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국제학술지

공지 (2025. 10. 28.)

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Effects of radiative cooling on the tropical convective response to sea surface temperature: 2-D large domain cumulus...

Abstract: The effects of radiative cooling on the tropical convective response to sea surface temperature (SST) are investigated using a series of two-dimensional large domain cloud-resolving simulations. The experiments are designed with an imposed warm-pool SST at 2.5°C, 3.5°C, and 4.5°C higher than the cold-pool SST, which is specified at 26°C. The area ratio of the model cold pool to the warm pool is set to 2.2. It is observed that the warm-pool convection intensifies when the SST difference between the warm and cold pools increases from 2.5°C to 3.5°C, whereas the warm-pool convection strength does not significantly change when the SST difference increases from 3.5°C to 4.5°C, which is qualitatively consistent with the observations. The analysis of the atmospheric heat budgets shows that the cap on the development of convection over the warm pool is due to a radiative cooling over the cold pool that has a small variability. The cloud-resolving model simulations indicate that the area of the radiatively driven subsidence expands to produce an enhanced mass exchange between the warm and cold pools in response to the enhanced SST difference between them. This acts against the tendency for increased clouds by the enhanced upward mass flux in response to the warmer SST over the warm pool; significantly stronger SST differences between the two pools (e.g., ≥3.5°C in the cloud-resolving model) do not proportionally produce further intensive convection activities over the warm pool. Full title: Effects of radiative cooling on the tropical convective response to sea surface temperature: 2-D large domain cumulus ensemble simulations
- 작성자Sui et al.
- 작성일2024.06.17
- 조회수68
- 2008
Land surface initialization using an offline CLM3 simulation with the GSWP-2 forcing dataset and its impact on CAM3 ...

Abstract: The impacts of initialized land surface conditions on the monthly prediction were investigated using ensemble simulations from the Community Atmosphere Model version 3 (CAM3). The land surface initialization was based on an offline calculation of Community Land Model version 3 driven by observation-based meteorological forcings from the Global Soil Wetness Project 2 (GSWP2). A simple but effective correction method was applied to the GSWP2 forcings prior to the offline calculation to reduce the discrepancies between the observation-forced land surface conditions and the modeling system, which can cause climate drift and initial shock problems. The climatological mean of GSWP2 forcings was adjusted to that of the target model (CAM3), while the monthly anomalies were scaled to the model statistics and high-frequency synoptic variabilities were included. Ensemble hindcast experiments with and without land surface initialization were conducted for the boreal summer (May–September), for 1983–95. The initialization process is shown to prevent climate drift and to transfer the atmospheric anomalies to the land surface memory. Statistical analyses of the simulation results reveal that the land surface initialization increased the externally forced variance over most continental regions, which is translated to enhanced potential predictability, particularly for regions with strong land–atmosphere coupling. Full title: Land surface initialization using an offline CLM3 simulation with the GSWP-2 forcing dataset and its impact on CAM3 simulations of the boreal summer climate
- 작성자Jeong et al.
- 작성일2024.06.17
- 조회수54
- 2008
Long-term variation in midweek/weekend cloudiness difference during summer in Korea

Abstract: A 58-year record (1950–2007) of cloudiness measured at 11 ground stations in South Korea revealed that summertime cloudiness for Wednesday through Friday versus that for Saturday through Monday exhibited a bell-shaped curve; the midweek/weekend difference increased up to 6% in the 1960s and early 1970s, and decreased in the mid and late 1970s. Since 1980, the anomaly has become as small as before 1960 (within ±2%). This bell-shaped interdecadal variation in midweek/weekend difference in cloudiness had a strong negative correlation with those in insolation and diurnal temperature range and a positive correlation with those in relative humidity and number of days with light rain (<5 mm day−1) from coincident ground measurements. Unlike the meteorological variables, the aerosol concentrations from the stations in the same cities appear to be consistently higher in the midweek than on the weekend in recent years (1990–2004). Therefore, the long-term variations in midweek/weekend differences in cloudiness and relevant meteorological variables suggest that the regional weekly weather variations are unpredictable despite the rapid industrial growth in South Korea in the past few decades. This study discusses plausible interpretations related to aerosol effects.
- 작성자Choi et al.
- 작성일2024.06.17
- 조회수65
- 2008
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
- 조회수61
- 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
- 조회수79
- 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
- 조회수53
- 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
- 조회수59
- 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
- 조회수74
- 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
- 조회수72
- 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
- 조회수66
- 2007