 record, seasonal variations in CO 2 have been recognized as a signal of the metabolism of land ecosystems and quantitative attribution of changes in the seasonal cycle amplitude (SCA) of CO 2 to ecosystem processes is critical for understanding and projecting carbon-climate feedbacks far into the 21st Century. Here, the impact of surface carbon fluxes on the SCA of CO 2 throughout the Northern Hemisphere troposphere is investigated, paying particular attention to isentropic transport across latitudes. The analysis includes both a chemical transport model (GEOS-Chem) and an idealized tracer in a gray-radiation aquaplanet. The results of the study can be summarized by two main conclusions: (1) the SCA of CO 2 roughly follows surfaces of constant potential temperature, which can explain the observed increase in SCA with latitude along pressure surfaces and (2) increasing seasonal fluxes in lower latitudes have a larger impact on the SCA of CO 2 throughout most of the troposphere compared to increasing seasonal fluxes in higher latitudes. These results provide strong evidence that recently observed changes in the SCA of CO 2 at high northern latitudes (poleward of 60° N) are likely driven by changes in mid-latitude surface fluxes, rather than changes in Arctic fluxes.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Moist synoptic transport of CO2 along the mid-latitude storm track (2011)
    Wiley
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    Publication Date: 2011-05-12
    Description: Atmospheric mixing ratios of CO2 are strongly seasonal in the Arctic due to mid-latitude transport. Here we analyze the seasonal influence of moist synoptic storms by diagnosing CO2 transport from a global model on moist isentropes (to represent parcel trajectories through stormtracks) and parsing transport into eddy and mean components. During winter when northern plants respire, warm moist air, high in CO2, is swept poleward into the polar vortex, while cold dry air, low in CO2, that had been transported into the polar vortex earlier in the year is swept equatorward. Eddies reduce seasonality in mid-latitudes by ∼50% of NEE (∼100% of fossil fuel) while amplifying seasonality at high latitudes. Transport along stormtracks is correlated with rising, moist, cloudy air, which systematically hides this CO2 transport from satellites. We recommend that (1) regional inversions carefully account for meridional transport and (2) inversion models represent moist and frontal processes with high fidelity.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    A sampling method for improving the representation of spatially varying precipitation and soil moisture using the Simple Biosphere Model (2013)
    Wiley
    Details
    Publication Date: 2013-12-13
    Description: Representing spatially varying precipitation for current grid length scales used in General Circulation Models (GCMs) is a continuing challenge. Furthermore, to fully capture the hydrologic effects of non-uniform precipitation, a representation of soil moisture heterogeneity and distribution of spatially varying precipitation must exist within the same framework. For this study, the explicit and sampling methods of Sellers et al . [2007] are tested off-line using the Simple Biosphere Model (SiB3) in an arid, semi-arid and wet site, and are numerically compared to the bulk method, which is currently used in GCMs. To carry out the numerical experiments, an arbitrary grid area was defined by (1) a single instance of SiB3 (bulk method), (2) 100 instances of SiB3 (explicit method) and (3) less than 100 instances of SiB3 (sampling method). Precipitation was randomly distributed over fractions of the grid area for the explicit and sampling methods, while the standard SiB3 exponential distribution relating precipitation intensity to the grid area wet fraction was used in the bulk method. Comparing the sampling and bulk method to the explicit method indicates that 10 instances of SiB3 in the sampling method better captures the spatial variability in soil moisture and grid area flux calculations produced by the explicit method, and deals realistically with spatially varying precipitation at little additional computational cost to the bulk method.
    Electronic ISSN: 1942-2466
    Topics: Geography , Geosciences
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  • 4
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    A global reanalysis of vegetation phenology (2011)
    Wiley
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    Publication Date: 2011-08-25
    Description: Simulations of the global water and carbon cycle are sensitive to the model representation of vegetation phenology. Current phenology models are empirical, and few predict both phenological timing and leaf state. Our previous study demonstrated how satellite data assimilation employing an Ensemble Kalman Filter yields realistic phenological model parameters for several ecosystem types. In this study the data assimilation framework is extended to global scales using a subgrid-scale representation of plant functional types (PFTs) and elevation classes. A reanalysis of vegetation phenology for 256 globally distributed regions is performed using 10 years of Moderate Resolution Imaging Spectroradiometer (MODIS) fraction of photosynthetically active radiation (FPAR) absorbed by vegetation and leaf area index (LAI) data. The 9 · 108 quality screened observations (corresponding to
    Print ISSN: 0148-0227
    Topics: Biology , Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    Estimates of North American summertime planetary boundary layer depths derived from space-borne lidar (2012)
    Wiley
    Details
    Publication Date: 2012-08-01
    Description: The planetary boundary layer (PBL) mediates exchanges of energy, moisture, momentum, carbon, and pollutants between the surface and the atmosphere. This paper is a first step in producing a space-based estimate of PBL depth that can be used to compare with and evaluate model-based PBL depth retrievals, inform boundary layer studies, and improve understanding of the above processes. In clear sky conditions, space-borne lidar backscatter is frequently affected by atmospheric properties near the PBL top. Spatial patterns of 5-year mean mid-day summertime PBL depths over North America were estimated from the CALIPSO lidar backscatter and are generally consistent with model reanalyses and AMDAR (Aircraft Meteorological DAta Reporting) estimates. The rate of retrieval is greatest over the subtropical oceans (near 100%) where overlying subsidence limits optically thick clouds from growing and attenuating the lidar signal. The general retrieval rate over land is around 50% with decreased rates over the Southwestern United States and regions with high rates of convection. The lidar-based estimates of PBL depth tend to be shallower than aircraft estimates in coastal areas. Compared to reanalysis products, lidar PBL depths are greater over the oceans and areas of the boreal forest and shallower over the arid and semiarid regions of North America.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    Biosphere model simulations of interannual variability in terrestrial 13C/12C exchange (2013)
    Wiley
    Details
    Publication Date: 2013-05-22
    Description: [1]  Previous studies suggest that a large part of the variability in the atmospheric ratio of 13 CO 2 / 12 Co 2 originates from carbon exchange with the terrestrial biosphere rather than with the oceans. Since this variability is used to quantitatively partition the total carbon sink, we here investigate the contribution of interannual variability (IAV) in biospheric exchange to the observed atmospheric 13 C variations. We use the SiBCASA biogeochemical model, including a detailed isotopic fractionation scheme, separate 12 C and 13 C biogeochemical pools, and satellite-observed fire disturbances. This model of 12 CO 2 and 13 CO 2 thus also produces return fluxes of 13 CO 2 from its differently aged pools, contributing to the so-called disequilibrium flux. Our simulated terrestrial 13 C budget closely resembles previously published model results for plant discrimination and disequilibrium fluxes, and similarly suggests that variations in C 3 discrimination and year-to-year variations in C 3 and C 4 productivity are the main drivers of their IAV. But the year-to-year variability in the isotopic disequilibrium flux is much lower (1 σ  = ± 1.5 PgC ‰ yr –1 ) than required (± 12.5 PgC ‰ yr –1 ) to match atmospheric observations, under the common assumption of low variability in net ocean CO 2 fluxes. This contrasts with earlier published results. It is currently unclear how to increase IAV in these drivers suggesting that SIBCASA still misses processes that enhance variability in plant discrimination and relative C 3 /C 4 productivity. Alternatively, 13 C budget terms other than terrestrial disequilibrium fluxes, including possibly the atmospheric growth rate, must have significantly more IAV in order to close the atmospheric 13 C budget on a year-to-year basis.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
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  • 7
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    Current status of drug screening and disease modelling in human pluripotent stem cells (2012)
    Wiley
    In: BioEssays
    Details
    Publication Date: 2012-08-09
    Description: The emphasis in human pluripotent stem cell (hPSC) technologies has shifted from cell therapy to in vitro disease modelling and drug screening. This review examines why this shift has occurred, and how current technological limitations might be overcome to fully realise the potential of hPSCs. Details are provided for all disease-specific human induced pluripotent stem cell lines spanning a dozen dysfunctional organ systems. Phenotype and pharmacology have been examined in only 17 of 63 lines, primarily those that model neurological and cardiac conditions. Drug screening is most advanced in hPSC-cardiomyocytes. Responses for almost 60 agents include examples of how careful tests in hPSC-cardiomyocytes have improved on existing in vitro assays, and how these cells have been integrated into high throughput imaging and electrophysiology industrial platforms. Such successes will provide an incentive to overcome bottlenecks in hPSC technology such as improving cell maturity and industrial scalability whilst reducing cost. Human pluripotent stem cells are fast becoming the resource of choice for in vitro biomedical research. This review explores the role of these cells in drug safety and disease modelling, with emphasis on cardiomyocytes and neurons, and how their use is being integrated into automated platforms used by industry.
    Print ISSN: 0265-9247
    Electronic ISSN: 1521-1878
    Topics: Biology , Medicine
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  • 8
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    Global Seasonal Variations of Midday Planetary Boundary Layer Depth from CALIPSO Space-Borne LIDAR (2013)
    Wiley
    Details
    Publication Date: 2013-01-24
    Description: [1]  We present a new global analysis of the depth of the planetary boundary layer (PBL) and consider regional variations throughout the year. PBL depth is estimated from the vertical variance of CALIPSO space-borne LIDAR backscatter associated with aerosol and shallow clouds during midday satellite overpasses, and is only retrieved in the absence of optically thick clouds. The resulting analysis of over 100 million retrievals per year is therefore only a sample with higher frequency over deserts and other regions of strong subsidence, and lower frequency over regions of deep convection such as the ITCZ, tropical rainforests, and the Asian Monsoon. [2]  The mean of sampled PBL depths range from 500 meters over cold oceans to more than 3000 meters over hot deserts. The seasonal cycle of analyzed PBL depth is stronger over land than over water and seasonality over land and Midlatitude oceans is of opposite sign. Wintertime storm tracks and stratocumulus regions over subtropical oceans are prominent features of the analysis. Although evaluation of the new analysis is difficult due to previous sparse sampling by other methods, comparison of LIDAR-retrieved PBL depth with data collected by commercial aircraft generally shows good agreement.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 9
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    Evaluating atmospheric CO2 inversions at multiple scales over a highly-inventoried agricultural landscape (2013)
    Wiley
    Details
    Publication Date: 2013-01-25
    Description: An intensive regional research campaign was conducted by the North American Carbon Program (NACP) in 2007 to study the carbon cycle of the highly productive agricultural regions of the Midwestern United States. Forty-_ve di_erent associated projects were conducted across _ve U.S. agencies over the course of nearly a decade involving hundreds of researchers. One of the primary objectives of the intensive campaign was to investigate the ability of atmospheric inversion techniques to use highly calibrated CO2 mixing ratio data to estimate CO2 ux over the major croplands of the U.S. by comparing the results to an inventory of CO2 uxes. Statistics from densely monitored crop production, consisting primarily of corn and soybeans, provided the backbone of a well studied bottom up inventory ux estimate that was used to evaluate the atmospheric inversion results. Estimates were compared to the inventory from three di_erent inversion systems, representing spatial scales varying from high resolution mesoscale (PSU), to continental (CSU) and global (CarbonTracker), coupled to di_erent transport models and optimization techniques. The inversion-based mean CO2-C sink estimates were generally slightly larger, 8% to 20% for PSU, 10% to 20% for CSU, and 21% for CarbonTracker, but statistically indistinguishable, from the inventory estimate of 135 TgC. While the comparisons show that the MCI region-wide C sink is robust across inversion system and spatial scale, only the continental and mesoscale inversions were able to reproduce the spatial patterns within the region. In general, the results demonstrate that inversions can recover CO2 uxes at sub-regional scales with a relatively high density of CO2 observations and adequate information on atmospheric transport in the region. © 2013 Blackwell Publishing Ltd
    Print ISSN: 1354-1013
    Electronic ISSN: 1365-2486
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Published by Wiley
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  • 10
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    A Coupled Model of the Global Cycles of Carbonyl Sulfide and CO2: A Possible New Window on the Carbon Cycle (2013)
    Wiley
    Details
    Publication Date: 2013-05-08
    Description: [1]  Carbonyl sulfide (COS) is an atmospheric trace gas that participates in some key reactions of the carbon cycle, and thus holds great promise for studies of carbon cycle processes. Global monitoring networks and atmospheric sampling programs provide concurrent data on COS and CO 2 concentrations in the free troposphere and atmospheric boundary layer over vegetated areas. Here, we present a modeling framework for interpreting these data, and illustrate what COS measurements might tell us about carbon cycle processes. We implemented mechanistic and empirical descriptions of leaf and soil COS uptake into a global carbon cycle model (SiB 3) to obtain new estimates of the COS land flux. We then introduced these revised boundary conditions to an atmospheric transport model (PCTM) to simulate the variations in the concentration of COS and CO 2 in the global atmosphere. To balance the 3-fold increase in the global vegetation sink relative to the previous baseline estimate ( Kettle et al . 2002), we propose a new ocean COS source. Using a simple inversion approach, we optimized the latitudinal distribution of this ocean source, and found that it is concentrated in the tropics. The new model is capable of reproducing the seasonal variation in atmospheric concentration at most background atmospheric sites. The model also reproduces the observed large vertical gradients in COS between the boundary layer and free troposphere. Using a simulation experiment, we demonstrate that comparing drawdown of CO 2 with COS could provide additional constraints on differential responses of photosynthesis and respiration to environmental forcing. The separation of these two distinct processes is essential to understand the carbon cycle components for improved prediction of future responses of the terrestrial biosphere to changing environmental conditions.
    Print ISSN: 0148-0227
    Topics: Biology , Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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