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Research Article
ScienceAsia 32 (2006): 107-114 |doi: 10.2306/scienceasia1513-1874.2006.32.107
Ultraviolet Forecasting in Thailand
Sumridh Sudhibrabha,a* Robert Harold Buchanan Exella and Dusadee Sukawatb
ABSTRACT: Total ozone and erythemal UV models have been created for UV Index forecasting in Thailand.
Versions of an ozone model for Chiangmai, Ubon Ratchathani, Bangkok and Songkhla and a UV model for
Bangkok and Songkhla are available for operation on a daily basis. The procedure is to forecast ozone from
upper air data, and then calculate the forecast erythemal UV irradiance from the ozone forecast. In the ozone
models, a linear regression technique was used with fifteen coefficients for temperature and dynamic height
at the 100 hPa and 50 hPa levels where the ozone exists and daily balloon observations are made. Simple
ozone models were also developed for use in the areas without upper air observations. The data are in the
form of time series over three consecutive days. The UV models were obtained from Brewer UV data from
Bangkok and Songkhla fitted to a non-linear three dimensional equation which is a function of ozone and its
air mass to obtain five coefficients for the empirical formula. The models are used to estimate cloud-free
values of the UV Index over the different areas of the country. The output of the erythemal UV for a clear sky
is converted to the UV Index. The UV Index is then used to select one of five categories for issuing to the
public every noon. Reductions of the UV Index for cloudy skies are also given. The average accuracy of the
models is acceptable as the squares of the correlation coefficients (R2) are 0.88 and 0.99 for the ozone and UV
models respectively, while the mean absolute percentage errors are 1.5 % and 7.5 % for the ozone and UV
forecasting respectively.
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a Joint Graduate School of Energy and Environment, King Mongkut’s University of Technology Thonburi,
Bangkok 10140.
b Department of Mathematics, Faculty of Science, King Mongkut’s University of Technology Thonburi,
Bangkok 10140.
* Corresponding author, E-mail: sumridh@metnet.tmd.go.th
Received 13 May 2005,
Accepted 27 Dec 2005
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