Abstract
A case study is made of the orographically distorted fields of surface meteorological elements in typhoons by using one pair of northern-crossing typhoons and another pair of southern-crossing ones over the Island of Taiwan. The orographic effects on the surface pressure, temperature and humidity are evaluated in terms of their anomalies from the corresponding five-year averaged monthly means.
The important results of the present investigation are as follows:
(1) Formation of a pressure trough occurs on the lee side, i.e., on the west (east) side for northern (southern)-crossing typhoons, of the Central Mountain Range (CMR), and a pressure ridge forms on its windward side. The ridge-trough system becomes more intense as the wind component across the mountain range increases.
(2) Generally heavy rainfall occurs over the windward side of the CMR and a Foehn, i.e., the warm and dry air, is observed on its lee side. The intensity of the Foehn is closely related to the strength of the wind across the mountain range and the rainfall intensity on the windward side.
(3) Formation of secondary vortices occurs on the west side of the CMR and over the southern tip of the island in the case of a smaller northern-crossing typhoon. In the case of the southern-crossing typhoon, a secondary vortex forms on the southwest side of CMR in advance of its crossing over the mountain range when the airstream approaches the north-eastern region of the island with a large angle of incidence to the CMR axis.
