Tropical Cyclone Genesis Frequency Research Articles

Distinct responses of tropical cyclone activity to spatio-uniform and nonuniform SST warming patterns

Abstract Most previous studies have reported a decrease in global tropical cyclone (TC) genesis frequency (TCGF) under anthropogenic warming. However, little attention has been drawn to the influence of sea surface temperature (SST) warming patterns on TCGF changes. Here, we investigate the impacts of three distinct SST warming patterns on global TCGF: uniform SST warming, nonuniform (El Niño-like) SST warming, and a combination of both. Results show that spatio-uniform SST warming has a limited impact on global TCGF, instead redistributing the TC genesis locations. Conversely, nonuniform SST warming significantly suppresses global TCGF. The combined warming produces a similar decrease in TCGF to nonuniform warming albeit with differences in spatial distribution. This indicates the dominant role of nonuniform SST warming in affecting TCGF and highlights the nonlinearity of the process. Further analysis shows that these differences in TCGF primarily stem from the distinct responses of tropical circulations to the three warming patterns.

Interannual synchronization of the North American summer monsoon and the North Atlantic tropical cyclone genesis frequency

Variations of the North American summer monsoon (NASM) and North Atlantic tropical cyclone (NATC) activities strongly influence climate anomalies in North America, with serious potential risk to life and property. Despite the scientific importance of this topic, the possible linkage between the NASM and the NATC genesis frequency remains unexplored. Here, we aim to examine the relationship between interannual variations of the NASM intensity and the NATC genesis frequency based on observations and Coupled Model Intercomparison Project Phase 6 (CMIP6) models. Our results show a strong association between the NASM intensity and the NATC genesis frequency during the extended boreal summer, with a good synchronization between their interannual variations. In years with stronger (weaker) NASM intensity, the NATC genesis frequency tends to be higher (lower). The observed NASM–NATC synchronization may be explained by two pathways: tropical-ocean-driven pathway and monsoon-heating-driven pathway. In the tropical-ocean-driven pathway, the tropical Pacific and Atlantic interbasin sea surface temperature (SST) anomalies play a critical role in bridging the NASM and NATC, by modulating the cross-Central American wind. Simulations of the tropical Pacific–Atlantic interbasin SST anomalies are critical for CMIP6 models to capture the observed linkage between the NASM and the vertical wind shear over the NATC main development region (MDR). In the monsoon-heating-driven pathway, the heating source due to the rainfall anomalies associated with the NASM can trigger atmospheric circulation anomalies through the Gill-type response, thereby affecting the NATC by changing the vertical wind shear over the MDR. This study demonstrates a connection between interannual variations of the NASM and the NATC genesis frequency, results of which can be used to advance our understanding of the monsoon–TC relationship and increase research focus on the interannual NASM–NATC synchronization in climate prediction.

Modulations of Madden–Julian Oscillation and Quasi-Biweekly Oscillation on Early Summer Tropical Cyclone Genesis over the Bay of Bengal and South China Sea

Abstract The Madden–Julian oscillation (MJO) and the quasi-biweekly oscillation (QBWO) are prominent components of the intraseasonal oscillations over the tropical Indo-Pacific Ocean. This study examines the tropical cyclone (TC) genesis over the Bay of Bengal (BOB) and the South China Sea (SCS) on an intraseasonal scale in May–June during 1979–2021. Results show that the convection associated with the two types of intraseasonal oscillations simultaneously modulates TC genesis in both ocean basins. As the MJO/QBWO convection propagated, TCs form alternately over the two basins, with a significant increase (decrease) in TC genesis frequency in the convective (nonconvective) MJO/QBWO phase. Based on the anomalous genesis potential index associated with the MJO/QBWO, an assessment of the influence of various factors on TC genesis is further assessed. Middle-level relative humidity and lower-level relative vorticity play key roles in the MJO/QBWO modulation on TC genesis. The MJO primarily enhances large-scale cross-equatorial moisture transport, resulting in significant moisture convergence, while the QBWO generally strengthens the monsoon trough and induces the retreat of the western North Pacific subtropical high, increasing the regional lower-level relative vorticity. The potential intensity and vertical wind shear make small or negative contributions. This study provides insights into the neighboring basin TC relationship at intraseasonal scales, which has a potential to improve the short-term prediction of regional TC activity. Significance Statement The Madden–Julian oscillation (MJO) and the quasi-biweekly oscillation (QBWO) are two types of intraseasonal tropical atmospheric oscillations. The development of tropical cyclones (TCs) is often accompanied by intraseasonal convection. This study highlights the distinct roles of MJO and QBWO in TC genesis over the South Asian marginal seas (e.g., Bay of Bengal and South China Sea). The QBWO can co-regulate TC genesis along with the background of the MJO, where the large-scale MJO mainly provides moisture, while the small-scale QBWO mainly contributes to vorticity. These findings provide useful information for subseasonal TCs forecasting. There are many developing countries along the South Asian marginal seacoast; therefore, further research on regional TC climate would help effectively reduce casualties and property damage.

Influence of spatial and seasonal asymmetries on long-range tropical cyclone prediction in the western North Pacific

The seasonal predictability of tropical cyclones (TC) in the western North Pacific (WNP) reported in previous studies are mainly based under the general consideration that the WNP is homogeneous in terms of its spatial and temporal characteristics. Here we present evidence that the western (Domain 1) and eastern (Domain 2) parts of the WNP exhibit spatial and seasonal asymmetric response to large-scale environments (e.g., asymmetrical sea surface temperature anomalies distribution) leading to distinct spatial and seasonal TC variability in the said domains. Exploring such asymmetries, we propose an alternative approach on the long-range predictability of TC genesis frequency in the WNP during its active TC season (i.e., June-November, JJASON) by separately predicting the TC genesis frequency in two domains (i.e., Domains 1 and 2) in two distinct seasons (i.e., June-August and September-October), respectively. Using a number of climate indices as predictors in different lead times, our regression-based models present its best significant seasonal predictability of TC genesis frequency during JJASON (i.e., r = 0.80, p < 0.01) that essentially captures the spatial and seasonal asymmetry in the WNP. It is expected that this study provides valuable insights on the long-range and more localized TC prediction in support of disaster risk reduction in the WNP region.

Mutating ENSO Impact on Northwest Pacific Tropical Cyclones Under Global Warming

AbstractA prominent feature of the western North Pacific tropical cyclone genesis frequency (TCGF) anomaly in response to El Niño‐Southern Oscillation (ENSO) is a distinct west‐east dipole structure in the present‐day (PD) climate. Here, large ensemble high‐resolution simulations show that the current dipole may transform into a monopole under global warming (GW). In the PD climate, the ENSO‐induced dipole effect on TCGF is mainly observed in late autumn. However, GW accelerates this effect into the summer by amplifying atmospheric circulation anomalies. Consequently, this leads to a significant increase in the coastal TCGF during the development phase of El Niño under GW. Meanwhile, it weakens the anomalous anticyclonic circulation during late autumn, leading to an increase in coastal TCGF during the mature phase of El Niño, and vice versa. Therefore, the combined effect suggests a potential trend toward spatial homogenization during ENSO phases under GW.

Atmospheric modes fiddling the simulated ENSO impact on tropical cyclone genesis over the Northwest Pacific

The El Niño-Southern Oscillation (ENSO) is crucial to the interannual variability of tropical cyclone (TC) genesis over the western North Pacific (WNP). However, most state-of-the-art climate models exhibit a consistent pattern of uncertainty in the simulated TC genesis frequency (TCGF) over the WNP in ENSO phases. Here, we analyze large ensemble simulations of TC-resolved climate models to identify the source of this uncertainty. Results show that large uncertainty appears in the South China Sea and east of the Philippines, primarily arising from two distinct atmospheric modes: the Matsuno-Gill-mode (MG-mode) and the Pacific-Japan-like pattern (PJ-mode). These two modes are closely associated with anomalous diabatic heating linked to tropical precipitation bias in model simulations. By conditionally constraining either of the modes, we can significantly reduce model uncertainty in simulating the dipole structure of the TCGF anomalies, confirming that it is the atmospheric circulation bias in response to tropical precipitation bias that causes uncertainty in the simulated WNP TCGF.

Unraveling the strong covariability of tropical cyclone activity between the Bay of Bengal and the South China Sea

Herein, we report a strong in-phase covariability of tropical cyclone (TC) activity between the Bay of Bengal (BOB) and the South China Sea (SCS) during October–December of 1979–2019, and which is also the dominant mode of BOB–SCS TC activity, accounting for 35% of the total variances in TC track density. This inter-basin TC covariance is closely linked to the anomalies of tropical sea surface temperature, appearing as the intrinsic Indo-Pacific Tripole mode, which significantly affects the atmospheric circulations overlying the BOB–SCS. Interestingly, this mechanism works via modulating the local TC genesis frequency in the BOB–SCS. However, in terms of the migrated TCs among them, the Indo-Pacific Tripole mainly regulates their genesis location but not their frequency. More importantly, such inter-basin TC covariability still exists significantly even when the TC track data migrating from the SCS into the BOB are excluded. After all, only 19 TCs during the 41 years (1979–2019) are observed to migrate from the SCS to the BOB, which can only contribute slightly to increasing the covariability of BOB–SCS TC-track activity, but do not play a dominant role. Further, the numerical simulations suggest that although both the Indian and Pacific Oceans contribute to the atmospheric anomalies that affect the BOB–SCS TC activity, the Pacific-effect is twice as important.

Moisture control of tropical cyclones in high-resolution simulations of paleoclimate and future climate

The intensity of tropical cyclones (TCs) is expected to increase in response to greenhouse warming. However, how future climate change will affect TC frequencies and tracks is still under debate. Here, to further elucidate the underlying sensitivities and mechanisms, we study TCs response to different past and future climate forcings. Using a high-resolution TC-resolving global Earth system model with 1/4° atmosphere and 1/10° ocean resolution, we conducted a series of paleo-time-slice and future greenhouse warming simulations targeting the last interglacial (Marine Isotope Stage (MIS) 5e, 125 ka), glacial sub-stage MIS5d (115 ka), present-day (PD), and CO2 doubling (2×CO2) conditions. Our analysis reveals that precessional forcing created an interhemispheric difference in simulated TC densities, whereas future CO2 forcing impacts both hemispheres in the same direction. In both cases, we find that TC genesis frequency, density, and intensity are primarily controlled by changes in tropospheric thermal and moisture structure, exhibiting a clear reduction in TC genesis density in warmer hemispheres.

The Relationship Between Indian Ocean SST and Tropical Cyclone Genesis Frequency over North Indian Ocean in May

The Relationship Between Indian Ocean SST and Tropical Cyclone Genesis Frequency over North Indian Ocean in May

Observed Interannual Relationship between ITCZ Position and Tropical Cyclone Frequency

Abstract There are no well-accepted mechanisms that can explain the annual frequency of tropical cyclones (TCs) both globally and in individual ocean basins. Recent studies using idealized models showed that the climatological frequency of TC genesis (TCG) is proportional to the Coriolis parameter associated with the intertropical convergence zone (ITCZ) position. In this study, we investigate the effect of the ITCZ position on TCG on the interannual time scale using observations over 1979–2020. Our results show that the TCG frequency is significantly correlated with the ITCZ position in the North Atlantic (NA) and western North Pacific (WNP), with more TCG events in years when the ITCZ is farther poleward. The ITCZ–TCG relationship in NA is dominated by TCG events in the tropics (0°–20°N), while the relationship in WNP is due to TCs formed in the east sector (140°E–180°). We further confirmed that ENSO has little effect on the ITCZ–TCG relationship despite the fact that it can affect the ITCZ position and TCG frequency separately. In NA and WNP, a poleward shift of ITCZ is significantly associated with large-scale environment changes favoring TCG in the main development region (MDR). However, the basinwide TCG frequency has a weak relationship with the ITCZ in other ocean basins. We showed that a poleward ITCZ in the eastern North Pacific and South Pacific favors TCG on the poleward flank of the MDR, while it suppresses TCG on the equatorward flank, leading to insignificant change in the basinwide TCG frequency. In the south Indian Ocean, the ITCZ position has weak effect on TCG frequency due to the mixed influences of environmental conditions.

On the mechanisms of the historical lowest/highest tropical cyclone genesis over the western North Pacific in July/October 2020

The tropical cyclone (TC) genesis over the western North Pacific (WNP) displayed two distinct features in 2020. The WNP experienced unprecedented TC silence in July 2020, whereas the TC genesis frequency reached the historical highest in October 2020 with all the TCs generated over the western part of the WNP. The present study reveals that the strong Indian Ocean basin warming (IOBW) and extremely prolonged Madden-Julian Oscillation (MJO) Phases 1 and 2 (MJO12) contributed to the TC genesis condition in different regions for the July TC silence. The IOBW explained the unfavorable TC genesis condition over the latitudes around 20°N, whereas the MJO12 was responsible for the unfavorable condition over the latitudes around 10°N. Although both IOBW and MJO12 resulted in a diminution in relative humidity and absolute vorticity, they exerted opposite influences on the vertical wind shear, which made IOBW more important than MJO12. The impacts of other factors, including the cooling in the Niño3.4 region and warming in the tropical Atlantic Ocean, were relatively smaller compared to IOBW and MJO12. The abnormal TC genesis in October 2020 is mainly attributed to the moderate La Niña and extremely prolonged MJO phase 5 (MJO5). The La Niña condition induced the shift of supportive genesis condition to the western part of the WNP, and MJO5 superimposed its impacts around the South China Sea and the Philippines. The analysis of the genesis potential index (GPI) highlights the crucial importance of the relative humidity to the October's aberrance. The La Niña played a major role in increasing the relative humidity over a vast area of the major genesis region (MGR), and the MJO5 played a subsidiary role. By inducing an increase in absolute vorticity over MGR and a decrease in vertical wind shear over the eastern MGR, the Pacific meridional mode also played a supportive role in October 2020.

How Does Tropical Cyclone Genesis Frequency Respond to a Changing Climate?

AbstractGlobal tropical cyclone (TC) genesis frequency (TCGF) has been documented to decrease or increase linearly in a changing climate. However, our numerical experiments show that the global TCGF exhibits a parabolic relation with spatio‐uniform climate changes in sea surface temperature (SST) from −15 K to 5 K relative to the present climate, with the peak in the 5 K‐cooler climate. The parabolic relation is found in all TC basins except the eastern North Pacific where TCGF keeps increasing with the changing climate. TCGF can be expressed as the product of the frequency of TC seeds and the TC survival rate (SR). Further analysis shows that this parabolic structure in the global TCGF depends on TC seeds rather than the TC SR. The TC SR exhibits an increasing trend with the SST increase, while TC seeds show a consistent change with TCGF, which might be linked to the changes in low‐level relative humidity.

Comprehensive Investigation on Spatiotemporal Variations of Tropical Cyclone Activities in the Western North Pacific, 1950–2019

Tropical Cyclones (TCs) are the most severe natural disasters in the Western North Pacific Ocean (WNP). While previous studies reported evident changes over certain regions or seasons between typical periods, there is a lack of a complete picture of the long-term variations in TC activities in the WNP. This study carried out a comprehensive investigation on the spatiotemporal variations in TC genesis locations and transit pathways in the WNP, based on the TC best-track datasets from the China Meteorological Administration Shanghai Typhoon Institute. The results showed that the TC genesis and occurrence frequencies showed drastic decreases and westward shifts in the WNP from 1950 to 2019. The greatest decrease in TC genesis occurred for Tropical Depressions (TDs: 10.8−17.1 m/s) and Typhoons (TYs: &gt; 32.7 m/s). The number of Tropical Storms (TSs: 17.2−32.6 m/s) and the mean intensity (2 min maximum sustained wind speed) of TCs overall showed no evident change. The decadal average of TC genesis frequency increased by 63% in the near-coast seas (WNPO), but decreased by 46% near the central Pacific Ocean (WNCP), demonstrating a westward shift for TC genesis locations. The TC genesis and occurrence frequencies also showed significant declines in the southern Philippine Sea (SPS) and South China Sea (SCS), while they showed a lower reduction in the Eastern East China Sea (EECS), the northern ocean edge of TC genesis areas, resulting in an increase in the average latitude of TC genesis locations, a spurious northward shift. The La Niña and El Niño years showed contrasting effects on TC genesis frequency and landfall ratios. There were greater instances of TC genesis and greater landfall ratios during the La Niña mature phase, while there were fewer TC formations and lower landfall ratios during the short duration (SD) El Niño developing phase. The TC genesis locations showed a distinct northwestward shift during La Niña years compared to those during El Niño years.

Impact of the winter Arctic sea ice anomaly on the following summer tropical cyclone genesis frequency over the western North Pacific

Impact of the winter Arctic sea ice anomaly on the following summer tropical cyclone genesis frequency over the western North Pacific

Combined effect of the solar activity and ENSO on the tropical cyclone genesis frequency in the southeastern part of the western North Pacific

This study analyzes the frequency characteristics of tropical cyclone (TC) genesis in the southeastern part of the western North Pacific (SEWNP) during June–November from 1965 to 2019 and investigates the possible combined effect of the solar activity and El Niño-Southern Oscillation (ENSO). Results suggest that TCs generated in the SEWNP have the longest lifetime and greatest strength, and its frequency has apparent interannual and decadal variations, which is jointly affected by the solar activity and ENSO. In El Niño years during declining phases of solar cycle (1–3 years following the solar maximum), positive TC genesis frequency anomalies in the SEWNP are significantly strong and tend to occur in extremes. While the opposite is true for La Niña during ascending phases of solar cycle (1–3 years following the solar minimum). However, there exists no significant feature in the combined effect of La Niña (El Niño) and declining (ascending) phases of solar cycle. When declining (ascending) phases of solar cycle and El Niño (La Niña) are combined, the overlapping effect leads to apparently warmer (colder) sea surface temperature (SST) anomalies in the central equatorial Pacific and colder (warmer) SST anomalies in the western Pacific, so the SST anomalies gradient are stronger. It enhances low-level westerly (easterly) wind anomalies and upper-level easterly (westerly) wind anomalies, which is favorable for the further decrease (increase) of the vertical wind shear in the eastern (most) part of SEWNP. Moreover, the stronger and more westward low-level convergence (divergence) center appears in the Pacific, causing stronger low-level convergent (divergent) flow and upper-level divergent (convergent) flow anomalies, and strengthened (suppressed) ascending movement anomalies in the SEWNP. As a result, the TC genesis frequency in the SEWNP is much higher (lower). Further diagnoses show that absolute vorticity plays a leading role in El Niño years during declining phases of solar cycle, and its contribution is obviously much greater than other environmental factors. It is not perfectly symmetrical in La Niña years during ascending phases of solar cycle when the contribution of absolute vorticity is the greatest, but vertical wind shear is also important.

What caused the salient difference in rapid intensification magnitudes of Northwest Pacific tropical cyclones between 1998 and 2010?

Both the years 1998 and 2010 were the transitional years from El Niño to La Niña with record-low tropical cyclone (TC) genesis frequency over the western North Pacific (WNP). However, their rapid intensification (RI) magnitudes of TCs, defined as TC intensity change within 24 h during the RI stage, exhibited salient differences. RI magnitude in 1998 reached the third highest, but the lowest in 2010 since 1979. Results show that this remarkable difference in RI magnitude is related to the extremely favorable and unfavorable large-scale conditions, respectively. The extreme warming coupled with unstable atmosphere in key RI region provided favorable conditions for the high RI magnitude in 1998, while the extremely decreased low-level relative vorticity led to the very low RI magnitude in 2010. Further analyses show that this extreme warming in 1998 was driven by the enhanced net heat flux associated with the increase in downward short-wave radiation and latent heat flux, which was mainly caused by the less total cloud cover and reduced evaporation induced by the anomalous anticyclonic circulation, respectively. In sharp contrast, the unfavorable dynamic condition in 2010 mainly resulted from the combined impact of the La Niña events and the tropical east Indian Ocean warming.

Mechanisms of tropical cyclone response under climate change in the community earth system model

Climate change induces a myriad of effects which influences the global tropical cyclone (TC) genesis frequency. Here we explore how North Atlantic and Western Pacific TCs are affected under climate change using a present-day and a future (1% pCO2 scenario) ensemble of high resolution simulations. We find that the number of TCs decreases (-45%) in the North Atlantic but increases (+15%) in the Western Pacific. Part of these opposing variations are linked to differences in the ocean’s meridional overturning circulation, which gives rise to a different sea surface temperature response and air-sea fluxes between the two basins. The results show the important role of oceanic climate change on TC response.

Can lightning indicate genesis frequency of tropical cyclones over the South China Sea?

AbstractThe present study identifies a significant negative correlation of the South China Sea (SCS) summer–fall (JJASON) tropical cyclone (TC) genesis with the previous boreal spring (MAM) total lightning flash rate east of the Philippines during 1996–2013. The increased lightning flash rate east of the Philippines signifies an enhancement in deep convection, which induces cyclonic wind anomalies to the west via a Gill‐type atmospheric response and results in an increase in convection and cloud cover over the SCS during spring. The atmospheric changes lead to a decrease in sea surface temperature (SST) and ocean heat content (OHC) in the SCS by reducing downward short‐wave radiation and enhancing oceanic upwelling. The negative SST and OHC anomalies persist from spring to summer–fall and induce unfavourable thermodynamic anomalies, suppressing the SCS TC genesis during JJASON. Thus, the spring total lightning flash rate east of the Philippines, as an indicator of deep convection, may serve as a precursor of the SCS TC genesis.

Observed decadal shifts and trends in global tropical cyclone activities from 1980 to 2021

This study investigates the variability of annual tropical cyclone (TC) frequency and intensity over six major ocean basins from 1980 to 2021. Statistical change-point and trend analyses were performed on the TC time series to detect significant decadal variation in TC activities. In the middle of the last decade of the 20th century, the frequency of TC genesis in the North Atlantic basin (NA) and North Indian Ocean (NIO) increased dramatically. In contrast, the frequency in the western North Pacific (WNP) decreased significantly at the end of the century. The other three basins—the East Pacific, southern Indian, and South Pacific—all experienced a declining trend in annual TC frequency. Over recent decades, the average TC intensity has decreased in the East Pacific and the NA, whereas it has risen in the other ocean basins. Specifically, from 2013 to 2021, the average peak TC intensity in the NIO has enhanced significantly. The magnitude of the Genesis Potential Index exhibits fluctuation that is consistent with large-scale parameters in the NIO, NA, and WNP, emphasizing the enhancing and declining trends in TCs. In addition, a trend and correlation analysis of the averaged large-scale characteristics with TCs revealed significant associations between the vertical wind shear and TC frequency over the NIO, NA, and WNP. Therefore, global TC trends and decadal variations associated with environmental parameters deserve further investigation in the future, mainly linked to the significant climate modes.摘要研究发现在1980–2021期间全球6个海域每年热带气旋的发生频次和强度具有显著年代际变化规律, 最近几十年, 北大西洋和北印度洋的热带气旋发生频次明显增加, 但西北太平洋的热带气旋却显著下降. 另外三个海域, 东太平洋, 南印度洋和南太平洋发现所生成的热带气旋有减少趋势. 但在过去十几年, 平均热带气旋的强度除了在东太平洋和北大西洋有所减弱但在其他几个海域有所加强, 特别是在 2013–2021期间, 北印度洋的平均热带气旋的强度增强明显. 热带气旋的潜在生成指数 (GPI) 增加或减少趋势变化与北印度洋, 北大西洋和西太平洋热带气旋变化相关的大尺度环流一致. 另外, 北印度洋, 北大西洋和西太平洋上空的垂直风切变是影响其区域热带气旋发生频次变化的主要因子, 不同的气候模态也可能对全球热带气旋的趋势变化和年代际变化有影响, 值得进一步研究.

A possible relationship between Changma and tropical cyclone genesis frequency in the western North Pacific linked to the North Atlantic Oscillation

AbstractThis study analysed the relationship between Changma and tropical cyclone (TC) genesis in the western North Pacific (WNP). The correlations between Changma onset, withdrawal, and duration in Jeju and the southern and central regions of Korea and TC genesis frequencies in June, July, and June–July in the WNP were analysed. The results showed that Changma duration in the southern region and June–July TC genesis frequency exhibited the highest negative correlation. To investigate the mechanism underlying the correlations, the differences in large‐scale environments between the 14 years with the longest Changma duration and the 14 years with the shortest Changma duration were analysed. For 850‐hPa stream flows, anomalous anticyclones are found in most WNP regions, while anomalous cyclones are located in the East Asian mid‐latitude region. In the long Changma duration years, the WNP subtropical high was strengthened in the north–south and east–west directions, the monsoon trough was weakened, and anomalous downward flows are formed at the latitudinal (longitudinal) band of 10°–27°N (100°–180°E) where TCs mainly occur. All these environments provide unfavourable conditions for TCs to occur. The difference in sea surface temperature revealed triple anomaly patterns, such as warm, cold, and warm, in the north–south direction in the North Atlantic. This spatial distribution was similar to the negative North Atlantic Oscillation (NAO) pattern. From the analysis of 500‐hPa stream flow, we confirmed that the NAO acts as a bridge connecting the TC and Changma in the WNP.