Byung-Kwon Moon

Variability and singularity of Seoul, South Korea, rainy season (1778-2004)

Abstract The 227-yr daily precipitation record gathered for Seoul, South Korea, represents one of the longest instrumental measurements, which provides an exceptional opportunity for detecting climate singularity (a property of phase locking to annual cycle) of extreme weather events and multidecadal–centennial variability of the rainy season structure. From late June to early September, the occurrence of heavy rain events shows a climatological quasi-biweekly oscillation. The rainy season characteristics, including the dates of onset, retreat, summit, and the duration, all show significant centennial variations. The rainy season summit shows a tendency toward delayed occurrence, which changed from the 37th pentad (P37; 30 June–4 July) during the 1778–1807 period to P44 (4–8 August) during the 1975–2004 period. The amplitude of the interannual (2–6 yr) variation of summer precipitation shows a prominent fluctuation with a 50-yr rhythm. A notable climatological break (around 9–13 August) divides the rainy ...

Rectification of ENSO variability by interdecadal changes in the equatorial background mean state in a CGCM simulation

The link between the changes in equatorial background stratification and El Nino-Southern Oscillation (ENSO) modulation is investigated using a simulation from a 260-yr-long coupled general circulation model (CGCM). The work focuses on the role of nonlinearities associated with equatorial wave dynamics. As a first step, the low-frequency change in mean stratification is diagnosed and documented from the shallow-water parameters derived from a vertical mode decomposition of the CGCM. The parameters vary differently according to the baroclinic mode order, which may explain why a flattening thermocline does not necessarily lead to reduced ENSO activity. Estimations of baroclinic mode contributions to zonal current anomalies indicate that the decadal variability projects differently for the baroclinic modes as compared to the interannual variability. In particular, the high-order modes associated with decadal variability have a more pronounced signature in the western Pacific, whereas that associated with interannual variability (i.e., ENSO) shows more energy in the eastern Pacific. In the light of the results of the CGCM vertical mode decomposition, an intermediate coupled model (ICM) is used to test whether the nonlinearities associated with the changes in the baroclinic mode energy distribution can lead to coherent ENSO modulation. The results indicate that rectification of the interannual variability (ENSO time scales) by the interdecadal variability associated with changes in the oceanic mean states takes place in the ICM. The rectified effect results mostly in an increased variability and skewness of the zonal advection, which tends to produce a zonal seesaw of the sea surface temperature anomaly. A tropical mechanism for producing ENSO modulation is then proposed that reconciles both the rectified effect resulting from nonlinearities associated with equatorial wave dynamics and the tropical decadal mode of thermocline depth arising from Ekman-pumping anomalies located in the central South Pacific.

Characteristics of Atmospheric Circulation over East Asia Associated with Unusual Climate of Korea in Winter 2006/2007

We examined the characteristics of atmospheric circulation over East Asia to find the causes of the unusual warm winter 2006/2007 in Korea. During that time, the anomalous atmospheric conditions are characterized by the weakening of the Siberian High and the Aleutian Low, the enhancement of low-level south easterlies near Korea, and the weakening of upper-level jet to the south of Japan. These patterns are considerably associated with the atmospheric condition of non-blocking year over the Siberia (60-140E). In addition, both El and Arctic Oscillation (AO) are likely to induce those patterns. Therefore, it is suggested that the anomalous atmospheric states related to non-blocking flow, El , and the positive phase of AO are responsible for the warmest winter season in 2006/2007 for the period of 1958/1959-2006/2007.

The Global Warming Hiatus Simulated in HadGEM2-AO Based on RCP8.5

National Institute of Meteorological Research, Jeju 697-845, KoreaAbstract: Despite the greenhouse gases like carbon dioxide have steadily increased in atmosphere, the overall trend of theglobal average surface air temperature has stalled during the last decade (2002-present). This phenomenon is often calledhiatus or warming pause, which is challenging the prevailing view that anthropogenic forcing causes warmingenvironment. Our study characterized the hiatus by analyzing the HadGEM2-AO (95 yrs) simulation data based onRCP8.5 scenario. The PC2 time series from the EOF of the zonal mean vertical ocean temperature has been defined asthe index that represents the warming pause. The relationship between the hiatus, ENSO and the changes in climatesystem are identified by utilizing the newly defined PC2. Since the La Nina index (defined as the negative of NINO3index) leads PC2 by about 11 months, it may be possible that the La Nina causes the warming to be interrupted. We alsoshow that the cooling of the climate system closed tied to the heat penetration into the deep ocean, indicating theweakening the warming rate is due to the oceanic heat uptake. Finally, the global warming hiatus is characterized by theanomalous warming in Arctic region as well as the intensification of the trade wind in the equatorial Pacific.Keywords: warming hiatus, HadGEM2-AO, La Nina, oceanic heat uptake요약: 대기 중 이산화탄소 등의 농도가 지속적으로 증가하고 있음에도 최근 10여 년 동안(2002-현재) 전지구 지표 온도는 거의 답보상태에 머물러 있다. 이처럼 온실기체 강제력에도 불구하고, 지구 온난화 경향이 사라진 듯 보이는 현상을 지구 온난화 멈춤(hiatus)이라 한다. 이 연구는 HadGEM2-AO가 모의한 RCP8.5 시나리오 실험(95년간) 자료를 분석하여, 온난화 멈춤 시기의 특징을 분석하였다. 온난화 멈춤 기간을 나타내는 시계열은 동서 평균한 연직 해수 온도 분포를 EOF 분석하여 구한 두 번째 PC (PC2)로 정의하였다. PC2를 이용하여 온난화 멈춤과 엔소와의 관련성, 기후시스템의 변화 등을 분석하였다. 라니냐 지수(NINO3지수에

The influences of interannual stratification variability and wind stress forcing on ENSO before and after the 1976 climate shift

In order to understand the change in oceanic variability associated with the climate shift of the mid-1970s, we analyze the contribution of momentum forcing to the leading baroclinic modes over the tropical Pacific using Simple Ocean Data Assimilation (SODA, version 2.0.2) for the period of 1958–1997. Specifically, we look at the statistical relationship between the wind projection coefficients and climate indices and attempt to provide a physical explanation for the observed changes. It is found that the wind stress projection coefficients according to the oceanic baroclinic modes are different in terms of their magnitude and phase in the tropical Pacific, reflecting a specific forcing associated with each mode before and after the 1976 climate shift. Compared to that before the 1970s, the first baroclinic mode is had a greater effect on the interannual sea surface temperature due to equatorial wave dynamics, and there was an increased delayed response of the second baroclinic mode variability to the interannual atmospheric forcing after the late 1970s. This reflects changes in ENSO feedback processes associated with the climate shift. Our analysis further indicates that, after the late 1970s, there was a decrease in the wind stress forcing projecting onto the Ekman layer, which is associated with increased mixed-layer depth. This result suggests that the changes in the ENSO properties before and after the late 1970s are largely associated with the changes in the way in which the wind stress forcing is dynamically projected onto the surface layer of the tropical Pacific Ocean over interannual timescales.

Development of an Experimental Method for Understanding the Effects of the Coriolis Force on the Typhoon Genesis and its Movement

A simple experimental method was developed to help students understand the effect of the Coriolis force on typhoon genesis and movement. It consists of rotating tanks with and without a sloping bottom, and a small stirrer to produce cyclonic typhoon-like vortices by locally stirring the water. Vortices were able to last for more than 3 minutes without dissipation in the rotating tank. However, vortices were hardly maintained without rotation, and would rather disappear as soon as the stirrer stopped mixing. Since the dynamical properties of the rotating water are similar to those of the atmosphere influenced by the Coriolis force, the experiments show that the Coriolis force is indispensable to the typhoon genesis. When the tank had both the sloping bottom and rotation, vortices would move in a particular direction. Considering the topographical beta effect, this result indicates that typhoons are drifted not only by the steering wind but also by the meridional gradient of the Coriolis force. The methodology developed in this study, would be useful for both students and teachers to better the relationship between the Coriolis force and the typhoon genesis.

A METHOD FOR THE SIMULTANEOUS ESTIMATION OF ATMOSPHERIC PARAMETERS USING THE PHOTOMETRIC INDICES IN THE uvby COLOR SYSTEM

A new method was developed to estimate the effective temperature, surface gravity, and metallicity of cool stars using only photometric indices in the uvby color system. In a graphical method, T{sub eff} and log g were determined for all of the different values of [Fe/H] using model atmosphere grids with respect to (b - y):c{sub 1} and (b - y):m{sub 1} pair indices. Then, a three-dimensional figure where X-, Y-, and Z-axes correspond to T{sub eff}, log g, and [Fe/H] was produced. By reading an intersection of two curves formed by a connection of three parameters obtained from the (b - y):c{sub 1} and (b - y):m{sub 1} pair indices on each of the three projected planes, T{sub eff}, log g, and [Fe/H] were determined simultaneously. In addition, an analytical method was devised based on the same algorithm developed for the graphical method. The new method was applied to a number of field dwarfs and giants, and the results were compared with those from a spectroscopic method and other photometric calibrations.

Characteristics of Summer Tropospheric Ozone over East Asia in a Chemistry-climate Model Simulation

It is important to understand the variability of tropospheric ozone since it is both a major pollutant affecting human health and a greenhouse gas influencing global climate. We analyze the characteristics of East Asia tropospheric ozone simulated in a chemistry-climate model. We use a global chemical transport model, driven by the prescribed meteorological fields from an air-sea coupled climate model simulation. Compared with observed data, the ozone simulation shows differences in distribution and concentration levels; in the vicinity of the Korean Peninsula, a large error occurred in summer. Our analysis reveals that this bias is mainly due to the difference in atmospheric circulation, as the anomalous southerly winds lead to the decrease in tropospheric ozone in this region. In addition, observational data have shown that the western North Pacific subtropical high (WNPSH) reduces tropospheric ozone across the southern China/ Korean Peninsula/Japan region. In the model, the ozone changes associated with WNPSH are shifted westward relative to the observations. Our findings suggest that the variations in WNPSH should be considered in predicting tropospheric ozone concentrations.

Effects of the El Niño on Tropospheric Ozone in a Simulation using a Climate-Chemistry Model

Department of Science Education, Chungbuk National Univerisity, Chungbuk 361-763, KoreaAbstract: We examine the effects of El Nino on tropospheric ozone through the simulation of a Climate-Chemistry modelfor a 40-year period (1971-2010). The Empirical Orthogonal Function (EOF) analysis reveals that the tropospheric ozoneconcentration in the central-eastern Pacific decreases when the El Nino occurs, which is consistent with the observation.However, the increase of ozone over Indian Ocean-Indonesia regions is weak in the simulation compared to theobservations. We analyze details of the 2006 El Nino event to understand the mechanism that caused the change of ozonedue to El Nino. It is found that enhanced convection as well as higher water vapor followed by shortened lifetime hasled to lower the tropospheric ozone. Downward motion induced by the changes of atmospheric circulation due to seasurface temperature forcing, together with the decrease of water vapor, has brought ozone produced in the uppertroposphere over the Indian OceanKeywords: climate model, global atmospheric chemistry model, tropospheric ozone, El Nino요약: 기후-전구대기화학모델을 이용하여 엘니뇨가 대류권 오존에 미치는 영향을 분석하였다. 40년간(1971-2010) 대류권 오존을 EOF 분석한 결과에서 열대 중앙-동태평양에서 오존의 감소가 관측과 유사하게 잘 모의되었다. 그러나 인도양-인도네시아 부근의 오존 증가는 관측에 비해 약하게 모의되었다. 엘니뇨에 의한 오존변동 과정을 이해하기 위하여

Assisting High School Students to Redefine the Principle of Coriolis Force

A new method was developed to better understand the principle of Coriolis force. We also investigated the understanding of 5 10th grade students and analyzed their responses. Since no clear explanation about the nature of a rotating disk is provided in school textbooks, it tends to be misunderstood as the earth surface revolving on its axis pointing to the North Pole. This study was carried out focusing on the fact that a rotating disk is the tangential plane at arbitrary latitude. Results showed that there are changes in students` conceptions on the principle of Coriolis force with a new understanding of the rotating disk. In conclusion, a new method used in this study helped students better understand the link between Coriolis force and rotating disk. The method would be helpful to clarify the principle of Coriolis force in school science.