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首页> 外文期刊>Journal of Geophysical Research. Biogeosciences >A MODEL INVESTIGATION OF TURBULENCE-DRIVEN PRESSURE-PUMPING EFFECTS ON THE RATE OF DIFFUSION OF CO2, N2O, AND CH4 THROUGH LAYERED SNOWPACKS
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A MODEL INVESTIGATION OF TURBULENCE-DRIVEN PRESSURE-PUMPING EFFECTS ON THE RATE OF DIFFUSION OF CO2, N2O, AND CH4 THROUGH LAYERED SNOWPACKS

机译：湍流驱动的抽气对层状烟囱扩散CO2，N2O和CH4速率的影响的模型研究

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Pressure pumping at the Earth's surface is caused by short-period atmospheric turbulence, longer-period barometric changes, and quasi-static pressure fields induced by wind blowing across irregular topography. These naturally occurring atmospheric pressure variations induce periodic fluctuations in airflow through snowpacks, soils, and any other porous media at the Earth's surface. Consequently, the uptake or release of trace-gases from soils and snowpacks is a combination of molecular diffusion and advection forced by pressure pumping. Using model-estimated fluxes, this study attempts to quantify the influence that turbulent pressure fluctuations with periods between 0.1 and 1000 s can have on the rate of exchange of CO2, N2O, and CH4 through a seasonal snowpack. Data for this study were collected at a forested subalpine meadow site in the Rocky Mountains of southern Wyoming, during February 1995 when the snowpack was distinctly layered and approximately 1.4 m deep. The data include mole fraction of CO2, N2O, and CH4 just above and at the base of the snowpack, several profiles of CO2, N2O, and CH4 mole fraction in the top 1 m of the snowpack, and a profile of snowpack density and tortuosity. Turbulent atmospheric pressure-pumping fluctuations, sampled at approximately 11 Hz for several hours, were obtained with a fast response differential pressure sensor. A one-dimensional steady state diffusion model and one- and three-dimensional time-dependent pressure-pumping models are used to estimate the gas fluxes through the snowpack. Boundary conditions are provided by grab samples just above the snowpack and at the soil/snow interface. The pressure-pumping models are driven by the observed pressure fluctuations, and all models include the observed layering of the snowpack. As with previous studies the present results indicate that the effects of pressure pumping are diminished with increasingly strong gradients. Furthermore, we conclude that unless pressure pumping influences the gas concentrations at the boundaries of the snowpack, it appears unlikely that it can significantly impact the rate of gaseous diffusion through the snowpack. Even two-and three-dimensional effects, which can have a significant shortterm impact on the flues and concentration profiles, are nearly eliminated when averaged over a period of hours. It is also suggested that vertical layering is important for three-dimensional pressure-pumping studies and that the time-dependent temperature term, which is traditionally ignored when modeling dynamic pressure variations, may in fact be dominant in some situations and probably should be incorporated in future modeling studies of pressure pumping. [References: 39]
机译：地球表面的压力泵是由短时期的大气湍流，长时期的气压变化以及风吹过不规则地形引起的准静态压力场引起的。这些自然发生的大气压力变化会引起通过积雪，土壤和地球表面其他任何多孔介质的气流周期性波动。因此，土壤和积雪中痕量气体的吸收或释放是分子扩散和压力泵强迫对流的结合。使用模型估计的通量，本研究试图量化在0.1到1000 s之间的周期内湍流压力波动对季节性积雪对CO2，N2O和CH4交换速率的影响。这项研究的数据是在1995年2月怀俄明州南部洛矶山脉的一个森林覆盖的高山草甸现场收集的，当时积雪被明显地分层并且深约1.4 m。数据包括雪堆正上方和底部的CO2，N2O和CH4的摩尔分数，雪堆顶部1 m处的一些CO2，N2O和CH4摩尔分数的分布以及雪堆密度和曲折度的分布。使用快速响应压差传感器获得了大约11 Hz的采样数小时的湍流大气压力波动。一维稳态扩散模型以及一维和三维时间相关的压力泵模型用于估算通过积雪的气体通量。边界条件是由积雪上方和土壤/雪界面的抓取样本提供的。压力泵模型是由观察到的压力波动驱动的，所有模型都包括观察到的积雪的分层。与以前的研究一样，目前的结果表明，随着梯度的增大，压力泵送的作用会减弱。此外，我们得出的结论是，除非压力泵影响积雪边界处的气体浓度，否则似乎不可能显着影响气体在积雪中的扩散速度。当在几个小时内求平均值时，甚至二维和三维效果（可能会对烟道和浓度曲线产生重大短期影响）也几乎被消除。还建议垂直分层对于三维压力泵研究很重要，并且在某些情况下，时间动态温度术语在建模动态压力变化时通常会被忽略，它实际上可能在某些情况下占主导地位，并且可能应纳入压力泵的未来模型研究。 [参考：39]

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