為探討塔塔加地區白天霧日之年變化趨勢，本研究先以麟芷山氣象站(23°28'38.68"N, 120°53'18.47"E, 2,780 m a.s.l.)之氣溫與相對濕度資料，應用Magnus公式，推算露點溫度，據之計算氣溫―露點溫度差(ATDPD)，並且配合短波入射輻射資料，作為推估白天時段之成霧條件基準值；另自2008年3月1日，於麟芷山氣象站設置能見度感應器，判讀白天的成霧時間，並擷取2008年至2009年有效的觀測值(實測值)，對照應用基準值所推估成霧時間(推估值)，結果顯示兩者呈現良好相關性(r2 = 0.66)。其次，依據所建立之基準值，進而推廣應用，以麟芷山與觀山(23°30'52.74"N, 120°54'42.72"E, 1,700 m a.s.l.)兩處氣象站歷史資料，推估兩站自1998年設站起至2009年為止各年之霧日，進而分析兩站白天霧日的年變化趨勢。分析結果表明，觀山氣象站呈現霧日逐漸減少之趨勢、麟芷山氣象站呈現霧日逐漸增加之趨勢。

To reveal the trends of annual daytime foggy days at Tatachia region of central Taiwan, we collected the air temperature and relative humidity from the Lintsushan Weather Station (23°28'38.68"N, 120°53'18.47"E, 2,780 m a.s.l.). The Magnus formula was used to estimate the dew point temperature, then the difference between air temperature and dew point (ATDPD) was calculated, and together with solar radiation data were used to determine fog formation time during daytime. To determine the actual fog formation time, a visibility sensor was installed at the Lintsushan Station at March 1, 2008. A linear regression model was then developed based on the measured (visibility sensor, independent variable) and estimated values from 2008 to 2009. The result showed a good agreement between the measured and estimated values (r2 = 0.66). Based on the regression model and the meteorological records, the historical annual foggy days from 1998 to 2009 at the Guanshan (23°30'52.74"N, 120°54'42.72"E, 1,700 m a.s.l.) and the Lintsushan Weather Stations were estimated. The results showed that annual foggy days decreased gradually at the Guanshan Station, but increased gradually at the higher elevation station.