The Importance of Advective Fluxes to Gas Transport Across the Earth-Atmosphere Interface: The Role of Thermal Convection

Nachshon, Uri; Weisbrod, Noam; Dragila, M. I.; Ganot, Yonatan

doi:10.5772/25108

Cited by 5 publications

(13 citation statements)

References 61 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This thermally-driven free convection is a venting of warm moist air from the cracks/fractures replaced by a cool, relatively dry air and thus enhances the evaporation from within cracks/fractures [83,84]. Indeed, Nachshon et al [85] (and references therein) estimated that nightly evaporation process, controlled by thermal convection, is of similar order of magnitude, as the one occurring at day.…”

Section: Influence Of the Surface Permeability Of Claysmentioning

confidence: 99%

“…Indeed, these cracks have been studied for their role in aquifer recharge under humid conditions and are considered as inactive during dry seasons [83,84]. However, desiccation cracks permit gas flux across unsaturated zones and the atmosphere by (i) wind pumping, (ii) atmospheric barometric changes, and (iii) thermally-driven convection flow in fractures during dry seasons [83][84][85]. The first two processes result in the advection of underground air towards the atmosphere [85], but are infrequent, as they depend on meteorological conditions.…”

Section: Influence Of the Surface Permeability Of Claysmentioning

confidence: 99%

“…However, desiccation cracks permit gas flux across unsaturated zones and the atmosphere by (i) wind pumping, (ii) atmospheric barometric changes, and (iii) thermally-driven convection flow in fractures during dry seasons [83][84][85]. The first two processes result in the advection of underground air towards the atmosphere [85], but are infrequent, as they depend on meteorological conditions. Thermally-driven convection flow inside cracks/fractures happens daily, only during winter nights in middle-latitudes, when the air inside cracks/fractures is warmer and less dense than the atmospheric air.…”

Section: Influence Of the Surface Permeability Of Claysmentioning

confidence: 99%

“…Thermally-driven convection flow inside cracks/fractures happens daily, only during winter nights in middle-latitudes, when the air inside cracks/fractures is warmer and less dense than the atmospheric air. During sunset, as the atmosphere cools down, unstable air-density gradient develops, creating an air overturning within the cracks/fractures [83][84][85]. This thermally-driven free convection is a venting of warm moist air from the cracks/fractures replaced by a cool, relatively dry air and thus enhances the evaporation from within cracks/fractures [83,84].…”

Section: Influence Of the Surface Permeability Of Claysmentioning

confidence: 99%

“…Convective venting from fractures is a phenomenon only described for its influence on the soil-atmosphere gas exchanges and particularly on water vapor flux [85]. Evaporation via convective venting is the most studied one.…”

Section: Influence Of the Surface Permeability Of Claysmentioning

confidence: 99%

See 4 more Smart Citations

Investigation of Short-Term Evolution of Soil Characteristics over the Lake Chad Basin Using GRACE Data

Lopez

Ramillien

Antoine³

et al. 2018

Remote Sensing

View full text Add to dashboard Cite

In the Sahelian region, the West African Monsoon (WAM) is an important phenomenon for land water storage evolution, as demonstrated by The Gravity Recovery and Climate Experiment (GRACE) estimations. The Monsoon leads to an annual increase of the water mass. However, GRACE data also displays the existence of a semi-annual cycle whose its origin is still uncertain. This cycle is characterized by a gain of water mass at the beginning of the dry season. In this study, 10-days GRACE data are used to understand the characteristics of this semi-annual cycle. Investigations of the rainfall events, rivers discharge peaks, and the Lake Chad water level variations suggest that they are not at the origin of this cycle. However, MODIS evapotranspiration data display an increase each 6 months, during the rainy season, and at the same time as the semi-annual cycle estimated by GRACE. This increase occurs in regions where the amount of clays at the surface exceeds 30%. The link between both signals and the proportion of clays at the surface leads us to the conclusion that the seasonal variation of the vertical permeability of clays controls the amount of water present in the unsaturated zone.

show abstract

Section: Influence Of the Surface Permeability Of Claysmentioning

confidence: 99%

Section: Influence Of the Surface Permeability Of Claysmentioning

confidence: 99%

Section: Influence Of the Surface Permeability Of Claysmentioning

confidence: 99%

Section: Influence Of the Surface Permeability Of Claysmentioning

confidence: 99%

Section: Influence Of the Surface Permeability Of Claysmentioning

confidence: 99%

See 3 more Smart Citations

Investigation of Short-Term Evolution of Soil Characteristics over the Lake Chad Basin Using GRACE Data

Lopez

Ramillien

Antoine³

et al. 2018

Remote Sensing

View full text Add to dashboard Cite

show abstract

Low-Cost Sensors Provide Insight into Temporal Variation in Fugitive Methane Gas Concentrations Around an Energy Well

Fleming

Morais

Ryan

2022

Preprint

View full text Add to dashboard Cite

Effective measurement of the presence and rate of methane gas migration (GM) outside the casing of energy wells is important for managing social and environmental impacts and financial liabilities in the upstream petroleum industry. Practitioners typically assess GM by above-background methane gas concentrations in-soil or at-grade; however, factors influencing the potential variation in these measurements are not well represented in industry recommended best-practices. Inexpensive chemoresistive sensors were used to record a one-minute frequency methane gas concentration time series over 19 days. Time series were recorded at three soil depths (0, 5, and 30 cm) at two locations <30m cm radially from a petroleum well with known GM, in addition to two 'control' locations. Observed concentration variations ranged over several orders of magnitude at all depths, with generally lower concentrations and more variation observed at shallower depths. Varying concentrations were correlated to meteorological factors, primarily including wind speed and shallow groundwater table elevation. The gas concentration patterns were affected by a 3.5 mm rainfall event, suggesting soil moisture changes affected preferential gas migration pathways. Results indicate potential variability in repeated snapshot GM test results. Although currently recommended GM detection methods would have effectively identified the presence/absence of GM, they would not have quantified order of magnitude changes in concentration. GM detection success at this site was increased with measurement at more than one location spatially within 30 cm of the well casing, lower concentration detection limits, and greater measurement depth. These findings indicate that meteorological factors should be considered when conducting gas migration surveys (particularly for improving at-grade test reliability). The low-cost approach for long-term concentration measurement facilitates insight into variable gas concentrations and may be advantageous in comparison to snapshot measurements in some circumstances.

show abstract

Temperature controls diel oscillation of the CO2 concentration in a desert soil

Spohn

Holzheu

2021

Biogeochemistry

View full text Add to dashboard Cite

The diel dynamic of the CO2 concentration in soils in relation to temperature is not yet fully understood. Air temperature might control the soil CO2 concentration due to thermal convective venting at sites experiencing large temperature differences between the atmosphere and the soil. Therefore, the objective of this study was to determine the soil CO2 concentration and its temporal dynamic in a deep desert soil in relationship to soil and air temperature based on high frequency measurements. For this purpose, CO2 concentration and temperature were measured in six soil depths (ranging from 15 to 185 cm) in a coarse-textured desert soil in the North of Chile every 60 min together with precipitation and air temperature for one year. The mean CO2 concentration calculated across the whole measuring period increased linearly with soil depth from 463 ppm in 15 cm to 1542 ppm in 185 cm depth. We observed a strong diel oscillation of the CO2 concentration that decreased with soil depth and a hysteretic relationship between the topsoil CO2 concentration and both air and soil temperature. The Rayleigh-Darcy number calculated for different times indicates that thermal convective venting of the soil occurred during the night and in the early morning. A small precipitation event (4 mm) increased the CO2 concentrations in 15, 30, and 50 cm depths for several days but did not alter the amplitude of the diel oscillation of the CO2 concentration. The diel oscillation of the CO2 concentration and the hysteretic relationship between soil CO2 concentration and air temperature were likely caused by thermal convection, leading to transport of CO2-rich air from the soil to the atmosphere at night. In conclusion, our results indicate that the soil CO2 concentration can be largely controlled by convection caused by temperature differences, and not only by diffusion. The results have important implications as they provide further evidence that thermal convective venting contributes to gas exchange at sites experiencing large temperature differences between the atmosphere and the soil, which is relevant for soil chemical reactions.

show abstract

The Importance of Advective Fluxes to Gas Transport Across the Earth-Atmosphere Interface: The Role of Thermal Convection

Cited by 5 publications

References 61 publications

Investigation of Short-Term Evolution of Soil Characteristics over the Lake Chad Basin Using GRACE Data

Investigation of Short-Term Evolution of Soil Characteristics over the Lake Chad Basin Using GRACE Data

Low-Cost Sensors Provide Insight into Temporal Variation in Fugitive Methane Gas Concentrations Around an Energy Well

Temperature controls diel oscillation of the CO2 concentration in a desert soil

Contact Info

Product

Resources

About