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1,176 results on '"Pitman, A. J"'

207. Opening Pandora's box: How to constrain regional projections of the carbon cycle.

Author

Teckentrup, Lina, De Kauwe, Martin G., Abramowitz, Gab, Pitman, Andrew J., Ukkola, Anna M., Hobeichi, Sanaa, François, Bastien, and Smith, Benjamin

Subjects
GENERAL circulation model, ECOSYSTEMS, RANDOM forest algorithms, CARBON cycle
Abstract

Climate projections from global circulation models (GCMs) part of the Coupled Model Intercomparison Project (CMIP6) are often employed to study the impact of future climate on ecosystems. However, especially at regional scales, climate projections display large biases in key forcing variables such as temperature and precipitation, which hamper predictive capacity. In this study we examine different methods to constrain regional projections of the carbon cycle in Australia. We employ a 5 dynamic global vegetation model (LPJ-GUESS) and force it with raw output from CMIP6 to assess the uncertainty associated with the choice of climate forcing. We then test different methods to either bias correct or calculate ensemble averages over the original forcing data to constrain the uncertainty in the regional projection of the Australian carbon cycle. We find that all bias correction methods reduce the bias of continental averages of steady-state carbon variables. Carbon pools are insensitive to the type of bias correction method applied for both individual GCMs and the arithmetic ensemble average across all corrected models. None of the bias correction methods consistently improve the change in carbon over time, highlighting the need to account for temporal properties in correction or ensemble averaging methods. Some bias correction methods reduce the ensemble uncertainty more than others. The vegetation distribution can depend on the bias correction method used. We further find that both the weighted ensemble averaging and random forest approach reduce the bias in total ecosystem carbon to almost zero, clearly outperforming the arithmetic ensemble averaging method. The random forest approach also produces the results closest to the target dataset for the change in the total carbon pool, seasonal carbon fluxes, emphasizing that machine learning approaches are promising tools for future studies. [ABSTRACT FROM AUTHOR]

Published
2022
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208. Influence of Leaf Area Index Prescriptions on Simulations of Heat, Moisture, and Carbon Fluxes

Author

Kala, Jatin, Decker, Mark, Exbrayat, Jean-Francois, Pitman, Andy J, Carouge, Claire, Evans, Jason P, Abramowitz, Gab, and Mocko, David

Subjects
Meteorology And Climatology, Earth Resources And Remote Sensing
Abstract

Leaf-area index (LAI), the total one-sided surface area of leaf per ground surface area, is a key component of land surface models. We investigate the influence of differing, plausible LAI prescriptions on heat, moisture, and carbon fluxes simulated by the Community Atmosphere Biosphere Land Exchange (CABLEv1.4b) model over the Australian continent. A 15-member ensemble monthly LAI data-set is generated using the MODIS LAI product and gridded observations of temperature and precipitation. Offline simulations lasting 29 years (1980-2008) are carried out at 25 km resolution with the composite monthly means from the MODIS LAI product (control simulation) and compared with simulations using each of the 15-member ensemble monthly-varying LAI data-sets generated. The imposed changes in LAI did not strongly influence the sensible and latent fluxes but the carbon fluxes were more strongly affected. Croplands showed the largest sensitivity in gross primary production with differences ranging from -90 to 60 %. PFTs with high absolute LAI and low inter-annual variability, such as evergreen broadleaf trees, showed the least response to the different LAI prescriptions, whilst those with lower absolute LAI and higher inter-annual variability, such as croplands, were more sensitive. We show that reliance on a single LAI prescription may not accurately reflect the uncertainty in the simulation of the terrestrial carbon fluxes, especially for PFTs with high inter-annual variability. Our study highlights that the accurate representation of LAI in land surface models is key to the simulation of the terrestrial carbon cycle. Hence this will become critical in quantifying the uncertainty in future changes in primary production.

Published
2013
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213. Key results and implications from phase 1(c) of the Project for Intercomparison of Land-surface Parametrization Schemes

Author

Pitman, A. J., Henderson-Sellers, A., Desborough, C. E., Yang, Z.-L., Abramopoulos, F., Boone, A., Dickinson, R. E., Gedney, N., Koster, R., Kowalczyk, E., Lettenmaier, D., Liang, X., Mahfouf, J.-F., Noilhan, J., Polcher, J., Qu, W., Robock, A., Rosenzweig, C., Schlosser, C. A., Shmakin, A. B., Smith, J., Suarez, M., Verseghy, D., Wetzel, P., Wood, E., and Xue, Y.

Published
1999
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220. Identifying areas at risk of drought‐induced tree mortality across South‐Eastern Australia

Author

De Kauwe, Martin G., primary, Medlyn, Belinda E., additional, Ukkola, Anna M., additional, Mu, Mengyuan, additional, Sabot, Manon E. B., additional, Pitman, Andrew J., additional, Meir, Patrick, additional, Cernusak, Lucas A., additional, Rifai, Sami W., additional, Choat, Brendan, additional, Tissue, David T., additional, Blackman, Chris J., additional, Li, Ximeng, additional, Roderick, Michael, additional, and Briggs, Peter R., additional

Published
2020
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237. Office-Based Procedure Training In Laryngology Fellowship Programs

Author

Enver, Necati, Ramaswamy, Apoorva, Sulica, Lucian, and Pitman, Michael J.

Abstract

Objective To assess the current practices and challenges of training office-based procedures to laryngology fellows in the United States. Methods An anonymous web-based survey study was distributed to laryngology fellowship program directors, as listed by the American Laryngological Association. The survey was a 19-item questionnaire with free-text, Likert scale, and multiple-choice answers. Results Twenty-two of 27 program directors (81.4%) replied to the survey. Many programs (8/16) have three or more laryngologists and do more than 10 procedures each week (10/16). Sixty-nine percent (11/16) of directors had not been trained for office procedures in their fellowship. The fellows are allowed to be primary surgeon on 68.75% and 75% of vocal fold augmentation and laser procedures, respectively. The expected competencies for these procedures on graduation are average-moderate and moderate. When program directors asked about the methods used for training, a minority of them use simulators (2/16), procedural checklists (2/16), or structured debriefing (2/16). The most commonly used methods were case-based troubleshooting (13/16) and unstructured debriefing (13/16). Patients being awake and patients' expectations are seen as the most important obstacles. Most of the directors thought office-based procedure training could be improved (14/16). The most common suggestions were using step-wise checklists, simulator-labs, and formal debriefings. Conclusion This is the first study evaluating the training of office-based laryngeal procedures during laryngology fellowship. Given the increasing importance of these procedures in practice and the herein identified barriers and need for improvement, fellowships should investigate the use of systematic training tools to improve fellow competency with office-based procedures.Laryngoscope, 2020

Published
2020

238. The Climate near the Ground

Author

Pitman, Andrew J., primary, Dolman, Han, additional, Kruijt, Bart, additional, Valentini, Riccardo, additional, and Baldocchi, Dennis, additional

Published
2004
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239. Existing Degrees of Consolidation

Author

Dirmeyer, Paul A., primary, Feddes, Reinder A., additional, Hall, Forrest G., additional, Halldin, Sven, additional, Hoff, Holger, additional, Houser, Paul, additional, Hutjes, Ronald W. A., additional, Jenne, Roy, additional, Leese, John, additional, Kittel, Timothy, additional, Meeson, Blanche W., additional, Olson, Richard J., additional, Phillips, Thomas J., additional, Pitman, Andrew J., additional, Takahashi, Kiyotoshi, additional, and Verdin, Kristine, additional

Published
2004
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241. The Regional Climate

Author

Avissar, Roni, primary, Weaver, Christopher P., additional, Werth, David, additional, Pielke, Roger A., additional, Rabin, Robert, additional, Pitman, Andrew J., additional, and Silva Dias, Maria Assuncão, additional

Published
2004
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250. Book reviews

Author

Reed, Richard J., Cortner, Hanna J., Morrisette, Peter M., and Pitman, A. J.

Published
1990
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