No abstract

A new version of hydrometeor videosonde (HYVIS) has been developed to measure the vertical distribution of hydrometeors in cirrus clouds with low ice crystal concentrations. This sonde has two small video cameras that take pictures of particles from 7 pm to 5 mm in size, and transmits particle images by 1.6 GHz microwave to a ground station. The original HYVIS did not have enough sampling volume to evaluate the size distribution of hydrometeors in clouds with low number concentrations. To increase sampling volume, a small suction fan was added. From laboratory experiments, we have estimated the variation in sampling volume with changes of ambient air pressure and ascent velocity of the sonde. Theoretical calculation showed that the collection efficiency of the new HYVIS should be unity for all ice crystals larger than 10um.Some examples of cirrus cloud observations have demonstrated that the new HYVIS enabled us to determine reliable size distributions of ice crystals larger than 10um at 250m intervals. The results of the new HYVIS measurements provide us with useful information about mechanisms for the formation and maintenance of cirrus clouds.

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 obtained with the lidar and the hygrometers on the meteorological tower agreed to within 0.4% at a height of 213 m, although the absolute values differed systematically by 9%–14% due to the incomplete overlap of the laser beam and the receiver’s field of view at heights between 50 and 150 m. The precipitable water vapor obtained with the lidar indicated a mean positive bias of 2 mm (9%–11%) relative to those obtained with GPS. The lidar water vapor calibration coefficient that was calculated using RS2-91 radiosonde data varied by 11% during an 18-month period. Therefore, it is necessary to develop an accurate, yet convenient, method for determining the calibration coefficient for the use of the lidar.

A new cloud simulation chamber was built at the Meteorological Research Institute (MRI) to investigate the details of the fundamental processes of cloud formation. The MRI cloud chamber was designed as an adiabatic-expansiontype cloud chamber covering temperatures from 30 to −100°C, pressures from 1030 to 30 hPa, and an evacuation rates corresponding to ascent rates from 0 to 30 m s −1. Improvements to the cooling system and cloud characterization instrumentation distinguish the new facility from past devices of this type that are no longer functional (e.g., the Colorado State University dynamic cloud chamber), and the capabilities exceed those of any other active facility (e.g., the Aerosol Interactions and Dynamics in the Atmosphere (AIDA) chamber) for covering a range of atmospheric conditions while reproducing approximately adiabatic parcel conditions. Results from the preliminary experiments demonstrate the accuracy of coordinated pressure and temperature controls to reproduce cloud formation processes (both dry and wet adiabatic expansion processes) and the ability of the chamberʼs instrumentation to measure aerosol, cloud droplet, and ice crystal characteristics. Performance tests demonstrate the chamberʼs usefulness as a facility to investigate cloud droplet and ice crystal formation processes through the activation of various types of aerosol particles.

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 m 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 measured data and theoretical calculations of the cloud optical properties suggests that the observed variations in the depolarization ratio and lidar ratio were primarily due to the variation in the proportion of the horizontally oriented ice crystals in the clouds. The optical thickness of the cloud obtained from the lidar was about 2 times lower than that calculated from the HYVIS data, and the maximum extinction coefficient was about 5 times lower than the HYVIS data. The most probable reason for the differences is the horizontal inhomogeneities of the cloud properties between the measurements sites for the two instruments.