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The present study examines variations in summertime (July–September) tropical cyclone (TC) activity over East Asia during the period 1951–2003. To represent TC activity, a total of 853 TC best tracks for the period were converted to TC passage frequencies (TPFs) within 5° × 5° latitude–longitude grids; TPFs are defined as the percentage values obtained by dividing the number of TC appearances in each grid box by the total number of TCs each year. Empirical orthogonal function analysis of the TPF showed three leading modes: two tropical modes that represent the long-term trend and the relationship with ENSO and one midlatitude mode that oscillates between south of Korea and southeast of Japan with an interannual time scale. The latter proved to be the most remarkable climatic fluctuation of summertime TC activity in the midlatitudes and is referred to as the East Asian dipole pattern (EADP) in this paper. Anomalous atmospheric flows directly connected to the EADP are an enhanced anticyclonic (cyclonic) circulation centering around Japan when the TPF is high south of Korea (southeast of Japan), thereby showing an equivalent barotropic structure in the entire troposphere. This regional circulation anomaly varies in conjunction with the zonally oriented quasi-stationary Rossby wave train in the upper troposphere. This wave train is meridionally trapped in the vicinity of the summer-mean jet stream; therefore, the mean jet stream alters its internal meandering structure according to the phase of the wave train. [ABSTRACT FROM AUTHOR]

This study examines daily longitudinal locations of South Asia High (SAH) in September and its connection with Asian September rainfall variation. Results suggest that daily longitudinal locations of September SAH exhibits as bimodality, which is featured by two preferable locations with one high‐frequency location lying over southern Tibetan Plateau and the other over southern Iranian Plateau. Referred to the two preferred locations, the SAH is classified into east and west SAH mode. The two modes may be attributed to a warm column over central eastern Tibetan or eastern Iranian Plateau, which warms the above troposphere and maintains a SAH at upper troposphere over corresponding location. In addition, bimodality of the SAH has a close relationship with Asian September rainfall. The east mode of SAH is associated with an increasing rainfall over western China and decreasing rainfall over northern Indian Peninsula, southwestern Tibetan Plateau, Indochina Peninsula, eastern China and Korea Peninsula, while the west mode of SAH is linked with the reverse pattern. Specifically, the atmospheric circulation at upper troposphere is featured by one large anticyclonic circulation above eastern Tibetan Plateau and two cyclonic circulations over northern Iranian Plateau and eastern Korea. In the lower troposphere, southerly and northerly anomalies form a convergence zone over western China. Meantime, a cyclonic moisture circulation with warm and wet southerly vapour flow results in above‐normal rainfall over western China. An anticyclone over northern Iranian Plateau at lower troposphere results in an anticyclonic moisture divergence and deficient rainfall over southwestern Tibetan Plateau and northern India. Moreover, a cyclonic circulation over eastern Korea Peninsula with marked northwesterly and moisture flux divergence results in below‐normal rainfall over eastern China and Korea Peninsula. [ABSTRACT FROM AUTHOR]

This paper proposes a complete framework of a machine learning-based model that detects convective initiation (CI) from geostationary meteorological satellite data. The suggested framework consists of three main processes: (1) An automated sampling tool; (2) machine learning-based CI detection modelling; (3) repeated model tuning through validation. In this study, the automated sampling tool was able to track the CI objects iteratively, even without ancillary data such as an atmospheric motion vector (AMV). The collected samples were used to train the machine learning model for CI detection. Random forest (RF) was used to classify the CI and non-CI. To enhance the advantages of the machine learning approach, we adopted model tuning to iteratively update the training dataset from each validation result by adding hits and misses to the CI samples, and false alarms and correct negatives to the non-CI samples. Using 12 interest fields from the Himawari-8 Advanced Himawari Imager (AHI) over the Korean Peninsula, this simple and intuitive tuning process increased the overall probability of detection (POD) from 0.79 to 0.82 and decreased the overall false alarm rate (FAR) from 0.46 to 0.37 with around 40 min of the lead-time. Amongst the 12 interest fields, T b (11.2) µm was identified as the most significant predictor in the RF model, followed by T b (8.6—11.2) µm, and T b (6.2–7.3) µm. The effect of model tuning on the CI detection performance was also analyzed using spatiotemporal validation maps. By automatically collecting and updating the machine learning training dataset, the suggested framework is expected to help the maintenance of the CI detection model from an operational perspective. [ABSTRACT FROM AUTHOR]

This paper investigates regional sources and transport routes of Asian dust observed in Korea over the past 40 years, that is from 1965 to 2004. These long-term changes were studied in relation to climatic changes and causes. About 87% of dust events in Korea occur in the spring and have been increasing steadily since the 1980s. These trends can be attributed to regional changes in dust sources to windward and the resultant transport pathways of dust storms. This study establishes that dust events have greatly increased during the 3 years from 2000 to 2002. It may be the result of not only an eastward shift in the regional source of dust but also changes in upper-level synoptic transport patterns. Intensified atmospheric circulation and an associated increase in wind speed as well as changes in snow cover, surface wetness and potential evaporation rates throughout Inner Mongolia and Manchuria are likely to be the main causes of the steadily increasing number of dusty days in Korea. [Copyright &y& Elsevier]

This study investigates the applicability of five cumulus parameterization schemes (CPSs) for precipitation simulation in East Asia with the atmospheric model ECHAM6.3. Besides the built-in Tiedtke–Nordeng–Tiedtke (TNT) scheme, four updated schemes are implemented in ECHAM6.3: two modified Tiedtke schemes, the simplified Arakawa–Schubert scheme (SAS), and the Betts–Miller–Janjić scheme (BMJ). An overall assessment of seasonal climatology shows that the SAS and the two modified Tiedtke schemes have clear advantages over the default TNT scheme. The spatial pattern of precipitation climatology and seasonal variations are successfully reproduced by all CPSs. Biases of rainfall distribution are strongly modulated by the simulation of atmospheric circulation systems over East Asia. The main characteristics of summer monsoonal precipitation, including the increase in rainfall and rain belt migration under the influence of the East Asian summer monsoon (EASM), are successfully captured. However, there are large model diversities in the location and intensity of rain centers around Southeast China and the Korean Peninsula. In addition, all simulations of Meiyu rain band migration are farther north than observed. The SAS scheme is the best of the five CPSs in simulating the timing and intensity of seasonal rainfall variations. The results also suggest that the environmental feedback of a CPS is a key factor that determines the applicability of the CPS in a particular climate model. [ABSTRACT FROM AUTHOR]

The heat wave in East Asia is examined by using empirical orthogonal function analysis to isolate dominant heat-wave patterns in the ground-based temperature observations over the Korean Peninsula and China and related large-scale atmospheric circulations obtained from the National Centers for Environmental Prediction–National Center for Atmospheric Research Reanalysis 1 during 1973–2012. This study focuses particularly on the interannual variability of heat waves and its decadal change. The analysis identifies two major atmospheric teleconnection patterns playing an important role in developing typical heat-wave patterns in East Asia—the Scandinavian (SCAND) and the circumglobal teleconnection (CGT) patterns, which exhibit a significant decadal change in the interannual variability in the mid-1990s. Before the mid-1990s, heat-wave occurrence was closely related to the CGT pattern, whereas the SCAND pattern is more crucial to explain heat-wave variability in the recent period. The stationary wave model experiments suggest an intensification of the SCAND pattern in the recent period driven by an increase in land–atmosphere interaction over Eurasia and decadal change in the dominant heat-wave patterns in East Asia. [ABSTRACT FROM AUTHOR]

The spatiotemporal distributions of latest frost dates (LFDs) on the Korean Peninsula and the atmospheric circulation patterns that resulted in the latest frosts (LFs) were investigated through the use of historical records and modern weather observation data. During the modern observation period since 1904, the most recent record of LF was April 28, 2013 at Daegwallyeong. On average, the LF occurred in Korea between March 17 (at Wando) and May 10 (at Daegwallyeong). Positive correlations were found between LFD and altitude and latitude. Additionally, inter- annual variation of LFD showed a trend of progressively earlier dates at 32 of the 48 stations at which data were available. The historic data set consists of the following: 39 records of frosts during the Three-States Period (57 BC-998 AD): 34 records during the Goryeo Dynasty (998-1391), among which the latest record was in July of the lunar calendar: and 498 during the Joseon Dynasty (1392-1928) with one LF dated August 31, 1417 on the solar calendar. Regarding LFD from The Annals of the Joseon Dynasty, April has 11 records, May has 55, June has 46, July has 21, and August has 5 LFD records. Various meteorological causes of the latest LF were then established. Firstly, a cold and humid north-easterly current that originates from high latitudes of more than 50°N and passes through the East Sea is considered one of the dominant causes of LF. Secondly, strong radiative cooling under clear skies is suspected as another important cause. Thirdly, a specific pressure pattern, called the 'inverted-S contour' or 'North High and South Low (NHSL) pattern' was found to be a favorable condition for LF. Finally the latest LF was not found to be related to monthly or longer-term cold climate, but are instead linked to the abrupt development of a strong ridge over inland Asia and the unusual southward movement of the tall polar cyclone over the North Pacific Ocean. [ABSTRACT FROM AUTHOR]

This study compares the impacts of El Niño Modoki and El Niño on precipitation over Korea during the boreal winters from 1954 to 2009. Precipitation in Korea tends to be equal to or greater than the normal level during an El Niño Modoki winter, whereas there is no significant change during an El Niño winter. Greater than normal precipitation during El Niño Modoki was also found over the lower reaches of the Yangtze River, China and much of southern Japan. The latitudes of these regions are 5-10° further north than in southern China, where precipitation increases during El Niño. The following two anomalous atmospheric circulations were found to be causes that led to different precipitation distributions over East Asia. First, an atmospheric wave train in the lower troposphere, which propagated from the central tropical Pacific (cyclonic) through the southern Philippine Sea (anticyclonic) to East Asia (cyclonic), reached the southern China and northern Philippine Sea during El Niño, whereas it reached Korea and southern Japan during El Niño Modoki. Second, an anomalous local meridional circulation, which consists of air sinking in the tropics, flowing poleward in the lower troposphere, and rising in the subtropics, developed between the southern Philippine Sea and northern Philippine Sea during El Niño. During El Niño Modoki, however, this circulation expanded further to the north and was formed between the southern Philippine Sea and regions of Korea and southern Japan. [ABSTRACT FROM AUTHOR]

n expanded planar-fit (PF) method over complex terrain is presented and applied to coordinate rotation of the eddy-covariance (EC) flux and vertical velocity estimation. Theoretical analysis indicates that PF coefficients depend on wind direction, and an expression of vertical velocity is deduced. We applied the theory using 1 year of observations from the KoFlux site in the Gwangneung Forest in Korea and investigated the influence of wind direction on the PF method. Then, we performed an expansion of the PF method to consider dependence of PF coefficients on wind direction and applied the PF method to every sector. The results show that the PF coefficients and tilt angles over complex terrain vary with wind direction. Two hundred 30-min data sets are sufficient to derive stable PF coefficients over hilly terrain for each sector. The relative difference in eddy-covariance flux between the general planar fit (GPF) and sector planar fit (SPF) is less than 10% for the scalar flux and about 18% for friction velocity. Vertical velocity and vertical advection (VA) terms were also calculated and compared using SPF and GPF methods, and a normal distribution and diurnal trend of real vertical velocity on clear days are presented. [ABSTRACT FROM AUTHOR]

The East Asian mei-yu (EAMY), which includes the mei-yu over eastern China, baiu over Japan, and changma over Korea, is an important component of the Asia summer monsoon system. The EAMY rain belt jumps northward to the Yangtze and Huaihe River valleys (in China), Japan, and Korea from mid-June to mid-July, with remarkable interannual variability. In this study, the variability and predictability of EAMY are investigated using the retrospective ensemble predictions of the NCEP Climate Forecast System (CFS). The CFS reasonably captures the centers, magnitude, northward jump, and other features of EAMY over most regions. It also reasonably simulates the interannual variations of EAMY and its main influencing factors such as the western Pacific subtropical high, the East Asian monsoon circulation, and El Niño--Southern Oscillation (ENSO). The CFS is skillful in predicting EAMY and related circulation patterns with a lead time of one month. An empirical orthogonal function analysis with maximized signal-to-noise ratio is applied to determine the most predictable patterns of EAMY. Furthermore, experiments in which the CFS is forced by observed sea surface temperature (SST) exhibit lower skill in EAMY simulation, suggesting the importance of ocean--atmosphere coupling in predicting EAMY. The CFS, which exaggerates the precipitation over the southern--southeastern hills of the Tibetan Plateau, overestimates the relationship between EAMY and tropical--subtropical atmospheric circulation due to the overly strong ENSO signals in the model, whereas the experiments forced by observed SST produce a weaker relationship. On the contrary, the CFS underestimates the link of EAMY to higher-latitude processes. An increase in the horizontal resolution of the CFS is expected to reduce some of these errors. [ABSTRACT FROM AUTHOR]

ABSTRACT In this study, we investigate the role of convective parameterization (CP) in simulations of a convection band over the mid-Korean Peninsula at grey-zone resolutions, at which convection is partially resolved, partially subgrid. An approach similar to that used in 'observing system simulation experiment' is adopted. Simulations with a 500-m grid size serve as benchmark simulations. The impacts of resolution and convective parameterization at grey-zone resolutions (i.e. 3, 6 and 9 km) are then investigated. Results indicate that a grid size of 3 km is sufficient to resolve the convection band and CP for this size grid is not necessary. With 6 and 9 km grids, explicit simulations or those based on a Kain-Fritsch CP scheme do not simulate the atmospheric structure surrounding the band accurately. A major problem with CP is excessive triggering of parameterized convection. False triggers of CP in the band adjacent area suppress evolution of the resolved convection band through excessive stabilization of inflow air. We obtain significant improvements by using a modified trigger function, resulting in reduction of the area of parameterized convection, which in turn leads to stronger development of a resolved convection band. Furthermore, our approach reduces bias in the domain-averaged vertical thermodynamic structure. [ABSTRACT FROM AUTHOR]