Isao Murata

Tsunami ascending in rivers as an undular bore

At time of the 1983 Japan Sea tsunami, waves in the form of a bore ascended many rivers. In some cases, bores had the form of one initial wave with a train of smaller waves, and in other cases, such a wave train did not appear and only a step with a flat water surface behind was observed. In the present study, it is clarified that both undular-type and nonundular-type bores can be recognized as solutions of the KdV-Burgers equation which was introduced by Johnson in 1972. Numerically obtained analytical solutions and results of laboratory experiments are compared.

Recent Northern Hemisphere stratospheric HCl increase due to atmospheric circulation changes

The abundance of chlorine in the Earth’s atmosphere increased considerably during the 1970s to 1990s, following large emissions of anthropogenic long-lived chlorine-containing source gases, notably the chlorofluorocarbons. The chemical inertness of chlorofluorocarbons allows their transport and mixing throughout the troposphere on a global scale, before they reach the stratosphere where they release chlorine atoms that cause ozone depletion. The large ozone loss over Antarctica was the key observation that stimulated the definition and signing in 1987 of the Montreal Protocol, an international treaty establishing a schedule to reduce the production of the major chlorine- and bromine-containing halocarbons. Owing to its implementation, the near-surface total chlorine concentration showed a maximum in 1993, followed by a decrease of half a per cent to one per cent per year, in line with expectations. Remote-sensing data have revealed a peak in stratospheric chlorine after 1996, then a decrease of close to one per cent per year, in agreement with the surface observations of the chlorine source gases and model calculations. Here we present ground-based and satellite data that show a recent and significant increase, at the 2σ level, in hydrogen chloride (HCl), the main stratospheric chlorine reservoir, starting around 2007 in the lower stratosphere of the Northern Hemisphere, in contrast with the ongoing monotonic decrease of near-surface source gases. Using model simulations, we attribute this trend anomaly to a slowdown in the Northern Hemisphere atmospheric circulation, occurring over several consecutive years, transporting more aged air to the lower stratosphere, and characterized by a larger relative conversion of source gases to HCl. This short-term dynamical variability will also affect other stratospheric tracers and needs to be accounted for when studying the evolution of the stratospheric ozone layer.

BSMILES - a balloon-borne superconducting submillimeter-wave limb-emission sounder for stratospheric measurements

A balloon-borne superconducting submillimeter-wave limb-emission sounder (BSMILES) was developed to observe thermal emission lines from stratospheric minor constituents. BSMILES carries a 300-mm-diameter offset parabolic antenna, a 624-639-GHz superconductor-insulator-superconductor (SIS) receiver, a three-axis fiber-optical gyroscope, and an acousto-optical spectrometer. BSMILES was launched from the Pacific Coast of Japan. All systems operated properly and emission line spectra of stratospheric gases, such as O/sub 3/, HCl, HO/sub 2/, and O/sub 3/ isotopes were measured. The system noise temperature in double sideband (DSB) during the flight was less than 460 K over the observing bandwidth with a best value of 330 K that is 11 times as large as the quantum limit (11h/spl nu//k/sub B/). After the observation, the gondola splashed down in the Pacific Ocean and was retrieved. Almost all instruments were waterproofed, and it has been proved that they are reusable.

Doppler detection of hydroxyl column abundance in the middle atmosphere

The hydroxyl column abundance in the middle atmosphere is measured with ground-based uv spectroscopy using the sun as a light source. The present method is distinctive in that it utilizes the Doppler shift of the solar spectrum due to the solar rotation to discriminate the slight terrestrial hydroxyl absorption from prominent solar features. By comparing the spectra measured on the east and the west edges of the solar disk, it is possible to cancel out most of the solar structures and to make the terrestrial features much more evident.

Carbon monoxide column abundances and tropospheric concentrations retrieved from high resolution ground-based infrared solar spectra at 43.5°N over Japan

High spectral resolution (0.0024 cm−1), ground-based infrared (IR) solar spectra were recorded at Rikubetsu, Japan (43.5°N, 143.8°E), by a Fourier transform infrared (FTIR) spectrometer covering the 4.8-μm fundamental absorption band of carbon monoxide (CO). Total vertical CO columns and tropospheric concentrations, from May 1995 to May 1996, were retrieved from these spectra using an iterative inversion algorithm. Microwindows at 2111.00–2112.00 cm−1 and 2157.40–2159.20 cm−1 were used for the retrievals. Tropospheric CO concentrations above Rikubetsu retrieved from the IR solar spectra are in good agreement with aircraft measurements performed in the nearby area in recent years. The data exhibit seasonal variations in tropospheric CO concentrations. The averaged mixing ratios between 0 and 3 km are 219±26 parts per billion by volume (ppbv) in April and 115±7 ppbv in September. The data also show CO concentrations and seasonal variations decreasing with altitude. The vertical change in CO concentration is the greatest in spring and the smallest in fall. A maximum CO column of 3.31±0.34×1018 molecules cm−2 in April and a minimum of 2.04±0.10×1018 molecules cm−2 in September were observed. The CO column above Rikubetsu is consistent with observations at Kitt Peak, the International Scientific Station of the Jungfraujoch (ISSJ), and Zvenigorod, considering differences in altitude and latitude between the observatories.

Assessment of the uncertainties in the NO2 and O3 measurements by visible spectrometers

The column amounts of nitrogen dioxide (NO2) and ozone (O3) were measured using a visible spectrometer based on the twilight zenith-sky technique at two observatories located at similar latitudes in the northern part of Japan separated by a distance of 150 km. The measurements began in April 1991 at the Moshiri Observatory (44.4°N, 142.3°E) and in April 1994 at the Rikubetsu Observatory (43.5°N, 143.8°E). Since weather conditions and the possible influence from tropospheric pollution were not always identical at these two observatories, the overall accuracy of the measurements was studied comparing these data sets. The first year data obtained at a solar zenith angle of 90 degrees indicated that the NO2 slant column values at sunrise and sunset agreed within 0.36 and 0.54 × 1016 cm-2, respectively, corresponding to 5 % (June) and to 12 % (December) of the columns. The O3 values agreed within 0.76 × 1019 cm-2, corresponding to 4 % (March) ∼6 % (August) of the columns, although a part of the difference was systematic. The O3 column amounts were also compared to those obtained by the Dobson spectrometer at Sapporo (43.5°N, 143.8°E), whose latitude is similar to these observatories. When an air mass factor of 17.5 was used, the two-year Moshiri vertical column values agreed with the Dobson direct sun values to within 15 Dobson Units, or 3 ∼ 6 % of the column. The difference between the two values was found to be due partly to the change in the air mass factor caused by seasonal and day-to-day changes in the shape of the O3 vertical profiles. These results confirm the reliability of the NO2 and O3 measurements by visible spectrometers at these sites for the Network for the Detection of Stratospheric Change (NDSC).

Retrieval of vertical profiles of ozone from high-resolution infrared solar spectra at Rikubetsu, Japan

Vertical profiles of volume mixing ratios (VMRs) of O 3 were retrieved from high-resolution, infrared solar absorption spectra taken at Rikubetsu, Japan (43.5°N), by a ground-based Fourier transform infrared spectrometer (FTIR). The VMR profile retrieval is based on an iterative inversion algorithm, which utilizes line-by-line, layer-by-layer calculations. Two different microwindow regions (1146 and 1163 cm -1 ) were used for the retrieval calculations. Eighty ozone vertical profiles were retrieved from the two spectral regions from 40 spectra and were compared with 17 ozonesonde measurements from a nearby station. Average differences between 18 and 34 km were less than ±12% for both 1146 and 1163 cm -1 retrievals. The standard deviation of the average differences between 18 and 34 km were less than 19% and 14% for respective windows. Effects of several different factors on errors of profile retrievals, such as initial guess, temperature profiles, and instrument line shape functions, were evaluated by numerical simulation. The estimated errors were extremely consistent with the observed errors between 18 and 34 km, suggesting that the FTIR was optically well adjusted. In general, retrieval of the O 3 profile gives VMRs in an accuracy better than 40% at 14 km, improving to 10-15% between 18 and 30 km, with precision of 30% and 20% for these altitude ranges, respectively.

Stratospheric ozone and ClO measurement using Balloon-Borne submillimeter limb sounder

Stratospheric O/sub 3/ and ClO were simultaneously observed off the northeastern coast of Japan by the Balloon-Borne Superconducting Submillimeter-Wave Limb-Emission Sounder (BSMILES) developed at National Institute of Information and Communications Technology. BSMILES is a highly sensitive submillimeter radiometer that exploits the superconductor-insulator-superconductor (SIS) technology for atmospheric research. This paper presents the first BSMILES spectra, and describes the details of the calibration process. The vertical profiles of O/sub 3/ and ClO have been also retrieved. In spite of some calibration uncertainties the obtained profiles are in relatively good agreement with previous and other available measurements.

Earth-satellite-Earth laser long-path absorption experiment using the Retroreflector in Space (RIS) on the Advanced Earth Observing Satellite (ADEOS)

This paper reports the results of the laser long-path absorption experiments carried out with the Retroreflector in Space (RIS) on the Advanced Earth Observing Satellite (ADEOS). The RIS is a 0.5 m diameter single-element hollow retroreflector with a unique optical design which uses a curved mirror surface to correct velocity aberrations caused by the satellite movement. In the RIS experiments a laser beam was transmitted from a ground station, reflected by the RIS, and received back at the ground station. The absorption of the intervening atmosphere was measured in the round-trip optical path. After the launch of the ADEOS in August 1996, the optical characteristics of the RIS were tested, and it was confirmed that the RIS worked well in orbit. The spectroscopic measurement was carried out with the single-longitudinal-mode TEA lasers by means of the method utilizing the Doppler shift of the reflected beam caused by the movement of the satellite. The spectrum of ozone was successfully measured in the region, and the measurement of the column contents of ozone was validated with the simultaneous heterodyne spectrometer measurement. In June 1997, however, the experiment with the RIS was discontinued due to the malfunction of the ADEOS solar paddle.

Measurements of stratospheric ozone with a balloon-borne optical ozone sensor

We have developed a balloon-borne optical ozone sensor and since 1994 have observed the vertical distribution of upper stratospheric ozone in summer using a thin-film high-altitude balloon at Sanriku, Japan. The sensor measures solar ultraviolet radiation in ozone Hartley band absorption at wavelength of 300 nm, and vertical ozone distributions higher than 15 km were obtained with 1 km resolution. The temporal variations of ozone concentrations above 30 km from 1994 to 2007 show correlations with 11-year variation of solar F10.7 flux and we could not detect decreasing or increasing trends.