Abstract
The WBGT index is commonly used to indicate heatstroke disease risk but the index does not always expect the risk in night time correctly. The puopose of the present study is to examine whether daily fluctuation patterns of surface wind directions can be a indicator which appropriately expresses the night time risk. It is shown that fluctuation characteristics of the WBGT vary by the daily fluctuation patterns. A new index Y(T) which is calculated by time integrations of the WBGT and can take past records of sultry environments into consideration is proposed and it is also shown that fluctuation characteristics of Y(T) differ by the patterns. It is indicated that night time averages of Y(T) for each pattern correlate closely with nocturnal heatstroke desease risks and the pattern W which means that west wind blows all day long has the highest risk for nocturnal heatstrokes. From the above results, we concluded the daily fluctuation patterns of surface wind directions can be utilized as a indicator to expect heatstroke disease risks in the night time.
