Penetration of the non-migrating atmospheric diurnal tide into polar latitudes

Classical theory of atmospheric tide predicts the confinement of propagating diurnal tide to lower latitudes equatorward of 30° latitude for which diurnal frequency exceeds the local Coriolis frequency. Observations so far averaged over appropriate periods, however, suggest the pervasion of propagating tide at meteor heights especially in wintertime in view of vertical phase structure. These might possibly be interpreted by the numerical modeling as the penetration of non-migrating higher zonal wave number tides which can be propagating in the counter-stream Doppler effect of the background mean zonal wind

An overview of the terdiurnal tide observed by polar radars and optics

A terdiurnal 8hr period component is often observed in the radar and optical measurements of wind and temperature field at mesospheric heights. This might be either a global tidal wave of the 3rd harmonics of diurnal tide or locally confined gravity wave component or normal mode Lamb waves. Observationally, it has been found that in winter it is more evident and stable with longer vertical wavelength than in summer. Here, a brief overview is given in view of the latitudinal comparison of modeled and recently observed terdiurnal components, mostly at higher latitudes which might reflect higher order modes and relevant generation mechanism either by solar direct drive or by non-linear interaction or by local agent

Simulation of high energy tail of electron distribution function

This report presents Monte Carlo simulations of the electron energy distribution for alow ionized plasma interacting with the F-region neutral gas. The results show a depletion in theelectron distribution above 2 eV between 10 and 80 %, decreasing with altitude. The depletion ismainly due to electron energy loss to . This micro-physical energy transfer model gives goodagreement with optical observations of enhanced emissions from at 6300Å and EISCATUHF measurements of electron cooling during HF radio wave heating experiments. Someimplications for incoherent scatter spectra are derived. The results suggest that a weak(approximately 1000 times weaker than the ion-line) and wide (2 MHz) peak around +-1 MHz fromthe ion-line in the EISCAT VHF incoherent scatter spectrum should be a consequence of theelectron-neutral interaction

Initial results of Syowa MF radar observations in Antarctica

Observations of the neutral atmosphere from the mesosphere to the lower thermosphere were performed using the MF radar system that was installed at Syowa Station (69°S, 39°E), Antarctica in April 1999. The radar is equipped with four antennas and independent receivers and is able to conduct interferometric observations, such as meteor echo observations, in addition to observations based on conventional spaced antenna techniques. Observational parameters are carefully designed so that the same raw data can be processed using various analysis techniques, including correlation analyses, meteor echo analysis and electron density analysis. The radar equipment specifications and preliminary results of wind observations are presented

Vision-based Vehicle Navigation Using the Fluorescent Lamp Array on the Ceiling

In this paper, autonomous navigation based on a TV vision system on board a vehicle is proppsed. Our method is to use fluorescent lamp arrays on the ceiling as a lighthouse for vehicle motion. First, experimental study of vehicle control based on information from photo-sensors, set up on a TV screen, is worked out using an actual size model. Then, numerical simulations for this control scheme are carried out in detail. Moreover, a more vision-based approach is investigated which extracts information aspects from the images of fluorescent lamp arrays to realize more exact motion along the lamp array. Finally, a practical autonomous vehicle which is controlled by a photo-sensor system is constructed and its experimental results are shown

EISCAT Svalbard radar-derived atmospheric tidal features in the lower thermosphere as compared with the numerical modeling ATM2

The EISCAT Svalbard radar (ESR) has obtained neutral wind field data down to 90 km altitude in two period runs in August 1998. This has been rendered possible by successful elimination of ground clutter echoes by the ESR staff. Features of the obtained tidal components are then comparatively studied with the ATM2 (Atmospheric Tidal Modeling Version 2) steady tidal model which assumes climatological background zonal flow. It is found that the results are fairly consistent with theoretical predictions that the diurnal component is almost evanescent with some indication of propagating characteristics, and that the semi-diurnal one is dominated by short vertical wavelength higher order mode prevalent at higher latitudes. The ter-diurnal component is also not in contradiction with non-linear interaction theory. Convincing delineation of these behaviors, however, awaits further study on the zonal wave number characteristics of relevant waves by longitudinal network collaborations

Auroral O+ 732/733 nm emission and its relation to ion upflow

Observations of auroral oxygen ion emission at 732/733 nm were made at the Aurora station in Longyearbyen (78.2.N, 16.3.E; lm=74.9.) using an all-sky spectrograph (ASG) during the winter season of 2000/2001. A statistical analysis showed that the highest occurrence of oxygen ion auroras at Longyearbyen was seen in the dayside of the 09-12MLT region; the intensities of these auroras were also larger than those on the night side. To study the mechanism of ion up゜ow in the polar ionosphere, ASG data obtained on December 7, 2000, was analyzed together with simultaneous ionospheric data obtained by EISCAT Svalbard radar (ESR). Enhancements of electron temperature and ion upward velocity were associated with an increase in the auroral OII intensity at the magnetic zenith. This result suggests that an ambipolar electric field associated with electron temperature enhancement caused by soft electron precipitation may be involved in the mechanisms that drive ionospheric ions upward

Auroral field-aligned currents by incoherent scatter plasma line observations in the E region

The aim of the Swedish-Japanese EISCAT campaign in February 1999 was to measure the ionospheric parameters inside and outside the auroral arcs. The ion line radar experiment was optimised to probe the E-region and lower F-region with as high a speed as possible. Two extra channels were used for the plasma line measurements covering the same altitudes, giving a total of 3 upshifted and 3 downshifted frequency bands of 25 kHz each. For most of the time the shifted channels were tuned to 3 (both), 4 (up), 5.5 (down) and 6.5 (both) MHz. Weak plasma line signals are seen whenever the radar is probing the diffuse aurora, corresponding to the relatively low plasma frequencies. At times when auroral arcs pass the radar beam, significant increases in return power are observed. Many cases with simultaneously up and down shifted plasma lines are recorded. In spite of the rather active environment, the highly optimised measurements enable investigation of the properties of the plasma lines. A modified theoretical incoherent scatter spectrum is used to explain the measure-ments. The general trend is an upgoing field-aligned suprathermal current in the diffuse aurora. There are also cases with strong suprathermal currents indicated by large differences in signal strength between up- and downshifted plasma lines. A full fit of the combined ion and plasma line spectra resulted in suprathermal electron distributions consistent with models

A new meridian imaging spectrogarph for the auroral spectroscopy

Spectroscopic and monochromatic imaging observations of emissions in the upper atmosphere are mutually complementary. A meridian imaging auroral spectrograph (ASG) that can measure a spectrum in the visible region along a meridian has been developed for research on the auroral physics and the polar upper-atmosphere dynamics. Combination of a fast optical system inherited from a monochromatic all-sky imager, a grism as a dispersive element, and a cooled CCD camera has enabled a wide field-of-view of 180° along a meridian, spectral coverage of 420-730 nm, spectral resolution of 1.5-2.0 nm, and high sensitivity to be obtained. The absolute sensitivity over a full-image field was calibrated using a National Institute of Standards and Technology (NIST) traceable integrating sphere and determined to be 0.06 cts/s/R at a wavelength of 560 nm at the zenith. The ASG was installed at Longyearbyen in March 2000, and routine operation was started in the 2000/2001 winter season. An example of an auroral spectral image is presented in this report to demonstrate the performance of the ASG