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Sensitivity of Historical Simulation of the Permafrost to Different Atmospheric Forcing Data Sets from 1979 to 2009 Print


【Introduction】

      Numerical simulation is of great importance to the investigation of changes in frozen ground on large spatial and long temporal scales. Previous studies have focused on the impacts of improvements in the model for the simulation of frozen ground. Here the sensitivities of permafrost simulation to different atmospheric forcing data sets are examined using the Community Land Model, version 4.5 (CLM4.5), in combination with three sets of newly developed and reanalysis-based atmospheric forcing data sets (NOAA Climate Forecast System Reanalysis (CFSR), European Centre for Medium-Range Weather Forecasts Re-Analysis Interim (ERA-I), and NASA Modern Era Retrospective-Analysis for Research and Applications (MERRA)). All three simulations were run from 1979 to 2009 at a resolution of 0.5° × 0.5° and validated with what is considered to be the best available permafrost observations (soil temperature, active layer thickness, and permafrost extent). Results show that the use of reanalysis-based atmospheric forcing data set reproduces the variations in soil temperature and active layer thickness but produces evident biases in their climatologies. Overall, the simulations based on the CFSR and ERA-I data sets give more reasonable results than the simulation based on the MERRA data set, particularly for the present-day permafrost extent and the change in active layer thickness. The three simulations produce ranges for the present-day climatology (permafrost area: 11.31–13.57 × 106 km2; active layer thickness: 1.10–1.26 m) and for recent changes (permafrost area: 5.8% to 9.0%; active layer thickness: 9.9%–20.2%). The differences in air temperature increase, snow depth, and permafrost thermal conditions in these simulations contribute to the differences in simulated results.


【Citation】

Guo Donglin, Wang Huijun, Wang Aihui, 2017: Sensitivity of historical simulation of the permafrost to different atmospheric forcing datasets from 1979 to 2009. Journal of Geophysical Research: Atmospheres, 122, 12269–12284.


【Link】


http://onlinelibrary.wiley.com/doi/10.1002/2017JD027477/full


【Key figure】


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Figure 1. Distribution of trends in the simulated soil temperature (°C decade1) at a depth of 1 m over observed permafrost region during the period 1979–2009 based on the atmospheric forcing data sets from (a) CFSR, (b) ERA-I, and (c) MERRA and (d) the validation of soil temperature change from 1981 to 2009 based on observations from Russian meteorological stations, denoted with black hollow circles in Figure 3a. Areas with significance levels exceeding 95% are denoted with crosses. Area-averaged values are given in the bottom right corner of Figures 3a–3c. The observed and simulated trends are given in the top left corner of Figure 3d. Five countries and the Tibetan Plateau (TP), containing mostly permafrost, are outlined by the gray dashed lines.



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Figure 2. Comparison of the simulated present-day permafrost extent (shaded color) based on the atmospheric forcing data sets from (a) CFSR, (b) ERA-I, and (c) MERRA to observations (areas outlined in blue). The bias between the simulated and observed permafrost area is given in the bottom right corner of Figures 5a–5c. Five countries and the Tibetan Plateau (TP), containing mostly permafrost, are outlined by the gray dashed lines.



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Figure 3. Similar as in Figure 3 but for simulated active layer thickness (ALT) trends (m decade1) from 1979 to 2009 over the simulated permafrost region where permafrost remains in each year during the period 1979–2009. In addition, in Figure 8d, the validation for the period 1981–1990 (1996–2007) is based on observations from AL_RHST (CALM).



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Figure 4. Simulated changes in soil temperature (a), permafrost area (b), and active layer thickness (c) during 1979-2009 based on CFSR, ERA-I, and MERRA forcing datasets. 





 

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