The optical alignment of the axes of the laser transmitter and the receiving telescope is one of the fundamental problems in lidar systems. The receiver field of view is generally reduced to limit the sky background radiation. When the receiver's field of view is comparable to the divergence of the laser transmitter, accurate optical alignment is demanded. For checking the optical alignment, lidar backscatter signals at five wavelengths of ruby and YAG laser are calculated using a standard atmospheric model including the background stratospheric aerosols and mid-latitude ozone profile. Misalignment effects of the transmitter and receiver axes on the lidar signals and backscatter ratios of the stratospheric aerosols are investigated. When the transmitter and receiver axes are directed outward from a perfect optical alignment, the apparent backscatter ratio, R′B, increases downward in an altitude range of 10-30 km even if there are no stratospheric aerosols. If the transmitter and receiver axes intersect each other, R′B increases upward. A convenient method for the correction of R′B is shown. It goes without saying that it is important to design the lidar system so that such misalignment will not occur.
The growth parameters of ice crystals as a function of time were experimentally determined under free fall at and below water saturation at temperatures of −10, −15, and −20°C using the University of Utah Supercooled Cloud Tunnel. To stably suspend the ice crystals in the tunnel, various improvements were made including vortex and turbulence suppression. Results of the experiments showed that the shapes of ice crystals grown were plate and column, and not dendrite. Their mass and fall velocity after growth of 30 minutes were determined as about 10−5g and 50 cm/s or less, respectively. The relationships among the fall velocity (v cm/s), the mass (m g), and the maximum dimension (d cm) after 10 min. growth period were obtained as m=1.7×10−3d1.9 and v=4.8×103m0.38. Application of the results in cloud physics studies and precipitation control is envisaged.
A case study of long-range forecasting with the use of the Meteorological Research Institute general circulation model (MRI·GCM-I) is described. In this study, not only the predictability of anomalies on the monthly mean basis but also the time evolution of the initial condition (IC) impact and of the sea-surface temperature anomaly (SSTA) impact are discussed up to two months. May 1 of 1983 is chosen as the initial time, when El Niño was still active over the equatorial eastern Pacific Ocean. In the tropics, the SSTA impact dominates over the IC impact already in the first month (May). Large-scale monthly mean anomalies are predicted accurately. In the second month (June), good anomaly correlation is confined in the area from the equatorial eastern Pacific Ocean to the equatorial Atlantic Ocean. The IC impact is almost negligible at this stage. In the extratropics of the Northern Hemisphere (NH), the IC impact is larger than the SSTA impact in the first month, although the SSTA impact is already comparable with the IC impact in the Southern Hemisphere. Many monthly mean anomalies are judged significant with a 95% confidence level in the vicinity of their peaks. However, the predicted anomalies in the NH do not have good correspondence with the observed ones. In the second month, the SSTA impact dominates over the IC impact locally. The anomaly correlation coefficient in such an area is better in the second month than in the first.
A mathematical model is introduced to clarify the characteristics of the LiCl-hygrometer. From the past experiments the vapour pressure of the wicking of the LiCl-hygrometer is proved to be a function of temperature and liquid water content, and by using this relation the behaviour of the LiCl-hygrometer may be explained qualitatively. The main results are as follows. (1) The hygrometer system can be described by second order derivative equations, whose coefficients are functions of the operating conditions, i.e., heater voltage, ventilation wind speed and temperature of the ambient air. (2) The dynamic response to the step change of one parameter is equivalent to that of an ordinary second order system when both step and delta functions are applied. (3) Under fixed vapour pressure of the ambient air, the change of the operating conditions reducing the initial net heat loss of the wicking causes the equilibrium temperature to rise and the equilibrium liquid water content to diminish, and vice versa. (4) When the operating conditions are fixed, the increase of the vapour pressure of the ambient air raises the equilibrium liquid water content, so that the vapour pressure-temperature curve of the LiCl-hygrometer has steeper inclination than that of the saturated bulk LiCl solution.