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  • 1
    Electronic Resource
    Electronic Resource
    STARE observations of long discrete echoes (1982)
    [s.l.] : Nature Publishing Group
    Nature 299 (1982), S. 238-240 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The STARE system3 provides measurements of the back-scatter intensity and irregularity drift velocity over a large area (-200,000 km2) with good spatial resolution (20 x 20 km2) and a temporal resolution of -20 s. The twin radar system permits Doppler velocities of E-region ionospheric ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/299238a0
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  • 2
    Electronic Resource
    Electronic Resource
    VHF double-peaked spectra at negative Doppler shifts in the morning sector of radio aurora
    Amsterdam : Elsevier
    Planetary and Space Science 27 (1979), S. 233-241 
    Details
    ISSN: 0032-0633
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0032-0633(79)90065-5
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  • 3
    Electronic Resource
    Electronic Resource
    Observations of 50-MHz type-II coherent echoes from within the polar cap (1994)
    Springer
    Annales geophysicae 12 (1994), S. 765-774 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract 50-MHz type-II coherent echoes at geometrical aspect angles of 11.5○ have been observed in the northern polar cap during pre-noon hours. The echoes had an unusually large Doppler width of 1200–1400 m s−1 and were well correlated with strong magnetic disturbances in the range 500–1000 nT. The dependence of intensity, spectral width and skewness versus radial velocity were similar to those known from previous experiments at lower latitudes and at small aspect angles. It is concluded that echo onset was due to the combination of several factors, including a highly conducting ionosphere, the presence of a very intense electric field, and strong radar wave refraction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-994-0765-1
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  • 4
    Electronic Resource
    Electronic Resource
    Flow angle dependence for the asymmetry of broad 50-MHz coherent echoes at large magnetic aspect angles (1997)
    Springer
    Annales geophysicae 15 (1997), S. 671-684 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The skewness of broad Type 2-like spectra has been studied using data collected by two orthogonal CW 50-MHz radio links with co-located scattering volumes. Geometrical aspect angles of observations were about 10. One short event was considered. For this event, the electron flow direction was changing periodically (period about 9 minutes) presumably due to the passage of a magnetospheric MHD wave through the ionosphere. It was found that for the radar observations along the electrojet flow, the skewness had the same sign as the mean Doppler shift with average absolute values in between 0.5–1.0. For observations perpendicular to the electrojet flow, spectra were more symmetrical (average skewness was around 0) and the sign of the skewness was sometimes opposite to the sign of the mean Doppler shift. These observations are interpreted in terms of contribution from both the Farley-Buneman and gradient-drift instabilities to the resultant spectrum. Differences with radar observations at small aspect angles are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-997-0760-4
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  • 5
    Electronic Resource
    Electronic Resource
    Observations of polar patches generated by solar wind Alfvén wave coupling to the dayside magnetosphere (1999)
    Springer
    Annales geophysicae 17 (1999), S. 463-489 
    Details
    ISSN: 0992-7689
    Keywords: Ionosphere (polar ionosphere) ; Magnetospheric physics (magnetosphere-ionosphere interactions; polar wind-magnetosphere interactions)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A long series of polar patches was observed by ionosondes and an all-sky imager during a disturbed period (Kp = 7- and IMF Bz 〈0). The ionosondes measured electron densities of up to 9 × 1011 m−3 in the patch center, an increase above the density minimum between patches by a factor of ≈4.5. Bands of F-region irregularities generated at the equatorward edge of the patches were tracked by HF radars. The backscatter bands were swept northward and eastward across the polar cap in a fan-like formation as the afternoon convection cell expanded due to the IMF By 〉 0. Near the north magnetic pole, an all-sky imager observed the 630-nm emission patches of a distinctly band-like shape drifting northeastward to eastward. The 630-nm emission patches were associated with the density patches and backscatter bands. The patches originated in, or near, the cusp footprint where they were formed by convection bursts (flow channel events, FCEs) structuring the solar EUV-produced photoionization and the particle-produced auroral/cusp ionization by segmenting it into elongated patches. Just equatorward of the cusp footprint Pc5 field line resonances (FLRs) were observed by magnetometers, riometers and VHF/HF radars. The AC electric field associated with the FLRs resulted in a poleward-progressing zonal flow pattern and backscatter bands. The VHF radar Doppler spectra indicated the presence of steep electron density gradients which, through the gradient drift instability, can lead to the generation of the ionospheric irregularities found in patches. The FLRs and FCEs were associated with poleward-progressing DPY currents (Hall currents modulated by the IMF By) and riometer absorption enhancements. The temporal and spatial characteristics of the VHF backscatter and associated riometer absorptions closely resembled those of poleward moving auroral forms (PMAFs). In the solar wind, IMP 8 observed large amplitude Alfvén waves that were correlated with Pc5 pulsations observed by the ground magnetometers, riometers and radars. It is concluded that the FLRs and FCEs that produced patches were driven by solar wind Alfvén waves coupling to the dayside magnetosphere. During a period of southward IMF the dawn-dusk electric field associated with the Alfvén waves modulated the subsolar magnetic reconnection into pulses that resulted in convection flow bursts mapping to the ionospheric footprint of the cusp.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-999-0463-0
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  • 6
    Electronic Resource
    Electronic Resource
    SuperDARN studies of the ionospheric convection response to a northward turning of the interplanetary magnetic field (1998)
    Springer
    Annales geophysicae 16 (1998), S. 549-565 
    Details
    ISSN: 0992-7689
    Keywords: Ionosphere (Auroral ionosphere) ; Magnetospheric physics (Magnetopause, cusp, and boundary layers; Magnetosphere-ionosphere interaction)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The response of the dayside ionospheric flow to a sharp change in the direction of the interplanetary magnetic field (IMF) measured by the WIND spacecraft from negative Bz and positive By, to positive Bz and small By, has been studied using SuperDARN radar, DMSP satellite, and ground magnetometer data. In response to the IMF change, the flow underwent a transition from a distorted twin-cell flow involving antisunward flow over the polar cap, to a multi-cell flow involving a region of sunward flow at high latitudes near noon. The radar data have been studied at the highest time resolution available (∼2 min) to determine how this transition took place. It is found that the dayside flow responded promptly to the change in the IMF, with changes in radar and magnetic data starting within a few minutes of the estimated time at which the effects could first have reached the dayside ionosphere. The data also indicate that sunward flows appeared promptly at the start of the flow change (within ∼2 min), localised initially in a small region near noon at the equatorward edge of the radar backscatter band. Subsequently the region occupied by these flows expanded rapidly east-west and poleward, over intervals of ∼7 and ∼14 min respectively, to cover a region at least 2 h wide in local time and 5° in latitude, before rapid evolution ceased in the noon sector. In the lower latitude dusk sector the evolution extended for a further ∼6 min before quasi-steady conditions again prevailed within the field-of-view. Overall, these observations are shown to be in close conformity with expectations based on prior theoretical discussion, except for the very prompt appearance of sunward flows after the onset of the flow change.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-998-0549-0
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  • 7
    Electronic Resource
    Electronic Resource
    The ionospheric signature of transient dayside reconnection and the associated pulsed convection return flow (1999)
    Springer
    Annales geophysicae 17 (1999), S. 1166-1171 
    Details
    ISSN: 0992-7689
    Keywords: Ionosphere (plasma convection) ; Magnetospheric physics (magnetopause, cusp, and boundary layers; magnetosphere-ionosphere interactions)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Three SuperDARN coherent HF radars are employed to investigate the excitation of convection in the dayside high-latitude ionosphere in response to transient reconnection occurring in the cusp region. This study demonstrates the existence of transient antisunward-propagating backscatter features at the expected location of the ionospheric footprint of the cusp region, which have a repetition rate near 10 min. These are interpreted as the ionospheric signature of flux transfer events. Moreover, transient sunward-propagating regions of backscatter are observed in the convection return flow regions of both the pre- and post-noon sectors. These patches are observed to propagate towards the noon sector from at least as far around the auroral zone as 07 MLT in the pre-noon sector and 17 MLT in the post-noon sector, travelling with a veloCity of approximately 1.5 to 2 km s−1. These return flow patches have a repetition rate similar to that of the transient features observed at local noon. While providing supporting evidence for the impulsive nature of convection flow, the observation of sunward-propagating features in the return flow region is not consistent with current conceptual models of the excitation of convection.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-999-1166-2
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  • 8
    Electronic Resource
    Electronic Resource
    DARN/SuperDARN (1995)
    Springer
    Space science reviews 71 (1995), S. 761-796 
    Details
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The Dual Auroral Radar Network (DARN) is a global-scale network of HF and VHF radars capable of sensing backscatter from ionospheric irregularities in the E and F-regions of the high-latitude ionosphere. Currently, the network consists of the STARE VHF radar system in northern Scandinavia, a northern-hemisphere, longitudinal chain of HF radars that is funded to extend from Saskatoon, Canada to central Finland, and a southern-hemisphere chain that is funded to include Halley Station, SANAE and Syowa Station in Antarctica. When all of the HF radars have been completed they will operate in pairs with common viewing areas so that the Doppler information contained in the backscattered signals may be combined to yield maps of high-latitude plasma convection and the convection electric field. In this paper, the evolution of DARN and particularly the development of its SuperDARN HF radar element is discussed. The DARN/SupperDARN network is particularly suited to studies of large-scale dynamical processes in the magnetosphere-ionosphere system, such as the evolution of the global configuration of the convection electric field under changing IMF conditions and the development and global extent of large-scale MHD waves in the magnetosphere-ionosphere cavity. A description of the HF radars within SuperDARN is given along with an overview of their existing and intended locations, intended start of operations, Principal Investigators, and sponsoring agencies. Finally, the operation of the DARN experiment within ISTP/GGS, the availability of data, and the form and availability of the Key Parameter files is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00751350
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  • 9
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    Tillage effects on the radar backscattering coefficient of grain stubble fields (1991)
    Taylor & Francis
    Details
    Publication Date: 1991-11-01
    Print ISSN: 0143-1161
    Electronic ISSN: 1366-5901
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Taylor & Francis
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  • 10
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    DARN/SuperDARN (1995)
    Springer
    Details
    Publication Date: 1995-02-01
    Print ISSN: 0038-6308
    Electronic ISSN: 1572-9672
    Topics: Physics
    Published by Springer
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