Westerly Winds Research Articles

Effect of Northeast Pacific Wind on the Improvement of El Niño Prediction in a Climate Model

Abstract The role of the northeast Pacific wind in the dynamics of El Niño has been proposed in previous theoretical studies. However, the actual effect of northeast Pacific wind on improving El Niño prediction remains unclear, and the mechanisms through which northeast Pacific improves El Niño predictions are not fully understood. In this study, we investigate the role of northeast Pacific wind in improving El Niño prediction. By utilizing CESM that assimilates the northeast Pacific wind, the model improves prediction skills of ENSO indices at a lead time of 6–12 months, with a correlation three times higher than the predictions without nudged northeast Pacific wind. Nudging northeast Pacific wind in the model enhances the prediction of central Pacific (CP) El Niño, thus leading to approximately 30% increase in the hit ratio of correct prediction of El Niño. However, the model overestimates CP El Niño predictions when the nudged northeast Pacific wind is incorporated. The mechanisms for the improvement of northeast Pacific wind in El Niño predictions are investigated. In spring, El Niño development is attributed to the wind–evaporation–SST (WES) feedback and oceanic downwelling induced by subtropical westerly wind stress. In contrast, during summer, El Niño development is dominated by the summer deep convection (SDC) response. During subsequent summer–autumn, anomalous surface latent heat flux related to wind speed and net shortwave radiation associated with the low cloud–SST feedback contribute to El Niño development. These processes are more favorable for CP El Niño development. This study implies that accurately simulating air–sea coupling associated with northeast Pacific wind may be an effective approach in improving El Niño prediction.

Provenance of late Pleistocene loess in central and eastern Europe: isotopic evidence for dominant local sediment sources

Loess profiles along the Danube River provide a record of long-term Quaternary dust (loess) deposition in central-eastern Europe. Here, Sr–Nd isotopic data from four loess-palaeosol profiles (47 samples) spanning the last two-glacial-interglacial cycles are presented. The isotopic compositions generated by this study are compared with bedrock and sedimentary samples from Europe and North Africa to decipher the sources of sediment. The results demonstrate that over the last 300 ka the alluvial plains of the Danube (which are themselves sourced from surrounding mountain belts) are a local source of material and consequently sediment experiences aeolian transport over relatively short distances. The results dispute the commonly held assumption that the Sahara was a sediment contributor to loess in central-eastern Europe as North African contributions are not needed to explain loess signatures. Consequently, the findings suggest a suppressed southerly wind direction and dominance of the westerly and north-westerly wind systems over the entirety of the record.

The impact of the AMO on wintertime surface wind speed reversal in Northeast Asia

Abstract Decadal variations in seasonal mean surface wind speed (SWS) and their underlying causes remain elusive. Here, we utilize wind data from in situ stations to demonstrate that the stilling reversed around 2002 and that wintertime wind speed in Northeast Asia has rebounded. We illustrate that decadal-scale variations of SWS are closely linked to the phase shift of the Atlantic Multidecadal Oscillation (AMO). Specifically, an AMO positive phase generates a wave train characterized by a cyclonic anomaly over Northeast Asia, which leads to the strengthened westerly wind, enhanced meridional temperature gradient, and increased transient eddy activities in Northeast Asia. These findings hold vital implications for considering changes in the AMO to gain a comprehensive understanding of SWS variations at the regional scale.

Aerosol forces mesoscale secondary circulations occurrence: evidence of emission reduction

Here, we present modeling evidence of the influences of aerosol feedback on secondary circulations (SCs). The results show that in heavily PM2.5 polluted Beijing-Tianjin-Hebei (BTH) areas, the aerosol feedback is the primary factor on the occurrence and development of mesoscale SCs in the atmospheric boundary layer. Modeling evidence reveal that the impact of aerosol feedback on SCs is proportional to PM2.5 concentrations or precursor emissions. During the 2014 Asia-Pacific Economic Cooperation (APEC) with extraordinary emission reduction, the time levels of SCs significantly decreases to ~37.3% of the periods without emission reduction before and after APEC period. The simulated PM2.5 during APEC are ~47.6% of before and after APEC period, and the measured concentration ratio at 47.7%. The largest variation in SC occurred during the afternoon, which should be related to the stronger solar radiation. We found that the reduction in wind speed caused by aerosol feedback and related convergence and divergence of the air mass play a pivotal role in SCs evolution. Against the background of prevailing westerly winds in BTH, the strengthening and appearance of clockwise SCs caused by aerosol feedback leads to an increase in the frequency of surface easterly U-wind. These phenomena have also been validated in two other emission reduction events and the emission reduction actions in the BTH region in January and July of 2014, 2017, and 2020, respectively. The results of this paper showing substantial impact of aerosol feedback on SCs, which could help promote our understanding of content and level of aerosol feedback to atmospheric changes.

Characteristics of Atmospheric Circulation Patterns and the Associated Diurnal Variation Characteristics of Precipitation in Summer over the Complex Terrain in Northern Xinjiang, Northwest China

Statistical characteristics of atmospheric circulation patterns (ACPs) and associated diurnal variation characteristics (DVCs) of precipitation in summer (June–August) from 2015 to 2019 over the complex terrain in northern Xinjiang (NX), northwestern arid region of China, were investigated based on NCEP FNL reanalysis data and Weather Research and Forecasting model simulation data from Nanjing University (WRF-NJU). The results show that six different ACPs (Type 1–6) were identified based on the Simulated ANealing and Diversified RAndomization (SANDRA), exhibiting significant differences in major-influencing synoptic systems and basic meteorological environments. Types 5, 3, and 2 were the most prevalent three patterns, accounting for 21.6%, 19.7%, and 17.7%, respectively. Type 5 mainly occurred in June and July, while Types 3 and 2 mainly occurred in August and July, respectively. From the perspective of DVCs, Type 1 reached its peak at midnight, while Type 5 was most frequent in the afternoon and morning. The overall DVCs of hourly precipitation intensity and frequency demonstrated a unimodal structure, with a peak occurring at around 16 Local Solar Time (LST). Basic meteorological elements in various terrain regions exhibit significant diurnal variation, with marked differences between mountainous and basin areas under different ACPs. In Types 3 and 6, meteorological elements significantly influence precipitation enhancement by promoting the convergence and uplift of low-level wind fields and maintaining high relative humidity (RH). The Altay Mountains region and Western Mountainous regions experience dominant westerly winds under these conditions, while the Junggar Basin and Ili River Valley regions benefit from counterclockwise water vapor transport associated with the Iranian Subtropical High in Type 6, which increases RH. Collectively, these factors facilitate the formation and development of precipitation.

The Distinct Spatial Patterns and Physical Mechanisms of Coastal Boundary Layer Jets over the Northern South China Sea

Abstract Two distinct spatial patterns of coastal boundary layer jets in the northern South China Sea (CBLJ-NSCS) in June 2015–22 are investigated using hourly output data from the Weather Research and Forecasting Model with a horizontal grid spacing of 9 km and ERA5 data. Spatial pattern 1 shows a high-incidence core on the east side of Hainan Island, while pattern 2 features dual high-incidence cores covering both the east side of Hainan Island and the waters south of Guangdong, with the latter being stronger and more extensive. Unique diurnal cycles have been observed in different high-incidence cores of CBLJ-NSCS: the western core, on the east side of Hainan Island, peaks at night and shows a secondary afternoon subpeak, while the eastern core, located south of Guangdong, reaches its maximum intensity at night with a morning subpeak. Inertial oscillations triggered by large-scale perturbation wind circulation and momentum propagation from upstream Indochina Peninsula CBLJs explain the nocturnal enhancement of both cores. The thermal effect exerted by Hainan Island largely contributes to the afternoon enhancement in the western core. The formation of the morning subpeak of the eastern core results from strong convergence and lifting in the northeast region of it. When upstream CBLJs along the Annamite Range intensify, more momentum is propagated to the eastern core instead of the western one due to wind field changes, which promotes the transition from spatial pattern 1 to pattern 2. Significance Statement Two spatial patterns of coastal boundary layer jets in the northern South China Sea have been identified. Spatial pattern 1 shows a high-incidence core on the east side of Hainan Island, while pattern 2 features dual high-incidence cores covering both the east side of Hainan Island and the waters south of Guangdong. The transition between these two spatial patterns is related to low-level westerly winds along the coast of the Annamite Range. This study has uncovered the novel spatial pattern of coastal boundary layer jets in the northern South China Sea and provides new insights into precipitation research in southern China, considering the substantial influence of these jets on coastal weather.

A Physics-Informed Auto-Learning Framework for Developing Stochastic Conceptual Models for ENSO Diversity

Abstract Understanding El Niño–Southern Oscillation (ENSO) dynamics has tremendously improved over the past few decades. The ENSO diversity in spatial pattern, peak intensity, and temporal evolution is, however, still poorly represented in conceptual ENSO models. In this paper, a physics-informed auto-learning framework is applied to derive ENSO stochastic conceptual models with varying degrees of freedom. The framework is computationally efficient and easy to apply. Once the state vector of the target model is set, causal inference is exploited to build the right-hand side of the equations based on a mathematical function library. Fundamentally different from standard nonlinear regression, the auto-learning framework provides a parsimonious model by retaining only terms that improve the dynamical consistency with observations. It can also identify crucial latent variables and provide physical explanations. This methodology successfully reconstructs the equations of a realistic six-dimensional reference ENSO model based on the recharge oscillator theory from its data. A hierarchy of lower-dimensional models is derived, and their representation of ENSO (including its diversity) is systematically assessed. The minimum model that represents ENSO diversity is four-dimensional, with three interannual variables describing the western Pacific thermocline depth, the eastern and central Pacific sea surface temperatures (SSTs), and one intraseasonal variable for westerly wind events. Without the intraseasonal variable, the resulting three-dimensional model underestimates extreme events and is too regular. A limited number of weak nonlinearities in the model are essential in reproducing the observed extreme El Niño events and the observed nonlinear relationship between eastern and western Pacific SSTs. Significance Statement This study develops a physics-informed auto-learning approach to improve the modeling and understanding of El Niño–Southern Oscillation (ENSO), a major climate phenomenon influencing global weather and climate. The auto-learning framework explores the causality between key processes to systematically produce stochastic conceptual models with different climate factors that simulate the diversity of observed ENSO events. The key finding is that the minimal model for characterizing the ENSO diversity (with the least number of climate factors) is a four-variable model capturing thermocline depth, sea surface temperatures, and wind bursts that can reproduce intensity and spatial pattern variation. This advancement provides an interpretable tool to identify the minimum sufficient processes governing ENSO behavior for improved predictability.

Mid-Pleistocene aridity and landscape shifts promoted Palearctic hominin dispersals

Population expansions and contractions out of and into Africa since the early Pleistocene have influenced the course of human evolution. While local- and regional-scale investigations have provided insights into the drivers of Eurasian hominin dispersals, a continental-scale and integrated study of hominin-environmental interactions across Palearctic Eurasia has been lacking. Here, we report high-resolution (up to ∼5-10 kyr sample interval) carbon isotope time series of loess deposits in Central Asia and northwest China, a region dominated by westerly winds, providing unique paleoecological and paleoclimatic records for over ~3.6 Ma. These data, combined with further syntheses of Pleistocene paleontological and archaeological records and spatio-temporal distributions of Eurasian eolian deposits and river terraces, demonstrate a pronounced transformation of landscapes around the Mid-Pleistocene Climate Transition. Increased climate amplitude and aridity fluctuations over this period led to the widespread formation of more open habitats, river terraces, and desert-loess landscapes, pushing hominins to range more widely and find solutions to increasingly challenging environments. Mid-Pleistocene climatic and ecological transitions, and the formation of modern desert and loess landscapes and river networks, emerge as critical events during the dispersal of early hominins in Palearctic Eurasia.

Vertical structure and occurrence patterns of the cross-equatorial northerly surge under different ENSO and MJO phases

This study investigated the vertical structure of 6 cross-equatorial northerly surge (CENS) events during the Year of Maritime Continent–Cold Surge Observation in 2021 (YMC-CSO2021) campaign. These events, named CENS1 (Jan. 18–20), CENS2 (Jan. 29–30), CENS3 (Feb. 2–5), CENS4 (Feb. 5–9), CENS5 (Feb. 18–20), and CENS6 (Feb. 25–26), occurred under different environmental conditions associated with cold surges (CSs) and the Madden–Julian Oscillation (MJO). Using radiosonde observations, we identified distinct characteristics in the northerly wind layer thickness, westerly wind bursts, and potential temperature anomalies among the events. Notably, CENS6 featured a deep northerly wind layer reaching 400 hPa, influenced by a southward pressure gradient linked to a cyclone in the Southern Hemisphere. Statistical analysis of past CENS events using reanalysis dataset showed that 80% occurred in January and February, with higher frequencies during La Niña years and active MJO phases over the western Pacific, aligning with YMC-CSO2021 observations. Composite analysis showed that CENS events induced significant ascending motion and localized potential temperature gradients, leading to positive precipitation anomalies around the Maritime Continent. These findings enhance our understanding of CENS dynamics and their impact on regional climate variability.

Atmospheric CO2 column concentration over Iran: Emissions, GOSAT satellite observations, and WRF-GHG model simulations

Regarding global warming and climate change, carbon dioxide (CO2) is one of the most important greenhouse gases. Simulating CO2 gas at hourly/weekly time intervals and desired vertical resolution is challenging due to the coarse horizontal resolution of global models. In this study, both column-averaged CO2 mixing ratio (XCO2) and vertical cross sections of CO2 mixing ratio were simulated by the Weather Research and Forecast Green House gas (WRF-GHG) model at spatial resolutions of 30 and 10 km for the Middle East region as the first domain, and Iran as the second domain. Simulations consider the primary CO2 sources (anthropogenic, biogenic, fire, and oceanic) and the Copernicus Atmosphere Monitoring Service (CAMS) dataset. XCO2 retrieved from GOSAT satellite observations was employed to evaluate the simulation results of the column-averaged CO2 concentrations in February and August 2010. The evaluations showed that the spatiotemporal variability of meteorological variables was well simulated by WRF-GHG with correlation coefficients r of 0.86–0.92, 0.67–0.75, and 0.76–0.82 for temperature, wind, and relative humidity, respectively, during February and August 2010. The evaluations also indicated that the WRF-GHG simulations outperformed the global model TM3, with mean bias error values of − 0.79 and 0.45 PPMV for WRF-GHG in February and August, respectively. The percentage contribution of net CO2 emissions from human activities in Iran was calculated as (38.33 % and 23.70 %) of the total emissions, respectively, with values of 4.4 and 0.85 kg/km2 in each month. The net emissions contributions of biogenic, fire, and oceanic sources were evaluated in February and August, with biogenic emissions contributing (31.901 % and 27.66 %), biogenic absorption contributing (24.07 % and 46.63 %), fire emissions contributing (5.7 % and 2.064 %), and oceanic emissions contributing (3.23 × 10−6 % and 2.23 × 10−6 %). Large-scale circulations and biogenic activity are responsible for the major features of the spatial and seasonal distribution of CO2 in the area. In February, column mixing ratios are higher in more northern latitudes; in August, they are higher to the south. Furthermore, the simulated vertical cross sections show high CO2 mixing ratios in the mid-lower troposphere and northerly/northeasterly advection in February; the vertical profile is inverted in August with high concentrations in the lower stratosphere associated with southwesterly advection. However, the interaction between the synoptic and sub-synoptic features with the topography determines the precise dispersion and distribution of CO2. Despite the negligible emissions in central and eastern Iran, these factors play an important role in the observed concentrations in February and August. In August, the areas between the 120-day low-level monsoon flow of Sistan in eastern Iran, and the westerlies over western/southwestern Iran and the Zagros Mountain range, interact with the heat-low in the Iranian plains and with the Arabian subtropical high. In February, the dominant winds in western Asia were west winds, with the main source of pollution coming from the northeastern regions flowing towards central and eastern Iran. The equatorward displacement of the polar jet stream and the passage of low-pressure systems from the west in winter cause a temporary reduction in CO2 concentrations.

Dominating Remote Source and Its Potential Contribution of Airborne Dust Over the Tibetan Plateau.

Dust particles, transported over long-distances and driven by westerly winds, dominate high-altitude (>4km) snow darkening and melting over the Tibetan Plateau (TP). A systematic assessment of their remote sources and potential contributions remains limited. In this paper, we present a novel algorithm for source-tracing of airborne dust designed to tackle the aforementioned challenges. The algorithm effectively constrains dust activity and guarantees precise tracking through using satellite and reanalysis-based estimates. The high-altitude airborne dust over the TP shows considerable spatial variation and primarily comes from the desert clusters in Central Asia, West Asia, and South Asia. The Karakum, Taklimakan, and Thar deserts are significant sources of high-altitude airborne dust in the northwest, northeast, and southwest regions of TP, with average mass loadings (mg m-2) contributing rates of 42.2% (32.9), 49.6% (48.3), and 16.4% (32.1), respectively. The results demonstrate significant differences in how adjacent deserts affect high-altitude snowmelt in the TP.

Atlantic Meridional Overturning Circulation slowdown modulates wind-driven circulations in a warmer climate

Wind-driven and thermohaline circulations, two major components of global large-scale ocean circulations, are intrinsically related. As part of the thermohaline circulation, the Atlantic Meridional Overturning Circulation has been observed and is expected to decline over the twenty-first century, potentially modulating global wind-driven circulation. Here we perform coupled climate model experiments with either a slow or steady Atlantic overturning under anthropogenic warming to segregate its effect on wind-driven circulation. We find that the weakened Atlantic overturning generates anticyclonic surface wind anomalies over the subpolar North Atlantic to decelerate the gyre circulation there. Fingerprints of overturning slowdown are evident on Atlantic western boundary currents, encompassing a weaker northward Gulf Stream and Guiana Current and a stronger southward Brazil Current. Beyond the Atlantic, the weakened Atlantic overturning causes a poleward displacement of Southern Hemisphere surface westerly winds by changing meridional gradients of atmospheric temperature, leading to poleward shifts of the Antarctic Circumpolar Current and Southern Ocean meridional overturning circulations.

Quantitative reconstruction of sedimentary processes, provenance, and binary sources in Horqin Sandy Land, NE China: An integrated approach

As the largest semi-fixed dune field in China, the Horqin Sandy Land (HSL) provides a valuable opportunity to study the surface processes and paleoenvironmental evolution of drylands in the monsoon region. However, limited data and a single qualitative approach hinder our understanding of the sediment erosion and transport process of the HSL. The ability to trace and quantify sediment provenance of the HSL is increasingly needed to properly understand the source-to-sink processes, and to accurately interpret aeolian–fluvial interactions in terms of a comprehensive database and multidisciplinary approach perspective. This study integrates previously existing grain-size, heavy mineral, element geochemistry, Sr-Nd-Hf isotopic, and zircon-geochronological databases with new petrographic, TIMA automation heavy mineral data and statistical analysis. Together, the high degree of recycling of HSL severely limits the provenance identification of element fingerprints, although these elements are largely inherited from the parent rocks and are not affected by chemical weathering. The heavy minerals, Sr-Nd-Hf isotopes, and zircon U-Pb age composition together reveal that the HSL sediments are a binary mixture of the Palaeozoic-Mesozoic igneous rocks in the Great Xing’an Range (GXR) and the Precambrian metamorphic rocks in the Yanshan Mountains. The isotopic end-element mixing models, multidimensional scaling (MDS) diagrams and inverse Monte Carlo models of detrital zircon ages indicate that GXR and Yanshan Mountains account for ∼ 60 % and ∼ 40 % of the source contributions, respectively. Under the strong influence of the northwest to west winds controlled by the Mongolia-Siberian High, detrital material from the GXR is consistently transported to the interior of the dune field and intensively reworked. The Laoha River and the Yangxumu River originating from the Yanshan Mountains provide stable detrital sources for the HSL. In addition, the transverse flow of the Xilamulun River and the West Liao River has provided sufficient space and sediment for the dunes, which is conducive to the full mixing of materials inside the dune field. The sediment in the southeast of HSL shows an obvious Yanshan Mountains source dominance and a grain-size dependence. The coarse fractions (>63 μm) mainly modified from the river channel sand and alluvial plain of the Yangxumu River (∼75.8 %), while the fine fractions (<63 μm) have a strong affinity with the loess deposit of Yanshan Mountains (∼52.4 %). The fluvial-lacustrine deposits during the last glacial maximum served as a temporary transit station, providing a direct dust source for the modern dunes in the HSL region. Aeolian–fluvial interaction controls the geomorphology and landscape evolution of the HSL in the monsoon region; however, it is challenging to derive insights into the landscape evolution from studying surface samples.

Stronger Westerly Wind Bursts in a Warming Climate: The Effects of the Pacific Warming Pattern, the Madden–Julian Oscillation, and Tropical Cyclones

Abstract Westerly wind bursts (WWBs) in the western–central equatorial Pacific are critical in El Niño–Southern Oscillation (ENSO) dynamics. Understanding how they may change with global warming has important implications for future projections of El Niño. In this study, we investigate how the enhanced eastern equatorial Pacific warming pattern, emerging in future climate projections, can influence WWB characteristics in an atmospheric general circulation model, CAM6. Changes in three main factors affecting WWBs—El Niño-conditions mean westerly wind stress anomalies, the Madden–Julian oscillation (MJO), and tropical cyclones (TCs)—are analyzed. We find that during El Niño onset (December–April), the WWB wind stress intensity remains largely unchanged but WWBs shift westward by about 20° of longitude. In contrast, during El Niño development (May–November), the WWB intensity increases by 41% or 79% in two warming scenarios considered [shared socioeconomic pathways (SSP5-8.5) and SSP2-4.5, respectively], which is mainly caused by a higher frequency of TC occurrence in the central tropical Pacific within 15°N/S. Further, we find that westerly wind speed anomalies associated with El Niño and the MJO also increase during El Niño development. However, as trade winds weaken in the central-eastern equatorial Pacific, the mean strength of the resulting westerly wind stress anomalies does not change much, and no significant eastward shift of WWBs is observed. Thus, our atmospheric model simulations suggest a strong TC-driven increase in WWB wind stress anomalies during El Niño development and hence a more important role of TCs in WWB generation, which in a coupled system could lead to stronger ENSO events, enhanced TC–ENSO coupling, and even greater intensification of WWBs.

Revisiting the Role of Atmospheric Initial Signals in Predicting ENSO

Abstract El Niño–Southern Oscillation (ENSO) provides an important source of global seasonal–interannual predictability, while its prediction encounters bottlenecks. Besides the slow-varying air–sea feedbacks, high-frequency atmospheric signals (HFASs) act on ENSO evolution. This study revisits the role of atmospheric initial signals in ENSO prediction using an atmosphere–ocean coupled model. Two sets of sensitivity hindcasts are conducted. One utilizes a pure sea surface temperature (SST) nudging for initialization so that no observed atmospheric internal signal is assimilated. The other applies a combination of the SST nudging and spectral nudging of JRA-55 reanalysis, which not only assimilates the observed atmospheric states and hence realizes skillful predictions of HFAS at the initial stage but also improves the oceanic initial conditions (ICs), especially around the thermocline. Unexpectedly, the better atmosphere–ocean ICs neither improve ENSO prediction nor overcome the spring prediction barrier. Further analysis of Bjerknes stability index suggests that underestimated negative feedbacks and insufficient responses of ocean currents and thermocline slope to atmospheric internal winds may account for the failure. Nevertheless, assimilating the atmospheric information partly improves the prediction of El Niño onset, especially for two recent extreme cases (i.e., 1997/98 and 2015/16). This improvement is associated with better representations of initial westerly wind bursts (WWBs) that excite subsequent downwelling equatorial Kelvin waves. However, due to unpredictable WWBs and underestimated wind response to the SST warming owing to the cold tongue biases in boreal summer, the zonal advective feedbacks are underestimated and thus further development of El Niño cannot be well predicted. This study suggests the importance of initial atmospheric signals despite the limitation, prompting further efforts to improve model physics.

Atlantic Meridional Overturning Response to Increased Southern Ocean Wind Stress in a Climate Model with an Eddy-Rich Ocean

Abstract The Southern Hemisphere westerly winds experienced significant changes over recent decades and are projected to further strengthen, altering ocean hydrography and dynamics. While anomalies of Southern Hemisphere origin are hypothesized to impact the Atlantic meridional overturning circulation (AMOC), many details of this relationship remain unknown as previous modeling studies are limited by the application of forced, coarse-resolution ocean models, or a short integration length. Here, a coupled, nested climate model configuration, covering the Atlantic Ocean at an eddy-rich 1/10° resolution is applied to study the adjustment of the large-scale circulation to a 30% increase in the Southern Ocean wind stress. The AMOC responds to the stronger wind stress with a strengthening of 0.6–1.4 Sv (1 Sv ≡ 106 m3 s−1) across the entire Atlantic after approximately 80 years. At that time, anomalous watermass transformation mainly occurs at the entry into the Nordic seas. A density anomaly in the overflow water then induces anomalous sinking in the eastern subpolar gyre, providing a link between AMOC changes in density and depth coordinates. Our study suggests that these watermass changes are caused by northward-propagating anomalies and provides a detailed hypothesis for the link between the Indian Ocean inflow via Agulhas leakage and the AMOC. Nevertheless, due to coupled ocean–atmosphere adjustments, anomalies do not simply follow the main volume transport pathways along the western boundary. Mixing between advectively transported and locally forced anomalies leads to an increasingly complex evolution of watermass anomalies and less certainty in the relative contributions of involved mechanisms toward subpolar latitudes.

Global geographical redistribution and source dynamics of selected semi-volatile organic compounds in the marine air boundary layer

The semi-volatile organic compounds (SVOCs), various priority pollutants of the marine air boundary layer (MABL), continue to elude full comprehension, creating substantial uncertainties about their global transport dynamics. We investigated 39 individual SVOCs during 3 large-scale Arctic and Antarctic expedition cruises. Our findings illuminate a discernable global gradient in their concentrations, with low molecular weight polycyclic aromatic hydrocarbons (PAHs) dominating. Interestingly, currently used pesticides (CUPs) have surpassed legacy organochlorine pesticides (OCPs) as primary pollutants. Despite international efforts to reduce emissions, SVOC mass inventories in polar regions have risen and are now identified as a significant source. The Westerlies disrupt SVOCs’ global transport pathways, resulting in the “Westerly Wind Wall Block” effect, substantially influencing their redistribution in the Southern Hemisphere (SH). Our analysis ultimately underscores the pivotal roles of air-seawater exchange mechanisms and oceanic currents in the global transport dynamics of SVOCs within the MABL.

Evaluation of Equatorial Westerly Wind Events in the Pacific Ocean in CMIP6 Models

Abstract Westerly wind events (WWEs) are anomalously strong, long-lasting westerlies over the Indian or Pacific Oceans that are capable of forcing oceanic wave modes, which in turn can impact the evolution of coupled ocean–atmosphere phenomena such as El Niño–Southern Oscillation (ENSO). This work examines the fidelity of equatorial WWEs over the Pacific Ocean in 30 CMIP6 historical simulations against observations. WWEs are identified using equatorially averaged zonal wind stress anomaly duration, zonal extent, and intensity criteria. Most simulations correctly place the majority of WWEs over the west Pacific although they are skewed westward and generally occur less frequently compared to observations. Simulated WWEs tend to be weaker than observations for a given duration and zonal extent with several models having shorter durations and zonal extents than observations. Biases in simulated WWEs are associated with biases in Madden–Julian oscillation (MJO) and convectively coupled Rossby wave (CRW) variability. Models that underpredict WWE forcing in the west Pacific also severely underpredict MJO and CRW variance. Further, the multimodel mean shows a smaller fraction of WWEs associated with both the MJO and CRW than observations.

Influence of Foehn‐Like Winds on Near‐Surface Temperature at Jang Bogo Station, Terra Nova Bay, East Antarctica

AbstractThe coast of Terra Nova Bay (TNB) is known as one of the intense katabatic wind confluence zones in Antarctica. Strong westerly winds with topography‐specific foehn effects (foehn‐like winds, FLWs) could have influenced surface temperatures in this area downwind of the Transantarctic Mountains, yet their impact remains unstudied. Jang Bogo Station (JBS) in TNB has weak winds year‐round, with occasional strong winds causing significant winter temperature increases. This study aims to investigate the FLWs and their recent variability in occurrence at JBS in terms of surface temperature variability. During the strong wind events, the surface warms due to foehn effects such as adiabatic heating and vertical mixing. FLWs occur approximately 16% (10%) of the time in winter (annually). FLWs are caused by cyclones in the eastern Ross Sea. Meteorological records for 2015–2022 revealed an increased FLW frequency, particularly in winter, which has increased temperatures in recent years.

Exploring fine-aerosol episodes in urban Seoul during the cold season of the 2021 SIJAQ campaign: Measurement evidences of heterogeneous reactions on black carbon particles

Significant PM2.5 pollution has been prevalent on a regional scale in East Asia including a megacity Seoul in South Korea. Here, we explore fine-aerosol episodes occurred in Seoul during the Satellite Integrated Joint monitoring of Air Quality (SIJAQ) campaign from October to November of the 2021, focusing on experimental evidences of heterogeneous reactions to form secondary aerosol under a highly oxidized atmospheric condition.At this urban site in Seoul, vehicle exhaust was the clear source of fresh emissions, leading to a high level of NO and small refractory black carbon (rBC) particles (mass median diameter of 162 nm ± 16 nm) in the morning time. The hourly mass concentration of PM2.5 ranged from 5.3 μg m−3 to 146.1 μg m−3, averaging at 24.5 ± 22.2 μg m−3. During the campaign, the most intense episode, EP3 (November 18–21), recorded an average PM2.5 concentration of 72.5 ± 38.2 μg m−3, peaking at 146.1 μg m−3, was characterized by relatively higher temperature (∼12 °C) and relative humidity (67 %) on average thoroughly governed by continental migratory high and westerly winds. While the average NO3− concentration was 27.7 μg m−3, four times the whole campaign's average, EP3 was highlighted by a high morning NO2/NOx ratio and significantly elevated daytime and nighttime Ox (O3+NO2) concentrations compared to non-episode days. Throughout the entire campaign, NOz surrogate (NO2(CL)-NO2(T)), Ox, and Fmoderate + thick (the combined number fractions of moderately and thickly coated-rBC particles) tended to increase with the PM2.5 concentration. During the daytime, as PM2.5 increased, Fmoderate + thick showed a monotonic increase, accompanied by RH rising from 54 ± 16% to 63 ± 11%. In contrast, at nighttime of humid condition with RH often exceeding 70% the enhancement of Fmoderate + thick was more sensitive to condensable gas levels than RH. Given that high levels of PM2.5 (>60 μg m−3) were observed only during EP3, enhanced levels of NOz surrogate, Ox, Fmoderate + thick, and RH were evident characteristics of EP3. Such chemical and meteorological conditions suggest that the chemically enhanced oxidation state was evident during EP3, which promoted the formation of secondary aerosols on primary particles including rBC, especially under conditions of elevated RH. Considering the recent trend of increasing number of vehicles and rising atmospheric O3 concentrations in East Asia, future studies should be well designed to investigate the detailed mechanisms involved in heterogeneous reactions that lead to the formation of secondary aerosols.