Polar Events Research Articles

New palaeoproterozoic palaeomagnetic data from Central and Northern Finland indicate a long-lived stable position for Fennoscandia

SUMMARYThe Svecofennian gabbro intrusions coincide temporally with the global 2100–1800 Ma orogens related to the amalgamation of the Mesoproterozoic supercontinent Nuna. We provide a new reliable 1891–1875 Ma palaeomagnetic pole for Fennoscandia based on rock magnetic and palaeomagnetic studies on the Svecofennian intrusions in central Finland to fill gaps in the Palaeoproterozoic palaeomagnetic record. By using the new pole together with other global high-quality data, we propose a new palaeogeographic reconstruction at 1885 Ma. This, together with previous data, supports a long-lived relatively stable position of Fennoscandia at low to moderate latitudes at 1890–1790 Ma. Similar stable pole positions have also been obtained for Kalahari at 1880–1830 Ma, Siberia at 1880–1850 Ma, and possibly India at 1980–1775 Ma. A new reconstruction at the beginning of this period indicates the convergence of several cratons at 1885 Ma in the initial stages of the amalgamation of the Nuna supercontinent at low to moderate latitudes. The close proximity of cratons at low to moderate latitudes is further supported by global and regional palaeoclimatic indicators. Stable position of several cratons could indicate a global period of minimal apparent drift at ca. 1880–1830 Ma. Before this period, the global palaeomagnetic record indicates large back-and-forth swings, most prominently seen in the high-resolution 2020–1870 Ma Coronation loops of the Slave craton. These large back-and-forth movements have been explained as resulting from an unstable geomagnetic field or basin- or local-scale vertical-axis rotations. However, the most likely explanation is inertial interchange true polar wander (IITPW) events, which is in line with the suggestion of large amplitude true polar wander events during the formation of the supercontinent.

CIPS Observations of Gravity Wave Activity at the Edge of the Polar Vortices and Coupling to the Ionosphere

AbstractA new Cloud Imaging and Particle Size (CIPS) gravity wave (GW) variance data set is available that facilitates automated analysis of GWs entering the mesosphere. This work examines several years of CIPS GW variances from 50 to 55 km in the context of the Arctic and Antarctic polar vortices. CIPS observes highest GW activity in the vortex edge region where horizontal wind speeds are largest, consistent with previously published GW climatologies in the stratosphere and mesosphere. CIPS observes the well‐documented planetary wave (PW)‐1 patterns in GW activity in both hemispheres. In the Northern Hemisphere, maximum GW activity occurs over the North Atlantic and western Europe. In the Southern Hemisphere, maximum GW activity stretches from the Andes over the South Atlantic and Indian Oceans, as expected. In the NH, CIPS GW spatial patterns are highly correlated with horizontal wind speed. In the SH, CIPS GW patterns are less positively correlated with the winds due to increased zonal symmetry and orographic forcing. The Andes Mountains and Antarctic Peninsula, South Georgia Island, Kerguelen/Heard Islands, New Zealand, and Tasmania are persistent sources of orographic GWs. Atmospheric Infrared sounder observations of stratospheric GWs are analyzed alongside CIPS to explore vertical GW coherence and to infer GW propagation and sources. NH midlatitude GW activity is reduced during the January 2021 SSW, as expected. This reduction in GWs leads to a simultaneous reduction in traveling ionospheric disturbances (TIDs), providing more evidence that weak polar vortex events with weak GW activity leads to reduced daytime TID activity.

Interhemispheric Coupling Study by Observations and Modelling (ICSOM): Concept, Campaigns, and Initial Results

AbstractAn international joint research project, entitled Interhemispheric Coupling Study by Observations and Modelling (ICSOM), is ongoing. In the late 2000s, an interesting form of interhemispheric coupling (IHC) was discovered: when warming occurs in the winter polar stratosphere, the upper mesosphere in the summer hemisphere also becomes warmer with a time lag of days. This IHC phenomenon is considered to be a coupling through processes in the middle atmosphere (i.e., stratosphere, mesosphere, and lower thermosphere). Several plausible mechanisms have been proposed so far, but they are still controversial. This is mainly because of the difficulty in observing and simulating gravity waves (GWs) at small scales, despite the important role they are known to play in middle atmosphere dynamics. In this project, by networking sparsely but globally distributed radars, mesospheric GWs have been simultaneously observed in seven boreal winters since 2015/16. We have succeeded in capturing five stratospheric sudden warming events and two polar vortex intensification events. This project also includes the development of a new data assimilation system to generate long‐term reanalysis data for the whole middle atmosphere, and simulations by a state‐of‐the‐art GW‐permitting general circulation model using the reanalysis data as initial values. By analyzing data from these observations, data assimilation, and model simulation, comprehensive studies to investigate the mechanism of IHC are planned. This paper provides an overview of ICSOM, but even initial results suggest that not only GWs but also large‐scale waves are important for the mechanism of the IHC.

Lineage segregation in human pre-implantation embryos is specified by YAP1 and TEAD1.

Lineage segregation in human pre-implantation embryos is specified by YAP1 and TEAD1.

Study on the Influencing Factors of Network Group Polarization Events

In the era of non-network communication, group polarization is a minority, mostly confined to one organization and one region. In the era of network communication, group polarization has a more prominent role and influence through the Internet, and its formation involves subjective factors such as herd mentality and objective factors such as social contradictions. Due to the role of new media technology and new communication context, the causes of group polarization in the network show more diversified characteristics of the times. As an IP that won Hugo Award, every step of the film and television road of "The Three-body Problem" has attracted worldwide attention. As the first derivative drama, "The Three-body Problem" animation bears great hope, but it also brings a lot of controversy and doubts. From the perspective of communication, this paper takes the cross-platform text of netizens' criticism of the animated version of "The Three-body Problem" as an example, and comprehensively uses the knowledge of journalism and communication, social psychology, sociology and psychology to study the connotation, types, causes and countermeasures of the phenomenon of network group polarization in contemporary China.

Dynamics Analysis for the Random Homogeneous Biased Assimilation Model

This paper studies the evolution of opinions over random social networks subject to individual biases. An agent reviews the opinion of a randomly selected one and then updates its opinion under homogeneous biased assimilation. This study investigates the impact of biased assimilation on random opinion networks, which is different from the previous studies on fixed network structures. If the bias parameters are static, it is proven that the event in which all agents converge to extreme opinions happens almost surely. Next, the opinion polarization event is proved to be a probability one event. While if the bias parameters are dynamic, the opinion evolution is proven to depend on early finite time slots for the dynamical individual bias parameter functions independent of the biased parameter values after the time threshold. Numerical simulations further show that opinion evolution depends on early finite time slots for some nonlinear dynamical individual bias parameter functions.

Paleomagnetism in the Cambrian Urda-Los Navalucillos Limestone (Montes de Toledo, Spain): Implications for late-Variscan kinematics and oroclinal bending in the Central Iberian Zone

A magnetic and paleomagnetic study was carried out on weakly metamorphic Cambrian limestones from the southern limb of the Central Iberian Arc (CIA), a late-Variscan orocline located to the south of the Ibero-Armorican Arc (IAA). >270 cores were obtained from 32 sites located at 5 outcropping structures in the Urda-Los Navalucillos Formation of Montes de Toledo (Central Iberian Zone, Spain), in an area close to the hinge zone of the CIA. These outcrops are affected by two regional-scale Variscan folding phases, namely C1 and C3, which developed interference patterns. A characteristic paleomagnetic component was isolated in 19 sites at 4 of the structures, which shows different temporal relationships with C3 folds, ranging from possibly syn-folding to clearly post-folding. The resulting mean directions of the magnetic vector, in geographic coordinates, always show northward to north-western declinations and negative, low inclinations, suggesting acquisition during some normal polarity event(s) when Iberia was located in the southern hemisphere, i.e. prior to the geomagnetic reverse polarity Kiaman superchron. While the inclination of the paleomagnetic mean directions is coherent between structures, the declination ranges from N to NW, suggesting a vertical axis rotation synkinematic to C3 folding, and older than 318 Ma. These directions suggest that the southern limb of the CIA first underwent a 42° clockwise rotation during the late Carboniferous that can be related to the development of the CIA, and which has been differentially recorded by the paleomagnetic directions of the different structures. This was later followed by a large counterclockwise rotation related to the formation of the IAA, which affects to the entire paleomagnetic dataset.

Understanding the Roles of the Hedgehog Signaling Pathway during T-Cell Lymphopoiesis and in T-Cell Acute Lymphoblastic Leukemia (T-ALL).

The Hedgehog (HH) signaling network is one of the main regulators of invertebrate and vertebrate embryonic development. Along with other networks, such as NOTCH and WNT, HH signaling specifies both the early patterning and the polarity events as well as the subsequent organ formation via the temporal and spatial regulation of cell proliferation and differentiation. However, aberrant activation of HH signaling has been identified in a broad range of malignant disorders, where it positively influences proliferation, survival, and therapeutic resistance of neoplastic cells. Inhibitors targeting the HH pathway have been tested in preclinical cancer models. The HH pathway is also overactive in other blood malignancies, including T-cell acute lymphoblastic leukemia (T-ALL). This review is intended to summarize our knowledge of the biological roles and pathophysiology of the HH pathway during normal T-cell lymphopoiesis and in T-ALL. In addition, we will discuss potential therapeutic strategies that might expand the clinical usefulness of drugs targeting the HH pathway in T-ALL.

Single-cell analysis of myeloid cells in HPV+ tonsillar cancer.

The incidence of human papillomavirus-positive (HPV+) tonsillar cancer has been sharply rising during the last decades. Myeloid cells represent an appropriate therapeutic target due to their proximity to virus-infected tumor cells, and their ability to orchestrate antigen-specific immunity, within the tonsil. However, the interrelationship of steady-state and inflammatory myeloid cell subsets, and their impact on patient survival remains unexplored. Here, we used single-cell RNA-sequencing to map the myeloid compartment in HPV+ tonsillar cancer. We observed an expansion of the myeloid compartment in HPV+ tonsillar cancer, accompanied by interferon-induced cellular responses both in dendritic cells (DCs) and monocyte-macrophages. Our analysis unveiled the existence of four DC lineages, two macrophage polarization processes, and their sequential maturation profiles. Within the DC lineages, we described a balance shift in the frequency of progenitor and mature cDC favoring the cDC1 lineage in detriment of cDC2s. Furthermore, we observed that all DC lineages apart from DC5s matured into a common activated DC transcriptional program involving upregulation of interferon-inducible genes. In turn, the monocyte-macrophage lineage was subjected to early monocyte polarization events, which give rise to either interferon-activated or CXCL-producing macrophages, the latter enriched in advanced tumor stages. We validated the existence of most of the single-cell RNA-seq clusters using 26-plex flow cytometry, and described a positive impact of cDC1 and interferon-activated DCs and macrophages on patient survival using gene signature scoring. The current study contributes to the understanding of myeloid ontogeny and dynamics in HPV-driven tonsillar cancer, and highlights myeloid biomarkers that can be used to assess patient prognosis.

RBL-2H3 Mast Cell Receptor Dynamics in the Immunological Synapse.

The RBL-2H3 mast cell immunological synapse dynamics is often simulated with reaction-diffusion and Fokker-Planck equations. The equations focus on how the cell synapse captures receptors following an immune response, where the receptor capture at the immunological site appears to be a delayed process. This article investigates the physical nature and mathematics behind such time-dependent delays. Using signal processing methods, convolution and cross-correlation-type delay capture simulations give a -squared range of 22 to 60, in good agreement with experimental results. The cell polarization event is offered as a possible explanation for these capture delays, where polarizing rates measure how fast the cell polarization event occurs. In the case of RBL-2H3 mast cells, polarization appears to be associated with cytoskeletal rearrangement; thus, both cytoskeletal and diffusional components are considered. From these simulations, a maximum polarizing rate ranging from 0.0057 s-2 to 0.031 s-2 is obtained. These results indicate that RBL-2H3 mast cells possess both temporal and spatial memory, and cell polarization is possibly linked to a Turing-type pattern formation.

Exploring the link between austral stratospheric polar vortex anomalies and surface climate in chemistry-climate models

Abstract. Extreme events in the stratospheric polar vortex can lead to changes in the tropospheric circulation and impact the surface climate on a wide range of timescales. The austral stratospheric vortex shows its largest variability in spring, and a weakened polar vortex is associated with changes in the spring to summer surface climate, including hot and dry extremes in Australia. However, the robustness and extent of the connection between polar vortex strength and surface climate on interannual timescales remain unclear. We assess this relationship by using reanalysis data and time-slice simulations from two chemistry-climate models (CCMs), building on previous work that is mainly based on observations. The CCMs show a similar downward propagation of anomalies in the polar vortex strength to the reanalysis data: a weak polar vortex is on average followed by a negative tropospheric Southern Annular Mode (SAM) in spring to summer, while a strong polar vortex is on average followed by a positive SAM. The signature in the surface climate following polar vortex weakenings is characterized by high surface pressure and warm temperature anomalies over Antarctica, the region where surface signals are most robust across all model and observational datasets. However, the tropospheric SAM response in the two CCMs considered is inconsistent with observations. In one CCM, the SAM is more negative compared to the reanalysis after weak polar vortex events, whereas in the other CCM, it is less negative. In addition, neither model reproduces all the regional changes in midlatitudes, such as the warm and dry anomalies over Australia. We find that these inconsistencies are linked to model biases in the basic state, such as the latitude of the eddy-driven jet and the persistence of the SAM. These results are largely corroborated by models that participated in the Chemistry-Climate Model Initiative (CCMI). Furthermore, bootstrapping of the data reveals sizable uncertainty in the magnitude of the surface signals in both models and observations due to internal variability. Our results demonstrate that anomalies of the austral stratospheric vortex have significant impacts on surface climate, although the ability of models to capture regional effects across the Southern Hemisphere is limited by biases in their representation of the stratospheric and tropospheric circulation.

Response of tropical convection over the western Pacific to stratospheric polar vortex during boreal winter

AbstractIt has been extensively discussed that stratospheric polar vortex significantly contribute to the variability and predictability of tropospheric weather and climate over midlatitudes and polar regions. However, we currently have little understanding of the exact influence of stratospheric polar vortex on tropical troposphere. Here, the exact responses of tropical convection to Northern Hemisphere (NH) extreme stratospheric polar vortex events (i.e., strong vortex [SV] events and weak vortex [WV] events) are investigated in this study. We find that the western Pacific region is particularly noteworthy when focusing on the spatial distribution of tropical convective activity. Significant enhancement of convective activity over the western Pacific is clearly observed in about 2 weeks after WV events, while opposite responses to SV events can also be expected. The change in convective activity over the western Pacific is considerably contributed by the intraseasonal variability, and thus MJO phase 7 (3) is dominant after WV (SV) events. The seesaw pattern of zonal‐mean convective activity near equator may be a property of MJO itself, not definitely caused by the stratospheric polar vortex as previously thought. A significantly linear correlation between anomalous convective activity and static stability near tropopause over the western Pacific is found, suggesting that circumstances in the tropical upper troposphere play a crucial role in the evolution of tropical convection, especially for the MJO.

Cell-to-Cell Interactions during Early Drosophila Oogenesis: An Ultrastructural Analysis.

Drosophila oogenesis requires the subsequent growth of distinct egg chambers each containing a group of sixteen germline cells surrounded by a simple epithelium of follicle cells. The oocyte occupies a posterior position within the germ cells, thus giving a distinct asymmetry to the egg chamber. Although this disposition is critical for the formation of the anterior–posterior axis of the embryo, the interplay between somatic and germ cells during the early stages of oogenesis remains an open question. We uncover by stage 2, when the egg chambers leaved the germarium, some unique spatial interactions between the posterior follicle cells and the oocyte. These interactions are restricted to the surface of the oocyte over the centriole cluster that formed during early oogenesis. Moreover, the posterior follicle cells in front of the oocyte display a convoluted apical membrane with extensive contacts, whereas the other follicle cells have a flat apical surface without obvious surface protrusions. In addition, the germ cells located at the posterior end of the egg chamber have very elongated protrusions that come into contact with each other or with facing follicle cells. These observations point to distinct polarization events during early oogenesis supporting previous molecular data of an inherent asymmetry between the anterior and the posterior regions of the egg chambers.

Exploring Jupiter's Polar Deformation Lengths with High-resolution Shallow Water Modeling

The polar regions of Jupiter host a myriad of dynamically interesting phenomena, including vortex configurations, folded-filamentary regions (FFRs), and chaotic flows. Juno observations have provided unprecedented views of the high latitudes, allowing for more constraints to be placed upon the troposphere and the overall atmospheric energy cycle. Moist convective events are believed to be the primary drivers of energetic storm behavior as observed on the planet. Here we introduce a novel single-layer shallow water model to investigate the effects of polar moist convective events at high resolution, the presence of dynamical instabilities over long timescales, and the emergence of FFRs at high latitudes. We use a flexible, highly parallelizable, finite difference hydrodynamic code to explore the parameter space set up by previous models. We study the long-term effects of deformation length (L d ), injected pulse size, and injected geopotential. We find that models with L d beyond 1500 km (planetary Burger number, Bu = 4.4 × 10−4) tend to homogenize their potential vorticity in the form of dominant stable polar cyclones, while lower-L d cases tend to show less stability with regard to Arnol’d-type flows. We also find that large turbulent forcing scales consistently lead to the formation of high-latitude FFRs. Our findings support the idea that moist convection occurring at high latitudes may be sufficient to produce the dynamical variety seen at the Jovian poles. Additionally, derived values of localized horizontal shear and L d may constrain FFR formation and evolution.

Stratospheric wave driving events as an alternative to sudden stratospheric warmings

Abstract. Natural variations in the strength of the northern stratospheric polar vortex, so-called polar vortex events, help to improve subseasonal-to-seasonal (S2S) predictions of winter climate. Past research on polar vortex events has been largely focused on sudden stratospheric warming events (SSWs), a class of relatively strong weakenings of the polar vortex. Commonly, SSWs are defined when the polar vortex reverses its climatological wintertime westerly wind direction. In this study, however, we use an alternative definition, based on the weighted time-integrated upward wave activity flux at the lower stratosphere. We use a long control simulation with a stratosphere-resolving model and the ERA5 reanalysis to compare various aspects of the wave activity definition with common SSWs over the Arctic. About half of the wave events are identical to common SSWs. However, there exist several advantages for defining stratospheric weak extremes based on wave events rather than using the common SSW definition: the wave activity flux definition captures with one criterion a variety of different event types, detects strong SSWs and strong final warming events, avoids weak SSWs that have little surface impact, and potentially lengthens the prediction horizon of the surface response. We therefore conclude that the wave driving represents a useful early indicator for stratospheric polar vortex events, which exploits the stratospheric potential for creating predictable surface signals better than common SSWs.

Impact of Strong and Weak Stratospheric Polar Vortices on the Mesosphere and Lower Thermosphere

AbstractThe impact of strong and weak Northern Hemisphere stratospheric polar vortices on the zonal mean and atmospheric tides in the mesosphere and lower thermosphere (MLT) is investigated using Specified Dynamics Whole Atmosphere Community Climate Model (WACCM) with thermosphere‐ionosphere eXtension (SD‐WACCM‐X) simulations and Aura Microwave Limb Sounder observations. The observed and simulated zonal mean anomalies during strong and weak vortices are in good agreement. Zonal mean and tidal anomalies during weak polar vortex events are consistent with those known to occur during sudden stratospheric warmings. Generally opposite, though weaker, anomalies are found to occur when the stratospheric polar vortex is strong. The most notable impact in the MLT is a reduction in the migrating semidiurnal tide of ∼25%–35% during strong polar vortex times. The results demonstrate that, in addition to weak polar vortex events, a strong stratospheric polar vortex can also have an appreciable impact on the middle and upper atmosphere.

Vangl as a Master Scaffold for Wnt/Planar Cell Polarity Signaling in Development and Disease.

The establishment of polarity within tissues and dynamic cellular morphogenetic events are features common to both developing and adult tissues, and breakdown of these programs is associated with diverse human diseases. Wnt/Planar cell polarity (Wnt/PCP) signaling, a branch of non-canonical Wnt signaling, is critical to the establishment and maintenance of polarity in epithelial tissues as well as cell motility events critical to proper embryonic development. In epithelial tissues, Wnt/PCP-mediated planar polarity relies upon the asymmetric distribution of core proteins to establish polarity, but the requirement for this distribution in Wnt/PCP-mediated cell motility remains unclear. However, in both polarized tissues and migratory cells, the Wnt/PCP-specific transmembrane protein Vangl is required and appears to serve as a scaffold upon which the core pathway components as well as positive and negative regulators of Wnt/PCP signaling assemble. The current literature suggests that the multiple interaction domains of Vangl allow for the binding of diverse signaling partners for the establishment of context- and tissue-specific complexes. In this review we discuss the role of Vangl as a master scaffold for Wnt/PCP signaling in epithelial tissue polarity and cellular motility events in developing and adult tissues, and address how these programs are dysregulated in human disease.

Deformation along the Deseado Massif (Patagonia, Argentina) during the Jurassic Period and its relationship with the Gondwana breakup: paleomagnetic and geochronological constraints

This work presents the analysis of paleomagnetic results obtained from four sampling areas of the Jurassic Bahía Laura Complex in the Deseado Massif and their implications on the regional deformation history during the breakup of Gondwana. Paleomagnetic data show cessation of tectonic block rotations about vertical axes around 160 Ma and a change from a transtensional to a mainly extensional tectonic regime. Two biotite samples yielded 40Ar–39Ar radiometric ages: one from the eastern outcrops of the Chon Aike Formation (plateau age of 184.66 ± 0.55 Ma) and the other from the La Matilde Formation (plateau age of 157.40 ± 0.65 Ma), located at the central part of the Deseado Massif. Finally, an apparent polar wander path (APWP) was calculated for the Jurassic of South America (200 to 140 Ma). This APWP indicates that South America experienced a northward drift between 200 Ma and 170 Ma, a clockwise rotation (~10°) between 170 Ma and 160 Ma, and a westward drift between 160 Ma and 140 Ma. The 170–160 Ma rotation could has been triggered by the combined effects of the uncoupling of the Antarctic Peninsula, the high rates of subduction of the Phoenix plate beneath Patagonia, the opening of the Rocas Verdes basin and the Weddell Sea, and the cessation of the Tethys slab-pull. Furthermore, the calculated APWP for South America does not support a Jurassic massive true polar wander event.

Polarity Events in the Drosophila melanogaster Oocyte.

Cell polarity is a pre-requirement for many fundamental processes in animal cells, such as asymmetric cell division, axon specification, morphogenesis and epithelial tissue formation. For all these different processes, polarization is established by the same set of proteins, called partitioning defective (Par) proteins. During development in Drosophila melanogaster, decision making on the cellular and organism level is achieved with temporally controlled cell polarization events. The initial polarization of Par proteins occurs as early as in the germline cyst, when one of the 16 cells becomes the oocyte. Another marked event occurs when the anterior–posterior axis of the future organism is defined by Par redistribution in the oocyte, requiring external signaling from somatic cells. Here, we review the current literature on cell polarity events that constitute the oogenesis from the stem cell to the mature egg.

Terminally differentiated osteoclasts organize centrosomes into large clusters for microtubule nucleation and bone resorption.

Osteoclasts are highly specialized, multinucleated cells responsible for the selective resorption of the dense, calcified bone matrix. Microtubules (MTs) contribute to the polarization and trafficking events involved in bone resorption by osteoclasts; however, the origin of these elaborate arrays is less clear. Osteoclasts arise through cell fusion of precursor cells. Previous studies have suggested that centrosome MT nucleation is lost during this process, with the nuclear membrane and its surrounding Golgi serving as the major MT organizing centers (MTOCs) in these cells. Here we reveal that precursor cell centrosomes are maintained and functional in the multinucleated osteoclast and interestingly form large MTOC clusters, with the clusters organizing significantly more MTs compared with individual centrosomes. MTOC cluster formation requires dynamic MTs and minus-end directed MT motor activity. Inhibition of these centrosome clustering elements had a marked impact on both F-actin ring formation and bone resorption. Together these findings show that multinucleated osteoclasts employ unique centrosomal clusters to organize the extensive MTs during bone attachment and resorption.