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Results from the validation campaign of the ozone radiometer GROMOS-C at the NDACC station of La Réunion Island
摘要： Ozone is a species of primary interest as it performs a key role in the middle atmosphere and its monitoring is thus necessary. At the Institute of Applied Physics of the University of Bern, Switzerland, we built a new ground based microwave radiometer, GROMOS-C (GRound based Ozone MOnitoring System for Campaigns). It has a compact design and can be operated at remote places with very little maintenance requirements, being therefore suitable for remote deployments. It has been conceived to measure the vertical distribution of ozone in the middle atmosphere, by observing pressure broadened emission spectra at a frequency of 110.836 GHz. In addition, meridional and zonal wind profiles can be retrieved, based on the Doppler shift of the ozone line measured in the 4 directions of observation (North-East-South-West). In June 2014 the radiometer was installed in the Ma?do observatory, on La Réunion Island (21.2°S, 55.5°E). High resolution ozone spectra were continuously recorded during 7 months. Vertical profiles of ozone have been retrieved through an optimal estimation inversion process, using the Atmospheric Radiative Transfer Simulator ARTS2 as the forward model. The best estimate of the vertical profile is done by means of the optimal estimation method. The validation is performed against ozone profiles from the Microwave Limb Sounder (MLS) on the Aura satellite, the ozone lidar located in the observatory and with ozone profiles from weekly radiosondes. Zonal and meridional winds retrieved from GROMOS-C data are validated against another wind radiometer located in situ, WIRA. In addition, we compare both ozone and winds with ECMWF model data. Results show that GROMOS-C provides reliable ozone profiles between 30 to 0.02 hPa. The comparison with lidar shows a very good agreement at all levels. The accordance with MLS is within less than 10% for pressure levels between 25 and 0.2 hPa.
关键词： ozone,validation,wind profiles,microwave radiometer,middle atmosphere,GROMOS-C
更新于2025-09-23 15:23:52
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Datasets on extinction coefficients for free space optical link survey and optimization
摘要： Based on visibilities data recorded from 2004 to 2013, the minimum, maximum and mean values of extinction coefficients were determined and analyzed in a monthly basis, a yearly basis and also for the whole period of observation. The extinction coefficients data are obtained for the 1330 and 1550 nm optical wavelengths and may be used inter alia for range and availability analyses of optical link for different weather conditions. The data are collected in the region of Dakar, but approach and model of investigation can be reproduced for other regions in Sahel, and in the World, for optical metrology and allied fields of study.
关键词： Optical signal metrology in atmosphere,Free Optical communication
更新于2025-09-23 15:23:52
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Magnetic Loops above a Small Flux-emerging Region Observed by <i>IRIS</i> , <i>Hinode</i> , and <i>SDO</i>
摘要： I report on observations of a set of magnetic loops above a region with late-phase ?ux emergence taken by IRIS, Hinode, and SDO. The loop system consists of many transition-region loop threads that are 5″–12″ in length and ～0 5 in width and coronal loops with similar length and ～2″ width. Although the loop system consists of threads with different temperatures, most individual loop threads have temperatures in a narrow range. In the middle of the loop system, there is a clear systematic blueshift of about 10 km s?1 in the transition region that is consistent with a ?ux-emerging picture, while a redshift of about 10 km s?1 in the corona is observed. The nonthermal velocity of the loop system is smaller than that of the surrounding region in the transition region but is comparable that in the corona. The electron densities of the coronal counterpart of the loop system range from 1×109 cm?3 to 4×109 cm?3. The electron density of a transition-region loop is also measured and found to be about 5×1010 cm?3, a magnitude larger than that in the coronal loops. In agreement with imaging data, the temperature pro?les derived from the differential emission measurement technique con?rm that some of the loops have been heated to corona level. Our observations indicate that the ?ux emergence in its late phase is much different from that at the early stage. While the observed transition region is dominated by emerging ?ux, these emerging loops could be heated to corona level, and the heating (if via nonthermal processes) most likely takes place only after they reach the transition region or lower corona.
关键词： Sun: atmosphere,Sun: transition region,Sun: corona
更新于2025-09-23 15:22:29
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The Spectral Content of <i>SDO</i> /AIA 1600 and 1700 ? Filters from Flare and Plage Observations
摘要： The strong enhancement of the ultraviolet emission during solar flares is usually taken as an indication of plasma heating in the lower solar atmosphere caused by the deposition of the energy released during these events. Images taken with broadband ultraviolet filters by the Transition Region and Coronal Explorer and Atmospheric Imaging Assembly (AIA; 1600 and 1700 ?) have revealed the morphology and evolution of flare ribbons in great detail. However, the spectral content of these images is still largely unknown. Without knowledge of the spectral contribution to these UV filters, the use of these rich imaging data sets is severely limited. Aiming to solve this issue, we estimate the spectral contributions of the AIA UV flare and plage images using high-resolution spectra in the range 1300–1900 ? from the Skylab NRL SO82B spectrograph. We find that the flare excess emission in AIA 1600 ? is dominated by the C IV 1550 ? doublet (26%), Si I continua (20%), with smaller contributions from many other chromospheric lines such as C I 1561 and 1656 ? multiplets, He II 1640 ?, and Si II 1526 and 1533 ?. For the AIA 1700 ? band, the C I 1656 ? multiplet is the main contributor (38%), followed by He II 1640 (17%), and accompanied by a multitude of other, weaker chromospheric lines, with minimal contribution from the continuum. Our results can be generalized to state that the AIA UV flare excess emission is of chromospheric origin, while plage emission is dominated by photospheric continuum emission in both channels.
关键词： Sun: UV radiation,Sun: flares,Sun: atmosphere,Sun: chromosphere,Sun: photosphere
更新于2025-09-23 15:22:29
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Chemical Vapor Deposition for Nanotechnology || Atmospheric Pressure Chemical Vapor Deposition of Graphene
摘要： Recently, graphene has gained significant interest owing to its outstanding conductivity, mechanical strength, thermal stability, etc. Among various graphene synthesis methods, atmospheric pressure chemical vapor deposition (APCVD) is one of the best syntheses due to very low diffusivity coefficient and a critical step for graphene-based device fabrication. High-temperature APCVD processes for thin film productions are being recognized in many diversity technologies such as solid state electronic devices, in particular, high quality epitaxial semiconductor films for silicon bipolar and metal oxide semiconductor (MOS) transistors. Graphene-based devices exhibit high potential for applications in flexible electronics, optoelectronics, and energy harvesting. In this chapter, recent advances of APCVD-based graphene synthesis and their related applications will be addressed.
关键词： large-scale,atmospheric pressure chemical vapor deposition (APCVD),graphene,bilayer graphene (BLG),single-layer graphene (SLG),atmosphere pressure
更新于2025-09-23 15:22:29
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[IEEE 2018 9th International Conference on Ultrawideband and Ultrashort Impulse Signals (UWBUSIS) - Odessa, Ukraine (2018.9.4-2018.9.7)] 2018 9th International Conference on Ultrawideband and Ultrashort Impulse Signals (UWBUSIS) - The Action of Ultra-Short Super-Powerful Radio Pulses on the Earth's Atmosphere and Ionosphere
摘要： Numerical simulations of disturbances in the electron temperature and density arising from the action of ultra-short super-powerful radio pulses with different durations and powers on the Earth's atmosphere and ionosphere are presented. It is demonstrated that the electron density in the 30–60 km altitude range can be increased by 12 orders of magnitude, while the electron temperature shows an increase of the order of 10 to 100 times. The pulse durations and powers needed to create artificial ionized layers have been estimated.
关键词： ultra-short radio pulse,disturbances,numerical simulation,atmosphere,electron temperature,ionosphere,super-powerful radio pulse,electron density
更新于2025-09-23 15:21:21
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Importance of carbon-monoxide-induced reaction in microwave heating synthesis of β-SiC from silicon powder in air
摘要： Microwave heating is known to provide extremely rapid synthesis of silicon carbide (SiC) from mixtures of silicon and carbon powders. The formation mechanism has long been considered to be a solid-state reaction among the powders in the mixture. Here, we present a new reaction mechanism via a gas-phase route. We have confirmed successful synthesis of ￠-SiC powder by microwave-heating of a small amount of Si powder that was entered into a quartz tube and then embedded in graphite powder, although no direct contact between the Si and graphite powders was allowed. Scanning electron microscopy observations revealed that the ￠-SiC powder was formed by direct carbonization of the Si powder. Since the atmosphere during the reaction comprises a vast majority of carbon monoxide (CO) gas according to the Boudouard equilibrium, the carbonization appears to have taken place via the CO gas. The contribution of such a gas-phase reaction could account in part for the rapidity of the microwave-heating reactions reported so far, which can hardly be explained solely by solid-state reactions among the mixed powders.
关键词： Carbon monoxide,Gas-phase reaction,Microwave heating,Silicon carbide,Air atmosphere,Silicon
更新于2025-09-23 15:21:21
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First simultaneous SST/CRISP and IRIS observations of a small-scale quiet Sun vortex
摘要： Context. Ubiquitous small-scale vortices have recently been found in the lower atmosphere of the quiet Sun in state-of-the-art solar observations and in numerical simulations. Aims. We investigate the characteristics and temporal evolution of a granular-scale vortex and its associated up?ows through the photosphere and chromosphere of a quiet Sun internetwork region. Methods. We analyzed high spatial and temporal resolution ground- and spaced-based observations of a quiet Sun region. The observations consist of high-cadence time series of wideband and narrowband images of both Hα 6563 ? and Ca II 8542 ? lines obtained with the CRisp Imaging SpectroPolarimeter (CRISP) instrument at the Swedish 1-m Solar Telescope (SST), as well as ultraviolet imaging and spectral data simultaneously obtained by the Interface Region Imaging Spectrograph (IRIS). Results. A small-scale vortex is observed for the ?rst time simultaneously in Hα, Ca II 8542 ?, and Mg II k lines. During the evolution of the vortex, Hα narrowband images at ?0.77 ? and Ca II 8542 ? narrowband images at ?0.5 ?, and their corresponding Doppler signal maps, clearly show consecutive high-speed up?ow events in the vortex region. These high-speed up?ows with a size of 0.5–1 Mm appear in the shape of spiral arms and exhibit two distinctive apparent motions in the plane of sky for a few minutes: (1) a swirling motion with an average speed of 13 km s?1 and (2) an expanding motion at a rate of 4–6 km s?1. Furthermore, the spectral analysis of Mg II k and Mg II subordinate lines in the vortex region indicates an upward velocity of up to ～8 km s?1 along with a higher temperature compared to the nearby quiet Sun chromosphere. Conclusions. The consecutive small-scale vortex events can heat the upper chromosphere by driving continuous high-speed up?ows through the lower atmosphere.
关键词： Sun: atmosphere,Sun: chromosphere,Sun: photosphere
更新于2025-09-23 15:21:21
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Analysis of helium used as protective gas in Laser Metal Deposition of Ti6Al4V highly reactive material
摘要： Laser Material Deposition (LMD) is an additive manufacturing near-net-shape process. Metal powder particles are molten by means of a laser heat source and added to a substrate creating geometries. This technology offers the possibility of generating coatings, repairing damaged high-added-value parts, and manufacturing components with complex 3D geometries. Many industrial sectors, including aerospace and die and mold industries, are interested in this process due to its capabilities and the wide range of materials that can be used with it. Previous works aimed to develop a protective gas module to be able to process highly reactive materials without the necessity of a complete inert atmosphere inside the machine. Additionally, the influence of a mixture of argon and helium on the LMD process for other non-highly reactive alloys was evaluated. Hence, the present work aims to broaden the understanding of how the combination of these two factors may affect the LMD process, combining these previous studies and evaluating the phenomenon for a highly reactive alloy like Ti6Al4V. The study involves the melt-pool temperature measurement and characterization of the deposited clads variating not only the composition of the protective gas but also the flow rates.
关键词： LMD,Ti6Al4V,Helium,Titanium,Shielding gas,protective atmosphere,He,Laser Metal Deposition,Argon,Ar
更新于2025-09-23 15:21:01
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Handbook of Exoplanets || The “Spectral Zoo” of Exoplanet Atmospheres
摘要： The great abundance of exoplanets and the unexpectedly wide range of their bulk properties create a huge realm of possibilities in exoplanet atmospheres. Opportunities for atmospheric characterization of other worlds abound, as well as pitfalls for the unwary. In this chapter, we make a first foray into exploring the richness of exoplanet atmospheres, with a tour of the exoplanet “spectral zoo.” We then follow the path of light from a star onto an exoplanet and to a distant spectrograph; the details of what happens to that light within the planet’s atmosphere will be discussed in other chapters. We briefly discuss how the light is then affected by the spectrograph and recorded by a detector, resulting in an observed planet spectrum. As will be seen, one of the major challenges for measuring the effects of a planet’s atmosphere in an observed spectrum is disentangling them from effects caused by the instrumentation used to acquire that spectrum. We conclude with a few thoughts on general strategies to overcome observational challenges and harvest the best science from the treasure trove of exoplanets we can and will study in the coming decades.
关键词： Spectroscopy,Atmosphere,Exoplanet
更新于2025-09-23 15:21:01