To achieve better agreement of simulated Arctic winter stratospheric dynamic with observations assimilation procedure nudging was incorporated in CCM SOCOL. Trajectories based on SOCOL output winds ...demonstrate the reasonable agreement with trajectories based on reanalysis data inside the polar vortex and can be used for analysis and forecast of ozone related processes in winter-spring seasons. Obtained results of several recent major Arctic SSW events analysis show that CCM SOCOL could be used for SSW forecast over the period up to 8 days.
Subvisible cirrus clouds (SVCs) may contribute to dehydration close to the tropical tropopause. The higher and colder SVCs and the larger their ice crystals, the more likely they represent the last ...efficient point of contact of the gas phase with the ice phase and, hence, the last dehydrating step, before the air enters the stratosphere. The first simultaneous in situ and remote sensing measurements of SVCs were taken during the APE-THESEO campaign in the western Indian ocean in February/March 1999. The observed clouds, termed Ultrathin Tropical Tropopause Clouds (UTTCs), belong to the geometrically and optically thinnest large-scale clouds in the Earth's atmosphere. Individual UTTCs may exist for many hours as an only 200--300 m thick cloud layer just a few hundred meters below the tropical cold point tropopause, covering up to 105 km2. With temperatures as low as 181 K these clouds are prime representatives for defining the water mixing ratio of air entering the lower stratosphere.
We report on the first simultaneous in situ and remote measurements of subvisible cirrus in the uppermost tropical troposphere. The observed cirrus, called UTTCs (ultrathin tropical tropopause ...clouds), are the geometrically (200–300 m) and optically (τ ≈ 10−4) thinnest large‐scale clouds ever sampled (≈105 km2). UTTCs consist of only a few ice particles per liter with mean radius ≈5 μm, containing only 1–5 % of the total water. Yet, brief adiabatic cooling events only 1–2 K below mean ambient temperature destabilize UTTCs, leading to large sedimenting particles (r ≈ 25 μm). Due to their extreme altitude above 17 km and low particle number density, UTTCs may efficiently dehydrate air during its last encounter with the ice phase before entering the stratosphere.
A solar occultation sensor, the Improved Limb Atmospheric Spectrometer (ILAS)‐II, measured 5890 vertical profiles of ozone concentrations in the stratosphere and lower mesosphere and of other species ...from January to October 2003. The measurement latitude coverage was 54–71°N and 64–88°S, which is similar to the coverage of ILAS (November 1996 to June 1997). One purpose of the ILAS‐II measurements was to continue such high‐latitude measurements of ozone and its related chemical species in order to help accurately determine their trends. The present paper assesses the quality of ozone data in the version 1.4 retrieval algorithm, through comparisons with results obtained from comprehensive ozonesonde measurements and four satellite‐borne solar occultation sensors. In the Northern Hemisphere (NH), the ILAS‐II ozone data agree with the other data within ±10% (in terms of the absolute difference divided by its mean value) at altitudes between 11 and 40 km, with the median coincident ILAS‐II profiles being systematically up to 10% higher below 20 km and up to 10% lower between 21 and 40 km after screening possible suspicious retrievals. Above 41 km, the negative bias between the NH ILAS‐II ozone data and the other data increases with increasing altitude and reaches 30% at 61–65 km. In the Southern Hemisphere, the ILAS‐II ozone data agree with the other data within ±10% in the altitude range of 11–60 km, with the median coincident profiles being on average up to 10% higher below 20 km and up to 10% lower above 20 km. Considering the accuracy of the other data used for this comparative study, the version 1.4 ozone data are suitably used for quantitative analyses in the high‐latitude stratosphere in both the Northern and Southern Hemisphere and in the lower mesosphere in the Southern Hemisphere.
Mechanisms by which subvisible cirrus clouds (SVCs) might contribute to dehydration close to the tropical tropopause are not well understood. Recently Ultrathin Tropical Tropopause Clouds (UTTCs) ...with optical depths around 10-4 have been detected in the western Indian ocean. These clouds cover thousands of square kilometers as 200-300 m thick distinct and homogeneous layer just below the tropical tropopause. In their condensed phase UTTCs contain only 1-5% of the total water, and essentially no nitric acid. A new cloud stabilization mechanism is required to explain this small fraction of the condensed water content in the clouds and their small vertical thickness. This work suggests a mechanism, which forces the particles into a thin layer, based on upwelling of the air of some mm/s to balance the ice particles, supersaturation with respect to ice above and subsaturation below the UTTC. In situ measurements suggest that these requirements are fulfilled. The basic physical properties of this mechanism are explored by means of a single particle model. Comprehensive 1-D cloud simulations demonstrate this stabilization mechanism to be robust against rapid temperature fluctuations of +/- 0.5 K. However, rapid warming (Δ T > 2 K) leads to evaporation of the UTTC, while rapid cooling (Δ T < -2 K) leads to destabilization of the particles with the potential for significant dehydration below the cloud
Ozone evolution and diabatic descent in the Arctic polar vortex in winter 1995/1996 was studied with a newly developed diabatic trajectory-chemistry model (DTCM). To study the chemical and dynamic ...evolution of the species in the polar vortex, 400 diabatic trajectories were calculated in the vortex core and edge region by using three-dimensional (3-D) wind data provided by the European Centre for Medium-Range Weather Forecasts (ECMWF). The averaged diabatic descending motion and ozone behavior were obtained for particles started from the core and from the edge region of the vortex. The difference in ozone-loss rates as well as the difference in descending rates between the vortex core and the vortex-edge region was not statistically significant. The average cumulative ozone loss of 65 ± 16% in the vortex core obtained from the model calculations was consistent with the estimates obtained with a different method (Match experiment). The model results for the vortex core were compared with those obtained using trajectories with the vertical winds calculated on the basis of radiative cooling rates as used by the SLIMCAT 3-D chemical transport model. Although the trajectories based on cooling rates exhibited lower descending rates than those based on 3-D analyzed wind data, the ozone behavior was similar for both types of trajectory. Ozonesonde data from two stations (Ny-Alesund in the vortex core and Yakutsk in the vortex edge) were compared with the model results. For Lagrangian estimation of the ozone loss at these stations, the descending rates obtained by the diabatic trajectory calculations were used. Good agreements were obtained between the model results and observations for both the vortex core and edge region. These results suggest that strong ozone depletion occurred not only in the core, but also in the edge region of the vortex, and that air masses from the mid-latitudes did not appreciably affect the degree of ozone depletion in this winter-spring period. The sensitivity of the model to different descending rates and to the presence of large nitric acid trihydrate (NAT) particles was also examined.PUBLICATION ABSTRACT
Simultaneous balloonborne measurements of ozone and polar stratospheric clouds (PSCs) were made over Heiss Island (80.5°N, 57.6°E) during the 1988–1989 winter. These soundings were supplemented with ...additional ozonesondes and meteorological information obtained from regular radiosondes and rocketsondes. The ozone measurements taken by themselves do not suggest a spring decrease in ozone over Heiss Island. However, a comparison with ozonesonde data from another location near the solar terminator can be interpreted as suggesting ∼20% ozone loss between 17.5 and 24 km in the outer vortex. This would roughly correspond to a loss of ∼10 Dobson units (DU) or 3–4% loss in total ozone column. Observed transport effects make the identification of true ozone loss considerably more difficult and uncertain. No statistically significant direct correlation in the vertical structure of PSCs and ozone near the center of the dark Arctic vortex was observed in the limited number of soundings.
We describe a novel method for electron-beam nitriding of metal (titanium) under medium (fore-vacuum) pressures (2–8 Pa) of nitrogen. Titanium sample was heated by a dc electron beam generated by a ...fore-vacuum plasma-cathode electron source with current up to 100 mA and energy up to 8 kV; this beam also generated beam-produced plasma with active nitrogen atoms, ions and other reactive species near the sample. SEM chemical composition analysis of the nitride layer have shown the presence of approximately 25 wt% of N, wt. 68% of Ti and only wt. 6% of O atoms within the processed layer. The X-ray diffraction spectrum of the nitride sample showed that the modified layer has a crystalline structure predominantly orientated along the crystallographic directions (111), (200), (220), characteristic of δ-TiN with a face-centered lattice. Besides the δ-TiN phase, there are present in the nitrided layer a γ phase of Ti2N (tetragonal nitride) with predominant orientation (200). These results show the advantage of using forevacuum sources for electron beam and plasma nitriding of metals.
•We show a novel method for electron-beam nitriding of sample in fore-vacuum pressures.•Nitriding occurs due to direct irradiation of sample by e-beam and beam plasma.•Dense beam plasma provides charge neutralization, so any material can be nitrided.•Analysis shows 25 wt% of N, 68 wt% of Ti and only 6 wt% of O in treated layer Ti sample.
This paper is devoted to the engineering embodiment of the
modern methods for producing charged ion and electron beams
by extracting them from the plasma of a discharge. Electron
beams use to execute ...electron-beam welding, annealing, and surface
heating of materials and to realize plasmochemical reactions
stimulated by fast electrons. Ion beams allow realization of
technologies of ion implantation or ion-assisted deposition
of coatings thereby opening new prospects for the creation of
compounds and alloys by the method that makes it possible to
obtain desired parameters and functional properties of the surface.
A detailed description is given to the performance and design
of devices producing beams of this type: the ion and electron
sources being developed at the laboratory of plasma sources
of the Institute of High-Current Electronics of the Russian
Academy of Sciences and the laboratory of plasma electronics
of Tomsk State University of Control Systems and Radioelectronics.
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