The Experts below are selected from a list of 4590 Experts worldwide ranked by ideXlab platform
David A. Paige - One of the best experts on this subject based on the ideXlab platform.
-
The influence of thermal inertia on Mars' seasonal pressure variation and the effect of the weather component
1993Co-Authors: Stephen E. Wood, David A. PaigeAbstract:Using a Leighton-Murray type diurnal and seasonal Mars thermal model, we found that it is possible to reproduce the seasonal variation in daily-averaged pressures (approximately 680-890 Pa) measured by Viking Lander 1 (VL1), during years without global dust storms, with a standard deviation of less than 5 Pa. In this simple model, surface CO2, frost condensation, and sublimation rates at each latitude are determined by the net effects of radiation, latent heat, and heat conduction in Subsurface Soil Layers. An inherent assumption of our model is that the seasonal pressure variation is due entirely to the exchange of mass between the atmosphere and polar caps. However, the results of recent Mars GCM modeling have made it clear that there is a significant dynamical contribution to the seasonal pressure variation. This 'weather' component is primarily due to large-scale changes in atmospheric circulation, and its magnitude depends somewhat on the dust content of the atmosphere. The overall form of the theoretical weather component at the location of VL1, as calculated by the AMES GCM, remains the same over the typical range of Mars dust opacities.
-
Modeling the Martian seasonal CO2 cycle. I - Fitting the Viking Lander pressure curves. II - Interannual variability
1992Co-Authors: Stephen E. Wood, David A. PaigeAbstract:The present diurnal and seasonal thermal model for Mars, in which surface CO2 frost condensation and sublimation are determined by the net effects of radiation, latent heat, and heat conduction in Subsurface Soil Layers, in order to simulate seasonal exchanges of CO2 between the polar caps and atmosphere, successfully reproduces the measured pressured variations at the Viking Lander 1 site. In the second part of this work, the year-to-year differences between measured surface pressures at Viking sites as a function of season are used as upper limits on the potential magnitudes of interannual variations in the Martian atmosphere's mass. Simulations indicate that the dust Layers deposited onto the condensing north seasonal polar cap during dust storms can darken seasonal frost deposits upon their springtime uncovering, while having little effect on seasonal pressure variations.
-
Modeling the Martian seasonal CO2 cycle 1. Fitting the Viking Lander pressure curves
Icarus, 1992Co-Authors: Stephen E. Wood, David A. PaigeAbstract:Abstract A diurnal and seasonal thermal model is used to simulate the seasonal exchange of carbon dioxide between the atmosphere and polar caps of Mars. Surface CO 2 frost condensation and sublimation rates are determined by the net effects of radiation, latent heat, and heat conduction in Subsurface Soil Layers. We show that this model can successfully reproduce the measured seasonal pressure variations at the Viking Lander 1 site using constant values for frost albedo and emissivity in each hemisphere. An exact treatment of heat conduction is found to have important effects, as our best-fit CO 2 frost albedos and emissivities are not unique, but depend on the value of Soil thermal inertia assumed in each hemisphere. We find that Martian seasonal pressure variations are primarily due to frost condensation and sublimation in the 55° to 70° latitude regions in both hemispheres. The observed retreat of the north and south seasonal polar caps can also be matched closely by this model, but no combination of best-fit frost albedos and emissivities was consistent with the stability of permanent CO 2 deposits at either pole. The fact that this relatively simple model can provide such a good fit to the Viking Lander 1 pressure curve makes it a useful platform for studying the Martian CO 2 cycle over seasonal, interannual, and climatic timescales.
A. Ojala - One of the best experts on this subject based on the ideXlab platform.
-
Carbon dynamics in a Boreal land-stream-lake continuum during the spring freshet of two hydrologically contrasting years
Biogeochemistry, 2020Co-Authors: H. Miettinen, J. Pumpanen, M. Rantakari, A. OjalaAbstract:We studied in 2013 and 2014 the spring carbon dynamics in a Boreal landscape consisting of a lake and 15 inflowing streams and an outlet. The first year had weather and a hydrological regime typical of past years with a distinct spring freshet connected with the thaw of the average snowpack. The latter year had higher air temperatures which did not permit snow accumulation, despite similar winter precipitation. As such, there was hardly any spring freshet in 2014, and stream discharge peaked in January, i.e., the conditions resembled those predicted in the future climate. Despite the hydrological differences between the years, there were only small interannual differences in the stream CO_2 and DOC concentrations. The relationship between the concentrations and discharge was stronger in the typical year. CO_2 concentrations in medium-sized streams correlated negatively with the discharge, indicating dilution effect of melting snowpacks, while in large-sized streams the correlation was positive, suggesting stronger groundwater influence. The DOC pathway to these streams was through the Subsurface Soil Layers, not the groundwater. The total amount of carbon transported into the lake was ca. 1.5-fold higher in the typical year than in the year with warm winter. In 2013, most of the lateral inputs took place during spring freshet. In 2014, the majority of inputs occurred earlier, during the winter months. The lateral CO_2 signal was visible in the lake at 1.5 m depth. DOC dominated the carbon transport, and in both years, 12% of the input C was in inorganic form.
Stephen E. Wood - One of the best experts on this subject based on the ideXlab platform.
-
The influence of thermal inertia on Mars' seasonal pressure variation and the effect of the weather component
1993Co-Authors: Stephen E. Wood, David A. PaigeAbstract:Using a Leighton-Murray type diurnal and seasonal Mars thermal model, we found that it is possible to reproduce the seasonal variation in daily-averaged pressures (approximately 680-890 Pa) measured by Viking Lander 1 (VL1), during years without global dust storms, with a standard deviation of less than 5 Pa. In this simple model, surface CO2, frost condensation, and sublimation rates at each latitude are determined by the net effects of radiation, latent heat, and heat conduction in Subsurface Soil Layers. An inherent assumption of our model is that the seasonal pressure variation is due entirely to the exchange of mass between the atmosphere and polar caps. However, the results of recent Mars GCM modeling have made it clear that there is a significant dynamical contribution to the seasonal pressure variation. This 'weather' component is primarily due to large-scale changes in atmospheric circulation, and its magnitude depends somewhat on the dust content of the atmosphere. The overall form of the theoretical weather component at the location of VL1, as calculated by the AMES GCM, remains the same over the typical range of Mars dust opacities.
-
Modeling the Martian seasonal CO2 cycle. I - Fitting the Viking Lander pressure curves. II - Interannual variability
1992Co-Authors: Stephen E. Wood, David A. PaigeAbstract:The present diurnal and seasonal thermal model for Mars, in which surface CO2 frost condensation and sublimation are determined by the net effects of radiation, latent heat, and heat conduction in Subsurface Soil Layers, in order to simulate seasonal exchanges of CO2 between the polar caps and atmosphere, successfully reproduces the measured pressured variations at the Viking Lander 1 site. In the second part of this work, the year-to-year differences between measured surface pressures at Viking sites as a function of season are used as upper limits on the potential magnitudes of interannual variations in the Martian atmosphere's mass. Simulations indicate that the dust Layers deposited onto the condensing north seasonal polar cap during dust storms can darken seasonal frost deposits upon their springtime uncovering, while having little effect on seasonal pressure variations.
-
Modeling the Martian seasonal CO2 cycle 1. Fitting the Viking Lander pressure curves
Icarus, 1992Co-Authors: Stephen E. Wood, David A. PaigeAbstract:Abstract A diurnal and seasonal thermal model is used to simulate the seasonal exchange of carbon dioxide between the atmosphere and polar caps of Mars. Surface CO 2 frost condensation and sublimation rates are determined by the net effects of radiation, latent heat, and heat conduction in Subsurface Soil Layers. We show that this model can successfully reproduce the measured seasonal pressure variations at the Viking Lander 1 site using constant values for frost albedo and emissivity in each hemisphere. An exact treatment of heat conduction is found to have important effects, as our best-fit CO 2 frost albedos and emissivities are not unique, but depend on the value of Soil thermal inertia assumed in each hemisphere. We find that Martian seasonal pressure variations are primarily due to frost condensation and sublimation in the 55° to 70° latitude regions in both hemispheres. The observed retreat of the north and south seasonal polar caps can also be matched closely by this model, but no combination of best-fit frost albedos and emissivities was consistent with the stability of permanent CO 2 deposits at either pole. The fact that this relatively simple model can provide such a good fit to the Viking Lander 1 pressure curve makes it a useful platform for studying the Martian CO 2 cycle over seasonal, interannual, and climatic timescales.
Caixian Tang - One of the best experts on this subject based on the ideXlab platform.
-
Impact of novel materials on alkalinity movement down acid Soil profiles when combined with lime
Journal of Soils and Sediments, 2020Co-Authors: Dominic Lauricella, Peter W. G. Sale, Clayton R. Butterly, Zhe (han) Weng, Gary J. Clark, Guangdi Li, Caixian TangAbstract:Purpose Subsurface Soil acidity in conjunction with aluminium (Al^3+) toxicity is a major limitation to agricultural production globally. The conventional use of surface-applied lime is often insufficient at correcting Subsurface acidity; therefore, new practices and ameliorants are required. Methods This 3-month leaching experiment investigated whether animal wastes and other novel ameliorants in combination with lime could improve alkalinity movement, leading to greater amelioration of acid Subsurface Soil Layers compared with lime alone. Five ameliorants (mature dairy compost, vegetable garden compost, poultry litter, potassium humate and gypsum) were added at a rate of 18 mg dry matter g^−1 to the topSoil layer either without or with lime (target pH 5.5). Results All ameliorants with lime improved alkalinity movement below the amended layer (0–10 cm), with pH increases of 0.03–0.10 units at 1 month and 0.02–0.20 units at 3 months. In comparison, the Al^3+ concentrations in 10–12-cm and 12–15-cm Layers were significantly decreased by 2–5.5 μg g^−1. With lime, the improvements in alkalinity movement with ameliorants were in the order of gypsum > vegetable garden compost > potassium humate > poultry litter > mature dairy compost. Without lime, each amendment increased Soil pH in the subSoil, with their effectiveness decreasing in the order of poultry litter > vegetable garden compost > mature dairy compost > gypsum > potassium humate. Conclusion Some organic amendments are effective in addressing subSoil acidity. When combined with lime, their additive effects are limited.
-
A combination of biological activity and the nitrate form of nitrogen can be used to ameliorate Subsurface Soil acidity under dryland wheat farming
Plant and Soil, 2011Co-Authors: Mark Kenneth Conyers, Caixian Tang, Graeme J. Poile, Deli Chen, Zaman NuruzzamanAbstract:The management of Subsurface Soil acidity remains a challenge. We tested the ability of calcium nitrate fertilization to force net anion uptake by wheat within acidic Subsurface Layers and hence its ability to increase, or at least maintain, Soil pH within the acidic layer. The trials were conducted at two field sites: the moderately acidic site ran for 3 years (2006–08) while the trial at the most acidic site was conducted for 2 years (2006–07). Five treatments (nitrogen form and application method) were compared. Uptake efficiency of nitrogen (N) as measured by ^15N was similar (at ~40 to 70%) for both urea and nitrate sources at both sites. The urea source acidified the Soils (up to 0.2 pH in 3 years) whilst the nitrate form resulted in increases in Soil pH (up to 0.3 pH). The increases in pH were of a similar magnitude to the acidification rate measured in a nearby long-term trial. The dry matter production and grain yield in our trials were compromised by the decade long drought in our region, so the work should be repeated during wetter seasons. Calcium nitrate fertilization is a useful tool for at least maintaining Soil pH, and even reversing Soil acidification, in acidic Subsurface Soil Layers.
-
Application of nitrogen in NO3− form increases rhizosphere alkalisation in the Subsurface Soil Layers in an acid Soil
Plant and Soil, 2010Co-Authors: Chandrakumara Weligama, Caixian Tang, Peter W. G. Sale, Mark Conyers, Deli. LiuAbstract:Leaching of NO3− derived from ammoniacal fertilizers in the topSoil and subsequent uptake of NO3− by plants from deeper Layers may be used as a method of biological amelioration of Subsurface Soil acidity. This paper reports a glasshouse column experiment testing the above concept. Nitrogen with labelled 15N was supplied with and without lime to the surface Soil (0–10 cm) as urea, (NH4)2SO4 or Ca(NO3)2 at a rate equivalent to 120 kg N ha−1. Soil columns were regularly watered from the top to facilitate NO3− leaching. An aluminium-tolerant wheat genotype was grown for 38 days. The application of lime with nitrogen fertilizers increased growth of shoot and roots in all Soil Layers. The application of Ca(NO3)2 resulted in about 66% of recovery efficiency irrespective of whether lime was applied in the surface. This in turn resulted in about 0.2 units increase in rhizosphere pH in the Subsurface (10–15 cm) Soil layer compared to the same layer of the unlimed control. The supply of urea and (NH4)2SO4 alone or with lime did not increase rhizosphere pH in the Subsurface Soil Layers. Importantly, this study indicates that it is possible to exploit the process of nitrate uptake by wheat to increase pH in acidic Subsurface Soil.
H. Miettinen - One of the best experts on this subject based on the ideXlab platform.
-
Carbon dynamics in a Boreal land-stream-lake continuum during the spring freshet of two hydrologically contrasting years
Biogeochemistry, 2020Co-Authors: H. Miettinen, J. Pumpanen, M. Rantakari, A. OjalaAbstract:We studied in 2013 and 2014 the spring carbon dynamics in a Boreal landscape consisting of a lake and 15 inflowing streams and an outlet. The first year had weather and a hydrological regime typical of past years with a distinct spring freshet connected with the thaw of the average snowpack. The latter year had higher air temperatures which did not permit snow accumulation, despite similar winter precipitation. As such, there was hardly any spring freshet in 2014, and stream discharge peaked in January, i.e., the conditions resembled those predicted in the future climate. Despite the hydrological differences between the years, there were only small interannual differences in the stream CO_2 and DOC concentrations. The relationship between the concentrations and discharge was stronger in the typical year. CO_2 concentrations in medium-sized streams correlated negatively with the discharge, indicating dilution effect of melting snowpacks, while in large-sized streams the correlation was positive, suggesting stronger groundwater influence. The DOC pathway to these streams was through the Subsurface Soil Layers, not the groundwater. The total amount of carbon transported into the lake was ca. 1.5-fold higher in the typical year than in the year with warm winter. In 2013, most of the lateral inputs took place during spring freshet. In 2014, the majority of inputs occurred earlier, during the winter months. The lateral CO_2 signal was visible in the lake at 1.5 m depth. DOC dominated the carbon transport, and in both years, 12% of the input C was in inorganic form.
