Microbreaking and the enhancement of air-water transfer velocity

The role of microscale wave breaking in controlling the air-water transfer of heat and gas is investigated in a laboratory wind-wave tank. The local heat transfer velocity, kH, is measured using an active infrared technique and the tank-averaged gas transfer velocity, kG, is measured using conservative mass balances. Simultaneous, colocated infrared and wave slope imagery show that wave-related areas of thermal boundary layer disruption and renewal are the turbulent wakes of microscale breaking waves, or microbreakers. The fractional area coverage of microbreakers, AB, is found to be 0.1–0.4 in the wind speed range 4.2–9.3 m s−1 for cleaned and surfactant-influenced surfaces, and kH and kG are correlated with AB. The correlation of kH with AB is independent of fetch and the presence of surfactants, while that for kG with AB depends on surfactants. Additionally, AB is correlated with the mean square wave slope, 〈S2〉, which has shown promise as a correlate for kG in previous studies. The ratio of kH measured inside and outside the microbreaker wakes is 3.4, demonstrating that at these wind speeds, up to 75% of the transfer is the direct result of microbreaking. These results provide quantitative evidence that microbreaking is the dominant mechanism contributing to air-water heat and gas transfer at low to moderate wind speeds

Air-sea gas transfer : its dependence on wind stress, small-scale roughness, and surface films

Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 109 (2004): C08S17, doi:10.1029/2003JC002131.The influence of wind stress, small-scale waves, and surface films on air-sea gas exchange at low to moderate wind speeds (<10 m s−1) is examined. Coincident observations of wind stress, heat transfer velocity, surface wave slope, and surface film enrichments were made in coastal and offshore waters south of Cape Cod, New England, in July 1997 as part of the NSF-CoOP Coastal Air-Sea Chemical Fluxes study. Gas transfer velocities have been extrapolated from aqueous heat transfer velocities derived from infrared imagery and direct covariance and bulk heat flux estimates. Gas transfer velocity is found to follow a quadratic relationship with wind speed, which accounts for ~75–77% of the variance but which overpredicts transfer velocity in the presence of surface films. The dependence on wind stress as represented by the friction velocity is also nonlinear, reflecting a wave field-dependent transition between limiting transport regimes. In contrast, the dependence on mean square slope computed for the wave number range of 40–800 rad m−1 is found to be linear and in agreement with results from previous laboratory wind wave studies. The slope spectrum of the small-scale waves and the gas transfer velocity are attenuated in the presence of surface films. Observations over large-scale gradients of biological productivity and dissolved organic matter show that the reduction in slope and transfer velocity are more clearly correlated with surface film enrichments than with bulk organic matter concentrations. The mean square slope parameterization explains ~89–95% of the observed variance in the data and does not overpredict transfer velocities where films are present. While the specific relationships between gas transfer velocity and wind speed or mean square slope vary slightly with the choice of Schmidt number exponent used to scale the heat transfer velocities to gas transfer velocities, the correlation of heat or gas transfer velocity with mean square slope is consistently better than with wind speed.Funding for this work was provided by the NSF Coastal Ocean Processes (CoOP) program (OCE-9410534, OCE- 9711285 (WHOI) and OCE-9409222, OCE-9711391(URI)). Additional support for data analysis was provided by NASA (NAGW-2431, JPL Contract 961425). Partial funding was also provided by the German Science Foundation (DFG) through the DFG research unit FOR240: Image Sequence Analysis to Investigate Dynamic Processes

Adaptive structure tensors and their applications

The structure tensor, also known as second moment matrix or Förstner interest operator, is a very popular tool in image processing. Its purpose is the estimation of orientation and the local analysis of structure in general. It is based on the integration of data from a local neighborhood. Normally, this neighborhood is defined by a Gaussian window function and the structure tensor is computed by the weighted sum within this window. Some recently proposed methods, however, adapt the computation of the structure tensor to the image data. There are several ways how to do that. This article wants to give an overview of the different approaches, whereas the focus lies on the methods based on robust statistics and nonlinear diffusion. Furthermore, the dataadaptive structure tensors are evaluated in some applications. Here the main focus lies on optic flow estimation, but also texture analysis and corner detection are considered

Rain-induced turbulence and air-sea gas transfer

Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 114 (2009): C07009, doi:10.1029/2008JC005008.Results from a rain and gas exchange experiment (Bio2 RainX III) at the Biosphere 2 Center demonstrate that turbulence controls the enhancement of the air-sea gas transfer rate (or velocity) k during rainfall, even though profiles of the turbulent dissipation rate ɛ are strongly influenced by near-surface stratification. The gas transfer rate scales with ɛ inline equation for a range of rain rates with broad drop size distributions. The hydrodynamic measurements elucidate the mechanisms responsible for the rain-enhanced k results using SF6 tracer evasion and active controlled flux technique. High-resolution k and turbulence results highlight the causal relationship between rainfall, turbulence, stratification, and air-sea gas exchange. Profiles of ɛ beneath the air-sea interface during rainfall, measured for the first time during a gas exchange experiment, yielded discrete values as high as 10−2 W kg−1. Stratification modifies and traps the turbulence near the surface, affecting the enhancement of the transfer velocity and also diminishing the vertical mixing of mass transported to the air-water interface. Although the kinetic energy flux is an integral measure of the turbulent input to the system during rain events, ɛ is the most robust response to all the modifications and transformations to the turbulent state that follows. The Craig-Banner turbulence model, modified for rain instead of breaking wave turbulence, successfully predicts the near-surface dissipation profile at the onset of the rain event before stratification plays a dominant role. This result is important for predictive modeling of k as it allows inferring the surface value of ɛ fundamental to gas transfer.This work was funded by a generous grant from the David and Lucile Packard Foundation and the Lamont-Doherty Earth Observatory Climate Center. Additional funding was provided by the National Science Foundation (OCE-05-26677) and the Office of Naval Research Young Investigator Program (N00014-04-1-0621)

A new approach to estimation of global air-sea gas transfer velocity fields using dual-frequency altimeter backscatter

Author Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 112 (2007): C11003, doi:10.1029/2006JC003819.A new approach to estimating air-sea gas transfer velocities based on normalized backscatter from the dual-frequency TOPEX and Jason-1 altimeters is described. The differential scattering of Ku-band (13.6 GHz) and C-band (5.3 GHz) microwave pulses is used to isolate the contribution of small-scale waves to mean square slope and gas transfer. Mean square slope is derived for the nominal wave number range 40–100 rad m−1 by differencing mean square slope estimates computed from the normalized backscatter in each band, using a simple geometric optics model. Model parameters for calculating the differenced mean square slope over this wave number range are optimized using in situ optical slope measurements. An empirical relation between gas transfer velocity and mean square slope, also based on field measurements, is then used to derive gas transfer velocities. Initial results demonstrate that the calculated transfer velocities exhibit magnitudes and a dynamic range which are generally consistent with existing field measurements. The new algorithm is used to construct monthly global maps of gas transfer velocity and to illustrate seasonal transfer velocity variations over a 1-year period. The measurement precision estimated from >106 duplicate observations of the sea surface by TOPEX and Jason-1 altimeters orbiting in tandem is better than 10%. The estimated overall uncertainty of the method is ±30%. The long-term global, area-weighted, Schmidt number corrected, mean gas transfer velocity is 13.7 ± 4.1 cm h−1. The new approach, based on surface roughness, represents a potential alternative to commonly used parameterizations based on wind speed.Financial support for this research from the National Aeronautics and Space Administration through Jet Propulsion Laboratory contract 961425 and the NOAA Global Carbon Cycle Program under grant NA16GP2918, Office of Global Programs is gratefully acknowledged

"World-Wide Spiritual Offensive": Evangelikale Protestanten und der U.S. National Security State während der 1940er bis 1970er Jahre

In dieser Dissertation wird die historische Genese einer Entwicklung untersucht, die zum Entstehen eines „evangelikalen Ethos“ in Teilen der US-Streitkräfte und weiteren Bereichen des National Security State geführt hat. Den Ausgangspunkt dieser Arbeit bilden Daten zur religiösen Zusammensetzung der amerikanischen Streitkräfte aus dem Jahr 2009. Sie verweisen auf einen überproportional hohen Anteil evangelikaler Protestanten in den amerikanischen Streitkräften. Der Untersuchungszeitraum reicht vom Aufbau des National Security State im Zweiten Weltkrieg bis zum Ende des Vietnamkrieges. Die Annäherung evangelikaler Protestanten an den nationalen Sicherheitsstaat fand bereits im Zweiten Weltkrieg statt. Vor allem im Kontext des Kalten Krieges setzte zudem die Erkenntnis einer ideologischen und kulturellen Nähe zwischen beiden Sphären ein, während die neoevangelikale Erweckungsbewegung zu neuer Blüte gelangte und eine religiöse Mobilisierung der Vereinigten Staaten im frühen Kalten Krieg stattfand. Die Arbeit beruht u.a. auf teil unveröffentlichten Archivbeständen des Billy Graham Center und des Wheaton College. Methodisch ist die Untersuchung der von Philip Sarasin geprägten Wissensgeschichte verpflichtet. Damit kann eine Vielfalt von Wissensbeständen analytisch gegriffen und ihre Bedeutung für politisches und militärisches Handeln entsprechend gefasst werden. Die Arbeit endet mit einem Ausblick auf die Gegenwart: Das missionarische Sendungsbewusstsein evangelikaler Gläubiger führt zu Konflikten innerhalb der Streitkräfte. Auch im Rahmen der Auslandseinsätze der amerikanischen Streitkräfte ereignen sich bedenkliche Vorfälle, in denen etwa das Verbot der Missionierung durch Militärangehörige missachtet wird.This dissertation examines the historical genesis of a development that lead to an „Evangelical ethos“ within the U.S. Arnmed Forces and other institutions of the National Security State. The starting point for this dissertation are empirical data from 2009 about the religious composition of the U.S. military. This data refers to a disproportional quota of Evangelical Protestants in the military. The period investigated reaches from the creation of the National Security State during World War 2 until the end of the war in Vietnam. The convergence of Evangelical Protestants and the National Security State began with World War 2. Furthermore, in the context of the Cold War a sense of shared ideological and cultural values developed, while the Neoevangelical revival movement blossomed and a religious mobilization of the United States during the early Cold War took place. This work is based on partly unpublished material from the Billy Graham Center and Wheaton College archives, among others. Methodically, it is committed to Philipp Sarasins approach of a history of knowledge. In this way, a variety of stocks of knowledge can be grasped analytically and their significance for political and military action can be grasped accordingly. This dissertation ends with an outlook on the present times: the evangelical zeal of the believers in uniform leads to conflicts within the military. Furthermore, during assigments abroad highly problematic incidents take place, e.g. the disregard of the prohibition of proselytizing by members of the military

Effects of Facebook News Reception on Threat Perceptions and Personality Traits in German Speaking Countries

Based on the dual process motivational model (Duckitt, 2001) and cultivation research (Gerbner, 1969), this study analyzes news reception on Facebook and its consequences for the recipient’s world view, right-wing authoritarianism, and threat perceptions in Germany. An online survey was completed by 429 Facebook users. Results demonstrate that Facebook news reception is relatively low but as predicted influenced by duration and intensity of Facebook use. No correlation occurred with general interest in news, which supports the idea that people find news coincidentally. Regression analyses revealed significant positive influences of duration on perceived economy-based threat and negative world view. The effects of news reception partly correspond to the findings of cultivation research; however, contrary findings appear with right-wing authoritarianism

Nachrichtenberichterstattung über Terrorismus. Eine Analyse der TV-Nachrichten über die Terroranschläge in Kenia 2002

Nach der starken Kritik der Medienberichterstattung über Terrorismus, besonders nach dem 11.09.2001, werden die theoretischen Hintergründe ausgewählter Kritikpunkte betrachtet und ein weiteres terroristisches Ereignis, die Anschläge in Kenia am 28.11.2002, inhaltsanalytisch untersucht. Ziel dabei ist es, Aussagen bezüglich inhaltlicher und formaler Merkmale der Fernseh-berichterstattung über ein terroristisches Ereignis zu treffen. Deshalb liegt der Fokus auf den folgenden drei Forschungsfragen: 1. Welche Nachrichtenfaktoren spielen für die Selektion und Intensität der Berichterstattung über das terroristische Ereignis eine Rolle? 2. Wird mit Emotionalisierung gearbeitet? 3. Liegen negative Stereotype und/oder Feindbilder bezüglich der islamischen und arabischen Welt vor? Die Ergebnisse der Untersuchung zeigen erwartete Tendenzen sowohl die Merkmale der Terrorismusberichterstattung als auch die Senderkonvergenzen und -divergenzen im dualen System betreffend. Der Nachrichtenwert eines terroristischen Ereignisses ist anfänglich sehr hoch, jedoch verliert das Ereignis ab dem dritten Tag aufgrund diverser Nachrichtenfaktoren deutlich an Beachtung in der Berichterstattung. Das Vorkommen emotionalisierender Mittel wird empirisch bestätigt. Nicht nur emotionale Sprache und Sprechweise, sondern vor allem Formen der expliziten Emotionalisierung sind vertreten. Damit wird die Vermutung bekräftigt, dass die Medien die mit den terroristischen Ereignissen verbundene beängstigende Stimmung senderabhängig unterschiedlich stark aufgreifen. Ein direkter islamischer Feindbildaufbau ist in der Berichterstattung nicht zu verzeichnen. Allerdings liegen latente negative Bewertungstendenzen sowie negative Stereotype bezüglich der arabischen und islamischen Welt vor, die das seit dem 11.09.2001 negativ geprägte Bild festigen. Die meist narrativ inszenierte Fixierung auf Bin Laden und al Qaida erfolgt oberflächlich und vernachlässigt mögliche Hintergründe sowie kontextuelle Einordnungen. Trotz der kritischen Stimmen nach dem 11.09.2001 findet der geforderte Wandel in der Terrorismus-Berichterstattung nicht in gewünschtem Ausmaß statt. Damals bemängelte Aspekte sind weiterhin vorzufinden, variieren jedoch senderspezifisch