Significant Negative Anomalies Research Articles

Evaluating Ionospheric Total Electron Content (TEC) Variations as Precursors to Seismic Activity: Insights from the 2024 Noto Peninsula and Nichinan Earthquakes of Japan

This study provides a comprehensive investigation into ionospheric perturbations associated with the Mw 7.5 earthquake on the Noto Peninsula in January 2024, utilizing data from the International GNSS Service (IGS) network. Focusing on Total Electron Content (TEC), the analysis incorporates spatial mapping and temporal pattern assessments over a 30-day period before the earthquake. The time series for TEC at the closest station to the epicenter, USUD, reveals a localized decline, with a significant negative anomaly exceeding 5 TECU observed 22 and 23 days before the earthquake, highlighting the potential of TEC variations as seismic precursors. Similar patterns were observed at a nearby station, MIZU, strengthening the case for a seismogenic origin. Positive anomalies were linked to intense space weather episodes, while the most notable negative anomalies occurred under geomagnetically calm conditions, further supporting their seismic association. Using Kriging interpolation, the anomaly zone was shown to closely align with the earthquake’s epicenter. To assess the consistency of TEC anomalies in different seismic events, the study also examines the Mw 7.1 Nichinan earthquake in August 2024. The results reveal a prominent negative anomaly, reinforcing the reliability of TEC depletions in seismic precursor detection. Additionally, spatial correlation analysis of Pearson correlation across both events demonstrates that TEC coherence diminishes with increasing distance, with pronounced correlation decay beyond 1000–1600 km. This spatial decay, consistent with Dobrovolsky’s earthquake preparation area, strengthens the association between TEC anomalies and seismic activity. This research highlights the complex relationship between ionospheric anomalies and seismic events, underscoring the value of TEC analysis as tool for earthquake precursor detection. The findings significantly enhance our understanding of ionospheric dynamics related to seismic events, advocating for a comprehensive, multi-station approach in future earthquake prediction efforts.

Subsurface complexity controls the aquifer heterogeneity: A case study from the Al-Hassa oasis, Eastern Saudi Arabia

Al-Hassa region in the eastern part of Saudi Arabia is well-known for its geological and hydrogeological importance since it has historically hosted over 280 natural springs, which were used to irrigate the largest oasis in the world. Al-Hassa is located near the renowned Ghawar oil field, the largest conventional oil field globally, which represents a potential pollution source. This study utilizes and integrate hydrochemical investigations and geophysical gravity surveys to understand and reconstruct the subsurface heterogeneity in the Al-Hassa area. The dataset encompasses 113 groundwater wells distributed across the Al-Hassa Oasis which have been analyzed for salinity major ions, and isotopic (oxygen and hydrogen) compositions. A total of 571 gravity stations covering the broader oasis area (approximately 350 km2) are collected, processed, and modeled. The combined hydrochemical and geophysical results show a good agreement between groundwater quality and density (gravity anomalies) distribution within the study area. The southeastern part of the study area exhibits distinctive positive gravity anomalies, indicating denser rock formations alongside high total dissolved solids (TDS) in groundwater, reflecting poor water quality. Conversely, the southwest displays significant negative gravity anomalies, suggesting basins filled with loose sediments and low TDS values, signifying good water quality. Furthermore, the study reveals a certain pattern in groundwater temperature distribution, with cooler waters in the areas characterized by negative gravity anomalies (basins), and hotter waters emerging from areas with positive gravity anomalies. These findings suggest that groundwater quality differences may stem from varying sub-basins and interactions with distinct geological substrates. Temperature variations may also be attributed to differing subsurface flow pathways. This study attempts to explain the controlling factors for groundwater heterogeneity in the Al-Hassa Oasis area, emphasizing the role of geological, tectonic, and hydrogeological elements in shaping the Oasis's hydrological and hydrochemical pattern.

Analysis on characteristics of extreme precipitation indices and atmospheric circulation in Northern Shanxi

This article utilizes daily precipitation data from 28 national meteorological stations in northern Shanxi Province spanning from 1972 to 2020, and the US NCEP/NCAR monthly average reanalysis and ERA5 monthly average reanalysis data. The study employs techniques such as empirical orthogonal function (EOF) decomposition, Mann-Kendall mutation and other methods to investigate the spatiotemporal distribution of extreme precipitation index in northern Shanxi and their correlation with atmospheric circulation. The research results show that: the absolute index, relative index, intensity index and sustained dry period index (CDD) in the continuous index appear from southwest to northeast. The spatial distribution characteristics of the central region decrease, while the continuous wet period (CWD) decreases from the central to the east and west. The three indices Rx1day, Rx5day, and CWD mutated in 1978, 1975, and 1983 respectively, and other extreme precipitation indices all appeared in a sudden change from a low-value period to a high-value period occurred around 2010. In the high-value years of the summer extreme precipitation index, there is a significant negative anomaly in the height field in the mid-high latitude regions of Eurasia. Northern Shanxi is controlled by a broad low-pressure trough in the Lake Baikal area. Water vapor transported via the east, west, and south routes converges in the northern Shanxi region and encounters cold air from the north. There is a strong upward motion anomaly at 500 hPa in the troposphere, and the dynamic conditions of upper-level divergence and lower-level convergence lead to more summer extreme precipitation in the northern Shanxi region. Conversely, in the low-value years of the summer extreme precipitation index, northern Shanxi is affected by a strong high-pressure ridge north of Lake Baikal. There is a downward motion anomaly at 500 hPa, and the northern Shanxi region lacks water vapor. The cold and warm air cannot converge, and both the water vapor conditions and dynamic conditions are poor, which is not conducive to the production of extreme precipitation in northern Shanxi.

Unravelling the genesis and depositional setting of Neoproterozoic banded iron formation from central Eastern Desert, Egypt

The Neoproterozoic banded iron formations (BIFs) are widely occurred in the Egyptian Eastern Desert. This study integrates field observations, petrographic studies, geochemical data, and lead isotopes to construct the genesis and depositional environment of Wadi El-Mis hama BIF deposits. The iron layers, primarily of oxide facies within a volcano-sedimentary sequence, comprise magnetite-rich beds alternating with jaspilite or silicate laminae. The studied BIFs exhibit a dominant composition of SiO2 and Fe2O3t with relatively low contents of TiO2 and Al2O3. The positive correlation of REEs (La, Sm, Yb) with Zr and low concentrations of HFSEs (Ta, Nb, Th, Hf) indicate a primary formation mechanism of chemical precipitation, maintaining original geochemical signatures. Geochemical patterns show depletion in LREEs, enrichment in HREEs (La/YbPAAS = 0.08–0.12), and positive La anomalies (La/LaPAAS = 1.15–8.57), consistent with seawater influence. Additionally, various geochemical discrimination diagrams supported by elevated super-chondritic Y/Ho values (29.6–38.7), weak positive Eu anomalies, and low contents of transition metals (Cu and Zn), point to the interaction of low-temperature (<200°C) hydrothermal fluids (bearing Fe and Si) with seawater during the deposition of the BIFs. The lack of significant negative Ce anomalies along with low Ni/Co, U/Th, and Cu/Zn ratios, imply that the iron mineralization was precipitated from dysoxic to oxic conditions. The geochemical and Pb isotopic data suggest that the iron deposits formed in an extensional geodynamic setting (intra-oceanic arc basin environment) due to the subduction of the Mozambique Plate, with signatures closely matching other Precambrian Algoma-type BIFs.

Mixed layer heat budget in the Mozambique channel: Interannual variability and influence of Rossby waves

The evolution of the mixed layer temperature anomalies in the Mozambique Channel is analysed using a mixed layer heat budget covering sub-seasonal to interannual time scales. Sub-seasonal variations in mixed layer temperature are largely dominated by surface heat fluxes, except along the southern coast of Mozambique and Madagascar, where both the advection and the residual terms become significant. The northern Channel is dominated by the mean flow while the southern Channel is modulated by both the mean and eddy terms. Minimum heat gain through advection is observed in the channel during January–February when the Northeast Madagascar current opposes the northwesterly monsoonal winds. During the 1997/98 El Niño/positive Indian Ocean dipole, extreme warming and coral bleaching events were noted in the northern Channel. Such warming was linked with the relaxation of local winds, positive heat gain from the atmosphere and the shedding of large anticyclonic eddies northwest of Madagascar, associated with the arrival of downwelling Rossby waves. By contrast, upwelling Rossby waves and large cyclonic eddies in the Channel occurred during the 1998–2001 protracted La Niña, but only the northern part of the Channel experienced significant negative anomalies in mixed layer temperature. While no coral bleaching hotspots were noted in the northern Channel in summer 1999/2000 due to negative anomalies in advection, marine heatwaves occurred in the southern Channel during that summer. Finally, the protracted 1998–2001 La Niña was the last time that substantial upwelling Rossby wave activity occurred in the tropical South Indian Ocean; recent La Niña events showed muted or weak upwelling Rossby wave activity, including the recent 2020–2022 protracted event. Post-2001 also occurs at the same time as a stronger warming trend in the southwest Indian Ocean region.

Ecosystems dynamics and environmental management: An NDVI reconstruction model for El Alto-Ancasti mountain range (Catamarca, Argentina) from 442 AD through 1980 AD

Vegetation dynamics play a crucial role in understanding the complex interactions between climate variability, ecosystem changes and human land use. In this study, we use the Hindcasting Ecosystems Model (HEMO) to reconstruct the paleo Normalized Difference Vegetation Index (paleo-NDVI), which provides valuable insights into the historical vegetation patterns. Our research focuses on the El Alto Ancasti mountain range, a region characterized by its rich environmental diversity, and archaeological evidence of pre-Hispanic agricultural village landscapes, showcasing the knowledge and management of diverse environments and their fluctuations.To reconstruct the paleo-NDVI, we employed a Neuronal Network trained with two datasets. First, we utilized NDVI data extracted from AVHRR/NOAA satellite images spanning from 1982 to 2015, representing 8 km pixels from the Global Inventory Modeling and Mapping Studies. Second, we incorporated growth ring chronologies from Northwest Argentina sourced from the International Tree Ring Data Bank, enabling the calibration of the NDVI-ring relationship. This methodology allowed us to reconstruct the paleo-NDVI back to 442 AD and to calculate anomalies.Our analysis revealed significant negative anomalies around 600 AD, coinciding with previous research conducted in the nearby Ambato valley. These anomalies may be attributed to the eruption of Tres Cruces volcano in Catamarca during that period. Additionally, extensive positive anomalies emerged from 1600 AD onwards, which align with anomalies detected in earlier studies. The eruption of Huaynaputina volcano in southern Peru in 1600 AD is a possible factor contributing to these positive anomalies.Ongoing investigations focusing on the paleoenvironment and human occupations in the El Alto-Ancasti area aim to provide further insights into how these detected changes could have influenced environmental management decisions. By integrating multidisciplinary approaches, we can better comprehend the complex relationship between vegetation dynamics, climatic events and human activities, ultimately enhancing our understanding of past environmental transformations and their implications for sustainable management strategies.

Spatial and temporal variability of rainfall in Western Bahia

Western Bahia is a region widely recognized for its significance in large-scale agricultural production, being one of the mainstays of the local economy. However, agricultural activities in this area are often challenged by extended periods of low precipitation, posing a constant threat to the productivity of major crops. Deep concerns are raised by unpredictability of rainfall, especially in February during the critical period of crops, which encompasses the flowering and/or grain filling stages of most crops in the region. In this scenario, this study assumes a central role in search for answers. Thus, this paper aimed to analyze the behavior of spatial and temporal variability of rainfall in the Western region of Bahia. The research focused on the month of February due to its critical relevance to the life cycle of local crops and its direct influence in agricultural productivity. Rainfall data were obtained from the stations network of the National Water Agency (ANA) through the Hydroweb platform for the period from 1986 to 2015. The Rain Anomaly Index (RAI) for the month of February was then calculated using equations developed by Rooy (1965). To analyze the space-time variability of drought events in their different intensities, RAI maps were generated containing eight categories ranging from extremely wet to extremely dry, for the measurement and classification of rainfall anomalies in relation to the historical average. The results revealed that throughout the analyzed period, approximately 53.33% of the February months exhibited negative anomalies, denoting drought events ranging from mild to extreme, while approximately 30% of the months displayed positive anomalies, indicating moisture levels ranging from low to extremely wet. Notably, in the years with the most significant negative anomalies (drought events), there was a predominance of spatial variability from east to west, with the lowest negative anomalies on the western side and the highest on the eastern side of the region. On the other hand, positive anomalies (wet events) exhibited a predominance of spatial variability from south to north in the region. This study provides valuable insights for the agricultural sector, water resource planning, and environmental management. It underscores the importance of adaptive strategies to address climatic fluctuations and ensure the sustainability of agricultural production in the Western Region of Bahia.

Impact of southern annular mode on the Indian Ocean surface waves

AbstractInterannual climate modes, especially the southern annular mode (SAM), significantly influence the wave climate modulation of the Indian Ocean (IO). The present study, aligned with previous research, identifies two crucial swell generation regions in the IO: the extratropical southern Indian Ocean (ETSI) and the tropical southern Indian Ocean (TSIO). The SAM, governing Southern Ocean surface winds, significantly shapes wave generation in these zones, thereby dominantly regulating IO wave conditions. Positive SAM phases shifts the westerlies poleward creating significant negative anomalies in the northern ETSI, reducing wave generation and swell propagation into the northern IO (NIO) basins, while the positive wind anomalies in the western TSIO creates a new swell generation area that directs swells towards the Arabian Sea, elevating wave heights there during monsoons. Conversely, negative SAM phases enhance TSIO easterlies, making it the primary IO swell source, increasing swell activity in the Bay of Bengal, notably during premonsoon and monsoon seasons. SAM impact expands beyond swells, influencing NIO wave climate by altering wind seas through Hadley cell (HC) circulation shifts. Positive SAM phases trigger NIO and midlatitude anomalous warming, intensifying HC and NIO surface winds in the next season, thereby affecting convection and subsequent sea surface temperature (SST) anomaly changes. The “SAM positive anomaly wind‐SST oscillations (SPAWSO)” pattern emerges, where warm SST anomalies in DJF and JJA precede increased surface winds in MAM and SON, thus increasing the wind‐sea conditions in the NIO. SPAWSO, hence, acts as a delayed mode, season‐dependent positive air–sea interaction cycle linked to positive SAM phases, significantly impacting NIO's wind‐sea dynamics. Thus the present study provides better insights into the long‐term wave prediction accuracy in the IO by considering the direct swell influence and SPAWSO‐driven wind‐sea changes, aiding preparations for changing wave dynamics and their impacts.

Influencing factors in the stagnation of the Baiu front that induced heavy rainfall in July 2020 over Kyushu, Japan

The influencing factors of the long-term stagnation of the Baiu front that induced heavy rainfall in July 2020 over Kyushu, Japan, were examined. In July 2020, the position of the Baiu front from a weather chart at 130° E remained stationary over Kyushu for 20 days, and that was the longest from 2002 to 2021. By examining a certain index of the Yellow Sea High (YSH), which is a necessary condition for Baiu front stagnation near Kyushu, it was confirmed that in 2020, a positive high-pressure anomaly persisted over the Yellow Sea until the end of July. The YSH maintenance was due to the significant negative sea surface temperature (SST) anomaly over the Yellow Sea. The significant negative SST anomalies in the Yellow Sea were due to vertical mixing in ocean mixed layer in response to the strong winds of the extratropical cyclones. A rapid SST decrease ranging from 0.5 to 1.5 °C/day was repeatedly occurred by ocean mixed layer deepening in association with the passage of the extratropical cyclones. The anomalous long-term stagnation of YSH due to the negative SST anomalies could have caused the Baiu front to remain stagnant over Kyushu until the end of July.

Understanding changes in heat waves, droughts, and compound events in Yangtze River Valley and the corresponding atmospheric circulation patterns

Heat waves, droughts, and compound drought and heat waves (CDHWs) have received extensive attention because of their disastrous impacts on agriculture, ecosystems, human health, and society. Here, we computed the heat wave magnitude index (HWMI), drought magnitude index (DMI), and compound drought and heat wave magnitude index (CDHMI) for Yangtze River Valley (YRV) from July to August during 1961–2022. We compared the large-scale atmospheric circulation characteristics of different extreme events based on these indexes. The results show that the positive center with sink motion in East Asia provides a favorable circulation background for heat wave events. Drought events are mainly affected by the zonal wave train dominated by a significant negative anomaly in Siberia and a high-pressure anomaly upstream, and a anticyclonic water vapor with strong divergence over the Yangtze River basin. During CDHW events, both anomalous systems that affect heat waves and droughts appear and strengthen simultaneously. Specifically, in the middle and upper troposphere, the positive height anomaly center in YRV expands abnormally, and the “+–+” wave train over the northern 50° N region of East Asia becomes more obvious. Therefore, the positive anomaly and water vapor anomaly brought by the two circulation patterns at different latitudes are superimposed over the YRV, leading to severe CDHWs. At the same time, the warm positive eddy center and cold negative eddy center in high latitudes exhibit more stable positive pressure features, which are conducive to the persistent development and strengthening of CDHWs. In addition, the anomalous warm sea surface temperature in western Pacific moderating the favorable circulation patterns may also promote the occurrence of CDHWs in the YRV during the same period.

Extreme precipitation patterns in the Asia–Pacific region and its correlation with El Niño-Southern Oscillation (ENSO)

In the Asia–Pacific region (APR), extreme precipitation is one of the most critical climate stressors, affecting 60% of the population and adding pressure to governance, economic, environmental, and public health challenges. In this study, we analyzed extreme precipitation spatiotemporal trends in APR using 11 different indices and revealed the dominant factors governing precipitation amount by attributing its variability to precipitation frequency and intensity. We further investigated how these extreme precipitation indices are influenced by El Niño-Southern Oscillation (ENSO) at a seasonal scale. The analysis covered 465 ERA5 (the fifth-generation atmospheric reanalysis of the European Center for Medium-Range Weather Forecasts) study locations over eight countries and regions during 1990–2019. Results revealed a general decrease indicated by the extreme precipitation indices (e.g., the annual total amount of wet-day precipitation, average intensity of wet-day precipitation), particularly in central-eastern China, Bangladesh, eastern India, Peninsular Malaysia and Indonesia. We observed that the seasonal variability of the amount of wet-day precipitation in most locations in China and India are dominated by precipitation intensity in June–August (JJA), and by precipitation frequency in December–February (DJF). Locations in Malaysia and Indonesia are mostly dominated by precipitation intensity in March–May (MAM) and DJF. During ENSO positive phase, significant negative anomalies in seasonal precipitation indices (amount of wet-day precipitation, number of wet days and intensity of wet-day precipitation) were observed in Indonesia, while opposite results were observed for ENSO negative phase. These findings revealing patterns and drivers for extreme precipitation in APR may inform climate change adaptation and disaster risk reduction strategies in the study region.

The rare earth elements of sequentially leached phases in the loess-paleosol sequence at Weinan on the southeastern Chinese Loess Plateau

The rare earth elements (REEs) in loess sediments may preserve key information of paleoenvironmental changes in East Asia but remain poorly explored. Here we present the REE compositions of sequentially leached phases of loess sediments from a 16 m long loess-paleosol sequence collected from Weinan at the southern margin of the Chinese Loess Plateau (CLP). The REEs associated with carbonates, easily reducible oxides, reducible oxides, clay minerals, and the residual silicate minerals were sequentially leached with Na-acetate, hydroxylamine-HCl, Na-dithionite/Na-citrate, 12 mol L−1 HCl and concentrated HF-HNO3 solutions. The results show that the REE concentrations of different phases vary in the loess-paleosol layers and are most enriched in the easily reducible phase (except for the residual phase), which is likely explained by the association of REEs with Mn-oxides. Significant Eu anomalies can only be found in the carbonate and easily reducible phases, with the carbonate phase being characterized by appreciable positive Eu anomalies and the easily reducible phase being characterized by negative Eu anomalies, indicating the incorporation of Eu2+ into secondary carbonates that leaves the authigenic Mn-oxides with depleted Eu relative to other REEs. The carbonate phase shows significant negative Ce anomalies, which is likely due to the preferential removal of Ce4+ by Mn oxides before the formation of secondary carbonates. Nevertheless, appreciable positive Ce anomalies for the easily reducible phase can only be found at the bottom of the paleosol S1 while significant negative Ce anomalies were found within the paleosol S1, indicating the downward leaching of Ce4+ that shows stronger complexation with the organic matters than REE3+ in the soil solution. This may partly account for the negative Ce anomalies previously found in the paleosols. Overall, our results suggest a two-stage evolution of Eu and Ce anomalies of the carbonate phase, with the first stage controlled by the formation of both Mn-oxides and secondary carbonates and the second stage dominated by the precipitation of secondary carbonates. The comparison of carbonate Eu and Ce anomalies with other paleoclimatic proxies indicates that the combination of Eu and Ce anomalies of the carbonate fraction of loess may be applied as novel proxy records of climate change in East Asia.

Redox-stratified seawater during the GOE: Evidences from rare earth elemental and C-O isotopic compositions of Paleoproterozoic BIF and carbonate rocks from the Taihua Group, North China Craton

The Paleoproterozoic Great Oxidation Event (GOE) is known for the dramatic change in atmospheric composition that led to oxygen becoming a persistent component of global surface processes. Drastic environmental changes greatly affected ocean and atmosphere chemistry. However, the distribution of dissolved oxygen in the ocean during the GOE is still unclear as rare contemporary sediment-records have been found. In order to identify the redox state of both shallow and deep water, and reveal the ocean redox structure during this time, we present new major and trace elemental and C-O isotopic data of bulk samples of the banded iron formation (BIF), dolomitic marble, and graphite-bearing marble of the early Paleoproterozoic upper Taihua Group in the Lushan area, southern margin of the North China Craton (NCC). The BIF samples exhibit typical major and trace element characteristics akin to very pure marine chemical sediments, such as the shale-normalized positive La, Ga, and Y anomalies, indicative of a marine depositional setting. In these BIF samples, both negative Ce anomalies and the lack of Ce anomalies reflect the presence of both oxic and suboxic/anoxic water in the ocean. Samples of the dolomitic marble are characterized by extremely low amounts of crustal material (such as Al, Ti, Zr, Hf) and high Y/Ho ratios (46–66), also implying a pure marine chemical origin. Excluding some contaminated samples, the rest of the graphite-bearing marble samples display similar features of the dolomitic marble. Significant positive Ce anomalies and high light to heavy REE (Pr/Yb(SN)) ratios in both dolomitic marble and graphite-bearing marble are essentially consistent with the 2.2–2.1 Ga carbonates from the Guanmenshan Formation of the Liaohe Group in the NE Sino-Korean Craton. Combined with the Ce anomalies in the BIF samples, we consider that the seawater when the upper Taihua Group deposited was redox-stratified from oxic shallow water to deeper anoxic water. Besides, the graphite-bearing marble record coeval surface water in the column that was enriched in nutritive materials and beneficial to microbiology and high productivity. Moreover, the early Paleoproterozoic IFs in the Songshan Group and the Lüliang Group in the NCC also exhibit significant both positive and negative Ce anomalies and enrichment of redox sensitive elements. These evidences, therefore, suggest that redox-stratified seawater occurred extensively during the GOE.

Influence of Madden–Julian Oscillation on Precipitation over the Tibetan Plateau in Boreal Summer

The influence of the Madden–Julian oscillation (MJO) on precipitation over the Tibetan Plateau (TP) during boreal summer is investigated using observational and reanalysis data during 1980–2020. The results show that summer precipitation over most areas of the eastern TP increases (decreases) in MJO Phases 1–2 (5–6), especially when the eastward-propagating MJO active convection is located over the Indian Ocean (Western Pacific) in Phase 2 (6). The most significant negative precipitation anomalies in Phase 4 (8) are located over the southern (northeastern) TP. Moreover, MJO has a relatively weakened effect on the TP summer precipitation in Phases 3 and 7 when its convection migrates to the eastern Indian Ocean and the western–central Pacific, respectively. The MJO-phase dependence of the TP summer precipitation anomalies is closely associated with the anomalous atmospheric circulation and evolution of the horizontal moisture flux convergence directly induced by MJO. When the MJO convection centers are located over the western Indian Ocean and the Pacific, high-level anticyclonic and low-level cyclonic anomalous circulations over the TP are excited. In contrast, when MJO locates over the Indian Ocean and the Maritime Continent, its diabatic heating can inspire high-level cyclonic and low-level anticyclonic circulation anomalies over the TP. The vertical motions and moisture transport from the Bay of Bengal caused by the MJO-excited large-scale circulation can modulate the TP summer precipitation. This study advances the understanding of the TP intraseasonal variability.

Zonally asymmetric influences of the quasi-biennial oscillation on stratospheric ozone

Abstract. The quasi-biennial oscillation (QBO), as the dominant mode in the equatorial stratosphere, modulates the dynamical circulation and the distribution of trace gases in the stratosphere. While the zonal mean QBO signals in stratospheric ozone have been relatively well documented, the zonal (longitudinal) differences in the QBO ozone signals have been less studied. Using satellite-based total column ozone (TCO) data from 1979 to 2020, zonal mean ozone data from 1984 to 2020, three-dimensional (3-D) ozone data from 2002 to 2020, and ERA5 reanalysis and model simulations from 1979 to 2020, we demonstrate that the influences of the QBO (using a QBO index at 20 hPa) on stratospheric ozone are zonally asymmetric. The global distribution of stratospheric ozone varies significantly during different QBO phases. During QBO westerly (QBOW) phases, the TCO and stratospheric ozone are anomalously high in the tropics, while in the subtropics they are anomalously low over most of the areas, especially during the winter–spring of the respective hemisphere. This confirms the results from previous studies. In the polar region, the TCO and stratospheric ozone (50–10 hPa) anomalies are seasonally dependent and zonally asymmetric. During boreal winter (December–February, DJF), positive anomalies of the TCO and stratospheric ozone are evident during QBOW over the regions from North America to the North Atlantic (120∘ W–30∘ E), while significant negative anomalies exist over other longitudes in the Arctic. In boreal autumn (September–November, SON), the TCO and stratospheric ozone are anomalously high from Greenland to Eurasia (60∘ W–120∘ E) but anomalously low in other regions over the Arctic. Weak positive TCO and stratospheric ozone anomalies exist over the South America sector (90∘ W–30∘ E) of the Antarctic, while negative anomalies of the TCO and stratospheric ozone are seen in other longitudes. The consistent features of TCO and stratospheric ozone anomalies indicate that the QBO signals in TCO are mainly determined by the stratospheric ozone variations. Analysis of meteorological conditions indicates that the QBO ozone perturbations are mainly caused by dynamical transport and also influenced by chemical reactions associated with the corresponding temperature changes. QBO affects the geopotential height and the polar vortex and subsequently the transport of ozone-rich air from lower latitudes to the polar region, which therefore influences the ozone concentrations over the polar region. The geopotential height anomalies associated with QBO (QBOW–QBOE) are zonally asymmetric with clear wave number 1 features, which indicates that QBO influences the polar vortex and stratospheric ozone mainly by modifying the wave number 1 activities.

Pan-Arctic melt pond fraction trend, variability, and contribution to sea ice changes

Because the Pan-Arctic melt pond significantly influences the mass balance of sea ice, analyzing changes in the Pan-Arctic melt pond can offer insights into the Arctic sea ice and environment. In this study, the MODIS level 2 surface reflectance product (MOD09A1) was used to calculate variability and trends in the Pan-Arctic melt pond fraction (MPF) from May 9 to August 29 during the period 2000–2019, along with its relationship with September sea ice extent (SIE). The results showed that as a result of advances in Arctic ice melt onset and the extension of the melting period, the MPF as a whole showed an insignificant upward trend but that the MPF in the multiyear ice area increased significantly. Melt pond distribution is closely related to atmospheric circulation over the Arctic. Significant positive and negative geopotential height anomalies at different locations in the Arctic will cause poleward winds from different directions, bringing warm, humid air and leading to an increase in MPF in different regions of the Arctic. There is a strong negative correlation between integrated MPF and September SIE, concentrated in the northern part of the Beaufort Sea. On June 18, the integrated MPF had the strongest correlation with September SIE, at −0.96. The use of linear regression and support vector machine combined with integrated MPF and 850-hpa average wind, Arctic Oscillation (AO) and North Atlantic Oscillation (NAO) indexes to forecast September SIE shows that the support vector machine is more suitable for forecasting September SIE. When the forecast factor is only the integrated MPF, the MPF is integrated from May 9 to June 10 has the forecast accuracy is the highest, with a considerable forecast skill. When the average May–June AO is combined with the integrated MPF, the forecast skill will be further improved.

Geology and geochemistry of the high-grade Zankan magnetite ore, Western Kunlun Mountains, NW China

Over the past decade, several magnetite-rich iron deposits have been discovered in the Taxkorgan region of the western Kunlun Mountains of northwestern China. These include the Zankan, Jiertieke, Laobing, Yelike, and Taaxi iron deposits. Prospective iron ore reserves are estimated at over 1 billion tons, with an average magnetite grade of 28% (Feng et al., 2018). The largest of the deposits, the Zankan Iron Deposit (ZID), is estimated to contain 628 million tons of iron ore, with at least 10% of the ores being high-grade (TFe > 50 wt%). However, the geological processes by which the high-grade ores in the ZID were formed remains poorly constrained. In this study, we combine whole rock and ore geochemistry data, oxygen and sulfur stable isotopes, and uranium-lead and hafnium isotopes from zircons to elucidate the plausible mechanisms underpinning the formation of the ZID ores. Based on mineralogy, we define two ore types. Type 1 is essentially comprised of quartz and magnetite, interlayered with schist, and it retains the sedimentary fabrics of the precursor iron-rich sediments which were an iron formation (IF). Type 2 formed by the intrusion of a dacite-porphyry into the IF which led to magnetite remobilization and recrystallization as manifest in magnetite-ferro actinolite veining. Rare earth element (REE) characteristics of the high-grade ores differs from those of the precursor IF, with chondrite normalized REE patterns showing enrichment of LREE and significant negative europium anomalies close to those of the dacite-porphyry. The oxygen and sulfur isotopic composition of magnetite and pyrite in the high-grade ores suggests a further meteoric influence on the ZID with silica enrichment driven by leaching of the precursor IF from elsewhere in the sequence. Circulation of the ore forming fluid is attributable to the development of faults and fracture zones that resulted from the intrusion of the dacite-porphyry. Laser ablation uranium-lead analyses of zircons from the dacite-porphyry yield two groups with ages of 551.25 ± 3.32 Ma and 497.82 ± 3.81 Ma, representing captured detrital zircons and the intrusive age of dacite porphyry, respectively. Given the intimate geological relationship between the dacite-porphyry and T2 ore, we suggest that the high-grade ores are formed after 497.82 Ma. Collectively our field observations and geochemical data reveal the detailed alteration processes that led to the development of the high-grade iron ores in the ZID, identifying distinctive features that may help to guide future exploration for additional high-grade ore deposits in the Taxkorgan region.

Geochronology and Geochemistry of the Mamupu Cu‐Au Polymetallic Deposit, Eastern Tibet: Implications for Eocene Cu Metallogenesis in the Yulong Porphyry Copper Belt

AbstractThe Mamupu skarn‐type Cu‐Au polymetallic deposit represents the first discovery of a medium deposit in the southern Yulong porphyry copper belt (YPCB), eastern Tibet. The Cu‐Au mineralization mainly occurs as chalcopyrite in breccia, within the plate‐like carbonate interlayer, being closely related to chloritization (e.g., chlorite, magnetite and epidote) and skarnization (e.g., diopside, tremolite and garnet). The ore‐related quartz syenite porphyry (QSP) and granodiorite porphyry (GP) were emplaced at 40.1 ± 0.2 Ma and 39.9 ± 0.3 Ma, respectively. The QSP of Mamupu is an alkaline‐rich intrusion, relatively enriched in LREE, LILE, depleted in HFSE, with no significant negative Eu and Ce anomalies, slightly high (87Sr/86Sr)i, low ∊Nd(t), uniform (206Pb/204Pb)i and ∊Hf(t) values, which indicates that the porphyry magma may be caused by both the mixing of metasomatized EM II enriched mantle and thickened juvenile lower crust. The QSP in the Mamupu deposit shares a similar genesis of petrology to other ore‐related porphyries within the YPCB. High oxygen fugacity and water content of the magmas are essential for the formation of porphyry and skarn Cu deposits. The QSP has similar high magmatic oxidation states and water content to the Yulong deposit, which indicates that the Mamupu has a high prospecting potential. Differences in the geological characteristics and scale of mineralization between the Mamupu and other YPCB deposits may be due to the different emplacement depths of ore‐related intrusions, as well as differences in the surrounding rocks.

Late Cretaceous Granitoids along the Northern Kuching Zone: Implications for the Paleo-Pacific Subduction in Borneo

Abstract The EW-trending Kuching zone in Borneo is a target region for exploring the southern continuation of Paleo-Pacific subduction from South China, Vietnam to SE Asia. Previous studies mainly focused on mafic igneous rocks, and poor attention has been paid to the contemporaneous granitoids in this zone. This study presented detailed zircon U-Pb geochronology and Lu-Hf isotope and whole-rock geochemistry analyses for late Cretaceous granitoids (granodiorites and granites) in the northern Kuching zone. These granitoids are dated at ~77.5-83.6 Ma with younger ages than the igneous rocks in the southern Kuching zone (~130-144 Ma). The granitoids have variable SiO2 (64.86-77.37 wt.%) and A/CNK (0.7-1.5) and are strongly enriched in LILE and depleted in HFSE with significant Ba, Nb, Sr, and Ti negative anomalies. They have variable (87Sr/86Sr)i (from 0.70656 to 0.71208), εNd(t) (from -4.4 to +0.9), and zircon εHf(t) (from -1.2 to +12.4) with high (206Pb/204Pb)i ratio of 18.78-19.74, suggesting derivation from a hybrid source involving meta-sedimentary and meta-igneous rocks. Combined with previously-published data, two episodes of Cretaceous (~77-98 Ma and ~130-144 Ma) magmatic activities are identified in the Kuching zone, showing a younging age trend from south to north. These episodes of Cretaceous igneous rocks and their spatial distribution in the Kuching zone can be totally comparable to those in South China and Vietnam. Thus, the Kuching zone was likely a part of the Paleo-Pacific subduction system during the Cretaceous, northerly linking to Vietnam and South China.

A Multi-Network based Hybrid LSTM model for ionospheric anomaly detection: A case study of the Mw 7.8 Nepal earthquake

We propose a Multi-Network-based Hybrid Long Short Term Memory (N-LSTM) model for ionospheric anomaly detection to forecast highly irregular data of the ionospheric Total Electron Content (TEC). Previously purposed models were suffering from the problems of vanishing gradient, exploding gradient, uncertainty, and parameter bias. LSTM is used to overcome the vanishing and exploding gradient problems and the remaining two (uncertainty and parameter bias) are subjugated by N-LSTM. We have also discussed the implementation of the model by using the Mw 7.8 Nepal Earthquake (EQ) that occurred on April 25, 2015. The proposed model detects a significant negative anomaly about 14 days before the impending EQ. Furthermore, we find gradual increments in the TEC time-series, where the TEC values gradually increased, in terms of positive anomalies, for four continuous days (April 21–24, 2015) till the mainshock. Further analysis revealed that the nighttime TEC enhancements are more dominant than the daytimes, which persisted for 10 h (22:00–08:00 LT) in the absence of the solar flux, we named them the absolute seismic precursors. These gradual enhancements establish a perfect correlation with several atmospheric anomalies, reported in the previous studies, where the variations in different atmospheric parameters like Outgoing Longwave Radiation (OLR), air temperature, Ozone, and sub-ionospheric Very-Low Frequency (VLF), were reported for 4 consistent days till the EQ day. The N-LSTM result was compatible with a 30-day running median, which is the classical method of ionospheric anomaly detection. We also examined the planetary K-index (Kp), disturbance storm-time (Dst), solar radio flux (F10.7), and solar wind speed (VSW) indices to check the possible attribution of space weather on the ionosphere during the analysis. The results showed that the anomalies of the ionospheric TEC were more dominantly caused by the EQ phenomenon than the space weather during the nighttime hours. Also, N-LSTM provided sufficient short-term prediction performance of the ionospheric TEC and anomaly detection.