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This study investigated a recent tendency of interannual precipitation variations during the Baiu season (June–July) in southern Kyushu, Japan. Long-term satellite precipitation observations revealed a significant amplification of the interannual variability of Baiu precipitation after the beginning of this century and the appearance of a quasi-quadrennial variation (QQV). Composite analyses with respect to the unstable regime of Baiu activity when the QQV prevailed suggested a possible link between the Indo-western Pacific Ocean Capacitor (IPOC) mode and the QQV. Regression analyses with an IPOC index showed the dominance of an anomalous anticyclone in the lower troposphere centered over the South China Sea and the Philippine Sea and enhanced poleward moisture transport along its western periphery. The interdecadal shift in remote IPOC influence seen around the year 2000 featured the westward (northward) extension of the low-level anomalous anticyclone toward the Bay of Bengal (southern Japan); consequently, the significant moisture flux convergence area covered southern Kyushu during the unstable Baiu regime, consistent with the QQV appearance during the same period. It is also inferred that the IPOC mode modulation may come from the increased impact of central Pacific El Niño/Southern Oscillation on the IPOC in recent decades.

This study investigated how warm-core eddies (WCEs) in the Gulf Stream (GS) modulated the intensity of a distant tropical cyclone (TC) approaching the current in October. We performed cloud-resolving regional simulations including a control run with the observed WCEs and a sensitivity run excluding the WCEs. These simulations found that the WCEs played a favorable role in the development of the distant TC. The WCEs affected the synoptic-scale thermodynamic environments over the North Atlantic through the enhanced heat and moisture supply from the GS, increasing the moisture imports toward the distant TC. The WCEs-enhanced moisture influx created very moist environments in the inner core. This inner-core moistening was favorable for deep eyewall convection and an associated TC secondary circulation, leading to TC development. This result indicates the importance of WCEs in facilitating the remote process leading to TC development that previous studies have proposed.

The climate feedback parameter is a useful indicator for estimating climate sensitivity relating to anthropogenic forcing. This study defines a new feedback parameter, the Perturbational Feedback Parameter (PFP), and the impacts of internally-generated climate variations are clarified using the MIROC piControl simulation. PFP values are found to vary significantly on interdecadal timescales. The equatorial sea surface temperature (SST) has a positive anomaly in the eastern Pacific and a negative anomaly in the western Pacific, and the thermocline tilts more gently than usual when the PFP is large. The statistical properties of the interannual fluctuations also simultaneously vary, and they correspond to the background state. For example, there is an increase in the El Niño Southern Oscillation (ENSO) amplitude relative to the global mean surface temperature rise, and the equatorial high SST more effectively contributes to the southward shift of the Intertropical Convergence Zone (ITCZ). In addition, a decadal fluctuation that dominates over the extratropical northern Pacific also plays an important role in PFP variations. These fluctuations on broad timescales cooperatively induce increases in lower clouds within the subtropics by strengthening the descending flow and static stability, and the consequential net downward radiation flux change through increases in reflection enhances the PFP. In summary, internal changes in both tropical and extratropical variability corresponding to the background state control the strength of the climate feedback on interdecadal timescales.

Moisture sources and their corresponding temperature and humidity are important for explosive extratropical cyclones’ development regarding latent heating. To clarify the water origins and moisture-transport processes within an explosive cyclone, we simulated an explosive cyclone migrating poleward across the Sea of Japan on November 30, 2014, by using an isotopic regional spectral model. In the cyclone’s center area, a replacement of water origins occurred during the cyclone’s development. During the early stage, the warm conveyor belt (WCB) transported large amounts of moisture from the East China Sea and Kuroshio into the cyclone’s inner region. While in the deepening stage, the cold conveyor belt (CCB) and dry intrusion (DI) conveyed more moisture from the Northwest Pacific Ocean and the Sea of Japan, respectively. Compared with the contribution of local moisture, that of remote moisture was dominant in the cyclone’s center area. Regarding the water origins of condensation within the frontal system in the deepening stage, the Northwest Pacific Ocean vapors, principally transported by the CCB, contributed 35.5% of the condensation in the western warm front. The East China Sea and Kuroshio moisture, conveyed by the WCB, accounted for 32.4% of the condensation in the cold and eastern warm fronts. In addition, condensation from the Sea of Japan, which was mainly triggered by the DI and induced by the topography, occurred on the west coast of the mainland of Japan and near the cyclone center. The spatial distribution of the isotopic composition in condensation and water vapor also supports the water-origin results.

The active roles of sensible heat supply from the Kuroshio/Kuroshio Extension in the rapid development of an extratropical cyclone, which occurred in the middle of January 2013, were examined by using a regional cloud-resolving model. In this study, a control experiment and three sensitivity experiments without sensible and latent heat fluxes from the warm currents were conducted. When the cyclone intensified, sensible heat fluxes from these currents become prominent around the cold conveyor belt (CCB) in the control run. Comparisons among the four runs revealed that the sensible heat supply facilitates deepening of the cyclone’s central pressure, CCB development, and enhanced latent heating over the bent-back front. The sensible heat supply enhances convectively unstable conditions within the atmospheric boundary layer along the CCB. The increased convective instability is released by the forced ascent associated with frontogenesis around the bent-back front, eventually promoting updraft and resultant latent heating. Additionally, the sensible heating leads to an increase in the water vapor content of the saturated air related to the CCB through an increase in the saturation mixing ratio. This increased water vapor content reinforces the moisture flux convergence at the bent-back front, contributing to the activation of latent heating. Previous research has proposed a positive feedback process between the CCB and latent heating over the bent-back front in terms of moisture supply from warm currents. Considering the above two effects of the sensible heat supply, this study revises the positive feedback process.

To clarify the time evolution of water origins in the vicinity of a tropical cyclone (TC)’s center, we have simulated Typhoon Man-yi (July 2007) in our case study, using an isotopic regional spectral model. The model results confirm that the replacement of water origins occurs successively as the TC develops and migrates northward over the western North Pacific. It is confirmed that, in this case, a significant proportion of total precipitable water around the cyclone center comes from external regions rather than the underlying ocean during the mature stage of a TC. Similar features can also be seen in the proportion of each oceanic origin to total condensation. Indian Ocean, South China Sea, and Maritime Continent water vapors begin to increase gradually at the developing stage and reach their peak at the decay stage when the TC approaches southwestern Japan. These remote ocean vapors are transported to the east of the cyclone via the moisture conveyor belt, a zone characterized by distinct low-level moisture flux that stretches from the Indian Ocean to the TC, and are further supplied into the inner region of the TC by inflow within the boundary layer associated with its secondary circulation. Since it takes time to undergo these two dynamic processes, the delayed influence of remote ocean vapors on the TC appears to become evident during the mature stage.

The dynamical response of rapidly developing extratropical cyclones to sea surface temperature (SST) variations over the western Kuroshio–Oyashio confluence (WKOC) region was examined by using regional cloud-resolving simulations. This study specifically highlights an explosive cyclone that occurred in early February 2014 and includes a real SST experiment (CNTL run) and two sensitivity experiments with warm and cool SST anomalies over the WKOC region (warm and cool runs). The results derived from the CNTL run indicated that moisture supply from the ocean was enhanced when the dry air associated with the cold conveyor belt (CCB) overlapped with warm currents. Further, the evaporated moisture contributed substantially to latent heat release over the bent-back front with the aid of the CCB, leading to cyclone intensification and strengthening of the asymmetric structure around the cyclone's center. Such successive processes were more active in the warm run than in the cool run. The dominance of the zonally asymmetric structure resulted in a difference in sea level pressure around the bent-back front between the two runs. The WKOC SST variations have the potential to affect strong wind distributions along the CCB through modification of the cyclone's inner system. Additional experiments with two other cyclones showed that the cyclone response to the WKOC SST variations became evident when the CCB north of the cyclone's center overlapped with that region, confirming that the dry nature of the CCB plays an important role in latent heat release by allowing for larger moisture supply from the ocean.

Using a cloud-resolving regional model and Lagrangian diagnostics, we assess a positive feedback process between tropical cyclone (TC) intensity and the moisture conveyor belt (MCB), which connects a TC and the Indian Ocean (IO), the South China Sea (SCS), and the Philippine Sea (PS) vapors, from a macroscopic view. We performed sensitivity experiments that modified the observed sea surface temperature (SST) field over the IO and the SCS to regulate the MCB behavior, and we examined the remote response of a prototypical TC. The results show that the connection between MCB formation and TC development is very robust, which was also observed in another TC's case. The MCB plays a vital role in transporting lots of moist air parcels toward the TC from the IO, SCS, and PS regions. The transported parcels, which further gained the underlying ocean vapor along the MCB, are easily trapped in the inner core by radial inflow in the atmospheric boundary layer and, subsequently, release latent heat around the eyewall, resulting in the TC's intensifying. This acts to further penetrate the moist parcels of remote ocean origin into the inner core through the enhanced and expanded inflow. An additional experiment suggested that the MCB is not formed unless the westward propagation of equatorial waves induced by TC heating overlaps with the background monsoon westerlies. These findings support the reliability and validity of TC-MCB feedback.

The role of remote ocean sea surface temperature (SST) in regulating tropical cyclone (TC) characteristics has been examined by performing numerical experiments with a regional scale model. Model simulations have been carried out to simulate typhoon Man-yi (July 2007), in our case study, under a range of SST conditions over the Indian Ocean and the South China Sea. The intensity and track of the cyclone have been systematically changed in sensitivity simulations of cool and warm SSTs over that region, following its peak phase. Warm oceans can substantially reduce the intensification of western North Pacific cyclones, whereas cool oceans can enhance their strength. This is intimately associated with the enhancement/weakening of the moisture supply through the moisture conveyor belt (MCB) in the lower troposphere, from the Indian Ocean and South China Sea into the vicinity of the cyclone center. When the MCB is interrupted over the South China Sea in warm SST occurrences, the large-scale transport of moisture into the cyclone system is significantly reduced, leading to the weakening of the cyclone intensity and to the eastward shift of its track. This study shows that changes in remote tropical ocean SST can also modulate TCs and thus can help in improving the forecasting of TC intensities and tracks.

This study focused on an explosive cyclone migrating along the southern periphery of the Kuroshio/Kuroshio Extension in the middle of January 2013 and examined how those warm currents played an active role in the rapid development of the cyclone using a high-resolution coupled atmosphere–ocean regional model. The evolutions of surface fronts of the simulated cyclone resemble the Shapiro–Keyser model. At the time of the maximum deepening rate, strong mesoscale diabatic heating areas appear over the bent-back front and the warm front east of the cyclone center. Diabatic heating over the bent-back front and the eastern warm front is mainly induced by the condensation of moisture imported by the cold conveyor belt (CCB) and the warm conveyor belt (WCB), respectively. The dry air parcels transported by the CCB can receive large amounts of moisture from the warm currents, whereas the very humid air parcels transported by the WCB can hardly be modified by those currents. The well-organized nature of the CCB plays a key role not only in enhancing surface evaporation from the warm currents but also in importing the evaporated vapor into the bent-back front. The imported vapor converges at the bent-back front, leading to latent heat release. The latent heating facilitates the cyclone’s development through the production of positive potential vorticity in the lower troposphere. Its deepening can, in turn, reinforce the CCB. In the presence of a favorable synoptic-scale environment, such a positive feedback process can lead to the rapid intensification of a cyclone over warm currents.

The dynamical impact of the Changbai Mountain Range in the Korean Peninsula on the extratropical cyclone activity over the Japan Sea in early winter is examined using the Weather Research Forecasting model. We have conducted two independent long-term integrations over 15 winter months (December only) from 2000 to 2014 with and without modified topography. The results show that the Changbai Mountain Range plays a vital role in increasing cyclone track frequency, low-level poleward eddy heat flux, and the local deepening rate over the Japan Sea through enhancement of the lower-tropospheric baroclinic zone (LTBZ). This mountain range gives rise to activation of the synoptic-scale cyclone activity over that region. From our case study on three typical cyclones, it is found that mesoscale structures in the vicinity of a cyclone’s center are dynamically modulated when it passes through the LTBZ and that cyclogenesis is triggered around that zone. A vorticity budget analysis shows that the stretching term relevant to enhanced low-level convergence plays a dominant role in intensifying cyclonic vorticities. We confirmed that the composite features of the three typical cases are consistent with the statistical ones of the dynamical modulation of the Changbai Mountain on synoptic-scale cyclone activity.

The modulation of large-scale moisture transport from the tropics into East Asia in response to typhoon-induced heating during the mature stage of the Baiu/Meiyu season is investigated using the Japanese 55-year reanalysis (JRA-55), aided by a Rayleigh-type global isotope circulation model (ICM). We highlighted the typhoons that migrate northward along the western periphery of the North Pacific subtropical high and approach the vicinity of Japan. Anomalous anticyclonic circulations to the northeast and southeast of typhoons and cyclonic circulation to their west become evident as they migrate toward Japan, which could be interpreted as a Rossby wave response to typhoon heating. These resultant anomalous circulation patterns form moisture conveyor belt (MCB) stretching from the South Asian monsoon region to East Asia via the confluence region between the monsoon westerlies and central Pacific easterlies. The ICM results confirm that the well-defined nature of the MCB leads to penetration of the Indian Ocean, South China Sea, Philippine Sea, and Pacific Ocean water vapors into western Japan. The typhoons have the potential to accumulate large amounts of moisture from distant tropical oceans through the interaction of their Rossby wave response with the background flow. In the case of a typical typhoon, the total precipitable water around the typhoon center as it approaches Japan is maintained by the moisture supply from distant oceans rather than from the underlying ocean, which indirectly leads to the occurrence of heavy rainfall over western Japan.

The interaction between typhoons and the North Pacific subtropical high and the associated remote impact on East Asian and North Pacific anomalous weather during the Baiu/Meiyu season have been investigated using the Japanese long-term Reanalysis project data aided by the Japan Meteorological Agency Climate Data Assimilation System. The typhoons that appeared in July have been categorized into two primary tracks, the Hainan Island course (HC) and the Okinawa Island course (OC). A typhoon gives rise to negative absolute vorticity advection along its eastern periphery, which locally reinforces the western ridge of the North Pacific subtropical high, whereas the resultant anomalous high stimulates the westward (northward) migration of the HC (OC) typhoon through its combination with the background flow. A combined effect of the typhoon and its induced anomalous anticyclonic circulation increases the transportation of moisture into the Baiu/Meiyu frontal zone in the vicinity of Japan. Over the East China Sea and the Sea of Japan, northward or northeastward moisture flux is pronounced along the western periphery of the typhoon-induced anticyclonic circulation anomaly in the HC category, triggering heavy rainfall on central Japan's Sea of Japan coast. Similar remote effects also operate in the OC category, which is responsible for the occurrence of extremely heavy rainfall along the Pacific coast of western Japan. When an OC typhoon approaches the Asian jet, it is capable of giving rise to anticyclonic vorticity within the jet, leading to the downstream development of stationary Rossby wave packets via the North Pacific waveguide.

[1] We examined possible responses of cyclone activities to the bimodal path states of the Kuroshio Current [i.e., large meander (LM) and non-LM (NLM)] by using the long-term reanalysis data and the 20th century hindcast experiment of a high-resolution atmosphere-ocean coupled model. Compared with a seasonal mean cyclone track frequency for the LM and NLM periods, a primary cyclone track shifts southward in association with the meander of Kuroshio Current. Composite analyses of the hindcast experiment showed remarkable atmospheric responses accompanying the Kuroshio LM. The Kuroshio LM causes a decrease in latent heat flux in the south of Japan and a southward shift of the near-surface baroclinic zone. Distinctive decreases in thermodynamic fluxes inhibit the rapid development of cyclones in the meander region, eventually inducing positive sea level pressure anomalies downstream from that region.

By applying the Japanese long-term Re-Analysis project (JRA-25) and the Japan Meteorological Agency Climate Data Assimilation System (JCDAS) data to a Rayleigh-type global one-layer isotope circulation model, we performed a long-term simulation and examined how water vapor is remotely transported to the vicinity of Japan from water source regions during the early summer rainy (Baiu) season. We validated the model outputs, comparing them with the stable hydrogen and oxygen isotope ratios (δD and δ18O) of precipitation observed at two in situ sites in southern and central Japan during the 2010 Baiu, and determined that the correlations between the simulation and observation are comparable to those in precipitation in Thailand from August to October when the Asian summer monsoon withdraws. The model results demonstrate that the Baiu is characterized by relatively low values of δD and that the δD values over central Japan are lower than those over southern Japan. When the Baiu commences, Indian Ocean water increases rapidly and then contributes substantially to the total precipitable water until the withdrawal of the Baiu, which is partially responsible for the low values of δD. Once the Baiu withdraws, alternatively, Pacific Ocean water occupies most of the total precipitable water. Another signature of its withdrawal is the decrease in land water of the Eurasian continent. It is also clear that the intrusion of the Indian Ocean water into central Japan remained until the end of August in the extremely cool summers of 1993 and 2003, which is interpreted as an extraordinary persistence of the Baiu period.

Using data from the Japanese long-term Re-Analysis project (JRA-25) and the Japan Meteorological Agency Climate Data Assimilation System (JCDAS), we examined how the East Asian winter monsoon variability regulates the surface cyclogenesis in the vicinity of the East China Sea and the Kuroshio Current in late winter. On a monthly basis, the surface cyclone occurrence has a tendency to concentrate over the East China Sea at the strong phase of the East Asian winter monsoon activity, while it disperses zonally along the Kuroshio Current to the south of Japan in the weak monsoon phase. The scatteredness of the surface cyclogenesis are mainly attributed to the change in the lower-tropospheric baroclinicity between the strong and weak monsoon phases. It is also suggested that, when the monsoon is strong, the enhanced baroclinic zone along the Kuroshio Current south of Japan provides a favorable condition for the rapid development of the surface cyclones that originate over the East China Sea and migrate northeastward.

The relationships between large-scale circulation and foehns observed during midsummer in Hokuriku district, located on the Japan Sea side of central Japan, are examined using Japanese long-term reanalysis project data, with additional data from the Japan Meteorological Agency climate data assimilation system. All foehn events are classified into two types: a tropical cyclone (TC)-induced foehn and an extratropical cyclone (EC)induced foehn. The occurrence of the TC type is attributed to a combination of a typhoon and its induced teleconnection pattern, the Pacific-Japan (PJ) pattern, in the lower troposphere. Local intensification of the North Pacific high just east of Japan, accompanied by the dominance of the PJ pattern, can in turn force a typhoon track to shift westward. The northward migration of the typhoon along the western periphery of the locally enhanced high strengthens a zonal pressure gradient across central Japan, thus producing a foehn. In contrast, an upper-level teleconnection along the Asian jet serves as a prominent trigger of the occurrence of an EC-type foehn. Stationary Rossby wave packets propagating eastward along the upper-level Asian waveguide facilitate not only the westward development of the North Pacific high but also the development of an extratropical cyclone in the vicinity of the Japan Sea by leading to the equatorward advection of higher potential vorticity from high latitudes. Both developments are crucial for the reinforcement of a northwest-southeast pressure gradient in the lower troposphere around Japan, thus providing a favorable condition for a foehn event.

In the tropics, the El Nino-Southern Oscillation (ENSO) occupies a major part of the interannual air-sea interactive system. The ENSO plays a vital role in triggering the occurrence of extraordinary anomalous climates and weather not only in the tropics but also in the extratropical regions. In the South Asian monsoon region, the ENSO can influence the interannual variability of the monsoon system through at least two different impacts. During the decay phase of ENSO (from winter to summer) its delayed impact operates through large-scale air-sea interaction in the tropical Indian Ocean and land-surface hydrological processes over the Asian Continent, eventually bringing about change in summer monsoon activity in June and July. During the ENSO growth phase (from summer to winter), in contrast, its direct impact is considered to account for monsoon interannual variability especially in August and September. East Asian monsoon variability is also significantly affected by ENSO-related tropical forcing. Especially in early winter, ENSO-related anomalous convection can give rise to a change in the East Asian winter monsoon system through stationary Rossby wave propagation along the South Asian waveguide, but the remote response depends on the geographical configuration of the anomalous tropical convection. In summer, the ENSO's delayed impact is associated with excitation of an extratropical teleconnection, which causes anomalous weather in northeastern Asia. Midlatitude air-sea interactions and their potential impact on large-scale atmospheric circulations are also discussed. The coexistence of the East Asian winter monsoon flow and western boundary current makes air-sea heat exchanges in the Kuroshio extension very active. Due to enhanced baroclinicity and surface heat fluxes from the ocean, a number of extratropical cyclones tend to develop explosively in the vicinity of Japan. The activity of these extratropical cyclones contributes to the downstream development of upper-level teleconnections.

Using the European Center for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA-40) data, we examined two summertime teleconnection patterns, the Europe-Japan (EJ) and the Pacic-Japan (PJ) patterns, which prevail over northern Eurasia and the western North Pacic, respectively, and high lighted the effects of the combination of the two on the East Asian summer monsoon variability on a high frequency (HF) component (sub-monthly timescales) and a low-frequency (LF) component (longer than about one month).The combination of positive EJ type 2 (EJ2+), which particularly accounts for the variability of the Ok hotsk high among the two types of EJ pattern (EJ type 1 and EJ type 2), and negative PJ (PJ-) patterns establishes a noticeable tripole structure in the mid-tropospheric geopotential height eld of East Asia that is characterized by two positive anomalies over the Okhotsk Sea and the western North Paci c to the north of the Philippines and a negative anomaly over Japan. It is found that the combination of both pat terns, EJ2+/PJ-, leads to a larger surface temperature decrease in the northeastern part of East Asia than a single teleconnection pattern alone, having a substantial impact on the East Asian summer monsoon circulation. The LF-combination also induces signicant cool sea surface temperature anomalies in the vicinity of Japan. In the HF-combined case, the time evolution of a positive height anomaly over the Ok hotsk Sea considerably differs from that of the LF-combined one. The HF-anomaly is extremely displaced eastward to the Aleutian Islands a few days after the peak day and occupies part of a newly organized wavetrain pattern across the central North Pacic. Further development of the wavetrain pattern may be attributed to anomalous convective heating related to enhanced synoptic-scale disturbances to the east of Japan.Both the LF-EJ2+ and LF-PJ- patterns tend to appear frequently during the post-1980 period, and, as a result, the number of LF-combined cases may have increased in the last two decades. Exceptionally cool summers with signicant amounts of rainfall, particularly in Japan, such as the 1993 and 2003 summers, often arise from such an LF-combination.

Using ERA-40 and NCEP/NCAR reanalysis data, the characteristics of major teleconnection patterns were examined, particularly the West Asia-Japan (WJ) and Pacific-Japan (PJ) patterns, with a high-frequency (HF) component (from half a week to two or three weeks), and a low-frequency (LF) component (greater than about one month), and discussed the combined effects of the teleconnection patterns on the anomalous summer weather in Japan and the surrounding regions.Both patterns of the HF-WJ and LF-WJ, which propagate eastward along the upper-level Asian jet, induce an anomalous barotropic anticyclone centered on the Japan Sea. The HF-WJ pattern has no close link with the Asian summer monsoon activity, but, in contrast, the LF-WJ pattern is significantly correlated with anomalous monsoonal heating over the summer monsoon region. The HF-PJ and LF-PJ patterns, which can be identified with stationary waves stimulated by intense convection around the Philippine Sea, generate a nearly barotropic anticyclone anomaly to the east of Japan. A combination of the HF-WJ and HF-PJ patterns establishes a zonally elongated anticyclonic anomaly over northern Japan, resulting in anomalous high surface temperatures in northern Japan. Such a coupling was found to lead to a larger temperature increase in that region than a single teleconnection pattern alone.A typical case of the LF-WJ and LF-PJ combination also indicates a zonally elongated anticyclonic anomaly over northern Japan, which is similar to the combined pattern of HF-WJ and HF-PJ. The dynamic impact of LF-WJ on the surface temperature field around Japan differs significantly from that of LF-PJ. The dominance of the LF-WJ causes enhanced subsidence over Japan, which can bring about adiabatic heating and increased incoming solar radiation. On the other hand, PJ-induced anomalous anticyclone in the lower troposphere facilitates northward warm advection to the east of northern Japan, where the north-south temperature gradient is large. As for the extreme hot summer of 2004, no combined patterns of the LF-WJ and LF-PJ were found during the summer. Alternatively, a tripole structure appeared in the lower geopotential height field in mid-June. Such a tripole pattern may be established by a combination of the LF-PJ and a barotropic Rossby wave train propagating southeastward from high latitudes.

Using the Japanese long-term Re-Analysis project (JRA-25) data, we investigated the seasonal dependence on dynamical links between the Pacific-Japan (PJ) pattern and typhoon activity. It was found that the PJ patterns tend to prevail soon after typhoons to the east of the Philippines migrating northward across the 20°N line during the period from July to October. Especially in early summer the low-level southwesterly jet formed by the penetration of the Asian summer monsoon westerlies into the Philippine Sea enables the typhoons to generate the PJ pattern, whereas in autumn the upper-level Asian jet contributes to the appearance of PJ as an alternative waveguide. The seasonal differences in latitudinal position and strength between the two different waveguides influence the vertical tilt structure of PJ in the vicinity of Japan. It also turns out that even though the typhoons are far away from Japan, they have the potential to indirectly and remotely activate stationary fronts around Japan during the rainy season through the dominance of PJ.