태백ㆍ소백 산맥 풍하측 강풍 및 산악파 연구

Abstract

ABSTRACT

A Study of Down-Slope Windstorms and Mountain Waves of the Taebaek and the Sobaek Mountains

Shin, Ki-Chang Advisor : Prof. Ryu, Chan-Su, Ph.D. Department of Atmospheric Sciences Graduate School of Chosun University

Down-slope windstorm as one of medium-scale atmospheric phenomena caused by topographic effects from mountain chains is investigated and analyzed. As the long-term Siberian High with lots of pressure gradient stays at the Korean peninsula, it is known well the stronger wind blows. This pressure gradient depends upon time and geography, and the continuity of bigger pressure gradient can cause a strong windstorm. There are quite a lot of cases that the wind velocities of upper-slope and down-slope show an outstanding difference, and so this was caused by the effects of mountain chains. In this study focuses on comparing the relationships between Fr numbers(Froude number) showing the nonlinear effects and wind velocities were conducted. Characteristics shown in mountain waves were examined to define whether the down-slope wind of the Taebaek and the Sobaek mountains was generally caused by the mechanism of mountain heights. As the results, first, as the aspect of gravity wave, the vertically uniform stream was passed through the east and the west mountain chains-like geography to cause vibrations of the east and the west waves. Buoyancy which is a kind of restoring force, was caused the greatest amplitude wave on the ground of down-slope to bring a windstorm on the ground of down-slope. And also this was connected to reflection of wave breaking in the sky of down-slope to continuously cause a windstorm locally. Second, the inversion layer occurred around the top height of mountain chains of upper-slope. Fr number was examined to find out quantitatively whether blocking phenomena of upper-slope wind occurred or not. As a result, both regions showed some hydraulic jumps. Kinetic energy of air current flowed from the upper-slope of mountain chains was changed to potential energy and conversed to kinetic energy when it went down to down-slope, causing wind velocity of down-slope to be amplified. If the ratio of potential energy and kinetic energy expressed by Fr number was closer to 1, the windstorm of down-slope has shown the greatest amplification. Third, wind velocity was amplified by pressure gradient of the east and the west mountain chains. Air parcel that crossed over mountain chains by the law of absolute vorticity conservation made an anticyclonic spin at the top altitude and a cyclonic spin at down-slope. This made pressure gradient stronger regionally between the top and the ground of down-slope to play a role of amplifying windstorm. Air current crossing over mountains was vertically delivered to cause warm current of mountain wave up to the upper tropopause. Especially, mountain wave as one of primary causes of air accident incurred by low altitude flight was one of important weather elements causing air accidents. Therefore, if the value of Fr number is obtained from recorded data and weather forecast of warm current to be produced using data of windstorm occurring at down-slope, it is assumed that more objective weather forecasts of mountain waves are available. The specific summery to be helpful for determining weather forecast is as follows. 1) Windstorms at inner zone of down-slope Youngdong and Youngnam of the Taebaek and Sobaek Mountains show a large number of frequency in Winter and Spring. In Winter, windstorms occurred at the inner zone of Youngnam region in distribution of West-High and East-Low systems relatively while in Spring it did mostly at Youngdong region in distribution of South-High and North-Low systems. But also, a considerable windstorm was accompanied by passing through Trough system. 2) Temporal frequency shows the maximum between 12:00 and 16:00 when the vertical unstability was shown, but the minimum at sunrise and sunset. 3) In down-slope Youngdong region of the Taebaek mountains, south wind or west wind was primary wind direction while at the inner zone of down-slope Youngnam region of the Sobaek mountains was main wind direction. This means that windstorm occurs when wind direction is made at a right angle in two mountain chains. 4) As a result of comparing pressure change between Fr number and down- and upper-slope, it made the difference of 2~3 hPa, and a large difference was made when Fr number was smaller than 1. This means that down-slope becomes cyclonic relatively for a cause to amplify wind velocity.