Shoichiro Fukao

TL;DR: Two-dimensional total electron content (TEC) perturbations over Japan are mapped with the Geographical Survey Institute (GSI) GPS network, GEONET (GPS Earth Observation Network) as mentioned in this paper.

TL;DR: The MU (middle and upper atmosphere) radar of Japan is a 46.5-MHz pulse-modulated monostatic Doppler radar with an active phased array system as discussed by the authors.

Abstract: Fine structures E region field-aligned irregularities were observed on June 24–25, 1989, with the MU radar at Shigaraki, Japan (34.9°N, 136.1°E; geomagnetic latitude 25.0°N). The 3.2-m scale irregularities were observed with the MU radar in five main beam directions, each of which was nearly perpendicular to the geomagnetic field at 100 km altitude. Doppler spectra were obtained every 20 s with a range resolution of 600 m. Field-perpendicular echoes appeared from 2130 to 2330 LT and from 0400 to 1100 LT, times that correspond to postsunset and postsunrise period in the E region. A preliminary examination of the Doppler spectra indicates spectral widths of 50–120 m s−1 and the mean Doppler velocities are well below the ion acoustic speed. These spectral characteristics are consistent with those obtained in the equatorial and auroral electrojets, and have been attributed to the gradient drift instability. The echoes observed during the postsunset and postsunrise periods showed quite different morphologies in the time-height distribution. For this reason, they are classified into two types, ‘continuous’ and ‘quasi-periodic.’ The appearance of the ‘continuous’ echoes was mainly continuous in time and situated between 90 and 100 km altitude during the postsunrise period. The appearance of the ‘quasi-periodic’ echoes was intermittent with periods of 5–10 min and situated above 100 km altitude during the postsunset period. The quasi-periodic echoes showed phase propagation toward the radar, while the averaged mean Doppler velocity was away from the radar. By measuring the time delays in echo regions from five directions, an apparent westward motion (approximately 120 m s−1) of the irregularity regions was estimated.

TL;DR: In this paper, a least squares fitting procedure is used to remove instrumental biases inherent in the GPS satellite and receiver to construct two-dimensional maps of absolute TEC over Japan by using GPS data from more than 1000 GPS receivers.

TL;DR: In this article, the authors investigated regional and interannual variations of the rainy season over Indonesia using daily rainfall data during 1961-90, and found that the rainfall amount throughout a rainy season is not dependent upon the length of the rain season (between onset and withdrawal) in many areas.