101 research outputs found
3-D tomographic observations of Rossby wave breaking over the North Atlantic during the WISE aircraft campaign in 2017
This paper presents measurements of ozone, water vapour and nitric acid (HNO3) in the upper troposphere/lower stratosphere (UTLS) over North Atlantic and Europe. The measurements were acquired with the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) during the Wave Driven Isentropic Exchange (WISE) campaign in October 2017. GLORIA is an airborne limb imager capable of acquiring both 2-D data sets (curtains along the flight path) and, when the carrier aircraft is flying around the observed air mass, spatially highly resolved 3-D tomographic data. Here, we present a case study of a Rossby wave (RW) breaking event observed during two subsequent flights 2âd apart. RW breaking is known to steepen tracer gradients and facilitate stratosphereâtroposphere exchange (STE). Our measurements reveal complex spatial structures in stratospheric tracers (ozone and nitric acid) with multiple vertically stacked filaments. Backward-trajectory analysis is used to demonstrate that these features are related to several previous Rossby wave breaking events and that the small-scale structure of the UTLS in the Rossby wave breaking region, which is otherwise very hard to observe, can be understood as stirring and mixing of air masses of tropospheric and stratospheric origin. It is also shown that a strong nitric acid enhancement observed just above the tropopause is likely a result of NOx production by lightning activity. The measurements showed signatures of enhanced mixing between stratospheric and tropospheric air near the polar jet with some transport of water vapour into the stratosphere. Some of the air masses seen in 3-D data were encountered again 2âd later, stretched to very thin filament (horizontal thickness down to 30âkm at some altitudes) rich in stratospheric tracers. This repeated measurement allowed us to directly observe and analyse the progress of mixing processes in a thin filament over 2âd. Our results provide direct insight into small-scale dynamics of the UTLS in the Rossby wave breaking region, which is of great importance to understanding STE and poleward transport in the UTLS
Impact of Lagrangian transport on lower-stratospheric transport timescales in a climate model
We investigate the impact of model trace gas transport schemes on the representation of transport processes in the upper troposphere and lower stratosphere. Towards this end, the Chemical Lagrangian Model of the Stratosphere (CLaMS) was coupled to the ECHAM/MESSy Atmospheric Chemistry (EMAC) model and results from the two transport schemes (Lagrangian critical Lyapunov scheme and flux-form semi-Lagrangian, respectively) were compared. Advection in CLaMS was driven by the EMAC simulation winds, and thereby the only differences in transport between the two sets of results were caused by differences in the transport schemes. To analyze the timescales of large-scale transport, multiple tropical-surface-emitted tracer pulses were performed to calculate age of air spectra, while smaller-scale transport was analyzed via idealized, radioactively decaying tracers emitted in smaller regions (nine grid cells) within the stratosphere. The results show that stratospheric transport barriers are significantly stronger for Lagrangian EMAC-CLaMS transport due to reduced numerical diffusion. In particular, stronger tracer gradients emerge around the polar vortex, at the subtropical jets, and at the edge of the tropical pipe. Inside the polar vortex, the more diffusive EMAC flux-form semi-Lagrangian transport scheme results in a substantially higher amount of air with ages from 0 to 2 years (up to a factor of 5 higher). In the lowermost stratosphere, mean age of air is much smaller in EMAC, owing to stronger diffusive cross-tropopause transport. Conversely, EMAC-CLaMS shows a summertime lowermost stratosphere age inversion â a layer of older air residing below younger air (an âeaveâ). This pattern is caused by strong poleward transport above the subtropical jet and is entirely blurred by diffusive cross-tropopause transport in EMAC. Potential consequences from the choice of the transport scheme on chemistryâclimate and geoengineering simulations are discussed
Non-supersymmetric heterotic model building
We investigate orbifold and smooth Calabi-Yau compactifications of the
non-supersymmetric heterotic SO(16)xSO(16) string. We focus on such Calabi-Yau
backgrounds in order to recycle commonly employed techniques, like index
theorems and cohomology theory, to determine both the fermionic and bosonic 4D
spectra. We argue that the N=0 theory never leads to tachyons on smooth
Calabi-Yaus in the large volume approximation. As twisted tachyons may arise on
certain singular orbifolds, we conjecture that such tachyonic states are lifted
in the full blow-up. We perform model searches on selected orbifold geometries.
In particular, we construct an explicit example of a Standard Model-like theory
with three generations and a single Higgs field.Comment: 1+30 pages latex, 11 tables; v2: references and minor revisions
added, matches version published in JHE
CAIRT - The changing-atmosphere infra-red tomography explorer
Optics InfoBase Conference Papers2021 Article number FTh4G.6. Fourier Transform Spectroscopy, FTS 2021 - Part of OSA Optical Sensors and Sensing Congress 2021Virtual, Online19 July 2021 through 23 July 2021Code 174136CAIRT, a candidate for ESAâs Earth Explorer 11 mission, will observe the Earthâs limb with an imaging Fourier-transform spectrometer. It will provide global observations of ozone, temperature, water vapour and key halogen and nitrogen compounds.With funding from the Spanish government through the Severo Ochoa Centre of Excellence accreditation SEV-2017-0709Peer reviewe
Revisiting Coupling Selection Rules in Heterotic Orbifold Models
We study L-point couplings between twisted sector fields in heterotic
orbifold compactifications, using conformal field theory. Selection rules
provide an easy way to identify which couplings are non-vanishing. Those used
in the current literature are gauge invariance, R-charge conservation and the
space group selection rule, but they are not the whole story. We revive and
refine a fourth selection rule, due to symmetries in the underlying torus
lattice, and introduce a fifth one, due to the existence or not of classical
worldsheet instanton solutions to mediate the couplings. We consider briefly
the phenomenological consequences of the additional rules, in particular for
recent orbifold constructions whose field content correspond to that of the
MSSM. The structure of the exotic mass matrices is unaltered and many
dimension-5 proton-decay operators vanish.Comment: 27 pages, v2: several clarifications, matches JHEP version. v3:
supercedes journal version, erratum to appear in JHEP; correction to "rule 5"
equations, main ideas unchange
Determination of nutrient salts by automatic methods both in seawater and brackish water: the phosphate blank
9 pĂĄginas, 2 tablas, 2 figurasThe main inconvenience in determining nutrients in seawater by automatic methods is simply solved:
the preparation of a suitable blank which corrects the effect of the refractive index change on the recorded
signal. Two procedures are proposed, one physical (a simple equation to estimate the effect) and the other
chemical (removal of the dissolved phosphorus with ferric hydroxide).Support for this work came from CICYT (MAR88-0245 project) and
Conselleria de Pesca de la Xunta de GaliciaPeer reviewe
An analysis of written lesson plans to examine pedagogical adaptivity in the planning competences of trainee teachers
Transport Across the TTL and Stratospheric Water Vapor Inferred from ERA-Interim Trajectories
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