Jung-Eun Chu

Nonlinear, Intraseasonal Phases of the East Asian Summer Monsoon: Extraction and Analysis Using Self-Organizing Maps

AbstractThe hypothesis that regional characteristics of the East Asian summer monsoon (EASM) result from the presence of nonlinear coupled features that modulate the seasonal circulation and rainfall at the intraseasonal time scale is advanced in this study. To examine this hypothesis, the authors undertake the analysis of daily EASM variability using a nonlinear multivariate data classifying algorithm known as self-organizing mapping (SOM).On the basis of various SOM node analyses, four major intraseasonal phases of the EASM are identified. The first node describes a circulation state corresponding to weak tropical and subtropical pressure systems, strong upper-level jets, weakened monsoonal winds, and cyclonic upper-level vorticity. This mode, related to large rainfall anomalies in southeast China and southern Japan, is identified as the mei-yu–baiu phase. The second node represents a distinct circulation state corresponding to a strengthened subtropical high, monsoonal winds, and anticyclonic upper-lev...

What caused the cool summer over northern Central Asia, East Asia and central North America during 2009?

Cool and wet weather conditions hit northern Central Asia, East Asia and central North America during the 2009 summer in concert with a strong jet stream and a prominent meandering upper-level circulation in the Northern Hemisphere mid-latitudes despite the fact that the year 2009 is the fifth warmest year globally in the modern record. It is found that the conspicuous atmospheric variability in the entire Northern Hemisphere mid-latitudes during the summer of 2009 was caused by a combination of teleconnections associated with significant tropical thermal forcings, strong polar forcing, and interaction between high-frequency weather events and climate anomalies. The strong negative circumglobal teleconnection pattern associated with the deficient Indian summer monsoon rainfall and developing El

Changes in climate classification and extreme climate indices from a high-resolution future projection in Korea

We investigate the future changes in the climate zone and six extreme temperature indices in Korea, using the 20-km high-resolution atmospheric general circulation model (MRI-AGCM3.1S). The Trewartha and Köppen climate classification schemes are applied, and four summer-based extreme temperature indices (i.e., summer days, tropical nights, growing degree days, and cooling degree days (CDD) and two winter-based indices (frost days and heating degree days (HDD) are analyzed. To represent significantly the change in threshold indices, the monthly mean bias is corrected in model. The model result reasonably captures the temporal and spatial distribution of the present-day extreme temperatures associated with topography. It was found that in the future climate, the area of the subtropical climate zone in Korea expands northward and increases by 21% under the Trewartha classification scheme and by 35% under the Köppen classification scheme. The spatial change in extreme climate indices is significantly modulated by geographical characteristics in relation to land-ocean thermal inertia and topographical effects. The change is manifested more in coastal regions than in inland regions, except for that in summer days and HDD. Regions with higher indices in the present climate tend to reveal a larger increase in the future climate. The summer-based indices display an increasing trend, while the winter-based indices show a decreasing trend. The most significant increase is in tropical nights (+452%), whereas the most significant decrease is in HDD (−25%). As an important indicator of energy-saving applications, the changes in HDD and CDD are compared in terms of the frequency and intensity. The future changes in CDD reveal a higher frequency but a lower temperature than those in HDD. The more frequent changes in CDD may be due to a higher and less dispersed occurrence probability of extreme temperatures during the warm season. The greater increase in extreme temperature events during the summer season remains an important implication of projecting future changes in extreme climate events.

Boreal Summer Intraseasonal Phases Identified by Nonlinear Multivariate Empirical Orthogonal Function–Based Self-Organizing Map (ESOM) Analysis

AbstractThis study develops an empirical orthogonal function (EOF)-based self-organizing map (SOM) (ESOM) analysis to identify the nonlinear characteristics of the boreal summer intraseasonal oscillation (BSISO), which involves interactions between the summer mean circulation and the convectively coupled equatorial waves, which make BSISO evolution more complex than the Madden–Julian oscillation. The method utilizes the first five principal components of the outgoing longwave radiation (OLR) and the zonal wind at 850 hPa (U850) and has the advantages of filtering out uncertainties from noise and being free from mathematical restrictions, such as orthogonality and linearity.The ESOM analysis enables the detection of BSISO over the Asian summer monsoon region with eight phases. The four most distinguishable phases represent 1) a pair of stationary patterns with a dipole between the eastern Indian Ocean and the Philippine Sea (phases 1 and 5) and 2) a pair of propagating patterns with a northwest–southeast-t...

How Light‐Absorbing Properties of Organic Aerosol Modify the Asian Summer Monsoon Rainfall?

Light absorbing aerosols not only contribute to Earths radiative balance but also influence regional climate by cooling the surface and warming the atmosphere. Following recent suggestions that organic aerosols (OAs) absorb substantial amount of solar radiation, we examine the role of light absorbing properties of OA on Asian summer monsoon rainfall redistribution using observational data and an atmospheric general circulation model (AGCM) experiment. Results suggest that the enhanced light absorption by OA in Southeast Asia and Northeast Asia are associated with the advance of the Indian summer monsoon in May and the southward shift of East Asian summer monsoon rain band in June. The rainfall redistribution in May is induced by elevated orographic effect with a warm-core upper-level anticyclone and surface warming of 1-2°C over the Tibetan Plateau whereas that of the East Asian summer monsoon in June is formed by stable conditions associated with surface cooling and atmospheric warming around 30°N.