• 한국제4기학회지
• /
• 제17권2호
• /
• pp.55-61
• /
• 2003

In the year 2000 we culminated a successful five year investigation of climate change by completing a preliminary east-west transect across Mongolia. An earlier tree-ring study at Tarvagatay Pass, Mongolia indicated unusual warming during the 20th century similar to other paleo-investigations of the northern hemisphere. This record had represented one of the few tree-ring records for central Asia. New data from several sites in western Mongolia confirmed the preliminary temperature. The highest twenty-year growth period for the composite record is from 1973-1994. The western Mongolian record was significantly correlated with the Taimyr Peninsula and two northern hemisphere temperature reconstructions reflecting large-scale temperature patterns while showing some important regional differences. These differences should prove useful for climate models. We have also developed a millennial length temperature-sensitive record at the Solongotyin Davaa site (formerly Tarvagatay Pass) using relict wood and living trees. Conspicuous features over the last 1000 years are a century scale temperature decline punctuated by the end of the Little Ice Age in the late-1800s and 20th century warming. The record also shows a cold period early in the 12th century and warm intervals late in the 10th, early in the 15th and at end of the 18th centuries. Despite a limited sample size before 900 AD, the long Solongotyin Davaa record is useful in indicating severe cold events and suggests some cold intervals nearly as severe. These tree ring series, spanning much of the circumpolar northern treeline, have been compiled to create a long-term reconstruction of the Earth's temperature over centuries. The new chronology, in addition to its value as a detailed record of Mongolian climate, provides independent corroboration for such hemispheric and global reconstructions and their indications of unusual warming during the 20th century.

• 한국제4기학회지
• /
• 제17권2호
• /
• pp.157-159
• /
• 2003

Much of northern Asia is lacking in high-resolution palaeoclimatic data coverage. This vast region thus represents a sizeable gap in data sets used to reconstruct hemispheric-scale temperature trends for the past millennium. To improve coverage, we present a regional-scale composite of four tree-ring width records of Siberian pine and Siberian larch from temperature-sensitive alpine timber-line sites in Mongolia. The chronologies load closely in principal components analysis (PCA) with the first eigenvector accounting for over 53% of the variance from ad 1450 to 1998. The 20-year interval from 1974 to 1993 is the highest such growth period in this composite record, and 17 of the 20 highest growth years have occurred since 1946. Thus these trees, unlike those recently described at some northern sites, do not appear to have lost their temperature sensitivity, and suggest that recent decades have been some of the warmest in the past 500 years for this region. There are, however, comparable periods of inferred, local warmth for individual sites, e.g., in 1520-1580 and 1760-1790. The percent common variance between chronologies has increased through time and is highest (66.1%) in the present century. Although there are obvious differences among the individual chronologies, this result suggests a coherent signal which we consider to be related to temperature. The PCA scores show trends which strongly resemble those seen in recent temperature reconstructions for the Northern Hemisphere, very few of which included representation from Eurasia east of the Ural Mountains. The Mongolia series therefore provides independent corroboration for these reconstructions and their indications of unusual wanning during the twentieth century.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2001년도 춘계학술대회논문집D
• /
• pp.497-502
• /
• 2001

Three-dimensional natural convection from a discrete flush-mounted circular heat source on the bottom of a cubic enclosure was studied by using a holographic interferometric tomography. The heat source was located at the off-center of the bottom plate so that three-dimensional temperature field can be achieved. A set of multidirectional holographic interferogram was recorded by employing a double-reference beam, double-exposure holographic technique in order to eventually reconstruct the temperature fields. The recorded interferometric data appear good enough to be further processed to extract optical pathlength data from them and finally reconstruct the temperature fields. A complete analysis of the temperature fields including the field reconstructions and comparison with thermocouple measurements is underway and will be reported shortly.

• 한국제4기학회:학술대회논문집
• /
• 한국제4기학회 2004년도 추계학술대회
• /
• pp.37-43
• /
• 2004

The response of the CCCma coupled climate model to the imposition of LGM conditions is investigated. The global mean SAT and SST decrease by about $10^{\circ}C$ and $5.6^{\circ}C$ in the coupled model. Tropical SST decreases by $6.5^{\circ}C$, whereas CLIMAP reconstructions suggest that the tropics cool by only about $1.7^{\circ}C$, although the larger tropical cooling is consistent with the more recent proxy estimates. With the incorporation of a full ocean component, the coupled model gives a realistic spatial SST pattern, capturing features associated with ocean dynamics that are seen in the CLIMAP reconstructions. The larger decrease of the surface temperature in the model is associated with a reduction in global precipitation rate (about 15%). The tropical Pacific warm pool retreats to the west and a mean La $Ni\tilde{n}a$-like response is simulated with less precipitation over the central Pacific and more in the western tropical Pacific. The more arid ocean climate in the LGM results in an increase in SSS almost everywhere. This is particularly the case in the Arctic Ocean where large SSS increase is due to a decrease in river discharge to the Arctic Ocean associated with the accumulation of snow over the ice sheet, but in the North Atlantic by contrast SSS decreases markedly. This remarkable reduction of SSS in the North Atlantic is attributed to an increase in fresh water supply by an increase in discharges from the Mississippi and Amazon rivers and an increase in P-E over the North Atlantic ocean itself. The discharges increase in association with the wetter LGM climate south of the Laurentide ice sheet and in South America. The fresh water capping of the northern North Atlantic results in a marked reduction of deep convection and consequently a marked weakening of the North Atlantic overturning circulation. In the LGM, the maximum overturning stream function associated with the NADW formation decreases by about 60% relative to the control run, while in the Southern Ocean, oceanic convection is stronger in the LGM due to reduced stratification associated with an increase in SSS and a decrease in SST and the overturning stream function associated with the formation of AABW and the outflow increases substantially.

• 대기
• /
• 제28권3호
• /
• pp.325-336
• /
• 2018

This study investigates robust features of interdecadal changes in the Northern hemisphere summer tropical-extratropical teleconnection occurred around the mid-to-late 1990s by analyzing four different reanalysis data for atmospheric circulation and temperature, two precipitation reconstructions, and two sea surface temperature (SST) data during the satellite observation era of 1980~2017. For the last 38 years, there has been a significant increasing trend in anticyclonic circulation at lower and upper troposphere and 2 m air temperature with wavenumber-5 Rossby wave structure in the Northern Hemisphere (NH) extratropics. The increase has been accompanied with the significant weakening and northward shift of jet stream over Eurasia and the North Pacific. It is further found that there has been a significant interdecadal shift occurred around the mid-to-late 1990s in the two distinct modes of tropical-extratropical teleconnection: Western Pacific-North America (WPNA) and circumglobal teleconnection (CGT) pattern. After mid-to-late 1990s, the WPNA has played more important role in modulating the extratropical atmospheric circulation and surface climate, which has been preferentially occurred during the El $Ni{\tilde{n}}o$-Southern Oscillation (ENSO) decaying or transition summer such as 1998, 2010 and 2016. During these summers, severe heat waves were occurred over many parts of the NH extratropics due to the combined effect of the increasing trend in the barotropic anticyclonic circulation and the significant WPNA across the NH. Although weakened, the CGT also contributed to some of hot summers over many parts of the NH extratropics such as 1999, 2000, 2008, 2011, and 2012 when weak to moderate La $Ni{\tilde{n}}o$ was persisted.

• Journal of Korean Vacuum Science & Technology
• /
• 제2권2호
• /
• pp.63-77
• /
• 1998

The oxidation of NiAl(110) was investigated in the temperature regime between 300K and 1300 K using LEED (low energy electron diffraction), TPD (temperature programmed desorption) and HREELS (high resolution electron energy loss spectroscopy). The adsorption of N2O and O2 up to reconstructions. Stepwise annealing of the oxygen-saturated sample from 600 K to 1300K in UHV (ultra-high vacuum,) results in firstly the onset of randomly oriented then finally fairly well-ordered. 5 ${\AA}$ Al2O3 film with quasi-hexagonal periodicity. Ordered thicker oxide films of 18-30 ${\AA}$ seem to be grown on this interfacial oxide layer by direct oxidation of sample at elevated temperature between 1150 and 1300 K because of the LEED pattern consisting of new broad hexagonal spots and the previous 5 ${\AA}$ spots. Although the periodicity of surface oxygen arrays shows no significant change from an hexagonal close-packing, the O-O distance changes from ∼3.0 ${\AA}$ film to ∼2.9 ${\AA}$ for thicker oxides. with the appearance of Auger parameter, for the 5${\AA}$ film can be described better as an interfacial oxide layer. The observation of three symmetric phonon peaks can be also a supporting evidence for this phase assignment since thicker oxide films on the Same Ni2Al3(110) show somewhat different phonon structure much closer to that of the ${\gamma}$-Al2O3. The adsorption/desorption of methanol further proves the preparation of less-defective and/or oxygen-terminated Al2O3 films showing ordered phase transitions with the change of oxide thickness between 5 ${\AA}$ to 30 ${\AA}$.

• Journal of Advanced Marine Engineering and Technology
• /
• 제5권1호
• /
• pp.12-19
• /
• 1981

As the fuel oil cost covers from 45% to 60% of the total expenditure for fishing boat operation, the energy saving is now an urgent problem to be taken a countermeasure for engineers, manufacturers or specialists engaging in this field. Undertaking a second-hand engine of the trainging ship, the author made several reconstructions to restore its performances. By inserting foot linears of connecting rods the compression ratio was increased and by adjusting both the fuel injection timing and the cooling water outlet temperature, its thermal efficiency was improved. The results of the experimental operation were summarized as follows. 1. By raising the piston top position 0.75mm more than the value of the operating manual, the compression pressure increased 1.3 kg/$cm^2$ and the maximum pressure did 3.4 kg/$cm^2$ at 75% load. 2. At 75% load, the difference of the maximum pressure between each cylinder was decreased from 2.4 kg/$cm^2$ to 1.8 kg/$cm^2$. 3. The fuel consumption was decreased about 8 g/ps.h at 75% load, and about 5.3 g/ps.h at 85% load. 4. The brake thermal efficiency was improved about 1.5% at 75% load and 0.9% at 85% load.