• 대기
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• 제15권1호
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• pp.17-25
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• 2005

A significant number of tropical cyclones move into the midlatitudes and go through transformation procedure into extratropical cyclones. This process is generally referred to as extratropical transition of the tropical cyclone. In this study, MIDULLE(0407) case is selected. A thorough analysis is made using the GDAPS analysis data and MTM (Moving-nest Typhoon Model) model output. It is found that during the extratropical transition an important dynamics in the environmetal flow field occurs in which colder, drier (warm, moist) air penetrates in the western (eastern) quadrant of MINDULLE's outer circulation, which in turn initiates an asymmetry in the distribution of wind and temperature of the tropical cyclone. Simulated MTM result also reveals similar properties as in GDAPS analysis data. MTM result shows the gradual transition to the asymmetric distribution of wind and thickness as the extratropical transition proceeds. It is also found that the warm core disappears during the extratropical transition stage. Also, vortex tube is shown tilting towards the west during the transition. And the precipitation expands poleward of the center and the maximum precipitation appears to the left of MINDULLE which is consistent to the observations.

• 대기
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• 제18권3호
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• pp.159-169
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• 2008

The characteristics of the typhoon's extratropical transition (ET) over the western North Pacific area were investigated using the cyclone phase space (CPS) diagram method suggested by Hart (2003). The data used in this study were the global data assimilation prediction system (GDAPS) and NCEP data set. The number of typhoons selected were 75 cases during 2002 to 2007, and the three parameters were analyzed : the motion relative thickness asymmetry of the storm (B), the upper thermal wind shear and the lower thermal wind shear. Comparing the best-track data provided by the Regional Specialized Meteorological Center /Tokyo, the time of the ET based on CPS was 2~6 hours earlier than the best-track data. And it was shown that the 400- km and 30 kt wind radius of storm for the CPS method were better agreement than the previous suggested radius 500- km.

• 한국지구과학회지
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• 제28권7호
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• pp.947-956
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• 2007

이 연구는 태풍의 온대성 저기압화에 대해 간단히 소개하고 Evans and Hart(2003)와 Hart(2003_의 객관적 온대성 저기압화 판별식을 이용하여 최근 온대성 저기압화를 거친 세 태풍(Shanshan, Yaki, Soulik)에 대한 사례분석이 이루어졌다. 500-hPa 고도장분석에서 온대성 저기압화 시작시 세 태풍 모두 중위도 경압지역으로 북상하는 공통된 특성을 보였다. 그러나 연직단면 분석에서는 온대성 저기압화의 시작전 시 태풍 중심부근의 모든 층에서 온난 다습한 특성을 보였다. 온대성 저기압화 이후에는 이 개념모델의 전형적 특성인 태풍의 서쪽영역에 한랭 건조한 특성을 나타내었다. 따라서 Evans and Hart(2003)와 Hart(2003)의 객관적 온대성저기압화의 판별식은 태풍의 온대성저기압화 시작 및 구조변화를 잘 반영하므로 기상청 예보현업에서도 유용하게 사용될 수 있을 것으로 판단된다.

• 대기
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• 제28권3호
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• pp.325-336
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• 2018

This study investigates robust features of interdecadal changes in the Northern hemisphere summer tropical-extratropical teleconnection occurred around the mid-to-late 1990s by analyzing four different reanalysis data for atmospheric circulation and temperature, two precipitation reconstructions, and two sea surface temperature (SST) data during the satellite observation era of 1980~2017. For the last 38 years, there has been a significant increasing trend in anticyclonic circulation at lower and upper troposphere and 2 m air temperature with wavenumber-5 Rossby wave structure in the Northern Hemisphere (NH) extratropics. The increase has been accompanied with the significant weakening and northward shift of jet stream over Eurasia and the North Pacific. It is further found that there has been a significant interdecadal shift occurred around the mid-to-late 1990s in the two distinct modes of tropical-extratropical teleconnection: Western Pacific-North America (WPNA) and circumglobal teleconnection (CGT) pattern. After mid-to-late 1990s, the WPNA has played more important role in modulating the extratropical atmospheric circulation and surface climate, which has been preferentially occurred during the El $Ni{\tilde{n}}o$-Southern Oscillation (ENSO) decaying or transition summer such as 1998, 2010 and 2016. During these summers, severe heat waves were occurred over many parts of the NH extratropics due to the combined effect of the increasing trend in the barotropic anticyclonic circulation and the significant WPNA across the NH. Although weakened, the CGT also contributed to some of hot summers over many parts of the NH extratropics such as 1999, 2000, 2008, 2011, and 2012 when weak to moderate La $Ni{\tilde{n}}o$ was persisted.

• Asia-Pacific Journal of Atmospheric Sciences
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• 제54권4호
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• pp.575-585
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• 2018

In the case study of this paper, sensitivity experiments are carried out using the mesoscale non-hydrostatic Weather Research and Forecasting (WRF) model to investigate the impact of tropical cyclone (TC) Soudelor (2003) on the East Asian subtropical upper-level jet (EASJ) before TC Soudelor transformed into an extratropical cyclone. The physical mechanism for changes in the EASJ intensity and position caused by TC Soudelor is explored. Results indicate that TC Soudelor would warm the air in the middle and upper troposphere over the Japan Sea and the adjacent areas through stimulating northward propagating teleconnection pattern as well as releasing large amounts of latent heat, which led to increase (decrease) the meridional air temperature gradient to the south (north) below the EASJ axis. As a result, the geopotential height abnormally increased in the upper troposphere, resulting in an anomalous anticyclonic circulation belt along the EASJ axis. Correspondingly, the westerly winds to the north (south) of the EASJ axis intensified (weakened) and the EASJ axis shifted northward by one degree. The case study also suggests that before the extratropical cyclone transition of TC Soudelor, the TC activities had exerted significant impacts on the EASJ through thermodynamic processes.

• 한국지구과학회지
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• 제29권7호
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• pp.567-578
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• 2008

온대저기압화는 중위도 기압계에 큰 영향을 주고 때로는 악기상의 원인이 되기도 한다. 그러나 온대저기압화에 대한 예보와 연구 양쪽 모두 많은 과제가 남아있다. 왜냐하면 태풍으로부터 변질된 온대저기압 자체의 모호한 형태 때문이다. 또한, 온대저기압화의 정의가 예보나 연구 양쪽 모두 만족시켜줄 만큼 정확하지도 않다 따라서 기상청은 2007 년에 "온대저기압화 현엽매뉴얼"을 개발하여 온대저기압화의 일련의 과정과 구조 변화 진단에 사용하였다. 이 매뉴얼에서는 1단계 최대풍속과 해수면온도, 2단계 위성영상, 3단계 단열선도, 그리고 최종단계인 4단계에서 지상일기도를 분석하였다. 이 현업매뉴얼은 온대저기압화가 일어날 때 구조변화의 이해와 감시에 도움이 될 것이다.

• 한국지구과학회지
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• 제31권4호
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• pp.322-334
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• 2010

최근 30년간(1979-2008년) 한반도 주변($32-36^{\circ}N$, $122-132^{\circ}E$)에서 태풍이 약화될 때 한국에서 나타나는 시공간적 강수 특징을 분석하였다. 약화 유형은 온대저기압으로 약화되는 태풍(Weakened to Extratropical Cyclone, WEC)과 열대성 저압부로 약화되는 태풍(Weakened to Tropical Depression, WTD)으로 구분하였다. WEC의 경우, 강수량은 전국에 걸쳐 골고루 분포하였으며 남해안에서 가장 많았다. WTD의 경우, 강수량은 남해안에서 가장 많았지만 중부 및 내륙지역은 적었다. 두 경우의 강수량 차이는 Region 2(전라남도, 경상남도, 경상북도 남동부 지역, 제주도)에서는 거의 없었으며, Region 1(중부지방, 전라북도, 경상북도 내륙)에서는 WTD보다 WEC일 때 강수량이 더 많았다. 태풍이 한반도로 접근 할 때 WEC의 경우 태풍의 북서쪽에는 상층의 발달된 잠재소용돌이도와 하층의 온도골이 위치하고 있었으며, 태풍의 북동쪽에는 상층 제트 및 강한 상층 발산역이 위치하였다. 이는 태풍 전면에 경압교란과 비단열 과정을 발달시켰고 이로 인해 강수영역이 넓게 형성된 것으로 추측되었다. 그러나 WTD의 경우에서는 강한 잠재소용돌이도나 온도골, 상층제트가 태풍 주변에 나타나지 않았으며, 이로 인해 강수영역이 좁게 형성되었다.

• 대기
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• 제26권1호
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• pp.203-214
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• 2016

This study explores the 6-month lead prediction skill of stratospheric temperature and circulations in the Global Seasonal forecasting model version 5 (GloSea5) hindcast experiment over the period of 1996~2009. Both the tropical and extratropical circulations are considered by analyzing the Quasi-Biennial Oscillation (QBO) and Northern Hemisphere Polar Vortex (NHPV). Their prediction skills are quantitatively evaluated by computing the Anomaly Correlation Coefficient (ACC) and Mean Squared Skill Score (MSSS), and compared with those of El Nino-Southern Oscillation (ENSO) and Arctic Oscillation (AO). Stratospheric temperature is generally better predicted than tropospheric temperature. Such improved prediction skill, however, rapidly disappears in a month, and a reliable prediction skill is observed only in the tropics, indicating a higher prediction skill in the tropics than in the extratropics. Consistent with this finding, QBO is well predicted more than 6 months in advance. Its prediction skill is significant in all seasons although a relatively low prediction skill appears in the spring when QBO phase transition often takes place. This seasonality is qualitatively similar to the spring barrier of ENSO prediction skill. In contrast, NHPV exhibits no prediction skill beyond one month as in AO prediction skill. In terms of MSSS, both QBO and NHPV are better predicted than their counterparts in the troposphere, i.e., ENSO and AO, indicating that the GloSea5 has a higher prediction skill in the stratosphere than in the troposphere.

• Ocean and Polar Research
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• 제41권3호
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• pp.121-133
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• 2019

Natural variability associated with a variety of large-scale climate modes causes regional differences in sea level rise (SLR), which is particularly remarkable in the Pacific Ocean. Because the superposition of the natural variability and the background anthropogenic trend in sea level can potentially threaten to inundate low-lying and heavily populated coastal regions, it is important to quantify sea level variability associated with internal climate variability and understand their interaction when projecting future SLR impacts. This study seeks to identify the dominant modes of sea level variability in the tropical Pacific and quantify how these modes contribute to regional sea level changes, particularly on the two strong El $Ni{\tilde{n}}o$ events that occurred in the winter of 1997/1998 and 2015/2016. To do so, an adaptive data analysis approach, Ensemble Empirical Mode Decomposition (EEMD), was undertaken with regard to two datasets of altimetry-based and in situ-based steric sea levels. Using this EEMD analysis, we identified distinct internal modes associated with El $Ni{\tilde{n}}o$-Southern Oscillation (ENSO) varying from 1.5 to 7 years and low-frequency variability with a period of ~12 years that were clearly distinct from the secular trend. The ENSO-scale frequencies strongly impact on an east-west dipole of sea levels across the tropical Pacific, while the low-frequency (i.e., decadal) mode is predominant in the North Pacific with a horseshoe shape connecting tropical and extratropical sea levels. Of particular interest is that the low-frequency mode resulted in different responses in regional SLR to ENSO events. The low-frequency mode contributed to a sharp increase (decrease) of sea level in the eastern (western) tropical Pacific in the 2015/2016 El $Ni{\tilde{n}}o$ but made a negative contribution to the sea level signals in the 1997/1998 El $Ni{\tilde{n}}o$. This indicates that the SLR signals of the ENSO can be amplified or depressed at times of transition in the low-frequency mode in the tropical Pacific.