Masahisa Nakazato

Ice clouds and Asian dust studied with lidar measurements of particle extinction-to-backscatter ratio, particle depolarization, and water-vapor mixing ratio over Tsukuba

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 (RHice) obtained from the lidar-derived water-vapor mixing ratio and radiosonde-derived temperature; they were mostly higher than 30 sr in dry air (RHice < 50%), whereas they were mostly lower than 30 sr in ice-supersaturated air (RHice > or = 100%), where the apparent extinction coefficients were larger than 0.036 km(-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 Sp on RHice 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.

Development of a 1.6 μ m differential absorption lidar with a quasi-phase-matching optical parametric oscillator and photon-counting detector for the vertical CO 2 profile

We have developed a 1.6 microm carbon dioxide (CO(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<--0001) band of CO(2), which was insensitive to atmospheric temperature. The established OPO laser achieved a 10 mJ, 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 CO(2) density profile less than 5.2 km. Also, the statistical error of 1% at an altitude of 2 km was demonstrated. The results of the vertical CO(2) concentrations acquired using a 1.6 microm wavelength are presented.

Tropospheric ozone differential-absorption lidar using stimulated Raman scattering in carbon dioxide

A UV ozone differential-absorption lidar (DIAL) utilizing a Nd:YAG laser and a single Raman cell filled with carbon dioxide (CO(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 CO(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.

Comparisons of Raman Lidar Measurements of Tropospheric Water Vapor Profiles with Radiosondes, Hygrometers on the Meteorological Observation Tower, and GPS at Tsukuba, Japan

Abstract The vertical distribution profiles of the water vapor mixing ratio (w) were measured by Raman lidar at the Meteorological Research Institute, Japan, during the period from 2000 to 2004. The measured values were compared with those obtained with radiosondes, hygrometers on a meteorological observation tower, and global positioning system (GPS) antennas near the lidar site. The values of w obtained with the lidar were lower than those obtained with the corrected Meisei RS2-91 radiosonde by 1.2% on average and higher than those obtained with the corrected Vaisala RS80-A radiosonde by 17% for w ≥ 0.5 g kg−1. The lidar data were higher than those radiosondes’ data by 19% or 33% for w < 0.5 g kg−1. The vertical variations of w obtained with the lidar differed from those obtained with the Meisei RS-01G radiosonde and Meteolabor Snow White radiosonde by 5% on average for w ≥ 0.5 g kg−1. The lidar data were lower than those radiosondes’ data by 37% or 39% for w < 0.5 g kg−1. The temporal variations of w o...

Stimulated Raman Scattering Laser Oscillation around 1.6 µm Carbon Dioxide Absorption Line

A solid-state stimulated Raman scattering (SRS) laser oscillation around the 1.6 µm carbon dioxide absorption lines is demonstrated. The stokes output of the SRS radiation at 1.57 µm is generated from the frequency conversion of the 1.35 µm laser radiation of Nd3+:KGd(WO4)2 (Nd:KGW) in the cavity. The maximum output energy was 13.8 mJ with a repetition rate of 10 Hz, in response to the incident laser pumped from the laser diode to the Nd:KGW. To our knowledge, this result of a 1.57 µm intracavity SRS oscillation at CO2 absorption lines around 1.6 µm is gained for the first time.

Measurement of Pressure-Induced Broadening and Shift Coefficients of Carbon Dioxide Absorption Lines around 1.6 µm for using Differential Absorption Lidar

A precise measurement of the vertical profiles of carbon dioxide is required for reducing the uncertainty in the carbon budget. In order to achieve measurements of the vertical CO2 distribution with an uncertainty better than approximately 4 ppm, a precise knowledge of the pressure-dependent broadening and shift coefficients of CO2 absorption lines is indispensable. In this paper, we report the measurement of air pressure-induced shift coefficients for eight absorption lines at around 1.57 µm. On average, the pressure shift coefficients are -0.30 MHz/Torr for pure CO2 and -0.24 MHz/Torr under an air-mixed condition.

Diurnal and daily variations in surface ultraviolet radiation due to ozone variations in the troposphere at Tsukuba, Japan: Lidar observations and chemistry-climate model simulation

Ozone vertical profile in the troposphere was continually measured by lidar at Tsukuba, Japan and diurnal variations of ozone was investigated in relation to the daily weather system variations. A chemistry-climate model including detailed tropospheric chemistry was also run to get continuous ozone distribution. Based on the observed and simulated ozone profile in the troposphere, diurnal and daily variations in the actinic flux of ultraviolet radiation at the surface were calculated under a clear sky assumption. A preliminary calculation shows that the reduction in UVB due to tropospheric ozone decreases in magnitude with wavelengths, while the reduction displays greater diurnal variations at middle wavelengths (290 and 300 nm) than the shorter (280 nm) and the longer (310 nm) wavelengths.

Multi‐wavelength radar algorithm with Doppler function for the retrieval of cloud microphysics with precipitation

We developed the retrieval algorithm for clouds accompanying precipitation. In order to obtain the vertical structure of cloud microphysics, W‐, Ka‐ and X‐ band radars with Doppler capability were used. We first considered six different particle types and the scattering properties of the non‐spherical ice particles were calculated at these frequencies by using the discrete dipole approximation (DDA). Then dual wavelength ratios (DWR) and the reflectivity‐weighted terminal velocities (Vtz) for the six particle types were estimated. It was found that the DWR for W‐ and Ka‐ band radars depended on particle shape, orientation and size when particle effective radius exceeds about 60 μ m . DWR for Ka‐ and X‐ band radars also showed the similar dependences but for larger size than the DWR for X and Ka band radars. The Vtz also show the strong dependence on shape, orientation and size for large size. The retrieval algorithm consists of two parts; (1) large particle mode from the combination of DWRs and VTzs from W‐, Ka‐ and X‐ band radars measurements and (2) small particle mode from the radar reflectivity and Vtz from Ka‐ band. We examined the cloud microphysics from the radar data observed in Niigata in December 2007, in the field experiment of Japanese Cloud Seeding Experiment for Precipitation Augmentation (JACSEPA). Retrievals of microphysics were performed for two cases. The retrieval results were compared with the in‐situ data and found some agreement.

Comparisons of the Raman lidar measurements of the tropospheric water vapor profiles with radiosondes, meteorological observation tower, and GPS at Tsukuba, Japan

The vertical distributions of the water vapor mixing ratio (w) were measured by Raman lidar at the Meteorological Research Institute, Japan, in 2000 to 2004. The measured values were compared with those obtained with radiosondes, hygrometers on the meteorological observation tower, and Global Positional System (GPS) antennas. The values of w obtained with the lidar agreed within 9% with those obtained with the Meisei RS2-91 radiosonde for w > 0.5 g/kg-1. However, they were systematically higher than those obtained with the Vaisala RS80-A radiosonde for that region. The vertical variations of w obtained with the lidar were similar to those obtained with the Meisei RS-01G and Meteolabor Snow White radiosondes for w > 0.3 g/kg-1. The temporal variations of w obtained with the lidar were similar to those obtained with the hygrometers at heights between 50 and 213 m on the tower, although the absolute values differed systematically due to the incomplete overlap of the laser beam and the receivers field of view at the lower heights. The precipitable water vapor content obtained with the lidar generally agreed with those obtained with GPS, except for the period when the large spatial inhomogeneity of w was present.