Bonfils Celine

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  • Article
    Extending the record of photosynthetic activity in the eastern United States into the presatellite period using surface diurnal temperature range
    (American Geophysical Union, 2005-04-26) Bonfils, Celine ; Angert, Alon ; Henning, Cara C. ; Biraud, Sebastien ; Doney, Scott C. ; Fung, Inez Y.
    In this study, we demonstrate that mid-latitude surface measurements of diurnal temperature range (DTR) can be used to reconstruct decadal variability of regional-scale terrestrial photosynthetic activity 1) during and prior to the period with satellite retrievals of land greenness and 2) without the need for moisture data. While the two relative maxima present in the seasonal evolution of DTR can determine the beginning and the end of the growing season, the summertime average DTR can be used as a proxy of summertime terrestrial photosynthesis. In a case study in the eastern United States (1966–1997), the DTR reconstructions indicate significant natural decadal variability in photosynthetic activity, but no secular, long-term trend. The summertime photosynthesis was found to be controlled primarily by moisture availability. Also, contrary to existing model parameterizations, the timing of spring onset was found to depend on both temperature and moisture.
  • Article
    On the detection of summertime terrestrial photosynthetic variability from its atmospheric signature
    (American Geophysical Union, 2004-05-11) Bonfils, Celine ; Fung, Inez Y. ; Doney, Scott C. ; John, Jasmin G.
    We identify the climatic signatures of the summertime terrestrial photosynthesis variability using a long simulation of pre-industrial climate performed with the NCAR coupled global climate-carbon model. Since plant physiology controls simultaneously CO2 uptake and surface fluxes of water, changes in photosynthesis are accompanied by changes in numerous climate variables: daily maximum temperature, diurnal temperature range, Bowen ratio, canopy temperature and tropospheric lapse rate. Results show that these climate variables may be used as powerful proxies for photosynthesis activity for subtropical vegetation and for tropical vegetation when photosynthetic variability may be limited by water availability.