The Earth's Atmosphere (the + earth_atmosphere)

Distribution by Scientific Domains


Selected Abstracts


Orbit characteristics of the tristatic EISCAT UHF meteors

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008
C. Szasz
ABSTRACT The tristatic EISCAT 930-MHz UHF system is used to determine the absolute geocentric velocities of meteors detected with all three receivers simultaneously at 96 km, the height of the common radar volume. The data used in this study were taken between 2002 and 2005, during four 24-h runs at summer/winter solstice and vernal/autumnal equinox to observe the largest seasonal difference. The observed velocities of 410 tristatic meteors are integrated back through the Earth atmosphere to find their atmospheric entry velocities using an ablation model. Orbit calculations are performed by taking zenith attraction, Earth rotation as well as obliquity of the ecliptic into account. The results are presented in the form of different orbital characteristics. None of the observed meteors appears to be of extrasolar or asteroidal origin; comets, particularly short-period (<200 yr) ones, may be the dominant source for the particles observed. About 40 per cent of the radiants can be associated with the north apex sporadic meteor source and 58 per cent of the orbits are retrograde. There is evidence of resonance gaps at semimajor axis values corresponding to commensurabilities with Jupiter, which may be the first convincing evidence of Jupiter's gravitational influence on the population of small sporadic meteoroids surveyed by radar. The geocentric velocity distribution is bimodal with a prograde population centred around 38 km s,1 and a retrograde population peaking at 59 km s,1. The EISCAT radar system is located close to the Arctic Circle, which means that the North Ecliptic Pole (NEP) is near zenith once every 24 h, i.e. during each observational period. In this particular geometry, the local horizon coincides with the ecliptic plane. The meteoroid influx should therefore be directly comparable throughout the year. [source]


Ultraviolet Sensors: An Efficient Way to Assemble ZnS Nanobelts as Ultraviolet-Light Sensors with Enhanced Photocurrent and Stability (Adv. Funct.

ADVANCED FUNCTIONAL MATERIALS, Issue 3 2010
Mater.
On page 500, Xiaosheng Fang and co-workers demonstrate the successful development of high-performance "visible-blind" microscale ZnS nanobelt-based ultraviolet (UV) light sensors through a newly developed non-lithographic method. Such sensors may prove extremely useful for the detection of harmful near-visible-wavelength UV radiation, of particular interest in locations where the shielding effect of the Earth's atmosphere is deteriorating. [source]


Biogeochemical modelling of the rise in atmospheric oxygen

GEOBIOLOGY, Issue 4 2006
M. W. CLAIRE
ABSTRACT Understanding the evolution of atmospheric molecular oxygen levels is a fundamental unsolved problem in Earth's history. We develop a quantitative biogeochemical model that simulates the Palaeoproterozoic transition of the Earth's atmosphere from a weakly reducing state to an O2 -rich state. The purpose is to gain an insight into factors that plausibly control the timing and rapidity of the oxic transition. The model uses a simplified atmospheric chemistry (parameterized from complex photochemical models) and evolving redox fluxes in the Earth system. We consider time-dependent fluxes that include organic carbon burial and associated oxygen production, reducing gases from metamorphic and volcanic sources, oxidative weathering, and the escape of hydrogen to space. We find that the oxic transition occurs in a geologically short time when the O2 -consuming flux of reducing gases falls below the flux of organic carbon burial that produces O2. A short timescale for the oxic transition is enhanced by a positive feedback due to decreasing destruction of O2 as stratospheric ozone forms, which is captured in our atmospheric chemistry parameterization. We show that one numerically self-consistent solution for the rise of O2 involves a decline in flux of reducing gases driven by irreversible secular oxidation of the crust caused by time-integrated hydrogen escape to space in the preoxic atmosphere, and that this is compatible with constraints from the geological record. In this model, the timing of the oxic transition is strongly affected by buffers of reduced materials, particularly iron, in the continental crust. An alternative version of the model, where greater fluxes of reduced hydrothermal cations from the Archean seafloor consume O2, produces a similar history of O2 and CH4. When climate and biosphere feedbacks are included in our model of the oxic transition, we find that multiple ,Snowball Earth' events are simulated under certain circumstances, as methane collapses and rises repeatedly before reaching a new steady-state. [source]


Inversion of terrestrial ecosystem model parameter values against eddy covariance measurements by Monte Carlo sampling

GLOBAL CHANGE BIOLOGY, Issue 8 2005
Wolfgang Knorr
Abstract Effective measures to counter the rising levels of carbon dioxide in the Earth's atmosphere require that we better understand the functioning of the global carbon cycle. Uncertainties about, in particular, the terrestrial carbon cycle's response to climate change remain high. We use a well-known stochastic inversion technique originally developed in nuclear physics, the Metropolis algorithm, to determine the full probability density functions (PDFs) of parameters of a terrestrial ecosystem model. By thus assimilating half-hourly eddy covariance measurements of CO2 and water fluxes, we can substantially reduce the uncertainty of approximately five model parameters, depending on prior uncertainties. Further analysis of the posterior PDF shows that almost all parameters are nearly Gaussian distributed, and reveals some distinct groups of parameters that are constrained together. We show that after assimilating only 7 days of measurements, uncertainties for net carbon uptake over 2 years for the forest site can be substantially reduced, with the median estimate in excellent agreement with measurements. [source]


UV Photodetectors: Single-Crystalline ZnS Nanobelts as Ultraviolet-Light Sensors (Adv. Mater.

ADVANCED MATERIALS, Issue 20 2009
20/2009)
Xiaosheng Fang and and co-workers demonstrate on p. 2034 that single-crystalline ZnS nanobelts that display sharp UV emission (, 337 nm) at room temperature can be assembled into UV sensors that are highly selective and display ultrafast response to radiation stimuli. Such sensors would prove extremely useful for the detection of harmful near-visible-wavelength UV radiation, of particular interest in locations where the shielding effect of the Earth's atmosphere is deteriorating. [source]


Hydrodynamic modelling of cometary particles captured in aerogel and the Earth's atmosphere

METEORITICS & PLANETARY SCIENCE, Issue 10 2009
S. G. Coulson
We present a simplified model for the formation of the tracks formed in aerogel by hypervelocity impacts of cometary material. Using a hydrodynamic approach to model this class of problem overcomes some of the errors associated with previous semi-analytical models for track formation (Coulson 2009). The hydrodynamic models developed allow the particle velocity, temperature and pressure to be calculated as a function of track length within aerogel. A qualative description of how this model can be extended to the formation of bulbous cavities using the Chapman-Jouquet theory is provided. [source]


Ernst Florens Friedrich Chladni (1756,1827) and the origins of modern meteorite research

METEORITICS & PLANETARY SCIENCE, Issue S9 2007
Ursula B. Marvin
These ideas violated two strongly held contemporary beliefs: 1) fragments of rock and metal do not fall from the sky, and 2) no small bodies exist in space beyond the Moon. From the beginning, Chladni was severely criticized for basing his hypotheses on historical eyewitness reports of falls, which others regarded as folk tales, and for taking gross liberties with the laws of physics. Ten years later, the study of fallen stones and irons was established as a valid field of investigation. Today, some scholars credit Chladni with founding meteoritics as a science; others regard his contributions as scarcely worthy of mention. Writings by his contemporaries suggest that Chladni's book alone would not have led to changes of prevailing theories; thus, he narrowly escaped the fate of those scientists who propose valid hypotheses prematurely. However, between 1794 and 1798, four falls of stones were witnessed and widely publicized. There followed a series of epoch-making analyses of fallen stones and "native irons" by the chemist Edward C. Howard and the mineralogist Jacques-Louis de Bournon. They showed that all the stones were much alike in texture and composition but significantly different from the Earth's known crustal rocks. Of primary importance was Howard's discovery of nickel in the irons and the metal grains of the stones. This linked the two as belonging to the same natural phenomenon. These chemical results, published in February 1802, persuaded some of the leading scientists in England, France, and Germany that bodies do fall from the sky. Within a few months, chemists in France reported similar results and a new field of study was inaugurated internationally, although opposition lingered on until April 1803, when nearly 3,000 stones fell at L'Aigle in Normandy and transformed the last skeptics into believers. Chladni immediately received full credit for his hypothesis of falls, but decades passed before his linking of falling bodies with fireballs received general acceptance. His hypothesis of their origin in cosmic space met with strong resistance from those who argued that stones formed within the Earth's atmosphere or were ejected by lunar volcanoes. After 1860, when both of these hypotheses were abandoned, there followed a century of debate between proponents of an interstellar versus a planetary origin. Not until the 1950s did conclusive evidence of their elliptical orbits establish meteorite parent bodies as members of the solar system. Thus, nearly 200 years passed before the questions of origin that Chladni raised finally were resolved. [source]


Heating effects of the matrix of experimentally shocked Murchison CM chondrite: Comparison with micrometeorites

METEORITICS & PLANETARY SCIENCE, Issue 1 2007
Naotaka TOMIOKA
However, if a major fraction of micrometeorites are produced by impacts on porous asteroids, they may have experienced shock heating before contact with the Earth's atmosphere (Tomeoka et al. 2003). A transmission electron microscope (TEM) study of the matrix of Murchison CM chondrite experimentally shocked at pressures of 10,49 GPa shows that its mineralogy and texture change dramatically, mainly due to shock heating, with the progressive shock pressures. Tochilinite is completely decomposed to an amorphous material at 10 GPa. Fe-Mg serpentine is partially decomposed and decreases in amount with increasing pressure from 10 to 30 GPa and is completely decomposed at 36 GPa. At 49 GPa, the matrix is extensively melted and consists mostly of aggregates of equigranular grains of Fe-rich olivine and less abundant low-Ca pyroxene embedded in Si-rich glass. The mineralogy and texture of the shocked samples are similar to those of some types of micrometeorites. In particular, the samples shocked at 10 and 21 GPa are similar to the phyllosilicate (serpentine)-rich micrometeorites, and the sample shocked at 49 GPa is similar to the olivine-rich micrometeorites. The shock heating effects also resemble the effects of pulse-heating experiments on the CI and CM chondrite matrices that were conducted to simulate atmospheric entry heating. We suggest that micrometeorites derived from porous asteroids are likely to go through both shock and atmospheric-entry heating processes. [source]


Hard X-ray emission of the Earth's atmosphere: Monte Carlo simulations

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007
S. Sazonov
ABSTRACT We perform Monte Carlo simulations of cosmic ray-induced hard X-ray radiation from the Earth's atmosphere. We find that the shape of the spectrum emergent from the atmosphere in the energy range 25,300 keV is mainly determined by Compton scatterings and photoabsorption, and is almost insensitive to the incident cosmic ray spectrum. We provide a fitting formula for the hard X-ray surface brightness of the atmosphere as would be measured by a satellite-borne instrument, as a function of energy, solar modulation level, geomagnetic cut-off rigidity and zenith angle. A recent measurement by the INTEGRAL observatory of the atmospheric hard X-ray flux during the occultation of the cosmic X-ray background by the Earth agrees with our prediction within 10 per cent. This suggests that Earth observations could be used for in-orbit calibration of future hard X-ray telescopes. We also demonstrate that the hard X-ray spectra generated by cosmic rays in the crusts of the Moon, Mars and Mercury should be significantly different from that emitted by the Earth's atmosphere. [source]


Potential of combined spaceborne infrared and microwave radiometry for near real-time rainfall attenuation monitoring along earth-satellite links

INTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 4 2001
Frank S. Marzano
Abstract The objective of this paper is to investigate how spaceborne remote sensors, and their derived products, can be exploited to optimize the performances of a satellite communication system in the presence of precipitating clouds along the path. The complementarity between sun-synchronous microwave (MW) and geo-stationary infrared (IR) radiometry for monitoring the earth's atmosphere is discussed and their potential as a rain detection system within near real-time countermeasure techniques for earth-satellite microwave links is analysed. A general approach, consisting in estimating rainfall intensity and attenuation by polar-orbiting microwave radiometers and temporally tracking the rainfall areas by geo-stationary infrared radiometers, is delineated. Multiple regression algorithms for predicting rainfall attenuation from spaceborne brightness temperatures and from surface rainrate, trained by radiative transfer and cloud models, are illustrated. A maximum likelihood technique is delineated to discriminate stratiform and convective rainfall from spaceborne brightness temperatures. The differences among attenuation estimates derived from layered raining-cloud structures with respect to those obtained from simple rain slabs, as recommended by ITU-R, are also quantified. A test of the proposed attenuation prediction methods is performed using raingage and Italsat data acquired in Spino d'Adda (Italy) during 1994. A description of the statistical method, based on the probability matching technique, adopted to combine MW and IR data for retrieving and tracking precipitating cloud systems in terms of path attenuation and accumulated rain at ground is finally provided together with its application to a case study over the Mediterranean area during October 1998. Copyright © 2001 John Wiley & Sons, Ltd. [source]


A 15N-aided artificial atmosphere gas flow technique for online determination of soil N2 release using the zeolite Köstrolith SX6®

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 22 2006
Oliver Spott
N2 is one of the major gaseous nitrogen compounds released by soils due to N-transformation processes. Since it is also the major constituent of the earth's atmosphere (78.08% vol.), the determination of soil N2 release is still one of the main methodological challenges with respect to a complete evaluation of the gaseous N-loss of soils. Commonly used approaches are based either on a C2H2 inhibition technique, an artificial atmosphere or a 15N-tracer technique, and are designed either as closed systems (non-steady state) or gas flow systems (steady state). The intention of this work has been to upgrade the current gas flow technique using an artificial atmosphere for a 15N-aided determination of the soil N2 release simultaneously with N2O. A 15N-aided artificial atmosphere gas flow approach has been developed, which allows a simultaneous online determination of N2 as well as N2O fluxes from an open soil system (steady state). Fluxes of both gases can be determined continuously over long incubation periods and with high sampling frequency. The N2 selective molecular sieve Köstrolith SX6® was tested successfully for the first time for dinitrogen collection. The presented paper mainly focuses on N2 flux determination. For validation purposes soil aggregates of a Haplic Phaeozem were incubated under aerobic (21 and 6 vol.% O2) and anaerobic conditions. Significant amounts of N2 were released only during anaerobic incubation (0.4 and 640.2,pmol N2 h,1,g,1 dry soil). However, some N2 formation also occurred during aerobic incubation. It was also found that, during ongoing denitrification, introduced [NO3], will be more strongly delivered to microorganisms than the original soil [NO3],. Copyright © 2006 John Wiley & Sons, Ltd. [source]


The impact of urban areas on weather

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 614 2006
C. G. Collier
Abstract The industrial revolution led to a rapid development of urban areas. This has continued unremittingly over the last 200 years or so. In most urban areas the surface properties are heterogeneous, which has significant implications for energy budgets, water budgets and weather phenomena within the part of the earth's atmosphere that humans live. In this paper I discuss the structure of the planetary boundary layer, confining our analysis to the region above the rooftops (canopy layer) up to around the level where clouds form. It is in this part of the atmosphere that most of the weather impacting our lives occurs, and where the buildings of our cities impact the weather. In this review, observations of the structure of the urban atmospheric boundary layer are discussed. In particular the use of Doppler lidar provides measurements above the canopy layer. The impact of high-rise buildings is considered. Urban morphology impacts energy fluxes and airflow leading to phenomena such as the urban heat island and convective rainfall initiation. I discuss in situ surface-based remote sensing and satellite measurements of these effects. Measurements have been used with simple and complex numerical models to understand the complexity and balance of the interactions involved. Cities have been found to be sometimes up to 10 degC warmer than the surrounding rural areas, and to cause large increases in rainfall amounts. However, there are situations in which urban aerosol may suppress precipitation. Although much progress has been made in understanding these impacts, our knowledge remains incomplete. These limitations are identified. As city living becomes even more the norm for large numbers of people, it is imperative that we ensure that urban effects on the weather are included in development plans for the built environment of the future. Copyright © 2006 Royal Meteorological Society [source]


Aircraft observations of cloud droplet number concentration: Implications for climate studies

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 602 2004
I. Gultepe
Abstract Droplet number concentration (Nd) is a major parameter affecting cloud physical processes and cloud optical characteristics. In most climate models, Nd is usually assumed to be constant or a function of the droplet and aerosol number concentration (Na). Three types of cloud systems over Canada, namely Arctic clouds, maritime boundary-layer clouds, and winter storms, were studied to obtain values of Nd as a function of temperature (T). The probability density function of Nd was also calculated to show the variability of this parameter. The results show that Nd reaches a maximum at about 10 °C (200 cm,3) and then decreases gradually to a minimum (,1,3 cm,3) at about ,35°C. A comparison of relationships between Nd and Na indicates that estimates of Nd from Na can have an uncertainty of about 30,50 cm,3, resulting in up to a 42% uncertainty in cloud short-wave radiative forcing. This study concludes that the typical fixed values of Nd, which are ,100 cm,3 and ,200 cm,3 for maritime and continental clouds, respectively, and the present relationships of Nd to Na, could result in a large uncertainty in the heat and moisture budgets of the earth's atmosphere. It is suggested that the use of relationships between Nd and T can improve climate simulations. © Crown copyright, 2004. Royal Meteorological Society [source]


Multi-resolution analysis, entropic information and the performance of atmosoheric sounding radiometers

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 569 2000
G. E. Peckham
Abstract The performance of remote-sounding radiometers measuring properties of the earth's atmosphere is analysed through a multi-resolution wavelet transform. This technique allows the uncertainty in retrieved atmospheric profiles to be determined as a function of both altitude and scale of patterns in the profile. Multi-resolution analysis may be applied to a number of indicators of the quality of a measurement including entropic information. The apportionment of performance indicators to specific altitude ranges and pattern scales facilitates a comparison with performance requirements. The analysis is illustrated through a simple model of a remote-sounding radiometer and by application to the Infrared Atmospheric Sounding Interferometer. [source]


Low-power millimeter wave radiations do not alter stress-sensitive gene expression of chaperone proteins

BIOELECTROMAGNETICS, Issue 3 2007
M. Zhadobov
Abstract This article reports experimental results on the influence of low-power millimeter wave (MMW) radiation at 60 GHz on a set of stress-sensitive gene expression of molecular chaperones, namely clusterin (CLU) and HSP70, in a human brain cell line. Selection of the exposure frequency is determined by its near-future applications for the new broadband civil wireless communication systems including wireless local area networks (WLAN) for domestic and professional uses. Frequencies around 60 GHz are strongly attenuated in the earth's atmosphere and such radiations represent a new environmental factor. An exposure system operating in V-band (50,75 GHz) was developed for cell exposure. U-251 MG glial cell line was sham-exposed or exposed to MMW radiation for different durations (1,33 h) and two different power densities (5.4 µW/cm2 or 0.54 mW/cm2). As gene expression is a multiple-step process, we analyzed chaperone proteins induction at different levels. First, using luciferase reporter gene, we investigated potential effect of MMWs on the activation of transcription factors (TFs) and gene promoter activity. Next, using RT-PCR and Western blot assays, we verified whether MMW exposure could alter RNA accumulation, translation, or protein stability. Experimental data demonstrated the absence of significant modifications in gene transcription, mRNA, and protein amount for the considered stress-sensitive genes for the exposure durations and power densities investigated. The main results of this study suggest that low-power 60 GHz radiation does not modify stress-sensitive gene expression of chaperone proteins. Bioelectromagnetics 28:188,196, 2007. © 2006 Wiley-Liss, Inc. [source]