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국제학술지

공지 (2024. 9. 4.)

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Reduction of spring warming over East Asia associated with vegetation feedback

Abstract: Over East Asia, surface air temperature displays a significant increasing trend particularly in early months of the year for the period of 1982–2000. Warming per decade is strongest in late winter, 1.5°C in February and 1.1°C in March, but is significantly reduced in spring, 0.4°C in April and 0.1°C in May. During the analysis period, the reduced temperature increase from late winter to spring is found to be in contrast with the increased vegetation greenness derived from the satellite-measured leaf area index over the domain. We examined this inverse relationship using two climate model experiments— coupled with and without a dynamic vegetation model. In both experiments, strong warming in winter is relatively well reproduced, but weak warming in spring is observed only in the coupled experiment. Analysis of the surface energy budget indicates that weaker spring warming results from an evaporative cooling effect due to the increased vegetation greenness. Over East Asia, the vegetation-evaporation feedback, therefore, may produce seasonal asymmetry in the warming trend.
- 작성자Jeong et al.
- 작성일2024.06.17
- 조회수12
- 2009
Seasonal prediction of tropical cyclone frequency over the East China Sea through a Bayesian Poisson-regression method

Abstract: In this study, a Bayesian method has been used to predict the seasonal number of tropical cyclones (TCs) over the East China Sea (25°N–35°N, 120°E–130°E). The method considers two periods each year and provides several different predictions of the number of TCs that will enter the target area during a typhoon season, assigning a probability value to indicate the likelihood of each prediction. The method was used to forecast the number of TCs that would occur over the extended season (June–September) issued by June 1 and over the peak season (July–September) issued by July 1. The three parameters of sea surface temperature (SST), outgoing longwave radiation (OLR), and 850-hPa vorticity (VOR850) were used as predictors, based on lag correlation coefficients with the TCs over the target region for 1979–2003. For the extended season prediction, the SST for February–April, the VOR850 for February 16–May 15, and the OLR for May 1–May 15 were chosen as predictors in the TC forecast system. The three predictors for the peak season prediction are delayed one month relative to those for the extended season prediction. The observed TCs over the target region mainly fall into the prediction range within 25% probability from the median during the period from 1979 to 2007. The method predicts the mean TC frequency with a high level of accuracy, yielding a correlation coefficient of 0.69 and 0.71 and a root mean square error of 1.48 and 1.20 between the predicted and observed TCs for the extended and peak season forecasts, respectively. This TC prediction method may soon be used for operational purposes.
- 작성자Ho et al.
- 작성일2024.06.17
- 조회수9
- 2009
Spatial and seasonal variations of surface PM10 concentration and MODIS aerosol optical depth over China

Abstract: We examine the spatial and temporal variabilities of ground-observed concentrations of particulate matter with diame-ters ≤ 10 μm (PM10) over China and compare them with satellite-retrieved data on the aerosol optical depth (AOD) collected over the period 2003–2005 using a moderate resolution imaging spectroradiometer (MODIS). Annual mean values of the PM10 concentrations and AOD show a strong spatial correlation, indicating the consistent presence of aerosol concentrations. However, the temporal correlation between the monthly values of the PM10 concentrations and AOD indicates a regional contrast in their seasonality. The correlation coefficients are 0.6 or higher in the southeastern coast region, whereas they are −0.6 or lower in the north-central region. The regional discrepancy is most likely due to the difference in the size distributions of aerosols. This is also supported by the data on the distribution of the Angstrom ex-ponent and fine mode fraction obtained from the MODIS. The characteristics of the aerosols with respect to coarse and fine particles are discussed in this study.
- 작성자Song et al.
- 작성일2024.06.17
- 조회수11
- 2009
Validation of the cloud property retrievals from the MTSAT-1R imagery using MODIS observations

Abstract: A cloud property retrieval algorithm optimized for five channels (centred at 0.6, 3.7, 6.7, 10.8, and 12.0 μm) has been explored for application to onboard meteorological radiometers on geostationary satellites; however, its validity remains to be established. Here, we present validation results for the cloud properties retrieved by the developed algorithm from the full-disk imagery of the Multi-functional Transport Satellite (MTSAT-1R) for August 2006. The considered cloud properties include cloud phase (CP), cloud optical thickness (COT), effective radius (ER) and cloud top pressure (CTP). Their one-month averages, daily variations, and respective collocated values are compared with the Moderate Resolution Imaging Spectroradiometer cloud data. Our validation results show that an additional 6.7 μm brightness temperature test in CP retrieval identifies water and ice phases that may be overlooked in the 10.8- and 12.0-μm bands. Our method to extract cloud-reflected radiances at the 0.6- and 3.7-μm bands contributes to the accuracy of the COT for values between 5 and 60, and the ER for values less than 40 μm. Estimating high-cloud top pressure from the radiance ratio in the 6.7- and 10.8-μm bands remarkably reduces (by up to 70%) large uncertainties in the CTP, which may be found in the presence of high thin cirrus clouds.
- 작성자Choi and Ho
- 작성일2024.06.17
- 조회수6
- 2009
Weekly periodicities of meteorological variables and their possible association with aerosols in Korea

Abstract: The weekly periodicities in meteorological variables and its association with aerosols in Korea are investigated using long-term surface measurements of meteorology (1975–2005) and aerosols (1999–2005). Through an analysis of the annual (and/or seasonal) values averaged over 10 stations, we identified distinct weekly periodicities in the daily minimum temperature (Tmin), diurnal temperature range (DTR), cloud fraction, and solar insolation, although they have different characteristics from each other. The weekly association among variables is discussed in this study. Positive anomalies of the cloud fraction and Tmin and negative anomalies of solar insolation and DTR are seen for the second half of the week and the reverse for the first half of the week, i.e., more cloudiness and less insolation for Wednesday−Thursday and less cloudiness and more insolation for Monday−Tuesday. Furthermore, seasonal dependence of weekly anomalies shows that the weekly periodicities are enhanced especially in autumn, more than 2–3 times as great as those of the annual mean. The weekly cycles in such variables are most likely driven by changes in cloud fraction, possibly through aerosol–cloud interactions induced by aerosol variations between working weekdays and Sunday, which are clearly identified in PM10 weekly cycles. This study also suggests that the weekly periodicities in meteorological variables are possibly associated with long-range transport of weekly periodicities, as well as aerosol–cloud-precipitation interactions over the region.
- 작성자Kim et al.
- 작성일2024.06.17
- 조회수7
- 2009
Change in the western North Pacific summer monsoon circulation due to the CO2 increase in IPCC AR4 CGCMs

In order to investigate the change in the western North Pacific summer monsoon (WNPSM) caused by an increase in the level of atmospheric carbon dioxide (CO2), nine coupled general circulation models (CGCMs) designed for the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) are chosen, and their simulations are analyzed for the 20th century (20C3M) and CO2-quadrupling scenario (1pctto4x) experiments. The summer (JJA) mean climatology for several variables is analyzed in order to investigate the mean field change in the WNPSM circulation and the cause of this change. By performing the JJA mean analysis, we found that the rainfall over the WNPSM region, especially summer rainfall, increases with the CO2 concentration, which results from the enhanced conditional instability caused by the warm sea-surface temperature (SST) and increased moisture, despite a slight weakening of the low-level convergence. On the other hand, to examine the change in the interannual variability of the WNPSM, we performed a composite analysis of the differences between the strong and the weak monsoon years with respect to a newly defined WNPSM index. In the precipitation analysis, it was clarified that the monsoon variability would increase with global warming over the WNPSM region. The SST analysis revealed that the lag relationship between El Niño-Southern Oscillation (ENSO) and WNPSM would be weakened with an increase in the CO2 concentration, implying that prediction of the WNPSM would become slightly difficult. On the basis of global warming scenario results obtained from the IPCC AR4 models, it is concluded that both the intensity and variability of the WNPSM would increase with CO2 concentration.
- 작성자Lee et al.
- 작성일2024.06.17
- 조회수5
- 2008
Characteristics of atmospheric circulation associated with cold surge occurrences in East Asia: A case study ...

Abstract: The characteristics of the upper-level circulation and thermodynamical properties for the period when two distinct cold surges broke out over East Asia during the 2005/06 winter are investigated. From early December 2005 to early January 2006, exceptionally cold weather lasted for approximately one month due to two successive cold surges that took place on 2 December 2005 and 2 January 2006, respectively. This study reveals that both involve the upper-tropospheric circulation, which induces the amplification and expansion of the surface Siberian high toward East Asia, but arose from different causes: the former is caused by the upper-level blocking originated from the North Pacific and the latter is caused by the upper-level wave train across the Eurasian Continent. In particular, it is suggested that the lower-tropospheric anomalous wind caused by upper-level circulation anomalies and a steep meridional temperature gradient amplified by phase-locked annual cycle combined to induce very strong cold advection in East Asia, which resulted in exceptionally cold weather that lasted for several weeks. The present results emphasize that the characteristics of the upper-tropospheric circulation can be considered as important precursors to cold surge occurrences in East Asia. Full title: Characteristics of atmospheric circulation associated with cold surge occurrences in East Asia: A case study during 2005/06 winter
- 작성자Park et al.
- 작성일2024.06.17
- 조회수7
- 2008
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
- 조회수17
- 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
- 조회수11
- 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
- 조회수11
- 2008