Observations collected in the Badan Jaran desert hinterland and edge during 19-23 August 2009 and in the Jinta Oasis during 12-16 June 2005 are used to assess three methods for calculating the heat storage of the5-20-...Observations collected in the Badan Jaran desert hinterland and edge during 19-23 August 2009 and in the Jinta Oasis during 12-16 June 2005 are used to assess three methods for calculating the heat storage of the5-20-cm soil layer.The methods evaluated include the harmonic method,the conduction-convection method,and the temperature integral method.Soil heat storage calculated using the harmonic method provides the closest match with measured values.The conduction-convection method underestimates nighttime soil heat storage.The temperature integral method best captures fluctuations in soil heat storage on sub-diurnal timescales,but overestimates the amplitude and peak values of the diurnal cycle.The relative performance of each method varies with the underlying land surface.The land surface energy balance is evaluated using observations of soil heat flux at 5-cm depth and estimates of ground heat flux adjusted to account for soil heat storage.The energy balance closure rate increases and energy balance is improved when the ground heat flux is adjusted to account for soil heat storage.The results achieved using the harmonic and temperature integral methods are superior to those achieved using the conduction-convection method.展开更多
Tamarix ramosissima Ledeb. is a typical hardy desert plant growing in arid regions of Northwest China. Sap flow in stems of Z ramosissima plants were measured continuously to determine the diurnal and seasonal variati...Tamarix ramosissima Ledeb. is a typical hardy desert plant growing in arid regions of Northwest China. Sap flow in stems of Z ramosissima plants were measured continuously to determine the diurnal and seasonal variations of sap flow and to understand the water requirements of this species and the response of sap flow to meteorological factors. This article compared the sap flow rate measured by the heat balance method with the transpiration rate measured by rapid weighing, and validated that heat balance sap flow gauges were reliable for monitoring transpiration. The influence of meteorological factors on stem sap flow during the growing season was： solar radiation 〉 vapor pressure deficit 〉 air temperature 〉 rela- tive humidity 〉 wind speed. Bidirectional sap flows occurred at night, and negative sap flow generally corresponded to high atmospheric humidity. The average error in predicted sap flow rate ranged from -0.78% to 14.00% from June to September and for transpiration the average error was 8.19%. Therefore, based on the functional equations between sap flow and meteorological factors as well as sapwood area, transpiration of an individual plant, and even the stand-level transpiration, can be estimated accurately through extrapolation.展开更多
基金Supported by the National Science and Technology Support Program of China(2012BAH29B03)National(Key) Basic Research and Development(973)Program of China(2009CB421402)
文摘Observations collected in the Badan Jaran desert hinterland and edge during 19-23 August 2009 and in the Jinta Oasis during 12-16 June 2005 are used to assess three methods for calculating the heat storage of the5-20-cm soil layer.The methods evaluated include the harmonic method,the conduction-convection method,and the temperature integral method.Soil heat storage calculated using the harmonic method provides the closest match with measured values.The conduction-convection method underestimates nighttime soil heat storage.The temperature integral method best captures fluctuations in soil heat storage on sub-diurnal timescales,but overestimates the amplitude and peak values of the diurnal cycle.The relative performance of each method varies with the underlying land surface.The land surface energy balance is evaluated using observations of soil heat flux at 5-cm depth and estimates of ground heat flux adjusted to account for soil heat storage.The energy balance closure rate increases and energy balance is improved when the ground heat flux is adjusted to account for soil heat storage.The results achieved using the harmonic and temperature integral methods are superior to those achieved using the conduction-convection method.
基金financially supported by the National Natural Science Foundation of China (No. 91125025)
文摘Tamarix ramosissima Ledeb. is a typical hardy desert plant growing in arid regions of Northwest China. Sap flow in stems of Z ramosissima plants were measured continuously to determine the diurnal and seasonal variations of sap flow and to understand the water requirements of this species and the response of sap flow to meteorological factors. This article compared the sap flow rate measured by the heat balance method with the transpiration rate measured by rapid weighing, and validated that heat balance sap flow gauges were reliable for monitoring transpiration. The influence of meteorological factors on stem sap flow during the growing season was： solar radiation 〉 vapor pressure deficit 〉 air temperature 〉 rela- tive humidity 〉 wind speed. Bidirectional sap flows occurred at night, and negative sap flow generally corresponded to high atmospheric humidity. The average error in predicted sap flow rate ranged from -0.78% to 14.00% from June to September and for transpiration the average error was 8.19%. Therefore, based on the functional equations between sap flow and meteorological factors as well as sapwood area, transpiration of an individual plant, and even the stand-level transpiration, can be estimated accurately through extrapolation.
