Geostationary satellites are well suited for radiation budget computations due to their high temporal resolution. In order to validate satellite observations and the radiative properties derived from the GMS-5/SVISSR, we compared its cloud optical depth (COD) with that from the polar orbiting satellite, TERRA/MODIS. It appears that there's a good agreement between both COD sets in thin cloud areas while, major differences (MODIS COD higher) occur in thick cloud regions. Factors affecting accurate observations of clouds by satellites range from the solar and satellites geometries to the sun-cloud scale of interaction. This study focuses on the latter effect, as the solar and satellite zenith angles are relatively low in the area and time selected. The sun-cloud interactions refer here to the three-dimensional radiative effects (e.g. asymmetry, smoothing) due to the horizontal spatial variability of clouds and their structural inhomogeneity. These are analyzed through the IR thermal gradient and small areas' standard deviation (STDEV) respectively. By combining these two parameters, it is possible to reasonably explain the differences in cloud physical and optical properties noticed between both satellites. Results show that, asymmetry and smoothing effects seem to be stronger for SVISSR data than MODIS. At the sides of the clouds SVISSR observed cloud properties are more or less comparable to MODIS data. At the top of the clouds, SVISSR data are systematically lower and do not match MODIS data. SVISSR observations fail to detect cloud inhomogeneity mostly at the top of the clouds, and therefore seem to underestimate the cloud optical properties.
The data analyses of the ADEOS-II (Midori-II) GLI data have started. The optical and microphysical properties of warm water and cold ice clouds were retrieved by use of originally developed GLI data analysis algorithms. On the one-month mean results of warm water cloud in April 2003, very thick cloud optical thickness appeared in the east coast of the North America, the East Europe, and the South-East Asia. The moderately optically thick area spread over the Atlantic Ocean and West to Middle Pacific oceans. The effective radius was smaller on the continents and coastal area than ocean area. Especially, the South-East Asia to the middle pacific area where often covered with aerosols coming from continent in April, is the region of the smaller cloud effective particles. For the cirrus clouds, the smaller effective radii and larger effective radii can be obtained in low-to-mid and mid-to-high latitude area, respectively. Very low cloud top temperatures around 210K were often observed in the tropics. Warmer cloud top temperatures ranging from 220 to 240K were widely seen both over continental and oceanic area in mid-to-high latitude area.
Cloud is an important factor for the radiation budget through reflection of solar radiation and absorption of terrestrial radiation. Climate change is dependent on these two effects and focusing on an aerosol-cloud interaction. In East Asian region, consumption of fossil fuels is increasing and emits many kinds of gas and particles in addition of natural sources. The indirect effect of aerosol depends on the aerosol characteristics and weather conditions. The particle size and chemical features of aerosols affect cloud formation and particle size. Therefore, it is interesting to understand cloud properties such as a liquid water path (LWP) and cloud effective radius (Reff). This study is to estimate these two parameters with ground-based observations. In the paper a method to estimate a cloud effective radius and optical thickness is proposed using a combination of corrected LWP and the downward solar radiation. It is useful for continuous observation, especially LWP can be estimated for all day.
KEYWORDS: Calibration, Temperature metrology, Atmospheric modeling, Satellites, Troposphere, Transmittance, Algorithm development, Data analysis, Gases, Water
Water vapor is one of the most significant green house effect gases. A monitoring of water vapor behavior with operational satellite is important to investigate the global changes. Water vapor usually exists at lower troposphere. However, precipitable water is a key property to comprehend the variation since sometimes humid air mass moves to the upper troposphere. Using split window channel data with optical sensors such as AVHRR and VISSR, several retrieval algorithm has been proposed and among them, transmittance ratio method has been often utilized. However, the approach is still controversial because some studies concluded it was available and others not. We investigated the availability of the method with split window channels' data of GMS-5/VISSR on a semi-continental scale. A calibration curve of the precipitable water with radiosonde observation had been made in course of the retrieval procedure. However, the calibration curve are hardly sensitive to the precipitable water. Numerical simulations were carried out for the possible condition, and it turned out that calibration was insensitive to precipitable water under some condition at all: larger water water variation for a given surface temperature range within a given region. The results of a feasibility study will be discussed.
A quasi real time system for estimate of the surface solar flux is introduced. The system will start to be operated in this year, and provide the solar flux until tomorrow’s morning. The system uses 0.09-degree resolution products from the GMS-5 image data of CEReS, Chiba Univ. It also uses the six-hourly atmospheric objective analysis data from the Japan Meteorological Agency. The solar flux is estimated at each pixel. This system includes four steps to estimate the surface solar flux. (1) The first step discriminates cloud pixel from clear one. The adopted method is similar to ISCCP, in which the reference Tbb for discrimination is created by data before and after the target day. In this system, it is impossible to use tomorrow’s data, because real time operation is needed. Therefore historical data is used to create the reference. (2) Cloud pixel is analyzed using 11/12 micron split window methods and 6.7 micron channel. The methods determine that the pixel is water or ice cloud, and derives the optical thickness for ice cloud. (3) The optical thickness for water cloud is retrieved from the reflection method using visible channel with assumption of the effective radius. (4) Cloud optical thickness and atmospheric information is converted to the surface solar flux from the package RSTAR5B for radiation transfer calculation. The surface solar flux using typical pixels from 0.5-degree grid area had been already derived. A comparison of satellite derived solar flux and the surface observation shows fair result in clear sky days, and overestimate in cloudy days.
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