Kazuaki Kawamoto

A possible correlation between satellite-derived cloud and aerosol microphysical parameters

The column aerosol particle number and low cloud microphysical parameters derived from AVHRR remote sensing are compared over ocean for four months in 1990. There is a positive correlation between cloud optical thickness and aerosol number concentration, whereas the effective particle radius has a negative correlation with aerosol number. The cloud liquid water path (LWP), on the other hand, tends to be constant with no large dependence on aerosol number. This result contrasts with results from recent model simulations which imply that there is a strong positive feedback between LWP and aerosol number concentration. Estimates for indirect forcing over oceans derived from the satellite data/model comparison range from −0.7 to −1.7 Wm−2.

A Global determination of cloud microphysics with AVHRR remote sensing

An algorithm is developed for determining the cloud optical thickness and effective particle radius simultaneously on a global scale using Advanced Very High Resolution Radiometer (AVHRR) multispectral radiance data. In the algorithm, the treatment of thermal radiation in Nakajima and Nakajima is improved by reformulating the thermal emission in the atmospheric layers. At the same time, the lookup table for thermal emission is parameterized in terms of the equivalent water vapor path in order to include the effect of various vertical water vapor profiles. The algorithm is applied to AVHRR radiance data corresponding to reported aircraft and balloon measurements of cloud microphysical parameters. A comparison shows a good agreement between in situ and satellite-retrieved values thus obtained. The algorithm is further applied to 4-month Global Area Coverage data of 1987 to generate global distributions of the cloud optical thickness and effective particle radius for every 0.5 83 0.58 box in a 2608‐608 latitudinal region. Similarities and differences in the global features of the effective particle radius and the optical thickness are found as compared with the previous studies.

Significance of direct and indirect radiative forcings of aerosols in the East China Sea region

� 8W /m 2 at the top of atmosphere (TOA) and � 10 to � 23 W/m 2 at Earth’s surface of Gosan (33.28N, 127.17E) and Amami-Oshima (28.15N, 129.30E) sites, though there is a large regional difference caused by changes in the aerosol optical thickness and single scattering albedo. The cloud forcing is estimated as � 20 to � 40 W/m 2 , so that the aerosol direct forcing can be comparable to the cloud radiative forcing at surface. However, the estimate of the aerosol direct forcing thus obtained strongly depends on the estimation method of the aerosol properties, especially on the single scattering albedo, generating a method difference about 40%. The radiative forcing of the aerosol indirect effect is roughly estimated from satellite method and SPRINTARS model as � 1t o� 3W /m 2 at both TOA and surface. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 1610 Global Change: Atmosphere (0315, 0325); 9320 Information Related to Geographic Region: Asia;

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.

Effect of precipitation on water cloud properties over China

[i] I compared the amount of precipitation P and non-precipitation water cloud properties (effective radius r e and columnar number density N c of droplets) over China in the mid-latitude frontal zone. In general, N c decreased and r e increased as P increased. The rates of variation also became less steep beyond a certain P for both parameters, suggesting saturation. These relationships could be interpreted as due to the effect of scavenging of aerosols via precipitation on the cloud properties. The observed cloud properties of fewer cloud condensation nuclei (CCN) in the rain-rich regions and of more CCN in the rain-poor regions support a previously proposed mechanism. Comparison with an Amazon case in the convective zone revealed some similarities and differences in the characteristics of the obtained relationships.

Aerosol climatology over Japan site measured by ground-based sky radiometer

Aerosol and cloud optical properties are studied using data from ground-based and ship-borne sky radiometer measurements in the world. We are seeking in this data information on the aerosol optical characteristics with respect to their temporal and spatial variability and validation of Satellite and numerical models. The aerosol optical thickness has clear temporal and spatial variability at six sites in Japan. Comparisons between aerosol optical thickness at 0.5 μm retrieved with a sky radiometer and SPRINTAS at six Japan sites. Model of all sky AOT500 is good correlation. But, model of clear sky AOT500C is not good correlation. We will confirm the trends of aerosol climatology and help explain the reason.

Shortwave Absorption Properties of Atmosphere over China

The absorption of shortwave radiation in the atmosphere was investigated by using ISCCP‐FD monthly data and quality‐controlled pyranometer monthly data in China for the period from 1984 to 1999. The net shortwave radiation at the top of the atmosphere was evaluated from ISCCP‐FD data, while that at the surface was evaluated from pyranometer data of Chinese Meteorological Administration with ISCCP surface albedo values. The absorptance of the atmosphere was obtained by normalizing with solar insolation at the top of the atmosphere. The results obtained from 44 locations are as follows. The absorptance of the atmosphere over China is 27.1% which is larger than that estimated to be global average of 20%, and becomes up to 40% in several locations. The large abosorptance is found in the central, east and southeast regions of China. The absorptance in the north and northeast regions of China has a maximum in spring or summer season, while that in the central region, particularly in the Sichuan basin, has a maximum in winter season. The absorption properties in the latter region might be attributed to absorbing aerosols. Clouds, in general, do not affect the shortwave absorptance so much while aerosols as well as water vapor affect it particularly in small cloud amount cases and in the high latitude regions in winter where optical path of direct solar radiation is large.

Introducing Potential Radiative Forcing (PRF) for quantifying the Earth radiation budget

In order to investigate the contributions of atmospheric factors to variability in surface shortwave irradiance (S) under both cloud‐free and cloudy sky conditions, we defined the sensitivity of S to differential increases from given values of cloud, aerosol, and water vapor as potential radiative forcing (PRF). The expected change in S due to one factor would be the product of the PRF and the change in that factor. We formulated the PRF from a simple equation and described the geographical features of the PRF over China in January and July. We noted some shortcomings, but confirmed the usefulness of the PRF for determining the relative contributions. In particular, we suggested that accurate knowledge of aerosol absorption properties was critical for quantitative radiation budget estimates.

Retrieval of optical properties of water cloud from VIS/IR and comparison with TMI/TRMM

We studied a method to retrieve the optical thickness and effective particle radius of water clouds using the split-window channels and the 8.7-μm channel of Meteosat-8. Valid ranges are approximately from 1 to 9 for optical thickness and smaller than 18 micron for effective particle radius. The retrieval used the brightness temperature (TBB) and brightness temperature difference (BTD) between the split windows, as computed with the radiation code RSTAR5b for various properties of water clouds and vertical profiles of temperature and water vapor. The retrieved cloud parameters were then compared to those retrieved by the solar reflection method, which employs the 0.6-, 3.9-, and 11- μm channels of Meteosat-8. Comparison between the two methods revealed that the split-window technique could capture spatial features for both optical thickness and effective particle radius. The BTD is a good indicator for optical thickness. The diurnal variation of BTD shows the minimum value (thickest) before sunrise. Further precipitation and optical depth estimated from TMI/TRMM are compared with optical properties.