The Contemporary and Historical Budget of Atmospheric CO2CO_2

Observations of $CO_2$ and $O_2$ are interpreted to develop an understanding of the changes in the abundance of atmospheric $CO_2$ that have arisen over the period 1995–2007. Fossil fuels accounted for an addition of 89.3 Gt of carbon to the atmosphere over this time period, 29% of which was transferred to the ocean, 15% to the global biosphere, with the balance (57%) retained by the atmosphere. Analysis of historical data for $CO_2$ derived from studies of gases trapped in ice at Law Dome in Antarctica indicate that the biosphere represented a net source of atmospheric $CO_2$ prior to 1940, switching subsequently to a net sink.Engineering and Applied Science

Contributions of the Hadley and Ferrel Circulations to the Energetics of the Atmosphere over the past 32-years

The Hadley system provides an example of a thermally direct circulation, the Ferrel system in contrast an example of a thermally indirect circulation. In this study, we develop an approach to investigate the key thermodynamic properties of the Hadley and Ferrel systems, quantifying them using assimilated meteorological data covering the period January 1979 to December 2010. This analysis offers a fresh perspective on the conversion of energy in the atmosphere from diabatic heating to the production of atmospheric kinetic energy. The results indicate that the thermodynamic efficiency of the Hadley system, considered as a heat engine, has been relatively constant over the 32 year period covered by the analysis, averaging 2.6 %. Over the same interval, the power generated by the Hadley regime has risen at an average rate of about 0.54 TW per year, reflecting an increase in energy input to the system consistent with the observed trend in the tropical sea surface temperatures. The Ferrel system acts as a heat pump with a coefficient of performance of 12.1, consuming kinetic energy at an approximate rate of 275 TW, exceeding the power production rate of the Hadley system by 77 TW.Engineering and Applied Science

A Climate-friendly Energy Future: Prospects for Wind

The objective of this thesis is to evaluate the potential for wind as an alternative energy source to replace fossil fuels and reduce global CO2 emissions. From 1995 to 2007, fossil fuels as the major energy source accounted for an addition of 89.3 Gt of carbon to the atmosphere over this period, 29 % of which was transferred to the ocean, 15 % to the global biosphere, with the balance (57 %) retained in the atmosphere. Building a low-carbon and climate-friendly energy system is becoming increasingly urgent to combat the threat of global warming.Engineering and Applied Science

Meteorologically Defined Limits to Reduction in the Variability of Outputs from a Coupled Wind Farm System in the Central US

Studies suggest that onshore wind resources in the contiguous US could readily accommodate present and anticipated future US demand for electricity. The problem with the output from a single wind farm located in any particular region is that it is variable on time scales ranging from minutes to days posing difficulties for incorporating relevant outputs into an integrated power system. The high frequency (shorter than once per day) variability of contributions from individual wind farms is determined mainly by locally generated small scale boundary layer. The low frequency variability (longer than once per day) is associated with the passage of transient waves in the atmosphere with a characteristic time scale of several days. Using 5 years of assimilated wind data, we show that the high frequency variability of wind-generated power can be significantly reduced by coupling outputs from 5 to 10 wind farms distributed uniformly over a ten state region of the Central US in this study. More than 95% of the remaining variability of the coupled system is concentrated at time scales longer than a day, allowing operators to take advantage of multi-day weather forecasts in scheduling projected contributions from wind.Engineering and Applied Science

Optimal Integration of Offshore Wind Power for a Steadier, Environmentally Friendlier, Supply of Electricity in China

Demand for electricity in China is concentrated to a significant extent in its coastal provinces. Opportunities for production of electricity by on-shore wind facilities are greatest however in the north and west of the country. Using high resolution wind data derived from the GEOS-5 assimilation, this study shows that investments in off-shore wind facilities in these spatially separated regions (Bohai-Bay or BHB, Yangtze-River Delta or YRD, Pearl-River Delta or PRD) could make an important contribution to overall regional demand for electricity in coastal China. An optimization analysis indicates that hour-to-hour variability of outputs from a combined system can be minimized by investing 24% of the power capacity in BHB, 30% in YRD and 47% in PRD. The analysis suggests that about 28% of the overall off-shore wind potential could be deployed as base load power replacing coal-fired system with benefits not only in terms of reductions in CO2 emissions but also in terms of improvements in regional air quality. The interconnection of off-shore wind resources contemplated here could be facilitated by China’s 12th-five-year plan to strengthen inter-connections between regional electric-power grids.Engineering and Applied Science

Numerical Simulation of the Dynamics of Water Droplet Impingement on a Wax Surface

The impact of droplets on solid surfaces is important for a wide range of engineering applications, such as ink-jet printing, spray cooling of hot surfaces, spray coating and painting, solder-drop deposition, blood spattering for criminal forensics and disease detection, etc. This paper simulated the dynamic process of a water droplet impinging onto a wax substrate in COMSOL, using the Phase Field method for tracking the free surface. The predicted spreading factor and apex height were validated against experimental results, showing good agreement during the dynamic impingement process. The effect of contact angles on the impingement process was also studied. The initial inertia driven spreading process is not affected by the contact angle, but the later spreading process and recoil process are significantly affected by the contact angle. The simulation results can provide a good understanding of the dynamic impingement process and provide insights on how surface wettability can affect the droplet spreading and rebounding process

Biases and improvements of the boreal winter–spring equatorial undercurrent in the Indian Ocean in the CMIP5 and CMIP6 models

We assessed the performance of state-of-the-art coupled models in reproducing the equatorial undercurrent (EUC) in the Indian Ocean based on the outputs of the Coupled Model Intercomparison Project Phase 6 (CMIP6) models and compared with the Phase 5 (CMIP5) models. Our results showed that the CMIP6 models reproduced the boreal winter–spring Indian Ocean EUC more realistically than the CMIP5 models, although both generations of models underestimated the strength of the Indian Ocean EUC compared with the observations. This underestimation of the Indian Ocean EUC can be attributed to the excessively strong and westward-extended cold tongue in the equatorial Pacific. In the CMIP models, a stronger winter-mean cold tongue favors a stronger zonal sea surface temperature gradient, which forces a strong easterly wind bias over the equatorial western Pacific. This, in turn, contributes to an acceleration of the Walker circulation. This enhanced Walker circulation over the Indo-Pacific Ocean directly causes a lower level westerly wind bias over the equatorial Indian Ocean and drives a shallow west–deep east thermocline tilt bias, ultimately leading to an excessively weak EUC in the Indian Ocean via wind-induced thermocline processes. Compared with the CMIP5 models, the overall improvement in the strength of the winter–spring Indian Ocean EUC in the CMIP6 models can be traced back to the improvement in the degree of the strong and westward-extended cold tongue bias. Our results suggest that efforts should be made to reduce the bias in the mean-state equatorial Pacific sea surface temperature to further improve the simulation and projection of the atmospheric and oceanic circulations in the Indian Ocean