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101.
102.
Jang-Woon WANG Jae-Jin KIM Wonsik CHOI Da-Som MUN Jung-Eun KANG Hataek KWON Jin-Soo KIM Kyung-Soo HAN 《大气科学进展》2017,34(12):1404-1414
This study investigated the flow characteristics altered by Jang Bogo Antarctic Research Station using computational fluid dynamics(CFD) modeling. The topography and buildings around Jang Bogo Station were constructed with computeraided-design data in the CFD model domain. We simulated 16 cases with different inflow directions, and compared the flow characteristics with and without Jang Bogo Station for each inflow direction. The wind data recorded by the site's automatic weather station(AWS) were used for comparison. Wind rose analysis showed that the wind speed and direction after the construction of Jang Bogo Station were quite different from those before construction. We also investigated how virtual wind fences would modify the flow patterns, changing the distance of the fence from the station as well as the porosity of the fence. For westerly inflows, when the AWS was downwind of Jang Bogo Station, the decrease in wind speed was maximized(-81% for west-northwesterly). The wind speed reduction was also greater as the distance of the fence was closer to Jang Bogo Station. With the same distance, the fence with medium porosity(25%–33%) maximized the wind speed reduction.These results suggest that the location and material of the wind fence should be selected carefully, or AWS data should be interpreted cautiously, for particular prevailing wind directions. 相似文献
103.
Yoo-Jun KIM So-Ra IN Hae-Min KIM Jin-Hwa LEE Kyu Rang KIM Seungbum KIM Byung-Gon KIM 《大气科学进展》2021,38(3):413-429
This study investigates the characteristics of cold clouds and snowfall in both the Yeongdong coastal and mountainous regions under different meteorological conditions based on the integration of numerical modeling and three-hourly rawinsonde observations with snow crystal photographs for a snowfall event that occurred on 29?30 January 2016.We found that rimed particles predominantly observed turned into dendrite particles in the latter period of the episode when the 850 hPa temperature decreased at the coastal site,whereas the snow crystal habits at the mountainous site were largely needle or rimed needle.Rawinsonde soundings showed a well-defined,two-layered cloud structure along with distinctive wind-directional shear,and an inversion in the equivalent potential temperature above the low-level cloud layer.The first experiment with a decrease in lower-layer temperature showed that the low-level cloud thickness was reduced to less than 1.5 km,and the accumulated precipitation was decreased by 87%compared with the control experiment.The difference in precipitation amount between the single-layered experiment and control experiment(two-layered)was not so significant to attribute it to the effect of the seeder?feeder mechanism.The precipitation in the last experiment by weakening winddirectional shear was increased by 1.4 times greater than the control experiment specifically at the coastal site,with graupel particles accounting for the highest proportion(~62%).The current results would improve snowfall forecasts in complicated geographical environments such as Yeongdong in terms of snow crystal habit as well as snowfall amount in both time and space domains. 相似文献
104.
This study presents an exploratory analysis aimed at improving understanding
of the variability of Hong Kong air quality associated with different
climate conditions. Significantly negative correlations were found when
Nino 3 led particulate matter ≤10 μm PM10) and NO2
by 2--3 months over the Hong Kong territory, while the other pollutants
(e.g., O3, SO2) showed modest correlations. A significant
decreasing trend in visibility was observed during the autumn and winter,
which has potential implications for the air-quality degradation and the
endangerment of human health in Hong Kong. In an El Nino summer, the
visibility was relatively better, while visibility in other seasons was
diminished. On the other hand, in La Nina events, significant changes
occurred in visibility in winter and autumn. Air pollution indices were less
sensitive to the South China Summer Monsoon (SCSM), but a relatively high
correlation existed between the East Asian Winter Monsoon (EAWM) and air
pollutants. Rainfall was lower during most of the strong EAWM years compared
to the weak years. This result suggests that the pollutants that accumulate
in Hong Kong are not easy to wash out, so concentrations remain at a higher
level. Finally, based on the conditional Air Pollution Index (API) risk
assessment, site-specific vulnerabilities were analyzed to facilitate the
development of the air-quality warning systems in Hong Kong. 相似文献
105.
106.
In an effort to assess the reliability of satellite altimeter systems, the authors conduct a comparative analysis of sea level data that were collected from the TOPEX/POSEIDON (T/P) altimeter and 10 tide gauges (TG) near the satellite passing ground tracks. The analysis is made using datasets collected from marginal sea regions surrounding the Korean Peninsula at T/P cycles of 2 to 230, which correspond to October 1992 to December 1998. Proper treatment of tidal errors is a very critical step in data processing because the study area has very strong tide. When the T/P data are processed, the procedures of Park and Gamberoni (1995) are adapted to reduce errors associated with the tide. When the T/P data are processed in this way, the alias periods of M2, $2, and K1 constituents are found to be 62.1, 58.7, and 173 days repectively. The compatibility of the T/P and TG datasets are examined at various filtering periods.The results indicate that the low-frequency signals of the T/P data can be interpreted more safely with longer filtering periods (such as up to the maximum selected value of 200 days). When RMS errors for the 200-day low-pass filter period are compared with all 10 tidal stations, the values span the range of 2.8 to 6.7 cm. The results of a correlation analysis for this filtering period also show a strong agreement between the T/P and TG datasets across all stations investigated (e.g., p-values consistently less than 0.001). Hence according to the analysis, the conclusion is made that the analysis of surface sea level using satellite altimeter data can be made safely with reasonably extended filtering periods such as 200 days. 相似文献
107.
Local Meteorological and Synoptic Characteristics of Fogs Formed over Incheon International Airport in the West Coast of Korea 总被引:2,自引:0,他引:2
Fogs observed over Incheon international airport (IIA) in the westcoast of Korea from January 2002 to August 2006 are classified into categoriesof coastal fog, cold sea fog, and warm sea fog based on the areal extent of thefogs and the difference between the air temperature (T) and the SST, i.e.,cold sea fog if TSST = T-SST>0oC and warm sea fog if TSST<0oC. The numbers of coastal, cold, and warm sea fog casesare 64, 26, and 9. Coastal fogs form most frequently in winter, while cold seafogs occur mostly in summer and warm sea fogs are observed from January to Maybut not in November and December. On average the air gets colder by1.6oC during the three hours leading up to the coastal fogformation, and an additional cooling of 1.1oC occurs during thefog. The change in the dew point temperature (Td) is minimal exceptduring the fog (0.6oC). Decreases in T for the cold and warmsea fogs are relatively smaller. The average Td is higher than SSTduring the cold sea fog periods but this Td is more than4oC higher than that for the corresponding non-fog days,suggesting that cold sea fogs be formed by the cooling of already humid air(i.e., Td>SST). Increases of Td are significant during thewarm sea fog periods (1.4oC), implying that efficient moisturesupply is essential to warm sea fog formation. Four major synoptic patterns areidentified in association with the observed fogs. The most frequent is a northPacific high that accounts for 38% of cases. Surface or upper inversions arepresent in 77%, 69%, and 81% of the fog periods for coastal, cold, andwarm sea fogs, respectively. 相似文献
108.
A three-component decomposition is applied to global analysis data to show the existence of a beta gyre, which causes Tropical Cyclone (TC) to drift from a large-scale environmental steering current. Analyses from the Global Data Assimilation and Prediction System (GDAPS) of the Korea Meteorological Adminis-tration (KMA), the Global Forecast System (GFS) of NCEP, and the Navy Operational Global Atmospheric Prediction System (NOGAPS) are used in this study. The structure of the beta gyre obtained in our anal... 相似文献
109.
110.
TEM and XRD determination of crystallite size and lattice strain as a function of illite crystallinity in pelitic rocks 总被引:2,自引:0,他引:2
W.-T. JIANG D. R. PEACOR P. ÁRKAI M. TÓTH & J. W. KIM 《Journal of Metamorphic Geology》1997,15(2):267-281
Average crystallite size and mean-square strain of illite in rock specimens and clay separates were measured independently in TEM images and by single-line Fourier (Voigt method) profile analysis of the c. 1 nm peak of XRD patterns for a prograde sequence of pelitic rocks (illite crystallinity indices=0.17–0.58°Δ2θ) from the Gaspé Peninsula, Quebec. The TEM-determined crystallite sizes in clay separates approximate those determined by Fourier profile analyses and those calculated from illite crystallinity indices by the Scherrer equation, with the exception of the diagenetic sample. The crystallite sizes and mean-square strains of illite in rock samples exhibit a trend similar to that determined by profile analyses, but the average crystallite sizes are up to five times larger than those measured for clay separates. TEM images show that all rock samples have a wide range of crystallite sizes, and the proportions of larger crystallites increase with metamorphic grade. The diagenetic illite is defect-rich, fine-grained (mean thickness by volume=c. 70 nm), 1Md material. Anchizonal illite tends to occur as separate aggregates of small 1Md and larger 2M1 crystals (c. 200 nm), comprising arrays of subparallel coalescing packets. The epizone sample has thick (c. 400 nm), defect-free crystals of muscovite occurring in stacks of parallel layers, or subhedral crystals intergrown with large-angle boundaries. Cleaved crystals that are free of intracrystalline layer terminations are dominant in clay separates of all samples, having ranges of smaller sizes with volume-average thicknesses of c. 43, 43, and 81 nm (c. 14, 28, 67 nm by the Voigt method), respectively, for the three zones. The results suggest that illite crystallinity indices do not provide a direct measure of a single microstructural state of illite in rocks, although they yield consistent limits for average crystallite sizes for the anchizone (23 & 48 nm here). Therefore, they serve as a general parameter of the degree of recrystallization on a relative basis, in part because the contributions of all peak-broadening variables (mixed layering, size and strain) decrease regularly with prograde regional metamorphism of pelites. The microstructural changes caused by rock disaggregation are probably a function of those variables as well. The data collectively demonstrate a trend from metastable, defect-rich, small crystals towards a stable assemblage of larger, defect-free crystals, through dissolution of strained crystals and neocrystallization, consistent with the Ostwald step rule. 相似文献