Narihiro Orikasa

The Characteristics and Evolution of Orographic Snow Clouds under Weak Cold Advection

Abstract On 25 February 1999, on the western side of the central mountain range of Japan, orographic snow clouds had formed under conditions of weak cold advection due to a winter monsoon after a cyclonic storm. The data from Ka-band Doppler radar, microwave radiometer, hydrometeor videosondes, and 2D Grey imaging probe provided unique datasets that were used to analyze the evolution of meso- and microscale structures, especially ice and supercooled liquid water (SLW) evolutions associated with variations in surrounding conditions. In the present case, four stages were identified in the evolution of the clouds: stratiform (I), transition (II), shallow convective (III), and dissipating (IV). During stage I, substantial blocking of the low-level flow occurred. The echo top was relatively flat and the echo pattern was stratiform with a bright band. The clouds were considered to be almost glaciated, primarily by the deposition growth of ice crystals. The wind speed up the slope gradually increased in the latt...

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...

Optical and Microphysical Properties of Upper Clouds Measured with the Raman Lidar and Hydrometeor Videosonde: A Case Study on 29 March 2004 over Tsukuba, Japan

Abstract Optical and microphysical properties of the upper clouds at an altitude range of 5–11 km were measured over Tsukuba, Japan, on 29–30 March 2004 using a ground-based Raman lidar and a balloon-borne hydrometeor videosonde (HYVIS). The Raman lidar measured the vertical distributions of the particle extinction coefficient, backscattering coefficients, depolarization ratio, and extinction-to-backscatter ratio (lidar ratio) at 532 nm; further, it measured the water vapor mixing ratio. The HYVIS measured the vertical distributions of the particle size, shape, cross-sectional area, and number concentration of the cloud particles by taking microscopic images. The HYVIS measurement showed that the cloud particles were ice crystals whose shapes were columnar, bulletlike, platelike, and irregular, and 7–400 μm in size. The Raman lidar measurement showed that the depolarization ratio ranged from 0% to 35% and the lidar ranged from 0.3 to 30 sr for the clouds in ice-saturated air. The comparison between the me...

Observations of quasi-stationary and shallow orographic snow clouds: Spatial distributions of supercooled liquid water and snow particles

Abstract On 25 February 1999, due to a winter monsoon after a cyclonic storm, orographic snow clouds formed under conditions of weak cold advection on the western side of the central mountain range of Japan. In this study, the Ka-band Doppler radar and vehicle-mounted microwave radiometer and 2D-Grey imaging probe were used to obtain unique datasets for analyzing the spatial distributions of microphysical structures of the snow clouds at the windward slope. The liquid water path, number concentration of snow particles (0.1–6.4 mm diameter), and precipitation rate were found to be correlated with altitude. The greater concentration of larger particles tended to appear up the slope. The echo top was at about 2.5 km (−30 dBZ), and the relatively strong echo region (>−3 dBZ) appeared at 5 km up the slope and extended nearly parallel to the slope. According to the echo pattern, the ice water path increased with terrain height and reached the maximum intensity at about 14 km up the slope. These observations pro...

Balloon-borne and Raman lidar observations of Asian dust and cirrus cloud properties over Tsukuba, Japan

The vertical distributions of the microphysical and optical properties of tropospheric aerosols and cirrus cloud were measured using an instrumented balloon and a ground-based Raman lidar over Tsukuba, Japan (36°N, 140°E), during the Asian dust events on 9 and 21 May 2007 to investigate the influence of Asian mineral dust on ice cloud formation in the upper troposphere. The instrumented balloon measured the particle size distribution, ice crystal images, dew/frost point, relative humidity, and temperature. The Raman lidar measured the particle backscattering and extinction coefficients and the depolarization ratio at a wavelength of 532 nm. The results of the balloon measurements showed that supermicrometer (0.7 to 2.8 µm in optical-equivalent radius) dust particles and ice crystals (10 to 400 µm in maximum dimension) were present in the upper troposphere (8 to 12 km in altitude), with number concentrations varying from 5 × 10−3 to 0.6 cm−3 for dust and from 5 × 10−3 to 0.15 cm−3 for ice crystals. The Raman lidar measurement indicated that the particle depolarization ratios were 15 to 35% in the altitude range of 6 to 12 km, indicating the predominance of nonspherical particles in the region. The temperature ranged from −33 to −63°C, and the relative humidity with respect to ice (RHi), estimated from the total (vapor plus condensate) water content obtained with the Snow White hygrometer in the cloud, was 130% at maximum on 9 May, which was close to the activation point of Asian mineral dust as ice nuclei to form ice crystals.

Optical modeling of irregularly shaped ice particles in convective cirrus

A model of convectively generated cirrus particles consistent with the shape properties of measured cirrus particles is proposed. A database of single scattering properties of modeled ice particles at visible to infrared wavelengths was constructed using the finite-difference time-domain and geometric-optics-integral-equation methods for advanced analysis of satellite/ground-based remote sensing data.

CCN ability of atmospheric aerosols and microphysical structures of shallow warm clouds in western Japan

The aerosol size distributions and CCN spectra in the Pacific Ocean region air masses showed that their shapes were similar to those in the East Asia coastal region air masses, but total number concentrations of aerosol particles and CCN number concentrations were about 1/2 of those in the continental/polluted air masses from the East Asia coastal region. Shallow warm clouds showed a wide range of ability for producing drizzle and rain drops. Usually the ability depends on number concentrations of cloud droplets; clouds forming in maritime air mass with less CCN tend to easily produce precipitation and vise versa.

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.