Tectonic Pattern Imaging of Southern Sumatra Region Using Double Difference Seismic Tomography

The transformation of magnetic anomalies to magnetic potential or pseudo-gravity simplifies the complexities of magnetic anomaly interpretation. We present new pseudo-gravity maps, derived from EMAG2v3 data, for the South Atlantic Ocean and adjacent continent to reveal insights into crust and lithosphere composition.The pseudo-gravity transformation of the full-field magnetic anomaly consists of three steps: (i) reduction to the pole (RTP); (ii) integration to determine magnetic potential; and (iii) scaling to determine the pseudo-gravity, assuming a constant ratio of density contrast to magnetization. This transformation produces a gravity-like anomaly that would be observed if the magnetization were replaced by a density distribution of proportional magnitude. We use magnetic data from the public domain EMAG2 v3 as the primary input. The South Atlantic region was divided into 90 tiles of 5º to account for regional variations in magnetic inclination and declination. An important assumption for the transformation is that the magnetization is induced. The pseudo-gravity mapping shows large amplitude positive anomalies consistent with the assumption of induced magnetization; negative anomalies identify areas of remnant magnetization. In the oceanic domain, alternating positive and negative anomalies reflect magnetic reversals and are not an artifact.On the South American plate, the Rio-Grande-Rise exhibits three distinct high positive pseudo-gravity anomalies, reflecting thick magmatic crust. The São-Paulo-Plateau in the Santos Basin, Florianópolis-Ridge and Torres-High also show high positive anomalies. The Campos Basin has lower-amplitude positive anomalies, suggesting localized magmatic crust. In the continents, high-amplitude positive anomalies correlate with magmatic intrusion. The high positive pseudo-gravity anomalies form an NW-SE arc from magmatic material in the Paraná Basin to the São-Paulo-Plateau, continuing through the Florianópolis-Ridge and Rio-Grande-Rise.Strong positive anomalies along the Namíbia-Ridge, Walvis-Ridge, and southwestern African margin form a "7"-shaped uniform anomaly, corresponding to magmatic crust. In contrast, the oceanic crust offshore Orange Basin shows a north-south region of negative anomalies. No significant anomalies are seen in the Tristan-Gough Guyot Province (nor are they seen on the Vitória-Trindade or Tristan-Gough Guyot Province hot-spot tracks).A comparison of the pseudo-gravity map with crustal thickness from gravity inversion shows that many large, high-amplitude positive pseudo-gravity anomalies in the oceanic domain correlate strongly with anomalously thick crust (>12.5 km thickness) on the Rio-Grande-Rise, São-Paulo-Plateau, Florianópolis-Ridge, Namíbia-Ridge and Walvis-Ridge. Plate reconstruction of pseudo-gravity anomalies and crustal thickness suggest that the Namíbia-Ridge and western Florianópolis-Ridge, both with thick magmatic crust, have a common origin at approximately 110 Ma but were later separated by the Florianópolis-Fracture-Zone. The spatial relationship of observed high positive pseudo-gravity anomalies on magmatically intruded crust in the South American and African continents, the hybrid or magmatic crust on their rifted margins and thickened magmatic crust within the South Atlantic shows the major role of mantle inheritance in their origin.

Petrogenesis of Late Paleoproterozoic Liangcheng charnockites and S-type granites in the central-northern margin of the North China Craton: Implications for ridge subduction

Coastal stations are critical for interpretation of continental‐scale CO2 exchanges although the impacts of land and sea breezes, local topography, katabatic winds, and CO2 transport from nearby terrestrial ecosystems are not well characterized. We applied a modeling framework that couples meteorological (MM5), land‐surface (LSM1), and tracer models to investigate the impact of these factors on coastal CO2 measurements. Model predictions compared well with measurements over 4 months at our case study site (Trinidad Head, California). We predicted that during midday and under strong onshore wind conditions, positive and negative CO2 anomalies from the assumed “background” marine layer air were sampled at the station. These anomalies resulted from two classes of mechanisms that couple transport and recent terrestrial ecosystem exchanges. First, and most important, are local and large‐scale recirculation of nighttime positive CO2 anomalies resulting from katabatic flows off the coastal mountain range. Second, negative anomalies generated by daytime net ecosystem uptake can be transported offshore in the residual layer and then entrained in the marine boundary layer. We predicted monthly averaged CO2 anomalies associated with terrestrial exchanges of 0.53, 0.34, 3.1, and 0.05 ppm during March, June, September, and December of 2002. Positive anomalies from nighttime ecosystem respiration were more likely to be sampled than are negative anomalies associated with daytime net ecosystem uptake. Current atmospheric models used in continental‐scale inverse studies do not resolve these two classes of mechanisms and therefore may infer incorrect CO2 exchange rates.

The influence of the Arctic Oscillation (AO) on the vertical distribution of stratospheric ozone in the Northern Hemisphere in winter is analyzed using observations and an offline chemical transport model. Positive ozone anomalies are found at low latitudes (0°–30°N) and there are three negative anomaly centers in the northern mid- and high latitudes during positive AO phases. The negative anomalies are located in the Arctic middle stratosphere (~30 hPa; 70°–90°N), Arctic upper troposphere–lower stratosphere (UTLS; 150–300 hPa, 70°–90°N), and midlatitude UTLS (70–300 hPa, 30°–60°N). Further analysis shows that anomalous dynamical transport related to AO variability primarily controls these ozone changes. During positive AO events, positive ozone anomalies between 0° and 30°N at 50–150 hPa are related to the weakened meridional transport of the Brewer–Dobson circulation (BDC) and enhanced eddy transport. The negative ozone anomalies in the Arctic middle stratosphere are also caused by the weakened BDC, while the negative ozone anomalies in the Arctic UTLS are caused by the increased tropopause height, weakened BDC vertical transport, weaker exchange between the midlatitudes and the Arctic, and enhanced ozone depletion via heterogeneous chemistry. The negative ozone anomalies in the midlatitude UTLS are mainly due to enhanced eddy transport from the midlatitudes to the latitudes equatorward of 30°N, while the transport of ozone-poor air from the Arctic to the midlatitudes makes a minor contribution. Interpreting AO-related variability of stratospheric ozone, especially in the UTLS, would be helpful for the prediction of tropospheric ozone variability caused by the AO.

El Niño Southern Oscillation- (ENSO) related anomaly patterns of monthly specific humidity (q), precipitable water content (PW) and temperature (T) over South America are analysed using the FORMOSAT-3/COSMIC mission data (August 2006–December 2013). The Global Positioning System radio occultation (GPS RO) technique provides high vertical resolution profiles of atmospheric properties (refractivity, density, temperature and water vapour pressure) with a global coverage under any weather condition. During the ENSO warm phase (or El Niño), positive PW anomalies are found over the equatorial Pacific Ocean, southeastern Brazil, Bolivia, Paraguay and northern Argentina. Negative anomalies are found in the northern part of South America, but covering a smaller area. During the ENSO cold phase (or La Niña), positive anomalies are found in the northern part of the continent whereas negative anomalies are found over the Amazon Basin region. A Morlet continuous wavelet transform analysis is applied to deseasonalized PW anomaly time series. Over the areas showing PW anomalies related to ENSO, main modes of oscillation between 35 and 38 months are found, similar to the main oscillation mode of the Oceanic Niño index. Consistent with previous studies, PW anomalies in almost all these areas show a general behaviour towards opposite signals during the opposite ENSO phases. q patterns show a linear (in phase with Oceanic Niño Index) response to ENSO along the equator below 8 km height. The Andes mountains separate positive (west) from negative (east) anomalies during El Niño (EN) events (reversing during LN). The higher q positive anomalies are found over the equatorial Pacific Ocean and over 60°–50°W, 35°–20°S during EN months. T patterns show positive anomalies in the whole tropical troposphere during EN months, with higher values over the equatorial Pacific, west of the Andes between 7 and 15 km height.

Under the Sumatran plate boundary the Australian-Indian plate is subducting at about 60 mm/yr in the direction N110E. The oblique convergence is partitioned into trench-parallel slip?accommodated largely by the Sumatran fault zone and trench-perpendicular slip?accommodated by the subduction zone. Our detailed map of the Sumatran fault zone (SFZ) shows that the Sumatran fault is highly segmented. The influence of these fault segmentations on historical seismic source dimensions suggests that the dimensions of future events will also be influenced by fault geometry. The largest geomorphic offsets along the Sumatran fault zone are about 20 km, and may represent the total offset across the fault. The shape and location of the Sumatran fault and the active volcanic arc are highly correlated with the shape and character of the underlying subducting oceanic lithosphere. We utilize coral microatolls in west Sumatra to document evidence for deformation of the underlying subduction interface. Microatolls are very sensitive to fluctuations in sea level, and thus act as natural tide gauges. They record not only the magnitude of vertical deformation associated with earthquakes (paleoseismic data), but also continuously track long-term aseismic deformation that occurs during intervals between earthquakes (paleogeodetic data). Numerous microatolls from the region around the equator record a simple pattern of tilt away from the trench axis in 1935 related to an Mw7.7 earthquake. About 115 km from the trench axis, uplift was nil. Nearer to the trench, uplift progressively increased trench-ward to at least 90 cm. Farther than 115 km from the trench, submergence of up to 35 cm occurred. We model these paleogeodetic data by a 2.3 m slip event on the interface between 88 and 125 km from the trench axis. A large aseismic event or ?silent earthquake? in 1962 is among the most interesting phenomena discovered in the coral record, and is the second largest short-lived event recorded throughout the equatorial region. Furthermore, paleogeodetic data reveal that the interseismic deformation rates have varied both temporally and spatially.

Linkages between the sea surface temperature anomalies (SSTAs) in the southern tropical Atlantic (STA) and in the Pacific on decadal time scales were examined. Seven to eight years before warming in the STA, an ENSO‐like decadal SSTA pattern with positive anomalies in the Tropics and negative anomalies in the subtropics appears in the Pacific. In the Atlantic, negative anomalies are located in the North Atlantic, while the corresponding sea level pressure anomaly (SLPA) composite resembles a North Atlantic Oscillation (NAO) pattern. After the establishment of the NAO, a pattern with the band structure of alternating positive and negative anomalies with warming in the STA appears 6 years later in the Atlantic. In the Pacific, warm SSTAs shift from the date line to the eastern Pacific three to four years later after the ENSO ‐like pattern appears. Soon after, a wave train extends from the Pacific to the tip of Argentina and negative anomalies appear in the South Atlantic. Warming starts in the STA. While SSTAs in the Pacific and the Atlantic may not vary as a single mode, two oceans interact when SSTAs in the Pacific are strong enough to generate downstream responses. These anomalies in turn contribute to the variations of SSTAs over the STA.

Mitigating the impacts of droughts and floods over East Africa (EA) may largely be possible through accurate predictions of the long rains (March–May). Though the close interannual variability between the long rains, Indian and Pacific Oceans has been widely studied, Tanzania's long rain variability remains unclear. This paper examines the Tanzanian long rains dominant modes through an empirical orthogonal function (EOF) analysis, and their relationship with winter sea surface temperature (SST) for the period 1951–2018. Correlation and composite analyses were applied to explore the associated mechanisms. The first EOF (EOF1) mode is characterized by negative anomalies over Tanzania. The second EOF (EOF2) mode depicts positive (negative) anomalies over northern (southern) Tanzania. The third EOF (EOF3) mode reveals positive (negative) anomalies over eastern (western) Tanzania. EOF1 is closely related to the SST anomalies (SSTAs) in the southeastern Indian Ocean (SEIO). When the SSTAs are positive, they subsequently linked to upper (lower) level convergence (southeasterly winds) over Tanzania. Associated with this convergence entails a sinking motion, leading to a negative rainfall anomaly. The southeasterly winds indicate an early onset of the southeast monsoon, leading to normal rainfall been recorded. EOF2 is linked to the SSTAs in the central Pacific (CP). Positive SSTAs are related to reversed Walker circulation (WC) over northern Tanzania, while the upper‐level convergence was observed around southern Tanzania. This meridional dipole vertical motion pattern enhances (suppresses) rainfall anomalies. EOF3 is associated with mega El Niño–Southern Oscillation (ENSO)‐like SSTAs. The SSTAs are related to eastward shift of WC over the Indian Ocean, and zonal cell over the western Indian Ocean with rising limb is located east of Tanzania. The ascending motion enhances rainfall over eastern Tanzania. Predictions based on the SEIO, CP, and mega ENSO index may significantly support long rains prediction efforts and provide early warning.

Mature El Nino-Southern Oscillation (ENSO) conditions dominated the central and eastern tropical Pacific during the March-April-May (MAM) 1993 season. Weaker than normal trade winds, anomalous easterly flow at 200 mb, enhanced convection in the equatorial central Pacific, and the negative phase of the Tahiti-Darwin Southern Oscillation index (SOI) were all prevalent throughout the season. Sea surface temperature (SST) anomalies increased dramatically during MAM 1993, with positive anomalies exceeding 1 C covering the entire equatorial Pacific from about 170 deg W to the South American coast. The depth of the equatorial oceanic thermocline remained greater than normal east of 140 deg W and less than normal in the western Pacific throughout the entire season. The positive phase of the North Pacific Oscillation (NPO) teleconnection pattern dominated the circulation over the Pacific/North American sector during all 3 months of the season bringing much-above-normal surface temperatures over Alaska and western North America and below-normal temperatures over the southeastern United States. The pattern was also associated with above-normal precipitation in the Pacific Northwest during April and May. Over Europe, seasonal positive 500-mb height anomalies were associated with positive temperature anomalies and drier than normal conditions. Negative height anomalies dominated the polar region of themore » Southern Hemisphere during MAM 1993. Positive height anomalies at high latitudes of the South Pacific and negative anomalies in the middle and subtropical latitudes of the Southern Hemisphere also persisted throughout the season.« less

Bengkulu is located in the southern region of Sumatra, where the Indo-Australian and Eurasian plates are subducted. As a consequence of the subduction, seismicity in the area increases, as well as volcanic activity and the appearance of structures such as the Sumatran and the Mentawai faults. Seismic velocity structures were reconstructed using earthquake tomography in Bengkulu and the surrounding areas using data from the International Seismological Center (ISC) and the Meteorology, Climatology, and Geophysics Agency (BMKG). The earthquake data collection period was from January 1, 2010 to December 31, 2018. 19 stations recorded 1721 earthquakes. LOTOS-12 is used to do a tomography inversion, starting with a 1D velocity model and wadati’s Vp/Vs ratio and iteratively inverting for Vp, Vs, and Vp/Vs ratios. The bending algorithm is used to calculate the arrival time, and the LSQR method is used to invert it. The Checkerboard Resolution Test (CRT) yielded Tomography results. The results revealed the existence of zones with low-velocity anomalies and low-values of Vp/Vs ratios, indicating the presence of weak zones caused by Sumatra faults, Mentawai faults, and other local faults. Low-velocity anomalies with high-values of Vp/Vs ratios are related to volcanic activity, hereas high-velocity anomalies are associated with the existence of subduction plates and compact rocks. The low-velocity anomalies in the fore-arc at 30-50 km depths coincide with fluid circulation caused by slab dehydration.

Investigation of heat flow anomalies in some regions of the Ukraine

With a few exceptions, most studies on tropospheric ozone (O3) variability during and following the COrona VIrus Disease (COVID-19) economic downturn focused on high-emission regions or urban environments. In this work, we investigated the impact of the societal restriction measures during the COVID-19 pandemic on surface O3 at several high-elevation sites across North America and western Europe. Monthly O3 anomalies were calculated for 2020 and 2021, with respect to the baseline period 2000–2019, to explore the impact of the economic downturn initiated in 2020 and its recovery in 2021. In total, 41 high-elevation sites were analyzed: 5 rural or mountaintop stations in western Europe, 19 rural sites in the western US, 4 sites in the western US downwind of highly polluted source regions, and 4 rural sites in the eastern US, plus 9 mountaintop or high-elevation sites outside Europe and the United States to provide a “global” reference. In 2020, the European high-elevation sites showed persistent negative surface O3 anomalies during spring (March–May, i.e., MAM) and summer (June–August, i.e., JJA), except for April. The pattern was similar in 2021, except for June. The rural sites in the western US showed similar behavior, with negative anomalies in MAM and JJA 2020 (except for August) and MAM 2021. The JJA 2021 seasonal mean was influenced by strong positive anomalies in July due to large and widespread wildfires across the western US. The polluted sites in the western US showed negative O3 anomalies during MAM 2020 and a slight recovery in 2021, resulting in a positive mean anomaly for MAM 2021 and a pronounced month-to-month variability in JJA 2021 anomalies. The eastern US sites were also characterized by below-mean O3 for both MAM and JJA 2020, while in 2021 the negative values exhibited an opposite structure compared to the western US sites, which were influenced by wildfires. Concerning the rest of the world, a global picture could not be drawn, as the sites, spanning a range of different environments, did not show consistent anomalies, with a few sites not experiencing any notable variation. Moreover, we also compared our surface anomalies to the variability of mid-tropospheric O3 detected by the IASI (Infrared Atmospheric Sounding Interferometer) satellite instrument. Negative anomalies were observed by IASI, consistent with published satellite and modeling studies, suggesting that the anomalies can be largely attributed to the reduction of O3 precursor emissions in 2020.

By using the second version of the Community Atmosphere Model (CAM2) of NCAR, the general circulations of the Earth's atmosphere were simulated under different rotation rates conditions. The results imply that the intensity of three-cell circulation turn strong when the rotation rate turn slow. Furthermore, under slow rotation rate, for annual mean temperature field, there exist the negative anomalies in the Northern Hemisphere and positive anomalies in the Southern Hemisphere. The region of negative anomaly and that of positive anomaly are divided by 15°S. The annual mean zonal wind field has positive anomaly and negative anomaly when the roattion rate is changed. The positive anomalies and negative anomalies are cross. Compared with summer and autumn, in spring, the changes of geopotential height field, temperature field, meridional wind field in the stratosphere and vertical velocity field are opposite under different rotation rates. Compared with annual mean result, the situation of these three fields is reverse. The westerly in mid-latitude are all strengthened in four seasons under slow rotation rate. The change trends of the zonal wind in two Hemisphere are opposite in spring and autumn. The changes of physical quantities have significant seasonal difference. The change in autumn is the biggest. For monsoon, there are three regions of the linear response - African, Middle East and temperate zone and Frigid Zone.

Earthquakes are natural disasters with sudden and destructive effects that can cause large casualties and property damage within a short time. Therefore, researchers have paid considerable attention to the study of anomalies prior to earthquakes, especially strong ones. Using the global ionosphere map of total electron content (TEC), we attempted to identify local disturbances potentially associated with earthquakes by analyzing the daily accumulation of TEC anomalies. Based on a statistical study of 2707 M ≥ 6.0 earthquakes, it was found that positive and negative anomalies are obvious at 3 days and 7 days prior to earthquakes, respectively. The occurrence probability of seismo-ionospheric anomalies for 7.5 ≤ M < 8.0 earthquakes is slightly higher than that for earthquakes with magnitudes less than 7.5. The ratio of earthquakes with TEC precursors to the total number of analyzed cases varies with latitude, exhibiting a descending trend from low to mid and then to high latitudes. The analysis revealed that the region of seismo-ionospheric anomalies generally expands with increasing earthquake magnitude. The spatial distributions of positive and negative TEC anomalies differ between the geomagnetic Northern and Southern Hemispheres. These observational findings indicate that acoustic-gravity waves and perturbed electric fields may act as potential pathways in the lithosphere‒atmosphere‒ionosphere coupling process.

This study investigates the variability and predictability of snow depth anomalies over the Eurasian continent at the end of winter, as represented in 12 ensembles of General Circulation Model simulations performed at the European Centre for Medium‐Range Weather Forecasts. Each ensemble includes nine integrations performed with the same prescribed sea surface temperature, but started from time‐lagged initial conditions. An empirical orthogonal function (EOF) analysis shows that the leading EOF of Eurasian snow depth in March has a zonally‐oriented dipole structure, with a band of positive anomalies covering northern Europe and Siberia, and negative anomalies over central Europe, the Himalayas and north China. A significant relationship is found between the positive/negative phase of this snow‐depth anomaly and warm/cold El Niño Southern Oscillation events. The positive phase of the snow‐depth EOF1 is associated with a wintertime circulation characterized by a strengthening of the westerly winds over Europe and Siberia; in the upper troposphere, this westerly anomaly is accompanied by negative zonal wind anomalies over Eurasia around 30‐40°N and positive zonal wind anomalies between the equator and 25°N over Africa and south‐east Asia. A good degree of predictability is found in the snow‐related circulation anomalies; considering 500‐hPa height, 850‐hPa zonal wind and 200‐hPa zonal wind, the interannual variations of the ensemble‐mean fields show a correlation of 48%, 56% and 65% (respectively) with the corresponding observed anomalies over the eastern half (0° to 180° E) of the northern hemisphere. The tropical component of the zonal wind anomaly associated with snow‐depth EOF1 is strongly predictable; it shows a marked persistence from winter to the early summer, and affects the large‐scale circulation over south Asia in the early and central periods of the monsoon season.