Model calculations of possible ionospheric backscatter echo area for a mid-latitude HF radar

HF ray path calculation is performed in order to identify possible ionospheric backscatter echo area for an HF radar at mid-latitude. The calculation is made on the basis of the R.M. Jones and J.J. Stephenson (U.S. Dept. of Commerce, OT Rep. 75-76, 1975) HF ray path tracing algorithm plus the IRI-2001 ionosphere model. It is shown that depending on the local time and geomagnetic activity, the possible ionospheric backscatter regions have different distributions. In any case the backscatter region is large enough, indicating the capability of a planned HF radar in Hokkaido (43.5°N, 143.6°E), Japan

Studies on the Determination of Tellurium and Selenium. II : Determination of Tellurium and Selenium in Presence of Sulfuric Acid with Sulfur Dioxide

Tellurium was precipitated quantitatively with sulfur dioxide from the hydrochloric acid solution of 2N even in the presence of 5 ml of sulfuric acid in the total volume of 100ml, but not in a higher concentration than 9N of the hydrochloric acid. Selenium was precipitated quantitatively under the same condition as in the case of tellurium, when the hydrochloric acid concentration was higher than 4 N. Therefore, the separation of tellurium and selenium would be possible also in the presence of sulfuric acid, when selenium was precipitated in a higher concentration than 9N of hydrochloric acid and tellurium was precipitated from the filtrate after diluting the filtrate to 2 N of the acid

Implications of statistics of near-range Doppler velocity observed with the Syowa East HF radar

A large data-set of line-of-sight Doppler velocity obtained with the Antarctic Syowa East HF radar from February to December 1997 is analyzed to discuss the statistical characteristics of Doppler velocity (V_D) at ranges of 180-1200 km and their implications. Syowa Station K-indices during the observation period were between 0 and 7 with a maximum occurrence at K = 1. On average V_D has a minimum of about 100 m/s at 180-225 km ranges. With increasing range it increases monotonically to attain a maximum of 300-350 m/s at 400-500 km, decreases gradually to reach 250-300 m/s at about 700km, and again increases slowly at farther ranges. These values of V_D and the range vary depending on both local time and radar beam direction. In the light of recent knowledge of plasma instabilities in the ionosphere we suggest that such range profile of V_D is mainly caused by the combined effects of altitude-dependent phase velocities of ionospheric plasma waves, HF wave refraction due to enhanced E region electron density, and latitude-dependent electric field. We infer that the low V_D (～ 100 m/s) at ranges of 180-225 km may originate in part from neutral winds and/or turbulence of the neutral atmosphere

Summer time dayside ionospheric backscatter echoes observed by the SuperDARN Hokkaido radar

第2回極域科学シンポジウム/第35回極域宙空圏シンポジウム 11月14日（月） 国立極地研究所 2階大会議

E region echoes observed with the Syowa HF radar under disturbed geomagnetic conditions

E region radar echo parameters (echo power, Doppler velocity and spectral width) obtained with the Syowa Station HF radar under disturbed geomagnetic conditions are qualitatively analyzed to study how echoing region changes due to HF wave refraction caused by ionospheric disturbance. It is found that with increasing disturbance level, echo ranges become shorter because of wave refraction during propagation due to more enhanced D and E region electron density. When geomagnetic H component variation (ΔH) is less than about -900 nT, echoes are returned from the central E region where geomagnetic aspect angle is close to zero. When ΔH is very high (= - 1500nT), the echoes are backscattered from the D and lower E regions and their power, Doppler velocity and spectral width are largely suppressed. The results suggest that we must always consider, more or less, wave refraction effect in analyzing near-range E region HF radar echoes

New auroral spectrometer using an acousto-optic tunable filter

This paper reports the performance and capability of a newly developed zenith spectrometer (for measurements of airglow and aurora) that uses an acousto-optic tunable filter (AOTF). The AOTF can scan the pass-band of the spectrometer between 450 and 700 nm with a bandwidth of 2-3 nm by changing the RF driver frequency from 180 to 100 MHz. The absolute sensitivity of the spectrometer is ～0.1-1.5 counts/Rayleigh/s per spectral step. The spectrometer is fully automated. The O I (557.7 nm) airglow line can be clearly identified in test observations of midlatitude airglow performed at Shigaraki Observatory, Japan. Based on an estimate of the signal-to-noise ratio, we conclude that the full auroral spectrum (450-700) nm can be measured by the AOTF spectrometer with a time resolution of ～100 s and a signal-to-noise ratio of ～100 for an auroral emission intensity of 10 kR. An example of the auroral spectra is shown for observations made at Syowa Station in Antarctica

Statistical study of Doppler velocity and echo power around 75゜ magnetic latitude using data obtained with the Syowa East HF radar in 1997

We present the statistical relationship between the echo power and Doppler velocity of radar echoes observed with the Syowa East HF radar in Antarctica in 1997. The objective of this analysis was to clarify the mechanisms by which high-latitude (～75° magnetic latitude) F region irregularities are generated. Although data points are scattered over a large area, a positive correlation between Doppler velocity and echo power appears to be present. This relationship can be interpreted in terms of gradient-drift instability, which is the most probable cause of the decameter-scale irregularities in the F region. The positive correlation deteriorates in the afternoon and midnight sectors, probably as a result of other mechanisms related to particle precipitation (field-aligned current), such as the current-convective instability

Statistical analysis of echo power, Doppler velocity and spectral width obtained with the Syowa South HF radar

Statistical analyses are made of the physical parameters (echo power, Doppler velocity and spectral width) of Doppler spectra obtained in September 1995 with the Syowa South HF radar. We present time and range distributions and histograms of the parameters and cross-correlations among them. With K index at Syowa Station the distributions and histograms vary slightly but the correlations do not change so much. The most noticeable feature is that there is a positive correlation between the absolute values of Doppler velocity and echo power. This relationship can be interpreted in terms of the gradient-drift instability which is the most probable cause to generate decameter-scale irregularities in the F-region ionosphere

Characteristics of polar mesosphere summer echoes observed with oblique incidence HF radars at Syowa Station

Polar mesosphere summer echoes(PMSE) are strong VHF-UHF radar echoes from the high-latitude cold mesopause at around 80-90km altitudes in summer. Although a number of in situ and radar observations of PMSE have been made until now, generation mechanisms of PMSE and scattering processes of radar waves due to PMSE-associated irregularities are still controversial. In this paper, PMSE detected for the first time in December 1997 and January 1998 with the oblique incidence SuperDARN HF radars at Syowa Station, Antarctica(69.0°S , 39.6°E ), are summarized to reveal the characteristics of PMSE at HF band. They appear at slant ranges of 180-315km with elevation angles of 15°-30° between 1030 and 1230UT or between 2100 and 0140UT, and are characterized by durations of 65-110min with intermittent subsidence and quasi-periodic oscillations of echo power with periods of 5-20min, due to short-period atmospheric gravity waves. Detailed analysis of the December 15, 1997 event reveals the followings: 1) echo power is less than 30dB, Doppler velocity between -40 and +40m/s, and spectral width less than 50m/s, respectively, 2) there exists no particular correlation among power, velocity and width, and 3) PMSE occurrence can be related to eastward neutral wind due to semi-diurnal tide that may induce the decrease in the mesospheric temperature