Debris flow overflowing flexible barrier: physical process and drag load characteristics

Landslides - The multiple-barrier mitigation strategy in the debris-flow source area is an effective approach to inhibit debris-flow entrainment and scale amplification along the flow path....     

Hybrid continuum–discrete simulation of granular impact dynamics

Acta Geotechnica - Granular impact—the dynamic intrusion of solid objects into granular media—is widespread across scientific and engineering applications including geotechnics....     

Improvement of daily precipitation estimations using PRISM with inverse-distance weighting

Improved daily precipitation estimations were attempted using the parameter-elevation regressions on a parameter-elevation regression on independent slopes model (PRISM) with inverse-distance weighting (IDW) and a precipitation-masking algorithm for precipitation areas. The PRISM (PRISM_ORG) suffers two overestimation problems when the daily precipitation is estimated: overestimation of the precipitation intensity in mountainous regions and overestimation of the local precipitation areas. In order to solve the problem of overestimating the precipitation intensity, we used the IDW technique that employs the same input stations as those used in the PRISM regression (PRISM_IDW). A precipitation-masking algorithm that selectively masks the precipitation estimation grid points was additionally applied to the PRISM_IDW results (PRISM_MSK). For 6 months from March to August 2012, daily precipitation data were produced in a horizontal resolution of 1 km based on the above two experiments and PRISM_ORG. Afterwards, each experiment was evaluated for improvements. The monthly root mean squared errors (RMSEs) of PRISM_IDW and PRISM_MSK were reduced by 0.83 mm/day and 0.86 mm/day, respectively, compared to PRISM_ORG.     

Photochemical characteristics of high and low ozone episodes observed in the Taehwa Forest observatory (TFO) in June 2011 near Seoul South Korea

We present a comprehensive discussion on what cause high ozone episodes at a suburban photochemical observation site of the Seoul Metropolitan Area (population ～23 million). The observational site, Taehwa Research Forest (TRF), is situated ～30 km from the center of Seoul. In June 2011, we observed two very distinctive ozone periods-high ozone (peak up to 120 ppbv) and low ozone (peak up to 60 ppbv) in the mid and early month, respectively. The trace gas measurement dataset, especially CO and NO _X clearly indicate that less anthropogenic influences during the high ozone period. Volatile organic compound (VOC) measurement results show that at the observational site, biogenic VOCs (mostly isoprene) contribute most of chemical reactivity towards OH, although toluene from anthropogenic activities was observed in higher concentrations. Back-trajectory analysis indicates that air-masses from the forest part of Korea Peninsula were dominant influences during the high ozone episode event. On the other hand, Aged air masses from China were the dominant influence during the low ozone episode event. Model calculations conducted using the University of Washington Chemical Mechanism (UWCM) box model, also consistently show that BVOC, especially isoprene photochemistry, can be the significantly contribution to local ozone formation in the given photochemical environments of TRF. These research results strongly suggest that ozone control strategy in the Eastern Asian megacities, mostly situated in surrounding forest areas should be based on the comprehensive scientific understanding in BVOC photochemistry and interplays between anthropogenic and biogenic interactions.     

Climate change in the 21st century simulated by HadGEM2-AO under representative concentration pathways

We present climate responses of Representative Concentration Pathways (RCPs) using the coupled climate model HadGEM2-AO for the Coupled Model Intercomparison Project phase 5 (CMIP5). The RCPs are selected as standard scenarios for the IPCC Fifth Assessment Report and these scenarios include time paths for emissions and concentrations of greenhouse gas and aerosols and land-use/land cover. The global average warming and precipitation increases for the last 20 years of the 21st century relative to the period 1986-2005 are +1.1°C/+2.1% for RCP2.6, +2.4°C/+4.0% for RCP4.5, +2.5°C/+3.3% for RCP6.0 and +4.1°C/+4.6% for RCP8.5, respectively. The climate response on RCP 2.6 scenario meets the UN Copenhagen Accord to limit global warming within two degrees at the end of 21st century, the mitigation effect is about 3°C between RCP2.6 and RCP8.5. The projected precipitation changes over the 21st century are expected to increase in tropical regions and at high latitudes, and decrease in subtropical regions associated with projected poleward expansions of the Hadley cell. Total soil moisture change is projected to decrease in northern hemisphere high latitudes and increase in central Africa and Asia whereas near-surface soil moisture tends to decrease in most areas according to the warming and evaporation increase. The trend and magnitude of future climate extremes are also projected to increase in proportion to radiative forcing of RCPs. For RCP 8.5, at the end of the summer season the Arctic is projected to be free of sea ice.     

Possible relationship between North Korean total rainfall and Arctic Oscillation in May

In this study, a negative correlation between the rainfall over North Korea in May and the Arctic Oscillation (AO) in the same month is analyzed. The reasons for rainfall declines in the positive AO phase are as follows: (a) the strengthening of anomalous anticyclone in the Maritime Province of Siberia, (b) the weakening of the subtropical western North Pacific high, and (c) the stabilization across all the atmospheric layers in North Korea. Anomalous anticyclone strengthened in the Maritime Province of Siberia plays a critical role in placing the North Korean region under the influence of anomalous northeasterlies. In addition, the development of the anomalous northeasterlies results in the supply of a large amount of cold and dry air into North Korea. This consequently stabilizes the atmosphere in North Korea. Moreover, the reinforcement of anomalous cold sea surface temperature in the mid-latitude region of East Asia is found to be another reason for the atmospheric stabilization.     

Ecosystem responses to climate change in a large on-river reservoir, Lake Paldang, Korea

The impact of climate change on a large river reservoir ecosystem was investigated. Long-term meteorological data showed that recent climate change, including warmer winters, increased precipitation intensity and extended dry periods, may have influenced the basin of Lake Paldang, the most downstream reservoir of a series of on-river reservoirs. Extreme hydrologic events and climate warming, acting independently and in combination, appear to be related to changes in the Lake Paldang ecosystem. A significant increase in chlorophyll a concentrations in early spring corresponded to the timing of ice break-up. An increase in winter temperatures, which resulted in a shorter time period of ice-cover and earlier ice break-up, appears to have stimulated phytoplankton growth in winter and early spring. Repeated intensive and extended influxes of turbid water, associated with more frequent extreme rainfall events, have increased concentration of suspended solids and may have influenced the biotic community structure of Lake Paldang. In the mid-2000s, the area vegetated by submerged hydrophytes, the abundance and biomass of the phylum Mollusca, as well as the abundance of fish from the subfamily Acheilognathinae, which spawn in the body of bivalve molluscs, was all smaller than in the late 1980s and early 1990s. Together, these results suggest that climate change may have contributed directly and indirectly to changes in each trophic level of the Lake Paldang ecosystem.     

Interdecadal change in North Korean winter mean rainfall

In the present study, it was found that there was a significant climate regime shift in 1993 from average rainfall amounts in winter (December of a year and January and February of the next year) in North Korea over the last 30 years (1982–2011). This significant climate regime shift in 1993 also appeared in empirical orthogonal function analysis conducted using the winter mean rainfall amounts observed at 26 weather observation stations in North Korea. The reason why winter mean rainfall amounts in North Korea were smaller during the period of 1994–2011 than during the period of 1982–1994 was that anomalous anticyclone was reinforced in regions near Lake Baikal while anomalous cyclone was reinforced on the sea on the east of Japan so that the winter pressure system pattern (west high-east low pattern) appeared and thus anomalous cold and dry northerlies were reinforced in most East Asian regions including North Korea. To figure out the reason why anomalous anticyclone was reinforced further in the East Asian continent in winters during the period of 1994–2011, differences in water equivalent of accumulated snow depths between the two periods were analyzed. As a result, more snow was observed in most East Asian regions during the period of 1994–2011. Therefore, anomalous anticyclone could be further reinforced in the East Asian continent because surface air temperature dropped further due to snow-albedo effect. The surface air temperature cooling deepened further in the East Asian continent during the period of 1994–2011 due to snow-albedo effect was identified through differences in sensible heat net flux between the two periods.