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Woosub Roh, Masaki Satoh, Tempei Hashino, Hajime Okamoto, and Tatsuya Seiki

Abstract

A new evaluation method for the thermodynamic phases of clouds in cloud-system-resolving models is presented using CALIPSO observations and a satellite simulator. This method determines the thermodynamic phases using the depolarization ratio and a cloud extinction proxy. For the evaluation, we introduced empirical parameterization of the depolarization ratio of ice and water clouds using temperatures of a reanalysis dataset and total attenuated backscatters of CALIPSO. We evaluated the mixed-phase clouds simulated in a cloud-system-resolving model over the Southern Ocean using single-moment and double-moment bulk cloud microphysics schemes, referred to as NSW6 and NDW6, respectively. The NDW6 simulations reproduce supercooled water clouds near the boundary layer that are consistent with the observations. Conversely, the NSW6 simulations failed to reproduce such supercooled water clouds. Consistencies between the cloud classes diagnosed by the evaluation method and the simulated hydrometeor categories were examined. NDW6 shows diagnosed water and ice classes that are consistent with the simulated categories, whereas the ice category simulated with NSW6 is diagnosed as liquid water by the present method due to the large extinction from the ice cloud layers. Additional analyses indicated that ice clouds with a small effective radius and large ice water content in NSW6 lead to erroneous values for the fraction of the diagnosed liquid water. It is shown that the uncertainty in the cloud classification method depends on the details of the cloud microphysics schemes. It is important to understand the causes of inconsistencies in order to properly understand the cloud classification applied to model evaluations as well as retrievals.

Open access
Tempei Hashino, Gijs de Boer, Hajime Okamoto, and Gregory J. Tripoli

Abstract

The number concentration of ice particles in Arctic mixed-phase clouds is a major controlling factor of cloud lifetime. The relationships between ice nucleation mode and ice crystal habit development are not yet constrained by observations. This study uses a habit-predicting microphysical scheme within a 3D large-eddy simulation model to evaluate the relationship between immersion freezing and ice habit in a simulated Arctic mixed-phase cloud case. Three immersion freezing parameterizations are considered: a volume-dependent freezing scheme (VF), a parameterization limited to activated droplets (C-AC), and a parameterization limited to coarse aerosol particles (C-CM). Both C-AC and C-CM are based on classical nucleation theory. The freezing rate with VF is found to be greater in downdraft regions than in updraft regions due to the downdraft having a higher number concentration of large droplets. The C-AC cases show active freezing of small droplets near cloud top, whereas in the C-CM cases, mainly the 8–32-μm-sized droplets freeze in updraft regions near the cloud base. Because the initial crystal size is assumed to affect the axis ratio of hexagonal plates, the VF cases produce crystals with larger axis ratios, resulting in smaller mode radii than the C-AC cases. In all cases, irregular polycrystals dominate near cloud top and a band-like structure develops within the cloud, which qualitatively agrees with previous observations. In the VF and C-CM cases, unactivated large droplets arising from coarse-mode aerosol particles contributed significantly to the freezing rate, producing an important influence on crystal habit.

Open access
Kazuaki Yasunaga, Kunio Yoneyama, Hisayuki Kubota, Hajime Okamoto, Atsushi Shimizu, Hiroshi Kumagai, Masaki Katsumata, Nobuo Sugimoto, and Ichiro Matsui

Abstract

In this study, cloud profiling radar and lidar were used to determine the frequency distribution of the base heights of cloudy layers with little (or no) falling condensate particles. The data were obtained from stationary observations conducted from Research Vessel Mirai over the tropical western Pacific (around 1.85°N, 138°E) from 9 November to 9 December 2001. The observed cloudy layers had base heights predominantly in the range of 4.5–6.5 km. Almost all cloudy layers with a base in the range of 4.5–6.5 km had thickness thinner than 500 m, and the frequency peak of the base heights of measured cloudy layers is considered to represent the common occurrence of midlevel thin clouds.

Midlevel thin clouds were frequently observed even during the active phase of the Madden–Julian oscillation (MJO). Composite analysis of radiosonde-derived relative humidity and temperature lapse rate indicates that the midlevel thin cloud in the MJO active period is generated via melting within the stratiform cloud, rather than by detrainment of surface-based convection.

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Takamichi Iguchi, Teruyuki Nakajima, Alexander P. Khain, Kazuo Saito, Toshihiko Takemura, Hajime Okamoto, Tomoaki Nishizawa, and Wei-Kuo Tao

Abstract

Numerical weather prediction (NWP) simulations using the Japan Meteorological Agency Nonhydrostatic Model (JMA-NHM) are conducted for three precipitation events observed by shipborne or spaceborne W-band cloud radars. Spectral bin and single-moment bulk cloud microphysics schemes are employed separately for an intercomparative study. A radar product simulator that is compatible with both microphysics schemes is developed to enable a direct comparison between simulation and observation with respect to the equivalent radar reflectivity factor Ze, Doppler velocity (DV), and path-integrated attenuation (PIA). In general, the bin model simulation shows better agreement with the observed data than the bulk model simulation. The correction of the terminal fall velocities of snowflakes using those of hail further improves the result of the bin model simulation. The results indicate that there are substantial uncertainties in the mass–size and size–terminal fall velocity relations of snowflakes or in the calculation of terminal fall velocity of snow aloft. For the bulk microphysics, the overestimation of Ze is observed as a result of a significant predominance of snow over cloud ice due to substantial deposition growth directly to snow. The DV comparison shows that a correction for the fall velocity of hydrometeors considering a change of particle size should be introduced even in single-moment bulk cloud microphysics.

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