This thesis investigates the characteristics of warm clouds off the coast of California by using a three-dimensional (3D) regional model with a Spectral Bin microphysical Model (SBM). To reproduce the characteristics of the warm clouds, the regeneration processes of aerosols have been implemented to the Japan Meteorological Agency Non-hydrostatical model with Hebrew University Cloud Model (JMA-NHM+HUCM). 3D idealized simulations with periodic boundary condition and downscaling simulations are conducted to verify model performance and to compare the model results with those obtained from observations. Numerical simulations by the model successfully reproduce the correlation pattern between cloud-droplet effective radius (RE γe) and cloud optical thickness (COT τc) (RE-COT pattern) and Contoured Frequency Optical Depth Diagram (CFODD) retrieved from satellite observations. Results of the idealized numerical experiments support the validity of an interpretation of previous studies on CFODD. The results also indicate that the characteristics of warm clouds are affected by grid resolution. However, the response of the cloud microphysical properties to aerosol amount and boundary layer (PBL) height does not depend on the grid resolution significantly. Therefore, the simulated results from coarse grid resolution experiments can acquire the fundamental features of the RE-COT pattern and CFODD. This finding is important for future global and/or long-term model simulations where it is difficult to adopt high resolution modeling like large eddy simulation (LES) modeling of several tens of meters. 3D-downscaling numerical experiments under a real atmospheric condition are also conducted to simulate the microphysical properties of warm clouds during the First ISCCP Regional Experiment (FIRE), and then combined analyses of RE-COT pattern and CFODD using the model results are, for the first time, conducted to investigate the cloud growth stage. The model simulates the radiances observed from the visible wavelength sensor onboard the Advanced Very High Resolution Radiometer (AVHRR) satellite. The combined analysis and a box model calculation indicate that each of the RE-COT patterns does not always represent the observed cloud characteristics, but mixtures of RE-COT patterns from different clouds show a similarity to the satellite-derived pattern. This finding presents a new interpretation of the cloud microphysical properties seen by satellite-derived RE-COT patterns, in contrast to the interpretation by previous studies. In conclusion the present results indicate that the characteristics of RE-COT patterns are totally dependent on the drizzling rate, PBL height (corresponds to dynamic stability), and the aerosol amounts. Therefore, a comprehensive model including all these processes for successful simulation of the low-level clouds in the target region is needed. The lower the stability is the larger liquid water path (LWP) takes place at the right edge of the RE-COT patterns. The higher the aerosol amount is the larger the cloud droplet number concentration is found at the lower edge of RE-COT patterns. The geometrical center of the RE-COT pattern is mainly determined by the drizzling rate. It shifts to an area of larger RE and smaller COT values on the RE-COT plane when the drizzling rate is large, while it shifts to an area of smaller RE and larger COT values with a small drizzling rate.
発行年
2012-03-22
日本十進分類法
451
学位名
博士(理学)
学位
doctoral
学位分野
Science(Rigaku)(理学)
学位授与機関
University of Tokyo (東京大学)
研究科・専攻
Department of Earth and Planetary Science, Graduate School of Science (理学系研究科地球惑星科学専攻)
学位授与年月日
2012-03-22
学位授与番号
甲第27800号
学位記番号
博理第5803号
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A numerical study on the microphysical properties of warm clouds off the west coast of California
Thesis_satoyousuke.pdf
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