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Hongshou Li

Abstract

Because of Earth’s motion, periodic temperature fluctuations occur in soil on daily and yearly time scales, which inevitably lead to pulsation of the air pressure in the soil. The Earth–air pressure monitoring technique called “hou-qi” is the basis of a calendar formulated by the ancient Chinese. However, the daily/yearly variation of air pressure in the soil is very weak, according to practical monitoring experiments, so hou-qi has long been considered a pseudoscience. To determine the potential maximum change of Earth–air pressure, identify what is causing the underlying Earth–air pressure variation, and reveal the mechanism, we use a closed system, which is a more appropriate system test of the possible validity of hou-qi, to monitor Earth–air pressure variation in this paper. The results show that there are potential air pressure fluctuations of about 120–190 hPa in closed soil over the daily/yearly temperature range of 5°–40°C. This provides ample magnitude for hou-qi. The largest contribution made to Earth–air pressure variation was pressurization due to air warming, with vapor due to water evaporation and desorbed gas having smaller effects. The soil’s water content has a significant effect on Earth–air pressure amplitude. Dry soil contributes almost no water vapor, but the adsorbed gases from dry soil have up to a 38-hPa influence on air pressure. The soil’s salt content also has an important regulating role on Earth–air pressure and can reduce the influence of vapor pressure. This paper provides a scientific basis for the ancient Earth–air monitoring system of hou-qi and also has important significance for hydrometeorology and research on the ancient Chinese civilization.

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Youyue Wen, Xiaoping Liu, and Guoming Du

Abstract

Climate warming exhibits asymmetric patterns over a diel time, with the trend of nighttime warming exceeding that of daytime warming, a phenomenon commonly known as asymmetric warming. Recently, increasing studies have documented the significant instantaneous impacts of asymmetric warming on terrestrial vegetation growth, but the indirect effects of asymmetric warming carrying over vegetation growth (referred to here as time-lag effects) remain unknown. Here, we quantitatively studied the time-lag effects (within 1 year) of asymmetric warming on global plant biomes by using terrestrial vegetation net primary production (NPP) derived by the Carnegie–Ames–Stanford Approach (CASA) model and accumulated daytime and nighttime temperature (ATmax and ATmin) from 1982 to 2013. Partial correlation and time-lag analyses were conducted at a monthly scale to obtain the partial correlation coefficients between NPP and ATmax/ATmin and the lagged durations of NPP responses to ATmax/ATmin. The results showed that (i) asymmetric warming has nonuniform time-lag effects on single plant biomes, and distinguishing correlations exist in different vegetation biomes’ associations to asymmetric warming; (ii) terrestrial biomes respond to ATmax (4.63 ± 3.92 months) with a shorter protracted duration than to ATmin (6.06 ± 4.27 months); (iii) forest biomes exhibit longer prolonged duration in responding to asymmetric warming than nonforest biomes do; (iv) mosses and lichens (Mosses), evergreen needleleaf forests (ENF), deciduous needleleaf forests (DNF), and mixed forests (MF) tend to positively correlate with ATmax, whereas the other biomes associate with ATmax with near-equal splits of positive and negative correlation; and (v) ATmin has a predominantly positive influence on terrestrial biomes, except for Mosses and DNF. This study provides a new perspective on terrestrial ecosystem responses to asymmetric warming and highlights the importance of including such nonuniform time-lag effects into currently used terrestrial ecosystem models during future investigations of vegetation–climate interactions.

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Jinyun Tang and William J. Riley

Abstract

While coupling carbon and nitrogen processes is critical for Earth system models to accurately predict future climate and land biogeochemistry feedbacks, it has not yet been analyzed how numerical methods that land biogeochemical models apply to couple soil mineral nitrogen mobilizing and immobilizing processes affect predicted ecosystem carbon and nitrogen cycling. These effects were investigated here by using the E3SM land model and an evaluation of three plausible and widely used numerical couplings: 1) the mineral nitrogen–based limitation scheme, 2) the net uptake–based limitation scheme, and 3) the proportional nitrogen flux–based limitation scheme. It was found that these three schemes resulted in large differences (with a range of 316 PgC) in predicted cumulative land–atmosphere carbon exchanges under the RCP4.5 atmospheric CO2 simulations. This large uncertainty is without accounting for the different representations of the many land biogeochemical processes, but is about 73% of the range (434 PgC) reported for CMIP5 RCP4.5 simulations. These results help explain the large uncertainty found in various model intercomparison experiments and suggest that more robust numerical implementations are needed to improve carbon–nutrient cycle coupling in terrestrial ecosystem models.

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David M. Schultz, Timothy M. DelSole, Robert M. Rauber, and Walter A. Robinson
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Gretchen Keppel-Aleks, Samantha J. Basile, and Forrest M. Hoffman

Abstract

Earth system models (ESMs) simulate a large spread in carbon cycle feedbacks to climate change, particularly in their prediction of cumulative changes in terrestrial carbon storage. Evaluating the performance of ESMs against observations and assessing the likelihood of long-term climate predictions are crucial for model development. Here, we assessed the use of atmospheric growth rate variations to evaluate the sensitivity of tropical ecosystem carbon fluxes to interannual temperature variations. We found that the temperature sensitivity of the observed growth rate depended on the time scales over which atmospheric observations were averaged. The temperature sensitivity of the growth rate during Northern Hemisphere winter is most directly related to the tropical carbon flux sensitivity since winter variations in Northern Hemisphere carbon fluxes are relatively small. This metric can be used to test the fidelity of interactions between the physical climate system and terrestrial ecosystems within ESMs, which is especially important since the short-term relationship between ecosystem fluxes and temperature stress may be related to the long-term feedbacks between ecosystems and climate. If the interannual temperature sensitivity is used to constrain long-term temperature responses, the inferred sensitivity may be biased by 20%, unless the seasonality of the relationship between the observed growth rate and tropical fluxes is taken into account. These results suggest that atmospheric data can be used directly to evaluate regional land fluxes from ESMs, but underscore that the interaction between the time scales for land surface processes and those for atmospheric processes must be considered.

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Farhat Abbas, Nida Sarwar, Muhammad Ibrahim, Muhammad Adrees, Shafaqat Ali, Farhan Saleem, and Hafiz Mohkum Hammad

Abstract

Climatic extremes have direct and indirect effects on an ecosystem, whereby thermal variations bring warm and cold weather, and hydrological anomalies cause droughts and floods. Changing patterns of 13 temperature and 11 precipitation extreme indices for a 36-yr period (1980–2015) for four cities of the Balochistan province of Pakistan (Pasni, Jiwani, Khuzdar, and Dalbadin) were computed using RClimdex. A nonparametric Mann–Kendall test and Sen’s slope estimates were used to determine the statistical significance and magnitude of a trend, respectively. Most of the indices calculated for temperature extremes show statistically significant changes in their historic pattern, depicting a clear picture of warming in the regions. The indices calculated for precipitation extremes show statistically significant as well as nonsignificant results, depicting asymmetrical droughts in the region. If the patterns of humid weather with hot and wet extremes in the coastal cities of Balochistan continue for a couple of future decades, there will be challenges in implementing the multibillion-dollar Balochistan coastal development projects of the Pakistani port of Gwadar—a doorway to the Middle East for Chinese-planned business endeavors through Pakistan.

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Virnei Silva Moreira, Luiz Antonio Candido, Debora Regina Roberti, Geovane Webler, Marcelo Bortoluzzi Diaz, Luis Gustavo Gonçalves de Gonçalves, Raphael Pousa, and Gervásio Annes Degrazia

Abstract

The water balance in agricultural cropping systems is dependent on the physical and hydraulic characteristics of the soil and the type of farming, both of which are sensitive to the soil management. Most models that describe the interaction between the surface and the atmosphere do not efficiently represent the physical differences across different soil management areas. In this study, the authors analyzed the dynamics of the water exchange in the agricultural version of the Integrated Biosphere Simulator (IBIS) model (Agro-IBIS) in the presence of different physical soil properties because of the different long-term soil management systems. The experimental soil properties were obtained from two management systems, no tillage (NT) and conventional tillage (CT) in a long-term experiment in southern Brazil in the soybean growing season of 2009/10. To simulate NT management, this study modified the top soil layer in the model to represent the residual layer. Moreover, a mathematical adjustment to the computation of leaf area index (LAI) is suggested to obtain a better representation of the grain fill to the physiological maturity period. The water exchange dynamics simulated using Agro-IBIS were compared against experimental data collected from both tillage systems. The results show that the model well represented the water dynamics in the soil and the evapotranspiration (ET) in both management systems, in particular during the wet periods. Better results were found for the conventional tillage management system for the water balance. However, with the incorporation of a residual layer and soil properties in NT, the model improved the estimation of evapotranspiration by 6%. The ability of the Agro-IBIS model to estimate ET indicates its potential application in future climate scenarios.

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Richard Seager, Nathan Lis, Jamie Feldman, Mingfang Ting, A. Park Williams, Jennifer Nakamura, Haibo Liu, and Naomi Henderson

Abstract

John Wesley Powell, in the nineteenth century, introduced the notion that the 100th meridian divides the North American continent into arid western regions and humid eastern regions. This concept remains firmly fixed in the national imagination. It is reexamined in terms of climate, hydrology, vegetation, land use, settlement, and the agricultural economy. It is shown there is a stark east–west gradient in aridity roughly at the 100th meridian that is well expressed in hydroclimate, soil moisture, and “potential vegetation.” The gradient arises from atmospheric circulations and moisture transports. In winter, the arid regions west of the 100th meridian are shielded from Pacific storm-related precipitation and are too far west to benefit from Atlantic storms. In summer, the southerly flow on the western flank of the North Atlantic subtropical high has a westerly component over the western plains, bringing air from the interior southwest, but it also brings air from the Gulf of Mexico over the eastern plains, generating a west–east moisture transport and precipitation gradient. The aridity gradient is realized in soil moisture and a west-to-east transition from shortgrass to tallgrass prairie. The gradient is sharp in terms of greater fractional coverage of developed land east of the 100th meridian than to the west. Farms are fewer but larger west of the meridian, reflective of lower land productivity. Wheat and corn cultivation preferentially occur west and east of the 100th meridian, respectively. The 100th meridian is a very real arid–humid divide in the physical climate and landscape, and this has exerted a powerful influence on human settlement and agricultural development.

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Richard Seager, Jamie Feldman, Nathan Lis, Mingfang Ting, Alton P. Williams, Jennifer Nakamura, Haibo Liu, and Naomi Henderson

Abstract

The 100th meridian bisects the Great Plains of the United States and effectively divides the continent into more arid western and less arid eastern halves and is well expressed in terms of vegetation, land hydrology, crops, and the farm economy. Here, it is considered how this arid–humid divide will change in intensity and location during the current century under rising greenhouse gases. It is first shown that state-of-the-art climate models from phase 5 of the Coupled Model Intercomparison Project generally underestimate the degree of aridity of the United States and simulate an arid–humid divide that is too diffuse. These biases are traced to excessive precipitation and evapotranspiration and inadequate blocking of eastward moisture flux by the Pacific coastal ranges and Rockies. Bias-corrected future projections are developed that modify observationally based measures of aridity by the model-projected fractional changes in aridity. Aridity increases across the United States, and the aridity gradient weakens. The main contributor to the changes is rising potential evapotranspiration, while changes in precipitation working alone increase aridity across the southern and decrease across the northern United States. The “effective 100th meridian” moves to the east as the century progresses. In the current farm economy, farm size and percent of county under rangelands increase and percent of cropland under corn decreases as aridity increases. Statistical relations between these quantities and the bias-corrected aridity projections suggest that, all else being equal (which it will not be), adjustment to changing environmental conditions would cause farm size and rangeland area to increase across the plains and percent of cropland under corn to decrease in the northern plains as the century advances.

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Daniel Brown and Gerhard Reuter

Abstract

The Athabasca oil sands development has created a land surface disturbance of almost 900 km2 in northeastern Alberta. Both through industrial processes and the removal of boreal forest vegetation, this surface disturbance impacts meteorology in the vicinity by releasing waste heat, raising the surface temperature, and lowering the surface humidity. To investigate the effects of the Athabasca oil sands development on thunderstorm intensity, initiation time, and duration, the Weather Research and Forecasting (WRF) Model was employed to simulate the effect of the surface disturbance on atmospheric conditions on 10 case study days. The results suggested the oil sands surface disturbance was not associated with substantial increases in thunderstorm intensity on any of the case study days. On two case study days, however, the WRF Model simulations differed substantially from the observed meteorological conditions and only approached the observations when the oil sands surface disturbance was included in the model simulation. Including the oil sands surface disturbance in the model simulations resulted in thunderstorm initiation about 2 h earlier and increased thunderstorm duration. Data from commercial aircraft showed that the 850–500-mb temperature difference was greater than 30°C (very unstable) only on these 2 days. Such cases are sufficiently rare that they are not expected to affect the overall thunderstorm climatology. Still, in these very unstable cases, the oil sands development appears to have a significant effect on thunderstorm initiation time and duration.

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