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국제학술지

공지 (2025. 10. 28.)

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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
- 조회수71
- 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
- 조회수81
- 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
- 조회수81
- 2006
Large increase in heavy rainfall associated with tropical cyclone landfalls in Korea after the late 1970s

Abstract: This study presents a new demonstration of the abrupt increase in the heavy rainfall events (≥100 mm day−1) during August–September in Korea around the late 1970s. The accumulated heavy rainfall averaged for the two months over 12 stations was 57 mm during 1954–77 (ID1); however, it changed to 103 mm during 1978–2005 (ID2). This change is found to be associated with landfalling tropical cyclones (TCs). The most plausible mechanism that accounts for the TC–heavy rainfall relationship is an enhanced TC–upper-tropospheric trough (UTT) interaction, which results from a southward shift of the upper-tropospheric jet in East Asia during ID2. While the intensity and duration of the landfalling TCs in Korea does not appear to exhibit such an interdecadal change based on the data available, the enhanced TC–UTT interaction increases the upper(lower)-tropospheric divergence (convergence) and coherent ascending motion, which strengthen the frontal zone around Korea.
- 작성자Kim et al.
- 작성일2024.06.17
- 조회수69
- 2006
Radiative effect of cirrus with different optical properties over the tropics in MODIS and CERES observations

Abstract: The radiative effects of cirrus clouds are evaluated based on observations extending over a period of six years (2000–2005) from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Clouds and the Earth's Radiant Energy System (CERES) over the Tropics (25°S–25°N). The cloud radiative effect (CRE) shows a positive sign for optically thin cirrus (total-column cloud optical depth: τ 60%), their net effective CRE (net CRE × cloud amount) is roughly twice as strong as that of thicker clouds; the modulation of the net radiative flux by variations in thin cirrus (particularly with 1 ≤ τ < 9) dominates—up to 15 W m−2—that by thicker clouds. These results suggest that thin cirrus has a significant effect on the tropical energy balance.
- 작성자Choi and Ho
- 작성일2024.06.17
- 조회수71
- 2006
Roles of wind stress variations in the western North Pacific on the decadal change of ENSO

Abstract: This paper investigated the effects of wind stress forcing in the western North Pacific on ENSO decadal change before and after the late 1970s. The SVD analysis of SODA data shows that a positive wind stress curl is dominant in the western North Pacific at the ENSO mature phase, which leads to the ENSO phase change by discharge/recharge heat contents in the equatorial Pacific. Before the late 1970s, the wind stress curl in the western North Pacific was strong. This strong wind forcing that is associated with the fast discharge of heat contents in the equator led to the short period and the weak intensity of ENSO occurred during the 1960-1970. On the other hand, after the late 1970s the relatively weak wind stress curl was accompanied with the long period and the strong intensity of ENSO. The simple coupled model experiments also confirm that the amplitude and dominant period of ENSO decrease when the wind stress curl in the western North Pacific projects more strongly into the ocean at the TNSO mature phase. Our results support that the changes in the behavior of ENSO after the late 1970s are associated with the wind stress variation in the western North Pacific.
- 작성자Lee et al.
- 작성일2024.06.17
- 조회수103
- 2006
Stratospheric origin of cold surge occurrence in East Asia

Abstract: In the present study, we have found a precursory signal in the stratospheric circulation prior to the cold surge occurrence in East Asia. Over northern Eurasia, about one week before the cold surge occurrence, strong stratospheric negative potential vorticity anomalies and rising of geopotential height are observed. The dynamic linkage between the stratospheric perturbations and the tropospheric adjustment, along with initial disturbances for a cold surge occurrence, are discussed.
- 작성자Jeong et al.
- 작성일2024.06.17
- 조회수60
- 2006
Variability of the Indian Ocean sea surface temperature and its impacts on Asian-Australian monsoon climate

Abstract: In this study, the authors investigate the relationships between the Indian Ocean (IO) sea surface temperature (SST) and the Asian-Australian monsoon (AAM) on seasonal to interannual timescales. They focus on the dominant features of IO SST, the impacts of IO SST on different monsoon components, and the relative importance of the northern and southern IO for the AAM. The dominant mode of IO SST is often characterized by uniform warming or cooling, with maximum variance in the Southern Hemisphere. This mode exerts a larger impact on monsoon variability than does the tropical IO dipole. The IO SST is strongly persistent from the boreal fall to the next spring even summer and less persistent from boreal summer to fall, a feature related to seasonal alternation of the dominance of the impacts of Pacific and IO SSTs on the Asian-Australian monsoons. While the tropical central Pacific SST exerts an apparently larger impact on the monsoon climate in the boreal winter and the transitional seasons, the IO SST affects the summer regional climate more strongly. The springtime IO SST leads to opposite changes in the south Asian monsoon (SAM) and the Southeast Asian monsoon (SEAM), reinforcing the out-of-phase relationship that appears often between the two monsoon components. While a warmer IO strengthens the SAM, it weakens the SEAM. Furthermore, the southern IO SST is related to the Asian summer monsoon more closely than the northern IO SST. The boreal fall IO SST, especially that in the north IO, is strongly associated with the subsequent Australian summer monsoon.
- 작성자Yoo et al.
- 작성일2024.06.17
- 조회수66
- 2006
Variation of tropical cyclone activity in the South Indian Ocean: ENSO and MJO effects

Abstract: The present study examines variation of tropical cyclone (TC) activity in the South Indian Ocean (SIO) during TC seasons (December–March) for the period 1979–2004. The impact of the El Niño–Southern Oscillation and the Madden-Julian Oscillation (MJO) on the variation is revealed through a composite analysis. During El Niño periods TC genesis was shifted westward, enhancing the formation west of 75°E and reducing it east of 75°E. These changes in the genesis correspond to a westward shift of convection. It may be explained by a remote effect on the SIO; that is, the increase in sea surface temperature in the central eastern Pacific alters the Walker circulation and forms an anomalous anticyclonic circulation in the east SIO during El Niño. The spatial difference in TC passages between El Niño and La Niña shows a significant decrease to the southeast of Madagascar but a moderate increase in the central midlatitude SIO, indicating that TCs move farther east during El Niño. This change is possibly due to the anomalous southwesterlies east of Madagascar. Variation of TC activity also depends on various MJO phases: frequent TC passages for phases 2–4 (strong convective activity straddles along the equatorial Indian Ocean) versus infrequent TC passages for other phases. TC tracks tend to be more south oriented in phase 3 compared with those in phases 2 and 4. This is possibly caused by the increased steering northerlies which are a part of the anticyclonic Rossby wave of Gill type in response to the suppressed MJO-related convection in the maritime continent. Full title: Variation of tropical cyclone activity in the South Indian Ocean: El Niño–Southern Oscillation and Madden-Julian Oscillation effects
- 작성자Ho et al.
- 작성일2024.06.17
- 조회수245
- 2006
Weekend effect in diurnal temperature range in China: Opposite signals between winter and summer

Abstract: Intense human activity can impact weather and climate in many ways. One possible important consequence is the weekly cycle (so-called weekend effect) in the diurnal temperature range (DTR). The weekend effect is defined as the average DTR for Saturday through Monday minus the average DTR for Wednesday through Friday. In the present study, the weekend effect in the DTR over east China combined with station observations of maximum and minimum temperatures, relative humidity, and total solar irradiance for the period 1955–2000 was analyzed. Results show that the weekend effect in the DTR has the opposite signal between winter (December, January, and February) and summer (June, July, and August). Wintertime DTR tends to have a positive weekend effect (i.e., larger DTR in weekend days compared to weekdays), in association with increased maximum temperature and total irradiance but decreased relative humidity. While summertime DTR displays a much stronger and significantly negative weekend effect (i.e., smaller DTR in weekend days), in association with decreased maximum temperature and total solar irradiance but increased relative humidity and a greater number of rainy days. This study indicates that the DTR difference between weekend and weekdays is predominantly related to weekly changes in the maximum temperature. The weekend effect in the DTR and maximum temperature is also found in the Reanalysis 2 data. The weekend effect in winter is supported by an analogous holiday (Spring Festival) effect. Since the late 1970s, the weekend effect has been enhanced in both winter and summer, concurrent with rapid development and enhanced human activity in China. The direct and indirect effects of human-related aerosols on radiation, cloud, precipitation, and so on, might play an important role in generating the opposite signal in the weekend effect for different seasons. During a dry winter, the reduction of aerosol concentrations may overwhelmingly impact on the DTR through a direct effect, i.e., by increasing total solar irradiance near the surface and raising the daytime temperature and maximum temperature and lowering relative humidity. By contrast, in summer the indirect effect of aerosols, i.e., reduction in precipitation efficiency caused by more numerous and smaller cloud droplets, would largely be responsible for the increased numbers of rainy days, the reduction of the total solar irradiance, and the lowering of the maximum temperature and DTR.
- 작성자Gong et al.
- 작성일2024.06.17
- 조회수79
- 2006