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  • 1
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Advances in Space Research 14 (1994), S. 49-52 
    ISSN: 0273-1177
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this paper we utilize the latitude distribution of the coronal temperature during the period 1984–1992 that was derived in a paper by Guhathakurta et al, 1993, utilizing ground-based intensity observations of the green (5303Å Fe XIV) and red (6374Å Fe X) coronal forbidden lines from the National Solar Observatory at Sacramento Peak, and estabish its association with the global magnetic field and the density distributions in the corona. A determination of plasma temperature,T, was estimated from the intensity ratio Fe X/Fe XIV (whereT is inversely proportional to the ratio), since both emission lines come from ionized states of Fe, and the ratio is only weakly dependent on density. We observe that there is a large-scale organization of the inferred coronal temperature distribution that is associated with the large-scale, weak magnetic field structures and bright coronal features; this organization tends to persist through most of the magnetic activity cycle. These high-temperature structures exhibit time-space characteristics which are similar to those of the polar crown filaments. This distribution differs in spatial and temporal characterization from the traditional picture of sunspot and active region evolution over the range of the sunspot cycle, which are manifestations of the small-scale, strong magnetic field regions.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Space science reviews 87 (1999), S. 199-206 
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have developed a 2D semi-empirical model (Sittler and Guhathakurta 1999) of the corona and the interplanetary medium using the time independent MHD equations and assuming azimuthal symmetry, utilizing the SOHO, Spartan and Ulysses observations. The model uses as inputs (1) an empirically derived global electron density distribution using LASCO, Mark III and Spartan white light observations and in situ observations of the Ulysses spacecraft, and (2) an empirical model of the coronal magnetic field topology using SOHO/LASCO and EIT observations. The model requires an estimate of solar wind velocity as a function of latitude at 1 AU and the radial component of the magnetic field at 1 AU, for which we use Ulysses plasma and magnetic field data results respectively. The model makes estimates as a function of radial distance and latitude of various fluid parameters of the plasma such as flow velocity V, temperature Teff, and heat flux Qeff which are derived from the equations of conservation of mass, momentum and energy, respectively, in the rotating frame of the Sun. The term "effective" indicates possible wave contributions. The model can be used as a planning tool for such missions as Solar Probe and provide an empirical framework for theoretical models of the solar corona and solar wind.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Space science reviews 72 (1995), S. 29-38 
    ISSN: 1572-9672
    Keywords: Solar wind ; UV spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Spartan 201 is a shuttle deployed spacecraft that is scheduled to perform ultraviolet spectroscopy and white light polarimetry of the extended solar corona during two 40 hour missions to occur in September 1994 and August 1995. The spectroscopy is done with an ultraviolet coronal spectrometer which measures the intensity and spectral line profile of HI Lyα up to heliocentric heights of 3.5 solar radii. It also measures the intensities of the OVI doublet at 1032 and 1037 Å and of Fe XII at 1242 Å. The HI Lyα line profile measurements are used to determine the random velocity distribution of coronal protons along the line-of-sight. The absolute HI Lyα intensities can be used together with electron densities from the white light coronagraph to estimate electron temperatures from hydrogen ionization balance calculations, and bulk outflow velocities from models of Doppler dimmed resonant scattering. Intensities of minor ion lines are used to determine coronal abundances and outflow velocities of O5+. Ultraviolet spectroscopy of extended coronal regions from the 11 April 1993 mission of Spartan 201 are discussed.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Space science reviews 70 (1994), S. 267-272 
    ISSN: 1572-9672
    Keywords: Sun ; Corona
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A white light coronagraph was launched into orbit aboard the space shuttle OV 103 (Discovery) on 7 April 1993. This device was one of two instruments included in the SPARTAN 201-1 payload, a completely autonomous sub-satellite deployed from the shuttle for a period of about 47 hours. The WLC system is an externally occulted coronagraph system which incorporates a rotating half-wave plate polarimeter, and the image data is used to infer the brightness, the polarized brightness and the degree of polarization of the white light emission from the solar corona. These data are in turn used to infer estimates of the K- and F-coronal brightnesses and density distributions. We shall present preliminary results of the electron density estimate in the coronal streamer and hole region and describe the methods employed.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1572-9672
    Keywords: corona ; coronal holes ; line profiles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We compared the H I Lyα polar coronal hole profiles obtained during the three Spartan 201 flights (in 1993, 1994, and 1995) and during the more recent UVCS/SOHO mission. We found that at 2.1 R⊙ there are no significant variations of the line shape over the several years of the descending phase of the solar cycle. However, there may be some evidence for the 1.8 R⊙ profiles being broader towards solar minimum. The profiles at 2.1 R⊙ are different from profiles obtained at 1.8 R⊙; they have clearly narrower cores and wide wings. We fitted the profiles with single and/or multiple Gaussian functions and calculated their typical 1/e half widths.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The Spartan 201 flights from 1993 to 1995 provided us with observations in H I Lyman-α of several coronal hole/streamer boundaries and adjacent streamers during the declining phase of the current solar cycle: Analysis of the latitudinal dependence of the line intensities clearly shows that there is a boundary region at the coronal hole/streamer interface where the H I Lyman-α intensity reaches a minimum value. Similar results are also found in UVCS/SOHO observations. We also discuss differences in the coronal hole/streamer boundaries for different types of streamers and their changes over the three year period of Spartan 201 observations.
    Type of Medium: Electronic Resource
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  • 8
    Publication Date: 2014-07-18
    Description: ABSTRACT The trends and epochal variability of southwest monsoon over the country as a whole and four homogeneous regions are examined using monthly rainfall data (1901–2011) of 640 political districts of India. The district rainfall data is computed from station rainfall data. The same station data is used to analyse the trends in the frequency of rainfall events of different intensities for examining extreme rainfall events. The existence of the multidecadal epochal variability of rainfall is clearly established in the all-India monsoon rainfall as well as monsoon rainfall over the four homogenous regions. However, over different homogenous regions, the phases of multidecadal variability are found to be different. Principal component analysis brings out Northeast India (NEI) rainfall as more dominant mode for all-India rainfall. Significant decrease in southwest monsoon rainfall over NEI is observed during the post 1950 period. Decreasing trends are also observed over the monsoon core region during the post-1950 period. Over these regions, monsoon rainfall has increased significantly during the pre-1950 period. It has been shown that the decreasing trend in monsoon rainfall during the post 1950 period is the result of multidecadal epochal variability. Geographical regions that experienced significant changes in the frequency of days of rainfall with different intensities are also identified. Significant change/turning points are also detected in the southwest monsoon rainfall. Frequency of moderate rainfall events (5 mm ≤ daily rainfall 〈 100 mm) decreased significantly during the period 1951–2010 over the monsoon core region of India whereas no significant changes are observed in the frequencies of heavy (daily rainfall 〉100 mm) or very heavy rain (daily rainfall 〉150 mm) during the southwest monsoon season. Climatic shift or change point in monsoon rainfall in India is also detected by an established statistical test.
    Print ISSN: 0899-8418
    Electronic ISSN: 1097-0088
    Topics: Geosciences , Physics
    Published by Wiley
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  • 9
    Publication Date: 1995-04-01
    Print ISSN: 0038-6308
    Electronic ISSN: 1572-9672
    Topics: Physics
    Published by Springer
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  • 10
    Publication Date: 1994-06-01
    Print ISSN: 0038-0938
    Electronic ISSN: 1573-093X
    Topics: Physics
    Published by Springer
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