A three-dimensional tropical cyclone model is developed with a new parameterization of cumulus convection, based on the results from the non-parameterized model of Yamasaki (1977, 83). In order to simulate the important features and mechanisms of tropical cyclones obtained in the non-parameterized model, cloud water and rainwater are included as predicted variables. The effects of evaporation of rainwater and convective downdrafts are taken into account. Heating due to parameterized convection is assumed to depend on the vertical velocity at a low level and the degree of the conditional instability. Results from a numerical experiment indicate that the present model is capable of describing mesoscale convections which are pronounced in the non-parameterized model. Mesoscale convections behave in different ways, depending on the stage (or intensity) of a simulated tropical cyclone and on the location relative to the tropical cyclone center. Simulated spiral rainbands consist of mesoscale convections which form around the trailing edge of a rainband in many cases and move on the spiral band cyclonically towards the eyewall. In the case of spiral bands which are strongly affected by frictional inflow, mesoscale convections are maintained for a long period of time by successive formation of convective elements at the outer edge of the band in which warm moist air flows. The spiral bands do not behave like gravity waves. Most of the properties of mesoscale convections (including those at the pre-typhoon stage) and the tropical cyclone simulated in this study are similar to those obtained from the non-parameterized model. The essential aspects of the parameterization scheme which leads to such results and its shortcomings are also discussed.
In order to investigate air-earth interaction, a systematic measurement system near the surface was developed and installed in the observation field after careful examination of instruments and data processing. Some aerodynamic approaches are provided for the determination of the vertical turbulent fluxes of heat and water vapor. Actual evaporation from the land surface is obtained from a weighable lysimeter of high sensitivity. The gradient method among the aerodynamic approaches provides a good estimate of evaporation. The relationships between evaporation and soil water content are investigated in detail by means of the lysimeter and electrical capacitance meters placed in the soil container of the lysimeter. The data show that the soil water content in the skin layer changes appreciably in a day and that its variation corresponds closely to the unevenness of the evaporation.
90Sr and 239+240Pu concentrations in the surface air were observed at Tsukuba and Tokyo during the period from 1978 to 1983. They showed remarkable seasonal variation with a spring maximum and a fall minimum. The pronounced peak in these concentrations observed in the spring season of 1981, which was maximum in this period of study, is attributed to the stratospheric fallout derived from the 26th Chinese explosion. Marked increases of the 90Sr and 239+240Pu concentrations were observed in the smallest particles (less than 1.6 μm) at the spring maximum. The resupension of the radionuclide bearing soil particles, as one of the sources besides the stratospheric fallout, will be significant for the airborne 239+240Pu rather than 90Sr in near future.
A precise gravity survey in Izu-Oshima Island was carried out in November 1985 using the LaCoste & Romberg Model D gravity meter No.109. The measurements were made on the bench marks of the leveling route rounding the island which was established by the Geographical Survey Institute (GSI) in 1979 and on gravity points of the Earthquake Research Institute (ERI) and GSI as well as other several newly established stations. The accuracy of the measurements is estimated to be within ±10 μgal for the leveling route around the island and about ± 20 μgal for the inland mountainous route. By comparing the results with the measurements made by GSI and ERI, it is found that gravity values in the island have a general tendency to decrease in the past several to 15 years. This is concordant with the fact that volcanic activity at Mt. Miharayama has been quiet in recent years.