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국제학술지

공지 (2024. 9. 4.)

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Relationship between intraseasonal oscillation and diurnal variation of summer rainfall over the South China Sea

Abstract: The diurnal variations in summer rainfall over the South China Sea (110°E−120°E, 10°N−20°N) are examined for active and inactive intraseasonal oscillation (ISO) periods that are characterized by strong and weak 850-hPa zonal winds, respectively. By analyzing the rainfall retrievals from the Tropical Rainfall Measuring Mission Precipitation Radar for the period 1999–2006, it is found that the peak rainfall during the active and inactive ISO periods occurs in the late morning and late evening, respectively. The morning peak in the active ISO period arises from the organized oceanic convective systems associated with the local convergence along the west coast of the Philippines. The evening peak in the inactive ISO period originates from a stratiform morphology that is initiated by land-based convective systems owing to the increased thermodynamic instability over the Philippines during daytime.
- 작성자Ho et al.
- 작성일2024.06.17
- 조회수6
- 2008
Spectral analysis of weekly variation in PM10 mass concentration and environment conditions over China

Abstract: This study investigates the region-dependent anthropogenic weekly variation in air pollutants and its relationship with the meteorological conditions over China for the summers of 2001–2005. Spectral analysis was applied to the local daily observations of PM10 (aerosol particulate matter with a diameter <10 μm) mass concentrations and precipitation from 31 ground stations, reanalysis estimates of regional atmospheric variables, and satellite retrievals of clouds. Our analysis shows that the 6–8-day variance of PM10 concentrations from the periodogram is closely correlated with the mean PM10 concentration, which may depend on the size (population) and geographical setting of a city, its prevailing climatic conditions, and the type/degree of human activities. We define normalized variance as the ratio of the 6–8-day to 2–14-day variance of PM10 concentrations, possibly indicating the relative anthropogenic signal to the noise of natural weather variability. The normalized variance of PM10 concentrations has a distinct regional rainfall distribution from that of the mean PM10 concentration in China. As compared to regions with lower normalized variance of PM10 concentrations, the regions with higher normalized variance generally show higher normalized variance of rainfall events, 1000 hPa wind speeds, sea-level pressure, size spectrum and phase of cloud particles, cloud optical depth, and cloud top pressure. Our results confirm the presence of the interaction between PM10 and the meteorological conditions in the boundary layer, and suggest a possible link of cloud formation to PM10 on a weekly scale.
- 작성자Choi et al.
- 작성일2024.06.17
- 조회수18
- 2008
Systematic variation in wintertime precipitation in East Asia by MJO-induced extratropical vertical motion

Abstract: The variations in the wintertime precipitation over East Asia and the related large-scale circulation associated with the Madden–Julian oscillation (MJO) are examined. By analyzing the observed daily precipitation for the period 1974–2000, it is found that the MJO significantly modulates the distribution of precipitation over four East Asian countries; the precipitation rate difference between wet and dry periods over East Asia, when the centers of MJO convective activities are located over the Indian Ocean and western Pacific, respectively, reaches 3–4 mm day−1, which corresponds to the climatological winter-mean value. Composite analysis with respect to the MJO suggests that the MJO–precipitation relation is mostly explained by the strong vertical motion anomalies near an entrance region of the East Asia upper-tropospheric jet and moisture supply in the lower troposphere. To elucidate different dynamic origins of the vertical motion generated by the MJO, diagnostic analysis of a generalized omega equation is adopted. It is revealed that about half of the vertical motion anomalies in East Asia are induced by the quasigeostrophic forcings by the MJO, while diabatic heating forcings explain a very small fraction, less than 10% of total anomalies.
- 작성자Jeong et al.
- 작성일2024.06.17
- 조회수7
- 2008
Systematic variation of summertime tropical cyclone activity in the western North Pacific in relation to the MJO

Abstract: The variability of observed tropical cyclone (TC) activity (i.e., genesis, track, and landfall) in the western North Pacific (WNP) is examined in relation to the various categories of the Madden–Julian oscillation (MJO) during summer (June–September) for the period 1979–2004. The MJO categories are defined based on the empirical orthogonal function analysis of outgoing longwave radiation data. The number of TCs increases when the MJO-related convection center is located in the WNP. The axis of a preferable genesis region systematically shifts like a seesaw in response to changes in the large-scale environments associated with both the eastward and northward propagation of the MJO and the intraseasonal variability of the WNP subtropical high. Furthermore, the authors show that the density of TC tracks in each MJO category depends on the systematic shift in the main genesis regions at first order. Also, the shift is affected by the prevailing large-scale steering flows in each MJO category. When the MJO-related convection center is found in the equatorial Indian Ocean (the tropical WNP), a dense area of tracks migrates eastward (westward). The effects of extreme ENSO events and the variations occurring during ENSO neutral years are also examined. A statistical analysis of TC landfalls by MJO category is applied in seven selected subareas: the Philippines, Vietnam, South China, Taiwan, East China, Korea, and Japan. While a robust and significant modulation in the number of TC landfalls is observed in south China, Korea, and Japan, the modulation is marginal in the remaining four subareas. Full title: Systematic variation of summertime tropical cyclone activity in the western North Pacific in relation to the Madden–Julian oscillation
- 작성자Kim et al.
- 작성일2024.06.17
- 조회수7
- 2008
The impact of aerosols on the summer rainfall frequency in China

Abstract: The authors investigate the short-term relationship between aerosol concentrations and summer rainfall frequency in China using the daily surface observations of particulate matters with a diameter of less than 10 μm (PM10) mass concentration, rainfall, and satellite-observed cloud properties. Results in this study reveal that on the time scale of a few days aerosol concentration is positively correlated with the frequency of moderate-rainfall (10–20 mm day−1) days but is negatively correlated with the frequency of light-rainfall (<5 mm day−1) days. Satellite observations of cloud properties show that higher aerosol concentrations are positively correlated with the increase in mixed cloud amount, cloud effective radius, cloud optical depth, and cloud-top heights; this corresponds to the decrease in low-level liquid clouds and the increase in midlevel ice–mixed clouds. Based on this analysis, the authors hypothesize that the increase in aerosol concentration results in the increase in summer rainfall frequency in China via enhanced ice nucleation in the midtroposphere. However, over the past few decades, observations show an increasing long-term trend in aerosol concentration but decreasing trends in summer rainfall frequency and relative humidity (RH) in China. Despite the short-term positive relationship between summer rainfall frequency and aerosol concentration found in this study, the long-term variations in summer rainfall frequency in China are mainly determined by other factors including RH variation possibly caused by global and regional climate changes. A continuous decrease in RH resulting in less summer rainfall frequency may further enhance aerosol concentrations in the future in conjunction with the increase in the anthropogenic emissions.
- 작성자Choi et al.
- 작성일2024.06.17
- 조회수11
- 2008
An exploratory study of cloud remote sensing capabilities of the COMS imagery

Abstract: The present study documents optimal methods for the retrieval of cloud properties using five channels (0.6, 3.7, 6.7, 10.8 and 12.0 µm) that are used in many geostationary meteorological satellite observations. Those channels are also to be adopted for the Communication, Ocean and Meteorological Satellite (COMS) scheduled to be launched in 2008. The cloud properties focused on are cloud thermodynamic phase, cloud optical thickness, effective particle radius and cloud‐top properties with specific uncertainties. Discrete ordinate radiative transfer models are simulated to build up the retrieval algorithm. The cloud observations derived from the Moderate‐resolution Imaging Spectroradiometer (MODIS) are compared with the results to assess the validity of the algorithm. The preliminary validation indicates that the additional use of a band at 6.7 µm would be better in discriminating the cloud ice phase. Cloud optical thickness and effective particle radius can also be produced up to, respectively, 64 and 32 µm by functionally eliminating both ground‐reflected and cloud‐ and ground‐thermal radiation components at 0.6 and 3.7 µm. Cloud‐top temperature (pressure) in ±3 K (±50 hPa) uncertainties can be estimated by a simple 10.8‐µm method for opaque clouds, and by an infrared ratioing method using 6.7 and 10.8 µm for semitransparent clouds. Full title: An exploratory study of cloud remote sensing capabilities of the Communication, Ocean and Meteorological Satellite (COMS) imagery
- 작성자Choi et al.
- 작성일2024.06.17
- 조회수10
- 2007
Arctic Oscillation and ice severity in the Bohai Sea, East Asia

Abstract: The Bohai Sea is the southernmost sea in the Northern Hemisphere where seasonal freezing takes place in winter. Climate and ice conditions there are very sensitive to large-scale climatic variations. In the present study, the authors investigated the relationships of ice severity in the Bohai Sea to the planetary Arctic Oscillation (AO) during the period 1954/55–2001/02. It has been found that during low-AO winters the regional mean temperature around the Bohai Sea is evidently lower, and the number of freezing days, freezing degree days and the length of freezing duration all change significantly. Daily temperature distribution shows a significant difference in both mean and variance between high-AO and low-AO phases, and the changes in the temperature means dominate over that of the variance in the context of sea ice severity. The temperature-AO relation is well supported by the corresponding features of the large-scale atmospheric circulation system. AO-related changes in the Siberian High and East Asian Trough cause remarkable changes to the thermal conditions at the surface and to the dynamical conditions in the middle troposphere, consequently affecting the air temperature over the Bohai Sea and ice severity. The AO-sea ice severity relation has been generally stationary over time during the last one hundred years. Analysis of cross-power coherency between the AO and ice indices for the last century shows that the highest and significant covariance stands at periods of about 2.1, 3, and 7.5–14 years. The Bohai Sea ice severity has declined rapidly since the 1970s, which is unprecedented since 1880, and this feature is in agreement with the positively upward trend in the AO and the associated changes in the Siberian sea level pressure, East Asian Trough, and the regional temperature.
- 작성자Gong et al.
- 작성일2024.06.17
- 조회수7
- 2007
Regional cloud characteristics over the tropical northwestern Pacific as revealed by TRMM PR and TRMM MI

Abstract: The present study investigates regional cloud characteristics over the tropical northwestern Pacific using Tropical Rainfall Measuring Mission (TRMM) data sets such as rain rate, radar reflectivity, and passive microwave radiometer polarization corrected temperature (PCT). In particular, the tropical northwestern Pacific is divided into two surface rain maxima regions: the South China Sea (SCS) and the Philippine Sea (PS). The TRMM variables are retrieved by a pair of spaceborne microwave sensors, Precipitation Radar (PR) and TRMM Microwave Imager (TMI). It is revealed that the SCS contains more frequent deeply developed convective systems relative to the PS on the basis of the analysis of the PR and TMI version-6 data during a 4-year period (1998–2001) of summers. This is mainly indicated by two factors: strong PR reflectivity (≥30 dBZ) above the freezing level (∼5 km) and TMI ice-scattering signature (PCT at 85.5 GHz ≤ ∼190 K, and PCT at 37.0 GHz ≤ ∼260 K), which are more frequent over the SCS than over the PS. Comparison of TMI and PR rain rates, a relatively small (large) positive PR–TMI bias is observed for an average of rainy areas over the SCS (PS). This region-dependent PR–TMI bias can arise from the regionally different extents of both (1) the PR's underestimate by attenuation correction and (2) the TMI's overestimate by emission from the melting layer (i.e., SCS > PS in (1) and (2)). These differences are due to the excess of heavy rainfall events, high rain rates, strong convective intensities, and high cloud top heights in the SCS compared with the PS. Full title: Regional cloud characteristics over the tropical northwestern Pacific as revealed by Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar and TRMM Microwave Imager
- 작성자Park et al.
- 작성일2024.06.17
- 조회수8
- 2007
Weekly cycle of aerosol-meteorology interaction over China

Abstract: Weekly cycles of the concentration of anthropogenic aerosols have been observed in many regions around the world. The phase and the magnitude of these cycles, however, vary greatly depending on region and season. In the present study the authors investigated important features of the weekly cycles of aerosol concentration and the covariations in meteorological conditions in major urban regions over east China, one of the most polluted areas in the world, in summertime during the period 2001–2005/2006. The PM10 (aerosol particulate matters of diameter < 10 μm) concentrations at 29 monitoring stations show significant weekly cycles with the largest values around midweek and smallest values in weekend. Accompanying the PM10 cycle, the meteorological variables also show notable and consistent weekly cycles. The wind speed in the lower troposphere is relatively small in the early part of the week and increases after about Wednesday. At the same time, the air temperature anomalies in low levels are positive and then become negative in the later part of the week. The authors hypothesize that the changes in the atmospheric circulation may be triggered by the accumulation of PM10 through diabatic heating of lower troposphere. During the early part of a week the anthropogenic aerosols are gradually accumulated in the lower troposphere. Around midweek, the accumulated aerosols could induce radiative heating, likely destabilizing the middle to lower troposphere and generating anomalously vertical air motion and thus resulting in stronger winds. The resulting circulation could promote ventilation to reduce aerosol concentrations in the boundary layer during the later part of the week. Corresponding to this cycle in anthropogenic aerosols the frequency of precipitation, particularly the light rain events, tends to be suppressed around midweek days through indirect aerosol effects. This is consistent with the observed anthropogenic weather cycles, i.e., more (less) solar radiation near surface, higher (lower) maximum temperature, larger (smaller) diurnal temperature range, and fewer (more) precipitation events in midweek days (weekend).
- 작성자Gong et al.
- 작성일2024.06.17
- 조회수13
- 2007
Earlier spring in Seoul, Korea

Abstract: In the present study, long-term changes in the first bloom date of shrub and tree species in Seoul (126.56°E, 37.34°N), Korea were examined using historical observational data for the period 1922–2004 (83 years). The study focused on two shrub species, golden-bell (Forsythia koreana) and azalea (Rhododendron mucronulatum), and three tree species, cherry (Prunus yedoensis), peach (Prunus persica), and American locust (Robinia pseudoacacia). The annual-mean temperature has increased by about 2 °C in Seoul over the 83 years analyzed. The temperature increase is significant during the winter and early spring and becomes less significant during late spring. As a result of this regional warming, all five species showed an advance in the first bloom date over this time period. The advanced date is particularly apparent in early-spring flowering species like golden-bell (−2.4 days 10-year−1), azalea (−2.4 days 10-year−1), cherry (−1.4 days 10-year−1), and peach (−1.4 days 10-year−1) as compared to late-spring flowering species like American locust (−0.5 days 10-year−1). The present results have demonstrated that the major factor for the determination of flower blooming is heat accumulation, i.e. a certain threshold of growing degree-days (GDD) index. In particular, early spring flowers were sensitive to the accumulation of warm temperature than late-spring flowers.
- 작성자Ho et al.
- 작성일2024.06.17
- 조회수9
- 2006