Pacific Ocean Basin Research Articles

Diagnostic Metrics for Evaluating Model Simulations of the East Asian Monsoon

AbstractThe distinctive monsoon climate over East Asia, which is affected by the vast Eurasian continent and Pacific Ocean basin and the high-altitude Tibetan Plateau, provides arguably the best testbed for evaluating the competence of Earth system climate models. Here, a set of diagnostic metrics, consisting of 14 items and 7 variables, is specifically developed. This physically intuitive set of metrics focuses on the essential features of the East Asian summer monsoon (EASM) and East Asian winter monsoon (EAWM), and includes fields that depict the climatology, the major modes of variability, and unique characteristics of the EASM. The metrics are applied to multimodel historical simulations derived from 20 models that participated in phases 3 and 5 of the Coupled Model Intercomparison Project (CMIP3 and CMIP5, respectively), along with the newly developed Nanjing University of Information Science and Technology Earth System Model, version 3. The CMIP5 models show significant improvements over the CMIP3 models in terms of the simulated East Asian monsoon circulation systems on a regional scale, major modes of EAWM variability, the monsoon domain and precipitation intensity, and teleconnection associated with the heat source over the Philippine Sea. Clear deficiencies persist from CMIP3 to CMIP5 with respect to capturing the major modes of EASM variability, as well as the relationship between the EASM and ENSO during El Niño developing and decay phases. The possible origins that affect models’ performance are also discussed. The metrics provide a tool for evaluating the performance of Earth system climate models, and facilitating the assessment of past and projected future changes of the East Asian monsoon.

Первые данные о двустворчатых миксоспоридиях кефалевых рыб залива Нячанг (Вьетнам)

Кефалевые рыбы являются объектом промысла во Вьетнаме; некоторых из них разводят на рисовых чеках. Интенсивное развитие в этой стране марикультуры рыб, а также большая доля гидробионтов в рационе населения требуют знаний не только о видовом составе паразитов, но и об их жизненных циклах, патогенности, медицинском и эпизоотологическом значении. Фауна морских миксоспоридий в этом районе изучена крайне слабо. В пресноводных видах Вьетнама известно 36 видов и 10 не идентифицированных до вида миксоспоридий; в морских рыбах найдено 7 видов и 9 не определённых до вида Myxosporea. В марте — апреле 2018 г. в заливе Нячанг (Вьетнам, Восточное море) на предмет обнаружения миксоспоридий методом неполного паразитологического вскрытия исследовали 71 экз. рыб 7 видов из сем. Mugilidae (4 экз. Chelon planiceps, 25 экз. Valamugil speigleri, 10 экз. V. formosae, 1 экз. Planiliza subviridis, 19 экз. Paramugil parmatus, 9 экз. Mugil cephalus, 3 экз. Moolgarda seheli). Все органы просматривали под бинокуляром Olympus SZ61 при увеличении от ×15 до ×25. Мазки из тканей различных органов рыб исследовали на микроскопе Olympus CKX53 с фазовым контрастом при увеличении ×400 и на микроскопе Olympus CX41 с цифровой камерой Olympus SC50 и фазовым контрастом при увеличении ×800. Миксоспоридий фиксировали в глицерин-желатине по общепринятой методике. Промеры паразитов базировались на 20 спорах Myxobolus spinacurvatura, 25 спорах Sphaerospora dicentrarchi и 10 спорах Henneguya sp. Все промеры выполнены по стандартной методике. Для оценки численности паразитов использованы показатели экстенсивности и интенсивности инвазии. Получены первые сведения о миксоспоридиях отр. Bivalvulida кефалевых рыб залива Нячанг: найдены Myxobolus spinacurvatura в жёлчном пузыре и кишечнике у 78 % лобана M. cephalus при интенсивности инвазии, составляющей единичные споры в мазке из жёлчного пузыря и 5–11 цист в кишечнике; Sphaerospora dicentrarchi в жёлчном пузыре у 5 % черноплавничных хелонов Paramugil parmatus, 12 % Valamugil speigleri, 20 % V. formosae и 56 % Mugil cephalus при интенсивности инвазии, составляющей единичные споры в мазке; Henneguya sp. в жёлчном пузыре 8 % V. speigleri и 10 % V. formosae при интенсивности инвазии, составляющей единицы, десятки спор в мазке. Сделаны описания обнаруженных видов. Указано их распространение в других регионах Мирового океана. S. dicentrarchi — новый вид в фауне Восточного моря и Вьетнама. Он был найден не только в известном для него в других регионах M. cephalus, но и в новых хозяевах — P. parmatus, V. speigleri и V. formosae. Myxobolus spinacurvatura впервые констатирован в заливе Нячанг. Myxobolus spinacurvatura и Sphaerospora dicentrarchi известны от лобана в бассейне не только Тихого, но и Атлантического океана, поэтому предполагается, с учётом связи этих водоёмов в глубокой древности, наличие у каждого из данных паразитов в прошлом единого большого ареала, который затем был разорван вследствие мощных геологических преобразований нашей планеты.

Influence of Track Changes on the Poleward Shift of LMI Location of Western North Pacific Tropical Cyclones

AbstractThe annual mean latitude at which tropical cyclones (TCs) reach their lifetime maximum intensity (LMI) over the western North Pacific Ocean basin has shifted northward since the early 1980s, and it is suggested that the shift is due to the northward migration of the mean TC formation location. In this study, the TC intensity is simulated with an intensity model to assess the historical records of TC intensity. During the period 1980–2015, the simulated poleward trend in the mean latitude of LMI is 0.44° (10 yr)−1, which agrees well with the one [0.48° (10 yr)−1] derived from the Joint Typhoon Warning Center (JTWC) dataset. This suggests that the observed poleward trend in the mean latitude of LMI is physically consistent with changes in the large-scale ocean–atmosphere environment and TC track. This study also demonstrates that the temporal change in the environmental parameters (sea surface temperature, outflow temperature, vertical wind shear, and ocean mixed layer depth) has little influence on the observed shift of the mean LMI latitude. The poleward migration of the mean LMI latitude is mainly due to the TC track shift, which results primarily from the change in the large-scale steering flow.

Special issue «environmental change on the Mongolian plateau: atmosphere, forests, soils and water»

The Mongolian Plateau forms a part of the Central Asian Plateau and covers an area of approximately 3,200,000 square kilometers in Mongolia and adjacent areas in China and Southern Siberia. It contains one of the world’s largest grassland areas, with the Gobi desert in the south and a transition via steppe and forest steppe to the taiga and mountain tundra in the North (Dulamsuren et al. 2005; Miao et al. 2015). Due to its location, the Plateau's climate is continental and semi-arid to arid, characterized by low precipitation (about 250 mm on average), high potential evapotranspiration (almost 1000 mm on average), large temperature amplitudes, long and harsh winters and recurrent droughts (Dorjgotov 2009; Liu et al. 2019). The Mongolian Plateau mostly drains into the Arctic Ocean basin, including the system of the Selenga River and Lake Baikal, which is not only the world's largest freshwater lake but also a natural heritage of global importance (Kasimov et al. 2017). Hydrologically, parts of the plateau also belong to the Pacific Ocean and Central Asian internal drainage basins.

Development of a Numerical Algorithm Considering Tide–Tsunami Interaction

Yoon, J.-S.; Lee, J., and Ha, T., 2019. Development of a numerical algorithm considering tide–tsunami interaction. In: Lee, J.L.; Yoon, J.-S.; Cho, W.C.; Muin, M., and Lee, J. (eds.), The 3rd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 91, pp. 76-80. Coconut Creek (Florida), ISSN 0749-0208.The perimeter of the Pacific Ocean Basin, known as the Ring of Fire, has several sources that can produce strong earthquakes of magnitude ≥7.0. The earthquake of magnitude 9.0-9.1, occurred in 2011 off the Pacific coast of Tohoku, produced a devastating tsunami that affected the Pacific Basin. The lead time before the subsequent tsunami of such an earthquake reaches the coastal areas of the Korean peninsula varies. A tsunami from a distant location like Chile or California, USA, will take 12 h or more to reach the Korean peninsula, while that from Japan or the Ryuku Trench will take only 1–4 h. The tide–tsunami interaction may be strengthened significantly in some regions with very strong tides and could be used to predict tsunami hazards in Korea. Therefore, to develop a plan for mitigating tsunami hazards around the Korean peninsula, the tide–tsunami interaction that occurs during the propagation of a tsunami over regions with strong tides and tidal currents should be properly evaluated and its impact on a local community should be considered during numerical simulations. We developed a new numerical algorithm that includes tide–tsunami interactions for the national tsunami forecasting system. Numerical experiments using this tsunami forecasting algorithm were conducted to investigate the impact of tide–tsunami interactions as the tsunami propagates toward coastal areas of the Korean peninsula.

A Feed Forward Neural Network Based on Model Output Statistics for Short-Term Hurricane Intensity Prediction

Abstract A feed forward neural network (FFNN) is developed for tropical cyclone (TC) intensity prediction, where intensity is defined as the maximum 1-min average 10-m wind speed. This deep learning model incorporates a real-time operational estimate of the current intensity and predictors derived from Hurricane Weather Research and Forecasting (HWRF; 2017 version) Model forecasts. The FFNN model is developed with the operational constraint of being restricted to 6-h-old HWRF data. Best track intensity data are used for observational verification. The forecast training data are from 2014 to 2016 HWRF reforecast data and cover a wide variety of TCs from both the Atlantic and eastern Pacific Ocean basins. Cross validation shows that the FFNN increasingly outperforms the operational observation-adjusted HWRF (HWFI) in terms of mean absolute error (MAE) at forecast lead times from 3 to 57 h. Out-of-sample testing on real-time data from 2017 shows the HWFI produces lower MAE than the FFNN at lead times of 24 h or less and similar MAEs at later lead times. On the other hand, the 2017 data indicate significant potential for the FFNN in the prediction of rapid intensification (RI), with RI defined here as an intensification of at least 30 kt (1 kt ≈ 0.51 m s−1) in a 24-h period. The FFNN produces 4 times the number of hits in HWFI for RI. While the FFNN has more false alarms than the HWFI, Brier skill scores show that, in the Atlantic, the FFNN has significantly greater skill than the HWFI and probabilistic Statistical Hurricane Intensity Prediction System RI index.

A New Hypothesis of the Phylogenetic Relationships of the Tylosaurinae (Squamata: Mosasauroidea)

Tylosaurinae Williston, 1897, is reconstructed in most analyses as the sister group of the Plioplatecarpinae Dollo, 1884. The most distinctive characteristic of the group is an elongate edentulous rostrum on the premaxilla. Members of the tylosaurine subfamily are divided into two genera: Tylosaurus Marsh, 1872, and Taniwhasaurus Hector, 1874. When all arguably valid tylosaurine species are included in a single phylogenetic analysis, some clades are well supported, i.e., the clade formed by T. proriger (Cope, 1869) + T. bernardi (Dollo, 1885), or the clade T. pembinensis (Nicholls, 1988) + T. saskatchewanensis. In contrast, clade relationships for other species are unresolved, i.e., T. gaudryi (Thevenin, 1896), T. nepaeolicus (Cope, 1874), and the several species within the genus Taniwhasaurus. When T. gaudryi (Thevenin, 1896), Ta. ‘mikasaensis’ Caldwell et al., 2008, and ‘T’. capensis ' Broom, 1912 were removed from the analysis, T. nepaeolicus appeared as the basal member of the genus. The relationships within the genus Taniwhasaurus are unresolved; however, when the problematic taxa are removed, the genus is monophyletic, with Ta. oweni as the sister group of Ta. antarcticus. Based on morphological characters present in the holotype of ‘T’. capensis Broom, 1912, we suggest a re-assignation to the genus Taniwhasaurus, based on the flutes and facets in the crown of the two preserved replacement teeth. The lack of a clear diagnosis of Hainosaurus/Tylosaurus neumilleri leaves this taxon as nomen dubium; the few characters visible on the specimen show strong similarities to both T. pembinensis and T. saskatchewanensis; therefore the specimen cannot be identified beyond Tylosaurus sp. Reassessment of the known materials of the Japanese species Ta. ‘mikasaensis’ suggests that the various specimens do not display sufficient diagnostic characters to support ‘mikasaensis’ as distinct from Taniwhasaurus oweni. The hypothesis for a North Atlantic Circle Basin distribution for species of the genus Tylosaurus from the Coniacian to the Maatrichtian is supported, and a more cosmopolitan distribution is suggested for the genus Taniwhasaurus (Santonian to Maastrichtian) with species present along the margins of the Pacific, Indian and Antarctic Ocean Basins.

Interdecadal Pacific Oscillation reconstructed from trans-Pacific tree rings: 1350\u20132004 CE

The interdecadal Pacific Oscillation (IPO) represents the decadal mode of the El Niño-Southern Oscillation phenomenon. As such the IPO is one of the dominant modes of decadal climate variability on both sides of the Pacific Ocean basin. For this paper we utilized a newly developed tree-ring data network comprised of five multi-centennial Vietnamese cypress ring-width chronologies that range from around 11°N–23°N latitude. We combined these data with an average of tree-ring derived drought indices from the North American Drought Atlas over the south central USA, from a box that spans from 27.5°N–35.0°N, 85.0°–110.0°W and contains 55 gridpoints and more than 100 tree ring site chronologies, these 2 locations exhibit rainfall variations that are strongly, negatively correlated with each other and are representative of the influence of the IPO on terrestrial rainfall. The final reconstruction model, weighted most heavily on the three most southerly of the five Vietnamese cypress records, spans from 1350 to 2004, and explains nearly 57% of the variance in the original IPO data for the 5-month season of October–February. The reconstruction model passes all standard statistical tests using a split calibration-verification scheme. We reveal 15 positive and 15 negative phase shifts of the IPO prior to the period of instrumentation, suggesting that the IPO has been active for at least the past seven centuries with varying degrees of intensity. We compare our reconstruction with two related millennial records: the MacDonald and Case (Geophys Res Lett 32(8):L08703, 2005) tree ring-derived reconstruction of the Pacific Decadal Oscillation, and an ice core-derived reconstruction of the IPO from the Law Dome Ice core in Antarctica by Vance et al. (Geophys Res Lett 33(6):L06712, 2015). While there is good general agreement with the latter record, there are three key periods of the past where the two records are out of phase, and we explore the reasons for this disparity. Direct comparison with the related Tripole Index (TPI) shows weaker correlation, likely owing to the stronger relationship between our tree ring data and the equatorial Pacific region relative to the north and south regions of the Pacific that combine to comprise the TPI calculation.

A Proposed Exogenous Cause of the Global Temperature Hiatus

Since 1850, the rise in global mean surface temperatures (GMSTs) from increasing atmospheric concentrations of greenhouse gases (GHGs) has exhibited three ~30-year hiatus (surface cooling) episodes. The current hiatus is often thought to be generated by similar cooling episodes in Pacific or Atlantic ocean basins. However, GMSTs as well as reconstructed Atlantic and Pacific ocean basin surface temperatures show the presence of similar multidecadal components generated from a three-dimensional analysis of differential gravitational (tidal) forcing from the sun and moon. This paper hypothesizes that these episodes are all caused by external tidal forcing that generates alternating ~30-year zonal and meridional circulation regimes, which respectively increase and decrease GMSTs through tidal effects on sequestration (deep ocean heat storage) and energy redistribution. Hiatus episodes consequently coincide with meridional regimes. The current meridional regime affecting GMSTs is predicted to continue to the mid-2030s but have limited tendency to decrease GMSTs from sequestration because of continuing increases in radiative forcing from increasing atmospheric GHGs. The tidal formulation also generates bidecadal oscillations, which may generate shorter ~12-year hiatus periods in global and ocean basin temperatures. The formulation appears to assimilate findings from disciplines as disparate as geophysics and biology.

Степные сообщества класса Cleistogenetea squarrosae Mirkin et al. ex Korotkov et al. 1991 в Восточном Забайкалье

Transbaikalia is the vast region in Southern Siberia which includes numerous mountain ridges within the upper basins of the three big rivers, the Amur (Pacific Ocean basin), the Yenisey, and the Lena (Arctic Ocean basin). The most part of Transbaikalia territory is covered by woodlands, however, the steppes are an inherent component in the southern part of the region. Due to broad distribution they form the steppe and forest-steppe altitudinal belts in the mountains, and even totally predominate in the vast plains of the southeastern part of studied territory. Steppe communities occur throughout the broad range of habitats varying in humidity, edaphic conditions, and anthropogenic disturbance.

Seasonal climate summary for the southern hemisphere (spring 2016): strong negative Indian Ocean Dipole ends, bringing second wettest September to Australia

This summary looks at the southern hemisphere and equatorial climate patterns for spring 2016, with particular attention given to the Australasian and equatorial regions of the Pacific and Indian Ocean basins. Spring 2016 was marked by the later part of a strong negative phase of the Indian Ocean Dipole, alongside cool neutral El Niño–Southern Oscillation conditions. September was exceptionally wet over much of Australia, contributing to a wet spring with near-average temperatures. The spring was one of the warmest on record over the southern hemisphere as a whole, with Antarctic Sea ice extent dropping to record low levels for the season.

Tropical Cyclone Unusual Intensity and Structure Change in the Western North Pacific Observed by Reconnaissance Aircraft During TPARC/TCS08 and ITOP/TCS10

ABSTRACT The combined Tropical Cyclone Structure (TCS-08) and THORPEX Pacific-Asia Regional Campaign (T-PARC) field programs during August and September 2008 and the combined Impact of Typhoons on the Ocean in the Pacific (ITOP) and TCS-10 field programs during August, September, and October 2010 have provided unique simultaneous observations of typhoon structure and intensity together with underlying oceanic conditions during rapid intensification and rapid decay events in the northwest Pacific Ocean basin during the tropical cyclone life cycle. A new observational strategy from aircraft reconnaissance, involving combination (‘COMBO’) deployments of Global Positioning System (GPS) dropwindsondes and Airborne expendable Bathythermographs (AXBTs) has allowed for simultaneous observations of TC structure and intensity while also observing oceanic eddy structure beneath the TC. This strategy, together with deployment of drifting buoys and floats ahead of the TC, has led to observations in Super-TYphoon (STY) Jangmi (2008) and STY Megi (2010) that show the ocean control over TC Rapid Intensification (RI) and Rapid Decay (RD) due to pre-existing warm and cold ocean eddy features, as well as the intensity-limiting effects of oceanic ‘cold wakes’ generated by Typhoons (TYs) Fanapi (2010) and Malakas (2010). Observations made during ‘unusual’ track changes in TY Fanapi illustrate how the TC passes over different ocean eddy features than would have occurred with a ‘normal’ straight track. These track changes led to unusual intensity changes due to subsequent movement over a warm ocean eddy feature that led to unexpected TC intensification, and this was followed by movement over shallow ocean mixed layers that led to strong ‘cold wake’ generation. This feature of ocean control then limited Fanapi’s intensification to values well below their Maximum Potential Intensity (MPI). In addition, ‘COMBO’ observations within pre-TC disturbances show contrasting impacts on typhoon development/non-development for cases of strong ocean control and weak environmental shear (pre-Fanapi, 2010) versus cases of weak ocean control and strong environmental shear (disturbance TCS025, 2008).

Twenty‐first‐century climate change impacts on marine animal biomass and ecosystem structure across ocean basins

Climate change effects on marine ecosystems include impacts on primary production, ocean temperature, species distributions, and abundance at local to global scales. These changes will significantly alter marine ecosystem structure and function with associated socio-economic impacts on ecosystem services, marine fisheries, and fishery-dependent societies. Yet how these changes may play out among ocean basins over the 21st century remains unclear, with most projections coming from single ecosystem models that do not adequately capture the range of model uncertainty. We address this by using six marine ecosystem models within the Fisheries and Marine Ecosystem Model Intercomparison Project (Fish-MIP) to analyze responses of marine animal biomass in all major ocean basins to contrasting climate change scenarios. Under a high emissions scenario (RCP8.5), total marine animal biomass declined by an ensemble mean of 15%-30% (±12%-17%) in the North and South Atlantic and Pacific, and the Indian Ocean by 2100, whereas polar ocean basins experienced a 20%-80% (±35%-200%) increase. Uncertainty and model disagreement were greatest in the Arctic and smallest in the South Pacific Ocean. Projected changes were reduced under a low (RCP2.6) emissions scenario. Under RCP2.6 and RCP8.5, biomass projections were highly correlated with changes in net primary production and negatively correlated with projected sea surface temperature increases across all ocean basins except the polar oceans. Ecosystem structure was projected to shift as animal biomass concentrated in different size-classes across ocean basins and emissions scenarios. We highlight that climate change mitigation measures could moderate the impacts on marine animal biomass by reducing biomass declines in the Pacific, Atlantic, and Indian Ocean basins. The range of individual model projections emphasizes the importance of using an ensemble approach in assessing uncertainty of future change.

Summer Covariability of Surface Climate for Renewable Energy across the Contiguous United States: Role of the North Atlantic Subtropical High

AbstractThis study examines the joint spatiotemporal variability of summertime climate linked to renewable energy sources (precipitation and streamflow, wind speeds, and insolation) and energy demand drivers (temperature, relative humidity, and a heat index) across the contiguous United States (CONUS) between 1948 and 2015. Canonical correlation analysis is used to identify the primary modes of joint variability between wind speeds and precipitation and related patterns of the other hydrometeorological variables. The first two modes exhibit a pan-U.S. dipole with lobes in the eastern and central CONUS. Composite analysis shows that these modes are directly related to the displacement of the western ridge of the North Atlantic subtropical high (NASH), suggesting that a single, large-scale feature of atmospheric circulation drives much of the large-scale climate covariability related to summertime renewable energy supply and demand across the CONUS. The impacts of this climate feature on the U.S. energy system are shown more directly by examining changes in surface climate variables at existing and potential sites of renewable energy infrastructure and locations of high energy demand. Also, different phases of the NASH are related to concurrent and lagged modes of oceanic and atmospheric climate variability in the Pacific and Atlantic Ocean basins, with results suggesting that springtime climate over both oceans may provide some potential to predict summer variability in the NASH and its associated surface climate. The implications of these findings for the impacts of climate variability and change on integrated renewable energy systems over the CONUS are discussed.

Cloud impacts on photochemistry: building a climatology of photolysis rates from the Atmospheric Tomography mission

Abstract. Measurements from actinic flux spectroradiometers on board the NASA DC-8 during the Atmospheric Tomography (ATom) mission provide an extensive set of statistics on how clouds alter photolysis rates (J values) throughout the remote Pacific and Atlantic Ocean basins. J values control tropospheric ozone and methane abundances, and thus clouds have been included for more than three decades in tropospheric chemistry modeling. ATom made four profiling circumnavigations of the troposphere capturing each of the seasons during 2016–2018. This work examines J values from the Pacific Ocean flights of the first deployment, but publishes the complete Atom-1 data set (29 July to 23 August 2016). We compare the observed J values (every 3 s along flight track) with those calculated by nine global chemistry–climate/transport models (globally gridded, hourly, for a mid-August day). To compare these disparate data sets, we build a commensurate statistical picture of the impact of clouds on J values using the ratio of J-cloudy (standard, sometimes cloudy conditions) to J-clear (artificially cleared of clouds). The range of modeled cloud effects is inconsistently large but they fall into two distinct classes: (1) models with large cloud effects showing mostly enhanced J values aloft and or diminished at the surface and (2) models with small effects having nearly clear-sky J values much of the time. The ATom-1 measurements generally favor large cloud effects but are not precise or robust enough to point out the best cloud-modeling approach. The models here have resolutions of 50–200 km and thus reduce the occurrence of clear sky when averaging over grid cells. In situ measurements also average scattered sunlight over a mixed cloud field, but only out to scales of tens of kilometers. A primary uncertainty remains in the role of clouds in chemistry, in particular, how models average over cloud fields, and how such averages can simulate measurements.

New Data on the Age and Growth of Greenland Halibut, Reinhardtius hippoglossoides (Pleuronectidae), from the Laptev Sea

The age and growth characteristics of the Greenland halibut, Reinhardtius hippoglossoides, have been described from the Laptev Sea for the first time. In recent years, the species has substantially expanded its range eastward. The age of juveniles is from 2 to 4 years at a body length of 12.5–17.7 cm. The age of females varies from 2 yr (11.5 cm) to 10 yr (43.5–53.7 cm). The minimum age of males is 3 yr at a body length of 17.3–21.5 cm; the maximum age is 11 yr at 48.2–54.8 cm. The data obtained indicate a slower growth of Greenland halibut in the Laptev Sea compared to that of individuals from the Atlantic and Pacific Ocean basins. The main causes of this difference are the harsh Arctic conditions of the region and a poor forage base, represented mainly by Polar cod, Boreogadus saida.

Drivers of the Low-Cloud Response to Poleward Jet Shifts in the North Pacific in Observations and Models

The long-standing expectation that poleward shifts of the midlatitude jet under global warming will lead to poleward shifts of clouds and a positive radiative feedback on the climate system has been shown to be misguided by several recent studies. On interannual time scales, free-tropospheric clouds are observed to shift along with the jet, but low clouds increase across a broad expanse of the North Pacific Ocean basin, resulting in negligible changes in total cloud fraction and top-of-atmosphere radiation. Here it is shown that this low-cloud response is consistent across eight independent satellite-derived cloud products. Using multiple linear regression, it is demonstrated that the spatial pattern and magnitude of the low-cloud-coverage response is primarily driven by anomalous surface temperature advection. In the eastern North Pacific, anomalous cold advection by anomalous northerly surface winds enhances sensible and latent heat fluxes from the ocean into the boundary layer, resulting in large increases in low-cloud coverage. Local increases in low-level stability make a smaller contribution to this low-cloud increase. Despite closely capturing the observed response of large-scale meteorology to jet shifts, global climate models largely fail to capture the observed response of clouds and radiation to interannual jet shifts because they systematically underestimate how sensitive low clouds are to surface temperature advection, and to a lesser extent, low-level stability. More realistic model simulations of cloud–radiation–jet interactions require that parameterizations more accurately capture the sensitivity of low clouds to surface temperature advection.

Low-frequency ambient noise trends of (almost) 2 decades in the northern Pacific Ocean

Nearly two decades of low-frequency (20–500 Hz) ambient noise measurements at seven open-ocean sites in the North Pacific Ocean basin have revealed a complex pattern of long-term trends. The trends in the Northeastern Pacific Ocean show a significant decrease of almost 2 dB/decade. Along the Aleutian archipelago, the levels are either slightly increasing or remaining flat. Levels in two north central Pacific Ocean sites are essentially flat. Comparisons with very sparse measurements made over the last 5 decades suggest that the mid-latitude noise levels may have peaked in the 1990s. These measurements also show, however, that the noise level is still rising elsewhere. The mechanisms driving these trends appear to be more subtle than simply the number of merchant ships or the local wind speed. Climatically-influenced basin-scale acoustic propagation conditions may have an important role.

Probabilistic Prediction of Tropical Cyclone Intensity with an Analog Ensemble

An analog ensemble (AnEn) technique is applied to the prediction of tropical cyclone (TC) intensity (i.e., maximum 1-min averaged 10-m wind speed). The AnEn is an inexpensive, naturally calibrated ensemble prediction of TC intensity derived from a training dataset of deterministic Hurricane Weather Research and Forecasting (HWRF; 2015 version) Model forecasts. In this implementation of the AnEn, a set of analog forecasts is generated by searching an HWRF archive for forecasts sharing key features with the current HWRF forecast. The forecast training period spans 2011–15. The similarity of a current forecast with past forecasts is estimated using predictors derived from the HWRF reforecasts that capture thermodynamic and kinematic properties of a TC’s environment and its inner core. Additionally, the value of adding a multimodel intensity consensus forecast as an AnEn predictor is examined. Once analogs are identified, the verifying intensity observations corresponding to each analog HWRF forecast are used to produce the AnEn intensity prediction. In this work, the AnEn is developed for both the eastern Pacific and Atlantic Ocean basins. The AnEn’s performance with respect to mean absolute error (MAE) is compared with the raw HWRF output, the official National Hurricane Center (NHC) forecast, and other top-performing NHC models. Also, probabilistic intensity forecasts are compared with a quantile mapping model based on the HWRF’s intensity forecast. In terms of MAE, the AnEn outperforms HWRF in the eastern Pacific at all lead times examined and up to 24-h lead time in the Atlantic. Also, unlike traditional dynamical ensembles, the AnEn produces an excellent spread–skill relationship.

Future changes in rainfall associated with ENSO, IOD and changes in the mean state over Eastern Africa

This study examines the projected changes in the characteristics of the El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) in terms of mean state, intensity and frequency, and associated rainfall anomalies over eastern Africa. Two regional climate models driven by the same four global climate models (GCMs) and the corresponding GCM simulations are used to investigate projected changes in teleconnection patterns and East African rainfall. The period 1976–2005 is taken as the reference for present climate and the far-future climate (2070–2099) under Representative Concentration Pathway 8.5 (RCP8.5) is analyzed for projected change. Analyses of projections based on GCMs indicate an El Niño-like (positive IOD-like) warming pattern over the tropical Pacific (Indian) Ocean. However, large uncertainties remain in the projected future changes in ENSO/IOD frequency and intensity with some GCMs show increase of ENSO/IOD frequency and intensity, and others a decrease or no/small change. Projected changes in mean rainfall over eastern Africa based on the GCM and RCM data indicate a decrease in rainfall over most parts of the region during JJAS and MAM seasons, and an increase in rainfall over equatorial and southern part of the region during OND, with the greatest changes in equatorial region. During ENSO and IOD years, important changes in the strength of the teleconnections are found. During JJAS, when ENSO is an important driver of rainfall variability over the region, both GCM and RCM projections show an enhanced La Niña-related rainfall anomaly compared to the present period. Although the long rains (MAM) have little association with ENSO in the reference period, both GCMs and RCMs project stronger ENSO teleconnections in the future. On the other hand, during the short rains (OND), a dipole future change in rainfall teleconnection associated with ENSO and IOD is found, with a stronger ENSO/IOD related rainfall anomaly over the eastern part of the domain, but a weaker ENSO/IOD signal over the southern part of the region. This signal is consistent and robust in all global and regional model simulations. The projected increase in OND rainfall over the eastern horn of Africa might be linked with the mean changes in SST over Indian and Pacific Ocean basins and the associated Walker circulations.