• Atmosphere
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• v.33 no.1
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• pp.21-32
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• 2023

Characteristics of downslope windstorm (DW) has been examined mainly based on 1-min average wind and the other meteorological conditions in the Yeongdong region for 2000~2020. First, a classification procedure for the downslope windstorm is proposed using surface wind speed (greater than 99 percentile), 1-hour longevity of strong wind (SW), westerly wind direction, low humidity (less than 20 percentile), and leeside warming. The number of DW days satisfying the proposed criteria is 221 (2.9% of total days and 47.5% of SW days) while the number of SW days is 465 (6.1% of total days) for 2000~2020. The occurrences of both SW and DW shows distinctive annual variation with its peak in April. In addition, mean wind speed of DW days is 8.2 m s^-1 with its duration of 2 hr 30 min and relative humidity of 28% at Gangneung. An episode (7 May 2021) was selected by applying the proposed criteria to SW days of 2021. The sounding shows that the layer of wind speed greater than 25 m s^-1 was lowered down to 925 hPa at Gangneung (leeside) relative to 850 hPa at Hoengseong (Wonju), in the afternoon along with significant warming and drying. Froude numbers of Wonju and Gangneung for the DW events were increased 4 and 5 times greater than those of normal days, respectively. This kind of DW long-term statistics in the leeside of the mountains is thought to build a foundation of further understanding DW mechanism.

• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.4
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• pp.403-410
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• 2009

This paper discusses an application method of critical strains concept for tunnels' safety by using the values of measured displacements which are obtained in the field. The aim of this paper is to: (1) study on the engineering meanings of critical strains concept by reviewing the previous researches and application examples with measured displacement values; (2) study on the engineering reasonability of critical strains concept with the view point of a tunnel engineering and a geotechnical engineering; (3) study on the features of ground deformation due to tunneling and reciprocal relation between total displacement and measured displacement; (4) evaluate a tunnel safety by using domestic measurements collected in the field; and (5) re-evaluate the control criteria which were previously used in the field, with the view point of critical strains concept. Consequently, it was confirmed that critical strains in the ground has a reasonability and a possibility of unified or common concept with the view point of a tunnel engineering.

• Journal of the Korean earth science society
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• v.37 no.4
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• pp.187-199
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• 2016

The purpose of this study is to investigate the formation mechanism of landspout by using the Cloud Resolving Storm Simulator (CReSS). The landspout occurred over Ilsan, Goyang City, the Republic of Korea on June 10, 2014 with the damage of a private property. In synoptic environment, a cold dry air on the upper layers of the atmosphere, and there was an advection with warm and humid air in the lower atmosphere. Temperature differences between upper and lower layers resulted in thermal instability. The storm began to arise at 1920 KST and reached the mature stage in ten minutes. The cloud top height was estimated at 9 km and the hook echo was appeared at the rear of a storm in simulation result. Model results showed that the downburst was generated in the developed storm over the Ilsan area. This downburst caused the horizontal flow when it diverged near the surface. The horizontal flow was switched to updraft at the rear of storm, and the rear-flank downdrafts (RFDs) current occurred from simulation result. The RFDs took down the vertical flow to the surface. After then, the vertical vorticity could be generated on the surface in simulation result. Subsequently, the vertical vorticity was stretched to form a landspout. The cyclonic vorticity of echo hook from simulation was greater than $3{\times}10^{-2}s^{-1}$(height of 360 m) and landspout diameter was estimated at 1 km.