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Mark Z. Jacobson

Abstract

An extension of the correlated-k distribution method that uses spectral-mapping techniques was derived to parameterize line-by-line absorption coefficients for multiple gases simultaneously for use in three-dimensional atmospheric models. In a variation from previous correlation techniques, this technique ensures exact correlation of absorption frequencies within a probability interval for all gases through all layers of the atmosphere when multiple gases are considered. The technique is physical since, in reality, gases are correlated in wavelength space. The technique, referred to as the “multiple-absorber correlated-k distribution spectral-mapping method,” was found to be accurate to <0.7% of incident radiation for 16 probability intervals per wavelength interval, integrated over 0.4–1000-μm wavelengths and accounting for 11 absorbing gases simultaneously and multiple layers, compared with an exact line-by-line solution. A method was also derived to reduce the number of probability intervals required for a radiative transfer solution without suffering the same inaccuracy as merely reducing the number of probability intervals when parameterizing the absorption coefficient. The new coefficients were tested in a global model, and results were compared with mean thermal-IR irradiance data.

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Mark Z. Jacobson

Abstract

Biomass burning releases gases (e.g., CO2, CO, CH4, NOx, SO2, C2H6, C2H4, C3H8, C3H6) and aerosol particle components (e.g., black carbon, organic matter, K+, Na+, Ca2+, Mg2+, NH4+, H+, Cl, H2SO4, HSO4, SO42−, NO3). To date, the global-scale climate response of controlling emission of these constituents together has not been examined. Here 10-yr global simulations of the climate response of biomass-burning aerosols and short-lived gases are coupled with numerical calculations of the long-term effect of controlling biomass-burning CO2 and CH4 to estimate the net effect of controlling burning over 100 yr. Whereas eliminating biomass-burning particles is calculated to warm temperatures in the short term, this warming may be more than offset after several decades by cooling due to eliminating long-lived CO2, particularly from permanent deforestation. It is also shown analytically that biomass burning always results in CO2 accumulation, even when regrowth fluxes equal emission fluxes and in the presence of fertilization. Further, because burning grassland and cropland yearly, as opposed to every several years, increases CO2, biofuel burning, considered a “renewable” energy source, is only partially renewable, and biomass burning elevates CO2 until it is stopped. Because CO2 from biomass burning is considered recyclable and biomass particles are thought to cool climate, the Kyoto Protocol did not consider biomass-burning controls. If the results here, which apply to a range of scenarios but are subject to uncertainty, are correct, such control may slow global warming, contrary to common perception, and improve human health.

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Mark Z. Jacobson

Abstract

This paper examines the effects of soil moisture initialization in a coupled air quality–meteorological model on temperature profiles, wind speeds, and pollutant concentrations. Three simulations, each with different initial soil moisture fields, were run. In the baseline simulation, predicted temperatures, wind speeds, and gas/aerosol pollutant concentrations accurately matched observations. In the other two simulations, soil moisture contents were initialized about 4% lower and higher, respectively, than in the baseline simulation. In the low-moisture case, predicted temperature profiles were hotter, near-surface wind speeds were faster, and near-surface pollutant concentrations were lower than observations and baseline predictions. In the high-moisture case, predicted temperatures were colder, wind speeds were slower, and pollutant concentrations were higher than observations and baseline predictions. Initial soil moisture contents affected vertical temperature profiles up to 600-mb altitude after two days. Elevated temperature changes were due in part to changes in sensible heat fluxes from the surface and in part to changes in elevated heat advection fluxes. Changes in temperature profiles affected wind speeds and boundary layer depths, which affected times and magnitudes, respectively, of peak concentrations. Slower wind speeds, associated with high soil moisture contents, delayed times of peak concentrations in the eastern Los Angeles basin. Faster wind speeds, associated with low soil moisture contents, advanced times of peak concentrations. High soil moisture contents resulted in thinner boundary layer depths, increasing average near-surface pollutant concentrations, including that of ozone. Low soil moisture contents resulted in thicker boundary layer depths, decreasing average concentrations, including that of ozone. At some locations, changes in the magnitude of peak ozone concentrations depended on how changes in soil moisture affected ozone precursors and destroyers.

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Cristina L. Archer and Mark Z. Jacobson

Abstract

The formation mechanism of the Santa Cruz eddy (SCE) is investigated using the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5). Simulations of 25–26 August 2000 showed that two eddy instances formed on that night, a finding supported by observations. The two eddies had similar behavior: they both formed in the sheltered Santa Cruz, California, area and then moved southeastward, to finally dissipate after 7–11 h. However, the first eddy had greater vorticity, wind speed, horizontal and vertical extents, and lifetime than the second eddy. Numerical simulations showed that the SCEs are formed by the interaction of the main northwesterly flow with the topographic barrier represented by the Santa Cruz Mountains to the north of Monterey Bay. Additional numerical experiments were undertaken with no diurnal heating cycle, no (molecular or eddy) viscosity, and no horizontal thermal gradients at ground level. In all cases, vertical vorticity was still created by the tilting of horizontal vorticity generated by the solenoidal term in the vorticity equation. This baroclinic process appeared to be the fundamental formation mechanism for both SCEs, but more favorable conditions in the late afternoon (including a south-to-north pressure gradient, flow turning due to the sea breeze, and an expansion fan) coincided to intensify the first eddy.

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Mark Z. Jacobson and John E. Ten Hoeve

Abstract

Land use, vegetation, albedo, and soil-type data are combined in a global model that accounts for roofs and roads at near their actual resolution to quantify the effects of urban surface and white roofs on climate. In 2005, ~0.128% of the earthrsquo;s surface contained urban land cover, half of which was vegetated. Urban land cover was modeled over 20 years to increase gross global warming (warming before cooling due to aerosols and albedo change are accounted for) by 0.06–0.11 K and population-weighted warming by 0.16–0.31 K, based on two simulations under different conditions. As such, the urban heat island (UHI) effect may contribute to 2%–4% of gross global warming, although the uncertainty range is likely larger than the model range presented, and more verification is needed. This may be the first estimate of the UHI effect derived from a global model while considering both UHI local heating and large-scale feedbacks. Previous data estimates of the global UHI, which considered the effect of urban areas but did not treat feedbacks or isolate temperature change due to urban surfaces from other causes of urban temperature change, imply a smaller UHI effect but of similar order. White roofs change surface albedo and affect energy demand. A worldwide conversion to white roofs, accounting for their albedo effect only, was calculated to cool population-weighted temperatures by ~0.02 K but to warm the earth overall by ~0.07 K. White roof local cooling may also affect energy use, thus emissions, a factor not accounted for here. As such, conclusions here regarding white roofs apply only to the assumptions made.

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Cristina L. Archer and Mark Z. Jacobson

Abstract

Wind is the world’s fastest growing electric energy source. Because it is intermittent, though, wind is not used to supply baseload electric power today. Interconnecting wind farms through the transmission grid is a simple and effective way of reducing deliverable wind power swings caused by wind intermittency. As more farms are interconnected in an array, wind speed correlation among sites decreases and so does the probability that all sites experience the same wind regime at the same time. The array consequently behaves more and more similarly to a single farm with steady wind speed and thus steady deliverable wind power. In this study, benefits of interconnecting wind farms were evaluated for 19 sites, located in the midwestern United States, with annual average wind speeds at 80 m above ground, the hub height of modern wind turbines, greater than 6.9 m s−1 (class 3 or greater). It was found that an average of 33% and a maximum of 47% of yearly averaged wind power from interconnected farms can be used as reliable, baseload electric power. Equally significant, interconnecting multiple wind farms to a common point and then connecting that point to a far-away city can allow the long-distance portion of transmission capacity to be reduced, for example, by 20% with only a 1.6% loss of energy. Although most parameters, such as intermittency, improved less than linearly as the number of interconnected sites increased, no saturation of the benefits was found. Thus, the benefits of interconnection continue to increase with more and more interconnected sites.

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Cristina L. Archer, Mark Z. Jacobson, and Francis L. Ludwig

Abstract

A shallow cyclonic circulation that occurs in the summertime over the Monterey Bay (California) is investigated. Since it is often centered offshore from the city of Santa Cruz and has never been studied in detail before, it is named the Santa Cruz eddy (SCE) in this study. Its horizontal size is 10–40 km, and its vertical extent is 100–500 m. The SCE is important for local weather because it causes surface winds along the Santa Cruz coast to blow from the east instead of from the northwest, the latter being the climatological summer pattern for this area. As a consequence of the eddy, cool and moist air is advected from the south and southeast into the Santa Cruz area, bringing both relief from the heat and fog to the city.

The SCE is unique in its high frequency of occurrence. Most vortices along the western American coast form only during unusual weather events, whereas the SCE forms 78%–79% of the days during the summer. The SCE frequency was determined after analyzing two years of data with empirical orthogonal functions (EOFs) from a limited observational network and satellite imagery. An explanation of the formation mechanism of the SCE will be provided in Part II of this study.

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Guy P. Brasseur, Mohan Gupta, Bruce E. Anderson, Sathya Balasubramanian, Steven Barrett, David Duda, Gregg Fleming, Piers M. Forster, Jan Fuglestvedt, Andrew Gettelman, Rangasayi N. Halthore, S. Daniel Jacob, Mark Z. Jacobson, Arezoo Khodayari, Kuo-Nan Liou, Marianne T. Lund, Richard C. Miake-Lye, Patrick Minnis, Seth Olsen, Joyce E. Penner, Ronald Prinn, Ulrich Schumann, Henry B. Selkirk, Andrei Sokolov, Nadine Unger, Philip Wolfe, Hsi-Wu Wong, Donald W. Wuebbles, Bingqi Yi, Ping Yang, and Cheng Zhou

Abstract

Under the Federal Aviation Administration’s (FAA) Aviation Climate Change Research Initiative (ACCRI), non-CO2 climatic impacts of commercial aviation are assessed for current (2006) and for future (2050) baseline and mitigation scenarios. The effects of the non-CO2 aircraft emissions are examined using a number of advanced climate and atmospheric chemistry transport models. Radiative forcing (RF) estimates for individual forcing effects are provided as a range for comparison against those published in the literature. Preliminary results for selected RF components for 2050 scenarios indicate that a 2% increase in fuel efficiency and a decrease in NOx emissions due to advanced aircraft technologies and operational procedures, as well as the introduction of renewable alternative fuels, will significantly decrease future aviation climate impacts. In particular, the use of renewable fuels will further decrease RF associated with sulfate aerosol and black carbon. While this focused ACCRI program effort has yielded significant new knowledge, fundamental uncertainties remain in our understanding of aviation climate impacts. These include several chemical and physical processes associated with NOx–O3–CH4 interactions and the formation of aviation-produced contrails and the effects of aviation soot aerosols on cirrus clouds as well as on deriving a measure of change in temperature from RF for aviation non-CO2 climate impacts—an important metric that informs decision-making.

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