A comparison of three methods of measuring tidal oscillations in the lower thermosphere using EISCAT common programmes

Williams, P. J. S.; Virdi, T. S.; Jones, G. O. L.; Huuskonen, A.

doi:10.1016/0021-9169(94)90072-8

Cited by 16 publications

(20 citation statements)

References 29 publications

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“…The ion-neutral momentum transfer collision frequency, ν in , is calculated according to Schunk and Walker (1973). In deriving the neutral velocity from the measured ionospheric parameters, there is an uncertainty caused by the ion-neutral collision frequency (Williams et al, 1994). The best way to avoid such uncertainties is to use data taken under conditions of low electric fields and high signal to noise ratio in a limited height range below about 120 km (Kofman, 1992;Williams et al, 1994).…”

Section: Methods Of Analysismentioning

confidence: 99%

“…In deriving the neutral velocity from the measured ionospheric parameters, there is an uncertainty caused by the ion-neutral collision frequency (Williams et al, 1994). The best way to avoid such uncertainties is to use data taken under conditions of low electric fields and high signal to noise ratio in a limited height range below about 120 km (Kofman, 1992;Williams et al, 1994). Although the present analysis was limited to the region below 120 km, it included the interval of electric field up to 80 mV/m.…”

Section: Methods Of Analysismentioning

confidence: 99%

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Ion and neutral temperature distributions in the E-region observed by the EISCAT Tromsø and Svalbard radars

et al. 2002

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Abstract. Simultaneous Common Program Two experiments by the EISCAT UHF radar at Tromsø and the EISCAT Svalbard radar at Longyearbyen from 00:00 to 15:00 UT on 22 September 1998 and 9 March 1999 have been utilized to investigate distributions of the ion and neutral temperatures in the E-region between 105 and 115 km. During the experiments, soft particle precipitations in the dayside cusp were observed over the Svalbard radar site by the Defense Meteorological Satellite Program (DMSP) F11 satellite. It is found that the dayside electric field in the regions of the lowlatitude boundary of the polar cap and the cusp was greater and more variable than that in the auroral region. The ion temperature, parallel to the geomagnetic field at Longyearbyen, was higher than that at Tromsø during the daytime from 06:00 to 12:00 UT. The steady-state ion energy equation has been applied to derive neutral temperature under the assumption of no significant heat transport and viscous heating. The estimated neutral temperature at Longyearbyen was also higher than that at Tromsø. The ion and neutral energy budget was discussed in terms of the ion frictional heating and the Joule heating. The results indicate two possibilities: either the neutral temperature was high in the low latitude boundary of the polar cap and the cusp, or the heat transport by the polar cap neutral winds toward the dayside sector was significant.

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Section: Methods Of Analysismentioning

confidence: 99%

Section: Methods Of Analysismentioning

confidence: 99%

Ion and neutral temperature distributions in the E-region observed by the EISCAT Tromsø and Svalbard radars

et al. 2002

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“…In particular, for this study, we have employed data from ground-based facilities which include medium-frequency, high-frequency, meteor, and incoherent-scatter radars, and satellite-borne optical instruments. Rather than discuss each technique in detail we will highlight only the issues pertinent to this study, and refer the reader to references on the speci®ed technique for more details (Evans, 1978;RoÈ ttger et al, 1983;Briggs, 1984;Roper, 1984;Hays et al, 1993;Shepherd et al, 1993;Virdi and Williams, 1993;Williams et al, 1994;Tsuda, 1995).…”

Section: Data Processingmentioning

confidence: 99%

An intercomparison between the GSWM, UARS, and ground based radar observations: a case-study in January 1993

et al. 1997

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Abstract. The Global-Scale Wave Model (GSWM) is a steady-state two-dimensional linearized model capable of simulating the solar tides and planetary waves. In an e ort to understand the capabilities and limitations of the GSWM throughout the upper mesosphere and thermosphere a comparative analysis with observational data is presented. A majority of the observational data used in this study was collected during the World Day campaign which ran from 20 January to 30 January 1993. During this campaign data from 18 ground-based observational sites across the globe and two instruments located on the UARS spacecraft were analyzed. Comparisons of these data with the simulations from the GSWM indicate that the GSWM results are in reasonable agreement with the observations. However, there are a number of cases where the agreement is not particularly good. One such instance is for the semidiurnal tide in the northern hemisphere, where the GSWM estimates may exceed observations by 50% . Through a number of numerical simulations, it appears that this discrepancy may be due to the eddy di usivity pro®les used by the GSWM. Other di erences relating to the diurnal tide and the quasi-two-day wave are presented and discussed. Additionally, a discussion on the biases and aliasing di culties which may arise in the observational data is also presented.

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“…MF radar winds were shown to be ∼0.65 of those from the Andenes data (rocket and VHF radar). However, until 1988 neutral wind velocities could not be derived below 100 km using the CP‐1 mode with the tristatic method [e.g., Williams et al , 1994]. Thus, during these campaigns too few events occurred for comparing winds derived from simultaneous EISCAT and MF radar data.…”

Section: Introductionmentioning

confidence: 99%

A comparison study of the auroral lower thermospheric neutral winds derived by the EISCAT UHF radar and the Tromsø medium frequency radar

et al. 2002

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[1] A comparative study of the neutral wind in the polar upper mesosphere/lower thermosphere is conducted using two radars, the European Incoherent Scatter (EISCAT) UHF radar (n = 931 MHz) and the Tromsø MF radar (n = 2.8 MHz) colocated in northern Scandinavia. Comparisons of winds are made in case studies as well as on a statistical basis. On the basis of simultaneous observations obtained by the two radars, comparisons over a height range from $90 to $100 km are made for about 20 days between February and October 1999. In these comparisons we directly compare temporal wind variations. On the other hand, mean winds as well as diurnal and semidiurnal components are derived using 1-month-averaged wind data obtained by the medium frequency (MF) radar for 1999. They are compared with those derived from 56 days of EISCAT data studied by Nozawa and Brekke [1999a, 1999b]. In the case studies, we have also utilized altitude profiles of electron density obtained by the EISCAT radar at and above 62 km height to determine the total reflection height as well as to estimate the effect of group retardation for 2.8 MHz radio wave. It can be seen that the effect of particle precipitation sometimes penetrates into the D region (down to $84 km). Generally, wind velocities derived by EISCAT with the monostatic method exhibit significant scatter with time below 100 km, while the number of the MF radar wind data sharply decreases above 90 km except for summer. These facts make the comparison difficult, but no significant departures between different radar winds are identified on an instantaneous basis. In the statistical studies, generally both altitude profiles are well connected, or continuous, but significant disagreements are observed for the mean wind and the tidal components for summer. On the basis of these comparisons, we raise strong concerns regarding the use of summer wind data above 91 km obtained by MF radar located at high latitude under high solar activity conditions. The wind values during the winter and equinox observed by the two radars are complementary. Thus here is a good opportunity to utilize wind data from the two different radars through a year, which then enables us to cover a wide height range (approximately 70-120 km). This wide range gives us good opportunities to examine the mesosphere/lower thermosphere coupling processes based on observational data. INDEX

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A comparison of three methods of measuring tidal oscillations in the lower thermosphere using EISCAT common programmes

Cited by 16 publications

References 29 publications

Ion and neutral temperature distributions in the E-region observed by the EISCAT Tromsø and Svalbard radars

Ion and neutral temperature distributions in the E-region observed by the EISCAT Tromsø and Svalbard radars

An intercomparison between the GSWM, UARS, and ground based radar observations: a case-study in January 1993

A comparison study of the auroral lower thermospheric neutral winds derived by the EISCAT UHF radar and the Tromsø medium frequency radar

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