Premium
Implementation of Improved Parameterization of Terrestrial Flux in WRF‐VPRM Improves the Simulation of Nighttime CO 2 Peaks and a Daytime CO 2 Band Ahead of a Cold Front
Author(s) -
Hu XiaoMing,
Gourdji Sharon M.,
Davis Kenneth J.,
Wang Qingyu,
Zhang Yao,
Xue Ming,
Feng Sha,
Moore Berrien,
Crowell Sean M. R.
Publication year - 2021
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1029/2020jd034362
Subject(s) - weather research and forecasting model , environmental science , atmospheric sciences , ecosystem respiration , soil respiration , flux (metallurgy) , daytime , biomass (ecology) , ecosystem , photosynthetically active radiation , photosynthesis , primary production , chemistry , soil science , physics , soil water , ecology , biochemistry , organic chemistry , biology
Enhanced CO 2 mole fraction bands were often observed immediately ahead of cold front during the Atmospheric Carbon and Transport (ACT)‐America mission and their formation mechanism is undetermined. Improved understanding and correct simulation of these CO 2 bands are needed for unbiased inverse CO 2 flux estimation. Such CO 2 bands are hypothesized to be related to nighttime CO 2 respiration and investigated in this study using WRF‐VPRM, a weather‐biosphere‐online‐coupled model, in which the biogenic fluxes are handled by the Vegetation Photosynthesis and Respiration Model (VPRM). While the default VPRM satisfactorily parameterizes gross ecosystem exchange, its treatment of terrestrial respiration as a linear function of temperature was inadequate as respiration is a nonlinear function of temperature and also depends on the amount of biomass and soil wetness. An improved ecosystem respiration parameterization including enhanced vegetation index, a water stress factor, and a quadratic temperature dependence is incorporated into WRF‐VPRM and evaluated in a year‐long simulation before applied to the investigation of the frontal CO 2 band on August 4, 2016. The evaluation shows that the modified WRF‐VPRM increases ecosystem respiration during the growing season, and improves model skill in reproducing nighttime near‐surface CO 2 peaks. A nested‐domain WRF‐VPRM simulation is able to capture the main characteristics of the August 4 CO 2 band and informs its formation mechanism. Nighttime terrestrial respiration leads to accumulation of near‐surface CO 2 in the region. As the cold front carrying low‐CO 2 air moves southeastward, and strong photosynthesis depletes CO 2 further southeast of the front, a CO 2 band develops immediately ahead of the front.