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1

Electronic Resource

Analysis and interpretation of VHF-radar data (1994)

Rüster, R.

Springer

Annales geophysicae 12 (1994), S. 725-732

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ISSN: 0992-7689

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract Doppler measurements have been carried out during a variety of observational campaigns using the stationary and the mobile SOUSY-VHF-Radars. The general data reduction procedure is presented in some detail. Particular emphasis is placed upon possible problems arising from contaminated data and solutions are proposed. Some results from measurements at tropospheric and mesospheric heights are presented.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s00585-994-0725-9

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2

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Spatial variability of the aspect sensitivity of VHF radar echoes in the troposphere and lower stratosphere during jet stream passages (1994)

Yoe, J. G. ; Czechowsky, P. ; Rüster, R. ; [et al.]

Springer

Annales geophysicae 12 (1994), S. 733-745

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ISSN: 0992-7689

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract The aspect sensitivity of SOUSY-VHF-radar oblique-beam echoes from the troposphere and lower stratosphere has been examined for a number of jet stream passages during the years 1990 - 1992. When the core of the jet is overhead or nearly so, vertical profiles of the aspect sensitivity display two notable features. First, the distinction between mainly isotropic and strongly aspect-sensitive echoes in the troposphere and the lower stratosphere, respectively, often reported for measurements made during calm conditions, does not necessarily prevail in the vicinity of the jet stream. Second, echoes obtained at altitudes near the height of the horizontal wind maximum are found to be more aspect sensitive for beams directed parallel to the horizontal flow or nearly so, than for other beam directions. It is demonstrated that time-averaged horizontal wind speeds estimated from the radar data, taking into account the reduced effective oblique-beam zenith angle resulting from aspect sensitivity, may exceed uncorrected wind speeds by as much as 10 m s−1 in these circumstances. Implications for wind profiling and for describing the backscattering process are discussed. Doppler spectral widths examined for one jet stream passage are found to be narrower in a beam aligned with the horizontal wind at heights near the wind speed maximum than corresponding widths measured in a beam projected at right angles to the jet. The narrowest spectra thus coincide with the most aspect-sensitive echoes, consistent with the hypothesis that such returns result from specular backscattering processes.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s00585-994-0733-9

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3

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VHF radar observations of turbulent structures in the polar mesopause region (1997)

Czechowsky, P. ; Rüster, R.

Springer

Annales geophysicae 15 (1997), S. 1028-1036

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ISSN: 0992-7689

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract The mobile SOUSY VHF Radar was operated in the summer of 1987 during the MAC/SINE campaign in northern Norway to study the polar mesosphere summer echoes (PMSE). Measurements of the spectral width indicate that two types of structures occur. In general mesospheric layers are bifurcated exhibiting a narrow spectral width and a well-defined aspect sensitivity. However, for about 10% of the observation time cells of enhanced turbulence characterized by extremely broad spectral widths appear predominantly in the upper sublayer above 86 km. Identification and separation of beam and shear broadening allows a determination of the turbulence-induced component of the spectral width. This case study reveals that during several events these cloud-like structures of enhanced turbulence move with an apparent velocity of several tens of meters per second which is almost identical with the phase trace velocity of simultaneously observed waves. Since, at that time, the Richardson number was less than a quarter, it was concluded that these turbulent cells were generated by a Kelvin-Helmholtz mechanism. The horizontal extent of these structures was calculated to be less than 40 km. A general relation between spectral width and echo power was not detected. The turbulent component of the spectral width was used to calculate typical values of the energy dissipation rate at times where narrow spectral width dominates and during periods of enhanced turbulence. In addition, the outer scale of the inertial subrange (buoyancy scale) was estimated. For the first time the occurrence and motion of this type of structures of enhanced spectral width is analyzed and discussed in detail.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s00585-997-1028-8

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4

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PMSE observations at three different frequencies in northern Europe during summer 1994 (1997)

Bremer, J. ; Hoffmann, P. ; Manson, A. H. ; [et al.]

Springer

Annales geophysicae 14 (1997), S. 1317-1327

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ISSN: 0992-7689

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract Simultaneous observations of polar mesosphere summer echoes (PMSE) have been carried out during summer 1994 in northern Norway using three radars on different frequencies: the ALOMAR SOUSY radar at Andenes on 53.5 MHz, the EISCAT VHP radar at Tromsø on 224 MHz and the MF radar at Tromsø on 2.78 MHz. During the common measuring period in July/August 1994, PMSE could be detected at 224 and 53.5 MHz, and there are strong hints that PMSE also occur at 2.78 MHz. Reliable correlations between hourly backscattered power values indicate that the PMSE structures have zonal extensions of more than 130 km and can be detected at very different scales (half wavelength) between 0.67 (EISCAT VHP radar) and 54 m (MF radar). Using the wind values derived by the MF radar it can be shown that the mesospheric wind field influences the structure of PMSE. The diurnal variation of PMSE is strongly connected with tidal-wind components, whereas spatial differences of PMSE can partly be explained by the mean wind field.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s00585-996-1317-7

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5

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Field campaign for the comparison of SOUSY radar wind measurements with rawinsonde and model data (1994)

Steinhagen, H. ; Christoph, A. ; Czechowsky, P. ; [et al.]

Springer

Annales geophysicae 12 (1994), S. 746-764

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ISSN: 0992-7689

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract A field campaign was carried out from 26 October to 7 November 1992, using the SOUSY-VHF radar and a mobile rawinsonde system installed and operated nearby to produce vertical wind profiles. The purpose of this campaign was to compare the two types of wind measurements with one another and with results from forecast models. Numerical algorithms were developed and applied to the radar data in order to eliminate random errors, correct for velocity aliasing, and calculate the effective zenith angle of the off-vertical beams. Differences between wind profiler data and rawinsonde or model results depend not only upon the errors of the different systems, but also on temporal and spatial variations of the wind field. Therefore, methods for the comparison of radar and rawinsonde data were developed which take into consideration these variations. The practical potential of these methods is demonstrated by comparisons of rawinsonde and radar wind profiles. The comparison of radar data and model output shows excellent agreement in the direction and in the speed of the wind at virtually all altitudes. An evaluation of the quality of wind profiler measurements is possible using the estimation of variance and variability of wind components.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s00585-994-0746-4

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6

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Non-magnetic aspect sensitive auroral echoes from the lower E region observed at 50 MHz (1999)

Rüster, R. ; Schlegel, K.

Springer

Annales geophysicae 17 (1999), S. 1284-1292

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ISSN: 0992-7689

Keywords: Ionosphere (plasma waves and instabilities; ionosphere irregularities; particle precipitaion) ; Meteorology and atmospheric dynamics (middle atmosphere dynamics)

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract Backscatter from E-region irregularities was observed at aspect angles close to 90° (almost parallel to the direction of the magnetic field) using the ALOMAR SOUSY radar at Andoya/Norway. Strong electric fields and increased E-region electron temperatures simultaneously measured with the incoherent scatter facility EISCAT proved that the Farley-Buneman plasma instability was excited. In addition, strong particle precipitation was present as inferred from EISCAT electron densities indicating that the gradient drift instability may have been active, too. Backscatter at such large aspect angles was not expected and has not been observed before. The characteristics of the observed echoes, however, are in many aspects completely different from usual auroral radar results: the Doppler velocities are only of the order of 10 m/s, the half-width of the spectra is around 5 m/s, the echoes originate at altitudes well below 100 km, and they seem to be not aspect-sensitive with respect to the magnetic field direction. We, therefore, conclude that the corresponding irregularities are not caused by the mentioned instabilities and that other mechanism have to be invoked.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s00585-999-1284-x

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7

Electronic Resource

Gravity wave signatures at mesopause heights (1997)

Rüster, R. ; Czechowsky, P. ; Hoffmann, P. ; [et al.]

Springer

Annales geophysicae 14 (1997), S. 1186-1191

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ISSN: 0992-7689

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract The ALOMAR SOUSY Radar operated at 53.5 MHz has been used in a five-beam configuration to study dynamical processes at gravity wave periods in the summer polar mesosphere. A case study of a gravity wave with a period of about 9 min is presented and analysed in some detail. The three-dimensional wave number vector is determined from the phase information of the 9-min velocity oscillations obtained in all beam directions and all range gates. The horizontal wavelengths in the north and east direction are estimated to be about 60 and 50 km, respectively. The echo power variations, simultaneously observed at different beam pointing positions, are investigated using cross-correlation analysis. The results show that these wave-associated variations lead to horizontal and vertical deformation of the echoing layers. The horizontal wavelength in the north-south direction, derived from the echo power modification, is in good agreement with the one obtained from the velocity analysis.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s00585-996-1186-0

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8

Electronic Resource

Remote sensing of the atmosphere by VHF radar experiments (1978)

Röttger, J. ; Klostermeyer, J. ; Czechowsky, P. ; [et al.]

Springer

Naturwissenschaften 65 (1978), S. 285-296

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ISSN: 1432-1904

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General

Notes: Abstract Problems in atmospheric dynamics, in particular in micro- and mesoscale processes, which can be solved by radar investigations, are summarized. The method of atmospheric radar experiments is described. Some relevant results obtained with the new SOUSY-VHF-Radar are presented, including observations of a warm-front passage, of layered structures, and of vertical and horizontal velocities in the troposphere. A power profile of radar echoes from heights up to the stratosphere proves that the SOUSY-VHF-Radar in its final operating state will be able to investigate structures and dynamics in the mesosphere too.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00368369

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