臺灣北部和南部氣壓日變化之分析研究

The Study of Diurnal Surface-Pressure Variations in the Northern and Southern Taiwan

蒲金標(Chin-Piao Pu)

《大氣科學》 29卷3期 (2001/09) Pp. 191-202

摘要

本文就1979~1998年台北松山、桃園中正、高雄小港以及1987~1998年台東豐年等四機場航空氣象台每天逐時海平面氣壓和溫度，分析其氣壓和溫度日變化之時空變化。研究顯示台灣無論是北部或南部，年平均逐時海平面氣壓之日變化曲線皆有兩次升降，唯主要最高氣壓皆發生在上午9時，其相位提早1小時；第二最高氣壓皆發生在晚上22時，但南部第二最高還持續延至23時。主要最低氣壓，北部發生在下午15時；高雄發生在下午16時；台東發生在下午17時，相位則落後1小時。台灣地處副熱帶地區，午後盆地溫度高於海岸邊，導致松山氣壓日變化之振幅大於中正機場。氣壓日變化，緯度越低，振幅越大。無論是北部或南部氣壓日變化，主要最高或主要最低氣壓皆發生在白天，也即白天振幅大於晚間，尤其以高雄主要最低氣壓之振幅為最大（距平-1.4hPa）。惟台灣無論北部或南部，夏季氣壓日變化振幅較小；春秋和冬季振幅較大；其中以冬季高雄最主要最低氣壓之振幅為最大(-1.8hPa)。
四季除了夏季之外，春、秋及冬等三季季節平均氣壓日變化，皆與全年平均氣壓日變化曲線之主要與第二最高和最低氣壓所發生時間，大約一致。夏季，台北、桃園及高雄等地氣壓日變化曲線，主要最高氣壓發生在晚上22時，第二最高氣壓發生在上午8~9時，即與全年和其他季節平均氣壓日變化曲線之主要最高發生在白天，第二最高發生在晚間，兩者大不相同。台東夏季平均氣壓日變化曲線之主要最高和第二最高，兩者氣壓値相同，前者發生在上午8~9時，後者發生在晚上22~23時。夏季四機場氣壓日變化曲線，白天主要最低氣壓發生在下午16~17時，第二最低氣壓發生在清晨3~5時。
台灣南北各地在中午12時至下午1~2時溫度達到最高，對機場在下午3時至4時較低氣壓之振幅有加深之作用；晚上溫度下降，對機場在清晨4時發生較低氣壓之振幅，有塡塞之作用。所以氣壓日變化在下午3~4時發生主要最低之振幅比在清晨4時發生另一個較低氣壓之振幅為大。惟夏季主要最高氣壓發生在晚上，第二最高氣壓發生在白天，且第二最高氣壓發生時間提早2小時，可能與上午10~16時溫度高達30℃以上似乎有相關，上午10時高溫，致氣柱膨脹，氣壓變低，降低原本在上午10時應為主要最高氣壓，使氣壓反而比原本在晚上22時應為第二最高氣壓還低。
台北松山、桃園中正、高雄小港以及台東豐年等四個機場年平均逐時氣壓之日變化，可作為考慮測站氣壓變化趨勢以及分析綜觀和中尺度天氣系統移動和發展之參考。

關鍵字

氣壓日變化 ； 溫度日變化 ； 振幅

並列摘要

This paper presents the results of a detailed study of the spatial and temporal variation in the diurnal components of sea level pressure and temperature in the Northern and Southern Taiwan. The data adopted for this study is the hourly surface observation from the Aeronautic Meteorological Stations of Sungshan (RCSS), Chiang Kai Shek (RCTP) and Kaohsiung (RCKH) during 1979~1998 and Fengnian (RCFN) during 1987~1998, the hourly pressure and temperature were expressed as annual average for each day.
It is shown that the mean sea level pressure variation at RCSS, RCTP, RCKH and RCFN virtually consist primary diurnal components. The diurnal wave can be determined for these stations from long-term averages of hourly surface-pressure readings. The primary maximum in this wave occurs at 0900L; thesecondary maximum at 2200L; the primary minimum at 1500L at RCSS and RCTP, 1600L at RCKH, 1700L at RCFN; and the secondary minimum at 0300L at RCSS and RCTP, 0400L at RCKH, 0500L at RCFN, respectively.
Taiwan is located in the subtropical area. The amplitude of the pressure diurnal wave are greater at RCSS (located in basin) than at RCTP (located at offshore area), in the southern than in the northern Taiwan, in daytime than in nighttime, in winter than in summer. At RCKH the amplitude of the primary minimum is greatest (-1.8hPa) in winter. The primary maximum and minimum occur at daytime, but the primary maximums occur at 2200L in summer for RCSS, RCTP and RCKH.
The component of sea level pressure at these locations reaches two relative maximums, one (the primary maximum) is at 0900L and the other (the second maximum) is at 2200L. It also reaches two relative minimums, one (the primary minimum) is at 1500L at RCSS and RCTP, 1600L at RCKH, 1700L at RCFN, the other (the second minimum) is at RCSS and RCTP, at 0400L at RCKH, 0500LST at RCFN.
The diurnal surface pressure changes can also be affected by the heating and the cooling at the lower troposphere or by the resulting diurnal circulation. A larger amplitude of the primary minimum is observed at 1500~1700L at RCSS, RCTP, RCKH and RCFN. This may be due to the highest temperature at1200~1300L, therefore the heating at the lower troposphere results in substantial pressure falls. At RCKH large surface diabatic forcing; diurnal pressure changes exceed -1.4hPa at 1500~1600L. A smaller diurnal pressure variation is observed at 0300~0500L at RCSS, RCTP, RCKH and RCFN when nighttime radiation cooling at the lower troposphere results in substantial pressure rise.
These variations obscure pressure changes associated with the movement and evolution of transient synoptic and mesoscale systems and dominate the pressure under quiescent conditions.

並列關鍵字

Diurnal pressure variation ； Diurnal temperature variation ； Amplitude