Field‐based determination of air diffusivity using soil air and atmospheric pressure time series
Field‐based determination of air diffusivity using soil air and atmospheric pressure time series
复制标题
使用土壤空气和大气压力时间序列现场测定空气扩散率
DOI：
10.1029/95wr02115
复制
发表时间：
1995
影响因子：
5.4
通讯作者：
John Tunks
中科院分区：
文献类型：
--
作者：
S. Rojstaczer;John Tunks
空气扩散系数在两个区域超过4.6米的非饱和带的间隔，通过分析大气压力和土壤空气压力的时间序列。回归分析被用来计算这些系列在昼夜和半日频率的振幅（导纳）和相位滞后之间的比率。对于两个频率，每个监测区的导纳接近于1。两个时间序列之间的相位滞后在周日频率下统计学上等于零，但在半日频率下大到20° ± 7°。每个区域的昼夜和半日频率的相位滞后进行了比较，土壤空气压力响应大气负荷的扩散模型。通过该比较，确定每个区域的复合空气扩散率。空气扩散率没有大的变化，并且随着深度的相移趋势表明，大孔隙或裂缝在0.5-1.2 m深度的粘土层中传播。时间序列的长度（110天）允许检查相移和空气扩散率的时间变化的幅度。相位滞后的时间和空间趋势小于相位估计的误差范围。从整个时间记录确定的空气扩散率仅略微偏离从一系列部分记录的分析确定的平均扩散率。
Air diffusivity in two zones over a 4.6-m interval of the unsaturated zone was determined through analysis of atmospheric pressure and soil air pressure time series. Regression analysis was used to calculate the ratio of amplitudes (admittance) and phase lag between these series at diurnal and semidiurnal frequencies. The admittance for each of the monitoring zones was close to unity for both frequencies. Phase lags between the two time series were statistically equivalent to zero at the diurnal frequency but were as large as 20° ± 7° at the semidiurnal frequency. The phase lag at diurnal and semidiurnal frequencies for each zone was compared to a diffusional model of soil air pressure response to atmospheric loading. From this comparison a composite air diffusivity was determined for each zone. The absence of large variability in air diffusivity and the trends in phase shift with depth suggest that macropores or fractures propagate through a clay layer at a depth of 0.5–1.2 m. The length of the time series (110 days) allowed for the examination of the magnitude of temporal changes in phase shift and air diffusivity. Temporal and spatial trends in phase lag are smaller than the error bounds in the phase estimates. Air diffusivity determined from the entire time record deviated only slightly from the average diffusivity determined from the analysis of a sequence of partial records.