Dominant Energy Source Research Articles

THE MORPHOLOGY OF THE EJECTA IN SUPERNOVA 1987A: A STUDY OVER TIME AND WAVELENGTH

We present a study of the morphology of the ejecta in Supernova 1987A based on images and spectra from the HST as well as integral field spectroscopy from VLT/SINFONI. The HST observations were obtained between 1994 - 2011 and primarily probe the outer hydrogen-rich zones of the ejecta. The SINFONI observations were obtained in 2005 and 2011 and instead probe the [Si I]/[Fe II] emission from the inner regions. We find a strong temporal evolution of the morphology in the HST images, from a roughly elliptical shape before ~5,000 days, to a more irregular, edge-brightened morphology thereafter. This transition is a natural consequence of the change in the dominant energy source powering the ejecta, from radioactive decay before ~5,000 days to X-ray input from the circumstellar interaction thereafter. The [Si I]/[Fe II] images display a more uniform morphology, which may be due to a remaining significant contribution from radioactivity in the inner ejecta and the higher abundance of these elements in the core. Both the H-alpha and the [Si I]/[Fe II] line profiles show that the ejecta are distributed fairly close to the plane of the inner circumstellar ring, which is assumed to define the rotational axis of the progenitor. The H-alpha emission extends to higher velocities than [Si I]/[Fe II] as expected. There is no clear symmetry axis for all the emission and we are unable to model the ejecta distribution with a simple ellipsoid model with a uniform distribution of dust. Instead, we find that the emission is concentrated to clumps and that the emission is distributed somewhat closer to the ring in the north than in the south. This north-south asymmetry may be partially explained by dust absorption. We compare our results with explosion models and find some qualitative agreement, but note that the observations show a higher degree of large-scale asymmetry.

Energy Transitions in the Early 21st Century

We are in the early stages of a long and complex transition from a global economy based on fossil energy to an economy based on low carbon renewable energy. However, fossil fuel resources are abundant and widely distributed, and they will remain the dominant source of primary energy for at least the next quarter century. In the United States, displacement of coal by natural gas for electric power generation has done more to reduce CO2 emissions than all new renewables combined, and this may occur globally for the next decade or two, even if the European Union does not take advantage of its large unconventional natural gas resources. Greater energy efficiency (not including the efficiencies associated with displacement of coal by gas) will also be more important than new renewables. Cost/benefit ratios are important for sustainability of the transition, and some energy efficiency technologies and displacement of coal by natural gas have lower cost/benefit ratios than wind power, solar power or biofuels. Money spent on the large scale deployment of wind, solar and especially biofuels would be better spent on research, development and demonstration of a broader suite of technologies that would support the energy transition, with a focus onmore » improving the cost benefit ratios of already deployed technologies and developing alternatives. Advanced nuclear reactors, engineered geothermal systems, fossil fuel recovery coupled with CO2 sequestration and pre-combustion or post-combustion decarbonation of fossil fuels with geological CO2 sequestration are among the technologies that might be more cost effective than wind, solar or biofuels, and biofuels have serious adverse societal and environment consequences.« less

The potential of forest-derived bioenergy to contribute to China's future energy and transportation fuel requirements

Increasing concerns of oil security, greenhouse gas emissions, and sustainability have encouraged nations to consider the contribution that agriculture/forestry for bioenergy (and biofuels in particular) could make as alternatives to current fossil-based energy and transportation fuels. Despite China's large population and geographical size, it has only relatively recently developed into a highly industrialized and energy-dependent economy. Coal is, and will remain, China's dominant energy source. However, over the last few years with China's growing middle class, increasing growth in production and sale of cars/trucks and a growing chemical based sector, oil and its derivatives are predicted to experience the fastest fossil fuel growth. China's ability to produce so-called “first-generation” or conventional biofuels from sugar, starch or vegetable oil based plants is very restricted because of “food vs. fuel” issues. Thus, biomass-based and forest-based biofuels, in particular, can form a medium-to-long-term solution that could contribute to China's national biofuels targets. Oilseed trees have been suggested as an initial forest-based biodiesel strategy with about 13 million ha of marginal land identified for possible plantation. It is also estimated that 17 million tonnes of cellulosic ethanol per annum could be derived from forest biomass that is currently available in China.

A tale of two villages: assessing the dynamics of fuelwood supply in communal landscapes in South Africa

SUMMARYFuelwood is the dominant source of energy used by most rural households in southern Africa to meet daily domestic energy requirements. Due to limited financial resources, most rural households are unable to make the transition to electricity thus they remain dependant on the woodlands surrounding their settlements as a source of cheap energy. Unsustainable fuelwood harvesting due to increasing demand as a result of growing human populations may result in environmental degradation particularly in the high-density, communal savannah woodlands of South Africa. Evaluating the sustainability of current fuelwood harvesting patterns requires an understanding of the environmental impacts of past logging practices to establish patterns of woodland degradation. This study evaluates impacts of fuelwood harvesting from 1992–2009 on the woodland structure and species composition surrounding two rural villages located within the Kruger to Canyons Biosphere Reserve (Mpumalanga Province, South Africa). Both villages (Welverdiend and Athol) were of similar spatial extent and exhibited similar socioeconomic characteristics. The total wood stock in the communal woodlands of both villages declined overall (with greater losses seen in Welverdiend) and, in Welverdiend, there were also changes in the woodland structure and species diversity of the species commonly harvested for fuelwood over this period. The woodlands in Welverdiend have become degraded and no longer produce fuelwood of preferred species and stem size in sufficient quantity or quality. The absence of similar negative impacts in Athol suggests more sustainable harvesting regimes exist there because of the lower human population and lower fuelwood extraction pressure. The Welverdiend community has annexed neighbouring unoccupied private land in a social response to fuelwood scarcity. Athol residents behaved similarly during drought periods. The potential for future conflict with neighbouring conservation areas within the Kruger to Canyons Biosphere is high if current land uses and fuelwood extraction patterns are maintained.

An Overview of Carbon Offsets from Agriculture

Although climate change has largely been removed from the federal policy agenda of the United States in the near term, the continued reliance on fossil fuels as a dominant energy source leaves many analysts to conclude that climate policy will eventually reappear on that agenda. We present a review of recent research related to the design and implementation of one instrument for greenhouse gas (GHG) reduction: offsets. As these are implemented, policy makers must understand the way these programs work. In this review, we describe the basic features of carbon offset markets, along with the potential supply of offsets from agricultural sources and associated cost considerations. In this discussion we highlight the role of institutional design of contracts and transactions costs. We then turn to the benefits of including offsets in policies to reduce GHGs and complete the review with a discussion of the challenges in implementing the programs.

The molecular gas in Luminous Infrared Galaxies: a new emergent picture

AbstractResults from a large, multi-J CO, 13CO, and HCN line survey of Luminous Infrared Galaxies (LIRGs: LIR≥ 1010 L⊙) in the local Universe (z≤0.1), complemented by CO J=4–3 up to J=13–12 observations from the Herschel Space Observatory (HSO), paints a new picture for the average conditions of the molecular gas of the most luminous of these galaxies with turbulence and/or large cosmic ray (CR) energy densities UCR rather than far-UV/optical photons from star-forming sites as the dominant heating sources. Especially in ULIRGs (LIR>1012 L⊙) the Photon Dominated Regions (PDRs) can encompass at most a few % of their molecular gas mass while the large UCR∼ 103 UCR, Galaxy, and the strong turbulence in these merger/starbursts, can volumetrically heat much of their molecular gas to Tkin∼ (100-200) K, unhindered by the high dust extinctions. Moreover the strong supersonic turbulence in ULIRGs relocates much of their molecular gas at much higher average densities (≥104 cm−3) than in isolated spirals (∼ 102–103 cm−3). This renders low-J CO lines incapable of constraining the properties of the bulk of the molecular gas in ULIRGs, with substantial and systematic underestimates of its mass possible when only such lines are used. Finally a comparative study of multi-J HCN lines and CO SLEDs from J=1–0 up to J=13–12 of NGC 6240 and Arp 193 offers a clear example of two merger/starbursts whose similar low-J CO SLEDs, and LIR/LCO,1−0 and LHCN, 1−0/LCO,1-0 ratios (proxies of the so-called SF efficiency and dense gas mass fraction), yield no indications about their strongly diverging CO SLEDs beyond J=4–3, and ultimately the different physical conditions in their molecular ISM. The much larger sensitivity of ALMA and its excellent site in the Atacama desert now allows the observations necessary to assess the dominant energy sources of the molecular gas and its mass in LIRGs without depending on the low-J CO lines.

OAO/ISLE Near-IR Spectroscopy of IRAS Galaxies

Abstract We present the results of the near-infrared (IR) spectroscopy of nine IRAS galaxies (NGC 1266, NGC 1320, NGC 2633, NGC 2903, NGC 3034, Mrk 33, NGC 7331, NGC 7625, NGC 7714) with the ISLE imager and spectrograph mounted on the Okayama Astrophysical Observatory 1.88-m telescope. [Fe II] 1.257$\ \mu$m and Pa$\beta$ emission lines were observed for the whole sample, while H$_2$ 2.121$\ \mu$m and Br$\gamma$ lines were additionally obtained for two sources, whose flux ratios were used as a diagnostic tool of dominant energy sources of the galaxies. We found that the nucleus of NGC 1266 is most likely a low-ionization nuclear emission-line region (LINER), while NGC 2633 and NGC 2903 possibly harbor active galactic nuclei (AGNs). No AGN or LINER signal is found for other objects. In addition, we found the spectral features, which are indicative of some unusual phenomena occurring in the galaxies, such as the large [Fe II] line widths compared to the local escape velocity in NGC 1266. The present work shows the potential ability of ISLE to shed new light on the nature of infrared galaxies, either through a statistical survey of galaxies or an exploration of spectral features found in individual objects.

Fenofibrate administration to arthritic rats increases adiponectin and leptin and prevents oxidative muscle wasting

Chronic inflammation induces skeletal muscle wasting and cachexia. In arthritic rats, fenofibrate, a peroxisome proliferator-activated receptor α (PPARα (PPARA)) agonist, reduces wasting of gastrocnemius, a predominantly glycolytic muscle, by decreasing atrogenes and myostatin. Considering that fenofibrate increases fatty acid oxidation, the aim of this study was to elucidate whether fenofibrate is able to prevent the effect of arthritis on serum adipokines and on soleus, a type I muscle in which oxidative metabolism is the dominant source of energy. Arthritis was induced by injection of Freund's adjuvant. Four days after the injection, control and arthritic rats were gavaged daily with fenofibrate (300 mg/kg bw) or vehicle over 12 days. Arthritis decreased serum leptin, adiponectin, and insulin (P<0.01) but not resistin levels. In arthritic rats, fenofibrate administration increased serum concentrations of leptin and adiponectin. Arthritis decreased soleus weight, cross-sectional area, fiber size, and its Ppar α mRNA expression. In arthritic rats, fenofibrate increased soleus weight, fiber size, and Ppar α expression and prevented the increase in Murf1 mRNA. Fenofibrate decreased myostatin, whereas it increased MyoD (Myod1) and myogenin expressions in the soleus of control and arthritic rats. These data suggest that in oxidative muscle, fenofibrate treatment is able to prevent arthritis-induced muscle wasting by decreasing Murf1 and myostatin expression and also by increasing the myogenic regulatory factors, MyoD and myogenin. Taking into account the beneficial action of adiponectin on muscle wasting and the correlation between adiponectin and soleus mass, part of the anticachectic action of fenofibrate may be mediated through stimulation of adiponectin secretion.

Introduction: A Decidedly Valuable and Dangerous Fuel

June 2012 The Journal of American History 19 This issue of the Journal of American History focuses on the history of oil, and for good reason. Modern societies as we have known them could not operate without ample and diverse supplies of energy, suggesting that the story of our major fuels can hardly be ignored in any attempt to understand American history. Among energy sources, oil retains a special significance that argues for the special scholarly attention found within these covers. Reflecting oil’s unique strategic importance, Daniel Yergin aptly titled his influential industrial history of the topic The Prize.1 At the dawn of the twentieth century, coal towered above its rivals as the United States’ dominant source of energy. Ranking a distant second came wood. Until 1902, no American president had ever ridden in an automobile, the machine most closely associated with oil. It was not until midcentury that oil replaced coal as the country’s most used fuel. Over the last three decades of the century, oil jumped well ahead of natural gas, by then its closest rival.2 The ascendancy of oil involved more than just replacing one fuel with another. Growing consumption of the fossil fuel in liquid form was deeply intertwined with how Americans lived, how they conducted business, and how they fought wars. Thus studying oil is required to understand twentieth-century American history—whether the approach is social, economic, environmental, scientific, political, diplomatic, or military. The impact of oil derived, in large part, from its attractiveness as an energy-dense, easily deliverable source of fuel for transportation. After the virtual disappearance of coal-driven railroads in the 1950s, most forms of U.S. transportation—including personal automobiles, farm tractors, commercial trucks, diesel trains, commercial aircraft, and military jets and tanks—were propelled by oil products.3 Introduction: A Decidedly Valuable and Dangerous Fuel

Climate change external cost appraisal of electricity generation systems from a life cycle perspective: the case of Greece

Abstract The aim of the present work is to estimate the carbon footprint of the Greek electricity sector and the associated damages. This is being realized by quantifying the external cost related with the climate change airborne emissions (i.e. carbon dioxide) generated during all stages of the power plants life cycle in Greece. For this purpose, the paper applies the EcoSenseLE tool, together with the basic principles of the Life Cycle Assessment (LCA) approach. The examined external cost has been calculated for seven types of power plants. Results show that hydro and wind power plants have an excellent performance; close to them is the performance of PV and biomass-fired power plants. The performance of natural gas-fired power plants is good, while the performance of oil-fired power plants is, as it is expected poor. Lignite clearly has the worst performance, which affects the average external cost of the sector, since it is the dominant energy source in electricity production in Greece. Regarding the life cycle stages, for thermal systems, the climate change external cost is primarily made of CO2 emitted at the power plant, while in hydro, wind and PV systems, it is totally associated with the plant construction stage. Moreover, the paper includes also issues regarding the evolution of the examined footprint within the next years, considering the various Greek national policies and measures that have been announced and started to be realized; the cost/benefit analysis (CBA) of these policies and measures based on this footprint; and the investigation if this CBA is being affected by the CO2 abatement cost associated with the various external cost estimation approaches.

Fully Nonadiabatic Analysis of Vibrational Instability of Population III Stars due to the ɛ-Mechanism

Abstract A linear nonadiabatic analysis of the vibrational stability of population III main-sequence stars was carried out. It was demonstrated that, in the case of massive stars with $M$$\gtrsim$ 5 $M_\odot$, helium burning (triple alpha reaction) starts during the main-sequence stage and produces $^{12}$C, leading to the activation of a part of the CNO-cycle. It was found that, despite of that, those stars with $M$$\lesssim$ 13 $M_\odot$ become unstable against the dipole g$_1$- and g$_2$-modes due to the $\varepsilon $-mechanism, during the early evolutionary phase at which the pp-chain is still the dominant nuclear energy source. The instability due to the $\varepsilon $-mechanism occurs against g-modes having a large amplitude in the off-centered $^3$He accumulation shell in the deep interior, and the growth time is much shorter than the evolutionary timescale. This instability is therefore likely to induce mixing in the stellar interior, and have a significant influence on the evolution of these stars.

Assessing Climate Change Impacts on Global Hydropower

Currently, hydropower accounts for close to 16% of the world’s total power supply and is the world’s most dominant (86%) source of renewable electrical energy. The key resource for hydropower generation is runoff, which is dependent on precipitation. The future global climate is uncertain and thus poses some risk for the hydropower generation sector. The crucial question and challenge then is what will be the impact of climate change on global hydropower generation and what are the resulting regional variations in hydropower generation potential? This paper is a study that aims to evaluate the changes in global hydropower generation resulting from predicted changes in climate. The study uses an ensemble of simulations of regional patterns of changes in runoff, computed from global circulation models (GCM) simulations with 12 different models. Based on these runoff changes, hydropower generation is estimated by relating the runoff changes to hydropower generation potential through geographical information system (GIS), based on 2005 hydropower generation. Hydropower data obtained from EIA (energy generation), national sites, FAO (water resources) and UNEP were used in the analysis. The countries/states were used as computational units to reduce the complexities of the analysis. The results indicate that there are large variations of changes (increases/decreases) in hydropower generation across regions and even within regions. Globally, hydropower generation is predicted to change very little by the year 2050 for the hydropower system in operation today. This change amounts to an increase of less than 1% of the current (2005) generation level although it is necessary to carry out basin level detailed assessment for local impacts which may differ from the country based values. There are many regions where runoff and hydropower generation will increase due to increasing precipitation, but also many regions where there will be a decrease. Based on this evaluation, it has been concluded that even if individual countries and regions may experience significant impacts, climate change will not lead to significant changes in the global hydropower generation, at least for the existing hydropower system.

Energy exchange in an array of vertical-axis wind turbines

We analyze the flow field within an array of 18 counter-rotating, vertical-axis wind turbines (VAWTs), with an emphasis on the fluxes of mean and turbulence kinetic energy. The turbine wakes and the recovery of the mean wind speed between the turbine rows are derived from measurements of the velocity field using a portable meteorological tower with seven, vertically-staggered, three-component ultrasonic anemometers. The data provide insight to the blockage effect of both the individual turbine pairs within the array and the turbine array as a whole. The horizontal and planform kinetic energy fluxes into the turbine array are analyzed, and various models for the roughness length of the turbine array are compared. A high planform kinetic energy flux is measured for the VAWT array, which facilitates rapid flow recovery in the wake region behind the turbine pairs. Flow velocities return to 95% of the upwind value within six rotor diameters downwind from each turbine pair. This is less than half the recovery distance behind a typical horizontal-axis wind turbine (HAWT). The observed high level of the planform kinetic energy flux is correlated with higher relative roughness lengths for the VAWT array as compared to HAWT farms. This result is especially relevant for large wind farms with horizontal dimensions comparable to the height of the atmospheric boundary layer. As shown in recent work and confirmed here, the planform kinetic energy flux can be the dominant source of energy in such large-scale wind farms.

Performance of planar electrode-supported high-temperature solid oxide fuel cell using syngas

In China, coal is a dominant energy source. In order to ensure China’s energy security, coal should be used efficiently and cleanly. Integrated gasification fuel cell hybrid power generation system is a promising system for coal utilization. It combines clean coal gasification technology with high efficient fuel cell technology. In this work, the performance of solid oxide fuel cell using syngas as fuel was investigated, based on the commercial computational fluid dynamic software and the developed program used to analyze chemical, electrochemical, heat/mass transfer, current, and electric potential. The results show that the temperature difference is about 300 K in the cell under all calculation conditions. Along the cell length, hydrogen concentration rapidly reduces, and its decrement is larger than that of carbon monoxide. The variation of current density in electrolyte layer is relatively small along the direction of gas flow, but it is obvious along the direction vertical to gas flow.

Energy and exergy utilization, and carbon dioxide emission in vegetable oil production

Energy and exergy utilization and carbon dioxide emission during production of soybean, sunflower, and olive oils are assessed. In all cases, agriculture is the most energy and exergy intensive process and emits most of the carbon dioxide, and diesel is the dominant energy and exergy source. The cumulative degree of perfection (CDP) for soybean and olive oil is 0.92 and 0.98, respectively, whereas the CDP for the sunflower oil is 2.36. Decreasing diesel consumption with good agricultural practices and substituting with biodiesel from renewable resources would decrease the cumulative exergy consumption, as a result, CDP of olive and soybean oil rises to 1.6 and sunflower oil to 2.9. Major contribution to the carbon dioxide emission is due to the excessive use of fertilizers. The most energy intensive process is olive oil production. However, since the fertilizer consumption here is limited, total carbon dioxide emission is less than those of the other two processes are. On the other hand, excessive fertilizer consumption during the soybean agriculture results in a rather large CO 2 emission.

Numerical investigation of different loads effect on the performance of planar electrode supported SOFC with syngas as fuel

Reducing greenhouse gas emission such as carbon dioxide is the goal of each country. As a developing country with coal as the dominant energy source, China confronts the pressure of saving energy and reducing emission by using coal efficiently and cleanly. Integrated gasification fuel cell (IGFC) hybrid power generation system is one of optimal system for clean coal utilization. In this work, the three-dimensional mathematical models for planar solid oxide fuel cell (SOFC) with syngas as fuel was constructed, and its performance was numerically investigated at different loads. Under all calculating conditions, the optimal power density is obtained at current density of 4700 A m −2, where the output voltage is 0.57 V and the power density is 2671.01 W m −2. With the increasing of current density, the temperature increase as well. And also the difference of max- and min-temperature in SOFC enhances. But the ohmic over-potential changes unobvious. Furthermore, the change rate of species is nearly linear with the increment of current density.

Glucose, not glutamine, is the dominant energy source required for proliferation and survival of head and neck squamous carcinoma cells

Tumor metabolism is an essential contributor to disease progression and response to treatment. An understanding of the metabolic phenotype of head and neck squamous cell carcinoma (HNSCC) will allow the development of appropriate antimetabolic strategies for this tumor type. A panel of 15 HNSCC cell lines was assayed for glucose and glutamine dependence and sensitivity to metabolic inhibitors. In addition, broad-spectrum metabolomic analysis using mass spectrometry/liquid chromatography was combined with individual measurements of reducing potential, adenosine triphosphate, and lactate production to characterize cellular metabolic phenotypes. HNSCC energy and reducing potential levels closely mirrored extracellular glucose concentrations. Glucose starvation induced cell death despite the activation of secondary energetic pathways. Conversely, glutamine was not required for HNSCC survival and did not serve as a significant source of energy. 2-deoxyglucose (2-DG) and its fluorinated derivative decreased glycolytic and Krebs cycle activity, cellular energy, and reducing potential and inhibited HNSCC cell proliferation. 2-DG effects were potentiated by the addition of metformin, but not by inhibitors of the pentose phosphate pathway or glutaminolysis. Despite dependence on glucose catabolism, the authors identified a subset of cell lines with relative resistance to starvation. Exploration of 1 such cell line (HN30) suggested that the presence of wild-type p53 can partially protect tumor cells from glucose starvation. HNSCC tumor cells are dependent on glucose, not glutamine, for energy production and survival, providing a rationale for treatment strategies that target glucose catabolism. However, antimetabolic strategies may need to be tailored to the tumor background, more specifically, p53 status.

Household energy use and emission reduction effects of energy conversion in Lanzhou city, China

Creating better understanding between environmental quality and energy use, this paper collects 150 household energy use data sets, using questionnaires, from households in Lanzhou, China. Converted to kilograms of coal standardized energy equivalent, urban energy usage is calculated at a yearly rate of 490.37 kgce/a per capita and 1598.61 kgce/a per household. Types of emissions are also specified. Coal is the dominant energy source, and maximum environmental benefit is shown to be gained from substituting natural gas and solar energy for coal, and specific measures for substitution are identified.

HIGH-REDSHIFT STAR-FORMING GALAXIES: ANGULAR MOMENTUM AND BARYON FRACTION, TURBULENT PRESSURE EFFECTS, AND THE ORIGIN OF TURBULENCE

The structure of a sample of high-redshift (z=2), rotating galaxies with high star formation rates and turbulent gas velocities of sigma=40-80 km/s is investigated. Fitting the observed disk rotational velocities and radii with a Mo, Mao, White (1998) (MMW) model requires unusually large disk spin parameters lambda_d>0.1 and disk-to-dark halo mass fraction m_d=0.2, close to the cosmic baryon fraction. The galaxies segregate into dispersion-dominated systems with 1<vmax/sigma<3, maximum rotational velocities vmax<200 km/s and disk half-light radii rd=1-3 kpc and rotation-dominated systems with vmax>200 km/s, vmax/sigma>3 and rd=4-8 kpc. For the dispersion-dominated sample, radial pressure gradients partly compensate the gravitational force, reducing the rotational velocities. Including this pressure effect in the MMW model, dispersion-dominated galaxies can be fitted well with spin parameters lf lambda_d=0.03-0.05 for high disk mass fractions of m_d=0.2 and with lambda_d=0.01-0.03 for m_d=0.05. These values are in good agreement with cosmological expectations. For the rotation-dominated sample however pressure effects are small and better agreement with theoretically expected disk spin parameters can only be achieved if the dark halo mass contribution in the visible disk regime (2-3*rd) is smaller than predicted by the MMW model. We argue that these galaxies can still be embedded in standard cold dark matter halos if the halos did not contract adiabatically in response to disk formation. It is shown that the observed high turbulent gas motions of the galaxies are consistent with a Toomre instability parameter Q=1 which is equal to the critical value, expected for gravitational disk instability to be the major driver of turbulence. The dominant energy source of turbulence is then the potential energy of the gas in the disk.

In‐cloud turbulence structure of marine stratocumulus

This study quantifies the level of turbulence inside the marine stratocumulus cloud deck over Pt. Reyes, CA, during the Marine Stratus Radiation, Aerosol, and Drizzle Experiment (MASRAD) in July 2005, and identifies the dominant sources of turbulent kinetic energy. We used vertical velocity data from a 3 mm wavelength (94‐GHz) vertically pointing Doppler radar in combination with collocated radiosonde data. The results show that the stratocumulus observed at Pt. Reyes behaves differently from that expected on the basis of previous studies due to the modified marine environment that exists there. In particular, we found a decrease of turbulence levels with height within the cloud both during day and during night. The analysis highlights that for the conditions of our study longwave radiative cooling at cloud top was compensated by a number of mechanisms, resulting in the observed profiles. The production of turbulent kinetic energy is dominantly driven by wind shear.