The response of the coastal ocean to strong offshore winds: With application to circulations in the Gulfs of Tehuantepec and Papagayo

Two ocean models are used to investigate the response of the coastal ocean to strong offshore winds: a linear 1½-layer model, and a nonlinear 1½-layer model that allows entrainment of cool water into the surface layer. The models are forced by wind stress fields similar in structure to the intense winter-time, mountain-pass jets (∼20 dyne/cm2) that appear in the Gulfs of Tehuantepec and Papagayo for periods of 3–10 days. Solutions are arranged in a hierarchy of increasing dynamical complexity, in order to illustrate the important physical processes. They compare favorably with observations in several ways. Some properties of solutions are the following. While the wind strengthens there is an ageostrophic current (not Ekman drift) that is directed offshore. This offshore drift forces coastal upwelling, thereby lowering the local sea level and sea surface temperature (SST). Although the drop in sea level at the coast can be large and rapid (of the order of 20 cm at the peak of a wind event), none of this signal propagates poleward as a coastally trapped wave. While the wind weakens the ageostrophic current is directed onshore, and consequently the coastal ocean readjusts toward its initial state. Throughout the wind event, cyclonic and anticyclonic gyres spin up offshore on either side of the jet axis due to Ekman pumping. Entrainment cools SST offshore, on and to the right (looking onshore) of the jet axis, and virtually eliminates the cyclonic gyre. The advection terms intensify the anticyclonic gyre and give it a more circular shape. After a wind event, the anticyclonic gyre propagates westward due to β. Its propagation speed is enhanced over that of a linear Rossby wave due to the nonlinear terms associated with the increased layer thickness at the center of the gyre and with the divergence of momentum flux

Atmospheric effects of the emerging mainland Chinese transportation system at and beyond the regional scale

Local surface travel needs in the People's Republic of China (mainland China) have traditionally been met largely by nonpolluting bicycles. A major automobile manufacturing/importing effort has begun in the country over the last decade, and planning documents indicate that the Chinese may strive to acquire more than 100 million vehicles early in the next century. By analogy with large automotive fleets already existing in the western world, both regional and global scale pollution effects are to be expected from the increase. The present work adopts the latest projections of Chinese automobile manufacture and performs some quantitative assessments of the extent of pollution generation. Focus for the investigation is placed upon the oxidant ozone. Emissions of the precursor species nitrogen oxides and volatile organics are constructed based on data for the current automotive sector in the eastern portion of the United States. Ozone production is first estimated from measured values for continental/oceanic scale yields relative to precursor oxidation. The estimates are then corroborated through idealized two dimensional modeling of the photochemistry taking place in springtime air flow off the Asian land mass and toward the Pacific Ocean. The projected fleet sizes could increase coastal and remote oceanic ozone concentrations by tens of parts per billion (ppb) in the lower troposphere. Influences on the tropospheric aerosol system and on the major greenhouse gas carbon dioxide are treated peripherally. Nitrogen oxides created during the vehicular internal combustion process will contribute to nitrate pollution levels measured in the open Pacific. The potential for soot and fugitive dust increases should be considered as the automotive infrastructure develops. Since the emerging Chinese automotive transportation system will represent a substantial addition to the global fleet and all the carbon in gasoline is eventually oxidized completely, a significant rise in global carbon dioxide inputs will ensue as well. Some policy issues are treated preliminary. The assumption is made that alterations to regional oxidant/aerosol systems and to terrestrial climate are conceivable. The likelihood that the Chinese can achieve the latest vehicle fleet goals is discussed, from the points of view of new production, positive pollution feedbacks from a growing automobile industry, and known petroleum reserves. Vehicular fuel and maintenance options lying before the Chinese are outlines and compared. To provide some perspective on the magnitude of the environmental changes associated with an Asian automotive buildup, recent estimates of the effects of future air traffic over the Pacific Rim are described

Discovering the mechanisms underlying serotonin (5-HT)2A and 5-HT2C receptor regulation following nicotine withdrawal in rats

We have previously demonstrated that nicotine withdrawal produces depression-like behavior and that serotonin (5-HT)2A/2C receptor ligands modulate that mood-like state. In the present study we aimed to identify the mechanisms (changes in radioligand binding, transcription or RNA-editing) related to such a behavioral outcome. Rats received vehicle or nicotine (0.4 mg/kg, s.c.) for 5 days in home cages. Brain 5-HT2A/2C receptors were analyzed on day 3 of nicotine withdrawal. Nicotine withdrawal increased [(3) H]ketanserin binding to 5-HT2A receptors in the ventral tegmental area and ventral dentate gyrus, yet decreased binding in the nucleus accumbens shell. Reduction in [(3) H]mesulergine binding to 5-HT2C receptors was seen in the ventral dentate gyrus. Profound decrease in the 5-HT2A receptor transcript level was noted in the hippocampus and ventral tegmental area. Out of five 5-HT2C receptor mRNA editing sites, deep sequencing data showed a reduction in editing at the E site and a trend toward reduction at the C site in the hippocampus. In the ventral tegmental area, a reduction for the frequency of CD 5-HT2C receptor transcript was seen. These results show that the reduction in the 5-HT2A receptor transcript level may be an auto-regulatory response to the increased receptor density in the hippocampus and ventral tegmental area during nicotine withdrawal, while decreased 5-HT2C receptor mRNA editing may explain the reduction in receptor labeling in the hippocampus. Serotonin (5-HT)2A/2C receptor ligands alleviate depression-like state in nicotine-withdrawn rats. Here, we show that the reduction in 5-HT2A receptor transcript level may be an auto-regulatory response to the increased receptor number in the hippocampus and ventral tegmental area during nicotine withdrawal, while attenuated 5-HT2C receptor mRNA editing in the hippocampus might explain reduced inverse agonist binding to 5-HT2C receptor and suggest a shift toward a population of more active receptors. 5-HT, serotonin; 5-HT2A R, 5-HT2A receptor; 5-HT2C R, 5-HT2C receptor

On Sub-ENSO Variability

Multichannel singular spectrum analysis (MSSA) of surface zonal wind, sea surface temperature (SST), 20° isotherm depth, and surface zonal current observations (between 1990 and 2004) identifies three coupled ocean–atmosphere modes of variability in the tropical Pacific: the El Niño–Southern Oscillation (ENSO), the annual cycle, and a mode with a 14–18-month period, which is referred to as sub-ENSO in this study. The sub-ENSO mode accounts for the near 18-month (near annual) variability prior to (following) the 1997/98 El Niño event. It was strongest during this El Niño event, with SST anomalies exceeding 1°C. Sub-ENSO peak SST anomalies are ENSO-like in structure and are associated with eastward propagating heat content variations. However, the SST anomalies are preceded by and in near quadrature with relatively strong remotely forced westward propagating zonal current variations, suggesting the sub-ENSO mode arises from the zonal-advective feedback. The sub-ENSO mode is found to exist also in an intermediate complexity model (ICM) of the tropical Pacific. A heat budget analysis of the model’s sub-ENSO mode shows it indeed arises from the zonal-advective feedback. In the model, both ENSO and sub-ENSO modes coexist, but there is a weak nonlinear interaction between them. Experiments also show that the observed changes in sub-ENSO’s characteristics may be explained by changes in the relative importance of zonal and vertical advection SST tendencies

Measurements of interfacial area concentration in two-phase bubbly flow

Interfacial area concentration is an important parameter in the two-fluid model for two-phase flow analysis, which is defined as the total interface area per unit mixture volume and has the following local time-averaged expression: {bar a}{sup t} = 1/{Delta}T {Sigma}{sub j}(1/{vert_bar}V{sub i} {center_dot} n{sub i}{vert_bar}){sub j}, where j denotes the j-th interface that passes the point of interest in a time interval {Delta}T. V{sub i} and n{sub i} refer to the bubble interface velocity and surface normal vector, respectively. To measure this parameter, the double-sensor probe technique is commonly used. Due to the influences of the bubble lateral motions, however, the measurement results should be interpreted via a certain statistic approach. Recently, to take into account the effects of the probe spacing, Wu and Ishii provided the following new formula to correlate the measurable values to the interfacial area concentration: {bar a}{sub i}{sup t} = 2N{sub b}/{Delta}T ({Delta}{bar t}/{Delta}s) [2 + (1.2{sigma}{sub {Delta}t}/{Delta}{bar t}){sup 2.25}], for D = 1.2 {approximately} 2.8 {Delta}s, where N{sub b} refers to the number of the bubbles that hit the probe front tip during time interval {Delta}T, {Delta}s denotes the distance between the two probe tips, D is the bubble diameter, {Delta}{bar t} represents the measured average time interval for an interface to travel through the two probe tips, and {sigma}{sub {Delta}t} is the standard deviation of {Delta}t. The theoretical accuracy of this formula is within {+-} 5% if the sample size is sufficiently large. The purpose of this study is to evaluate this method experimentally using an image processing method

Local density of states and scanning tunneling currents in graphene

We present exact analytical calculations of scanning tunneling currents in locally disordered graphene using a multimode description of the microscope tip. Analytical expressions for the local density of states (LDOS) are given for energies beyond the Dirac cone approximation. We show that the LDOS at the $A$ and $B$ sublattices of graphene are out of phase by $\pi$ implying that the averaged LDOS, as one moves away from the impurity, shows no trace of the $2q_F$ (with $q_F$ the Fermi momentum) Friedel modulation. This means that a STM experiment lacking atomic resolution at the sublattice level will not be able of detecting the presence of the Friedel oscillations [this seems to be the case in the experiments reported in Phys. Rev. Lett. {\bf 101}, 206802 (2008)]. The momentum maps of the LDOS for different types of impurities are given. In the case of the vacancy, $2q_F$ features are seen in these maps. In all momentum space maps, $K$ and $K+K^\prime$ features are seen. The $K+K^\prime$ features are different from what is seen around zero momentum. An interpretation for these features is given. The calculations reported here are valid for chemical substitution impurities, such as boron and nitrogen atoms, as well as for vacancies. It is shown that the density of states close to the impurity is very sensitive to type of disorder: diagonal, non-diagonal, or vacancies. In the case of weakly coupled (to the carbon atoms) impurities, the local density of states presents strong resonances at finite energies, which leads to steps in the scanning tunneling currents and to suppression of the Fano factor.Comment: 21 pages. Figures 6 and 7 are correctly displayed in this new versio

Precision Electron-Beam Polarimetry using Compton Scattering at 1 GeV

We report on the highest precision yet achieved in the measurement of the polarization of a low energy, $\mathcal{O}$(1 GeV), electron beam, accomplished using a new polarimeter based on electron-photon scattering, in Hall~C at Jefferson Lab. A number of technical innovations were necessary, including a novel method for precise control of the laser polarization in a cavity and a novel diamond micro-strip detector which was able to capture most of the spectrum of scattered electrons. The data analysis technique exploited track finding, the high granularity of the detector and its large acceptance. The polarization of the $180~\mu$A, $1.16$~GeV electron beam was measured with a statistical precision of $<$~1\% per hour and a systematic uncertainty of 0.59\%. This exceeds the level of precision required by the \qweak experiment, a measurement of the vector weak charge of the proton. Proposed future low-energy experiments require polarization uncertainty $<$~0.4\%, and this result represents an important demonstration of that possibility. This measurement is also the first use of diamond detectors for particle tracking in an experiment.Comment: 9 pages, 7 figures, published in PR