Motokazu Hirono

Observation of stratospheric ozone layer by a XeCl laser radar

We observed the stratospheric ozone layer by a newly designed powerful laser radar using a differential‐absorption technique. A discharge‐pumped XeCl excimer laser with a 308‐nm wavelength was used as an emitter in this system. The observed ozone concentrations in an altitude range 16–25 km are in good agreement with those measured by radiosonde. The present system is promising for the continuous monitoring of the stratospheric ozone concentration because of the simplicity of the construction.

Applications of excimer lasers to laser-radar observations of the upper atmosphere

Development of efficient ultraviolet (UV) rare-gas halide excimer lasers has added new possibilities for laser radar (lidar) technique for monitoring atmospheric constituents. An experimental result of the observation of the stratospheric ozone layer by a XeCl laser (308 nm) based on the differential-absorption-lidar (DIAL) technique is described. The obtained ozone profile in an altitude range of 15- 25 km are in good agreement with those measured by radiosonde. The measurement error is analyzed for one-wavelength lidar. The accuracy is estimated to be 10-30 percent within an altitude range of 10-30 km and at a range resolution of 1 km or less. The accuracy and the resolution are higher than the Umkehr method. Recent progress of rare-gas halide lasers and their frequency conversion techniques as a transmitter for lidar are reviewed. Many powerful and reliable new sources are available in almost every wavelength over the near UV region. New applications of these UV sources to the lidar system are also briefly discussed, especially from the scientific field on the middle atmosphere.

The El Chichon volcanic cloud in the stratosphere: lidar observation at Fukuoka and numerical simulation

Abstract The stratospheric volcanic cloud from the eruption.of El Chichon, Mexico, on 4 April 1982 was observed routinely by a Nd: YAG lidar system from 18 April 1982 at Kyushu University, Fukuoka, Japan. The observed layers of the cloud above 20 km were in the easterly wind region and those below 20 km were in the westerly region. The main part of the cloud mass was in the upper layer. This upper layer broadened slowly until September 1982, then broadened rapidly and merged with the lower layer as the easterly wind changed to the westerly wind. The vertical eddy diffusion coefficient estimated from the broadening of the upper layer was much smaller than the value usually used in the one-dimensional model calculation of chemical components until September and subsequently remained at about the same value. The increase of the integrated backscattering coefficient (IBC) was about two orders of magnitude larger than the largest increase after volcanic injections for the last 10 years. The IBC reached a maximum value on 3 May and gradually decreased until August 1982, then re-increased until December 1982. The IBC between December 1982 and February 1983 was about the same value as in May 1982. Using the one-dimensional stratospheric sulfate aerosol model simulations it was concluded that to explain the broadening of the upper layer an eddy diffusion coefficient of about 10 2 cm 2 s -1 would be needed in the easterly wind region in summer. It was also concluded that the IBC re-increase was caused after advective horizontal transport from lower to higher latitudes by chemical reactions within the upper layer without meridional diffusion during summer and that the transport was controlled by nucleation, which gives rise to small particles, a decreasing settling velocity of the volcanic cloud and then the cloud being less affected by horizontal transport.

Measurement of stratospheric vertical ozone distribution with a Xe-Cl lidar; estimated influence of aerosols.

Measurements of stratospheric vertical ozone distribution have been made with a Xe-Cl laser based on the differential absorption lidar technique. The effect of stratospheric aerosols observed by a frequency-doubled Nd:YAG lidar on the measured ozone density is corrected. Fourteen data sets were obtained at Fukuoka (33 degrees N) from September to December 1979. The ozone profiles obtained in an altitude range of 15-25 km are in good agreement with those measured by ozonesondes. The Xe-Cl lidar is promising for the continuous monitoring of stratospheric ozone concentration.

Lidar observation of sudden increases of aerosols in the stratosphere caused by volcanic injections. I. Soufrière 1979 event

Abstract A sudden increase of stratospheric aerosols over Fukuoka was observed by ruby lidar in May 1979 and the increase lasted until the end of June 1979. The event is thought to be caused by explosive injection of La Soufriere on 13–17 April 1979. The mean meridional speed of the volcanic aerosol is somewhat higher than that observed at the Fuego event in 1974. Significant increase of mixing ratio of aerosols is seen at the altitude about 16 km and often in the lower region. The progress in time of the change of profiles can be accounted for by the settling of particles with radius 1–3 μm. The integrated aerosol backscattering above the tropopause was of the order of 3 × 10−5sr−1 about 11 8 of that at the Fuego event and several times more aerosols were observed as descending in the upper troposphere immediately below the tropopause. The cause of high advection velocity of volcanic air parcels is briefly discussed.

Lidar observation of sudden increase of aerosols in the stratosphere caused by volcanic injections—II. Sierra Negra event

Abstract A striking disturbance in stratospheric aerosols over Fukuoka was observed by Nd-YAG laser radar in December 1979. It began with the appearance of a thin layer of enhanced scattering at an altitude of about 17 km and revealed remarkable variations of the layer in time and height. Measurements at two wavelengths suggest that the aerosols changed in size distribution, and the disturbance is inferred to be due to the Sierra Negra eruption. The integrated aerosol backscattering above the tropopause reached about 8 × 10 −5 sr −1 ; i.e. some six times that of the Soufriere event when converted to the ruby wavelength. The mean meridional transport speeds of the dust clouds were much larger than ever observed previously and this may be due to the activation of meridional transport associated with the Canadian sudden stratospheric warming in November-December 1979

A reliable efficient forced oscillator dye laser to measure the upper atmospheric sodium layer.

A tunable dye laser made up of a dye oscillator and a flashlamp-pumped dye amplifier with an effective power gain of 111, which had an energy output of 500 mJ in a bandwidth 0.01 nm at 589 nm, was applied to constant long-term monitoring of the mesospheric sodium layer. The technical properties and emission characteristics of the oscillator-amplifier system, and the observed profile of mesospheric sodium are described.

Lidar observations of atmospheric aerosols following the 1980 eruption Of Mt. St. Helens. Part I

Abstract A significant increase and subsequent variations of stratospheric aerosols caused by the eruption of Mt.St. Helens on 18 May 1980 have been observed using a Yag lidar at a wavelength of 1.06 μm for a period of one year at Fukuoka, Japan. The time variation of aerosols is compared with numerical results of two-dimensional model calculations, which show longer decay times, especially for column concentrations of aerosols. In the upper layer, transported by the easterly wind during summer, the effective vertical diffusion is quite small and this is explained,at least partly, by the influence of vertical shear of the easterly wind, which balances vertical eddy diffusion. Finally, it is suggested that the settling of giant particles might increase the precipitation near the Baiu front over Japan for July and August.