Tropical cyclone scale vortices and associated Rossby waves were investigated numerically using high-resolution barotropic models on the global domain. The equations of the barotropic model were discretized using the spectral transform method with the spherical harmonics function as orthogonal basis. The initial condition of the vortex was specified as an axisymmetric flow in the gradient wind balance, and four types of basic zonal states were employed. Vortex tracks showed similar patterns as those on the beta-plane but exhibited more eastward displacement as they moved northward. The zonal-mean flow appeared to control not only the west-east translation but also the meridional translation of the vortex. Such a meridional influence was revealed to be associated with the beta gyre and the Rossby wave, which are formed around the vortex due to the beta effect. In the case of the basic zonal state of climatological mean, the meridional translation speed reached the maximum value when the vortex underwent recurving.

To understand the genesis of tropical cyclones (TC), we computed TC genesis probability (GPr) by partitioning a highly localized genesis frequency (GFq) into nearby grid boxes in proportion to the spatial coherence of genesis potential index (GPI). From the analysis of TCs simulated by the Seoul National University Atmosphere Model Version 0 and the observed TCs, it was shown that GPr reasonably converges to GFq when averaged over a long-term period in a decent grid size, supporting its validity as a proxy representing a true TC GPr. The composite anomalies of the gridded GPr in association with the Asia summer monsoon, El Nino-Southern Oscillation (ENSO), and the Madden-Julian Oscillation (MJO) are much less noisy than those of GFq, and consequently are better interpretable. In summary, GPr converges to GFq, varies more smoothly than GFq, represents the spatiotemporal variations of GFq better than GPI, and depicts GFq with greater spatial details than other spatially smoothed GFqs.

최근 30년간(1979-2008년) 한반도 주변(32-36˚N, 122-132˚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.

The relationship between two interannual climate variabilities and the frequency of tropical cyclone (TC) that landed over the Korean Peninsula (KP) has investigated for the period of 1951-2004. In the analysis of the relationship between KP-landfall TC frequency and the ENSO phase, most TCs of C-14 (TCs that do not pass through mainland China before landing the KP) and C-23 (TCs that pass through mainland China before landing the KP) tended to more land in the warm phase than normal and cold phases. However, TC intensity at landfall was stronger in the cold and normal phases. In the analysis of the relationship between KP-landfall TC frequency and Arctic Oscillation (AO) phase, the TCs of C-14 tended to more land in the positive (POS) phase of AO and the negative (NEG) phase of AO for C-23. It was found that AO index was negatively correlated with the Niño-3.4 index. And then the TCs of C-14 landed more frequently over the KP in the AO POS - Niño-3.4 NEG phases and in the AO NEG - Niño-3.4 POS phases for the TCs of C-23.

Understanding solar influences on extreme weather is important. Insight into the causes of extreme weather events, including the solar-terrestrial connection, would allow better preparation for these events and help minimize the damage caused by disasters that threaten the human population. In this study, we examined category three, four, and five tropical cyclones that occurred in the western North Pacific Ocean from 1977 to 2016. We compared long-term trends in the positions of tropical cyclone occurrence and development with variations of the observed sunspot area, the solar North-South asymmetry, and the southern oscillation index (SOI). We found that tropical cyclones formed, had their maximum intensity, and terminated more northward in latitude and more westward in longitude over the period analyzed; they also became stronger during that period. It was found that tropical cyclones cannot be correlated or anti-correlated with the solar cycle. No evidence showing that properties (including positions of occurrence/development and other characteristics) of tropical cyclones are modulated by solar activity was found, at least not in terms of a spectral analysis using the wavelet transform method.

This paper reexamines the interannual intensity change of tropical cyclone (TC) over the western North Pacific. Analyses are done for the annual extreme intensity and the average intensity of the five strongest typhoons based on the best track data issued from the RSMC (Regional Specialized Meteorological Center) Tokyo and the JTWC (Joint Typhoon Warning Center). Trends over the last 30+ years in one data set are nearly opposite in another. Specifically, the TC intensity tends to increase with the years in the JTWC data, whereas the opposite is found in the RSMC data. Realizing that one data set shows a significant statistical difference from the other, a homogenization process has been applied to the original data so that comparisons of the two data sets and the trend analyses become more meaningful than those with solely the original data. With the homogenized data, we present some cautious conclusions regarding the TC intensity changes over the western North Pacific. The annual extreme TC intensity has been decreasing, while the strong TCs have become stronger over the years. For TCs entering the KMA emergency area and directly hitting Korea, we are hesitant to make any conclusions because the corresponding area is small so that the number of TCs entering the area each year is too small to have any statistically significant implications.