Northwesterly Winds Research Articles

Exploring the use of ground-based remote sensing to identify new particle formation events: A case study in the Beijing area

New Particle Formation (NPF) is an important process of secondary aerosol production in the atmosphere, which has significant impacts on the Earth's radiation balance, air quality, and climate change. In this study, we develop a method to identify NPF events based on ground-based remote sensing. We propose a proxy to characterize NPF events utilizing ground-based remote sensing of gaseous precursors and aerosol optical depth (AOD). This proxy is applied to identify the NPF events in Beijing in the winter of 2022 and tested by comparison with in-situ observations of aerosol particle number size distributions (PNSD) from SMPS. The comparison shows that the NPF events for regional nucleation can be identified effectively when the threshold for sulfur dioxide and organic gases (i.e. formaldehyde) are determined as 0.44 × 10−4 and 1.07 × 10−4. Based on these thresholds, the NPF events can be identified at a high percentage (84 %) compared with in-situ observations. The relationship between identification of NPF events and meteorological conditions shows that NPF events in Beijing winter occurred more frequently under weather conditions with north-west wind direction, high wind speed and low relative humidity.

Downwind Warming of Cities? Inequal Heat Distribution Attributed to Winds

Heat exposure within urban areas is strikingly uneven, posing disproportionate risks to certain communities. While nature-based solutions have gained attention, the role of wind in distributing heat remains less understood in an urban planning scale. This study assessed the interaction between wind direction, speed, and heat advection in Taipei Basin during summers from 2011 to 2020, using data from densely installed meteorological stations. A novel method was developed to capture multiple wind directions while accounting for local terrain and urban effects. Results revealed that wind-induced heat advection is complicated by local terrain and nearby cities in the conurbation, varying heat distribution. Windy conditions were mostly warmer than calm conditions, with north-westerly and westerly winds causing the strongest heat advection. Heat advection increased with wind speeds up to 5.4 m/s and decreased thereafter. Substantial intra-urban differences in heat advection were observed, reaching 4.33°C daytime and 3.34°C nighttime. Upwind areas were not necessarily cooler, while some downwind areas at mountain foot experienced greater warming. Up to 2.6SD of advected heat magnitude was found downwind at night. These findings underscore inequitable heat transfer to areas that do not generate heat and the critical need for wind-sensitive planning for both city-region and inter-urban areas.

Enhanced interannual variability of the May North Atlantic Oscillation and its impact on summer sea ice in the North Atlantic after the mid-2000s

Based on data diagnosis and numerical experiments, this study investigated the changes in the interannual properties of the May North Atlantic Oscillation (NAO) and their impact on summer (June–July) sea ice in the North Atlantic during 1979–2021. Results showed statistically significant increase in the interannual variability of the May NAO after the mid-2000s, which had remarkably enhanced impact on summer sea ice in the eastern Hudson Bay (EHB) and the western Labrador Sea (WLS). During 2005–2021, corresponding to a positive phase of the May NAO, anomalous surface westerly or northwesterly winds prevailed over the Hudson Bay and Labrador Sea in May. This led to statistically significant increase in sea ice in both the EHB and the WLS in May via dynamic processes (favoring southeastward movement of the sea ice) and thermal processes (changing surface turbulent heating and shortwave radiation). In comparison with the situation in May, the increase in sea ice in the EHB developed further during summer mainly via thermal processes (positive feedback between the increased sea ice and shortwave radiation). In contrast, amplitude of the increased sea ice in the WLS was comparable between May and summer. Dynamic processes (southeastward movement of sea ice), which was induced by a barotropic anomalous high in the troposphere centered over the Labrador Peninsula, favored the increase in sea ice in summer in the WLS. The tripole sea surface temperature anomalies in the North Atlantic and increased snowpack on the Labrador Peninsula in May, triggered by the positive phase of the May NAO, played an important role in the formation of the anomalous high. During 1979–2004, the surface wind, snowpack, and tripole sea surface temperature anomalies in May, triggered by the May NAO, were relatively weak, leading to statistically insignificant changes in summer sea ice in the EHB and WLS.

Revisiting the connection between variations in the Tsushima Warm Current and winter rainfall along the coast of Japan

AbstractEnhanced autumn transport via the Tsushima Warm Current (TWC) has been reported to increase winter rainfall along Japan’s northern coast. However, observations reveal a significantly weakened correlation after 2006. Although enhanced transport via the Eastern channel of the Tsushima Strait affects rainfall by enhancing latent heat flux along Japan’s northern coast, the role of oceanic flows in varying sea-surface temperatures has weakened since 2006. Stronger northwesterly winds co-occur with enhanced surface heat loss that overwhelms the impact of the TWC. Our findings imply that atmospheric conditions should be considered when using TWC transport as a precursor for winter rainfall.

Synoptic Conditions at Pressure Different Levels for the Dust Storm of May/ 2022 Over Iraq

This study examines the severe dust storm from May 12-16/2022,culminating on May 15, with a comprehensive analysis and explanation. The weather maps from the National Oceanic and Atmospheric Administration (NOAA) and the European Centre for Medium-Range Weather Forecasts (ECMWF) weather maps were used to identify systems and patterns that contributed to the storm's activity, continuity, and tracking as well as maps of pressure compounds and wind vectors in levels 1000 and 850 mbar that appear with the dust state for the same days accompanied by tracking patterns in the middle of the turbosphere 500 mbar to give a comprehensive analytical view of climate conditions at each level of pressure and higher systems supportive of their persistence on the surface. The northwesterly winds are the main factor that carries dust over long distances. The eastern desert in Syria, the Empty Quarter in the Kingdom of Saudi Arabia, the desert of western Iran, and the desert region of western Iraq are among the main sources of dust In its atmosphere. Based on weather maps of the surface and upper levels of storm days, the concentration of dust reached very high levels in Iraq's airspace and surrounding countries, including Egypt, Jordan, Lebanon, Palestine, and Syria. The intensity of the dust gradually decreased as the area was affected by wet westerly winds with relatively low temperatures and a relative increase in wind speeds due to the impact of the study area on the atmospheric decline centered around the Turkish island of Cyprus.

Characteristics of Water-soluble Ion Pollution in PM2.5 and the Causes of High Acidity of PM2.5 in Dalian

To gain a deeper understanding of the pollution status and influencing factors of fine particles （PM2.5） and their water-soluble ions （WSI） in Dalian and to implement precise control of pollution events such as haze and acid rain, PM2.5 samples were collected in Dalian from June 2021 to May 2022. Then, the mass concentrations of PM2.5 and WSI were determined using the weight method and ion chromatography, respectively, and the pollution characteristics and sources were analyzed. Furthermore, the causes of the high acidity of PM2.5 in spring were discussed. The results showed that the annual average mass concentrations of PM2.5 and WSI in Dalian during the sampling period were （33.24 ±28.87） μg·m-3 and （18.66 ±20.52） μg·m-3, respectively, and the secondary ions （SNA, including SO42-, NO3-, and NH4+） accounted for the highest proportion of WSI [（86.2 ±9.3）%]. The order of ion concentration levels from highest to lowest was： NO3->SO42->NH4+>Cl->K+>Ca2+>Na+>Mg2+>F-. Due to the influence of meteorological conditions and coal combustion emissions during the concentrated heating period from late autumn to early spring, the seasonal variation in PM2.5 and WSI was winter>spring>autumn>summer, whereas SNA was the highest in spring and the lowest in summer. The results of correlation and principal component analysis showed that WSI in PM2.5 was mainly from the secondary transformation of atmospheric SO2 and NO2 （contributing to the majority of SNA）, mixed sources of combustion and dust （characterized by K+, Mg2+, Cl-, and F-）, and sources of sand and sea salt （characterized by Na+, Ca2+, and Mg2+）. In summer, the main combustion source was biomass burning, whereas in autumn, winter, and spring, coal combustion emissions were predominant. The change in wind direction from autumn to winter brought by a shift from the source of sea salt to soil dust； additionally, the external pollution transported by northwest winds contributed to the complexity of the sources of WSI in PM2.5 during spring in Dalian. ISORROPIA-II model simulations suggested NH4NO3 as the most present solid aerosol form in PM2.5 in Dalian, followed by CaSO4 and （NH4）2SO4； compared to that in solid aerosols, more SNA existed in liquid aerosols. The annual average pH of PM2.5 in Dalian was 5.65 ±3.00, with pH values close to neutral in summer, autumn, and winter but significantly acidic in spring （2.03 ±3.18）. The high acidity observed in spring was attributed to the combination of low temperature, high humidity, and high SNA concentrations. These conditions resulted in higher aerosol water content and increased gas-to-particle conversion rates, ultimately leading to an ammonia-deficient environment. The backward trajectory and PSCF results indicated that the external transport of high acidity PM2.5 in spring mainly came from the northwest （45.0%） and southwest （40.8%） directions. Mobile source emissions made the most significant contribution to the transportation of pollutants in the former, forming high-pollution source areas in the Beijing-Tianjin-Hebei Region, which may have been mainly related to urban motor vehicle and port vessel emissions； the latter was influenced by relatively strong stationary sources and showed higher SO2 emissions in the southern part of Henan Province and the central part of Jiangsu Province.

Variations of dissolved trace elements in precipitation and stream water in Japanese forest area: additional evidence of changing air pollution in the region

Trace elements released into the atmosphere by human activities, such as fossil fuel combustion, flow into forest ecosystems via wet and dry deposition and can flow out via mountainous stream water. The Kajikawa catchment site in Niigata Prefecture, located on the Sea of Japan side in central Japan, suffers from large amounts of acidic substance deposition due to its geographical conditions and meteorological seasonality and is affected by transboundary air pollution originating from the Asian continent due to northwesterly seasonal winds in winter. This study determined the concentrations of trace elements dissolved in precipitation and stream water to comprehensively evaluate the effects of transboundary air pollution on forest ecosystems. The results showed that the concentrations of trace elements and major inorganic ions in precipitation tended to be high in winter and low in summer. The fluxes of many trace elements also increased in winter, reflecting high precipitation amount. Except for Sr, the enrichment factors of the highly enriched trace elements did not show clear seasonality. Therefore, they were continuously influenced by anthropogenic activities. Furthermore, the stable Pb isotope ratio changed significantly during the observation period; however, this was not explained by seasonal changes. This study revealed that trace elements are transported to the Sea of Japan side in central Japan, especially in winter; however, their quantity and content change in response to changes in local and transboundary air pollution.Graphical

The role of atmospheric conditions in the Antarctic sea ice extent summer minima

Abstract. Understanding the variability of Antarctic sea ice is still a challenge. After decades of modest growth, an unprecedented minimum in the sea ice extent (SIE) was registered in summer 2017, and, following years of anomalously low SIE, a new record was established in early 2022. These two memorable minima have received great attention as single cases, but a comprehensive analysis of summer SIE minima is currently lacking. Indeed, other similar events are present in the observational record, although they are minor compared to the most recent ones, and a full analysis of all summer SIE minima is essential to separate potential common drivers from event-specific dynamics in order to ultimately improve our understanding of the Antarctic sea ice and climate variability. In this work, we examine sea ice and atmospheric conditions during and before all summer SIE minima over the satellite period up to 2022. We use observations and reanalysis data and compare our main findings with results from an ocean–sea ice model (NEMO–LIM) driven by prescribed atmospheric fields from ERA5. Examining SIE and sea ice concentration (SIC) anomalies, we find that the main contributors to the summer minima are the Ross and Weddell sectors. However, the two regions play different roles, and the variability of the Ross Sea explains most of the minima, with typical negative SIE anomalies about twice as large as the ones in the Weddell Sea. Furthermore, the distribution of SIC anomalies is also different: in the Weddell Sea, they exhibit a dipolar structure, with increased SIC next to the continent and decreased SIC at the sea ice margin, while the Ross Sea displays a more homogenous decrease. We also examine the role of wintertime sea ice conditions before the summer SIE minima and find mixed results depending on the period: the winter conditions are relevant in the most recent events, after 2017, but they are marginal for previous years. Next, we consider the influence of the atmosphere on the SIE minima, which is shown to play a major role: after analyzing the anomalous atmospheric circulation during the preceding spring, we find that different large-scale anomalies can lead to similar regional prevailing winds that drive the summer minima. Specifically, the SIE minima are generally associated with dominant northwesterly anomalous winds in the Weddell Sea, while a southwesterly anomalous flow prevails in the Ross Sea. Finally, we investigate the relative contribution of dynamic (e.g., ice transport) and thermodynamic (e.g., local melting) processes to the summer minima. Our results indicate that the exceptional sea ice loss in both the Ross and Weddell sectors is dominated at the large scale by thermodynamic processes, while dynamics are also present but with a minor role.

Variations in the Thermal Low-Pressure Location Index over the Qinghai–Tibet Plateau and Its Relationship with Summer Precipitation in China

The thermal and dynamic effects of the special topography of the Qinghai–Tibet Plateau have a significant impact on rainfall in China. Utilizing NCEP/NCAR monthly reanalysis data alongside precipitation observations from 1936 monitoring stations across China spanning from 1966 to 2022, this study establishes a location index for the thermal low-pressure center situated over the Qinghai–Tibet Plateau. Temporal variations in the location index and summer (July) precipitation patterns in China were studied. Over the past six decades, thermal low-pressure centers have been predominantly positioned near 90° E and 32.5° N within a geopotential height of 4360 gpm, with their distribution extending from east to west rather than from south to north. The longitudinal and latitudinal position indices showed the same linear trend, with a negative trend before the 21st century, and then began to turn positive. Mutation analysis highlights pronounced weakening mutations occurring in 1981 and 1973, with the longitudinal index transitioning from an interannual cycle of approximately 6–8 years, while the latitudinal index displays quasi-cyclic oscillations of 5 and 8 and 12–14 years. Strong negative correlations are evident between the location indices and precipitation along the southeastern edge of the Qinghai–Tibet Plateau and in southern China, contrasting with the positive correlations observed in the central-eastern plateau, northwest, north, and the Huang-Huai region of China. The center of the thermal low is located to the east and north, corresponding to the deeper surface thermal low in most areas east of China, and the stronger transport of warm and wet air from the southwest wind, leading to greater convergence of southwest wind and northwest wind in China’s northern region. The south of the Yangtze River is controlled by the strengthening West Pacific subtropical high and South Asia high, resulting in a significant decrease in precipitation, and the warm and humid air from the southwest on the west side of the West Pacific subtropical high is also transported to the north, increasing the precipitation in most parts of the north.

A statistical study of precipitation on the eastern Antarctic plateau (Dome-C) using remote sensing and in-situ instrumentation.

Studying precipitation at very high latitudes is a challenge, particularly during the polar winter. Direct monitoring of ice habit and size in high latitude precipitation is crucial for validating the algorithms used to derive precipitation from radar, and for improving the climatological modeling of polar areas. The high plateau lacks long-term direct observations of precipitation. In this work, carried out at Concordia Station (Dome-C (DC), -75°S, 123°E, 3233 m a.m.s.l), the use of a depolarization LIDAR, a flatbed scanner (ICECAMERA), a microwave profiler (HAMSTRAD) and meteorological instrumentation made possible the study, over the period 2014-2021, of shape, size, height and temperature of formation of precipitation. The precipitation sources were classified into four types: ice fogs, liquid fogs, mixed-phase clouds, and cirrus. Ten representative ice habits for Dome-C were chosen. The size distribution for every habit was calculated, allowing for the estimation of the corresponding radar reflectivity. The use of W-band radars, such as CLOUDSAT, with a sensitivity of -28dB, resulted in capturing all the crystals observed in Concordia. A positive trend was observed between grain size and height in ice habits that are typical of cloud precipitation. North West (NW) and North East (NE) winds at cloud height, blowing from coastal regions, caused the majority of precipitation from clouds. The study also examined the height trend of the ice habit composition of precipitation. The ice habit composition for each of the four types of precipitation source was analyzed, and the possibility of determining the source by simply observing the precipitation was explored. This work marks the first comprehensive investigation of precipitation on the eastern Antarctic plateau.

Assessing Golden Tides from Space: Meteorological Drivers in the Accumulation of the Invasive Algae Rugulopteryx okamurae on Coasts

Massive accumulations of invasive brown algae Rugulopteryx okamurae are exacerbating environmental and socio-economic issues on the Mediterranean and potentially Atlantic coasts. These golden tides, likely intensified by global change processes such as changes in wind direction and intensity and rising temperatures, pose increasing challenges to coastal management. This study employs the Normalized Difference Vegetation Index (NDVI), with values above 0.08 from Level-2 Sentinel-2 imagery, to effectively monitor these strandings along the coastline of Los Lances beach (Tarifa, Spain) in the Strait of Gibraltar Natural Park from 2018 to 2022. Los Lances beach is one of the most affected by the R. okamurae bioinvasion in Spain. The analysis reveals that wind direction determines the spatial distribution of biomass accumulated on the shore. The highest average NDVI values in the western patch were observed with south-easterly winds, while in the eastern patch, higher average NDVI values were recorded with south-westerly, westerly and north-westerly winds. The maximum coverage correlates with elevated temperatures and minimal rainfall, peaking between July and October. Leveraging these insights, we propose a replicable methodology for the early detection and strategic pre-shore collection of biomass, which could facilitate efficient coastal cleanup strategies and enhance biomass utility for biotechnological applications. This approach promises cost-effective adaptability across different geographic areas impacted by golden tides.

Spatiotemporal variability and underlying large‐scale atmospheric mechanisms causing the change in the Black Sea surface temperature and associated extreme precipitation events in the northeastern of Turkiye

AbstractSea surface temperature (SST) has an important local and remote influence on global climate through the distribution and transport of heat and moisture. As a result of climate forcing, significant changes occur in the SSTs, which result in many natural disasters such as supercharged storms, higher wind speeds, heavier precipitation and flooding. This study investigates the spatiotemporal changes and underlying atmospheric mechanisms of the Black Sea (BLS) surface temperature. For this purpose, National Oceanicand Atmospheric Administration (NOAA) high‐resolution SST data (0.25°), which were verified with buoy observations, were used for the period 1982–2021. To investigate the circulation impacts, the relationship between North Atlantic Oscillation and East Atlantic/West Russia (EA/WR) phases and SSTs of the western BLS (WBLS) and eastern BLS (EBLS) was analysed. According to the results, SST values increased from 1.64°C (in winter) to 2.52°C (in summer) during the 40‐year period. Significant SST increases are shown in the EBLS during the summer and fall months. Statistically significant negative correlations (p < 0.05) were found between EA/WR and winter (r = −0.57) and summer (r = −0.56) SSTs in the EBLS. During winter, surface high located in the eastern Anatolia causes southerly winds, which blows from the terrestrial areas to the EBLS and result in above‐normal SST values. During summer (under negative EA/WR phases), the Azores high‐pressure centre extends to the Balkan Peninsula and WBLS and as a consequence, a significant amount of moisture associated with high sea surface temperature (>27°C, above‐normal 2.0°C) develops low‐level moisture convergence. Proper synoptic conditions, strong instability conditions between the surface and upper levels, and orographic forcing enable the occurrence of convective cloud cells. The movement of these cells to the northeastern part of Turkiye by strong northwesterly winds causes extreme precipitation and associated flash‐flood events in a limited area where land–sea interaction occurs (i.e., Artvin, Rize and Hopa provinces of Turkiye).

Sulfate runoff processes during rainfall events in a small forested catchment on the sea of Japan side recovering from acidification under climate change

AbstractChanges in rainfall patterns due to climate change may accelerate the runoff of sulfate (SO42−), which is anthropogenically emitted and deposited as an air pollutant, cycled in forest ecosystems, and partly accumulated in forest soils. A forested catchment on the Sea of Japan side in central Japan is significantly affected by transboundary air pollution from the Asian continent due to northwesterly seasonal winds in winter. In this study, intensive 24‐h observations were conducted every hour eight times from 2019 to 2020 to clarify changes in stream water quality and runoff processes during rainfall events. The pH, electrical conductivity, and SO42− concentration in stream water decreased with increasing hourly average discharge rate (L sec−1). The SO42− concentration was negatively correlated with discharge rate. Hydrograph separations using the water isotopic parameter (deuterium excess, d‐excess = δ2H – 8 × δ18O) showed that most of the stream flow during the rain events was derived from pre‐storm water. A significant negative correlation between the d‐excess and stream water discharge was found for all six events where the water isotope analysis was applied. However, the S isotope ratio (δ34S) in stream water was not correlated with discharge rate during rainfall events and was obviously different (>1.5‰) from rainwater δ34S in the same month. This suggests that rainwater SO42− during rainfall events did not directly flow to the stream but was retained in the forest ecosystem. The isotopically well homogenized internal SO42− appeared to be mainly released into the stream during rainfall events. Future climate change may further accelerate SO42− runoff from forest catchments and disrupt material cycles in the ecosystem if warming causes more intense rainfall.

Environmental conditions affecting air pollution dispersion over Richards Bay, South Africa

Air pollution dispersion over Richards Bay, South Africa is studied using satellite, reanalysis and in-situ measurements. Near-surface concentrations of trace gases and particulates reach high concentrations under dry stable ‘berg’ winds. Temporal records of CO, NO2, O3, PM2.5, SO2 (2000-2023) exhibit no trend and short-term dose exceedances of individual pollutants are rare and confined to winter mornings. Regional point-to-field correlation maps of a Richards Bay winter air pollution index found that anomalous warming of the west Indian Ocean accelerates the jet stream over Madagascar and pulls smoke- and dust-laden north-westerly winds across the South African plateau, implicating long-range transport. At daily and hourly time scales dewpoint temperature and boundary layer height best indicate changes in local air pollution dispersion that impact respiratory health. A case study of 15-17 June 2021 revealed a 10ºC thermal inversion caused by negative sensible heat fluxes of -40 W/m2 through the night, leading to SO2 concentrations above 100 ppb in the morning along the main access road (28.8ºS, 32ºE). Poor dispersion seldom happens in the summer when turbulent mixing and rainfall cleanse the air.

Visualising Daily PM10 Pollution in an Open-Cut Mining Valley of New South Wales, Australia—Part II: Classification of Synoptic Circulation Types and Local Meteorological Patterns and Their Relation to Elevated Air Pollution in Spring and Summer

Abstract: The Upper Hunter Valley is a major coal mining area in New South Wales (NSW), Australia. Due to the ongoing increase in mining activities, PM10 (air-borne particles with an aerodynamic diameter less than 10 micrometres) pollution has become a major air quality concern in local communities. The present study was initiated to quantitatively examine the spatial and temporal variability of PM10 pollution in the region. An earlier paper of this study identified two air quality subregions in the valley. This paper aims to provide a holistic summarisation of the relationships between elevated PM10 pollution in two subregions and the local- and synoptic-scale meteorological conditions for spring and summer, when PM10 pollution is relatively high. A catalogue of twelve synoptic types and a set of six local meteorological patterns were quantitatively derived and linked to each other using the self-organising map (SOM) technique. The complex meteorology–air pollution relationships were visualised and interpreted on the SOM planes for two representative locations. It was found that the influence of local meteorological patterns differed significantly for mean PM10 levels vs. the occurrence of elevated pollution events and between air quality subregions. In contrast, synoptic types showed generally similar relationships with mean vs. elevated PM10 pollution in the valley. Two local meteorological patterns, the hot–dry–northwesterly wind conditions and the hot–dry–calm conditions, were found to be the most PM10 pollution conducive in the valley when combined with a set of synoptic counterparts. These synoptic types are featured with the influence of an eastward migrating continental high-pressure system and westerly troughs, or a ridge extending northwest towards coastal northern NSW or southern Queensland from the Tasman Sea. The method and results can be used in air quality research for other locations of NSW, or similar regions elsewhere.

Influence of topography and synoptic weather patterns on air quality in a valley basin city of Northwest China

To clarify the mechanism underlying the effects of weather patterns and topography on air pollution, this study conducted the obliquely rotated principal component analysis in the T-mode to analyze ERA5 reanalysis data and categorize typical weather patterns at a 700-hPa geopotential height from 2015 to 2022. The probability of worsened air pollution attributable to weather patterns was quantitatively assessed using a generalized additive model. The results indicated that due to the influence of topography, Lanzhou was affected by an extended period of downdraft (with weak convective intensity) and the delayed formation of a convective boundary layer during the daytime by 1–2 h relative to other areas. Under the combined effect of low trough patterns (south low pressure type [SL] and south low weak pressure type [SL−]) and topography, the formation of a stable layer above the planetary boundary layer (PBL) would weaken the vertical exchange of the local airflow and inhibit the development of the PBL. The type of SL led to the most severe pollution, causing a 61.9 % (95 % confidence interval [CI]: 46.3 %–79.3 %) increase in PM2.5 concentration. For southwest high pressure patterns (south high [SH], southwest weak high [SWH−], southwest high [SWH], and southwest strong high [SWH+] pressure types), the prevailing northwest wind was the main transport path for pollutants. For the high pressure patterns (north high [NH] and northwest high [NWH] pressure types) and south wind patterns (southeast weak high [SEH−], southeast high [SEH], and northeast high [NEH] pressure types), the enhancement of vertical convection, deepening of the PBL, and reduction of pollution transport led to improved air quality. The NH, NWH, and NEH pressure types caused PM2.5 concentration to decrease by 18.4 % (95 % CI: 8.8 %–27.1 %), 14.9 % (95 % CI: 4.7 %–24.0 %), and 35.9 % (95 % CI: 9.7 %–54.6 %), respectively.

Intense lateral intrusion of offshore sub-surface waters in Halifax Harbour

The main physical processes affecting the circulation variability in Halifax Harbour (HH), including the intense lateral intrusion of offshore sub-surface waters into Bedford Basin (BB), are studied using a nested-grid modelling system (NGMS). The annual and monthly mean circulation in HH are characterized by a typical two-layer estuarine circulation, with seaward currents in the upper layer and landward currents in the lower layer, both showing strong temporal and spatial variability. The intense lateral intrusion of offshore sub-surface waters into BB occurs at time scales of a few days. The intense intrusion, in combination with winter connection, is important for the renewal of deep waters in BB. The model sensitivity experiments suggest that the persistent northwesterly winds strengthen the near-surface seaward currents and the lateral intrusion of offshore sub-surface waters into BB. The persistent southwesterly winds can also trigger the lateral intrusion, but are less effective than the northwesterly winds. The southeasterly winds, on the contrary, reduce significantly the seaward currents in the surface layer and prevent the lateral intrusion. The accumulative effects of winds and tides on the 3D hydrodynamics in HH are also examined. Local winds have dominant effects on the 3D currents and temperature/salinity, through driving vertical mixing and coastal upwelling. By comparison, tides play a secondly role in affecting the currents and temperature/salinity in BB but are important in the Narrows.

Quantification of Contributions from Different Dust Sources to the Distribution and the Variation of Spring Dust over the Tibetan Plateau and Corresponding Mechanisms since 2000

Abstract Dust is the predominant type of aerosol over the Tibetan Plateau (TP) due to the existence of surrounding significant dust sources. However, the contributions of different dust sources to the distribution and variation of dust over the TP and corresponding mechanisms are still being explored. By separating emissions from different dust sources in a numerical model, this study detected that dust originating from East Asia, the Middle East, and North Africa are the main contributors to spring dust over the TP, accounting for 42%–68%, 13%–27%, and 9%–25% of the total dust concentration, respectively. East Asian dust primarily affects the dust over the central and northern parts of the TP, whereas Middle Eastern and North African dust mainly contributes to the dust over the western and southern parts of the TP. Additionally, the variation in dust over the TP is related to East Asian and North African dust, which contribute 58% and 35% of the total variation, respectively. The mechanism underlying this association is attributable to the SST over the northern North Atlantic and updrafts over the northern slope of the TP: the increased SST enhances westerlies from North Africa to East Asia and northwesterly winds over the northern slope of the TP and combines with the stronger westerlies to promote the transport of East Asian and North African dust to the TP. Consequently, it is necessary to focus on the impact of multiple dust sources on the dust over the TP.

Tropical Atmospheric Intraseasonal Oscillations Leading to Sea Level Extremes in Coastal Indonesia during Recent Decades

Abstract Coastal flooding induced by sea surface high extreme (HEX) events is an increasing risk to human society and infrastructure as both urban growth in coastal areas and anthropogenic sea level rise continue, especially for island nations like Indonesia. This paper investigates the role of atmospheric intraseasonal oscillations (ISOs), which are dominated by the Madden–Julian oscillation (MJO), in forcing HEXs on the coasts of Indonesia bordering the Indian Ocean. We use satellite altimetry data from 1993 to 2021 and tide gauge observations to detect HEXs, and modeling experiments using both the Regional Ocean Modeling System and a Bayesian dynamic linear model to understand the forcing and processes. We find that HEXs exhibit strong seasonality, with most events occurring during boreal winter (December–February) and spring (March–May) that are dominated by seasonal-to-decadal and intraseasonal variability respectively. In 32% of the 56 HEX events detected, the amplitude of ISO-induced sea level anomalies (SLAs) exceeds that of seasonal-to-decadal SLAs. Surface wind stress associated with atmospheric ISOs is the major forcing for intraseasonal SLAs, and both the remote westerly wind stress from the Indian Ocean equator and northwesterly longshore wind stress at the Indonesian coasts play important roles in driving the HEXs. The MJO is the dominant cause of ISO-dominated HEXs and its impact shows strong seasonal differences. Spring MJOs are associated with stronger convective anomalies over the eastern Indian Ocean equator that drive stronger zonal winds across the equatorial basin that lead to more HEX events compared to winter MJOs when the convection is shifted southward.

Comparative analysis of multi-directional long-distance pollution transport effects on heavily polluted weather in the Liaoning region

In recent years, although the air quality in the Liaoning region has improved, heavy pollution weather is still caused by external pollution transportation. In order to study the influence of multi-directional long-distance pollution on the heavily polluted weather in Liaoning, this paper analyzes three types of transport channel (northerly, northwesterly, and southwesterly transport corridors) by combining ground observations, airborne observations, AQI and the concentration data of atmospheric pollutants such as PM2.5, PM10 and so on. The results show that both northerly and southwesterly winds caused widespread fog and haze in the Liaoning region. The PM2.5 concentration reached the second-highest value on record (1479 μg/m3) during the pollution period caused by northwesterly wind transport. Wind and sand transported from the northwest mainly caused dusty weather in Liaoning, with PM10 concentration reaching up to 1200 μg/m3 during the pollution period. Northeasterly and northwesterly wind transport mainly led to the accumulation of pollutants in high places to high pollution values. Convergence of winds due to southwesterly wind transport led to prolonged accumulation of pollutants in the Liaoning region, resulting in severe pollution. Long-distance pollution transport is now one of the main sources of heavy pollution in the Liaoning region.