Kentaroh Suzuki

Droplet Growth in Warm Water Clouds Observed by the A-Train. Part II: A Multisensor View

Abstract Hydrometeor droplet growth processes are inferred from a combination of Aqua/Moderate Resolution Imaging Spectroradiometer (MODIS) cloud particle size observations and CloudSat/Cloud Profiling Radar (CPR) observations of warm water clouds. This study supports the inferences of a related paper (Part I) (i) that MODIS-retrieved cloud droplet radii (CDR) from the 3.7-μm channel (R37) are influenced by the existence of small droplets at cloud top and (ii) that the CDR obtained from 1.6- (R16) and 2.1-μm (R21) channels contain information about drizzle droplets deeper into the cloud as well as cloud droplets. This interpretation is shown to be consistent with radar reflectivities when matched to CDR that were retrieved from MODIS data. This study demonstrates that the droplet growth process from cloud to rain via drizzle proceeds monotonically with the evolution of R16 or R21 from small cloud drops (on the order of 10–12 μm) to drizzle (CDR greater than 14 μm) to rain (CDR greater than 20 μm). Thus, R...

Droplet Growth in Warm Water Clouds Observed by the A-Train. Part I: Sensitivity Analysis of the MODIS-Derived Cloud Droplet Sizes

This study examines the sensitivity of the retrieved cloud droplet radii (CDR) to the vertical inhomogeneity of droplet radii, including the existence of a drizzle mode in clouds. The focus of this study is warm water-phase clouds. Radiative transfer simulations of three near-infrared Moderate Resolution Imaging Spectroradiometer (MODIS) channels centered on wavelengths of 1.6, 2.1, and 3.7 mm reveal that the retrieved CDR are strongly influenced by the vertical inhomogeneity of droplet size including (i) the existence of small cloud droplets at the cloud top and (ii) the existence of the drizzle mode. The influence of smaller droplets at cloud top affects the 3.7-mm channel most, whereas the presence of drizzle influences radiances of both the 2.1- and 1.6-mm channels more than the 3.7-mm channel. Differences in the CDR obtained from MODIS 1.6-, 2.1-, and 3.7-mm channels that appear in global analysis of MODIS retrievals and the CDR derived from data collected during the First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment (FIRE) intensive observation period in 1987 can be explained by the results obtained from the sensitivity experiments of this study.

Particle Growth and Drop Collection Efficiency of Warm Clouds as Inferred from Joint CloudSat and MODIS Observations

This study describes an approach for combining CloudSat and Moderate Resolution Imaging Spectroradiometer (MODIS) satellite observations to investigate the microphysical processes of warm clouds on the global scale. MODIS column optical thickness is vertically distributed between the cloud top and cloud bottom according to adiabatic and condensational growth assumptions and used as a vertical coordinate system to analyze profiles of CloudSat-observed radar reflectivity. The reflectivityprofiles thus rescaled as a function of the in-cloud optical depth clearly depict how the cloud-to-rain particle growth processes take place within the cloud layer and how these processes vary systematically with variations in MODIS-derived effective particle radius. It is also found that the effective radii retrieved using two different wavelengths of MODIS tend totracethe microphysical change of reflectivity profiles in a different way because of the difference in the layer depth that characterizes these two effective radii. The reflectivity profiles as a function of optical depth are also interpreted in terms of drop collection processes based on the continuous collection model. The slope of the reflectivity change with optical depth provides a gross measure of the collection efficiency factor. The systematic changes of reflectivity profiles with MODIS-derived particlesizesaretheninterpretedasdemonstratingastrongdependencyofthecollectionefficiencyonparticlesize. Theseresultsprovideaquantitativeinsightintothedropcollectionprocessofwarmcloudsintherealatmosphere.

Diagnosis of the Warm Rain Process in Cloud-Resolving Models Using Joint CloudSat and MODIS Observations

AbstractThis study examines the warm rain formation process in global and regional cloud-resolving models. Methodologies developed to analyze CloudSat and Moderate Resolution Imaging Spectroradiometer (MODIS) satellite observations are employed to investigate the cloud-to-precipitation processes and are applied to model results for comparisons with corresponding statistics from the observations. Three precipitation categories of no precipitation, drizzle, and rain are defined according to nonattenuated near-surface radar reflectivity, and their fractional occurrences and the probability of precipitation are investigated as a function of cloud properties such as droplet size, optical thickness, droplet number concentration, and liquid water path. The comparisons reveal how the models are qualitatively similar to, but quantitatively different from, observations in terms of cloud-to-rainwater conversion processes. Statistics from one model reveal a much faster formation of rain than observed, with drizzle oc...

A Study of the Aerosol Effect on a Cloud Field with Simultaneous Use of GCM Modeling and Satellite Observation

The indirect effect of aerosols was simulated by a GCM for nonconvective water clouds and was compared with remote sensing results from the Advanced Very High Resolution Radiometer (AVHRR) satellite-borne sensor for January, April, July, and October of 1990. The simulated global distribution of cloud droplet radius showed a land‐sea contrast and a characteristic feature along the coastal region similar to the AVHRR results, although cloud droplet radii from GCM calculations and AVHRR retrievals were different over tropical marine regions due to a lack of calculation of cloud‐aerosol interaction for convective clouds in the present model and also due to a possible error in the satellite retrieval caused by cirrus and broken cloud contamination. The simulated dependence of the cloud properties on the column aerosol particle number was also consistent with the statistics obtained by the AVHRR remote sensing when a parameterization with the aerosol lifetime effect was incorporated in the simulation. The global average of the simulated liquid water path based on the parameterization with the aerosol lifetime effect showed an insignificant dependence on the aerosol particle number as a result of a global balance of the lifetime effect and the wash-out effect. This dependence was contrary to the results of simulations based on the Sundqvist’s parameterization without aerosol lifetime effect; that is, the simulated cloud liquid water path showed a decreasing tendency with the aerosol particle number reflecting only the wash-out effect.

A Study of Microphysical Mechanisms for Correlation Patterns between Droplet Radius and Optical Thickness of Warm Clouds with a Spectral Bin Microphysics Cloud Model

Abstract This study investigates the correlation patterns between cloud droplet effective radius (CDR) and cloud optical thickness (COT) of warm clouds with a nonhydrostatic spectral bin microphysics cloud model. Numerical experiments are performed with the model to simulate low-level warm clouds. The results show a positive and negative correlation pattern between CDR and COT for nondrizzling and drizzling stages of cloud development, respectively, consistent with findings of previous observational studies. Only a positive correlation is simulated when the collection process is switched off in the experiment, whereas both the positive and negative correlations are reproduced in the simulation with collection as well as condensation processes. The positive and negative correlations can also be explained in terms of an evolution pattern of the size distribution function due to condensation and collection processes, respectively. Sensitivity experiments are also performed to examine how the CDR–COT correlat...

Physical properties of maritime low clouds as retrieved by combined use of Tropical Rainfall Measuring Mission (TRMM) Microwave Imager and Visible/Infrared Scanner. 2. Climatology of warm clouds and rain

[1] In this paper, we investigate characteristics of low clouds and warm-rain production in terms of droplet growth based on the effective droplet radii retrieved by a combined use of visible, infrared, and microwave satellite remote sensing. We propose to categorize low clouds into the following groups: (1) nondrizzling, nonraining clouds; (2) nonraining clouds with drizzling near the cloud top; (3) raining clouds; and (4) clouds with no clear interpretation in terms of the effective radii derived using two different schemes. This categorization is supported by examination of the correlation between static stability and the retrieved results in the three ‘‘precipitating regions’’ (the Middle Pacific, South Pacific Convergence Zone [SPCZ], and Intertropical Convergence Zone [ITCZ] cumulus regions) and in the four ‘‘nonprecipitating regions’’ (the Californian, Peruvian, Namibian, and eastern Asian stratus regions). The rain rate derived by Precipitation Radar (PR) provides global characteristics consistent with our results. Californian and Peruvian stratus clouds are found to frequently have the drizzle mode near the cloud top, whereas Namibian strati have fewer chances to drizzle. The drizzle mode almost completely disappears in the eastern Asian region in the winter. The cloud–aerosol interaction is a promising candidate for suppressing the drizzle mode formation in nonprecipitating clouds. INDEX TERMS: 0320 Atmospheric Composition and Structure: Cloud physics and chemistry; 1610 Global Change: Atmosphere (0315, 0325); 1640 Global Change: Remote sensing; 1655 Global Change: Water cycles (1836)

Well-type phoswich counter for low-flux X-ray/ gamma -ray detection

Novel phoswich counters have been developed that are capable of detecting low flux hard X-rays gamma -rays from localized sources. The counter consists of a small inorganic scintillator with a fast decay time (the detection part) glued to the interior bottom surface of a well-shaped block of another inorganic scintillator with a slow decay time (the shielding part). The well-shaped shielding part acts as an active collimator as well as an active shield. The whole assembly is viewed by a phototube from the exterior bottom surface of the shielding part. By using an appropriate pulse-shape discriminator, hard X-rays/ gamma -rays that have deposited energy only in the detection part can be selected. The first model counter was built by using a new scintillator, GSO, in the detection part and CsI(Tl) in the shielding part. A detector system consisting of 64 such phoswich counters (total area approximately 740 cm/sup 2/) was flown on board a balloon, setting a limit to the /sup 57/Co line flux from SN 1987A at around 10/sup -4//cm/sup 2/-s. The sensitivity for continuum flux was around a few*10/sup -6//cm/sup 2/-s-keV between 100 and 200 keV. >

Evaluation of the Warm Rain Formation Process in Global Models with Satellite Observations

AbstractThis study examines the warm rain formation process over the global ocean in global climate models. Methodologies developed to analyze CloudSat and Moderate Resolution Imaging Spectroradiometer (MODIS) satellite observations are employed to investigate the cloud-to-precipitation process of warm clouds and are applied to the model results to examine how the models represent the process for warm stratiform clouds. Despite a limitation of the present study that compares the statistics for stratiform clouds in climate models with those from satellite observations, including both stratiform and (shallow) convective clouds, the statistics constructed with the methodologies are compared between the models and satellite observations to expose their similarities and differences. A problem common to some models is that they tend to produce rain at a faster rate than is observed. These model characteristics are further examined in the context of cloud microphysics parameterizations using a simplified one-dim...

Ship track observations of a reduced shortwave aerosol indirect effect in mixed-phase clouds

Aerosol influences on clouds are a major source of uncertainty to our understanding of forced climate change. Increased aerosol can enhance solar reflection from clouds countering greenhouse gas warming. Recently, this indirect effect has been extended from water droplet clouds to other types including mixed-phase clouds. Aerosol effects on mixed-phase clouds are important because of their fundamental role on sea ice loss and polar climate change, but very little is known about aerosol effects on these clouds. Here we provide the first analysis of the effects of aerosol emitted from ship stacks into mixed-phase clouds. Satellite observations of solar reflection in numerous ship tracks reveal that cloud albedo increases 5 times more in liquid clouds when polluted and persist 2 h longer than in mixed-phase clouds. These results suggest that seeding mixed-phase clouds via shipping aerosol is unlikely to provide any significant counterbalancing solar radiative cooling effects in warming polar regions.