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The study examines spatial and temporal changes in monthly precipitable water vapour (PWV) over Thailand using 37 years of monthly ERA-Interim re-analysis data (1981–2017). PWV from ERA-Interim data was compared with that derived from radiosonde observations at four stations and it was shown to have an average root-mean-square error and mean bias error of 0.264 cm and −0.137 cm, respectively. Then, PWV from ERA data was used to estimate spatial patterns of monthly average PWV for the winter (Nov, Dec, Jan), summer (Feb, Mar, Apr, May) and rainy (Jun, Jul, Aug, Sep, Oct) seasons as well as the yearly averages. Statistically significant increases in PWV are found in the rainy season which has been related to the West Pacific index (WP). A second statistically significant increasing trend is found over the southern half of Thailand during the winter season which could be influenced by changes related to the Siberian High pressure. [ABSTRACT FROM AUTHOR]

The study examines three satellite-based data sets to estimate long-term precipitation for the Thailand region: the Tropical Rainfall Mapping Mission (TRMM) 3B43, the Climate Prediction Centre morphing technique (CMORPH), and a locally developed regression model using the geostationary meteorological satellite (GMS) covering the Thailand region. Data for the first two sets were available at a spatial resolution of 0.25° × 0.25°, while the local regression model used data from the GMS at a resolution of 5 km × 5 km. The statistical regression model was developed by relating long-term monthly average precipitation from 27 rain gauge stations with concurrent satellite data in the visible and thermal infrared bands. The model was then tested against independent data from 27 rain gauge stations. Satellite/rain gauge ratios were estimated, and a smooth spline surface was used to correct the error from the model. Data from the three approaches were compared with a rain gauge network. The TRMM relation performed better than CMORPH, and the performance for GMS was comparable to TRMM with root mean square different and mean bias difference of 33.6 and 4.2%, respectively. The locally developed regression model was used to produce monthly and yearly total rainfall maps from the GMS data for the entire country. [ABSTRACT FROM PUBLISHER]

This paper presents a statistical approach for estimating vertical diffuse illuminance in a tropical environment. A two-year period (2003–2004) of vertical and horizontal diffuse illuminance data from four measuring stations in Thailand were used for the model development. These data were divided into three groups according to sky conditions, namely clear, overcast and partly cloudy skies. Vertical and horizontal diffuse illuminances in overcast conditions were directly related using regression analysis and an equation relating vertical diffuse illuminance to horizontal diffuse illuminance was established. A similar set of equations was established for vertical sunlit and shaded surfaces under clear sky condition. To obtain the vertical illuminance model for all sky conditions, the correlation equations for clear and overcast skies were linearly combined using cloud cover as a weighting parameter. The performance of this regression model was evaluated using a one-year period (2005) of measured data. The discrepancies between the calculated and measured vertical illuminance in terms of RMSD range from 15.1% to 22.4%, depending on sky conditions, the orientation of the receiving surface and the positions of the sun relative to the surface. The performance of the proposed model was also compared to that of 12 models reported in literatures. It was found that the proposed model has the lowest RMSD for clear, partly cloudy and overcast sky conditions. [Copyright &y& Elsevier]

Aerosol optical depth and Angstrom coefficients for three sites in Bangkok and suburbs are examined: Silpakorn University at Nakhon Pathom, NP (13.82°N, 100.04°E), the Asian Institute of Technology at Phatum Thani, AIT (14.08°N, 100.62°E) and the Thai Meteorological Department at Bangkok, BK (13.73°N, 100.57°E). Sunphotometers have been used to measure direct normal spectral irradiance at these sites for a period of 2 years (2004–2005). Cloudless conditions were selected and Bouguer’s law was employed to obtain aerosol optical depth. All three sites exhibit strong seasonal variations, with the highest values occurring at the height of the dry season in April, and the lowest occurring during the rainy season in July. April turbidity conditions are very high, as evidenced by maximum 500 nm optical depths of between 1.4 to 2.0 that were measured at all three locations. The Angstrom exponent α also showed a marked seasonal change, with highest values at the height of the dry season. [ABSTRACT FROM AUTHOR]

In this paper, calculation of monthly average hourly diffuse photosynthetically active radiation (PAR) using satellite data is proposed. Diffuse PAR was analyzed at four stations in Thailand. A radiative transfer model was used for calculating the diffuse PAR for cloudless sky conditions. Differences between the diffuse PAR under all sky conditions obtained from the ground-based measurements and those from the model are representative of cloud effects. Two models are developed, one describing diffuse PAR only as a function of solar zenith angle, and the second one as a multiple linear regression with solar zenith angle and satellite reflectivity acting linearly and aerosol optical depth acting in logarithmic functions. When tested with an independent data set, the multiple regression model performed best with a higher coefficient of variance R 2 (0.78 vs. 0.70), lower root mean square difference (RMSD) (12.92% vs. 13.05%) and the same mean bias difference (MBD) of −2.20%. Results from the multiple regression model are used to map diffuse PAR throughout the country as monthly averages of hourly data. [ABSTRACT FROM AUTHOR]

This paper presents an algorithm for deriving the effective droplet radius and optical depth of liquid water clouds using ground-based measurements, aircraft observations and an adiabatic model of cloud liquid water. The algorithm derives cloud effective radius and cloud optical depth over a tropical site at Omkoi (17.80°N, 98.43°E), Thailand. Monthly averages of cloud optical depth are highest in April (54.5), which is the month with the lowest average cloud effective radius (4.2 μm), both occurring before the start of the rainy season and at the end of the high contamination period. By contrast, the monsoon period extending from May to October brings higher cloud effective radius and lower cloud optical depth to the region on average. At the diurnal scale there is a gradual increase in average cloud optical depth and decrease in cloud effective radius as the day progresses. [ABSTRACT FROM AUTHOR]

In this study, a model for calculating monthly average hourly diffuse erythemal solar ultraviolet (EUV) radiation under all sky conditions in Thailand was developed. The model is a function of air mass, aerosol optical depth and satellite-derived cloud index, as these parameters are sensitive to diffuse EUV radiation. Diffuse EUV irradiance were measured using UV-biometers equipped with shade ball during April 2011–March 2014 at four stations in Thailand. Data from these stations were used to formulate the model. The model was validated using an independent dataset (April 2014–March 2016) at the same sites. The modeled diffuse EUV irradiance showed good agreement with that from the ground-based measurements, with root mean square difference (RMSD) of 12.7% and mean bias difference (MBD) of −2.8%. The use of satellite data provided a simple and practical method to calculate monthly average hourly diffuse EUV irradiance over Thailand. Spatial monthly distributions are shown as maps. [ABSTRACT FROM AUTHOR]

Abstract: A technique for mapping global illuminance from satellite data was developed. A five-year (1998–2002) climatology of global solar illuminance obtained from this technique is presented for Thailand using hourly GMS-5 satellite data. The technique is based on a radiation budget model which traces solar radiation as it is scattered, absorbed and reflected back to space. The model produces an earth-atmospheric albedo in the satellite spectral window as well as global illuminance at the earth’s surface. The model is tuned using surface illuminance measurements at four stations in Thailand: Chiang Mai (18.78°N, 98.98°E), Ubon Ratchatani (15.25°N, 104.87°E), Songkhla (7.20°N, 100.60 °E) and Nakhon Pathom (13.82°N, 100.04°E). In the mapping process, a satellite earth-atmospheric albedo at any locations yields a cloud-atmospheric albedo in the satellite band, which is then transformed into a cloud-atmospheric albedo in the photopic band. Having obtained the photopic cloud-atmospheric albedo, the model calculates surface illuminance. The model gives a root mean square difference of 8.1% and a mean bias difference of −2.6% when tested against an independent data set. Monthly average maps are presented covering Thailand for local times of 10:30, 12:30 and 14:30. [Copyright &y& Elsevier]

This work has developed a semi-empirical model for estimating monthly average hourly diffuse solar near infrared (NIR) radiation in Thailand. Diffuse NIR radiation data were recorded at four stations in Thailand namely, Chiang Mai (18.78 o N, 98.98 o E), Ubon Ratchathani (15.25 o N, 104.87 o E), Nakhon Pathom (13.82 o N, 100.04 o E) and Songkhla (7.20 o N, 100.60 o E). Our analysis has shown that diffuse NIR radiation is related to cloud, precipitable water and cosine of solar zenith angle in terms of an exponential function. Therefore, the model was formulated with these parameters and validated with independent diffuse NIR measurements. The result showed that diffuse NIR radiation from the model and that from the measurements were in reasonable agreement with root mean square difference and mean bias difference of 16.7% and 1.5%, respectively. The semi-empirical model was used to generate diffuse maps of NIR for the country which displayed both diurnal and seasonal variations. [ABSTRACT FROM AUTHOR]