Diurnal Variation of Tropical Convection during TOGA COARE IOP

Jae-Young, Byon,Gyu-Ho, Lim China Ocean Press ; Springer-Verlag 2005 ADVANCES IN ATMOSPHERIC SCIENCES Vol.22 No.5

<P>Diurnal variation of tropical convection and kinematic and thermodynamic conditions was investigated for different large-scale environments of the convectively active and inactive periods by using satellite observations and surface measurements during the Intensive Observation Period (IOP) of the Tropical Ocean Global Atmosphere/Coupled Ocean-Atmosphere Response Experiment (TOGA/COARE). During the convectively active period, the features of nocturnal convection appear in vertical profiles of convergence, vertical velocity, heat source, and moisture sink. The specific humidity increases remarkably in the middle troposphere at dawn. On the other hand, the altitude of maximum convergence and that of the upward motion is lower during the convectively inactive period. The specific humidity peaks in the lower troposphere in the daytime and decreases in the middle troposphere. Spectral analyses of the time series of the infrared (IR) brightness temperature (TBB) and amounts of rainfall suggest multiscale temporal variation with a prominent diurnal cycle over land and oceanic regions such as the Intensive Flux Array (IFA) and the South Pacific Convergence Zone (SPCZ). Over land, the daily maximum of deep convection associated with cloud top temperature less than 208 K appears at midnight due to the daytime radiative heating and the sea-land breeze. Over the ocean, convection usually tends to occur at dawn for the convectively active period while in the afternoon during the inactive period. Comparing the diurnal variation of convection with large-scale variables, the authors inferred that moisture in the middle troposphere contributes mostly to the development of nocturnal convection over the ocean during the convectively active period.</P>

The Climate Variabilities of Air Temperature Around the Korean Peninsula

China Ocean Press ; Springer-Verlag 2005 ADVANCES IN ATMOSPHERIC SCIENCES Vol.22 No.4

<P>In this study, changes in climatological conditions around the Korean Peninsula are estimated quantitatively using various types of high order statistical analyses. The temperature data collected from Incheon station have been analyzed for the assessment of the climate variation. According to our analysis,the climate changes observed over the Korean Peninsula for the last century are similar to the global observational data in many respects. First of all, the warming trend [+1.5℃ (100 yr)-1] and the overall evolving pattern throughout the century are quite similar to each other. The temperature change in the Korean Peninsula is about two to three times larger than that of the global scale which may partially be ascribed to the influence of urbanization at mid and high latitudes. In this work, a new Winter Monsoon Index (WMI) is suggested based on the European continental scale circulation index (EU1) pattern. Our WMI is defined as the normalized sea level pressure (SLP) difference in the winter period between the centers of the East Sea and west of Lake Baikal in Siberia, the two eastern centers of the EU1 action patterns. A strong similarity is found between the time series of the WMI and surface air temperature at Incheon. The WMI has decreased gradually since the 1920s but has shifted to a rapid increasing trend in the last two decades; it was in fact accompanied by a weakening of the Siberian High and a decreasing of the northerly during winter. Our findings of the close correlations between the surface air temperature at Incheon and the WMI strongly indicate that our newly suggested index is unique and can be used as an efficient tool to predict climate variability in Korea.</P>

Climate Change Signal Analysis for Northeast Asian Surface Temperature

Jeong-Hyeong, LEE,Byungsoo, KIM,Keon-Tae, SOHN,Won-Tae, KOWN,Seung-Ki, MIN,Meteorological, Institute of the University of Bonn) China Ocean Press ; Springer-Verlag 2005 Advances in atmospheric sciences Vol.22 No.2

<P>Climate change detection, attribution, and prediction were studied for the surface temperature in the Northeast Asian region using NCEP/NCAR reanalysis data and three coupled-model simulations from ECHAM4/OPYC3, HadCM3, and CCCma GCMs (Canadian Centre for Climate Modeling and Analysis general circulation model). The Bayesian fingerprint approach was used to perform the detection and attribution test for the anthropogenic climate change signal associated with changes in anthropogenic carbon dioxide (CO2) and sulfate aerosol (SO42-) concentrations for the Northeast Asian temperature. It was shown that there was a weak anthropogenic climate change signal in the Northeast Asian temperature change. The relative contribution of CO2 and SOl- effects to total temperature change in Northeast Asia was quantified from ECHAM4/OPYC3 and CCCma GCM simulations using analysis of variance. For the observed temperature change for the period of 1959-1998, the CO2 effect contributed 10%-21% of the total variance and the direct cooling effect of SO42- played a less important role (0% 7%) than the CO2effect. The prediction of surface temperature change was estimated from the second CO2+SO24- scenario run of ECHAM4/OPYC3 which has the least error in the simulation of the present-day temperature field near the Korean Peninsula. The result shows that the area-mean surface temperature near the Korean Peninsula will increase by about 1.1° by the 2040s relative to the 1990s.</P>

Surface and Upper-Level Features Associated with Wintertime Cold Surge Outbreaks in South Korea

Sang, Boom Ryoo,Won, Tae Kwon,Jong, Ghap Jhun China Ocean Press ; Springer-Verlag 2005 Advances in atmospheric sciences Vol.22 No.4

<P>The surface and upper-level features associated with a sharp drop of wintertime daily temperature over South Korea is investigated in this study. This sharp drop in daily temperature is called a cold surge and is one of the most hazardous weather phenomena in East Asian winters. An upper-level baroclinic wave of 60° wavelength propagating eastward at a phase speed of 12° longitude per day across the continent of northern China from the west of Lake Baikal toward the eastern coast of China causes the outbreak of cold air over South Korea. The cooling associated with the upper-level baroclinic wave is found at all altitudes under the geopotential height-fall center near the tropopause. The development in the ridge seems to derive the early evolution of the eastward-propagating sinusoidal wave, whereas the trough is connected directly with the tropospheric temperature-drop. An enhancement of the wintertime East Asian jet stream after the outbreak of a cold surge is a response to the steep temperature gradient associated with the developing baroclinic wave.</P>

Statistical Prediction of Heavy Rain in South Korea

Keon, Tae Sohn,Jeong, Hyeong Lee,Soon, Hwan Lee,Chan, Su Ryu China Ocean Press ; Springer-Verlag 2005 Advances in atmospheric sciences Vol.22 No.5

<P>This study is aimed at the development of a statistical model for forecasting heavy rain in South Korea. For the 3-hour weather forecast system, the 10 km× 10 km area-mean amount of rainfall at 6 stations (Seoul, Daejeon, Gangreung, Gwangju, Busan, and Jeju) in South Korea are used. And the corresponding 45 synoptic factors generated by the numerical model are used as potential predictors. Four statistical forecast models (linear regression model, logistic regression model, neural network model and decision tree model) for the occurrence of heavy rain are based on the model output statistics (MOS) method. They are separately estimated by the same training data. The thresholds are considered to forecast the occurrence of heavy rain because the distribution of estimated values that are generated by each model is too skewed.The results of four models are compared via Heidke skill scores. As a result, the logistic regression model is recommended.</P>

Physical Experiments to Investigate the Effects of Street Bottom Heating and Inflow Turbulence on Urban Street-Canyon Flow

Jae-Jin, KIM,Jong-Jin, BAIK China Ocean Press ; Springer-Verlag 2005 Advances in atmospheric sciences Vol.22 No.2

<P>The effects of street bottom heating and inflow turbulence on urban street-canyon flow are experimentally investigated using a circulating water channel. Three experiments are carried out for a street canyon with a street aspect ratio of 1. Results from each experiment with bottom heating or inflow turbulence are compared with those without bottom heating and appreciable inflow turbulence. It is demonstrated that street bottom heating or inflow turbulence increases the intensity of the canyon vortex. A possible explanation on how street bottom heating or inflow turbulence intensifies the canyon vortex is given from a fluid dynamical viewpoint.</P>