Search

In recent years, the frequency of occurrence of locally heavy rainfall that can cause extensive damages, has been increasing in Japan. For early prediction of heavy rainfall, it is useful to measure the water vapor vertical distribution upwind cumulus convection beforehand. For that purpose, we have been developing compact water vapor differential absorption lidar (DIAL). We show the results of the measurements with lidar in summer when the local heavy rainfall frequently occurs in Japan. We also show the preliminary result of the assimilation of the lidar data to the numerical model and impact on the heavy rainfall prediction.

The backscattering linear depolarization ratios of major types of tropospheric aerosol particles (Asian and Saharan mineral dust, sea salt, and ammonium sulfate) were measured using a laboratory chamber for interpreting the polarization lidar measurement of tropospheric aerosols. The values obtained from Asian and Saharan mineral particles were 0.39 [+ or -] 0.04 to 0.05 (mean [+ or -] standard deviation) for a high number of concentrations in the supermicrometer range and 0.17 [+ or -] 0.03 to 0.14 [+ or -] 0.03 in the submicrometer range. The values were 0.08 [+ or -] 0.01 for sea-salt crystals, 0.04 [+ or -] 0.003 for ammonium sulfate crystals, and 0.01 [+ or -] [less than or equal to] 0.001 for both liquid droplets in the submicrometer range. These values can serve as a reference for estimating aerosol type using lidar measurement. OCIS codes: 010.3640, 010.1100.

We have developed a 1.6 [micro]m carbon dioxide (C[O.sub.2]) differential absorption lidar utilizing a quasi-phase-matching optical parametric oscillator (OPO) and a photon-counting detector. The operating wavelengths were chosen based on their low interference from water vapor and low temperature sensitivity. The online wavelength was in the (30012[left arrow]0001) band of C[O.sub.2], which was insensitive to atmospheric temperature. The established OPO laser achieved a 10mJ, 200 Hz repetition rate at the online and offline wavelengths. Our observations confirmed the statistical error of 2% with 5 h of accumulation for the C[O.sub.2] density profile less than 5.2km. Also, the statistical error of l% at an altitude of 2km was demonstrated. The results of the vertical C[O.sub.2] concentrations acquired using a 1.6[micro]m wavelength are presented. OCIS codes: 000.0280, 010.3640, 280.1910, 190.4970.

The vertical distribution of stratospheric aerosols has been measured with lidars at the Meteorological Research Institute (MRI) over Tsukuba since 1982. After two major volcanic eruptions (Mt. El Chichón in 1982 and Mt. Pinatubo in 1991), stratospheric aerosol loading increased about 50–100 times compared with the background level which was observed for 1997-2000. From 2000 to 2012, a slight increase (5.3% year–1) was observed by some volcanic eruptions. This long-term lidar data have been used for assessing of impact of the stratospheric aerosols on climate and the ozone layer.

In this paper, a field-deployable diode-laser-based differential absorption lidar (DIAL) has been developed for lower-tropospheric water vapor observation in Tokyo, Japan. A photoacoustic cell is used for spectroscopy experiment around absorption peaks of 829.022 nm and 829.054 nm. The water vapor density extracted from the observational data agrees with the referenced radiosonde data. Furthermore, we applied modulated pulse technique for DIAL transmitter. It enables DIAL to measure water vapor profile for both low and high altitude regions.

Backscattering properties of ice crystal models (Voronoi aggregates (VA), hexagonal columns (COL), and six-branched bullet rosettes (BR6)) are calculated by using geometrical-opticsintegral-equation (GOIE) method. Characteristics of depolarization ratio (δ) and lidar ratio (L) of the crystal models are examined. δ (L) values are 0.2~0.3 (4~50), 0.3~0.4 (10~25), and 0.5~0.6 (50~100) for COL, BR6, and VA, respectively, at wavelength λ=0.532 μm. It is found that small deformation of COL model could produce significant changes in δ and L.

A UV ozone differential-absorption lidar (DIAL) utilizing a Nd:YAG laser and a single Raman cell filled with carbon dioxide (C[O.sub.2]) is designed, developed, and evaluated. The generated wavelengths are 276, 287, and 299 nm, comprising the first to third Stokes lines of the stimulated Raman scattering technique. The correction terms originated from the aerosol extinction, the backscatter, and the absorption by other gases are estimated using a model atmosphere. The experimental results demonstrate that the emitted output energies were 13 mJ/pulse at 276 nm and 287 nm and 5 mJ/pulse at 299 nm, with pump energy of 91 mJ/pulse and a C[O.sub.2] pressure of 0.7 MPa. The three Stokes lines account for 44.0% of the available energy. The use of argon or helium as a buffer gas in the Raman cell was also investigated, but this leads to a dramatic decrease in the third Stokes line, which makes this wavelength practically unusable. Our observations confirmed that 30 min of integration were sufficient to observe ozone concentration profiles up to 10 km. Aerosol extinction and backscatter correction are estimated and applied. The aerosol backscatter correction profile using 287 and 299 nm as reference wavelengths is compared with that using 355 nm. The estimated statistical error is less than 5% at 1.5 km and 10% at 2.6 km. Comparisons with the operational carbon-iodine type chemical ozonesondes demonstrate 20% overestimation of the ozone profiles by the DIAL technique. OCIS codes: 010.3640, 010.4950.

The tropospheric particle extinction-to-backscatter ratio, the depolarization ratio, and the water-vapor mixing ratio were measured by use of a Raman lidar and a polarization lidar during the Asian dust seasons in 2001 and 2002 in Tsukuba, Japan. The apparent (not corrected for multiple-scattering effects) extinction-to-backscatter ratios (Sp) showed a dependence on the relative humidity with respect to ice ([RH.sub.ice]) obtained from the lidar-derived water-vapor mixing ratio and radiosonde-derived temperature; they were mostly higher than 30 sr in dry air ([RH.sub.ice])< 50%), whereas they were mostly lower than 30 sr in ice-supersaturated air ([RH.sub.ice])[greater than or equal to] 100%), where the apparent extinction coefficients were larger than 0.036 [km.sup.-1]. Both regions showed mean particle depolarization ratios of 20%-22%. Comparisons with theoretical calculations and the previous experiments suggest that the observed dependence of [S.sub.p] on [RH.sub.ice] is attributed to the difference in the predominant particles: nonspherical aerosols (mainly the Asian dust) in dry air and cloud particles in ice-supersaturated air. OCIS codes: 010.1100, 010.3640.