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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Annales geophysicae 15 (1997), S. 1447-1456 
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Two flights of the UK Meteorological Office’s Hercules aircraft through daytime frontal cirrus around Scotland have been analysed using wavelet analysis on the vertical velocity time-series from the horizontal runs. It is shown that wavelet analysis is a useful tool for analysing the turbulence data in cirrus clouds. It finds the largest scales involved in producing turbulence, as does Fourier analysis, such as the 2-km spectral peaks corresponding to convective activity during flight A283. Wavelet spectra have the added advantage that the position is shown, and so they identify smaller-scale, highly localised processes such as the production of turbulent kinetic energy by the breaking of Kelvin-Helmholtz waves due to the vertical shear in the horizontal wind. These may be lost in Fourier spectra obtained for long time-series, though they contribute something to the average spectral density at the appropriate scale. The main disadvantage of this technique is that only octave frequency bands are resolved.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0992-7689
    Keywords: Atmospheric composition and structure ; Cloud physics and chemistry ; Pollution ; Meteorology and atmospheric dynamics ; Precipitation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Many Large Eddy Simulation (LES) models use the classic Kessler parameterisation either as it is or in a modified form to model the process of cloud water autoconversion into precipitation. The Kessler scheme, being linear, is particularly useful and is computationally straightforward to implement. However, a major limitation with this scheme lies in its inability to predict different autoconversion rates for maritime and continental clouds. In contrast, the Berry formulation overcomes this difficulty, although it is cubic. Due to their different forms, it is difficult to match the two solutions to each other. In this paper we single out the processes of cloud conversion and accretion operating in a deep model cloud and neglect the advection terms for simplicity. This facilitates exact analytical integration and we are able to derive new expressions for the time of onset of precipitation using both the Kessler and Berry formulations. We then discuss the conditions when the two schemes are equivalent. Finally, we also critically examine the process of droplet evaporation within the framework of the classic Kessler scheme. We improve the existing parameterisation with an accurate estimation of the diffusional mass transport of water vapour. We then demonstrate the overall robustness of our calculations by comparing our results with the experimental observations of Beard and Pruppacher, and find excellent agreement.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Annales geophysicae 14 (1997), S. 1192-1197 
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Phase functions have been calculated using the Monte Carlo/geometric ray tracing method for single hexagonal pyramidal ice crystals (such as solid and hollow bullets) randomly oriented in space and horizontal plane, in order to study the concentric halo formations. Results from three dimensional model calculations show that 9° halo can be as bright as the common 22° halo for pyramidal angle of 28°, and the 18°, 20°, 24° and 35° halos cannot be seen due to the strong 22° halo domination in the scattering phase function between 18° and 35°. For solid pyramidal ice crystals randomly oriented horizontally, the 35° arc can be produced and its intensity depends on the incident ray solar angle and the particle aspect ratio.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Annales geophysicae 14 (1996), S. 845-852 
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The effects of cloud shadowing, channelling, cloud side illumination and droplet concentration are investigated with regard to the reflection of shortwave solar radiation. Using simple geometric clouds, coupled with a Monte Carlo model the transmission properties of idealized cloud layers are found. The clouds are illuminated with direct solar radiation from above. The main conclusion reached is that the distribution of the cloud has a very large influence on the reflectivity of a cloud layer. In particular, if the cloud contains vertical gaps through the cloud layer in which the liquid water content is zero, then, smaller more numerous gaps are more influential on the radiation than fewer, larger gaps with equal cloud fraction. At very low solar zenith angles channelling of the radiation reduces the reflection expected on the basis of the percentage cloud cover. At high solar zenith angles the illumination of the cloud edges significantly increases the reflection despite the shadowing of one cloud by another when the width of the gaps is small. The impact of droplet concentration upon the reflection of cloud layers is also investigated. It is found that at low solar zenith angles where channelling is important, the lower concentrations increase the transmission. Conversely, when cloud edge illumination is dominant the cloud distribution is found to be more important for the higher concentrations.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0992-7689
    Keywords: Meteorology and atmosphere dynamics ; Climatology ; Radiative process ; Atmospheric composition and structure ; Cloud physics and chemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Ice crystal clouds have an influence on the radiative budget of the earth; however, the exact size and nature of this influence has yet to be determined. A laboratory cloud chamber experiment has been set up to provide data on the optical scattering behaviour of ice crystals at a visible wavelength in order to gain information which can be used in climate models concerning the radiative characteristics of cirrus clouds. A PMS grey-scale probe is used to monitor simultaneously the cloud microphysical properties in order to correlate these closely with the observed radiative properties. Preliminary results show that ice crystals scatter considerably more at 90° than do water droplets, and that the halo effects are visible in a laboratorygenerated cloud when the ice crystal concentration is sufficiently small to prevent masking from multiple scattering.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 3481-3481 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: © American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 833-835 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experimental observation of transitions between discrete longitudinal wave modes in a dc neon glow discharge is reported. Experimental findings concerning the pattern selecting instability agree with observations of the Eckhaus instability in fluid systems. This is supported by theoretical considerations of a model equation (Complex Ginzburg–Landau equation) based on a fluid model. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 729-739 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Starting from the hydrodynamic description of the positive column in a neon glow discharge, a numerical approach is used in order to study the nonlinear properties of ionization waves. Within the instability region of the homogeneous equilibrium state, a secondary instability of the Eckhaus type is found. Compared to the classical results, the plasma system shows some peculiarities, e.g., an asymmetric stability band and strong selection of periodic patterns. The dependency of the shape and the width of this band on the discharge parameters is investigated. The spatiotemporal dynamics connected with the transitions from the stability band to the instability region have been studied showing different behavior on the upper and lower border of the stability region. Normally a subcritical Eckhaus instability has been revealed. Moreover, at selected sets of plasma parameters the phenomenon of spatiotemporal intermittency is found. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1365-2109
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The effects of temperature on the survival and behaviour of two size classes of Chlamys islandica was investigated in a laboratory study. The scallops were sampled in spring from three localities in Iceland, Breidafjördur (west), Húnaflói (north), and Hvalfjördur (southwest) and again in August from Breidafjördur and Hvalfjördur. Daily observations of mortality and behaviour were made over a 21-day period at sea temperatures ranging from 7 to 16°C in spring (April–May) and 11 to 14°C in August. During the spring experiment the tolerance of scallops, as expressed by mortality and behaviour, was distinctly reduced at sea temperatures above 12°C among scallops from Breidafjördur and Húnaflói and above 13°C among scallops from Hvalfjördur. During the second set of experiments, conducted in August, scallops were transported into the laboratory from a higher sea temperature than in the spring. As a result, mortality rates were much lower demonstrated by the fact that only scallops reared at sea temperature of 14°C died. This indicates that C. islandica may tolerate somewhat higher temperatures than have been observed in Icelandic waters in recent years. However, the gradual increase in temperature during the last 10 years has brought the mean temperature close to the species' tolerance limit.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Ultramicroscopy 38 (1991), S. 117-126 
    ISSN: 0304-3991
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Electrical Engineering, Measurement and Control Technology , Natural Sciences in General , Physics
    Type of Medium: Electronic Resource
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