Motowo Fujiwara

Polar stratospheric clouds observed by lidar over Spitsbergen in the winter of 1994/1995: Liquid particles and vertical “sandwich” structure

Polar stratospheric clouds (PSCs) were observed by lidar at Ny-Alesund, Spitsbergen, in December 1994 and January 1995. The backscattering coefficient at wavelengths of 1064 and 532 nm and the depolarization ratio at 532 nm of PSCs were measured by the lidar system. The stratospheric temperature was below the estimated frost point of nitric acid tri-hydrate (NAT) in the winter of 1994/1995. PSCs were observed more frequently in this low-temperature period than in previous winters since 1991. The characteristics of the PSCs were very variable but had a noticeable vertical “sandwich” structure in January in which a layer of liquid PSC particles at the altitude around 20 km existed between the two solid particle layers. The wavelength dependence of the backscattering shows that the size of both liquid and solid particles was larger than the average size of background stratospheric aerosols. Lidar observations of the liquid layer particles show characteristics in qualitative agreement with those expected from model PSC particles grown in ternary solutions of H2SO4, HNO3, and H2O with a temperature decrease. However, the observed backscattering coefficient and its wavelength dependence indicate that PSC particles require further growth than that predicted by the ternary solution model at temperature where most HNO3 molecules in the surrounding atmosphere are considered to be condensed on PSCs.

On the lidar‐observed sandwich structure of polar stratospheric clouds (PSCs): 1. Implications for the mixing state of the PSC particles

A vertical sandwich structure of (type I) polar stratospheric clouds (PSCs), in which layers of relative depolarization are above and below a scattering layer has frequently been observed by lidar at Ny-Alesund, Svalbard, when the stratospheric temperature decreases to near the frost point of ice. Using lidar observations and backward trajectory analysis, we studied the time evolution of this structure and its temperature history. The main difference between the temperature history of PSCs in the scattering layer and those in the depolarization layer was the temperature at which the structure is observed. The small increase in the scattering ratio over time at the altitude of the depolarization maximum implies a slow nucleation of solid particles. These lidar observations including temperature histories suggest that the sandwich structure arises from the external mixing of two different types of particles. A large fraction of liquid particles, grown at low temperature, constitutes the scattering layer, while at higher temperatures, a very small fraction of solid particles is responsible for the depolarization layer.

Calibration method for the lidar-observed stratospheric depolarization ratio in the presence of liquid aerosol particles

A fine calibration of the depolarization ratio is required for a detailed interpretation of lidar-observed polar stratospheric clouds. We propose a procedure for analyzing data by using atmospheric depolarization lidar. The method is based on a plot of deltaT versus (1 - RT(-1)), where deltaT is the total depolarization ratio and RT is the total backscattering ratio. Assuming that there are only spherical particles in some altitude ranges of the lidar data, the characteristics of the plot of deltaT versus (1 - RT(-1)) lead to a simple but effective calibration method for deltaT. Additionally, the depolarization of air molecules deltam can be determined in the process of deltaT calibration. We compared determined values with theoretically calculated values for the depolarization of air to test the proposed method. The deltam value was calculated from the lidar data acquired at Ny-Alesund (79 degrees N, 12 degrees E), Svalbard in winter 1994-1995. When only sulfate aerosols were present on 24 December 1994, deltam was 0.46 +/- 0.35%. When the particles consisted of sulfate aerosols and spherical particles of polar stratospheric clouds on 4 January 1995, deltam was 0.45 +/- 0.07%. Both deltam values were in good agreement with the theoretically calculated value, 0.50 +/- 0.03%.

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.

Tuning of a spectrally narrowed Ti/sup 3+/:sapphire laser by electro-optic modulation

A wavelength modulation method for tuning a self-injection-seeded Ti/sup 3+/:sapphire laser is reported that uses an electro-optic beam deflection technique. This approach can allow a fast and stable electronic wavelength switching without involving any mechanical movement.

Algorithm based on joint time-frequency analysis to eliminate noise from stratospheric laser data

The difficulties in extracting useful information from the noise-corrupted stratospheric laser echoes have elevated application of digital signal processing techniques to the atmospheric research. This paper focuses on the problem of noise elimination from the transient returns of stratospheric laser echoes, proposes a new solution approach to it. Unlike related methods which address signal modeling in time domain only, we formulate the problem in both time and frequency domain, present a new modeling environment for the joint time-frequency analysis and use a non-linear median filter for noise elimination. Experiments with various patterns of spectral clouds demonstrate that such an approach significantly increases readability and accuracy of results in terms of the back-scattering function and depolarization.