Assessing seasonal prediction of DGPI over the Western North Pacific by the Climate Forecast System and its improvement using deep learning

Nitrogenous sources for summertime phytoplankton at two contrasting stations in the subarctic and subtropical western North Pacific

Limpets of the family Lepetidae (Patellogastropoda) from the continental shelf of the Northwestern Pacific – generic and specific composition

The results of the trawl survey of the research vessel Professor Kaganovsky over four seamounts (Annei, Jingu, Ojin, and Koko) of the Emperor Seamount Chain in 2019 are presented. Seventy-three species of pelagic and bottom-dwelling cartilaginous and bony fishes from 40 families were collected. Morphological diagnoses are presented for each species, with taxonomic comments for the poorly known taxa. The obtained collection includes 11 species new to science or of uncertain taxonomic position, 9 species newly reported for the Emperor Seamounts, and one new record Linophryne arborifera for the Pacific Ocean. For individual seamounts, 27 fish species were recorded for the first time at Annei, 12 species at Ojin, 4 species at Koko, and 2 species at Jingu Seamounts. Cytochrome c oxidase subunit I (COI) or cytochrome b (Cyt b) sequences were obtained for 36 species belonging to 22 families, including 13 species for which the barcode was flagged for the first time and the sequences made available. Cryptic diversity was revealed within the genera Cyclothone, Argyropelecus, and Chauliodus. According to our data, a boundary between the boreal and subtropical fish communities was found between Nintoku and Jingu Seamounts, with a transitional zone over Jingu and Ojin Seamounts at 37–39° N. However, the distribution of the subtropical species to the north may be limited by the increasing of summit depths in the northern subsection of the chain rather than any oceanographic or climatic barriers.

We describe two new species of Paradraconema from subtidal sediments of Korean waters: P. tamraense sp. nov. from Jeju Island and P. gangchii sp. nov. from Dokdo Island. Although the epithet tamraense had appeared previously in the literature, it was treated as a nomen nudum and therefore lacked nomenclatural availability under the ICZN. In this study, the species is newly and validly established based on a critical reassessment of the original material, supported by new line drawings and detailed observations using differential interference contrast (DIC) and scanning electron microscopy (SEM). Paradraconema amraense sp. nov. is characterized by a slender body; pharyngeal annules bearing weakly developed longitudinal bars with smooth margins; a narrow lateral field at midbody; abundant and relatively long somatic setae; a head capsule partially covered with vacuolated ornamentation; an amphidial fovea that is elongate loop-shaped in males and circular, unispiral in females; eleven cephalic adhesion tubes (CAT); and comparatively long sublateral adhesion tubes (SlAT) and subventral adhesion tubes (SvAT). Paradraconema gangchii sp. nov. is characterized by a slender body; cuticle ornamentation with numerous longitudinal bars bearing finely crenulated margins in the pharyngeal region; sparse and short somatic setae; a head capsule fully covered with vacuolar ornamentation (reticulate under SEM); an amphidial fovea that is elongate loop-shaped in males and circular, unispiral, slightly over one coil in females; relatively short spicules (36–46 µm); eleven CAT; and relatively short SlAT and SvAT. SEM revealed several fine morphological features not previously documented in the genus, including the precise number and arrangement of CAT and detailed structures of the cuticle ornamentation and lip region. This study provides comprehensive SEM-based documentation for Paradraconema, increases the number of valid species in the genus to thirteen, and enhances our understanding of draconematid diversity in the northwestern Pacific.

Abstract. Atmospheric convection over the subtropical western North Pacific (SWNP) during boreal summer varies on timescales of around 10 d, with significant effects on both local and remote circulation. One of less understood effects of this variability is its coupling with equatorial wave dynamics. This paper quantifies equatorial wave perturbations and their evolution throughout the lifecycle of SWNP convection using wave-space regression between outgoing longwave radiation over the SWNP region and spectral expansion coefficients of global tropospheric circulation from ERA5 reanalyses. The regression distinguishes between convection-coupled linear Rossby and Kelvin waves, and mixed Rossby-gravity (MRG) and inertia-gravity (IG) waves. The former two correspond to the Gill-type tropical circulation response to asymmetric heating. The results show that MRG and IG waves exhibit amplitudes comparable to those of the Gill-response component in the upper troposphere. In particular, MRG and IG waves dominate the cross-equatorial northerly flow over the Maritime Continent, with MRG waves playing the larger role. These findings suggest caution when applying the Gill solution to interpret circulation responses to asymmetric heating in model simulations. As SWNP convection intensifies, the MRG-wave northerly winds across the equator strengthen, while IG waves represent enhanced upper-tropospheric outflow over the SWNP region. By contrast, the combined effect of Kelvin and Rossby waves reinforces circulation on the equatorward flank of the anticyclone over the SWNP region, with Rossby wave easterlies being about three times stronger than those associated with Kelvin waves. The Rossby wave signal resembles the n=1 Rossby wave, with its Southern Hemisphere (SH) subtropical anticyclonic gyre forming over the southern Indian ocean during the decay phase of the SWNP convection. This gyre, together with the SH IG meridional flow provides a dynamical bridge linking SWNP convection and extratropical circulation during austral winter.

Particulate thiols along a meridional transect in the western North Pacific: Insights from laboratory cultures of Synechococcus sp. and Thalassiosira nordenskioeldii.

Regional changes of tropical cyclone rainfall in the western North Pacific

ABSTRACT Aim For several decades, substantial efforts have monitored cetacean distribution and abundance in the western North Pacific. Large‐scale visual‐based line transect surveys have been conducted since the early 1980s, covering almost the entire western North Pacific. However, information on distribution patterns of cetacean species is concentrated in summer months when sighting conditions are preferred, while dolphin fisheries, one of the main threats to cetacean populations, are conducted mainly during winter months. Location The western North Pacific. Methods To fill information gaps between these seasons and improve conservation and management measures, we compiled long‐term sighting data. We constructed a simple species distribution model (SDM) to estimate the seasonal patterns for 14 delphinid and phocoenid species. Although the sighting data remained limited outside summer, the distribution probability was intra‐ and extrapolated to respective seasons using the constructed SDMs. Results Model fitting tended to be better for the species inhabiting higher latitudes than for those in lower latitudes. In addition, seasonal patterns observed in our habitat prediction maps roughly corresponded to those patterns previously reported from coastal fishers' logbooks and satellite‐tracking records. The model also estimated that some species distribution changes in response to long‐term warming in water temperature over the past 30 years. Main Conclusions The study addresses the seasonal gaps in conservation and management measures and improves understanding of population structures of the species targeted by dolphin fisheries. Our approach to predicting distribution patterns spatiotemporally is widely applicable to conservation systems for marine animals inhabiting dynamic ocean environments.

Accurate prediction of weather and climate conditions is vital for ensuring the safety of human environments. In this study, we developed a regional air-sea coupled weather forecasting model and conducted a preliminary evaluation of its performance concerning basic variables such as precipitation, typhoons, and 10-meter wind fields. The forecasting system covers the region from 15° to 40°N latitude and 108° to 146°E longitude, utilizing the Weather Research and Forecasting Model (WRF) for atmospheric components and the Regional Ocean Modeling System (ROMS) for oceanic components, integrated via the National Center for Atmospheric Research Coupler version 7 (CPL7). The system operates at a horizontal resolution of approximately 3 km. We performed daily rolling 96-hour forecast experiments, starting at 00:00 each day from January 1, 2024, to December 31, 2024. The results indicate that the annual mean rainfall root mean square error (RMSE) for the entire region is 13.7 mm/day for a 24-hour forecast and 16.3 mm/day for a 96-hour forecast. Spatially, the RMSE is generally smaller in the northwest land area of the region (inland China) compared to the ocean, with notably larger RMSE near Taiwan and the Philippines due to higher average precipitation in these areas. Southern Japan also exhibits relatively large RMSE values. The forecast skill demonstrates significant seasonal variation, with higher RMSE in summer compared to winter. For typhoon forecasts, the mean error distance is 74.1 km for 24–48 hours and 118.9 km for 48–72 hours. The RMSE of 10-meter wind over the oceans shows similar patterns to rainfall, with an annual mean RMSE of 1.5 m/s for a 24-hour forecast and 2.5 m/s for a 96-hour forecast.

Zostera japonica Ascherson et Graebner, 1907 is a dominant seagrass species that forms coastal habitats in the northwestern Pacific. Bare areas adjacent to these seagrass beds are also recognized as fish habitat. However, few studies have comparatively evaluated the ecological importance of Z. japonica beds and adjacent bare ground within estuarine environments. We conducted seine net sampling to compare ichthyofaunal composition between Z. japonica beds and adjacent bare ground in a small temperate estuary in Kyushu, southern Japan, during three summer seasons (2015, 2016, and 2019), when seagrass growth is at its peak. Fish species richness and the abundance of the predominant species, Redigobius bikolanus (Herre, 1927), were significantly higher in the seagrass beds than over bare ground. Additionally, the size distribution of R. bikolanus was broader in seagrass beds. PERMANOVA analysis revealed a significant difference in abundance-based species composition between the two habitats, and SIMPER analysis identified three species that contributed most to this distinction: R. bikolanus and Gerres japonicus Bleeker, 1854 (both more abundant in seagrass beds), and Gymnogobius breunigii (Steindachner, 1880) (more abundant over bare ground). These findings imply that Z. japonica beds enhance fish diversity and serve as key habitats for dominant fish species, while adjacent bare ground also supports specific fish communities. The results underscore the importance of conservation efforts within estuaries that account for the ecological roles of both seagrass and bare substrates.

This study investigates the interconnections and underlying causes of the inter-model variability in boreal summer precipitation across global monsoon regions, based on historical AMIP6 simulations. The results reveal significant connections among the leading modes of precipitation inter-model deviations in different monsoon domains, with the western North Pacific (WNP) emerging as a key driver. Deviations over the WNP modulate adjacent monsoon systems -- including the South Asian, North African, and Australian monsoons -- primarily through the Walker and Hadley circulations. In addition, WNP precipitation anomalies, via jet stream disturbances originating from the tropical Indian Ocean, indirectly generate zonal wave trains in the mid-to-high latitudes of both hemispheres, influencing the Somali and South American monsoon. The WNP also affects East Asian monsoon precipitation mainly through meridional wave trains along the East Asian coast, triggered by perturbations in the monsoon trough. These findings underscore the 'engine' role of WNP precipitation deviations -- via atmospheric dynamic process -- in shaping the global pattern of monsoon precipitation inter-model variability in AMIP6, and highlight the need for improved model performance over this region to enhance global monsoon simulation fidelity.

Abstract. Clear-air turbulence (CAT) endangers aviation safety and early understanding of the phenomenon was obtained mainly by analysing the corresponding synoptic weather situation. In this study, the relationship between CAT and different synoptic weather features is revisited based on in situ eddy dissipation rate measurements by commercial aircraft and modern reanalysis data (ERA5 reanalysis). In the years from 2019 to 2022, 4880 moderate-or-greater turbulence events are identified in predominantly clear-air conditions in the Northern Hemisphere. Most of the events identified occur over the contiguous U.S. and along the major flight corridors in the North Atlantic and western North Pacific. They are associated frequently with potential vorticity (PV) streamers, which are used as a proxy for Rossby wave breaking (RWB), and/or warm conveyor belt (WCB) ascents at the event locations. Events which are concurrent with RWB in the absence of WCB ascents are classified as type I. They constitute around 40 % of the events and are found evenly across the contiguous U.S. Events which are concurrent with WCB ascents are classified as type II. They account for around 30 % of the events and are more concentrated over the eastern U.S. and the East China Sea. Analysing the environmental conditions associated with the events, higher values of horizontal deformation are found on average in the vicinity of type I events, and the high horizontal deformation associated with RWB is considered as the possible cause of this type of CAT. Type II events occur more frequently in the presence of negative PV, together with higher averaged cloud ice water content and wind speed. The presence of negative PV, which is most likely due to diabatic PV reduction in clouds, may indicate that inertial or symmetric instabilities or enhanced local wind shear due to the strengthened outflow from WCBs are possible causes of CAT for type II events. The suggested linkages are further supported by examining the ERA5 grid point data. When grid points with high horizontal deformation are examined, they are mostly found in RWB regions and show an enhanced chance of turbulence. This collocation of RWB, high horizontal deformation, and turbulence is particularly prominent over the Western U.S. Similarly, grid points with negative PV values also show a higher probability of turbulence and a noteworthy fraction is collocated with WCB ascents. The results thus (i) reveal the important roles of RWB and WCB ascents for CAT, (ii) provide a better explanation of the physical mechanisms triggering CAT in the presence of RWB and WCB ascents, and (iii) highlight the importance of in situ observations for deepening the understanding of CAT. Furthermore, the weather-feature perspective employed in this study may also provide insights to interpret the climatology of CAT or projected changes of CAT in the future.

Abstract Based on tropical cyclone (TC) observation data over the South China Sea (SCS) from 1949 to 2023, this study analyzes the long-term changes in TC frequency, intensity, and duration. Using the generalized extreme value (GEV), we further identify and quantify the spatiotemporal characteristics of three categories of extreme tropical cyclones (ETCs) defined by maximum wind speed (Vmax), duration (Duration), and accumulated cyclone energy (ACE). The multiscale drivers behind these changes are also investigated. The results reveal an approximately 25% decrease in total TC frequency over the SCS in the past 75 years, with the most notable reduction occurring in locally formed TCs. Concurrently, the average Duration of TCs has increased by about 25%, while no significant trend is observed in mean intensity. ETCs exhibit metric-dependent changes: location parameters for Vmax- and ACE-based ETCs have declined significantly, whereas those for Duration-based ETCs have increased. Non-local ETCs contribute more substantially to the decreasing intensity trend, while local ETCs show prolonged residence within the basin. Spatially, the track density of both TCs and ETCs remains concentrated in the northern SCS, but has increased significantly for most TCs/ETCs in the Beibu Gulf Economic Zone of Guangxi Province and along the southwestern coast of Guangdong Province in China, as well as to the west of the Philippines, indicating a shift in regional exposure risk. Further analyses indicate that the El Niño-Southern Oscillation (ENSO) regulates ETC activity on interannual timescales, while the Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO) modulate ETC variability on decadal scales and likely contributed to the reversal in the trend of the Vmax-ETC location parameter around 2000. Moreover, Vmax-ETCs and ACE-ETCs are generally suppressed by vertical wind shear over both the SCS and the Western North Pacific main development region, whereas the prolonged Duration-ETCs appear to depend on enhanced low-level vorticity, mid-level humidity, sustained upward motion, and higher convective instability within the SCS. This study highlights the multi-metric and multiscale characteristics of ETC activity in the SCS, providing important scientific value for regional disaster prevention and climate risk assessment.

Abstract Lifetime maximum intensity (LMI) is a key metric for tropical cyclone (TC) intensity, providing insights into TC evolution and impact. However, research on LMI in the South China Sea (SCS) is limited. Our study found a significant increase in LMI amplitude in the SCS since the 1980s. This change was driven by decreasing LMI of local TCs and increasing LMI of migratory TCs from the western North Pacific. Attribution analysis showed that a westward shift in local TC genesis increased land constraints, suppressed TC development, and weakened LMI. In contrast, the poleward migration of TC tracks facilitated the increased entry of storms into the SCS through the Luzon Strait with minimal land interaction, thereby enhancing the LMI of migratory TCs. Additionally, favorable environmental conditions increase the frequency of rapid intensification events, further boosting LMI. These changes suggest the growing potential impact of TCs on countries and regions surrounding the SCS.

Aerosol emission reductions cause post-2011 rapid warming in the northwestern Pacific

Abstract Recent papers on planetary and safe Earth System boundaries have proposed a limit of 0.25 for regional aerosol optical depth (AOD) in South Asia (SA) with a zone of uncertainty of 0.25 to 0.50 to avoid major disruptions to regional hydrology. These values are based on expert judgement, and a rigorous model-based confirmation of these boundary values is lacking in literature. In this paper, we address this important research gap using idealized climate model simulations. We analyze the response of the South Asian summer monsoon precipitation when the regional mean AOD is increased from the current value of 0.14 to the proposed planetary boundary values of 0.25 and 0.5. Our simulations confirm that a regional AOD of 0.25 could indeed lead to drought conditions (>10% mean precipitation reduction) in India, while an AOD of 0.5 reduces Indian summer monsoon precipitation by about 19%.The reduction in the summer monsoon precipitation is driven by both fast adjustments (rapid adjustment of the atmosphere to aerosol radiative forcing) and slow responses (responses to changes in sea surface temperature). The rapid adjustment to anthropogenic aerosols, predominantly sulfates, involves enhanced atmospheric stability, subsidence, and suppressed cloud formation and precipitation. The slow response involves zonal surface temperature gradients between the North Indian Ocean and Western Pacific Ocean leading to changes in the Walker circulation, anomalous subsidence over South Asia, and a decrease in monsoon precipitation. Enhanced aerosol loading over South Asia reduces monsoon precipitation, regardless of aerosol composition, though the magnitude of reduction depends on whether the aerosols are primarily reflective or absorbing. Our findings confirm and highlight the risk of major disruptions to regional hydrology in South Asia when regional aerosol loading exceeds the boundary values. Future studies should assess the robustness of our results using other climate models and for other monsoon regions.

Potential Vorticity Perspective of Two Explosive Cyclones over the Northwestern Pacific Ocean

Modulation of Atlantic multidecadal oscillation on sea surface temperature anomalies in western North Pacific during El Niño decaying spring

Abstract This study investigates the diversity of the impact of the North Pacific Meridional Mode (NPMM) on western North Pacific (WNP) tropical cyclone (TC) genesis during June–November from 1961 to 2024. We consider preceding springtime NPMM events driven by tropical and extratropical forcings, and classify them as successive and stochastic events, respectively. In successive positive NPMM years, TC genesis changes only slightly over the entire WNP. In successive negative NPMM years, significant increases (decreases) in TC genesis are observed over a region spanning 20°–140°E, 0°–20°N (140°–160°E, 0°–20°N). In stochastic NPMM years, there are significant increases in TC genesis over a region spanning 135°–160°E, 5°–25°N. These changes in TC genesis can be explained by the anomalous environmental conditions in different NPMM years, which can be further linked to the NPMM's strength as well as sea surface temperature anomalies over the tropical western Pacific.