Global Lightning Activity and Its Relation to the Atmospheric Variability Measured by ELF Observations at Syowa Station

The Tenth Symposium on Polar Science/Special session: [S] Future plan of Antarctic research: Towards phase X of the Japanese Antarctic Research Project (2022-2028) and beyond, Tue. 3 Dec. / Entrance Hall (1st floor) at National Institute of Polar Research (NIPR

SENSU SuperDARN imaging radars and JARE project phase IX

第6回極域科学シンポジウム[OS] 宙空圏11月16日（月）　国立極地研究所１階交流アトリウ

New sounding modes for SuperDARN HF radars

We have developed several new sounding modes for SuperDARN HF radars to increase operation flexibility ("Nasu" mode, etc.) as well as to obtain both higher time resolution special camping beams data and global convection patterns simultaneously ("Basyouhu" mode). Utilizing the new "Basyouhu" mode, we were able to detect, for the first time, very rapidly moving transient phenomena (about 20 km/s) passing through the SuperDARN radar\u27s field of view without any ambiguity or uncertainty

A new method for monitoring and removing SuperDARN radar DC offsets

DC offsets in quadrature outputs (I/Q signals) pertinent to the SuperDARN HF radars can cause problems in determining and analysing auto-correlation functions, cross-correlation functions and raw time series data if they are not negligible. We have developed a new code to monitor and remove DC offsets. To obtain correct DC offset levels and noise levels, the offsets can be best removed using I/Q signals during the receive-only period, i.e., during each clear frequency search stage. We have implemented the new code in the current radar operating system, installed it at the SENSU Syowa radars, and have been obtaining and removing DC offset values continuously since October 2001

Characteristics of solar flare effect in the high-latitude ionosphere as observed by the SuperDARN radars

Sudden perturbations of the ground magnetic fields at solar flares are called geomagnetic Solar Flare Effect (SFE). An SFE is the extra ionization produced by the X-ray emission from a solar flare. We analyzed 10 intense SFE events from 1996 to 1998 using SuperDARN HF radar network and other instruments located in the northern hemisphere. Two typical ionospheric signatures associated with the solar flares are revealed, one is a sudden fade-out of backscatter echoes, and the other is an appearance or variation of field-aligned irregularities. Sudden fade-out is observed only in the sunlit hemisphere, and the appearance or variation of irregularities are observed only near the terminator. In addition, we investigated one event out of ten in detail and found that there exists a discontinuity of the electric field or conductivity around the irregularity. This fact suggests that the variation of conductivity or electric field in the E region could affect the irregularity formation in the F region

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

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

Improvement of SuperDARN electric field and refractive index measurements

第3回極域科学シンポジウム/第36回極域宙空圏シンポジウム 11月26日（月）、27日（火） 国立極地研究所 2階ラウン