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국제학술지

공지 (2024. 9. 4.)

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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
- 조회수12
- 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
- 조회수6
- 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
- 조회수4
- 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
- 조회수5
- 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
- 조회수4
- 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
- 조회수6
- 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
- 조회수6
- 2006
Changes in occurrence of cold surges over East Asia in association with Arctic Oscillation

Abstract: It has been newly found that the occurrence of cold surges in east Asia is significantly influenced by the Arctic Oscillation (AO). In the present study, the events of cold surge are objectively determined based on several synoptic criteria and the phase-dependency of its occurrences in association with the AO has been revealed. During the negative AO phase, the frequency of cold surge occurrence is relatively increased than that of neutral and positive AO phases. The variation of upper level trough and jet stream over east Asia and the Siberian High in association of AO are suggested to explain the change of cold surge occurrences.
- 작성자Jeong and Ho
- 작성일2024.06.17
- 조회수6
- 2005
Circulation features associated with the record-breaking typhoon landfall on Japan in 2004

Abstract: Ten typhoons struck Japan in 2004, which was an all-time high although the total number of typhoons formed over the western North Pacific was slightly above normal. The characteristics of typhoon activity are the unusually high number of typhoons approaching Japan in the early summer (June) and fall (September and October) and the frequent landfalls in the middle summer (July and August). Seasonal mean large-scale circulation in 2004 was characterized by a split of the North Pacific subtropical high (NPSH) east of Taiwan and persistent anticyclonic anomalies to the southeast of Japan, enabling typhoons to penetrate the weakened NPSH and move to Japan. Two possible causes are suggested here to maintain the persistent anticyclonic anomalies near Japan: one is positive feedback between typhoons moving northward and midlatitude circulation near Japan, the other is response to the broad-scale tropical deep convection. A further modeling study is required to substantiate these arguments.
- 작성자Kim et al.
- 작성일2024.06.17
- 조회수6
- 2005
Different optical properties of high cloud in GMS and MODIS observations

Abstract: The optical properties of high cloud are compared between two satellite retrievals taken from the Geostationary Meteorological Satellite-5 (GMS) and the Moderate-resolution Imaging Spectroradiometer (MODIS) in the tropical western Pacific (TWP) for the years 1998–2001. The MODIS high-cloud amount determined by 1.38-μm reflectances (>1.1%) is approximately twice that of GMS determined by 11-μm brightness temperatures (<260 K). The optical depths associated with the retrieved high clouds are calculated using a radiative transfer model. The minimum detectable value of optical depths by the MODIS and GMS measurements is around 0.1 and 2.0, respectively. Variations of MODIS and GMS high clouds with respect to the mean sea surface temperatures (SSTs) in the TWP are examined next. There exist large discrepancies in the change rates in high clouds with increasing SST between GMS and MODIS in the available data for the years 2000 and 2001.
- 작성자Choi et al.
- 작성일2024.06.17
- 조회수4
- 2005