Tropical Pacific Ocean Research Articles

Exploring the Symmetries of Pantropical Connections between the Tropical Atlantic and Pacific Basins

Abstract Recent analysis of pantropical interactions suggests that after 1980 the tropical Atlantic Ocean’s (TAO) influence on the tropical Pacific Ocean (TPO) appears to have become much more pronounced while the tropical Indian Ocean’s (TIO) influence appears to have weakened. This study explores whether and how decadal changes in TAO and TPO SSTs modulate these pantropical connections in an attempt to explain the recent dominance of the TAO. To this end, we carry out a series of idealized atmosphere-only experiments using the ACCESS atmospheric general circulation model where the magnitude and sign of the decadal TAO SST signal are varied, presenting various warm and cool Atlantic scenarios. To understand further if these pantropical connections are influenced by changes in TPO SST, we carry out the above TAO experiments with both warm and cool phases of Pacific decadal variability (PDV). We find that an imposed TAO warming leads to increases in TPO atmospheric temperature and stability, which lead to a decrease in average TPO precipitation, with the most prominent changes occurring in June–August. These changes in TPO precipitation induced by TAO warming are largely mirrored when TAO cooling is added, whereas the TPO rainfall response to TAO anomalies remains relatively unchanged for the different phases of PDV. In contrast to the precipitation response, the wind response did display some asymmetries between different phases of TAO SST variability. Specifically, surface winds in the western half of the Niño-4 region exhibited a significantly different response to positive versus negative Atlantic multidecadal variability (AMV), whereas the surface winds in the western equatorial Pacific were significantly stronger (roughly 40% larger) in the positive phase of PDV than in the negative phase. These results suggest that the phases of PDV and AMV may modulate pantropical interactions through their effect on zonal wind stress.

Response of ocean climate to different heat-flux perturbations over the North Atlantic in FAFMIP

The diversity of surface-flux perturbations, especially for heat-flux perturbations, notably leads to uncertainties surrounding the responses of ocean climate under global warming scenarios projected by climate/Earth system models. However, when imposing heat-flux perturbations on the models, strong feedback persists between the atmosphere and the ocean, resulting in nearly doubled heat-flux perturbation over the North Atlantic (NA). Herein, quantitative evaluation of the influences of magnitude change of heat-flux perturbations over the NA on the changes in the Atlantic Meridional Overturning Circulation (AMOC), ocean heat uptake (OHU) and dynamic sea level (DSL) has been conducted by analysis of eight coupled model responses to the heat-flux perturbation experiments in the Flux-Anomaly-Forced Model Inter-comparison Project. It has been demonstrated that the magnitude of the AMOC change is extremely sensitive to the magnitude change of imposed NA heat-flux perturbation, and the weakening amplitude of the AMOC is nearly halved as the imposed heat-flux perturbation F is halved over the NA. The most remarkable responses of both DSL and OHU to the magnitude changes of NA heat-flux perturbation have been primarily found in the Atlantic and Arctic basins, especially for the NA region. Both the added ocean heat uptake (OHUa) and redistributed ocean heat uptake (OHUr) play key roles in OHU changes among the various NA heat-flux perturbation experiments. The magnitude change of NA-mean OHUa is almost linearly related to the imposed NA heat-flux perturbation, while the magnitude change of NA-mean OHUr, which is primarily caused by AMOC change and redistributed heat flux, is not proportional to the imposed NA heat-flux perturbation. There is a nearly linear relationship between the magnitude of AMOC change and the OHUr in tropical regions, including the regions in the low-latitude South Atlantic, the tropical Pacific Ocean and the Indian Ocean.

The role of shallow and deep circulations in the Tropical Pacific Ocean heat budget

The Tropical Pacific Ocean plays an important role in setting the global ocean heat content and redistribution. We examined the role of the shallow and deep circulations in the tropical Pacific in unperturbed and transient climate change conditions in a global ocean model. We found that, in the Control state, the shallow circulation is by far the largest contributor to the overall balance of the column, where the balance is set as the residual between advective cooling and warming by vertical diffusive mixing. Subject to surface flux perturbations, changes in the tropical Pacific ocean heat budget can be explained by shallow wind-driven overturning circulation changes. For wind stress anomalies, the shallow ocean heat budget imbalance is directly related to overturning circulation changes, whereas under heat flux perturbations, warming of the shallow ocean is related to strengthened mid-latitude subduction and weakened dense water production at higher latitudes.

Taxonomy and molecular phylogenetic position of new species and new records of Coelosphaeridae (Demospongiae: Poecilosclerida) from the Mexican Pacific

Abstract Poecilosclerida is the largest and the most diverse order in the class Demospongiae and one of the least studied in the tropical Pacific Ocean. In this study, two new species and two new faunistic records of Coelosphaeridae are described from the Mexican Pacific Ocean. Celtodoryx chichiltik sp. nov. and Lissodendoryx (Anomodoryx) incrustans sp. nov. also constitute the first records of the monotypic genus Celtodoryx and the subgenus Anomodoryx from the Eastern Pacific Region. In addition, the re-description of Lissodendoryx (Waldoschmittia) hawaiiana and Lissodendoryx (Lissodendoryx) albemarlensis with new regional records are included. The cytochrome c oxidase subunit I (COI) mtDNA and 28S rDNA (C1–D2 domains) were sequenced, and molecular phylogenetic analyses of the two loci revealed that Coelosphaeridae is not monophyletic. In the 28S tree topology, neither Lissodendoryx nor Celtodoryx are monophyletic, and sequences of the two genera are members of two distinct clades containing sequences of other Poecilosclerida species. 28S sequences of L. (W.) hawaiiana show high similarities between specimens from the Mexican Pacific and a specimen from Hawaii (type locality), suggesting a wide distribution range of this sponge species in the Pacific Ocean. COI topology shows that the majority of Lissodendoryx (including our sequences) were grouped within the same molecular clade.

Movement behavior of swordfish provisions connectivity between the temperate and tropical southwest Pacific Ocean

Swordfish (Xiphias gladius) are a widely distributed (45°N–45°S) large pelagic fish targeted by fisheries worldwide. Swordfish that occur at high latitudes tend to disproportionately be large adults, so their movements have implications for population dynamics and fisheries management. In the southwest Pacific, little is known about this subset of the stock and existing evidence suggests limited movement from the subtropics into cooler high latitude waters. Here, we capitalize on the recent emergence of a recreational swordfish fishery off temperate southeast Australia to characterize movements of swordfish caught in the fishery with pop-up satellite archival transmitting tags. Data were recovered from tags deployed for 56–250 days on 11 swordfish (50–350 kg) tagged between 38 and 43°S in the western Tasman Sea. Five swordfish entered the Coral Sea (< 30°S), with four reaching north to 11–24°S, up to 3275 km away from location of capture. Behavior modelling suggests these four individuals rapidly transited north until encountering 23–27 °C water, at which point they lingered in the area for several months, consistent with spawning-related partial migration. One migrating swordfish still carrying a tag after the spawning season returned to ~ 120 km of its release location, suggesting site fidelity. Movements toward the central south Pacific were confined to two individuals crossing 165°E. Swordfish predominantly underwent normal diel vertical migration, descending into the mesopelagic zone at dawn (median daytime depth 494.9 m, 95% CI 460.4–529.5 m). Light attenuation predicted daytime depth, with swordfish rising by up to 195 m in turbid water. At night, swordfish were deeper during the full moon, median night-time depth 45.8 m (37.8–55.5) m versus 18.0 m (14.9–21.8) m at new moon. Modelling fine-scale (10 min−1) swordfish depth revealed dynamic effects of moon phase varying predictably across time of night with implications for fisheries interactions. Studying highly migratory fishes near distribution limits allows characterization of the full range of movement phenotypes within a population, a key consideration for important fish stocks in changing oceans.

Contrasting responses of the ocean’s oxygen minimum zones to artificial re-oxygenation

Studies assessing potential measures to counteract the marine deoxygenation attributed to anthropogenic activities have been conducted in a few coastal environments and at regional scale, but not yet on a global scale. One way toward global scale artificial oxygenation would be to use oxygen produced as a by-product from hydrogen-production through electrolysis. The low-carbon footprint renewable production of hydrogen from offshore wind energy offers such a possibility. Here, we assessed the potential of this artificial oxygenation method on a global scale using a coupled physical-biogeochemical numerical model. The anthropogenic oxygen source scenario assumes worldwide adoption of hydrogen, considering demographic changes and the feasibility of offshore wind turbine deployment. Following this scenario, artificial oxygenation had a negligible effect on the overall oxygen inventory (an increase of 0.07%) but showed a reduction in the overall volume of Oxygen Minimum Zones (OMZs) between 1.1% and 2.4%. Despite the decrease in the mean OMZ volume globally, OMZs display distinct and contrasting regional patterns notably due to the oxygen impacts on the nitrogen cycle. Artificial oxygenation can inhibit denitrification resulting in a net gain of nitrate that promotes locally and remotely increased biological productivity and consequent respiration. Increased respiration could ultimately lead to an oxygen loss at and beyond injection sites as in the Tropical Pacific and Indian Ocean and particularly expand the Bay of Bengal OMZ. In contrast, the tropical OMZ shrinkage in the Atlantic Ocean is attributed to oxygen enrichment induced by advective transport into the OMZ, while the absence of denitrification in this area precludes any biochemical feedback effect on oxygen levels. These results suggest that the impacts of artificial oxygenation on oxygen concentrations and ecosystems are highly non-linear. It can produce unexpected regional responses that can occur beyond the injection sites which make them difficult to forecast.

Response of the tropical Pacific Ocean to wind changes related to global warming from simulations with an ocean general circulation model

A suite of numerical experiments is implemented with an ocean general circulation model (OGCM) to ex-amine the roles of wind stress and wind speed for oceanic changes in the tropical Pacific under global warming. In particular, we turned off the changes of wind stress and/or wind speed in the model to identify the effects of wind-driven ocean circulation and air-sea latent heat flux (i.e., its portion through the wind speed influence on the efficiency of latent heat flux). Results show that 1) the wind stress change appears to be a key forcing mechanism for weakening the tropical surface currents as well as for the oceanic changes in the equatorial thermocline, while it only contributes secondarily to the sea surface temperature (SST) pattern formation in the tropics; 2) the wind speed change is the leading cause for the minimum warming over the southeast subtropics and for a stronger surface warming in the northern hemisphere than in the southern hemisphere; and 3) the enhanced surface warming along the equator is mainly due to the effect of warming in the absence of wind stress and wind speed changes, and this effect also plays a significant role for changing the equatorial thermocline.

Resolving the Tropical Pacific/Atlantic Interaction Conundrum

AbstractUnderstanding the interaction between the tropical Pacific and Atlantic Oceans has challenged the climate community for decades. Typically, boreal summer Atlantic Niño events are followed by vigorous Pacific events of opposite sign around two seasons later. However, incorporating the equatorial Atlantic information to variabilities internal to the Pacific lends no significant additional predictive skill for the subsequent El Niño‐Southern Oscillation (ENSO). Here we resolve this conundrum in a physically consistent frame, in which the nascent onset of a Pacific event rapidly induces an opposite‐signed summer equatorial Atlantic event and the lead correlation of Atlantic over Pacific is a statistical artifact of ENSO's autocorrelation. This Pacific‐to‐Atlantic impact is limited to a short window around late spring due to seasonally‐amplified Atlantic atmosphere‐ocean coupling. This new frame reconciles the discrepancies between the observed and multi‐model simulated inter‐basin relationship, providing a major advance in understanding seasonally‐modulated inter‐basin climate connections as well as their predictability.

Correcting Subseasonal Forecast Errors with an Explainable ANN to Understand Misrepresented Sources of Predictability of European Summer Temperatures

Abstract Subseasonal forecasts are challenging for numerical weather prediction (NWP) and machine learning models alike. Forecasting 2-m temperature (t2m) with a lead time of 2 or more weeks requires a forward model to integrate multiple complex interactions, like oceanic and land surface conditions leading to predictable weather patterns. NWP models represent these interactions imperfectly, meaning that in certain conditions, errors accumulate and model predictability deviates from real predictability, often for poorly understood reasons. To advance that understanding, this paper corrects conditional errors in NWP forecasts with an artificial neural network (ANN). The ANN postprocesses ECMWF extended-range summer temperature forecasts by learning to correct the ECMWF-predicted probability that monthly t2m in western and central Europe exceeds the climatological median. Predictors are objectively selected from ECMWF forecasts themselves, and from states at initialization, i.e., the ERA5 reanalysis. The latter allows the ANN to account for sources of predictability that are biased in the NWP model itself. We attribute ANN corrections with two explainable artificial intelligence (AI) tools. This reveals that certain erroneous forecasts relate to tropical western Pacific Ocean sea surface temperatures at initialization. We conjecture that the atmospheric teleconnection following this source of predictability is imperfectly represented by the ECMWF model. Correcting the associated conditional errors with the ANN improves forecast skill. Significance Statement We want to understand occasions in which a numerical weather prediction (NWP) model fails to forecast a predictable event existing in the real world. For forecasts of European summer weather more than 2 weeks in advance, real predictable events are rare. When misrepresented by the model, predicted future states become needlessly biased. We diagnose these missed opportunities with an explainable neural network. The neural network is aware of the initial state and learns to correct the NWP forecast on occasions when it misrepresents a teleconnection from the western tropical Pacific Ocean to Europe. The explainable architecture can be useful for other applications in which conditional model errors need to be understood and corrected.

GEFSv12 High- and Low-Skill Day-10 Tornado Forecasts

Abstract On average, modern numerical weather prediction forecasts for daily tornado frequency exhibit no skill beyond day 10. However, in this extended-range lead window, there are particular model cycles that have exceptionally high forecast skill for tornadoes because of their ability to correctly simulate the future synoptic pattern. Here, model initial conditions that produced a more skillful forecast for tornadoes over the United States were exploited while also highlighting potential causes for low-skill cycles within the Global Ensemble Forecasting System, version 12 (GEFSv12). There were 88 high-skill and 91 low-skill forecasts in which the verifying day-10 synoptic pattern for tornado conditions revealed a western U.S. thermal trough and an eastern U.S. thermal ridge, a favorable configuration for tornadic storm occurrence. Initial conditions for high skill forecasts tended to exhibit warmer sea surface temperatures throughout the tropical Pacific Ocean and Gulf of Mexico, an active Madden–Julian oscillation, and significant modulation of Earth-relative atmospheric angular momentum. Low-skill forecasts were often initialized during La Niña and negative Pacific decadal oscillation conditions. Significant atmospheric blocking over eastern Russia—in which the GEFSv12 overforecast the duration and characteristics of the downstream flow—was a common physical process associated with low-skill forecasts. This work helps to increase our understanding of the common causes of high- or low-skill extended-range tornado forecasts and could serve as a helpful tool for operational forecasters. Significance Statement This research provides a framework for the anticipation of a more (or less) skillful 10-day tornado forecast in an operational numerical weather prediction system. High-skill forecasts were associated with substantial tropical convection and warm sea surface temperature throughout the Pacific Ocean and Gulf of Mexico, whereas the underlying cause of low-skill forecasts were typically associated with a blocking anticyclone over eastern Russia. These findings are important because they permit increased or decreased confidence in a long-range forecast of tornado occurrence based on a dynamical prediction system.

Automatic Detection of Rainfall at Hourly Time Scales from Mooring Near-Surface Salinity in the Eastern Tropical Pacific

Abstract We explore the use of ocean near-surface salinity (NSS), that is, salinity at 1-m depth, as a rainfall occurrence detector for hourly precipitation using data from the Salinity Processes in the Upper-Ocean Regional Studies–2 (SPURS-2) mooring at 10°N, 125°W. Our proposed unsupervised learning algorithm consists of two stages. First, an empirical quantile-based identification of dips in NSS enables us to capture most events with hourly averaged rainfall rate of &gt;5 mm h−1. Overestimation of precipitation duration is then corrected locally by fitting a parametric model based on the salinity balance equation. We propose a local precipitation model composed of a small number of calibration parameters representing individual rainfall events and their location in time. We show that unsupervised rainfall detection can be formulated as a statistical problem of predicting these variables from NSS data. We present our results and provide a validation technique based on data collected at the SPURS-2 mooring. Significance Statement Continuous monitoring of precipitation in the ocean is challenging when a physical rain gauge is not available in the region of interest. Indirect detection of precipitation using available data, such as changes in ocean near-surface salinity (NSS) can be used to construct a virtual rainfall detector. We propose to combine data-based and model-based methods to detect rainfall without the use of a physical rain gauge. We use NSS and precipitation data from a mooring in the eastern tropical Pacific Ocean to develop and test the method.

Balancing Volume, Temperature, and Salinity Budgets During 2014–2018 in the Tropical Pacific Ocean State Estimate

AbstractA state estimate of the tropical Pacific Ocean is used to analyze regional volume, temperature, and salinity budgets during 2014–2018. The simulated ocean state is constrained by both model dynamics and assimilated observations. Comparisons with independent mooring data show that the state estimate is consistent with the observed variability in temperature and velocity. Budgets are analyzed between 5°S and 5°N in the upper 300 m, inside a box defined to represent the central and eastern equatorial Pacific. Transports through the faces of this box are quantified to understand the processes responsible for variability in box‐mean properties. Vertical mixing across 300 m is negligible; temperature and salinity tendencies are balanced by surface fluxes and advective divergence, which is decomposed into geostrophic and ageostrophic components. The onset and recovery of the 2015/2016 El Niño event is found to be dominated by anomalous surface fluxes and horizontal advection. During the onset phase, weaker trade winds cause the shallow meridional overturning circulation to slow down, which reduces the poleward transport of heat and leads to upper ocean warming. Anomalous precipitation and advection of fresh water from the western Pacific drive the net freshening of the region. Relaxation from El Niño conditions is dominated by wind‐driven meridional advection at 5°N. As the meridional advection regains strength, Ekman advection efficiently exports the warm, fresh surface water out of the equatorial region. Quantifying the heat and salt transport changes in response to wind variability strengthens our understanding of global ocean heat transport.

Dynamic and thermodynamic causes of summer extreme precipitation over South China

The summer days between 1961 and 2017 are divided into two categories: extreme precipitation days (EPDs) and general precipitation days (GPDs). Compared to GPDs, on EPDs, South China (SC) is affected by a local trough in the lower troposphere and the East Asian subtropical westerly jet (EAWJ) is strengthened in the upper troposphere. The anomalous extension of the western Pacific subtropical high (WPSH) in the South China Sea (SCS) is a key of EPDs. The reason for the extension of WPSH is due to a Kelvin wave-induced Ekman divergence (WIED) response to the SST anomaly zonal contrast between the tropical Indian Ocean (TIO) and tropical Pacific Ocean (TPO). The vertical velocity gradient ∂ω/∂p anomaly in accord with Sverdrup vorticity balance plays a secondary reinforcing role. Utilizing the quasi-geostrophic omega (QG ω) equation, the quantitative contributions of the dynamic term ωD and thermodynamic term ωQ are examined. On EPDs, the ωQ term over SC has the largest contribution to total ω, accounting for 46.2%, while the ωD term accounts for only 16.7%. The variation of ωQ is the main contributor to the variation of ω within different precipitation ranges, with time and with vertical levels. Water vapor plays a crucial role in adiabatic heating. The moisture budget analysis suggests that water vapor transport is significantly converted into precipitable water from 3 days before EPDs, increasing the humidity of the atmosphere and providing favorable conditions for adiabatic heating.

Wind work on oceanic mesoscale eddies in the Northeast Tropical Pacific Ocean

The transfer of atmospheric kinetic energy to the ocean is one of the major concerns in climate research. According to previous studies, the work of wind stress on oceanic mesoscale eddy is negative in most oceans, referred to as “eddy killing”. However, another recent work, finds that the wind work on an eddy varies with interaction time. To better understand the wind work on eddies, the present study uses satellite remote sensing wind stress data and eddy data from 2000 to 2021 to investigate the effects of wind stress on eddies in the northeast tropical Pacific (NETP). The study demonstrates that the work done by the wind stress on eddies in this region varies seasonally and that there is a strong spatiotemporal link between the work done and the wind stress curl. The work of wind stress with positive (negative) curl on the entire area of a cyclonic eddy is positive (negative), and vice versa on an anticyclonic eddy. These results indicate that wind energy input is sensitive to wind stress curl, and eddies do not always hinder wind energy input in this area.

Variability in billfish vertical distribution and fishing interactions driven by environmental conditions in the Eastern Tropical Pacific Ocean

Abstract Blue marlin (Makaira nigricans) and sailfish (Istiophorus platypterus) are ecologically important predators and valuable species throughout the world’s recreational, commercial, and subsistence fisheries. Comparing multi-species vertical habitat use can inform ecological uncertainties such as inter-species competition, as well as relative vulnerabilities to fishing activities. In this study, we identified key differences in both depth use and which environmental variables drive these selections, which highlights the variability in the catchability both as target species in recreational fisheries and bycatch in commercial fisheries. To understand these two species’ vertical habitat use, we examined depth profiles from 26 sailfish and 48 blue marlin tagged with pop-up satellite archival tags deployed in the Eastern Tropical Pacific Ocean. While both species are surface-oriented, we found evidence of vertical niche partitioning where sailfish spend more time at deeper depths than blue marlin. Blue marlin recorded an average mean depth of 18.5 m (±10.8 m) during daytime and 5.2 m (±5.5 m) at nighttime (Figure 31a), while sailfish recorded an average mean depth of 23.6 m (±11.1 m) during daytime and 6.45 m (±4.64 m) at nighttime. Generalized additive mixed models fitted to predict mean and max depth revealed sea level anomaly (SLA), oxygen, sea surface temperature, and mixed layer depth as significant predictors of vertical habitat use for both species. We also examined catch logs from three recreational fishing lodges in Central America to understand the influence of environmental conditions on billfish sightings per unit effort. For blue marlin and sailfish, SLA was a significant predictor in each of the four depth models (mean day, mean night, max day, max night). SLA was the variable with highest percent deviance explained for all four sailfish depth models and three of the four blue marlin depth models and had a positive relationship with all response variables for all four blue marlin depth models and three sailfish depth models (mean daytime, max daytime, max nighttime), where higher positive SLA values were associated with deeper depth responses.

IONOSPHERIC TOTAL ELECTRON CONTENT VARIATIONS CAUSED BY THE TONGA VOLCANO EXPLOSION ON JANUARY 15, 2022

The capability of volcanoes to generate powerful explosive eruptions influencing the state of the ionosphere became known back in the 1980th. The Hunga-Tonga-Hunga-Ha’apai (Tonga for short) volcano explosion on January 15, 2022, has shown a surge of renewed interest in investigating effects in the Earth — atmosphere — ionosphere — magnetosphere system since this volcano can be rightfully classified as unique. A number of papers have already dealt with the ionospheric effects generated by the Tonga volcano. The temporal variations in the total electron content (TEC) were used to determine the number of volcano explosions to be five. The second and third explosions were the strongest, with the second being the most intense. The response of the ionosphere to the Tonga volcano explosion has been studied on local and global scales by making use of the Global Positioning System satellite constellation and measurements onboard the Swarm satellite network. In the vicinity of the volcano explosion, disturbances in TEC attained 5—10 TECU. In addition to the local effect, traveling ionospheric disturbances were observed to propagate, which were due to the generation and propagation of atmospheric gravity waves with speeds of 180 m/s to 1,050 m/s. Of particular importance to global-scale perturbations is the Lamb wave, which propagated with a speed of 315 m/s. At nighttime, plasma depletions of the equatorial ionosphere were revealed over the tropical Pacific Ocean when the electron density at 400—500 km altitude showed a decrease by 2-3 orders of magnitude. The length of these formations in longitude exceeded ~10 Mm, and they were observed for more than 4—5 h. The scientific objective of this study is further analysis of aperiodic and quasi-periodic perturbations in the ionosphere, which were caused by the Tonga volcano explosion, in a wide range of distances from the source of disturbance (from ~0.1 Mm to 5 Mm). To reveal the ionospheric response to the Tonga volcano explosion, the records of signals from Global Positioning System satellites have been analyzed. The intercomparison of temporal variations in TEC observed on the reference days and on the day when the volcano explosion occurred has resulted in the determination of basic principles of the generation of ionospheric perturbations and the estimation of numerical magnitudes of the parameters of the perturbations. Four groups of disturbances have been detected, each of which arrived at different time delays with respect to the moment of the volcano explosion. It is important to note that the time delay increases with increasing distance from the volcano to the observational instruments. The first group of speeds included the disturbances traveling with a speed close to 1,000 m/s and having an N-shaped profile. This perturbation was generated by a blast wave whose speed depended on the excess pressure and a priori exceeded the speed of sound. In the second group, the speed varied in the 336 m/s to 500 m/s range, within which the speeds of atmospheric gravity waves are found. The speeds in the third group exhibited variability within the 260—318 m/s limits, within which the Lamb wave propagates. The speed in the fourth group was estimated to be 190—220 m/s, which is a characteristic speed of the tsunami that was caused directly by the volcano explosion. The period of quasi-periodic perturbations varied from ~10 min to 20 min, while their amplitudes were from 0.5 TECU to 1 TECU. The observed ionospheric «hole» was proved to be produced by the volcano explosion directly, with the modules of the absolute and relative magnitudes of disturbances showing a tendency for decreasing with increasing distance from the explosion epicenter, from ~10 TECU to 2 TECU and from 37 % to 7 %, respectively. Contrary to the amplitude, the «hole» time delay and its duration exhibited an increase with distance from the volcano to the observational sensors, from 35 min to 100 min and from ~ 30—40 min to 120— 150 min, respectively. A mechanism for generating the ionospheric «hole» has been advanced, which is based on both the electric and non-electric processes (cracking, the friction of particles, condensation of water vapor, coagulation of water droplets, attachment of electrons, gravity segregation, etc.). The ionospheric «hole» is formed as a result of perturbing the global electric circuit, arising external electric currents, an increase in the electric field strengths by orders of magnitude in the atmosphere and the ionosphere, diffusion of the ionospheric plasma down to lower altitudes where the recombination processes become fast. The basic numerical characteristics have been established of the disturbances, whose fluctuations account for local time, the dusk terminator, sensor geographic locations, the location of subionospheric points on the satellite to receiver ray paths with respect to the equatorial anomaly, etc.

Morphology and molecular phylogeny of Pleurosigmapacificum sp. nov. (Pleurosigmataceae), a new tropical pelagic species from the Western Pacific Ocean.

A new species of pelagic diatom, Pleurosigmapacificumsp. nov., is described from the tropical Western Pacific Ocean. It has the typical features of Pleurosigma, including a slightly sigmoid raphe, intersected transverse and oblique striae, and loculate areolae with external opening slits and internal poroids. Morphologically, P.pacificum belongs to a species group of Pleurosigma with lanceolate valves, including P.atlanticum Heiden & Kolbe, P.nubecula W. Smith, P.indicum Simonsen, and P.simonsenii Hasle. However, P.pacificum differs by its smaller lanceolate valve and smaller intersection angle as well as elliptical areolae without a silica bar. The SSU rDNA and rbcL sequence data place P.pacificum in a basal position relative to other species of Pleurosigma. Our molecular phylogenetic analyses did not support the monophyly of lanceolate and slightly sigmoid species. Thus, the sigmoidality of valve outline cannot be considered as a criterion to define the species group.

A Trans-Season Out-of-Phase Relationship of Tropical Cyclogenesis between the Western North Pacific and South China Sea

Abstract The present study investigates the relationship of tropical cyclone (TC) genesis between the western North Pacific (WNP) and South China Sea (SCS) from 1979 to 2020. A significantly out-of-phase variation is found between spring [March–May (MAM)] TC genesis over the WNP and the following summer–fall [June–November (JJASON)] TC genesis over the SCS. More TCs over the WNP in MAM are followed by fewer TCs over the SCS in the succeeding JJASON. Composite analysis and numerical model experiments show that negative sea surface temperature (SST) anomalies during MAM in the tropical central-eastern Pacific (CEP) and southeastern Indian Ocean work together to induce a lower-level cyclonic circulation over the WNP, with the latter more important. The positive specific humidity and ascending motion favor the TC genesis over the WNP in MAM. In the following JJASON, the SST anomalies are reversed in the tropical CEP. The positive precipitation anomalies over the western-central Pacific induced by positive SST anomalies further stimulate an anomalous zonal overturning circulation with anomalous descending motion and boundary layer divergence over the SCS. In addition, the persistent negative SST anomalies around the Maritime Continent (MC) induce an anomalous anticyclone to the west. Both processes lead to negative genesis potential index (GPI) anomalies and thus inhibit the TC genesis over the SCS. This out-of-phase relationship of TC genesis between the WNP and SCS also exists when the El Niño–Southern Oscillation (ENSO) transition years are removed. This finding may be helpful to improve the seasonal prediction of the SCS TC activity over the peak TC season.

Impacts of seasonal variations of the Tropical Pacific ocean temperatures on upper ocean oxygen response

The El Niño–Southern Oscillation (ENSO) is the most dominant natural variability in the Earth system, which represents seasonal-to-interannual variations of the surface equatorial Pacific Ocean temperatures and subsurface ocean interior. Impacting the physical upper ocean characteristics, ENSO exerts significant influences on the marine ecosystem, such as oxygen and phytoplankton concentrations via strong quasiperiodic oscillation between El Niño (warm phase) and La Niña (cold phase) events. The present study uses observational reanalysis and satellite data to investigate seasonal variations of ENSO and their impacts on marine biogeochemical processes. The results show that the oxygen and chlorophyll anomalies in the upper ocean exhibit different seasonal responses to ENSO. While both the summer and winter season biological responses significantly lag ENSO, the concentration of oxygen and phytoplankton during summer (winter) has no (large) concurrent covariability with ENSO. Given a strong negative correlation between chlorophyll-based indices and El Niño events, increasing mean ocean temperatures and ocean extreme events may induce lower upper-ocean oxygen levels, leading to possible risks in the ecosystem over the tropical Pacific Ocean.

Connection between the Tropical Pacific and Indian Ocean and Temperature Anomaly across West Antarctic

West Antarctic and the Antarctic Peninsula have experienced dramatic warming in austral spring since the 1970s. Using observations and the Community Atmosphere Model version 4 (CAM4), this study explores the physical mechanism by which the tropical Pacific and Indian Ocean temperature anomaly mode (PIM) affects the dipolar surface air temperature (SAT) anomalies across the West Antarctic in austral spring. The positive phase of the PIM, characterized by positive sea surface temperature anomalies (SSTAs) in the tropical central-eastern Pacific and western Indian Ocean and negative SSTAs in the Maritime Continent, can generate two branches of stationary Rossby wave trains propagating from the tropical central Pacific and southeastern Indian Ocean to the West Antarctic, with an anticyclonic anomaly appearing over the Amundsen Sea. The northerlies advect warmer air to the Ross–Amundsen Seas, but southerlies advect colder air to the Antarctic Peninsula–Weddell Sea, resulting in the dipole of SAT anomalies over the West Antarctic. In this process, the role of tropical central-eastern Pacific SSTAs dominate, and it is amplified by the SSTAs around the Maritime Continent. The SSTAs in the western Indian Ocean combined with the SSTAs over the Maritime Continent further contribute to the western pole of the SAT. Only simulation that includes a prescribed PIM forcing can exactly reproduce the observations of the dipolar SAT response across the West Antarctic, indicating the need to treat the tropical Pacific and Indian Oceans as a unified whole.