Structural analysis of stratocumulus convection

The 1 and 20 Hz data are examined from the Electra flights made on July 5, 1987. The flight legs consisted of seven horizontal turbulent legs at the inversion, midcloud, and below clouds, plus 4 soundings made within the same period. The Rosemont temperature sensor and the top and bottom dewpoint sensors were used to measure temperature and humidity at 1 Hz. Inversion structure and entrainment; local dynamics and large scale forcing; convective elements; and decoupling of cloud and subcloud are discussed in relationship to the results of the Electra flight

Simulations and observations of cloudtop processes

Turbulent entrainment at zero mean shear stratified interfaces has been studied extensively in the laboratory and theoretically for the classical situation in which density is a passive tracer of the mixing and the turbulent motions producing the entrainment are directed toward the interface. It is the purpose of the numerical simulations and data analysis to investigate these processes and, specifically, to focus on the following questions: (1) Can local cooling below cloudtop play an important role in setting up convective circulations within the cloud, and bringing about entrainment; (2) Can Cloudtop Entrainment Instability (CEI) alone lead to runaway entrainment under geophysically realistic conditions; and (3) What are the important mechanisms of entrainment at cloudtop under zero or low mean shear conditions

Large-eddy simulation of mesoscale dynamics and entrainment around a pocket of open cells observed in VOCALS-REx RF06

Large-eddy simulations of a pocket of open cells (POC) based on VOCALS Regional Experiment (REx) NSF C-130 Research Flight 06 are analyzed and compared with aircraft observations. A doubly-periodic domain 192 km × 24 km with 125 m horizontal and 5 m vertical grid spacing near the capping inversion is used. The POC is realized in the model as a fixed 96 km wide region of reduced cloud droplet number concentration (<i>N</i><sub>c</sub>) based on observed values; initialization and forcing are otherwise uniform across the domain. The model reproduces aircraft-observed differences in boundary-layer structure and precipitation organization between a well-mixed overcast region and a decoupled POC with open-cell precipitating cumuli, although the simulated cloud cover is too large in the POC. A sensitivity study in which <i>N</i><sub>c</sub> is allowed to advect following the turbulent flow gives nearly identical results over the 16 h length of the simulation (which starts at night and goes into the next afternoon). <br><br> The simulated entrainment rate is nearly a factor of two smaller in the less turbulent POC than in the more turbulent overcast region. However, the inversion rises at a nearly uniform rate across the domain because powerful buoyancy restoring forces counteract horizontal inversion height gradients. A secondary circulation develops in the model that diverts subsiding free-tropospheric air away from the POC into the surrounding overcast region, counterbalancing the weaker entrainment in the POC with locally weaker subsidence

The EU and Asia within an evolving global order: what is Europe? Where is Asia?

The papers in this special edition are a very small selection from those presented at the EU-NESCA (Network of European Studies Centres in Asia) conference on "the EU and East Asia within an Evolving Global Order: Ideas, Actors and Processes" in November 2008 in Brussels. The conference was the culmination of three years of research activity involving workshops and conferences bringing together scholars from both regions primarily to discuss relations between Europe and Asia, perceptions of Europe in Asia, and the relationship between the European regional project and emerging regional forms in Asia. But although this was the last of the three major conferences organised by the consortium, it in many ways represented a starting point rather than the end; an opportunity to reflect on the conclusions of the first phase of collaboration and point towards new and continuing research agendas for the future

Quasi-Lagrangian Large Eddy Simulations of Cross-Equatorial Flow in the East Pacific Atmospheric Boundary Layer

Using a large eddy simulation (LES), the atmospheric boundary layer (ABL) is numerically modeled along 95°W from 8°S to 4°N during boreal autumn, and compared to observations from the East Pacific Investigation of Climate Processes in the Coupled Ocean–Atmosphere System (EPIC) 2001. Since the local ABL winds are predominantly southerly in this season, a “quasi-Lagrangian” forcing is used in which the ABL air column is forced as if it were advecting northward with the mean September–October 2001 meridional wind across the equatorial cold tongue and the rapidly warming SSTs to the north. Pressure gradients and large-scale zonal advective tendencies are prescribed as a function of latitude. Where possible, observations from the EPIC 2001 experiment are used for forcing and for comparison with model results. The ABL's modeled vertical structure accords with the conceptual model of Wallace et al. and agrees well with observations. Surface stability accounts for the minimum in surface wind over the equatorial cold tongue and the maximum over the warm water to the north. Stability of the lower ABL over the cold tongue allows a jet to accelerate at about 500-m height, relatively uncoupled to the frictional surface layer. Vertical mixing over the warm water to the north distributes this momentum to the surface. Additional simulations were performed to explore the modeled ABL's sensitivity to pressure gradients, zonal advection, free-tropospheric humidity, and initial conditions. The model ABL was robust: changing the forcings resulted in little change in the modeled structure. The strongest sensitivity was of stratocumulus clouds over the cold tongue to cloud-top radiative cooling. Once formed at the southern edge of the cold tongue, modeled stratocumulus clouds demonstrate a remarkable ability to maintain themselves over the cold tongue in the absence of surface fluxes by radiative cooling at their tops. The persistence of thin stratocumulus clouds in this Lagrangian model suggests that horizontal advection of condensate might be an important process in determining cloudiness over the cold tongue

Expanding actorness to explain EU External engagement in originally internal policy areas

© 2018, © 2019 Informa UK Limited, trading as Taylor & Francis Group. Despite its increasing importance for European integration, there remains a lack of scholarly attention to the growth of EU external action in originally internal policy areas. This article advances a comprehensive framework for understanding and explaining the emergence of EU external engagement in such areas. It combines insights from two sets of literatures: the EU external relations literature offers useful concepts–particularly ‘actorness’–as building blocks for explanatory purposes, while the public policy literature provides relevant insights regarding policy entrepreneurship and agenda-setting. The article contends that EU external engagement results from a favourable interplay between an external ‘opportunity’ and the EU’s ‘presence’ in a given domain, which is identified and capitalized upon by a set of policy entrepreneurs, who are driven by interest-based and/or ideational motives. To evaluate the salience of the framework, the article applies it across several policy areas.status: publishe

Amplitude equations for a system with thermohaline convection

The multiple scale expansion method is used to derive amplitude equations for a system with thermohaline convection in the neighborhood of Hopf and Taylor bifurcation points and at the double zero point of the dispersion relation. A complex Ginzburg-Landau equation, a Newell-Whitehead-type equation, and an equation of the $\phi^4$ type, respectively, were obtained. Analytic expressions for the coefficients of these equations and their various asymptotic forms are presented. In the case of Hopf bifurcation for low and high frequencies, the amplitude equation reduces to a perturbed nonlinear Schr\"odinger equation. In the high-frequency limit, structures of the type of "dark" solitons are characteristic of the examined physical system.Comment: 21 pages, 8 figure

Phase Bubbles and Spatiotemporal Chaos in Granular Patterns

We use inelastic hard sphere molecular dynamics simulations and laboratory experiments to study patterns in vertically oscillated granular layers. The simulations and experiments reveal that {\em phase bubbles} spontaneously nucleate in the patterns when the container acceleration amplitude exceeds a critical value, about $7g$, where the pattern is approximately hexagonal, oscillating at one-fourth the driving frequency ($f/4$). A phase bubble is a localized region that oscillates with a phase opposite (differing by $\pi$) to that of the surrounding pattern; a localized phase shift is often called an {\em arching} in studies of two-dimensional systems. The simulations show that the formation of phase bubbles is triggered by undulation at the bottom of the layer on a large length scale compared to the wavelength of the pattern. Once formed, a phase bubble shrinks as if it had a surface tension, and disappears in tens to hundreds of cycles. We find that there is an oscillatory momentum transfer across a kink, and this shrinking is caused by a net collisional momentum inward across the boundary enclosing the bubble. At increasing acceleration amplitudes, the patterns evolve into randomly moving labyrinthian kinks (spatiotemporal chaos). We observe in the simulations that $f/3$ and $f/6$ subharmonic patterns emerge as primary instabilities, but that they are unstable to the undulation of the layer. Our experiments confirm the existence of transient $f/3$ and $f/6$ patterns.Comment: 6 pages, 12 figures, submitted to Phys. Rev. E on July 1st, 2001. for better quality figures, visit http://chaos.ph.utexas.edu/research/moo

Spatial distribution of beef cattle on a New Zealand hill country farm: monitoring the use of streams and wet areas

Grazing livestock are an important source of contamination of freshwater, particularly when they have direct access to streams. Cattle in particular contribute to riparian habitat deterioration through stream bank destruction and direct defecation and urination in streams. Exclusion of stock or planting of riparian areas, are the most common catchment management methods used to protect waterways. Given the relatively low returns from beef and sheep farming, both of these strategies are very expensive and often logistically prohibitive in steep hill county landscapes. Despite this, policy trends indicate that fencing of streams in agricultural catchments may become mandatory in the future. It is important that we understand how much time cattle spend in and around hill country streams and wet areas (wetlands and hill side seeps), in order to quantify the likely environmental benefits from such policies. The current study examined cattle movement data obtained using Global Positioning System (GPS) collars from experiments undertaken at Massey University’s hill country research farm, Tuapaka, near Palmerston North, to investigate the amount of time cattle spent in and around streams and wet areas. Animal movement data were collected over seven grazing events, in three winter periods (2012, 2013 and 2015). Permanent streams and wet areas were identified using a digital elevation model derived from 1m LiDAR data, aerial RGB images and RTK measurements. Cattle spent 3.3 – 6% (48 – 86 min/day) of their day in streams and wet areas consistently across the 7 data collections. Cattle spent more time in streams and wet areas during the afternoon. There are differences in the median amount of time individual animals spend in non-risk areas. Further research is necessary to evaluate how we can influence the amount of time cattle spend in riparian areas on hill country and how stream bank behaviour varies at different times of the year

Angular momentum transport by internal gravity waves III - Wave excitation by core convection and the Coriolis effect

This is the third in a series of papers that deal with angular momentum transport by internal gravity waves. We concentrate on the waves excited by core convection in a 3Msun, Pop I main sequence star. Here, we want to examine the role of the Coriolis acceleration in the equations of motion that describe the behavior of waves and to evaluate its impact on angular momentum transport. We use the so-called traditional approximation of geophysics, which allows variable separation in radial and horizontal components. In the presence of rotation, the horizontal structure is described by Hough functions instead of spherical harmonics. The Coriolis acceleration has two main effects on waves. It transforms pure gravity waves into gravito-inertial waves that have a larger amplitude closer to the equator, and it introduces new waves whose restoring force is mainly the conservation of vorticity. Taking the Coriolis acceleration into account changes the subtle balance between prograde and retrograde waves in non-rotating stars. It also introduces new types of waves that are either purely prograde or retrograde. We show in this paper where the local deposition of angular momentum by such waves is important.Comment: 9 pages, 10 figures, accepted for publication by A&