Synoptic scale analyses of the cloud microphysical properties using MODIS 5-kilometers sub-sampling radiance dataset

5-km sub-sampling MODIS radiance dataset (MOD02SSH) were analyzed to retrieve cloud optical thickness and effective radius over the synoptic scale of FIRE, ASTEX, and GAME region. Since MOD02SSH dataset retains IFOV of each pixel and “texture” of images reducing the data size of 1/25, the results contribute to the process studies such as the cloud droplet growth that needs many sample results with fine spatial resolution.

Spatial distributions, optical and microphysical properties of clouds are the important observing targets in climate studies. In this decade, cloud optical thickness and effective particle radius have been retrieved from narrow band multi-channel spectrometers aboard the aircraft (Nakajima et al. 1991), AVHRR aboard NOAA satellite for regional scale (Nakajima and Nakajima 1995) and for global scale (Han et al. 1995, Kawamoto et al. 2001). The retrieval technique has gradually matured and been promissing, so that the MODIS aboard Terra/Aqua and GLI aboard Midori2 missions processed cloud properties systematically in these years.

Since the cloud retrieval requires relatively high-cost computing resources, the most analyses for global scales used the reduced-size subsets of satellite-borne radiance. For example, Han et al. (1994) retrieved cloud properties for global scale using near-nadir looking AVHRR data (satellite zenith angle < 26 degs). Kawamoto et al. used segment AVHRR data that are map-projected radiances at every 0.5 degrees in latitude and longitude segment boxes for a whole globe (each segments has 10x10=100 pixels of radiance data). In fact, these subsets degrade the spatial fineness of analyses (and textures were disturbed), whereas reduce the computer resource requirements in both CPU powers and data storage volume. The studies of cloud droplet growth process need finer results than these subsets. Utilizing the sub-sampling radiance dataset will be one of suitable solutions for the problem. For example, AVHRR GAC (Global Area Coverage) and MODIS MOD02SSH dataset reduced the dataset size by 5-km sub-sampling, and GLI L2A_OA dataset by 4-km sub-sampling. It is notable that they are retaining the IFOV of each pixel and “texture” of images, but simply reduced data size by 1/25 and 1/16, respectively.

The cloud properties over the synoptic scale at off the coast of California (FIRE region) the Azores Islands (ASTEX region), and Asia monsoon (GAME region) were retrieved from MOD02SSH dataset. About three-hours computing time retrieved one-month MOD02SSH data for synoptic scale of 30 x 30 degrees latitude and longitude in mid-latitude. The spatial resolution and the computing time are realistic and reasonable for the process studies. Optical thickness (Tau) vs effective particle radius (Re) scatter diagrams at each area will have a information of cloud growth at the certain area, thus, comparison between satellite results and model-simulated results of Tau-Re scatter diagram will yield better understandings of the obtained cloud properties. We found interesting features in MODIS-retrieved Tau-Re diagrams that will be explained as the cloud properties under the pristine and turbid environments, by the spectral microphysics cloud model.

In the presentation, we will discuss about the system design for the synoptic scale cloud analysis and about cloud retrieval algorithm, then show the typical and interesting features appeared in observed Tau-Re diagram in FIRE, ASTEX, and GAME regions.