North Pacific Research Articles

Testing the feasibility of coral nurseries in an upwelling area in the North Pacific of Costa Rica

The decline of coral reefs has increased interest in ecological restoration. Due to the scarcity of coral gardening projects in the Eastern Tropical Pacific, improving our understanding of such techniques is key. We report the results of coral gardening using the branching Pocillopora spp. and massive coral species (Pavona gigantea, Pavona clavus and Porites lobata) in an upwelling area in Costa Rica. We examined whether nursery type influenced Pocillopora spp. survival and growth, and how environmental conditions shaped restoration. We monitored the survival and growth of Pocillopora spp. fragments (n = 334) and microfragments of massive species (P. gigantea [n = 148], P. clavus [n = 37], P. lobata [n = 66]) over 11 months. Survival at the end of the gardening period was 51% for Pocillopora spp., 59% for P. clavus, 55% for P. gigantea, and 17% for P. lobata, with a decline after a cease in maintenance caused by the COVID-19 lockdown. Pocillopora spp. fragments in the floating nurseries exhibited higher growth (7.52 ± 1.98 and 6.64 ± 2.91 cm yr-1) than in the A-frame (4.16 ± 2.35 cm yr-1), which suggests the benefits of suspending fragments. For massive microfragments coral growth was 1.92-4.66 cm2 yr-1 and were affected by pigmentation loss, causing partial tissue loss and mortality. Our results point towards acclimation to local conditions, and show the need to develop site-specific cost-efficient gardening techniques for massive species, allowing for a multi-species approach to ensure long-term ecosystem recovery.

Feeding habits of splendid alfonsino Beryx splendens in the vicinity of Kuroshio, the south of Japan

AbstractGut contents and nitrogen isotope ratio (δ15N) analyses were conducted on splendid alfonsino Beryx splendens collected in the vicinity of Kuroshio from May 2015 to November 2016 (n = 708) to identify their feeding habits in the Western North Pacific. Micronektonic fish, shrimp, and squid were the dominant prey species, with the Decapoda Acanthephyra quadrispinosa, Prehensilosergia prehensilis, Cephalopoda Enoploteuthis chunii, Chiroteuthis calyx, Teleostei Sigmops gracilis, and Gonostoma elongatum. These micronektons are common in the Kuroshio Current; thus, B. splendens is a possible opportunistic feeder. Gut content weight (GCW), occurrence (%O) of fish and squid, and δ15N were significantly increased with the fork length (FL) of B. splendens. Only the %O of shrimp does not show a significant relationship with the FL of B. splendens. These indicated the ontogenetic shift of dominant prey from shrimp to fish. Fattened specimens could also prey on a greater number of fish. The seasonality of GCW and %O values was high in spring and autumn and low in summer and winter. This seasonality indicated that the feeding habits of B. splendens are controlled by primary productivity in the surface layer and/or by maturity. When the Kuroshio flowed in the north of Hachijojima Island, the GCW was significantly increased, and some organisms, including C. calyx, G. elongatum, and S. gracilis, were preyed on more. While the offshore area of the Kuroshio has low productivity, B. splendens can actively prey in this area, indicating that it is an important feeding ground for this species.

Assessment of the Dynamical Linkages and Flow Evolution Governing Multiple Extreme Weather Events over Western North America in February 2019

Abstract We present an extended case study analysis based on observed extreme weather events (EWEs) and the planetary- and synoptic-scale variability of a persistent flow regime spanning the month of February 2019 across the North Pacific (NPAC) basin and western North America. The EWEs are clustered into two periods during February 2019: record cold and kona low conditions over Hawaii, lower elevation snow across Washington, and heavy AR-related rainfall in Southern California from 9 to 15 February; and heavy snow in Arizona and Oregon and heavy rainfall in Northern California from 21 to 28 February. From a weather regime perspective, the NPAC flow was dominated by a persistent ridge around 150°W, a retracted NPAC jet stream, repeated western NPAC (WPAC) cyclogenesis events, and frequent positively tilted troughs in the eastern NPAC and over western North America. Dynamically relevant features on the subseasonal-to-seasonal (S2S) time scale include a slowly propagating MJO signal in phases 6 and 7, a rapid NPAC jet retraction around 9 February, and subsequent eastward extension toward a climatological jet position around 21 February. On synoptic time scales, Rossby wave breaking on the southern flank of the NPAC jet and within the aforementioned persistent ridge led to the kona low formation and many of the positively tilted troughs responsible for the extreme precipitation events. In addition, frequent cyclogenesis west of the date line helped to maintain the persistent ridge strength and location through favorable heat and vorticity fluxes. The chronology and complex linkages between these aforementioned features and mechanisms are explained in depth in this paper. Significance Statement This study identified several extreme cold, rain, and snow events across the western contiguous United States and Hawaii, showed how these events are all connected to a persistent weather pattern upstream over the North Pacific basin, and identified key mechanisms for why the weather pattern was so persistent. Some of the physical mechanisms for keeping the weather pattern stagnant include anomalous convection within the tropics off the east coast of Asia, breaking waves in the atmosphere like waves breaking on a beach, and repeated cyclone development off the coast of Russia and Alaska. We hope that the results of this paper encourage others to look for similar mechanisms for similar stagnant weather patterns in a more holistic manner.

Spatiotemporal weighted neural network reveals surface seawater pCO2 distributions and underlying environmental mechanisms in the North Pacific Ocean

The North Pacific Ocean plays a pivotal role as a carbon sink within the global carbon cycle. However, a comprehensive understanding of the spatiotemporal dynamics of carbon dioxide concentration and its determinants in this domain remains elusive due to its vast dimensions and the intricacies of influencing factors, with previous research on carbon dioxide partial pressure in the North Pacific Ocean also being relatively scarce. While prevalent machine learning methodologies have been extensively applied to predict the partial pressure of ocean carbon dioxide (pCO2), their limited interpretability has impeded substantial progress in elucidating the underlying mechanisms. This study introduces a gridded spatiotemporal neural network weighted regression (GSTNNWR) model to illuminate temporal and spatial relationships among relevant environmental variables and pCO2. The GSTNNWR model achieves high-precision and high-resolution forecasts of surface pCO2 in the North Pacific Ocean, demonstrating commendable performance (R2 = 0.863 and RMSE=15.123 µatm). Simultaneously, we obtain a quantitative characterization of how various environmental factors influence pCO2 across different temporal and spatial scales. Results show a dominant positive effect of temperature on the pCO2, with an averaged normalized coefficient of 0.28, and variability in the effects of chlorophyll and salinity on the pCO2 at different spatial and temporal locations and temperatures, whose average normalized coefficients are −0.10 and −0.04.The findings of our study will provide insights into the mechanisms and interactions within the North Pacific carbon cycle, contributing to a better understanding of ocean carbon sink formation and the dynamic regulation of the North Pacific carbon cycle.

The complete mitochondrial genome of the leopard shark Triakis semifasciata (Triakidae)

ABSTRACT The leopard shark Triakis semifasciata (family Triakidae) is threatened by habitat loss and targeted by recreational and commercial fishermen in the Eastern Pacific Ocean, from Oregon, USA, to the Gulf of California, Mexico. Despite environmental issues, there are few genetic and genomic resources available for this species. This study assembled the complete mitochondrial genome of T. semifasciata from a skin metagenomic sample and described it in detail. The phylogenetic position of T. semifasciata amongst closely related species was also examined using mitochondrial protein-coding genes (PCGs). The mitochondrial genome of T. semifasciata is 16,613 bp in length and consists of 13 PCGs, two ribosomal RNA (rRNA) genes, and 22 transfer RNA (tRNA) genes. A 30 bp long region was identified as the origin of replication for the light strand (OL) between the trnN and trnC genes, and a 974 bp long putative control region (CR) contains the origin of replication for the heavy strand (OH). The gene order in T. semifasciata is identical to that of cofamilial species. An analysis of Ka/Ks ratios for all PCGs yielded values < 1, indicating that all PCGs experience strong purifying selection. All tRNAs exhibit a canonical ‘cloverleaf’ secondary structure except for tRNA-Ser1 which lacks the stem of the dihydrouridine (DHU) arm and in place possesses a simple loop. A phylomitogenomic maximum likelihood (ML) analysis did not support the monophyly of the family Trakidae and placed T. semifasciata in a sister position to Hemitriakis japanica. However, the aforementioned sister position was poorly supported by ML bootstrap values. This study represents a new genomic resource for this commercially and recreationally important species and confirms that mitochondrial genomes can be assembled from skin metagenomic samples as shown before in an unrelated shark species.

Aequorivita flava sp. nov., isolated from deep-sea sediments.

Three Gram-stain-negative, aerobic, non-motile, chemoheterotrophic, short-rod-shaped bacteria, designated CDY1-MB1T, CDY2-MB3, and BDY3-MB2, were isolated from three marine sediment samples collected in the eastern Pacific Ocean. Phylogenetic analysis based on 16S rRNA gene sequences indicated that these strains were related to the genus Aequorivita and close to the type strain of Aequorivita vitellina F4716T (with similarities of 98.0-98.1%). Strain CDY1-MB1T can grow at 15-37 °C (optimum 30 °C) and in media with pH 6-9 (optimum, pH 7), and tolerate up to 10% (w/v) NaCl. The predominant cellular fatty acids of strain CDY1-MB1T were iso-C15 : 0 (20.7%) and iso-C17 : 0 3-OH (12.8%); the sole respiratory quinone was menaquinone 6; the major polar lipids were phosphatidylethanolamine, two unidentified aminolipids and two unidentified polar lipids. The digital DNA-DNA hybridization/average nucleotide identity values between strains CDY1-MB1T, CDY2-MB3, and BDY3-MB2 and A. vitellina F4716T were 24.7%/81.6-81.7%, thereby indicating that strain CDY1-MB1T should represent a novel species of the genus Aequorivita. The genomic DNA G+C contents were 37.6 % in all three strains. Genomic analysis showed the presence of genes related to nitrogen and sulphur cycling, as well as metal reduction. The genetic traits of these strains indicate their possible roles in nutrient cycling and detoxification processes, potentially shaping the deep-sea ecosystem's health and resilience. Based upon the consensus of phenotypic and genotypic analyses, strain CDY1-MB1T should be classified as a novel species of the genus Aequorivita, for which the name Aequorivita flava sp. nov. is proposed. The type strain is CDY1-MB1T (=MCCC 1A16935T=KCTC 102223T).

Evolution of West‐East Contrast in the Subarctic Pacific Gyre During the Plio‐Pleistocene Based on Palynological Evidence at ODP Sites 882 and 887

AbstractFragmentary and contradictory evidence prevents a clear understanding of the possible role of the North Pacific Ocean surface on the ice‐sheet evolution. New palynological data encompassing the Pliocene and Pleistocene at Ocean Drilling Program Site 882 in the northwest Pacific document sea‐surface conditions from dinoflagellate cysts in addition to atmospheric trajectories from pollen grains and spores. The comparison of the Site 882 record with that of Site 887 from the northeast Pacific also permits documenting West to East contrasts across the subarctic North Pacific. The dinocyst assemblages at the two sites indicate strong temperature contrasts until 4.2 Ma, with much warmer conditions in the East. From 4.2 to 3.6 Ma, dinocyst assemblages of both sites are characterized by alternated dominance of the extinct taxa Habibacysta tectata and Impagidinium detroitense suggesting homogenous and cool conditions across the subarctic Pacific gyre. A major transition is recorded in the palynological assemblages at Site 882 around 2.7 Ma. It is marked by the highest occurrence of Habibacysta tectata and high percentages of Filisphaera microornata additionally to thermophilic taxa. Dinocyst record indicates high seasonality and warmer surface conditions due to reinforced stratification, which support the hypothesis of high evaporation at the origin of atmospheric moisture supply to high latitudes. During the last 1.2 Ma, the increase of Operculodinium centrocarpum relative to Nematosphaeropsis labyrinthus is tentatively interpreted as a reinforced influence of the subtropical waters. Hence, we suggest that the warm surface ocean fostered the inception and growth of northwestern North American ice‐sheets during the Pliocene and Pleistocene.

Calm Before the Storm?

Atlantic hurricane season poses an annual threat to the billions of dollars of oil and gas hardware pumping hydrocarbons from the depths of the US Gulf of Mexico (GOM). The region’s offshore production amounts to about 1.8 million B/D—roughly 14% of the total crude output in the US, according to the US Energy Information Administration, so any disruption is felt by oil markets across the globe. Prior to the 2024 hurricane season, forecasters pegged this year as primed to be particularly intense. Colorado State University (CSU), known for its storm prognostication, estimated that the basin would experience 23 named storms, with a dozen of those becoming hurricanes (winds of 74 mph or higher), and six of those strengthening to major hurricanes (winds of 111 mph or higher). Similarly, AccuWeather meteorologists expect between 20 and 25 named storms with a possibility of 30 or more. As the season enters its busy period, the basin has only experienced five named storms to date; however, many forecasters are sticking to their initial forecasts and continue to warn of an intense September/October period. “The months of September and October should be very active across the Atlantic,” said AccuWeather lead hurricane expert Alex DaSilva. “We continue to remain very concerned about rapid intensification. Sea-surface temperatures and ocean heat content are near record levels across most of the Atlantic basin. This can act like jet fuel for tropical systems. We also continue to believe that La Niña will emerge sometime in November. When water temperatures near the equator of the eastern Pacific Ocean are lower than the long-term historical averages for an extended period, La Niña is declared. Although this is a phenomenon in the Pacific, it has ramifications for weather patterns over the Atlantic Ocean. Specifically, La Niña can reduce the wind shear across the basin. When wind shear is lower, it makes it easier for tropical systems to take shape and strengthen.” The GOM has experienced one disruption in 2024 courtesy of Hurricane Beryl. Once a Category 5 storm (winds 155 mph and higher)—and the earliest-forming Category 5 storm on record—Beryl weakened as it crossed the southern Yucatán. The storm regained Category 1 strength as it crossed the far western offshore oil patch enroute to landfall near Matagorda Bay, Texas. Shell shut in production at its Perdido spar because of the storm as well as evacuated personnel from it and its Whale facility. Chevron moved all non-essential personnel off its Anchor floating production unit, which was undergoing commissioning at the time. The last major storm to cut a path straight through the heart of the US offshore oil patch was 2021’s Hurricane Ida. Ida tore through the region as a Category 4 storm before slamming into the Louisiana coast near Port Fourchon packing 150 mph winds on 29 August. The storm prompted the shut in of almost 100% of the Gulf’s oil and gas production and caused extensive damage to major hubs in the region, including the Shell-operated West Delta Block 143 complex. The facilities, which serve as the transfer station for production from Shell’s robust Mars corridor, were off line for several months.

Effect of atmospheric response induced by preceding typhoon on movement of subsequent typhoon over Northwestern Pacific

This study investigates the atmospheric interactions between two closely located typhoons in 2019. Typhoons in the Western Pacific significantly impact Eastern and Southeastern Asian countries, leading to various damages. As global warming is expected to increase typhoon intensity, accurate track forecasting becomes crucial for coastal disaster management. Despite the existing knowledge about the influence of typhoon activities on the atmospheric background, limited research addresses the atmospheric response between two typhoons. The study focuses on the cases of LEKIMA and KROSA, occurring simultaneously in 2019, and utilizes the Weather Research and Forecasting (WRF) model for simulations. The experimental setup involves comparing two scenarios: one with both typhoons and one with LEKIMA removed. Results reveal LEKIMA-induced distinctive atmospheric responses, including the closure of the western North Pacific subtropical high (WNPSH) boundary and the formulation of a wave train, influencing KROSA’s stagnation. The absence of LEKIMA allows KROSA to move more freely along the steering flow. Furthermore, the study highlights the potential of atmospheric models for understanding typhoon effects at regional to mesoscale levels. A comprehensive analysis of similar cases could enhance typhoon predictions, contributing to better damage mitigation strategies.

Statistical seasonal forecasting of tropical cyclone landfalls on Taiwan Island

Forecasting tropical cyclone (TC) activities has been a topic of great interest and research. Taiwan Island (TW) is one of the key regions that is highly exposed to TCs originated from the western North Pacific. Here, the authors utilize two mainstream reanalysis datasets for the period 1979–2013 and propose an effective statistical seasonal forecasting model—namely, the Sun Yat-sen University (SYSU) Model—for predicting the number of TC landfalls on TW based on the environmental factors in the preseason. The comprehensive predictor sampling and multiple linear regression show that the 850-hPa meridional wind over the west of the Antarctic Peninsula in January, the 300-hPa specific humidity over the open ocean southwest of Australia in January, the 300-hPa relative vorticity over the west of the Sea of Okhotsk in March, and the sea surface temperature in the South Indian Ocean in April, are the most significant predictors. The correlation coefficient between the modeled results and observations reaches 0.87. The model is validated by the leave-one-out and nine-fold cross-validation methods, and recent 9-yr observations (2014–2022). The Antarctic Oscillation, variabilities of the western Pacific subtropical high, Asian summer monsoon, and oceanic tunnel are the possible physical linkages or mechanisms behind the model result. The SYSU Model exhibits a 98% hit rate in 1979–2022 (43 out of 44), suggesting an operational potential in the seasonal forecasting of TC landfalls on TW.摘要本文利用1979–2013年的两个主流再分析数据集, 提出了一个中山大学 (SYSU) 热带气旋统计季节预报模型, 基于4个季前环境因子对登陆台湾岛的热带气旋数量进行预报. 模型通过了留一法, 九折交叉验证法和近9年观测数据 (2014–2022) 的验证, 模型结果与实际观测的相关系数达0.87. 南极涛动, 西太平洋副热带高压变化, 亚洲夏季风和海洋通道是模型潜在的物理联系或机制. SYSU模型在1979–2022年期间的预报准确率为98%, 表现出其业务应用价值.

Verification of Tropical Cyclogenesis Forecasts of the Korean Integrated Model for 2020–21

Abstract Accurate tropical cyclogenesis (TCG) prediction is important because it allows national operational forecasting agencies to issue timely warnings and implement effective disaster prevention measures. In 2020, the Korea Meteorological Administration employed a self-developed operational model called the Korean Integrated Model (KIM). In this study, we verified KIM’s TCG forecast skill over the western North Pacific. Based on 9-day forecasts, TCG in the model was objectively detected and classified as well-predicted, early formation, late formation, miss, or false alarm by comparing their formation times and locations with those of 46 tropical cyclones (TCs) from June to November in 2020–21 documented by the Joint Typhoon Warning Center. The prediction of large-scale environmental conditions relevant to TCG was also evaluated. The results showed that the probability of KIM detection was comparable to or better than that of previously reported statistics of other numerical weather prediction models. The intrabasin comparison revealed that the probability of detection in the Philippine Sea was the highest, followed by the South China Sea and central Pacific. The best TCG prediction performance in the Philippine Sea was supported by unbiased forecasts in large-scale environments. The missed and false alarm cases in all three regions had the largest prediction biases in the large-scale lower-tropospheric relative vorticity. Excessive false alarms may be associated with prediction biases in the vertical gradient of equivalent potential temperature within the boundary layer. This study serves as a primary guide for national forecasters and is useful to model developers for further refinement of KIM.

Tropical Cyclones in the GEOS-S2S-2 Subseasonal Forecasts

Abstract This paper analyzes the climatology, prediction skill, and predictability of tropical cyclones (TCs) in NASA’s Goddard Earth Observing System Subseasonal to Seasonal (GEOS-S2S) forecast system version 2. GEOS reasonably simulates the number and spatial distribution of TCs compared to observations except in the Atlantic where the model simulates too few TCs due to low genesis rates in the Caribbean Sea and Gulf of Mexico. The environmental conditions, diagnosed through a genesis potential index, do not clearly explain model biases in the genesis rates, especially in the Atlantic. At the storm scale, GEOS reforecasts replicate several key aspects of the thermodynamic and dynamic structures of observed TCs, such as a warm core and the secondary circulation. The model, however, fails to simulate an off-center eyewall when evaluating vertical velocity, precipitation, and moisture. The analysis of the prediction skill of TC genesis and occurrence shows that GEOS has comparable skill to other global models in WMO S2S archive and that its skill could be further improved by increasing the ensemble size. After calibration, GEOS forecasts are skillful in the western North Pacific and southern Indian Ocean up to 20 days in advance. A model-based predictability analysis demonstrates the importance of the Madden–Julian oscillation (MJO) as a source of predictability of TC occurrence beyond the 14-day lead time. Forecasts initialized under strong MJO conditions show evidence of predictability beyond week 3. However, due to model biases in the forecast distribution, there are notable gaps between the MJO-related prediction skill and predictability, which require further study.

Synergistic Forcing of the Troposphere and Stratosphere on Explosively Developing Cyclones Over the North Pacific During Cold Season

AbstractThe mid‐latitude extreme weather disasters are often associated with explosively developing cyclones (ECs). Based on different vertical development characteristics, 4,608 ECs identified over the North Pacific in the cold season of 44 years of NCEP‐CFSR reanalyzes are divided into four types of upward development and four types of downward development categories. ECs with vertical upward (downward) development follow a northeastward (nearly eastward) path, mainly explosively developing over the Northwest Pacific (Asia continent and Pacific). Furthermore, utilizing the piecewise potential vorticity inversion method reveals the synergetic forcing of the turbulent heat transport and baroclinicity in the lower troposphere, the latent heat release in the middle levels, the upper‐level jet stream, and the downward intrusion of stratospheric potential vorticity on the ECs. Different configurations of these influences from the troposphere to the stratosphere result in the occurrences of eight types of ECs in the cold season over the North Pacific.

Genomics resources for the Rapa Nui (Eastern Island) spiny lobster Panulirus pascuensis (Crustacea: Decapoda: Achelata)

BackgroundThe Easter Island spiny lobster Panulirus pascuensis (Reed, 1954) or ‘Ura’ in the Rapa Nui language, is a little known species native to the south eastern Pacific Ocean, distributed along the coasts of Easter Island, Pitcairn Island, and the Salas y Gómez Ridge. In Easter Island, P. pascuensis is the target of a small and profitable and probably overexploited fishery. In this study, we profited from a series of bioinformatic analyses to mine biological insight from low-pass short-read next generation sequencing datasets; we have estimated genome size and ploidy in P. pascuensis using a k-mer strategy, discovered, annotated, and quantified mobile elements in the nuclear genome, assembled the 45S rRNA nuclear DNA cassette and mitochondrial chromosome, and explored the phylogenetic position of P. pascuensis within the genus Panulirus using the signal retrieved from translated mitochondrial protein coding genes.ResultsK-mer analyses predicted P. pascuensis to be diploid with a haploid genome size ranging between 2.75 Gbp (with k-mer = 51) and 3.39 Gbp (with k-mer = 18). In P. pascuensis, repetitive elements comprise at least a half and a maximum of three fourths of the nuclear genome. Almost a third (64.94%) of the repetitive elements present in the studied nuclear genome were not assigned to any known family of transposable elements. Taking into consideration only annotated repetitive elements, the most abundant were classified as Long Interspersed Nuclear Elements (22.81%). Less common repetitive elements included Long Terminal Repeats (2.88%), Satellite DNA (2.66%), and DNA transposons (2.45%), among a few others. The 45S rRNA DNA cassette of P. pascuensis was partially assembled into two contigs. One contig, 2,226 bp long, encoded a partially assembled 5′ ETS the entire ssrDNA (1,861 bp), and a partial ITS1. A second contig, 6,714 bp long, encoded a partially assembled ITS1, the entire 5.8S rDNA (158 bp), the entire ITS2, the entire lsrDNA (4,938 bp), and a partial 3′ ETS (549 bp). The mitochondrial genome of P. pascuensis was 15,613 bp long and contained 13 protein-coding genes (PCGs), 22 transfer RNA (tRNA) genes, and two ribosomal RNA genes (12S ribosomal RNA [rrnS] and 16S ribosomal RNA [rrnL]). A phylomitogenomic analysis based on PCGs retrieved Panulirus pascuensis as sister to a fully supported clade comprising P. cygnus and P. longipes.ConclusionWe expect that the information generated in this study will guide the assembly of a chromosome-level nuclear genome for P. pascuensis in the near future. The newly assembled 45S rRNA nuclear DNA cassette and mitochondrial chromosome can support bioprospecting and biomonitoring of P. pascuensis using environmental DNA. The same elements can help to survey the public market place and detect mislabelling of this and other spiny lobsters. Overall, the genomic resources generated in this study will aid in supporting fisheries management and conservation strategies in this iconic spiny lobster that is likely experiencing overexploitation.

Quantifying the relative contributions of three tropical oceans to the western North Pacific anomalous anticyclone

Quantifying the relative contributions of three tropical oceans to the western North Pacific anomalous anticyclone

Increasing heat waves frequencies over India during post-El Niño spring and early summer seasons

The increasing frequency of extreme Heat Waves (HWs) has generated significant societal impacts in recent years. This study used different observational datasets to investigate the HW characteristics over India during the post-El Niño spring and early summer seasons (April to June; AMJ). Analysis suggests that HW days are more prevalent over India, predominantly increased in south-central and northwest India, during the decaying phase of strong El Niño years. It is found that anomalous anticyclone circulation accompanied by high pressure extending from the Western North Pacific region towards the Bay of Bengal and India is responsible for enhanced HW days and intensity during the AMJ of strong El Niño decay years. This anomalous anticyclone-induced downdraft reduces the specific humidity in the lower troposphere, leading to decreased cloud cover over India. As a result, shortwave radiation is enhanced at the surface, which causes abnormal HWs over India. During the decaying phase of strong El Niño years, the HW days over India contributed to an increase in the frequency of Discomfort Index hours (above 28 °C), maximum temperatures exceeding 40 °C (hours per day), and Universal Thermal Climate Index days above 38 °C and 46 °C during the spring and early summer months, especially in the East Coast, central, and northwestern parts of India. Thus, proper prediction of large-scale atmospheric circulation over the Indo-western Pacific region during El Niño can help to predict the HW conditions three months in advance. This would help to implement suitable adaptation measures and put into practice strong mitigation policies to limit the increased risk of such events during AMJ of El Niño decay years.

Global convection-permitting model improves subseasonal forecast of plum rain around Japan

Abstract In 2020 early summer, a historically severe rainy season struck East Asia, causing extensive damage to life and property. Subseasonal forecast of this event challenges the limits of rainy season predictability. Employing the integrated Atmospheric Model Across Scales (iAMAS) and the Sunway supercomputer, we conducted ensemble one-month forecasts at global 3 km, variable 4-60 km, and global 60 km resolutions. The global convection-permitting forecast accurately captures the rainband, while other forecasts exhibited northward and weaker shifts due to the northward shifts of the atmospheric rivers (ARs) over Japan, attributed to intensified Western North Pacific Subtropical High (WNPSH). Further, the double-ITCZ-like tropical rainfall pattern in Western Pacific (D-ITCZ-WP) in global convection-permitting forecast contributes to a more accurate WNPSH and rainband. In contrast, other forecasts show a single-ITCZ-like pattern in Western Pacific (S-ITCZ-WP), leading to a northward-shifted WNPSH and rainband, advocating the importance of accurately representing tropical convections, as they can significantly affect mid-/high-latitude weather and climate.

Analysis of oceanic suspended particulate matter in the western North Pacific using the complex amplitude sensor

Oceanic suspended particulate matter (SPM) plays important roles in the coupling of climate and biogeochemical cycles via ocean–atmosphere interactions. However, methods for quantifying the properties of SPM in seawater have not yet been well established. Here we present the application of the recently developed complex amplitude sensor (CAS) for analyzing the complex forward-scattering amplitude of individual SPM (0.2–5.0 µm in diameter) obtained at depths of 0–100 m during a research cruise in the western North Pacific. The measured distribution of the complex amplitude indicated that the CAS-derived SPM data could be roughly classified into five major types. Comparison with reference sample’s complex amplitude data and scanning electron microscopy analysis suggested that these types could be attributed mainly to diatom fragments, carbonaceous materials (likely organic matter), mineral dusts, iron oxides, or black carbon. Depth profiles revealed that relatively high concentrations of SPM, presumably dominated by diatom fragments and carbonaceous materials with peak diameters of 0.7–1.0 µm, were typically associated with elevated turbidities and chlorophyll a concentrations. Based on this case study, we discuss the practical advantages and limitations of using the CAS to measure size-resolved concentrations of SPM in seawater and to characterize its composition.

Observed APO Seasonal Cycle in the Pacific: Estimation of Autumn O2 Oceanic Emissions

AbstractIn this work, we investigated the seasonal cycle of atmospheric potential oxygen (APO), a unique tracer of air‐sea gas exchanges of molecular oxygen (O2) and carbon dioxide (CO2), expressed as APO = O2 + 1.1 × CO2. APO data were obtained from flask air samples collected since the late 1990s at three Japanese ground stations and on commercial cargo ships sailing between Japan and Australia/New Zealand, North America, and Southeast Asia. We also analyzed the APO spatial distribution and seasonal cycles with simulations from an atmospheric transport model using climatological oceanic O2 fluxes from an empirical product that relate O2 flux to ocean heat as input. Model simulations reproduced the observed APO seasonal cycles generally well, but with larger amplitudes and earlier occurrence of seasonal minima and maxima than in the observations. Moreover, the observed seasonal cycles exhibited larger APO enhancements than the simulations in autumn and early winter, especially in the North Pacific at 20°N–60°N. These enhancements remained when refining the comparison by adjusting the simulated APO peak‐to‐peak amplitudes and seasonal phases to the observations. This suggests additional O2 emissions in the North Pacific, not well expressed in the air‐sea O2 fluxes used as input for our model simulations. The average autumn enhancement at 40°N–60°N was approximately twice that measured at 20°N–40°N. Confirming previous studies, our results indicate two distinct mechanisms possibly contributing to the additional oceanic O2 emissions: outgassing from a subsurface shallow oxygen maximum at 20°N–40°N and autumn phytoplankton bloom at 40°N–60°N.

Ocean windspeeds forecast by Gaidai multivariate risk assessment method, utilizing deconvolution scheme

The current work presents spatiotemporal analysis of areal windspeeds, using state-of-the-art Gaidai multivariate hazards evaluation approach. Environmental dynamic systems being challenging to forecast using existing reliability methods due to their high dimensionality and intricate nonlinear cross-correlations between different environmental system essential dimensions or components. Developing novel multivariate reliability methods for dynamic environmental systems may assist contemporary research on the global climate change effects. Multivariate Gaidai risks evaluation approach is especially well-suited for multi-dimensional structural and environmental dynamic systems, that have been monitored physically or numerically simulated across a representative time-lapse. The current study made use of raw in-situ windspeed data, collected by NOAA (i.e., National Oceanic and Atmospheric Administration) buoys near the Hawaiian Islands in the North Pacific. Resilient island communities/infrastructure can be designed, using advocated multivariate risk/hazard assessment methodology, particularly those that are close to the ocean and hence subject to extreme weather.As was demonstrated in this study, even given limited underlying dataset, it is feasible to conservatively estimate environmental system’s hazard risks. Novel non-parametric deconvolution extrapolation scheme has been utilized to accurately assess hazard risks.