Multiple time scale evaluation of the energy balance during the maize growing season,and a new reason for energy imbalance |
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Authors: | JianXia Guo LinGen Bian YongJiu Dai |
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Institution: | (1) Meteorological Observation Center of China Meteorological Administration, Beijing, 100081, China;(2) State Key Laboratory of Remote Sensing Science, School of Geography and Remote Sensing Science, Beijing Normal University, Beijing, 100875, China;(3) Chinese Academy of Meteorological Sciences, Beijing, 100081, China |
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Abstract: | Energy imbalance is a common problem associated with the measurement of surface energy using the eddy covariance method. In
the evaluation of the energy balance, people usually pay more attention to the statistical result that the effective energy
(the sum of sensible and latent heat) is systematically lower than the available energy (the difference of net radiation and
ground heat flux). However, little attention has been paid to the existence of the reversed situation when the effective energy
is larger than the available energy or their contribution to the overall energy closure rate. In this paper, based on the
analysis of the energy balance on multiple time scales across the maize growth season, we conclude that the non-synchronization
of energy components is the main reason for the existence of the reversed case. By shifting the phase of the effective energy
components half an hour ahead, the rates of energy closure over all time scales are improved and dramatically reduce the number
of the half-hourly samples when the energy ratio exceeds 1 or is below 0.5. According to the characteristics of the energy
distribution and transformation over multiple time scales, latent heat is always the main type of energy cost, and the residual
of the energy balance increases with the growth of the maize plant surpassing the sensible heat for seventy days. It is suggested
that the heat storage and photosynthetic energy play an important role in the energy balance during the growing period of
maize.
Supported by National Basic Research Program of China (Grant No.2007CB714402) and State Key Laboratory of Remote Sensing Science
(Beijing Normal University) |
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Keywords: | maize energy balance multiple time scale energy hysteresis |
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