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The East African March–April–May (MAM, "long rains") precipitation decline in recent decades remains a puzzle marked by various proposed large‐scale drivers. Here, the interannual variability of the long rains and their recent drying trend are examined using global model simulations and observations. Comparison of a control simulation and re‐initialized simulations in which land‐surface feedback is suppressed shows that much of the long rains deficit experienced between 1980 and 2014 is synchronized with the warming of the Northwestern Eurasian landmass. In agreement with the modeling results, multiple observational data sets reveal a strong negative correlation between MAM mean East African rainfall amount and the surface temperature over Northwestern Eurasia. Idealized simulations further indicate that warming in Northwestern Eurasia weakens the regional Hadley Cell and diverts the monsoonal transport of moisture away from Eastern Africa toward Europe and southern Africa, highlighting the role of remote land surface warming on the observed precipitation decline. Plain Language Summary: In this article the inter‐annual variability and the observed long‐term decline of Boreal spring rainfall over Eastern Africa are examined. Previous research on the causes of these droughts focused on sea surface temperature variability over tropical oceans. In this work through extensive analysis of observations and global modeling we show that land‐surface feedbacks over Northwestern Eurasia are the primary culprit. More broadly the work highlights the importance of teleconnections between regional climates through remote impacts of land surface feedbacks. Key Points: We demonstrate a co‐variability of East African March–April–May rainfall (long rains) and surface temperature over Northwestern EurasiaAnalysis of model simulations show warming Northwestern Eurasia weakens the local Hadley cell and introduces subsidence over East AfricaThe observed decline in East African March–April–May rainfall observed during 1980–2014 can be explained by this warming [ABSTRACT FROM AUTHOR]

Based on observation analysis and numerical simulation, this study reveals that the spring land-sea thermal contrast between Yun-Gui Plateau and Beibu Gulf has a significant triggering impact on the variations of South China Sea summer monsoon onset dates (SCSSMOD) at the interannual timescale. The March–April thermal contrast with warm Yun-Gui Plateau and cold Beibu Gulf results in an anomalous low-level anticyclone over the western North Pacific, which in turn causes the active convection in the tropical western Pacific via the friction convergence. This active convection persists into May and moves northward towards the South China Sea. It subsequently excites an anomalous low-level cyclone in situ via the Matsuno-Gill mechanism. Then, the western Pacific subtropical high is tending to retreat eastward and the westerly wind anomalies occupy the South China Sea, promoting an early SCSSMOD. When the thermal contrast reverses, the SCSSMOD is inclined to be late. The effects mentioned above are independent of ENSO, indicating an effective indicator for monitoring and predicting the SCSSMOD at the interannual timescale. [ABSTRACT FROM AUTHOR]

Accurate projections and attribution of Arctic Ocean changes in climate models require a good understanding of the mechanisms underlying interannual salinity variability in the region. Although some mechanisms have been extensively studied in idealized setting, in particular for the dynamics of the Beaufort gyre (BG), it remains unclear how applicable they are to more complex systems. This study introduces a new diagnostic based on salinity variance budget to robustly assess the mechanisms of salinity variations. The diagnostic is then applied to the "Estimating the Circulation and Climate of the Ocean" state estimate. Results indicate that the advection of salinity anomaly in the direction of the mean salinity gradient made by velocity anomalies is the primary source of interannual salinity variability. These velocities are primarily attributed to fluctuating winds via Ekman transports. Fluctuating surface freshwater fluxes from the atmosphere and sea ice are the second most important source of variability and cannot be neglected. The two sinks of interannual salinity variance are associated with the erosion of large scale gradients of the mean circulation by eddies and to a lesser extent to the diffusive terms. Over continental shelves, particularly over the East Siberian Shelf (ESS), ocean surface freshwater fluxes and diffusion play a more important role than in the deep basins. We also report a strong intensification of all sources and sinks of interannual salinity variability in the BG and an opposite weakening in the ESS in the second decade of the analysis (2004–2014) with respect to the first (1993–2003). Plain Language Summary: A clear understanding of the mechanisms of the slow salinity variations in the Arctic could help improving their representation in climate models and provide directions on where new in‐situ observing systems should be positioned. Most of the past studies of the mechanisms have used simple models in which several important realistic characteristics, such as the true bathymetry, are missing. In this work we develop a novel methodology that allows to robustly assess these mechanisms in realistic configurations. We then apply this methodology to an ocean state estimate ("Estimating the Circulation and Climate of the Ocean" v4r3) and study in details the forcing and damping mechanisms of the salinity variability in the Arctic. We find that the fluctuating wind is the main driver of the variability whereas mesoscale eddies are the main damping. Varying freshwater fluxes and diffusion also play a role and cannot be neglected. Key Points: A novel diagnostic is developed allowing the analysis of the mechanisms of salinity variability in realistic configurations of the ArcticThe main source of Arctic interannual salinity variability is associated to wind forcing variations, the main sink to mesoscale eddiesDiffusion and freshwater fluxes (mainly due to sea‐ice melt and freeze) play a non‐negligible role, particularly over the continental shelf [ABSTRACT FROM AUTHOR]

Comprehensive morphometric and hydrometeorological studies on Bacalar Lagoon, Mexico's largest tropical karstic lake and a significant aquatic system of the Yucatán Peninsula, are lacking. This study provides a detailed analysis of its bathymetry, morphometry, and hydrometeorological characteristics. The lake's main basin stretches more than 52.7 km in length, with widths varying from 0.18 km to 2.28 km. It has a volume of 554.4 million cubic meters, with an average depth of 8.85 m, reaching depths of up to 26 m in the north and featuring sub-lacustrine dolines in the south, with depths of 38 m, 48.5 m, and 63.6 m. The study reveals seasonal variations in surface water temperature, closely linked to air temperature (r = 0.89), and immediate responses of water levels to hydrometeorological events. Water level fluctuations also exhibit seasonal patterns that are correlated with regional aquifer conditions, with a lag of 2 months after seasonal rainfall. Interannual variability in rainfall and water levels was observed. From 2010 to 2012, rainfall consistently remained below its mean climatic value, due to a prolonged La Niña event, while the exceptionally wet conditions in 2020 were also associated with La Niña. Extreme and anomalous hydrometeorological events, such as those following tropical storm Cristobal in 2020, revealed the fragility of Bacalar Lagoon, causing a notable transformation in lake color and transparency, shifting it from its typical oligotrophic state to eutrophic conditions that lasted longer than a year. These color changes raise questions about the factors impacting ecological health in tropical karstic regions. Additional factors affecting water quality in the BL in 2020, such as deforestation, coastline changes, and urban growth, warrant further investigation. Our study can serve as a starting landmark. [ABSTRACT FROM AUTHOR]

We investigate rainfall variability in Indonesia using the Empirical Orthogonal Function (EOF) method. The analysis starts by taking three main modes of EOF results, namely EOF1, EOF2, and EOF3. The EOF1 region is southern Indonesia, from southern Sumatra to Timor Island, parts of Kalimantan, parts of Sulawesi, and parts of Irian Jaya. The EOF2 region is located in northwestern Indonesia and includes the northern part of Sumatra and the northwestern part of Kalimantan. The EOF3 region covers Maluku. This study aims to analyze the annual and inter-annual variability of rainfall in anticipation of the threat of hydrometeorological disasters. Based on the correlation value of the principal component (PC) with the dipole mode index (DMI) and Niño3.4 index, it has a period similar to El Niño-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD). Rainfall in Indonesia is very sensitive to sea surface temperature (SST) in the southeastern Indian Ocean and the central Pacific Ocean, which means that rainfall patterns in Indonesia can change significantly if SST in the region changes.

Long‐term (press) disturbances like the climate crisis and other anthropogenic pressures are fundamentally altering ecosystems and their functions. Many critical ecosystem functions, such as biogeochemical cycling, are facilitated by microbial communities. Understanding the functional consequences of microbiome responses to press disturbances requires ongoing observations of the active populations that contribute to functions. This study leverages a 7‐year time series of a 60‐year‐old coal seam fire (Centralia, Pennsylvania, USA) to examine the resilience of soil bacterial microbiomes to a press disturbance. Using 16S rRNA and 16S rRNA gene amplicon sequencing, we assessed the interannual dynamics of the active subset and the 'whole' bacterial community. Contrary to our hypothesis, the whole communities demonstrated greater resilience than active subsets, suggesting that inactive members contributed to overall structural resilience. Thus, in addition to selection mechanisms of active populations, perceived microbiome resilience is also supported by mechanisms of dispersal, persistence, and revival from the local dormant pool. [ABSTRACT FROM AUTHOR]

Satellite observations have given us a clear idea of the changes in chlorophyll in the surface ocean on both a seasonal and interannual basis, but repeated observations at depth are much rarer. The permanently-stratified subtropical gyres in the Atlantic are highly oligotrophic, with most production centred on a deep chlorophyll maximum (DCM) just above the nitracline. This study explores the variations in this feature in the core of both gyres, considering both seasonal and interannual variations, and the linkages between changes at the surface and sub-surface. The in situ observations come from the Atlantic Meridional Transect (AMT), a long-running UK monitoring programme, and also from biogeochemical Argo floats. AMT provides measurements spanning more than 25 years directed through the centres of these gyres, but samples only 2 to 4 months per year and thus cannot resolve the seasonal variations, whereas the profiling floats give coverage throughout the year, but without the rigid spatial repeatability. These observational records are contrasted with representation of the centres of the gyres in two different biogeochemical models: MEDUSA and ERSEM, thus fulfilling one of AMT’s stated aims: the assessment of biogeochemical models. Whilst the four datasets show broadly the same seasonal patterns and that the DCM shallows when surface chlorophyll increases, the depth and peak concentration of the DCM differ among datasets. For most of the datasets the column-integrated chlorophyll for both gyres is around 19 mg m-2 (with the AMT fluorescence-derived values being much lower); however the MEDUSA model has a disparity between the northern and southern gyres that is not understood. Although the seasonal increase in surface chlorophyll is tied to a commensurate decrease in concentration at depth, on an interannual basis years with enhanced surface levels of chlorophyll correspond to increases at depth. Satellite-derived observations of surface chlorophyll concentration act as a good predictor of interannual changes in DCM depth for both gyres during their autumn season, but provide less skill in spring. [ABSTRACT FROM AUTHOR]

Comprehensive morphometric and hydrometeorological studies on Bacalar Lagoon, Mexico’s largest tropical karstic lake and a significant aquatic system of the Yucatán Peninsula, are lacking. This study provides a detailed analysis of its bathymetry, morphometry, and hydrometeorological characteristics. The lake’s main basin stretches more than 52.7 km in length, with widths varying from 0.18 km to 2.28 km. It has a volume of 554.4 million cubic meters, with an average depth of 8.85 m, reaching depths of up to 26 m in the north and featuring sub-lacustrine dolines in the south, with depths of 38 m, 48.5 m, and 63.6 m. The study reveals seasonal variations in surface water temperature, closely linked to air temperature (r = 0.89), and immediate responses of water levels to hydrometeorological events. Water level fluctuations also exhibit seasonal patterns that are correlated with regional aquifer conditions, with a lag of 2 months after seasonal rainfall. Interannual variability in rainfall and water levels was observed. From 2010 to 2012, rainfall consistently remained below its mean climatic value, due to a prolonged La Niña event, while the exceptionally wet conditions in 2020 were also associated with La Niña. Extreme and anomalous hydrometeorological events, such as those following tropical storm Cristobal in 2020, revealed the fragility of Bacalar Lagoon, causing a notable transformation in lake color and transparency, shifting it from its typical oligotrophic state to eutrophic conditions that lasted longer than a year. These color changes raise questions about the factors impacting ecological health in tropical karstic regions. Additional factors affecting water quality in the BL in 2020, such as deforestation, coastline changes, and urban growth, warrant further investigation. Our study can serve as a starting landmark.

Using ERA5 reanalysis data, we conducted an EOF analysis of summer precipitation in the eastern part of southwestern China (ESWC) over the past 60 years. Our study aimed to investigate the spatial distribution characteristics and interannual variability of summer precipitation in the ESWC, as well as to reveal the possible physical mechanisms influencing its interannual variability. The results indicate that, at the interannual scale, the first two modes of summer precipitation in the ESWC exhibit a uniform pattern and a north–south dipole pattern, respectively. The maximum and minimum time coefficients of the first mode correspond to the severe flood and drought events in 1998 and 2006, respectively, indicating that their time coefficients reflect the typical events well. The tri-pole sea surface temperature anomaly in the North Atlantic, along with the sea ice anomaly near the Barents Sea, induces a quasi-zonal wave train in the upper troposphere. This wave train propagates from the tropical and mid-latitude Atlantic, traverses the mid-high latitudes of Eurasia, and reaches the eastern part of China. The wave train induces cyclonic (anticyclonic) anomalies in the north (south) of the ESWC, facilitating the convergence of high-latitude dry and cold air with warm and moist southwesterly winds from the tropical ocean. This convergence promotes increased summer precipitation in the ESWC. We provided valuable insights into the interannual variability of summer precipitation in the ESWC, shedding light on the physical mechanisms responsible for these variations. [ABSTRACT FROM AUTHOR]

The Southern Ocean is a major sink of atmospheric CO2, but the nature and magnitude of its variability remains uncertain and debated. Estimates based on observations suggest substantial variability that is not reproduced by process-based ocean models, with increasingly divergent estimates over the past decade. We examine potential constraints on the nature and magnitude of climate-driven variability of the Southern Ocean CO2 sink from observation-based air–sea O2 fluxes. On interannual time scales, the variability in the air–sea fluxes of CO2 and O2 estimated from observations is consistent across the two species and positively correlated with the variability simulated by ocean models. Our analysis suggests that variations in ocean ventilation related to the Southern Annular Mode are responsible for this interannual variability. On decadal time scales, the existence of significant variability in the air–sea CO2 flux estimated from observations also tends to be supported by observation-based estimates of O2 flux variability. However, the large decadal variability in air–sea CO2 flux is absent from ocean models. Our analysis suggests that issues in representing the balance between the thermal and non-thermal components of the CO2 sink and/or insufficient variability in mode water formation might contribute to the lack of decadal variability in the current generation of ocean models. This article is part of a discussion meeting issue 'Heat and carbon uptake in the Southern Ocean: the state of the art and future priorities'. [ABSTRACT FROM AUTHOR]

Few studies have explored the details of climatology in the Gulf of California (GoC) coastal zone, a region characterized by robust land–sea breeze circulation that results from land heating on both coasts of the GoC. Using hourly historical observations from automatic weather stations (AWSs) from 2008 to 2018, we performed harmonic and empirical orthogonal function analyses to describe the climatology of several characteristics that are regularly monitored in the GoC coastal zone. The characteristics included air temperature (°C), relative humidity (%), atmospheric pressure (hPa), wind intensity (m s−1), and wind direction (°). The National Water Commission (CNA) provided records for stations located along the coast of the GoC. The results revealed an intense annual and, to a lesser extent, interannual signal for all characteristics. The presence of synoptic patterns forces seasonal and intraseasonal variations to occur. In summer, tropical systems increase the seasonal variability, mainly at the eastern mouth of the GoC. Some stations display this increase until the cold season arrives with the passage of winter systems. Finally, we found that interannual variability could be associated with El Niño–Southern Oscillation events. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Henan Agricultural Sciences is the property of Editorial Board of Journal of Henan Agricultural Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Understanding long-term seasonal and interannual patterns of soil respiration with their controls is essential for accurately quantifying carbon fluxes at a regional scale. During the period from 2009 to 2014, an automatic measurement system (LI-8150, Licor Ldt., Lincoln, NE, USA) was employed for the measurement of soil respiration in a meadow steppe of eastern Inner Mongolia. We found that the seasonal pattern of soil respiration was controlled mainly by the soil temperature, which explained about 82.19% of the variance. Annual soil respiration varied between 391.4 g cm−2 and 597.7 g cm−2, and significantly correlated with soil moisture, suggesting that soil moisture was the most predominant factor controlling the annual variations of soil respiration in this meadow steppe. A double factorial exponential model including both soil temperature (TS) and soil water content (SWC) (y = 6.084 × exp(0.098 TS × SWC) − 5.636) explains 72.2% of the overall variance in soil respiration. We also detected a temporal inconsistency of 2–3 months in the effects of precipitation on soil respiration versus canopy biomass production, which was presumably a main mechanism explaining the weak relationships between soil respiration and phytomass components in this ecosystem. Our findings have important implications for better understanding and accurately assessing the carbon cycling characteristics of terrestrial ecosystems in response to climate change in a temporal perspective. [ABSTRACT FROM AUTHOR]

Stratospheric processes and their role in weather and climate have attracted increasing interests. The correspondence between the occurrence of pulse-like, stronger stratospheric poleward warm airmass transport (PULSE) events and the continental-scale cold air outbreak (CAO) events in northern hemispheric winter is found to be unstable from year to year. This increases the difficulties in utilizing the more predictable stratospheric variability in the sub-seasonal forecasts of CAOs, which can cause cold hazards. Using the ERA5 reanalysis data covering 37 winters (November–March) in the period 1979–2015, this study categorizes the CAO events over mid-latitudes of Eurasia (CAO_EA) and those over North America (CAO_NA) into two groups: those coupled with and those decoupled with the PULSE events. The coupled CAOs are further categorized into events that are, respectively, lead-coupled and lag-coupled with PULSEs. The intensity and affected area of extremely cold temperatures tend to be larger during CAOs that are coupled with PULSEs, particularly during the CAO_NA events that are lag-coupled with PULSEs and the CAO_EA events that are lead-coupled with PULSEs. Remarkable interannual and interdecadal variations are observed in the percentage of CAOs that are coupled with PULSEs for each winter, which is an important reference for determining the window of opportunity for skillful sub-seasonal forecasts of CAO by using the stratospheric signals. At both interdecadal and interannual timescales, a warm phase of the El Niño–Southern Oscillation (ENSO) in winter is favorable for the higher lag-coupling rate of CAO_NA and the lead-coupling rate of CAO_EA, and vice versa. The ENSO signals related to the interdecadal changes of the CAO coupling rate in winter can be traced back to the previous winter, while an ENSO phase transition from the previous winter to the current winter is closely related to the interannual changes of the CAO coupling rate.

Timing of the rainy season is essential for a number of climate sensitive sectors over Eastern Africa. This is particularly true for the agricultural sector, where most activities depend on both the spatial and temporal distribution of rainfall throughout the season. Using a combination of observational and reanalysis datasets, the present study investigates the atmospheric and oceanic conditions associated with early and late onset for Eastern Africa short rains season (October–December). Our results indicate enhanced rainfall in October and November during years with early onset and rainfall deficit in years with late onset for the same months. Early onset years are found to be associated with warmer sea surface temperatures (SSTs) in the western Indian Ocean, and an enhanced moisture flux and anomalous low‐level flow into Eastern Africa from as early as the first dekad of September. The late onset years are characterized by cooler SSTs in the western Indian Ocean, anomalous westerly moisture flux and zonal flow limiting moisture supply to the region. The variability in onset date is separated into the interannual and decadal components, and the links with SSTs and low‐level circulation over the Indian Ocean basin are examined separately for both timescales. Significant correlations are found between the interannual variability of the onset and the Indian Ocean dipole mode index. On decadal timescales the onset is shown to be partly driven by the variability of the SSTs over the Indian Ocean. Understanding the influence of these potentially predictable SST and moisture patterns on onset variability has huge potential to improve forecasts of the East African short rains. Improved prediction of the variability of the rainy season onset has huge implications for improving key strategic decisions and preparedness action in many sectors, including agriculture. [ABSTRACT FROM AUTHOR]

Using ERA5 reanalysis data, we conducted an EOF analysis of summer precipitation in the eastern part of southwestern China (ESWC) over the past 60 years. Our study aimed to investigate the spatial distribution characteristics and interannual variability of summer precipitation in the ESWC, as well as to reveal the possible physical mechanisms influencing its interannual variability. The results indicate that, at the interannual scale, the first two modes of summer precipitation in the ESWC exhibit a uniform pattern and a north–south dipole pattern, respectively. The maximum and minimum time coefficients of the first mode correspond to the severe flood and drought events in 1998 and 2006, respectively, indicating that their time coefficients reflect the typical events well. The tri-pole sea surface temperature anomaly in the North Atlantic, along with the sea ice anomaly near the Barents Sea, induces a quasi-zonal wave train in the upper troposphere. This wave train propagates from the tropical and mid-latitude Atlantic, traverses the mid-high latitudes of Eurasia, and reaches the eastern part of China. The wave train induces cyclonic (anticyclonic) anomalies in the north (south) of the ESWC, facilitating the convergence of high-latitude dry and cold air with warm and moist southwesterly winds from the tropical ocean. This convergence promotes increased summer precipitation in the ESWC. We provided valuable insights into the interannual variability of summer precipitation in the ESWC, shedding light on the physical mechanisms responsible for these variations.

Elevated inputs of sulfate to freshwater systems can increase sulfide concentrations in anoxic soils and subsequently destabilize aquatic plant populations, but the interactions between sulfate, other geochemical cycles, and interannual plant population cycles are poorly understood. Increased sulfate loading increases mineralization of nitrogen from litter, but the sulfide produced during this process can limit nitrogen uptake by plants. In some cases, iron may mitigate sulfide's impacts on plants by precipitating iron sulfide. We examined the interannual effects of sulfate loading on mesocosm populations of wild rice, an emergent aquatic plant that undergoes population oscillations and is sensitive to sulfide. Using experimental mesocosms with self‐perpetuating populations, we investigated how population dynamics respond to manipulations of surface water sulfate (10 mg L−1 or 300 mg L−1), sediment iron (4.3 mg g−1 or 10.9 mg g−1 dry weight), and shoot litter (present or removed). Populations exposed to constant 10 mg L−1 sulfate concentrations had stable biomass oscillations of approximately 3‐year periods, consistent with previous studies that demonstrated litter‐driven oscillations in nitrogen availability. Populations exposed to 300 mg L−1 sulfate concentrations produced fewer and smaller seeds and declined to extinction in 6 years or less. We did not find a strong effect of iron loading or litter removal on wild rice biomass or seed production. Our observations show the potential of elevated surface water sulfate to rapidly destabilize wild rice populations under varying iron and organic carbon concentrations. Plain Language Summary: Plants that naturally grow in freshwater do not survive well if the water contains elevated concentrations of sulfate. Sulfate reduction produces sulfide that subsequently inhibits the uptake of nitrogen, an essential plant nutrient. Some annual plants go through boom‐bust cycles with years alternating between high and low biomass because nitrogen takes more than a year to be released from dead plant matter. We investigated the combined effect of sulfate and natural biomass cycles on the stability of wild rice populations by growing plants in large tanks and exposing them to high‐sulfate and low‐sulfate concentrations, high and low iron concentrations, and with plant matter from the previous growing season either returned or removed. Nearly all plant populations exposed to high sulfate had died by 6 years into the experiment, regardless of iron concentration or litter removal. We show a method to analyze population stability with just a few years of data. Key Points: Populations exposed to elevated sulfate went extinct in 6 years, overriding interannual biomass oscillationsIron addition and litter removal slightly alleviated sulfide toxicity but did not prevent population extinctionStability of oscillating populations can be evaluated with only a few years' data using an eigenvalue [ABSTRACT FROM AUTHOR]

Abstract Background The analysis of bird community assembly rules is fundamental to understand which mechanisms determine the composition of bird species in urban areas. However, the long-term variation of community assembly rules has not been analyzed yet. The objectives of this study are (1) to analyze the variation of community assembly rules along rural-urban gradients of three cities in central Argentina and (2) to compare the patterns of community assembly between two periods separated by 6 years. Bird surveys were performed along transects in urban, suburban, and rural habitats during 2011 and 2017. Departures from null models that took into account differences in species richness (standardized effect size, SES) were calculated for functional and phylogenetic diversities. Results A total of 57 species were recorded. Bird species richness was higher in suburban than in urban and rural habitats. SES of functional diversity increased over the years and was significantly lower in urban habitats than in rural habitats, showing a pattern of functional clustering in the most urbanized areas and functional randomness in rural ones. Phylogenetic diversity was higher in both suburban and urban habitats than rural ones, and the phylogenetic clustering in rural bird assemblages changed to randomness in suburban and urban habitats. Conclusions Bird communities in urban habitats were phylogenetically random and functionally clustered, evidencing environmental filtering by urbanization. In contrast, bird communities in rural areas tended to be phylogenetically clustered, evidencing that certain clades are adapted to rural areas. The processes structuring bird communities along rural-urban gradients were consistent between the 2 years compared.

The global mean sea level (GMSL) has been measured precisely by the space geodetic remote-sensing technique of radar altimetry since the 1990s. Aside from the well-studied seasonality and secular sea level rise, here we focus on GMSL variation on the interannual–decadal (ID) timescales (GMSL-ID) and investigate the influences of the climatic oscillations as physical causes. We conduct correlation analyses on the GMSL-ID time series with several climatic oscillations represented by their respective meteorological indices, including El Niño-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), Atlantic Multidecadal Oscillation (AMO), Arctic Oscillation (AO), and Antarctic Oscillation (AAO). From the time-domain cross-correlation functions and the corresponding frequency-domain cross-coherence spectra, we find the following: (i) high correlation between GMSL-ID and ENSO, primarily befalling on the Central-Pacific (as opposed to the Eastern-Pacific) type of ENSO, on timescales longer than 1.5 years; (ii) moderate correlations of GMSL-ID with PDO on long-period timescales of over 4 years, and with AMO on a timescale of 2–10 years, with AMO leading in phase by 8 months; (iii) weak or practically no correlation of GMSL-ID with either AO or AAO, in the former case given the fact that our GMSL-ID data actually do not cover the Arctic sea. Finally, we least-squares fit the above five indices to GMSL-ID to assess the relative contribution of each oscillation in causing the observed GMSL-ID, for a better understanding of the GMSL under the influences of on-going climate change. [ABSTRACT FROM AUTHOR]

The Mediterranean Sea is considered a hot spot of global warming because it has been changing faster than the global ocean, creating a strong impact on the marine environment. Recent studies agree on the increase in the sea level, in the sea surface temperature, and in the sea surface salinity in the Mediterranean Sea over the last two decades. In this research, the possible interconnection between these and other parameters that contribute to the regulatory effect of the sea on the climate are identified and discussed. Spatio-temporal variability of four oceanographic and air–sea interaction parameters (sea-level, sea surface temperature, sea surface salinity, and freshwater flux) are estimated over the last 27 years by performing the empirical orthogonal function analysis. Climatic trends, and interannual and decadal variability of the different datasets are delineated and described in the whole Mediterranean and in its sub-basins. On the climatic scale, the Mediterranean and its sub-basins behave in a coherent way, showing the seal level, temperature, salinity, and freshwater flux rise. On the interannual scale, the temporal evolution of the sea level and sea surface temperature are highly correlated, whereas freshwater flux affects the variability of sea level, temperature, and the salinity field mainly in the Western and Central Mediterranean. The decadal signal associated with the Northern Ionian Gyre circulation reversals is clearly identified in three of the four parameters considered, with different intensities and geographical extents. This signal also affects the intermediate layer of the Eastern Mediterranean, from where it is advected to the other sub-basins. Decadal signal not associated with the Northern Ionian Gyre reversals is strongly related to the variability of main sub-basin scale local structures. [ABSTRACT FROM AUTHOR]

Copyright of Railway Investigation & Surveying is the property of Railway Investigation & Surveying Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We revisit longstanding controversies regarding summer‐mean relationships among the all‐India rainfall index (AIRI), sub‐India rainfall, El Niño‐Southern Oscillation (ENSO), and the Indian Ocean dipole (IOD) using 120‐year sea surface temperature and high‐resolution rainfall datasets. AIRI closely tracks with the spatial extent of wet anomalies and with the average across grid points in rainy day count. The leading rainfall variability mode is a monopole associated primarily with rainy day count and ENSO. The second mode is a tripole with same‐signed loadings in the high‐rainfall Western Ghats and Central Monsoon Zone regions and opposite‐signed loadings in Southeastern India between. The IOD projects onto this tripole and, as such, is weakly correlated with AIRI. However, when the linear influence of ENSO is removed, the IOD rainfall regressions become quasi‐homogeneously more positive, making the ENSO‐residual IOD and AIRI time series significantly correlated. Plain Language Summary: The Indian summer monsoon generates copious rainfall each June through September, but more in some years than others, and more in some Indian sub‐regions than others. We use observational datasets spanning 1901–2020 to reconcile past disagreements about these fluctuations. There has long been concern that the rainfall rate averaged over the whole summer and whole of India—the all‐India rainfall index—doesn't necessarily track with the spatial extent of wet or dry anomalies within India which is more relevant for many societal purposes, but we show that the two measures vary closely with one another. There has been disagreement about how the all‐India average relates to rainfall in fixed sub‐regions of India, and we show using high‐resolution rainfall data that the issue stems in part from the use of coarse datasets in the past. Finally, we reconcile disagreements about whether or not the Indian Ocean dipole (IOD) teleconnection influences all‐India rainfall by showing that, when the El Niño‐Southern Oscillation signal that influences both the IOD and the monsoon rains is removed, the IOD significantly influences the all‐India average and with a distinct sub‐India spatial pattern. Key Points: We examine Indian summer monsoon rainfall interannual variability and teleconnections 1901–2020All‐India Rainfall Index (AIRI) closely tracks spatial and temporal extent of wet anomaliesEl Niño‐Southern Oscillation teleconnection projects onto AIRI but Indian Ocean Dipole onto a known tripole pattern [ABSTRACT FROM AUTHOR]

The interdecadal change in the relationship between summer (June—August) tropical cyclone genesis frequency (TCGF) over the western North Pacific (WNP) and tropical sea surface temperature anomaly (SSTA) is investigated in this paper. Results show that the tropical SSTA pattern affecting the WNP TCGF has experienced an interdecadal change in 1991 / 92. Before the early 1990s, the positive TCGF anomaly corresponds to the eastern Pacific La Niña decaying phase. From the preceding winter to spring, the WNP local warming triggers an anomalous cyclone to its northwest, which is maintained by the cold SSTA over the tropical Indian Ocean in summer. After the early 1990s, the positive TCGF anomaly is related to the transition phase from eastern Pacific La Niña to central Pacific El Niño. In summer, an anomalous cyclone is induced by the warm SSTA over the central Pacific to its northwest and further intensified by the cold SSTA over the tropical eastern Indian Ocean, Maritime Continent and the tropical Atlantic, which could strengthen the convergent and upward motions over the central Pacific through vertical circulations. Since the warm SSTA is located further southward and eastward in the later period, the cyclonic anomaly and positive TCGF anomaly are both located more southward and extend further eastward in the later period. The interdecadal change in the relationship between the WNP TCGF and tropical SSTA is related to the accelerated evolution of El Niño-Southern Oscillation after the early 1990s. [ABSTRACT FROM AUTHOR]

Understanding long-term seasonal and interannual patterns of soil respiration with their controls is essential for accurately quantifying carbon fluxes at a regional scale. During the period from 2009 to 2014, an automatic measurement system (LI-8150, Licor Ldt., Lincoln, NE, USA) was employed for the measurement of soil respiration in a meadow steppe of eastern Inner Mongolia. We found that the seasonal pattern of soil respiration was controlled mainly by the soil temperature, which explained about 82.19% of the variance. Annual soil respiration varied between 391.4 g cm−2 and 597.7 g cm−2, and significantly correlated with soil moisture, suggesting that soil moisture was the most predominant factor controlling the annual variations of soil respiration in this meadow steppe. A double factorial exponential model including both soil temperature (TS) and soil water content (SWC) (y = 6.084 × exp(0.098 TS × SWC) − 5.636) explains 72.2% of the overall variance in soil respiration. We also detected a temporal inconsistency of 2–3 months in the effects of precipitation on soil respiration versus canopy biomass production, which was presumably a main mechanism explaining the weak relationships between soil respiration and phytomass components in this ecosystem. Our findings have important implications for better understanding and accurately assessing the carbon cycling characteristics of terrestrial ecosystems in response to climate change in a temporal perspective.

Reservoir eutrophication is a global problem that needs to be urgently solved, and exploring phytoplankton dynamics in young reservoirs is extremely important for artificial intervention during the process of eutrophication. However, the succession of phytoplankton communities and their responses to environmental variables in young canyon reservoirs remain obscure. Therefore, phytoplankton functional group data were collected from a young canyon reservoir for 2 years, and the succession pattern and its response to environmental variables were simultaneously evaluated. The results revealed significant spatial differences and rapid interannual changes in some environmental variables (water temperature, suspended solids) in the young canyon reservoir. Non-metric multidimensional scaling showed that phytoplankton functional group structure differed obviously among the zones of the reservoir, while significant interannual succession (from the Lo and Y groups to the X2 group) occurred in the lacustrine zone. Additionally, redundancy analysis demonstrated that the structure of phytoplankton functional groups varied significantly between the spatially different environments. Finally, the succession of phytoplankton functional groups in the lacustrine zone was mainly driven by increases in nutrients and water temperature. The rules underlying and dominant mechanism driving short-term succession in the young canyon reservoir revealed in this study may provide a deeper understanding of the intervention mechanisms that could be implemented to alleviate reservoir eutrophication. [ABSTRACT FROM AUTHOR]

Background: The analysis of bird community assembly rules is fundamental to understand which mechanisms determine the composition of bird species in urban areas. However, the long-term variation of community assembly rules has not been analyzed yet. The objectives of this study are (1) to analyze the variation of community assembly rules along rural-urban gradients of three cities in central Argentina and (2) to compare the patterns of community assembly between two periods separated by 6 years. Bird surveys were performed along transects in urban, suburban, and rural habitats during 2011 and 2017. Departures from null models that took into account differences in species richness (standardized effect size, SES) were calculated for functional and phylogenetic diversities. Results: A total of 57 species were recorded. Bird species richness was higher in suburban than in urban and rural habitats. SES of functional diversity increased over the years and was significantly lower in urban habitats than in rural habitats, showing a pattern of functional clustering in the most urbanized areas and functional randomness in rural ones. Phylogenetic diversity was higher in both suburban and urban habitats than rural ones, and the phylogenetic clustering in rural bird assemblages changed to randomness in suburban and urban habitats. Conclusions: Bird communities in urban habitats were phylogenetically random and functionally clustered, evidencing environmental filtering by urbanization. In contrast, bird communities in rural areas tended to be phylogenetically clustered, evidencing that certain clades are adapted to rural areas. The processes structuring bird communities along rural-urban gradients were consistent between the 2 years compared. [ABSTRACT FROM AUTHOR]

Typhoon Sanba (2012), the strongest tropical cyclone (TC) of the year worldwide, moved northward almost along 130° longitude during its lifetime and passed through different background flows from low to high latitudes. The steering flows with different timescales for Sanba are retrieved by using the NCEP reanalysis data with the total wind field separated into: a mean state, an interannual component, an intraseasonal component, and a synoptic component. Our analysis indicates that the intraseasonal timescale wave train (WT) with east-west oriented circulations made the largest contribution to the movement of Sanba. The effects of the environmental steering with different timescales on Sanba's movement are investigated with numerical simulations using the Weather Research and Forecasting (WRF) model. In the control simulation, total fields from the NCEP reanalysis are used as initial and boundary conditions, and the northward motion of Sanba is well captured. In sensitivity experiments, each of the intraseasonal and interannual components is removed one at a time. The steering vectors associated with these timescales can explain their influences on the movement of Sanba in the experiments. Vorticity budget analyses indicate that the horizontal vorticity advection made the largest contribution to the movement of the storm. [ABSTRACT FROM AUTHOR]

The global mean sea level (GMSL) has been measured precisely by the space geodetic remote-sensing technique of radar altimetry since the 1990s. Aside from the well-studied seasonality and secular sea level rise, here we focus on GMSL variation on the interannual–decadal (ID) timescales (GMSL-ID) and investigate the influences of the climatic oscillations as physical causes. We conduct correlation analyses on the GMSL-ID time series with several climatic oscillations represented by their respective meteorological indices, including El Niño-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), Atlantic Multidecadal Oscillation (AMO), Arctic Oscillation (AO), and Antarctic Oscillation (AAO). From the time-domain cross-correlation functions and the corresponding frequency-domain cross-coherence spectra, we find the following: (i) high correlation between GMSL-ID and ENSO, primarily befalling on the Central-Pacific (as opposed to the Eastern-Pacific) type of ENSO, on timescales longer than 1.5 years; (ii) moderate correlations of GMSL-ID with PDO on long-period timescales of over 4 years, and with AMO on a timescale of 2–10 years, with AMO leading in phase by 8 months; (iii) weak or practically no correlation of GMSL-ID with either AO or AAO, in the former case given the fact that our GMSL-ID data actually do not cover the Arctic sea. Finally, we least-squares fit the above five indices to GMSL-ID to assess the relative contribution of each oscillation in causing the observed GMSL-ID, for a better understanding of the GMSL under the influences of on-going climate change.

Coupled Model Intercomparison Project Phase 5 (CMIP5) models have limited capacity for depicting the variability of precipitation at interannual and interdecadal timescales. This study analyses the relative magnitude of interannual to multidecadal variability in annual precipitation across the world in the recently released CMIP6 dataset by quantifying the discrepancy between observed and modelled CMIP5 and CMIP6 data, considering both the absolute and relative magnitude of precipitation variability. We found that: (a) similar to CMIP5, CMIP6 models were short of capacity to simulate the non‐homogeneity in the relative magnitude of interdecadal variability, which is linked to prolonged drought and pluvials in terms of the strength value. The relative value of the interdecadal variability ranged from 15% to more than 30% in observation. Compared with observational data, the relative magnitude, having spatial uniformity, mostly ranged from 10 to 20% in CMIP5 and CMIP6. This result suggests that future projections lack a sufficient decadal variability in CMIP6, indicating a limited capacity for the prediction of floods and droughts in regions like central Africa, North America, and Amazonia; (b) Most individual models in CMIP6 had a better performance in terms of the spatial distribution of the interdecadal precipitation as compared to CMIP5. However, the absolute variations of the overall, interannual, and interdecadal precipitation of multi‐model ensemble simulations (MME) in CMIP6 were larger than those in CMIP5; (c) the underestimation of the interdecadal component in different areas was markedly decreased in East Asia, South Asia but increased in North and South Africa in CMIP6, when compared with CMIP5 and (d) For future scenarios, the higher the range of future forcing pathway is, the larger interdecadal and interannual variabilities are in all regions in CMIP6. For future persistent droughts and floods predicting in a specific region, it is necessary to consider the discrepancy between historical simulations and observational data, and select the performance‐plus models. [ABSTRACT FROM AUTHOR]

We examined the dynamics of soil microbiomes under heat press disturbance from an underground coal mine fire in Centralia, PA. Here, we present metagenomic sequencing and assembly data from soil microbiomes across seven consecutive years at repeatedly sampled fire-affected sites along with unaffected reference sites., Competing Interests: The authors declare no conflict of interest.

This study reveals the impacts of cumulus parameterization schemes (CPSs) on the simulation of interannual and interdecadal variations of Meiyu in the middle and lower reaches of the Yangtze River valley (Yangtze Meiyu) by using a regional climate model. A multiple 55-year (1955-2009) simulation of Yangtze Meiyu is conducted using RegCM4.6 with different CPSs, including the Emanuel scheme, Kuo scheme, and Grell scheme. It is found that all the CPSs have good performances in simulating the interannual variation of Yangtze Meiyu rainfall amounts. However, a large bias is found in the simulated interdecadal variation of Yangtze Meiyu rainfall amount by the three CPSs. Because the Emanuel CPS has good performance in the simulation of both interannual and interdecadal variations of Yangtze Meiyu, its overall performance in the simulation of the total amount of Yangtze Meiyu is the best among the three CPSs. The second best CPS is the Grell scheme, and the worst is the Kuo scheme. The model convergence in simulating the distribution of Yangtze Meiyu shows an obvious characteristic of interdecadal variation. During the years with strong summer monsoon and northward rain belt, the simulated distributions of Yangtze Meiyu by the three CPSs are quite different, and the model convergence is weak. On the contrary, during the years with weak summer monsoon and southward rain belt, the simulated distributions of Yangtze Meiyu by the three CPSs are similar to each other, and the model convergence is strong. As a result, when the well-known interdecadal change happens in the late 1970s, the monsoon changes from strong to weak, whereas the model convergence changes from weak to strong.

Abstract The present study evaluates the performance of a Subseasonal to Seasonal (S2S) model (called The China Meteorological Administration) in simulating rainfall onset dates (RODs) over West Africa. Using two ROD definitions, we compared the model's ROD at six lead‐time forecasts (10, 20, 30, 40, 50, and 60 days) with the observed ROD from satellite data sets, statistically quantified the model's capability to reproduce the interannual variability of RODs over the climatological zones in the subcontinent, and investigated how well the model links RODs with the dynamics of monsoon system over the subregion. The results show that the mean RODs follow a latitudinal progression and the dates increases northward from the coast. The performance of the S2S model in reproducing RODs largely depends on the definition used. For instance, the ability of the model to replicate the observed spatial pattern of RODs and all the essential features over the three zones in West Africa is stronger with DEF1 than DEF2. Regardless of the ROD definition used, the 20‐ to 60‐day forecasts produced more realistic simulation than the 10‐day forecast. We also found that the performance of the model in reproducing the interannual variability of RODs depends on the zones (Guinea, Savanna, and Sahel). Moreover, the model could reproduce the three main phases of the West African Monsoon (the onset, the peak, and the southward retreat of rainfall) and other dynamics. The results of the study have application in improving S2S forecasting over West Africa.

Predictions of ocean biogeochemistry, such as primary productivity and CO2 uptake, would help to understand the changing marine environment and the global climate. There is an emerging number of studies where initialization of ocean physics has led to successful predictions of ocean biogeochemistry. It is, however, unclear how much these predictions could be improved by also assimilating biogeochemical data to reduce uncertainties of the initial conditions. Further, the mechanisms that lead to biogeochemical predictability are poorly understood. Here we perform a suite of idealized twin experiments with an Earth System Model (ESM) with the aim to (i) investigate the role of biogeochemical tracers' initial conditions on their predictability, and (ii) understand the physical processes that give rise to, or limit, predictability of ocean carbon uptake and export production. Our results suggest that initialization of the biogeochemical state does not significantly improve interannual-to-decadal predictions, which we relate to the strong control ocean physics exerts on the biogeochemical variability on these time scales. The predictability of ocean carbon uptake generally agrees well with the predictability of the mixed layer depth (MLD), suggesting that the predictable signal comes from the exchange of dissolved inorganic carbon (DIC) with deep-waters. The longest predictability is found in winter in at high latitudes, as for sea surface temperature and salinity, but the predictability of the MLD and carbon exchange is lower as it is more directly influenced by the atmospheric variability, e.g., the wind. The predictability of the annual mean export production is, on the contrary, nearly non-existing at high latitudes, despite the strong predictive skill for annual mean nutrient concentrations in these regions. This is related to the low predictability of the physical state of the summer surface ocean. Due to the shallow mixed layer it is decoupled from the ocean below and therefore strongly influenced by the chaotic atmosphere. Our results show that future studies need to target the predictability of the mixed layer to get a better understanding of the real-world predictability of ocean biogeochemistry.

This study examines the linkages between leading patterns of interannual sea level pressure (SLP) variability over the extratropical Pacific (20°–60°N) and the eastern Pacific (EP) and central Pacific (CP) types of El Niño–Southern Oscillation (ENSO). The first empirical orthogonal function (EOF) mode of the extratropical SLP anomalies represents variations of the Aleutian low, and the second EOF mode represents the North Pacific Oscillation (NPO) and is characterized by a meridional SLP anomaly dipole with a nodal point near 50°N. It is shown that a fraction of the first SLP mode can be excited by both the EP and CP types of ENSO. The SLP response to the EP type is stronger and more immediate. The tropical–extratropical teleconnection appears to act more slowly for the CP ENSO. During the decay phase of EP events, the associated extratropical SLP anomalies shift from the first SLP mode to the second SLP mode. As the second SLP mode grows, subtropical SST anomalies are induced beneath via surface heat flux anomalies. The SST anomalies persist after the peak in strength of the second SLP mode, likely because of the seasonal footprinting mechanism, and lead to the development of the CP type of ENSO. This study shows that the CP ENSO is an extratropically excited mode of tropical Pacific variability and also suggests that the decay of an EP type of ENSO can lead to the onset of a CP type of ENSO with the aid of the NPO. This extratropical linking mechanism appears to be at work during the 1972, 1982, and 1997 strong El Niño events, which were all EP events and were all followed by strong CP La Niña events after the NPO was excited in the extratropics. This study concludes that extratropical SLP variations play an important role in exciting the CP type of ENSO and in linking the transitions from the EP to CP events.

The Mediterranean Sea is considered a hot spot of global warming because it has been changing faster than the global ocean, creating a strong impact on the marine environment. Recent studies agree on the increase in the sea level, in the sea surface temperature, and in the sea surface salinity in the Mediterranean Sea over the last two decades. In this research, the possible interconnection between these and other parameters that contribute to the regulatory effect of the sea on the climate are identified and discussed. Spatio-temporal variability of four oceanographic and air–sea interaction parameters (sea-level, sea surface temperature, sea surface salinity, and freshwater flux) are estimated over the last 27 years by performing the empirical orthogonal function analysis. Climatic trends, and interannual and decadal variability of the different datasets are delineated and described in the whole Mediterranean and in its sub-basins. On the climatic scale, the Mediterranean and its sub-basins behave in a coherent way, showing the seal level, temperature, salinity, and freshwater flux rise. On the interannual scale, the temporal evolution of the sea level and sea surface temperature are highly correlated, whereas freshwater flux affects the variability of sea level, temperature, and the salinity field mainly in the Western and Central Mediterranean. The decadal signal associated with the Northern Ionian Gyre circulation reversals is clearly identified in three of the four parameters considered, with different intensities and geographical extents. This signal also affects the intermediate layer of the Eastern Mediterranean, from where it is advected to the other sub-basins. Decadal signal not associated with the Northern Ionian Gyre reversals is strongly related to the variability of main sub-basin scale local structures.

[1] Much understanding of the El Niño-Southern Oscillation (ENSO) has been obtained from the analyses of the climate simulations produced for World Climate Research Programme's Coupled Model Intercomparison Project phase 3 (CMIP3). However, most of these analyses do not consider the existence of the Eastern-Pacific (EP) and Central-Pacific (CP) types of ENSO events, which have been increasingly recognized as two distinct types of interannual sea surface temperature (SST) variation in the tropical Pacific. This study uses a regression-Empirical Orthogonal Function method to identify how well these two ENSO types are captured in the pre-industrial simulations of nineteen CMIP3 models. It is concluded that most CMIP3 models (13 out of 19) can produce realistically strong CP ENSOs, but only a few of them (9 out of 19) can produce realistically strong EP ENSOs. Six models that realistically simulate both the EP and CP ENSOs and their intensity ratio are identified. By separating the SST variability into these two types, it is further revealed that the leading periodicity of the simulated EP ENSO is linearly related to the latitudinal width of SST variability and varies from 1 to 5 years. As for the simulated CP ENSO, its leading periodicity is either 2 or 4 years depending on whether its SST variability is located to the east of the dateline or in the western-Pacific warm pool, respectively. The identification produced in this study offers useful information to further understand the two types of ENSO using the CMIP3 models.

Interannual sea surface temperature (SST) variability in the central equatorial Pacific consists of a component related to eastern Pacific SST variations (called Type-1 SST variability) and a component not related to them (called Type-2 SST variability). Lead–lagged regression and ocean surface-layer temperature balance analyses were performed to contrast their control mechanisms. Type-1 variability is part of the canonical, which is characterized by SST anomalies extending from the South American coast to the central Pacific, is coupled with the Southern Oscillation, and is associated with basinwide subsurface ocean variations. This type of variability is dominated by a major 4–5-yr periodicity and a minor biennial (2–2.5 yr) periodicity. In contrast, Type-2 variability is dominated by a biennial periodicity, is associated with local air–sea interactions, and lacks a basinwide anomaly structure. In addition, Type-2 SST variability exhibits a strong connection to the subtropics of both hemispheres, particularly the Northern Hemisphere. Type-2 SST anomalies appear first in the northeastern subtropical Pacific and later spread toward the central equatorial Pacific, being generated in both regions by anomalous surface heat flux forcing associated with wind anomalies. The SST anomalies undergo rapid intensification in the central equatorial Pacific through ocean advection processes, and eventually decay as a result of surface heat flux damping and zonal advection. The southward spreading of trade wind anomalies within the northeastern subtropics-to-central tropics pathway of Type-2 variability is associated with intensity variations of the subtropical high. Type-2 variability is found to become stronger after 1990, associated with a concurrent increase in the subtropical variability. It is concluded that Type-2 interannual variability represents a subtropical-excited phenomenon that is different from the conventional ENSO Type-1 variability.

The regional climate model (version RegCM4) is used in this study to simulate the Indian summer monsoon rainfall. Model integrations were carried out for 16 monsoon seasons from 1985 to 2000. The model-simulated rainfall at a daily scale as well the seasonal mean were compared with observed rainfall. It was observed that the model underestimates the rainfall amount, especially over the eastern and central parts of India. Frequency distributions of daily rainfall showed that there were more days with light rainfall and fewer days with moderate rainfall in the model as compared to the observation over most parts of India. The ability of the RegCM4 to simulate interannual variability in rainfall over two sub-regions of India (one in western parts and the other in eastern India) was examined for the months of July and August. Composite analyses of rainfall, winds, moisture and evaporation for excess and deficient rainfall years for these two regions were carried out and compared with similar analysis using ERA-Interim data. When the eastern parts of India experienced more rainfall, the cyclonic circulation over Odisha was more intense, with stronger easterlies over the Gangetic plains, enhancing moisture transport to the Indian land mass from the adjoining seas. A cyclonic circulation difference between excess and deficient years over this region and an anticyclonic circulation difference over peninsular India led to the development of a strong convergence zone over parts of Maharashtra and Gujarat in the excess years. Several sensitivity experiments were also carried out using various schemes, domain sizes and diffusion parameters to study the role of these parameters in defining the model bias. The key parameters that emerged from these experiments as affecting the moisture convergence and rainfall bias over the Indian region were the horizontal diffusion and auto-conversion of cloud water into precipitation. However, these parameters were not able to improve the simulation of interannual variability over most parts of India. [ABSTRACT FROM AUTHOR]

The present study evaluates the performance of a Subseasonal to Seasonal (S2S) model (called The China Meteorological Administration) in simulating rainfall onset dates (RODs) over West Africa. Using two ROD definitions, we compared the model's ROD at six lead‐time forecasts (10, 20, 30, 40, 50, and 60 days) with the observed ROD from satellite data sets, statistically quantified the model's capability to reproduce the interannual variability of RODs over the climatological zones in the subcontinent, and investigated how well the model links RODs with the dynamics of monsoon system over the subregion. The results show that the mean RODs follow a latitudinal progression and the dates increases northward from the coast. The performance of the S2S model in reproducing RODs largely depends on the definition used. For instance, the ability of the model to replicate the observed spatial pattern of RODs and all the essential features over the three zones in West Africa is stronger with DEF1 than DEF2. Regardless of the ROD definition used, the 20‐ to 60‐day forecasts produced more realistic simulation than the 10‐day forecast. We also found that the performance of the model in reproducing the interannual variability of RODs depends on the zones (Guinea, Savanna, and Sahel). Moreover, the model could reproduce the three main phases of the West African Monsoon (the onset, the peak, and the southward retreat of rainfall) and other dynamics. The results of the study have application in improving S2S forecasting over West Africa. Key Points: The RODs obtained by the two definitions used in this study are comparable, as the DEF2 gives a later RODs than DEF1The model realistically simulates the observed features of RODs irrespective of the definition used, although with some biasesThe model credibly captures the seasonal movement of the West African Monsoon as in observation, although with few biases [ABSTRACT FROM AUTHOR]

Sea surface temperature anomalies (SSTAs), including their spatial patterns and temporal evolution, are an important source of potential predictability for climate anomalies, especially on seasonal to interannual timescales. In this study, the spatial patterns and temporal evolution of tropical SSTAs are identified by applying an extended empirical orthogonal function (EEOF) analysis of observed data from autumn to the following spring. The positive phase of first EEOF mode (EEOF1) displays an El Niño–Southern Oscillation (ENSO) phase‐locking evolution pattern in the tropical Pacific, with accompanying warming in the Indian and Atlantic oceans. EEOF2 is characterized by the development of ENSO in the eastern tropical Pacific and a phase transition in the Indian Ocean and the tropical North Atlantic. The most noticeable feature of EEOF3 is the development of the central Pacific ENSO. The first three EEOF modes account for 44.7% of the total variance of tropical SSTAs over the course of the three seasons. EEOF1 is closely related to the tropical atmospheric circulation, especially over the western Pacific region, reflecting the strengthening effect of the three tropical oceans on the anomalous anticyclone over the tropical Northwest Pacific during the decaying phases of El Niño. EEOF2 significantly impacts the circulation anomalies over the Indian Ocean and western Pacific. A linear regression model is established using the time series of first four EEOF modes to forecast the June to August 500 hPa geopotential height anomalies. The forecasts show higher skill than a similar linear regression model using seasonal mean regional SST anomaly indices. The results reveal that EEOF modes could be used as a good indicator in the monitoring of tropical SSTA evolution patterns. [ABSTRACT FROM AUTHOR]

In this study, we analyzed the impacts of Western North Pacific Subtropical High (WNPSH) on tropical cyclone (TC) activity on both interannual and interdecadal timescales. Based on a clustering analysis method, we grouped TCs in the Western North Pacific into three clusters according to their track patterns. We mainly focus on Cluster 1 (C1) TCs in this work, which is characterized by forming north of 15° N and moving northward. On interannual timescale, the number of C1 TCs is influenced by the intensity variability of the WNPSH, which is represented by the first Empirical Orthogonal Function (EOF) of 850 hPa geopotential height of the region. The WNPSH itself is modulated by the El Niño–Southern Oscillation at its peak phase in the previous winter, as well as Indian and Atlantic Ocean sea surface temperature anomalies in following seasons. The second EOF mode shows the interdecadal change of WNPSH intensity. The interdecadal variability of WNPSH intensity related to the Pacific climate regime shift could cause anomalies of the steering flow, and lead to the longitudinal shift of C1 TC track. Negative phases of interdecadal Pacific oscillation are associated with easterly anomaly of steering flow, westward shift of C1 TC track, and large TC impact on the East Asia coastal area. [ABSTRACT FROM AUTHOR]

Changes in the stratosphere-troposphere exchange (STE) of ozone over the last few decades have altered the tropospheric ozone abundance and are likely to continue doing so in the coming century as climate changes. Combining an updated linearized stratospheric ozone chemistry (Linoz v2) with parameterized polar stratospheric clouds (PSCs) chemistry, a 5-year (2001–2005) sequence of the European Centre for Medium-Range Weather Forecasts (ECMWF) meteorology data, and the University of California, Irvine (UCI) chemistry transport model (CTM), we examined variations in STE O3 flux and how it perturbs tropospheric O3. Our estimate for the current STE ozone flux is 290 Tg/a in the Northern Hemisphere (NH) and 225 Tg/a in the Southern Hemisphere (SH). The 2001–2005 interannual root-mean-square (RMS) variability is 25 Tg/a for the NH and 30 Tg/a for the SH. STE drives a seasonal peak-to-peak NH variability in tropospheric ozone of about 7–8 Dobson unit (DU). Of the interannual STE variance, 20% and 45% can be explained by the quasi-biennial oscillation (QBO) in the NH and SH, respectively. The CTM matches the observed QBO variations in total column ozone, and the STE O3 flux shows negative anomalies over the midlatitudes during the easterly phases of the QBO. When the observed column ozone depletion from 1979 to 2004 is modeled with Linoz v2, we predicted STE reductions of at most 10% in the NH, corresponding to a mean decrease of 1 ppb in tropospheric O3.

The Yangtze-Huai River Basin (YHRB) is an economically developed area and one of the most densely populated regions in China. Based on ERA5 reanalysis and Meiyu monitoring data, this study investigates the relationship between interannual variability in atmospheric latent heating (LH) over the Southeast Asian low-latitude highlands (SEALLH) during early summer and the Meiyu onset date (MOD) in the YHRB. The mean MOD is 9 June, with a quasi-6-year interannual oscillation period. A stronger early summer LH over the SEALLH coincides with earlier MOD; below 500 hPa, LH increases with height and drives an anomalous southwesterly airflow from the Bay of Bengal (BOB) to the SEALLH via β effects. Circulation over the western North Pacific (WNP) is dominated by an anomalous anticyclone, causing the WNP subtropical high (WNPSH) to extend westward and northward. Continuous positive LH anomalies over the SEALLH cause anomalous southwesterly winds to transport moist enthalpy air masses from low latitudes into the YHRB, resulting in abnormal convergence there. Favorable dynamic and thermal conditions drive enhanced precipitation over the YHRB, eventually leading to a MOD that is 13 days earlier than that during periods when early summer LH is relatively weak over the SEALLH. This result potentially supports our capacity to predict the Meiyu in the YHRB. • The mean Meiyu onset date in the YHRB is 9 June, with a quasi-6-year interannual oscillation period. • The Meiyu onset date in the YHRB is significantly controlled by the May atmospheric latent heating over the SEALLH on interannual time scale. • The May atmospheric latent heating over the SEALLH causes the development of southwesterly winds in the YHRB via β effects, leading to an earlier onset of the Meiyu. [ABSTRACT FROM AUTHOR]