EISCAT observations of tidal modes in the lower thermosphere

Williams, P. J. S.; Virdi, T. S.

doi:10.1016/0021-9169(89)90055-x

Cited by 46 publications

(25 citation statements)

References 11 publications

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“…With these models i is found equal to ν in at 121 ± 0.5 km altitude under all conditions. There is not yet a consensus for the choice of the model for the ion-neutral collision frequency, and therefore it is possible that it can introduce uncertainties to the derived wind velocities at the uppermost heights (e.g., Johnson and Williams and Virdi, 1989). The MF radar co-located at the EISCAT Tromsø site (Hall, 2001) observed continually the horizontal mesospheric wind (70-91 km) with 3 km altitude and 5 min temporal resolutions.…”

Section: Data and Data Analysismentioning

confidence: 99%

EISCAT observational results during the DELTA campaign

et al. 2006

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This paper aims at describing the ionospheric conditions during the DELTA (Dynamics and Energetics of the Lower Thermosphere in Aurora) campaign period based on EISCAT radar observations conducted at Tromsø (69.6 • N, 19.2 • E). We conducted EISCAT UHF radar observations on December 5 and from December 8 to December 13, 2004 with a beam-scanning mode for a total of 74 hours. Except for December 8 during a 2 hr interval operation, we operated the EISCAT UHF radar for 12 hour intervals everyday to make it possible to derive semidiurnal tidal amplitudes and phases in the lower thermosphere. Observed electron densities and derived electric fields by the EISCAT UHF radar indicate that magnetospheric activity was high during the period from December 5 to 13 except for the night of December 13. Derived semidiurnal amplitudes during December 9-12, 2004 exhibited a day to day variation at and below 110 km, while the corresponding phase was relatively stable over the four days except for the zonal component on December 12. Neutral and electron temperatures measured by the DELTA rocket were compared with neutral/ion and electron temperatures from the EISCAT UHF radar observations. Comparison of neutral/ion temperatures show some agreement, while poor agreements were found for the electron temperature. Possible causes of the discrepancy are discussed.

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Section: Data and Data Analysismentioning

confidence: 99%

EISCAT observational results during the DELTA campaign

et al. 2006

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“…Many efforts have been invested in studying AGWs and TIDs both experimentally and theoretically (see, for example, Francis, 1975;Yeh and Liu, 1974;Hunsucker, 1982;Crowley and McCrea, 1988;Williams and Virdi, 1989;Williams, 1996;Williams et al, 1993;Hocke et al, 1996). TIDs are usually grouped into two classifications: largescale and medium-scale, depending on their wavelengths and periods.…”

Section: Introductionmentioning

confidence: 99%

Probing of medium-scale traveling ionospheric disturbances using HF-induced scatter targets

et al. 2006

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Abstract.Experimental results from the Tromsø and Sura heating experiments at high and mid-latitudes are examined. It is shown that the combination of HF-induced target and bi-static HF Doppler radio scatter observations is a profitable method for probing medium-scale traveling ionospheric disturbances (TIDs) at high and mid-latitudes. HF ionospheric modification experiments provide a way of producing the HF-induced scatter target in a controlled manner at altitudes where the sensitivity to TIDs is highest. Bi-static HF Doppler radio scatter observations were carried out on the LondonTromsø-St. Petersburg path in the course of a Tromsø heating experiment on 16 November 2004 when the pump wave was reflected from an auroral Es-layer. During Sura heating experiments on 19 and 20 August 2004, when the HF pump wave was reflected from the F2 ionospheric layer, multiposition bi-static HF Doppler radio scatter observations were simultaneously performed at three reception points including St. Petersburg, Kharkov, and Rostov-on-Don. Ray tracing and Doppler shift simulations were made for all experiments. A computational technique has been developed allowing the reconstruction of the TID phase velocities from multi-position bi-static HF Doppler scatters. Parameters of medium-scale TIDs were found. In all experiments they were observed in the evening and pre-midnight hours. TIDs in the auroral E-region with periods of about 23 min were traveling southward at speeds of 210 m/s. TIDs in the mid-latitudinalCorrespondence to: N. F. Blagoveshchenskaya (nataly@aari.nw.ru) F-region with periods from 20 to 45 min travelled at speeds between 40 and 150 m/s. During quiet magnetic conditions the waves were traveling in the north-east direction. In disturbed conditions the waves were moving in the south-west direction with higher speeds as compared with quiet conditions. Possible sources for the atmospheric gravity waves at middle and high latitudes are discussed.

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“…To sort out such rather subtle effects from the background E-region neutral wind, it is important to establish the neutral wind pattern for the quiet E-region. This is the background for recent studies of the E-region neutral wind by Johnson et al (1987), Williams and Virdi (1989), Manson et al (1990Manson et al ( , 1992, Kunitake and Schlegel (1991) and Brekke et al (1994).…”

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confidence: 86%

“…In recent years data obtained by the advanced EISCAT (European Incoherent Scatter) facility located at Tromso, Norway (69.6°N,19.2°E, A = 66.3°) (Folkestad et al, 1983) has been used by several authors to derive the auroral E-region neutral wind for different geomagnetic conditions (Williams and Virdi, 1989;Manson et al, 1990Manson et al, , 1992Kunitake and Schlegel, 1991;Virdi and Williams, 1993;Brekke et al, 1994;Nozawa and Brekke, 1995;Kofman et al, 1996).…”

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confidence: 99%

“…Usually the tidal components at a particular height are derived by the method of a least squares fit (LSF). The fit is often made by determining the mean wind and amplitude and phase of one or more tidal components such as the diurnal, semidiurnal and shorter period tides; this has been done in the works of Johnson et al (1987), Williams and Virdi (1989), Manson et al (1990Manson et al ( , 1992, Johnson (1991), Johnson and Virdi (1991), Kunitake and Schlegel (1991), Virdi and Williams (1993), and Kofman et al (1996). Brekke et al (1994) introduced the method of Fast Fourier Transform (FFT; discrete Fourier transform) for spectral analysis of averaged 24-hour data sets of the neutral wind velocities at different E-region heights.…”

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Studies of the E-Region Neutral Wind in the Auroral Ionosphere Using Two Long-Run Data.

Nozawa

Brekke

Fujii

1997

J. geomagn. geoelec

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EISCAT data obtained in the auroral ionosphere have been analyzed in terms of the E-region neutral wind behavior at three heights of 101, 109, and 119 km. We have analyzed two extended CP-1-H runs conducted over four consecutive days each for 21-25 September 1987 and 16-20 March 1988. Mean winds as well as tidal amplitudes and phases derived by both Fast Fourier Transform (FFT) and least square fit (LSF) methods are compared with those of corresponding seasonal winds from the quiet-time statistical study by Brekke et al. (1994). During 21-25 September 1987 the mean zonal wind derived by FFT with filling in zeroes in the data gaps blows eastward with a maximum of -20 m s-1 between 101 and 119 km and its direction is consistent with the average quiet-time fall wind. The directions of mean meridional and vertical winds, however, are opposite to those of the fall wind. The amplitudes and phases of the tidal winds are in reasonable agreement with those found. for fall quiet time. At 119 km the zonal wind shows a large enhancement during the very geomagnetically disturbed period between 16 UT on 22 September and 05 UT on 23 September and also for about 5 hours after the end of the disturbed period. During 16-20 March 1988 the amplitudes of the mean meridional and vertical winds are very small while the mean zonal wind blows eastward with a maximum of less than 18 m s-1 between 101 and 119 km, which is about half as large as that of the average quiet-time spring wind. Most diurnal meridional and semidiurnal horizontal wind amplitudes between 101 and 119 km are also about half of those found for spring quiet time. The height profiles of phases for most components are much the same as those of the spring wind. Comparisons are made with results obtained by the Sondre Stromfjord IS radar and model predictions, and geomagnetic disturbance effects on the wind are discussed.

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EISCAT observations of tidal modes in the lower thermosphere

Cited by 46 publications

References 11 publications

EISCAT observational results during the DELTA campaign

EISCAT observational results during the DELTA campaign

Probing of medium-scale traveling ionospheric disturbances using HF-induced scatter targets

Studies of the E-Region Neutral Wind in the Auroral Ionosphere Using Two Long-Run Data.

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