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국제학술지

공지 (2024. 9. 4.)

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Space observations of cold-cloud phase change

Abstract: This study examines the vertically resolved cloud measurements from the cloud-aerosol lidar with orthogonal polarization instrument on Aqua satellite from June 2006 through May 2007 to estimate the extent to which the mixed cloud-phase composition can vary according to the ambient temperature, an important concern for the uncertainty in calculating cloud radiative effects. At -20 °C, the global average fraction of supercooled clouds in the total cloud population is found to be about 50% in the data period. Between -10 and -40 °C, the fraction is smaller at lower temperatures. However, there are appreciable regional and temporal deviations from the global mean (> ± 20%) at the isotherm. In the analysis with coincident dust aerosol data from the same instrument, it appears that the variation in the supercooled cloud fraction is negatively correlated with the frequencies of dust aerosols at the -20 °C isotherm. This result suggests a possibility that dust particles lifted to the cold cloud layer effectively glaciate supercooled clouds. Observations of radiative flux from the clouds and earth’s radiant energy system instrument aboard Terra satellite, as well as radiative transfer model simulations, show that the 20% variation in the supercooled cloud fraction is quantitatively important in cloud radiative effects, especially in shortwave, which are 10 - 20 W m-2 for regions of mixed-phase clouds affected by dust. In particular, our results demonstrate that dust, by glaciating supercooled water, can decrease albedo, thus compensating for the increase in albedo due to the dust aerosols themselves. This has important implications for the determination of climate sensitivity.
- 작성자Choi et al.
- 작성일2024.06.19
- 조회수9
- 2010
Spatial interpolation of daily precipitation in China: 1951-2005

Abstract: Climate research relies heavily on good quality instrumental data; for modeling efforts gridded data are needed. So far, relatively little effort has been made to create gridded climate data for China. This is especially true for high-resolution daily data. This work, focuses on identifying an accurate method to produce gridded daily precipitation in China based on the observed data at 753 stations for the period 1951–2005. Five interpolation methods, including ordinary nearest neighbor, local polynomial, radial basis function, inverse distance weighting, and ordinary kriging, have been used and compared. Cross-validation shows that the ordinary kriging based on seasonal semi-variograms gives the best performance, closely followed by the inverse distance weighting with a power of 2. Finally the ordinary kriging is chosen to interpolate the station data to a 18 km× 18 km grid system covering the whole country. Precipitation for each 0.5° × 0.5° latitude-longitude block is then obtained by averaging the values at the grid nodes within the block. Owing to the higher station density in the eastern part of the country, the interpolation errors are much smaller than those in the west (west of 100°E). Excluding 145 stations in the western region, the daily, monthly, and annual relative mean absolute errors of the interpolation for the remaining 608 stations are 74%, 29%, and 16%, respectively. The interpolated daily precipitation has been made available on the internet for the scientific community.
- 작성자Chen et al.
- 작성일2024.06.19
- 조회수17
- 2010
Adaptive change in intra-winter distribution of relatively cold events to East Asian warming

Abstract: For the past few decades, daily winter temperatures over East Asia have been higher and less variable. Generally, these simple temperature-distribution shifts should lead to a decrease in the occurrence of cold extremes, but observations of the changes in the extremes are often complicated. In the present study, the change in the occurrence of relatively cold events (daily temperature anomaly, ≤ -2σ for that season) in each winter monsoon over East Asia was examined using ground observations of daily temperature for the period 1954 - 2006. The time-mean temperature for each winter was subtracted to remove the interannual variability and long-term trend. Our analyses reveal that the intraseasonal temperature distribution over East Asia has changed with a negative skew, and the frequency of the relatively cold events has slightly increased (by 0.09 days per decade) over the past few decades, on an average, for the entire analysis domain (east of 105°E, 122 stations). In particular, the increase occurs more dominantly (82% of the total stations) in regions north of 40°N where a stronger warming has progressed. The frequency of relatively cold events is found to be significantly correlated with the variance of the Siberian high and the mean of the Arctic Oscillation. The increasing trend in the frequency of relatively cold events may serve to partly countervail the decrease (-1.12 days per decade) in the frequency of absolute cold events (daily temperature anomaly, ≤ -2σ overall) across the entire observation period.
- 작성자Choi et al.
- 작성일2024.06.17
- 조회수10
- 2009
Arctic and Antarctic Oscillation signatures in tropical coral proxies over the South China Sea

Abstract: Arctic Oscillation (AO) and Antarctic Oscillation (AAO) are the leading modes of atmospheric circulation in mid-high latitudes. Previous studies have revealed that the climatic influences of the two modes are dominant in extra-tropical regions. This study finds that AO and AAO signals are also well recorded in coral proxies in the tropical South China Sea. There are significant interannual signals of AO and AAO in the strontium (Sr) content, which represents the sea surface temperature (SST). Among all the seasons, the most significant correlation occurs during winter in both hemispheres: the strongest AO-Sr and AAO-Sr coral correlations occur in January and August, respectively. This study also determined that the Sr content lags behind AO and AAO by 1–3 months. Large-scale anomalies in sea level pressure and horizontal wind at 850 hPa level support the strength of AO/AAO-coral teleconnections. In addition, a comparison with oxygen isotope records from two coral sites in neighboring oceans yields significant AO and AAO signatures with similar time lags. These results help to better understand monsoon climates and their teleconnection to high-latitude climate changes.
- 작성자Gong et al.
- 작성일2024.06.17
- 조회수12
- 2009
Estimates of ground-level aerosol mass concentrations using a chemical transport model with MODIS aerosol observations..

Abstract: We estimate ground-level mass concentrations of PM2.5 and PM10 (particulate matter smaller than 2.5 and 10 μm in diameter, respectively) for 2001 using a global chemical transport model with Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol optical depth (AOD) retrievals. Our method improves on previous techniques by using a new satellite product (fine-mode fraction (FMF)) and is applied to East Asia, where such an approach has not previously been attempted. We evaluate the method by comparing the PM estimates with the observations from Air Quality System sites and Acid Deposition Monitoring Network sites across East Asia. The spatial patterns of the annual and seasonal means of the estimated PM10 concentrations are in better agreement with the observations than the results of the model alone. The PM2.5 estimates based on both MODIS AOD and FMF data show considerable improvement relative to those using AOD data alone or simply the model and are in better agreement with the observations at three available sites in Korea and Japan. The greatest improvement is found in the cases where the model significantly underestimates the data. Our best estimates of the annual mean PM2.5 and PM10 concentrations over East Asia are 14.7 and 71.2 μg m−3, respectively. However, the uncertainties in our PM2.5 and PM10 estimates are up to 2.5 and 20 μg m−3, respectively. Full title: Estimates of ground-level aerosol mass concentrations using a chemical transport model with Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol observations over East Asia
- 작성자Choi et al.
- 작성일2024.06.17
- 조회수10
- 2009
Estimating bulk optical properties of aerosols over the western North Pacific by using MODIS and CERES measurements

Abstract: Over the western North Pacific, a large amount of land aerosols from Asian-Pacific countries is transported by the prevailing westerlies. This transport makes the radiative characteristics of these aerosols diverse, particularly when one compares those characteristics over the coastal sea with those over the open sea. In this paper we discuss a method that uses satellite data to obtain the single-scattering albedo (ω) and asymmetry factor (g) of atmospheric aerosols for two large-scale subdivisions—the coastal sea (within 250 km from the coast) and the open sea (the remaining area)—over the western North Pacific (110°E–180°, 20°N–50°N). Our estimation method uses satellite measurements, obtained over a six-year period (2000–2005), of aerosol optical depth (AOD) and shortwave fluxes at both the surface and the top of the atmosphere (TOA); the measurements are obtained using the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Clouds and the Earth's Radiant Energy System (CERES). For the two subdivisions, the estimated annual means of (ω, g) at 630 nm are significantly different: (0.94, 0.65) over the coastal sea and (0.97, 0.70) over the open sea. From a quantitative viewpoint, this result indicates that in comparison with aerosols over the open sea, those over the coastal sea show greater absorption and lesser forward scattering of solar radiation. The estimated optical properties are responsible for the aerosol surface cooling observed by MODIS and CERES, which is approximately 138 and 108 W m−2 per AOD over the coastal sea and open sea, respectively.
- 작성자Choi et al.
- 작성일2024.06.17
- 조회수12
- 2009
Flux-gradient relationship of water vapor in the surface layer obtained from CASES-99 experiment

Abstract: The flux-gradient relationship of water vapor Φq was obtained from the Cooperative Atmosphere-Surface Exchange Study-1999 (CASES-99) field experiment, which was conducted on a flat and grassy field in the southeastern part of Kansas, USA, during October 1999. The CASES-99 data include turbulence measurements of wind, temperature, and vapor density along with their time-averaged values at various levels above the ground. Quality control of the data on the turbulent wind velocity, sonic temperature, and vapor density was performed prior to flux calculation. The turbulent sensible heat and latent heat fluxes were calculated using a 30-min window, and they were subsequently corrected and checked for the fulfillment of the steady state and for turbulence intensity. Weak fluxes and through-tower wind data were also excluded from the analysis. Vertical gradients of the mean values were obtained by differentiating functions fitted to the measured mean profiles. It was found that Φq is comparable to ΦT for weakly stable stratification and less than ΦT for strongly stable stratification. On the contrary, Φq was found to be larger than ΦT by approximately 20% for the neutral and unstable stratifications. The best fitting functions for water vapor are found to be Φq = 1.21(1 − 13.1z/L)−1/2 and Φq = 1.21(1 + 60.4z/L)−1/3 for the unstable and stable stratifications, respectively.
- 작성자Park et al.
- 작성일2024.06.17
- 조회수5
- 2009
Increase in vegetation greenness and decrease in springtime warming over East Asia

Abstract: This study investigates the impact of increased vegetation greening on the springtime temperature over east Asia for 1982–2000. An analysis of station-based temperature records and satellite-measure normalized difference vegetation index (NDVI) indicates that slight warming (<0.4°C 10-yr−1) occurred over regions that experienced large increase in NDVI (≥0.08 10-yr−1). On the contrary, strong warming (≥0.8°C 10-yr−1) occurred over regions that exhibited minor changes in NDVI (<0.04 10-yr−1). For the most part, this inverse NDVI–temperature relationship observed with the daily maximum temperature. Thus, it is suggested that the decrease in warming was mostly attributable to the increase in evapotranspiration associated with increased vegetation greening. Earlier vegetation growth may have further strengthened the effect of this vegetation–evaporation on spring temperature.
- 작성자Jeong et al.
- 작성일2024.06.17
- 조회수17
- 2009
Influence of stratospheric quasi-biennial oscillation on tropical cyclone tracks in the western North Pacific

Abstract: The possible influence of the stratospheric quasi-biennial oscillation (QBO) on tropical cyclone (TC) passages in the western North Pacific (WNP) is examined using TC data recorded by the Tokyo Typhoon Center and the QBO index derived from reanalysis data. The influence is observed to be significant. The number of TCs approaching the East China Sea is large during the westerly phase of the QBO; however, during the easterly phase, the number of TCs approaching the eastern offshore of Japan is large. This difference in the TC tracks is found to be related to the background flow change associated with the QBO. However, the total number of TC events over the WNP and the sum of the number of TCs approaching the aforementioned two regions appear to be unrelated to the QBO phases.
- 작성자Ho et al.
- 작성일2024.06.17
- 조회수7
- 2009
Long-term changes in summer weekend effect over northeastern China and the connection with regional warming

Abstract: The 7-day cycle of human activities may lead to the “weekend effect” in climate variables and air pollutants. The weekend effect is defined as the average value (e.g., the diurnal temperature range) for Saturday through Monday minus the average value for Wednesday through Friday. A composite of the ground observations over northeastern China presents that, during 26-year (1980–2005) summers, the weekend effect in the diurnal temperature range increased by 1.2°C. Conversely, the weekend effects in the relative humidity, cloud amount, and light rain (≤5 mm day−1) events decreased. These changes are due to a shifted phase of the weekly cycle of the meteorological variables. The long-term change in weekend effects have a high correlation coefficient (∣r∣ ≈ 0.8) with the decrease in relative humidity over the region, which is likely induced by regional warming. The results suggest that regional warming is a possible factor in a transition of dominant aerosol effects in the weekend effect.
- 작성자Ho et al.
- 작성일2024.06.17
- 조회수8
- 2009