Land Ocean Research Articles

Mineralogy as a potential driver of irregular radiocarbon patterns among Icelandic fluvial carbon pools

Abstract Fluvial export of organic carbon (OC) from the terrestrial biosphere to the ocean forms a key component of the global carbon cycle. Carbon sources and transformations along the land–ocean aquatic continuum are dynamic with a complex interplay between particulate and dissolved organic and inorganic carbon pools (POC, DOC, DIC). Radiocarbon dating serves as a valuable tool, providing crucial insights into turnover and residence times within these pools. However, the myriad of carbon sources, including ancient ‘petrogenic’ OC from sedimentary rocks or freshly assimilated OC derived from aquatic in-situ production, makes it challenging to interpret 14C signatures in the context of terrestrial biospheric OC turnover and residence times. Icelandic rivers and streams offer an opportunity to examine biospheric carbon dynamics due to the virtual absence of petrogenic OC (e.g., shales, carbonates) in underlying bedrock. Our study of 43 rivers and streams, collectively draining approximately 42% of Iceland’s surface, revealed that radiocarbon signatures of POC largely align with global river patterns but lacked the presence of significantly old (14C-depleted) carbon likely reflecting the absence of ancient petrogenic OC. In contrast, DOC tended to be older compared to global rivers and the corresponding POC and DIC pools in Icelandic rivers. These observations challenge the paradigm that riverine POC generally exhibits longer turnover and residence times than DOC. After excluding other potential factors, we argue that this apparent age inversion among carbon pools in Icelandic rivers may reflect retention of DOC prior to its release to the aquatic continuum through interactions with high surface area minerals prevalent in the volcanic soils of Iceland. This finding may be relevant for other fluvial systems draining volcanic bedrock and have broader implications regarding biospheric OC dynamics in rivers and streams globally.

Extrapolation-Based Regionalized Re-evaluation of the Global Estuarine Surface Area

At the interface between the continental and oceanic domains, estuaries are essential components of the land–ocean aquatic continuum. These coastal ecosystems play a significant role in biogeochemical cycles, as they transform and export large amounts of terrigenous carbon and nutrients from rivers to marine waters. Because of this intense biogeochemical processing, they are significant ecosystems in terms of greenhouse gas exchange with the atmosphere. However, in spite of recent advances in remote sensing and the need for accurate estimates to calculate regional and global estuarine budgets, the global quantification of the estuarine spatial extent available for gas exchange has not been updated in over a decade and remains poorly constrained. This is due to the lack of a global extensive database, the diversity of estuaries, and the controversial definition of their boundaries. To address these challenges, a hybrid approach was developed that combines the surface areas of over 700 estuaries worldwide (extracted from the literature or calculated using geographical information systems) with a novel extrapolation method to provide type-specific regional estimates for 45 regions. The three estuarine types considered are ‘tidal systems and deltas’, ‘lagoons’, and ‘fjords’. The upscaling formula applied is determined and calibrated using data from several regions where an extensive survey of total estuarine surface areas was available. The new global estimate of 733,801 ± 39,892 km2 (mean ± 2 σ) is 31% lower than the previous global assessment. It also provides quantitative uncertainty estimates for regional and global estuarine surface areas as well as a breakdown between tidal systems and deltas (294,956 ± 30,780 km2), lagoons (179,946 ± 12,056 km2), and fjords (259,899 ± 22,328 km2). This decrease of the global estuarine surface area is related to the novel method used in this study and does not reflect a temporal trend.

Indian Summer Monsoon Rainfall Characteristics Derived From Multiple Gridded Precipitation Datasets: A Comparative Assessment

ABSTRACTPrecipitation, a crucial component of the Earth system processes, regulates the spatiotemporal cyclicity of water, energy, and carbon fluxes. Accurate precipitation datasets leverage the understanding of precipitation dynamics and are vital for hydro‐climatological studies. South Asian monsoon is a complex, multi‐scale interacting, synoptic, and ocean–land–atmosphere coupled system, contributing to significant spatial and temporal variability in summer monsoonal rainfall across India. This study evaluates four types of gridded (observational, satellite, reanalysis, and hybrid) precipitation products in their ability to replicate Indian Summer Monsoonal Rainfall (ISMR) characteristics using the India Meteorological Department (IMD) 0.25° gridded data as the baseline. A comparative assessment is performed in this study that uses several continuous and interval‐based performance measures to evaluate the overall rainfall magnitude detectability and time‐matched capturing of rainfall events. A new metric, rank score, is developed by aggregating multiple measures to find the best product. The analyses based on several performance measures indicate that MSWEP is the best dataset (rank one) that closely approximates the occurrence and magnitude of IMD‐based rainfall events, while APHRODITE, CHIRPS, and IMDAA are ranked as the next best set of products. PGF is ranked the lowest among all products evaluated and is not recommended for applications. Nonetheless, APHRODITE suffers from strong negative biases, while the reanalysis (IMDAA, ERA5‐Land, PGF) datasets show significant positive biases. Among the products evaluated, APHRODITE, ERA5‐Land, and IMDAA have shown a limited ability to detect excess, normal, and deficit monsoon years, respectively. In general, the performance of satellite‐based data products is superior to that of reanalysis datasets in accurately characterising the monsoon years. ERA5‐Land is noted to be the best‐performing dataset among the reanalysis products. The comprehensive comparative assessment carried out in this study benefits the selection and use of appropriate gridded precipitation products for hydroclimatic modelling, climate variability, and change studies.

Assessing the Interrelationship Between Microplastics and Polychlorinated Biphenyls Contamination in Chinese Mangrove Sediment

Mangrove ecosystems, critical intertidal zones at the land–ocean interface, are increasingly recognized for their role in microplastic (MP) pollution dynamics. Despite extensive research on the interaction of MPs with various chemical contaminants, the specific contamination levels of polychlorinated biphenyls (PCBs) associated with MPs in mangroves remain poorly understood. In this study, we quantified the concentrations of PCBs on MPs extracted from representative mangrove sediment samples across China, revealing values ranging from 9.80 to 13.91 ng/g. In contrast, PCB concentrations in sediment samples were found to vary between 25.67 and 69.85 ng/g. Our findings indicate a consistent level of PCB contamination on MPs across different sites, although these levels were marginally elevated compared to those in the surrounding sediments. Notably, Penta-PCBs were detected with the highest frequency across all samples analyzed. This study provides crucial insights into the occurrence and distribution of PCBs on MPs within the mangrove ecosystem, highlighting their significance in environmental contamination assessments.

Early-twentieth-century cold bias in ocean surface temperature observations

The observed temperature record, which combines sea surface temperatures with near-surface air temperatures over land, is crucial for understanding climate variability and change1–4. However, early records of global mean surface temperature are uncertain owing to changes in measurement technology and practice, partial documentation5–8, and incomplete spatial coverage9. Here we show that existing estimates of ocean temperatures in the early twentieth century (1900–1930) are too cold, based on independent statistical reconstructions of the global mean surface temperature from either ocean or land data. The ocean-based reconstruction is on average about 0.26 °C colder than the land-based one, despite very high agreement in all other periods. The ocean cold anomaly is unforced, and internal variability in climate models cannot explain the observed land–ocean discrepancy. Several lines of evidence based on attribution, timescale analysis, coastal grid cells and palaeoclimate data support the argument of a substantial cold bias in the observed global sea-surface-temperature record in the early twentieth century. Although estimates of global warming since the mid-nineteenth century are not affected, correcting the ocean cold bias would result in a more modest early-twentieth-century warming trend10, a lower estimate of decadal-scale variability inferred from the instrumental record3, and better agreement between simulated and observed warming than existing datasets suggest2.

Advancing an integrated understanding of land–ocean connections in shaping the marine ecosystems of coastal temperate rainforest ecoregions

AbstractLand and ocean ecosystems are strongly connected and mutually interactive. As climate changes and other anthropogenic stressors intensify, the complex pathways that link these systems will strengthen or weaken in ways that are currently beyond reliable prediction. In this review we offer a framework of land–ocean couplings and their role in shaping marine ecosystems in coastal temperate rainforest (CTR) ecoregions, where high freshwater and materials flux result in particularly strong land–ocean connections. Using the largest contiguous expanse of CTR on Earth—the Northeast Pacific CTR (NPCTR)—as a case study, we integrate current understanding of the spatial and temporal scales of interacting processes across the land–ocean continuum, and examine how these processes structure and are defining features of marine ecosystems from nearshore to offshore domains. We look ahead to the potential effects of climate and other anthropogenic changes on the coupled land–ocean meta‐ecosystem. Finally, we review key data gaps and provide research recommendations for an integrated, transdisciplinary approach with the intent to guide future evaluations of and management recommendations for ongoing impacts to marine ecosystems of the NPCTR and other CTRs globally. In the light of extreme events including heatwaves, fire, and flooding, which are occurring almost annually, this integrative agenda is not only necessary but urgent.

Intensified upwelling: normalized sea surface temperature trends expose climate change in coastal areas

Abstract. Eastern boundary upwelling systems (EBUSs) provide valuable natural resources due to their high primary production. However, there is significant uncertainty in how climate change may affect the mechanisms that sustain these ecosystems in the future. Therefore, assessing the effects of climate change on EBUSs under the current global warming scenario is crucial for efficient ecosystem management. In 1990, Andrew Bakun suggested an increase in the upwelling intensity due to the rise of the ocean–land pressure gradient. Since there is a significant link between thermal gradients and offshore Ekman transport, we use sea level pressure (SLP) and deseasonalized sea surface temperature (SST) data from remote sensing to elucidate this hypothesis and validate it using in situ observations. SST is an indicator of coastal upwelling, and our long-term analysis of monthly and deseasonalized SST records shows that the seasonal and synoptic processes have minimal influence on the SST–upwelling intensity relationship. Upwelling within the same EBUS is not usually evenly distributed along coastlines, leading to upwelling in specific areas, referred to as upwelling centers. We compare the SST trends in the main upwelling centers of the four EBUSs with those in open ocean waters through a new index, αUI, designed to characterize upwelling changes in the EBUS. An a-dimensional number allows us to normalize the trends independently of the upwelling system and compare all of them. Furthermore, we have complemented the SST index with sea level pressure gradient data. This new index (supported by SLP gradient trends) indicates intensification in all the EBUSs, revealing a coherent pattern within EBUSs in the same ocean (i.e., Canarian and Benguela or Californian and Humboldt upwelling systems).

NWSP: A Novel Indicator for Ocean–Land Interface Extraction Using Bathymetric LiDAR

NWSP: A Novel Indicator for Ocean–Land Interface Extraction Using Bathymetric LiDAR

Impact of the horizontal resolution of GEOS-Chem on land‒ocean and tropic‒extratropic partitioning and seasonal cycle in CO2 inversion

Abstract Credible regional carbon budget estimates from atmospheric CO2 measurements rely on the accuracy of atmospheric transport models (ATMs). However, the atmospheric transport in ATMs is usually simplified and spatiotemporally averaged, leading to systematic biases in simulating the atmospheric CO2 and estimating surface CO2 fluxes. We show that forward simulations of global CO2 using an ATM, GEOS-Chem, at a native resolution of 0.5°×0.625° and a coarse resolution of 4°×5° differ significantly near the surface in the Northern Hemisphere and the polar vortex, mainly because of advection in GEOS-Chem. Comparing observing system simulation experiments that assimilate synthetic observations sampled from the forward simulations, we separate the impact of coarse-resolution GEOS-Chem on regional flux estimates. The results suggest that a significant amount of annual carbon uptake from the ocean and tropics is improperly redistributed to the land and northern and southern extratropics, respectively. In addition, these errors lead to an underestimated seasonal amplitude in the northern extratropical land and a reversed sign of the seasonal cycle in the northern extratropical ocean. The reversed sign of the seasonal cycle has also been observed in a real data assimilation experiment and several state-of-the-art inversions, suggesting that reasonable ocean flux estimates depend strongly on the accuracy of the ATM.

Estimates of carbon sequestration potential in an expanding Arctic fjord (Hornsund, Svalbard) affected by dark plumes of glacial meltwater

Abstract. In polar regions, glaciers are retreating onto land, gradually widening ice-free coastal waters, which are known to act as new sinks of atmospheric carbon. However, the increasing delivery of inorganic suspended particulate matter (iSPM) with meltwater might significantly impact their capacity to contribute to carbon sequestration. Here, we present an analysis of satellite, meteorological, and SPM data as well as results of a coupled physical–biogeochemical model (1D GOTM-ECOSMO-E2E-Polar) with a newly implemented iSPM group to show the impact of iSPM on the ecosystem dynamics in a warming polar fjord (Hornsund, European Arctic) with numerous shallow-grounded marine-terminating glaciers. Our results indicate that with a longer melt season (9 d per decade, 1979–2022), the loss of sea ice cover (44 d per decade, 1982–2021) and the formation of new marine habitats after the retreat of marine-terminating glaciers (around 100 km2 in 1976–2022, a 38 % increase in the total area), glacial meltwater has transported increasing loads of iSPM from land (3.7 g m−3 per decade, reconstructed for 1979–2022). The simulated light limitation induced by the iSPM input delayed and decreased the peaks in phytoplankton, zooplankton, and macrobenthos. The newly ice-free areas still markedly contributed to plankton primary and secondary production and carbon burial in sediments (5.1, 2.0, and 0.9 Gg C yr−1, respectively, on average for 2005–2009 in the iSPM scenario). However, these values would have been 5.0, 2.1, and 0.1 Gg C yr−1 higher, respectively, without the iSPM input. Since carbon burial was the least affected by iSPM (a decrease of around 16 %, in comparison to 50 % for plankton primary and secondary production), the impact of marine ice loss and enhanced land–ocean connectivity should be investigated further in the context of carbon fluxes in expanding polar fjords.

Validation and Conformity Testing of Sentinel-3 Green Instantaneous FAPAR and Canopy Chlorophyll Content Products

This article presents validation and conformity testing of the Sentinel-3 Ocean Land Colour Instrument (OLCI) green instantaneous fraction of absorbed photosynthetically active radiation (FAPAR) and OLCI terrestrial chlorophyll index (OTCI) canopy chlorophyll content (CCC) products with fiducial reference measurements (FRM) collected in 2018 and 2021 over two sites (Las Tiesas—Barrax, Spain, and Wytham Woods, UK) in the context of the European Space Agency (ESA) Fiducial Reference Measurement for Vegetation (FRM4Veg) initiative. Following metrological principles, an end-to-end uncertainty evaluation framework developed in the project is used to account for the uncertainty of reference data based on a two-stage validation approach. The process involves quantifying uncertainties at the elementary sampling unit (ESU) level and incorporating these uncertainties in the upscaling procedures using orthogonal distance regression (ODR) between FRM and vegetation indices derived from Sentinel-2 data. Uncertainties in the Sentinel-2 data are also accounted for. FRM-based high spatial resolution reference maps and their uncertainties were aggregated to OLCI’s native spatial resolution using its apparent point spread function (PSF). The Sentinel-3 mission requirements, which give an uncertainty of 5% (goal) and 10% (threshold), were considered for conformity testing. GIFAPAR validation results revealed correlations > 0.95, RMSD ~0.1, and a slight negative bias (~−0.06) for both sites. This bias could be partly explained by the differences in the FAPAR definitions between the satellite product and the FRM-based reference. For the OTCI-based CCC, leave-one-out cross-validation demonstrated correlations > 0.8 and RMSDcv ~0.28 g·m−2. Despite the encouraging validation results, conclusive conformity with the strict mission requirements was low, with most cases providing inconclusive results (driven by large uncertainties in the satellite products as well as by the uncertainties in the upscaling approach). It is recommended that mission requirements for bio-geophysical products are reviewed, at least at the threshold level. It is also suggested that the large uncertainties associated with the two-stage validation approach may be avoided by directly comparing with spatially representative FRM.

Biogeochemical Markers to Identify Spatiotemporal Gradients of Phytoplankton across Estuaries

The spatiotemporal distribution of phytoplankton in estuaries is indicative of processes and transport across the land–ocean aquatic continuum (LOAC). Estuaries, as biogeochemically and physically active systems, process large amounts of nutrients and organic matter influencing the transformation of ecological functions. The transformation of the water column drives variation in phytoplankton composition, biomass, and their spatial distribution. Understanding the dynamics of nutrients and organic matter is challenging, yet it provides a comprehensive insight into phytoplankton spatiotemporal distribution across estuaries. Multiple studies have been conducted to understand the spatiotemporal distribution of phytoplankton. Recently, phytoplankton photosynthetic pigments, fatty acids and stable isotopes have been widely used to identify and quantify phytoplankton distribution. This review highlights the use of biogeochemical markers to identify phytoplankton functional groups. It also assesses the current understanding of patterns in the spatiotemporal distribution of phytoplankton and the impact of physical and environmental factors on their distribution in estuaries and coastal oceans. The review will also gather information from in situ sampling studies to evaluate the current state of knowledge and identify gaps.

A mechanism for coastal fog genesis at evening transition

AbstractTransitional changes in the atmospheric boundary layer (ABL) are known to facilitate the onset of terrestrial fog, which is defined as a condition with near‐surface visibility <1 km due to airborne water droplets. In particular, the evening transition from a daytime convective ABL to a night‐time stable ABL provides favorable conditions for fog. This article describes a local fog event observed during the evening transition at a Canadian islet in the north Atlantic known as Sable Island during the “Fog and Turbulence Interactions in the Marine Atmosphere (Fatima)” field campaign. The comprehensive set of data collected using a myriad of instruments covering a wide range of scales allowed identification of a novel mechanism underlying this fog event. Therein an ocean–land discontinuity created a flow regime consisting of several stacked boundary layers, interplay of which produced a thin low‐level cloud that then diffused downward to the surface, causing visibility reduction. This mechanism offers useful insights on the role of boundary layers, stratification, and turbulence in fog genesis over oceanic islands.

Evaluation of dynamical downscaling in a fully coupled regional earth system model

A set of decadal simulations has been completed and evaluated for gains using the Regional Arctic System Model (RASM) to dynamically downscale data from a global Earth system model and two atmospheric reanalyses. RASM is a fully coupled atmosphere–land–ocean–sea ice regional Earth system model. Nudging to the forcing data is applied to approximately the top half of the atmospheric domain. RASM simulations were also completed with a modification to the atmospheric physics for evaluating changes to the modeling system. The results show that for the top half of the atmosphere, the RASM simulations follow closely to that of the forcing data, regardless of the forcing data. The results for the lower half of the atmosphere, as well as the surface, show a clustering of atmospheric state and surface fluxes based on the modeling system. At all levels of the atmosphere the imprint of the weather from the forcing data is present as indicated in the pattern of the annual means. Biases, in comparison to reanalyses, are evident in the Earth system model forced simulations for the top half of the atmosphere but are not present in the lower atmosphere. This suggests that bias correction is not needed for fully coupled dynamical downscaling simulations. While the RASM simulations tended to go to the same mean state for the lower atmosphere, there are a differences in the variability and changes of weather patterns across the ensemble of simulations. These differences in the weather result in variances in the sea ice and oceanic states.

Groundwater, salt and contaminant transport in a coastal aquifer system with a low‐permeability layer in the intertidal zone

AbstractLow‐permeability layer (LPL), formed by natural deposit or artificial reclamation and commonly found below the intertidal zone of coastal groundwater system, can retard the ingress of seawater and contaminants, and shorten the travel time of the land‐sourced contaminant to the marine environment compared with a homogenous sandy coastal aquifer. However, there is limited understanding on how an intertidal LPL, a condition occurred in a coastal aquifer at Moreton Bay, Australia, influences the groundwater and contaminant transport across the shallow beach aquifer system. We characterized the aquifer hydrological parameters, monitored the in situ groundwater heads, and constructed a 2‐D numerical model to analyses the cross‐shore hydrological processes in this stratified system. The calibrated model suggests that in the lower aquifer, the inland‐source fresh groundwater flowed horizontally towards the sea, upwelled along the freshwater–saltwater interface, and exited the aquifer at the shore below the LPL. Whereas in the upper aquifer, the tidally driven seawater circulation formed a barrier that prevented fresh groundwater from horizontal transport and discharge to the beach above the LPL, thereby directing its leakage to the lower aquifer. A contaminant represented by a conservative tracer was ‘released’ the upper aquifer in the model and results showed that the spreading extent of the contaminant plume, the maximum rate of contaminant discharge to the ocean, and its plume length decreased compared with a simulation case in a homogenous sandy aquifer. Sensitivity analysis was also conducted to investigate the characteristics of the LPL, including its continuity and hydraulic conductivity, which were found to vary along the beach at Moreton Bay. The result shows that with a lower hydraulic conductivity and continuous layer of LPL reduced the groundwater exchange and contaminant transport between upper and lower aquifer. The findings from the combined field and modelling investigations on the impact of an intertidal LPL on coastal aquifer systems highlight its significant implications to alter the groundwater and mass transport across the land–ocean interface.

Nanoparticles in terrestrial sediments and the behavior of the spectral optics of Sentinel-3B OLCI Satellite images in a river basin of UNESCO World Cultural and Natural Heritage.

The dangerous chemical elements associated with nanoparticles (NPs) and ultra-fine sediment particles in hydrological bays have the capacity to move contaminants to large oceanic regions. The general objective of this study is to quantify the major chemical elements present in NPs and ultra-fine particles in aquatic sediments sampled from Guanabara Bay and compare these data to values determined through spectral optics using the Sentinel-3B Satellite OLCI (Ocean Land Color Instrument) during the winter and summer seasons of 2018, 2019, 2020, 2021, and 2022. This is done to highlight the impacts anthropogenic environmental hazards have on the marine ecosystem and human beings. Ten aquatic sediment field collection points were selected by triangulated irregular network (TIN). Samples were subjected to analysis by X-ray diffraction (XRD), scanning electron microscopy (SEM), electron dispersion spectroscopy (EDS), and transmission electron microscopy (TEM), which enabled a detailed analysis using scanning transmission electron microscopy (STEM). Geospatial analyses using Sentinel-3B OLCI Satellite images considered Water Full Resolution (WFR) at 300m resolution, in neural network (NN), normalized at 0.83µg/mg. A maximum average spectral error of 6.62% was utilized for the identification of the levels of Absorption Coefficient of Detritus and Gelbstoff (ADG443_NN) at 443m-1, Chlorophyll-a (CHL_NN) (m-3), and Total Suspended Matter (TSM_NN) (g m-3) at 581 sample points. The results showed high levels of ADG443_NN, with average values as high as of 4444m-1 (summer 2021). When related to the analyses of nanoparticulate sediments and ultrafine particles collected in the field, they showed the presence of major chemical elements such as Ge, As, Cr, and others, highly toxic to human health and the aquatic environment. The application of satellite and terrestrial surveys proved to be efficient, in addition to the possibility of this study being applied to other hydrological systems on a global scale.

ENSO weakens the co-variability between the spring persistent rains and Asian summer monsoon: Evidences from tree-ring data in southeastern China

The Spring Persistent Rains (SPR) and the Asian Summer Monsoon (ASM) are the two dominant rainfall systems in East Asia, providing together a majority of annual rainfall in southeastern China (SEC). Since observational data in SEC were mostly unavailable until the 1950s, proxy records that are capable of capturing the SPR and ASM variations are required to examine the long-term co-variability patterns between them. Tree-ring earlywood and latewood δ18O records in SEC were found to respond to relative humidity (RH) during the SPR and ASM seasons, respectively, allowing us, for the first time, to reconstruct the RH changes of SPR and ASM back to 1801. The two reconstructions can explain 44.9 % and 42.3 % of the instrumental variance. We observed a long-lasting wet epoch in the 1920s–60s for both the SPR and ASM, caused by a peak in the land–ocean thermal contrast. The El Niño-Southern Oscillation (ENSO) and the Intertropical Convergence Zone (ITCZ) were found to be the two leading tropical systems that modulated the SPR and ASM co-variability. During a period with weakened ENSO variance, the RH of SPR and ASM showed in-phase changes driven by the ITCZ. However, when the ENSO variance became strengthened, the co-variability collapsed since the ENSO can offset the influence of the ITCZ via teleconnections.

Response of the Current Climate to Land‐Ocean Contrasts in Parameterized Cumulus Entrainment

AbstractCumulus entrainment substantially regulates the earth's climate but remains poorly constrained in global climate models. Recent studies have shown that cumulus bulk entrainment (or dilution) is particularly sensitive to continentality, with the entrainment rate in simulated maritime cumuli nearly double that of continental cumuli. This study examines the impacts of such land–ocean entrainment contrasts on the current climate using 21‐year simulations with the Geophysical Fluid Dynamics Laboratory's High‐Resolution Atmospheric Model (HIRAM). In response to a 25% reduction in the HIRAM entrainment parameter c0 over land, precipitation over tropical land regions increases by up to 40%. Along with directly facilitating enhanced convective precipitation, this c0 reduction induces an increase in soil moisture, which may contribute to a further enhancement of convective precipitation over land. A 25% c0 reduction over the oceans leads to more widespread modifications of convection patterns, with the strongest signal in the tropical Pacific. Deep convection shifts upstream (eastward) there, inducing enhanced large‐scale ascent over the central Pacific with compensating subsidence and reduced humidity and precipitation over the western Pacific (WP). Land–ocean variations in c0 project onto the Pacific Walker circulation, with the 25% land reduction strengthening it by 4% and the 25% ocean reduction weakening it by 14%. These changes are driven by variations in convective and large‐scale stratiform heating over the Pacific. While reduced c0 over land enhances diabatic heating in the Maritime Continent to strengthen the Walker circulation, reduced c0 over the oceans decreases diabatic heating in the WP to weaken the Walker circulation.

The Indirect-Lightning Performance of Overhead Distribution Line Considering the Mixed Ocean–Land Propagation Path

The Indirect-Lightning Performance of Overhead Distribution Line Considering the Mixed Ocean–Land Propagation Path

Analyzing urban influence on extreme winter precipitation through observations and numerical simulation of two South China case studies

This study investigates the impact of urbanization on extreme winter rainfall in the South China Greater Bay Area (GBA) through the analysis of hourly station observations and simulations using the Weather Research and Forecasting Model with the Single Layer Urban Canopy Model (WRF-SLUCM). Data from 2008 to 2017 reveal that urban areas in the GBA experience lower 99th percentile hourly winter rainfall intensity compared to surrounding rural regions. However, urban locations exhibit higher annual maximum hourly rainfall (Rmax) and very extreme rainfall events (99.99th percentile) in winter, suggesting a positive influence of urbanization on extreme winter precipitation. A case study further underscores the role of the Urban Heat Island (UHI) effect in enhancing extreme rainfall intensity and probability in the GBA urban areas. Additionally, two extreme cases were dynamically downscaled using WRF-SLUCM, involving four parallel experiments: replacing urban land use with cropland (Nourban), using historical urban land use data from 1999 (99LS), projecting near-future urban land use for 2030 (30LS), and considering 2030 urban land use without anthropogenic heat (AH) (30LS-AH0). Synoptic analysis demonstrates that cold air intrusion suppresses the GBA UHI in Case 2013 but not in Case 2015. Reduced evaporation and humidity induced by urban surfaces significantly decrease urban precipitation in Case 2013. In contrast, the persistent UHI in Case 2015 enhances local convection and land–ocean circulation, leading to increased moisture flux convergence and amplified urban precipitation intensity and probability in 30LS compared to Nourban. This amplification is primarily attributed to AH, while the change in 99LS remains insignificant. These findings suggest that urban influences on extreme precipitation in the GBA persist during winter, particularly when the UHI effect is maintained.