국제학술지 게시판목록 | 이화여자대학교 기후물리실험실

Publications

국제학술지

공지 (2024. 9. 4.)

현재까지 출판된 논문 목록입니다. 아직 준비 중인 논문은 포함하지 않은 점 참고 바랍니다.

Observational diagnosis of cloud phase in the winter Antarctic atmosphere for parameterizations in climate models

Abstract: The cloud phase composition of cold clouds in the Antarctic atmosphere is explored using data from the Moderate Resolution Imaging Spectroradiometer (MODIS) and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) instruments for the period 2000–2006. We used the averaged fraction of liquid-phase clouds out of the total cloud amount at the cloud tops since the value is comparable in the two measurements. MODIS data for the winter months (June, July, and August) reveal liquid cloud fraction out of the total cloud amount significantly decreases with decreasing cloud-top temperature below 0°C. In addition, the CALIOP vertical profiles show that below the ice clouds, low-lying liquid clouds are distributed over ∼20% of the area. With increasing latitude, the liquid cloud fraction decreases as a function of the local temperature. The MODIS-observed relation between the cloud-top liquid fraction and cloud-top temperature is then applied to evaluate the cloud phase parameterization in climate models, in which condensed cloud water is repartitioned between liquid water and ice on the basis of the grid point temperature. It is found that models assuming overly high cut-offs (≫ −40°C) for the separation of ice clouds from mixed-phase clouds may significantly underestimate the liquid cloud fraction in the winter Antarctic atmosphere. Correction of the bias in the liquid cloud fraction would serve to reduce the large uncertainty in cloud radiative effects.
- 작성자Choi et al.
- 작성일2024.06.19
- 조회수11
- 2010
Bayesian forecasting of seasonal typhoon activity: A track-pattern-oriented categorization approach

Abstract: A new approach to forecasting regional and seasonal tropical cyclone (TC) frequency in the western North Pacific using the antecedent large-scale environmental conditions is proposed. This approach, based on TC track types, yields probabilistic forecasts and its utility to a smaller region in the western Pacific is demonstrated. Environmental variables used include the monthly mean of sea surface temperatures, sea level pressures, low-level relative vorticity, vertical wind shear, and precipitable water of the preceding May. The region considered is the vicinity of Taiwan, and typhoon season runs from June through October. Specifically, historical TC tracks are categorized through a fuzzy clustering method into seven distinct types. For each cluster, a Poisson or probit regression model cast in the Bayesian framework is applied individually to forecast the seasonal TC activity. With a noninformative prior assumption for the model parameters, and following Chu and Zhao for the Poisson regression model, a Bayesian inference for the probit regression model is derived. A Gibbs sampler based on the Markov chain Monte Carlo method is designed to integrate the posterior predictive distribution. Because cluster 5 is the most dominant type affecting Taiwan, a leave-one-out cross-validation procedure is applied to predict seasonal TC frequency for this type for the period of 1979–2006, and the correlation skill is found to be 0.76.
- 작성자Chu et al.
- 작성일2024.06.19
- 조회수13
- 2010
Dipolar redistribution of summertime TCG between the Philippine Sea and the northern SCS and its possible mechanisms

Abstract: Recent observational records show that the dipole oscillation between the Philippine Sea (PS) and the northern South China Sea (nSCS) is a leading empirical orthogonal function (EOF) of summertime tropical cyclone (TC) genesis in the western North Pacific (WNP). This PS-nSCS oscillation is characterized by a distinguished decadal variability in addition to an interannual variability. Meanwhile, the typical El Niño–Southern Oscillation (ENSO)-related mode is found in the second EOF mode, which is predominantly interannual. With regard to the PS-nSCS oscillation, its interannual component appears to be linked with the previous wintertime ENSO event, but the linkage is not so robust in the sense that about half of its significant events are classified as the ENSO-related case, whereas its decadal component is coupled to a sea surface temperature anomaly (SSTA) in the central Pacific with its equatorial core near the Niño-4 region, which is flanked by an opposite SSTA on both sides along the latitudinal belt. Interestingly, this SSTA pattern resembles that related to the ENSO Modoki, and equivalently, the transitional phase of ENSO. The ENSO Modoki is regionally manifested by the anomalous zonal SST gradient between the equatorial western and central Pacific; thus the decadal modulation of this anomalous zonal SST gradient can be regarded as an actual forcing that forms and modulates the decadal PS-nSCS oscillation. In addition, the decadal PS-nSCS oscillation is compared with the decadal basin-wide TC genesis variation in terms of the Pacific SSTA pattern and the associated anomalous large-scale environments. Full title: Dipolar redistribution of summertime tropical cyclone genesis between the Philippine Sea and the northern South China Sea and its possible mechanisms
- 작성자Kim et al.
- 작성일2024.06.19
- 조회수7
- 2010
Influence of tropical cyclone landfalls on spatiotemporal variations in typhoon season rainfall over South China

Abstract: This study examined the impact of tropical cyclone (TC) landfalls on the spatiotemporal variations in the rainfall over South China for the period 1957–2005. The target region was selected to show the noteworthy contribution of TC landfalls to the total rainfall during the typhoon season (July–October). Two prevailing spatial variations in the rainfall were obtained from an EOF analysis. The first EOF mode displays single-sign variability over South China with an explained variance of 23.4%. The associated time series of this mode fluctuates on a decadal timescale and was found to be correlated with TC genesis in the South China Sea. The second EOF mode shows a seesaw pattern between Hainan Island/Guangdong Province and the remaining regions with an explained variance of 11.4%. This seesaw pattern results from an anti-correlation in seasonal TC landfalls between the two regions, which was found in previous studies. This is related to the strengthening (weakening) of the upper tropospheric jets and the corresponding development of a massive anticyclonic (cyclonic) circulation over East Asia. The EOF analysis was also conducted using just the data for rainfall caused by landfalling TCs. This revealed that the first EOF mode using just the TC-induced rainfall is nearly identical to the second mode from the total rainfall. The obvious seesaw pattern of the first mode when employing just the TC-induced rainfall in the EOF analysis implies that this pattern has larger temporal variability than the single-signed pattern (i.e., the first EOF mode using the total rainfall) in terms of TC landfalls. This study suggests that TC landfalls over South China and the accompanying rainfall significantly modulate the spatial variation of the typhoon season rainfall there.
- 작성자Lee et al.
- 작성일2024.06.19
- 조회수9
- 2010
Influences of AO and MJO on cold surges and heavy snowfalls over Korea: A case study for the winter of 2009–2010

Abstract: In the winter of 2009–2010, frequent and long-lasting cold weather affected Korea. Four major cold surges and several heavy snowfall events were observed, including a record-breaking event on 4 January 2010. These four cold surges had distinct properties with regard to their relationships to the phases of the Arctic Oscillation (AO) and the Madden-Julian Oscillation (MJO), suggesting the possible influences of the AO and MJO on the cold surges and heavy snowfalls. The four cold surges were of two distinct types: the wave train type and the blocking type, which were differentiated by their mechanisms. With regard to the relationships of the cold surges to the AO, three cold surges occurred during a strongly negative AO period, which lasted for more than 1 month. The Siberian High expanded from the Arctic high-pressure region to East Asia during the negative AO period. A cold surge occurred during a positive AO, with the expansion of the Siberian High across the Eurasian continent. An MJO-induced circulation, corresponding to strong tropical convection over the tropical Indian Ocean, seems to have reinforced the cold surges over East Asia. In addition, the active local Hadley circulation modulated by a convection center over the Indian Ocean tends to enhance midlatitude synoptic disturbances across East Asia and provides favorable conditions for upward motion over the region. In short, the effects of the AO and MJO, along with the existing low-level moisture supply, contributed to heavy snowfalls associated with strong cold surges over Korea during the winter of 2009–2010. Full title: Influences of Arctic Oscillation and Madden-Julian Oscillation on cold surges and heavy snowfalls over Korea: A case study for the winter of 2009–2010
- 작성자Park et al.
- 작성일2024.06.19
- 조회수7
- 2010
On the relationship between Indian Ocean sea surface temperature and the transition from El Niño to La Niña

Abstract: The relationship between Indian Ocean sea surface temperature and the transition of El Niño events into either La Niña or El Niño–Southern Oscillation neutral conditions is examined in both observations and the retrospective ensemble hindcasts of the National Center for Environmental Prediction Climate Forecast System. The southern Indian Ocean is shown to demonstrate a particularly robust and consistent relationship with the evolution of these transitions. These associations are described, and a physical mechanism involving air-sea interaction in the Indian and western Pacific Oceans is proposed. Observations suggest that easterly surface wind anomalies in the western Pacific Ocean are associated with the emergence of La Niña during boreal summer and fall. Here it is shown that these winds are significantly correlated to southern Indian Ocean sea surface temperature in the preceding spring that is characterized by a large-scale zonal dipole of cool and warm anomalies in the southwestern and southeastern Indian Oceans, respectively. These associations are particularly pronounced for strong El Niño conditions, during the dissipation of which a pronounced wavetrain-like atmospheric pattern accompanies sea surface temperature anomalies in the southern Indian Ocean. Together, the circulation and sea surface temperature anomalies increase the meridional cross-equatorial temperature gradient in the western Indian Ocean and mute intraseasonal variability while strengthening surface equatorial easterly winds in the Indo-Pacific warm pool. Collectively, these anomalies favor subsequent La Niña development. On the basis of these observed associations, a predictive model that demonstrates skill in anticipating the nature of El Niño transitions, involving the southern Indian Ocean, Asian monsoon, and El Niño–Southern Oscillation, is proposed. In the National Center for Environmental Prediction Climate Forecast System, the relationships described above are simulated both consistently and realistically, despite model weaknesses, further bolstering a key role of southern Indian Ocean and predictive relationship. Comparison of fully coupled and sea surface temperature–forced simulations suggests a key role for air-sea interaction in the observed associations. Moreover, it is demonstrated that coupled simulations of El Niño–Southern Oscillation may benefit substantially from improved representation of Indian Ocean variability and Indo-Pacific interaction.
- 작성자Yoo et al.
- 작성일2024.06.19
- 조회수8
- 2010
Potential impact of vegetation feedback on European heat waves in a 2 x CO 2 climate

Abstract: Inclusion of the effects of vegetation feedback in a global climate change simulation suggests that the vegetation–climate feedback works to alleviate partially the summer surface warming and the associated heat waves over Europe induced by the increase in atmospheric CO2 concentrations. The projected warming of 4°C over most of Europe with static vegetation has been reduced by 1°C as the dynamic vegetation feedback effects are included. Examination of the simulated surface energy fluxes suggests that additional greening in the presence of vegetation feedback effects enhances evapotranspiration and precipitation, thereby limiting the warming, particularly in the daily maximum temperature. The greening also tends to reduce the frequency and duration of heat waves. Results in this study strongly suggest that the inclusion of vegetation feedback within climate models is a crucial factor for improving the projection of warm season temperatures and heat waves over Europe.
- 작성자Jeong et al.
- 작성일2024.06.19
- 조회수11
- 2010
Roughness length of water vapor over land surfaces and its influence on latent heat flux

Abstract: Latent heat flux at the surface is largely dependent on the roughness length for water vapor (z0q). The determination of z0q is still uncertain because of its multifaceted characteristics of surface properties, atmospheric conditions and insufficient observations. In this study, observed values from the Fluxes Over Snow Surface II field experiment (FLOSS-II) from November 2002 to March 2003 were utilized to estimate z0q over various land surfaces: bare soil, snow, and senescent grass. The present results indicate that the estimated z0q over bare soil is much smaller than the roughness length of momentum (z0m); thus, the ratio z0m/z0q is larger than those of previous studies by a factor of 20 - 150 for the available flow regime of the roughness Reynolds number, Re* > 0.1. On the snow surface, the ratio is comparable to a previous estimation for the rough flow (Re* > 1), but smaller by a factor of 10 - 50 as the flow became smooth (Re* < 1). Using the estimated ratio, an optimal regression equation of z0m/z0q is determined as a function of Re* for each surface type. The present parameterization of the ratio is found to greatly reduce biases of latent heat flux estimation compared with that estimated by the conventional method, suggesting the usefulness of current parameterization for numerical modeling.
- 작성자Park et al.
- 작성일2024.06.19
- 조회수8
- 2010
Satellite retrievals of (quasi-)spherical particles at cold temperatures

Abstract: Measurements from NASA's A-train satellites indicate that spherical or quasi-spherical particles may constitute up to 30% of the total cloud particles at temperatures below −30°C, and up to 10% even for temperatures below −40°C, the temperature range typically found in the upper troposphere and the lower stratosphere. Current climate models calculate cloud radiative forcing on the basis on an assumption that essentially no spherical or quasi-spherical particles exist below −40°C (even below −15°C). The findings in this study show that this widely used assumption in climate models may need re-examination. Further research is also needed to confirm and quantify these findings, especially improvements in the satellite retrievals of cloud particle shapes that, in the mean, currently contain about 10% uncertainties.
- 작성자Choi et al.
- 작성일2024.06.19
- 조회수8
- 2010
Seasonal prediction of summertime tropical cyclone activity over the East China Sea using the least absolute deviation..

Abstract: In the present study, we have employed two statistical models to predict summertime (July–September) tropical cyclone (TC) activity over the East China Sea using the least absolute deviation (LAD) regression and the Poisson regression method. Through a lagged correlation analysis of the relationship between the seasonal TC frequency in the target region and several pre-season environmental parameters for the period 1979–2003, physically interpretable and statistically significant large-scale environmental parameters were identified as potential predictors. After applying the predictor screening method based on the stepwise regression, three predictors, i.e. sea surface temperature, outgoing long-wave radiation and 850-hPa relative vorticity were finally chosen. They are related to the phase transition of El Niño/Southern Oscillation and the strength of the western North Pacific summer monsoon. The correlation coefficient between the predicted and the observed frequency is 0.75 for the LAD model and 0.78 for the Poisson model. The predictions using the two models have a skill improvement of about 60% compared to the reference forecasts. The present study suggests that both models are skillful in predicting summertime TC frequency over the East China Sea with the Poisson model being slightly more skillful than the LAD model. Full title: Seasonal prediction of summertime tropical cyclone activity over the East China Sea using the least absolute deviation regression and the Poisson regression
- 작성자Kim et al.
- 작성일2024.06.19
- 조회수6
- 2010