Takuo Tsuda

An Analysis Technique for Deriving Vector Winds and In-Beam Incidence Angles from Radar Interferometer Measurements

Abstract We present a method for deriving horizontal velocities, vertical velocities, and in-beam incidence angles from radar interferometer data. All parameters are calculated from the slope and intercept of straight lines fitted in a least-squares sense to the variation of the signal phase as a function of radial velocity for each pair of receiving antennas. Advantages of the method are that the calculations are computationally fast and simple, and the analysis leads to relatively simple expressions for the uncertainty in the velocity measurements.

Temperature enhancements and vertical winds in the lower thermosphere associated with auroral heating during the DELTA campaign

[1] A coordinated observation of the atmospheric response to auroral energy input in the polar lower thermosphere was conducted during the Dynamics and Energetics of the Lower Thermosphere in Aurora (DELTA) campaign. N2 rotational temperature was measured with a rocket-borne instrument launched from the Andoya Rocket Range, neutral winds were measured from auroral emissions at 557.7 nm with a Fabry-Perot Interferometer (FPI) at Skibotn and the KEOPS, and ionospheric parameters were measured with the European Incoherent Scatter (EISCAT) UHF radar at Tromso. Altitude profiles of the passive energy deposition rate and the particle heating rate were estimated using data taken with the EISCAT radar. The local temperature enhancement derived from the difference between the observed N2 rotational temperature and the MSISE-90 model neutral temperature were 70–140 K at 110–140 km altitude. The temperature increase rate derived from the estimated heating rates, however, cannot account for the temperature enhancement below 120 km, even considering the contribution of the neutral density to the estimated heating rate. The observed upward winds up to 40 m s �1 seem to respond nearly instantaneously to changes in the heating rates. Although the wind speeds cannot be explained by the estimated heating rate and the thermal expansion hypothesis, the present study suggests that the generation mechanism of the large vertical winds must be responsible for the fast response of the vertical wind to the heating event.

EISCAT observational results during the DELTA campaign

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.

Mesoscale observations of Joule heating near an auroral arc and ion‐neutral collision frequency in the polar cap E region

We report on the first meso-scale combined ionospheric and thermospheric observations, partly in the vicinity of an auroral arc, from Svalbard in the polar cap on 2 February 2010. The EISCAT Svalbard radar employed a novel scanning mode in order to obtain F- and E-region ion flows over an annular region centred on the radar. Simultaneously, a co-located Scanning Doppler Imager observed the E-region neutral winds and temperatures around 110 km altitude using the 557.7 nm auroral optical emission. Combining the ion and neutral data permits the E-region Joule heating to be estimated with an azimuthal spatial resolution of ∼64 km at a radius of ∼163 km from the radar. The spatial distribution of Joule heating shows significant meso-scale variation. The ion-neutral collision frequency is measured in the E-region by combining all the data over the entire field of view with only weak aurora present. The estimated ion-neutral collision frequency at ∼113 km altitude is in good agreement with the MSIS atmospheric model.

Tidal waves in the polar lower thermosphere observed using the EISCAT long run data set obtained in September 2005

[1] Characteristics are presented of the lower thermospheric wind from a long run data set obtained by the EISCAT UHF radar at Tromso (69.6°N, 19.2°E) over ~23 days, from September 6 to 29, 2005. The derived semidiurnal amplitude exhibited day-to-day variations (~5-30 ms -1 ) at and above 109 km, while the phase varied little with the day. We have found a mode change of the semidiurnal tide occurring during September 17-22, 2005. Between September 6 and 16, the vertical wavelengths were estimated to be ~58 km and ~76 km for the meridional and zonal components, respectively, while between September 23 and 29, they became less than -24 km. The day to day variability of the diurnal tide was less obvious than that of the semidiurnal tide. The diurnal amplitude of the meridional component increased with height except for 8 days between September 13 and 20, when the diurnal amplitudes were smaller values (<40 ms -1 ) at and above 111 km than those for the other intervals. Furthermore, the shapes of the altitude profiles of the meridional phase differ from those for the other intervals. We have evaluated contributions due to the electric field and the ion drag acceleration and showed that they were not the causes. From the analysis of 22.5 days of wind data, we found about 5-6 day oscillations in the lower thermosphere, probably where there were planetary wave activities in the lower thermosphere.

Meso-scale observations of Joule heating near an auroral arc and ion-neutral collision frequency in the polar cap E-region

We report on the first meso-scale combined ionospheric and thermospheric observations, partly in the vicinity of an auroral arc, from Svalbard in the polar cap on 2 February 2010. The EISCAT Svalbard radar employed a novel scanning mode in order to obtain F- and E-region ion flows over an annular region centred on the radar. Simultaneously, a co-located Scanning Doppler Imager observed the E-region neutral winds and temperatures around 110 km altitude using the 557.7 nm auroral optical emission. Combining the ion and neutral data permits the E-region Joule heating to be estimated with an azimuthal spatial resolution of ∼64 km at a radius of ∼163 km from the radar. The spatial distribution of Joule heating shows significant meso-scale variation. The ion-neutral collision frequency is measured in the E-region by combining all the data over the entire field of view with only weak aurora present. The estimated ion-neutral collision frequency at ∼113 km altitude is in good agreement with the MSIS atmospheric model.

All-solid-state, narrowband, pulsed sodium D 2 resonance light source

We are working on a sodium lidar project at the European Incoherent Scatter (EISCAT) association (69.6°N, 19.2°E) near Tromsø, Norway. Sodium lidar requires a pulsed narrowband sodium resonance light source [1]. Such a source based on nonlinear frequency mixing of all-solid-state lasers has several advantages over the more commonly used dye lasers [2]. However, it has not been put to practical use for sodium lidar.