A study of clouds in Thailand using ground and satellite based data

Abstract

This research can be divided into three parts. The first part is to investigate the optical thickness of low cloud at Nakhon Pathom station (13.82°N, 100.04°E), Thailand during 2019-2020. A method for determining the physical properties of cloud from a spectroradiometer with a radiative transfer model (LibRadtran) was carried out. According to the method, cloud optical thickness (COT) for ultraviolet, visible and near-infrared radiation were determined under an overcast sky. It was found that the COT in the UV and visible wavelengths are approximately similar and the COT increases in the near-infared wavelengths. These observation results correspond to the theory.

The second part of the research is a mapping of COT and cloud effective radius (re) over Thailand using satellite data. In this work, the COT and re have been derived using a radiative transfer model (SBDART) together with data from Himawari-8 satellite during 2016-2020. The maps of monthly average values of COT and re were generated, and the characteristics of COT and re were analyzed. The maps show the seasonal variations of COT and re.

In the final part, maps of total cloud amount over Thailand using satellite data were generated. In this study, a model relating cloud cover obtained from ground-based measurement (Skyviews, model PSV-100) and cloud index retrieved from MTSAT-1R satellite data at four stations in Thailand during 2009-2016 was developed. This model was used to estimate cloud cover at four sites. The result of the model validation in terms of root mean square difference (RMSD) and mean bias difference (MBD) were found to be 12.9% and 3.5%, respectively. After the validation, the model was used to estimate cloud amount over Thailand and the results are shown as monthly and yearly maps.

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