Polar Night Research Articles

Probabilistic Causal Network Modeling of Southern Hemisphere Jet Subseasonal to Seasonal Predictability

Abstract Skillful prediction of the Southern Hemisphere (SH) eddy-driven jet is crucial for representation of mid-to-high-latitude SH climate variability. In the austral spring-to-summer months, the jet and the stratospheric polar vortex variabilities are strongly coupled. Since the vortex is more predictable and influenced by long-lead drivers 1 month or more ahead, the stratosphere is considered a promising pathway for improving forecasts in the region on subseasonal to seasonal (S2S) time scales. However, a quantification of this predictability has been lacking, as most modeling studies address only one of the several interacting drivers at a time, while statistical analyses quantify association but not skill. This methodological gap is addressed through a knowledge-driven probabilistic causal network approach, quantified with seasonal ensemble hindcast data. The approach enables to quantify the jet’s long-range predictability arising from known late-winter drivers, namely, El Niño–Southern Oscillation (ENSO), Indian Ocean dipole (IOD), upward wave activity flux, and polar night jet oscillation, mediated by the vortex variability in spring. Network-based predictions confirm the vortex as determinant for skillful jet predictions, both for the jet’s poleward shift in late spring and its equatorward shift in early summer. ENSO, IOD, late-winter wave activity flux, and polar night jet oscillation only provide moderate prediction skill to the vortex. This points to early spring submonthly variability as important for determining the vortex state leading up to its breakdown, creating a predictability bottleneck for the jet. The method developed here offers a new avenue to quantify the predictability provided by multiple, interacting drivers on S2S time scales. Significance Statement Predictions of the Southern Hemisphere midlatitude jet stream are crucial for skillful forecasts of the austral mid-to-high latitudes. Several oceanic and atmospheric phenomena could, if better represented in models, improve spring-to-summer jet predictions on subseasonal to seasonal time scales. However, the combined potential skill arising from the inclusion of such phenomena has not been quantified. This study does so by using a probabilistic causal network model, representing the connections between those drivers and the jet with conditional probabilities, trained on large sets of model data. The stratospheric polar vortex is confirmed as crucial predictor of jet variability but is itself hard to predict a month in advance due to submonthly variability, creating a predictability bottleneck for the jet.

Geographical and seasonal variations of gravity wave activities in the upper mesosphere measured by space-borne imaging of molecular oxygen nightglow

Geographical and seasonal variations of gravity wave events in the upper mesosphere were investigated using the nightglow imaging data obtained by the Visible and near-Infrared Spectral Imager (VISI) on the Ionosphere, Mesosphere, upper Atmosphere and Plasmasphere (IMAP) onboard the International Space Station (ISS). The nadir-imaging data of the O2(0–0) atmospheric band (762 nm) with the typical emission peak around 95 km altitude was used to investigate small-scale waves (horizontal wavelengths less than ~ 200 km) on a global scale. To detect gravity wave events, the variance of high-pass filtered nightglow images within a local 100 km radius was evaluated, with a threshold set at three times the standard deviation from the average variance of the background level. A data screening algorithm that evaluates the variance of upwelling contamination light emission was also introduced to remove contaminated data. Applying the variance filter and data screening algorithm to a nearly 3-year data set, from November 2012 to August 2015, occurrence maps of wave events for four seasons were derived. The occurrence maps show a higher frequency of wave events in winter high latitudes (> 40° N/S), considerably attributed to gravity wave activity associated with the polar night jet. Hot spots were observed near orographic sources in winter high latitudes, including the eastern part of North America, Europe, and the southern Andes. In the summer hemisphere, hot spots were detected at mid-to-high latitudes such as North America, Europe, and the eastern side of the Eurasian continent, and at equatorial latitudes just above the intertropical convection zone (ITCZ). They are likely gravity waves from deep convection that arise from mid-latitude summertime thunderstorms and the ITCZ, respectively. During the equinox seasons, hot spots were detected near convective sources such as the Amazon Rainforest, Congo Rainforest, and the Indochina peninsula.Graphical

Comparisons of Underwater Light From Atmospheric and Mechanically Stimulated Bioluminescence Sources in High Arctic Polar Night

AbstractAt high latitudes, polar night is a prolonged period of seasonal darkness with the sun remaining below the horizon throughout the diel cycle for up to 177 days at the North Pole. Along with diffuse atmospheric light from the sun and the moon, bioluminescence is an in‐water light source that can facilitate ecological interactions in an otherwise dim‐light environment. At high latitudes during polar night, bioluminescence rather than sunlight represents a significant portion of the photons available in the pelagic. We investigated depths of transition zones (called the bioluminescence transition depth) in the pelagic light field during polar night, defining the transition of a light field dominated by atmospheric irradiance, to one dominated by bioluminescent point sources. We derived relationships between values of the transition depth, bioluminescence potential, surface irradiance due to atmospheric light and the diffuse attenuation coefficient. We conducted studies for two Svalbard, Norway fjords, as well as for offshore areas located in the shelf‐break, shelf‐slope and in the Arctic basin. Based on our results for two polar nights, the transition from underwater light dominated by atmospheric sources to that dominated by bioluminescence occurs between 10 and 40 m in two Svalbard fjords, and between 18 and 60 m for offshore areas. These transition depths may be of particular importance to understanding how bioluminescence structures planktonic communities both in polar regions and at lower latitudes.

Observing Gravity Waves Generated by Moving Sources With Ground‐Based Rayleigh Lidars

AbstractTemperature measurements by zenith‐pointing ground‐based Rayleigh lidars are often used to detect middle atmospheric gravity waves. In time‐height diagrams of temperature perturbations, stationary mountain waves are identifiable by horizontal phase lines. Vertically tilted phase lines, on the other hand, indicate that the wave source or the propagation conditions are transient. Idealized numerical simulations illustrate that and how a wave source moving in the direction of the mean wind entails upward‐tilted phase lines. The inclination angle depends on the horizontal wavelength and the wave source’s propagation speed. On this basis, the goal is to identify and characterize non‐orographic gravity waves (NOGWs) from propagating sources, for example, upper‐level jet/front systems, in simulated lidar observations and actual Rayleigh lidar measurements. Compositions of selected atmospheric variables from a meteorological forecast or reanalysis are thoughtfully combined to associate NOGWs with processes in the troposphere and stratosphere. For a virtual observation over the Southern Ocean, upward‐tilted phase lines indeed dominate the time‐height diagram during the passage of an upper‐level trough. The example also emphasizes that temporal filtering of temperature measurements is appropriate for NOGWs, especially in the presence of a strong polar night jet that implies large vertical wavelengths. During two selected observational periods of the COmpact Rayleigh Autonomous Lidar (CORAL) in the lee of the southern Andes, upward‐tilted phase lines are mainly associated with mountain waves and transient background wind conditions. One nighttime measurement by CORAL coincides with the passage of an upper‐level trough, but large‐amplitude mountain waves superpose the small‐amplitude NOGWs in the middle atmosphere.

High temporal resolution records of the velocity of Hansbreen, a tidewater glacier in Svalbard

Abstract. Monitoring changes in glacial dynamics is essential for understanding the environmental response to accelerated climate warming in the Arctic. However, geodetic surveys in polar regions continue to present considerable challenges because of the harsh environmental conditions and the polar night. This study records a 14-year-long time series (2006–2019) of global navigation satellite system (GNSS) surveys of the positions of 16 ablation stakes distributed across Hansbreen, a tidewater glacier in southern Svalbard. The measurements were conducted with an exceptionally high temporal resolution, from about 1 week to about 1 month, and covering altitudes ranging from 20 to 490 m a.s.l. The position of one stake was surveyed every day. The primary data products consist of the stake coordinates and velocities. Time series of annual and seasonal velocities are also provided. This dataset may be a subject of further studies of glacier dynamics in relation to the long-term and seasonal impact of climate change on ice flow in the region. It also offers unique material for tuning numerical models of glacier dynamics and for validating satellite-derived products such as velocity and digital elevation models. The dataset described here has been made publicly available through the Zenodo repository: https://doi.org/10.5281/zenodo.8289380 (Błaszczyk et al., 2023).

Antarctic benthic diatoms after 10 months of dark exposure: consequences for photosynthesis and cellular integrity.

Antarctic algae are exposed to prolonged periods of extreme darkness due to polar night, and coverage by ice and snow can extend such dark conditions to up to 10 months. A major group of microalgae in benthic habitats of Antarctica are diatoms, which are key primary producers in these regions. However, the effects of extremely prolonged dark exposure on their photosynthesis, cellular ultrastructure, and cell integrity remain unknown. Here we show that five strains of Antarctic benthic diatoms exhibit an active photosynthetic apparatus despite 10 months of dark-exposure. This was shown by a steady effective quantum yield of photosystem II (Y[II]) upon light exposure for up to 2.5 months, suggesting that Antarctic diatoms do not rely on metabolically inactive resting cells to survive prolonged darkness. While limnic strains performed better than their marine counterparts, Y(II) recovery to values commonly observed in diatoms occurred after 4-5 months of light exposure in all strains, suggesting long recovering times. Dark exposure for 10 months dramatically reduced the chloroplast ultrastructure, thylakoid stacking, and led to a higher proportion of cells with compromised membranes than in light-adapted cells. However, photosynthetic oxygen production was readily measurable after darkness and strong photoinhibition only occurred at high light levels (>800 µmol photons m-2 s-1). Our data suggest that Antarctic benthic diatoms are well adapted to long dark periods. However, prolonged darkness for several months followed by only few months of light and another dark period may prevent them to regain their full photosynthetic potential due to long recovery times, which might compromise long-term population survival.

Featured data sources and normalised indices of use in small Arctic catchments research

The development of remote sensing instruments and methods has revolutionised work practices worldwide, resulting in a new field of research. Remote sensing has significantly expanded the possibilities for detailed research, spanning from biological to urban studies, by constantly imaging the Earth. Numerous photogrammetric campaigns and satellite missions have been increasing the possibilities for conducting research that includes larger areas and time scales while minimising the need for fieldwork. This is particularly useful in polar regions, where fieldwork is complicated by harsh weather conditions, hard-to-reach research areas, polar nights, and the need for high funding and logistical support. Here available algorithms that help to track environmental shifts in the small Arctic catchments, such as changes in ice, snow, vegetation, and water are presented.

Terminator effect in the model Schumann resonance signals

We model Schumann resonance (SR) amplitude variations driven by the diurnal and seasonal motion of the day–night interface in the Earth – ionosphere cavity that is regarded as the terminator effect. The current moment of the equatorial source is a constant. The observer occupies the middle, the high latitudes, or the South Pole. Vertical electric field is calculated at the frequencies 8, 14, and 20 Hz. The following results were obtained. Amplitude modulations relevant to the day-night interface acquire ubiquitous patterns in the local time of the observer. The date–time changes have a convex lens-like structure at the mid-latitude observatory. The simultaneous displacement of the source and observer along the longitude causes an appropriate shift of the date–time pattern plotted in the universal time (UT). Relocation of the observer from the Northern to the Southern Hemisphere shifts the pattern by 6 months. These changes might totally alter the outline of the observed “12 months - 24 h” pattern. The shape of date–time variation alters from the convex lens-like to the cross-like when the observer is located in the high latitudes owing to the polar day and the polar night periods. When the observatory occupies a geographic pole, the season-diurnal variations resemble a ‘chessboard’. The Wentzel – Kramers – Brillouin (WKB) approximation allows obtaining the general outline of the date–time variations. The data obtained might be interpreted as a combination of two effects. The first one forms the general outline of temporal changes; and it is linked to the height of the Earth-ionosphere cavity above the source and the observer. The second one is related to "reflections" of ELF radio waves from the day–night interface, and it drives oscillations with the period equivalent to the wavelength at the particular frequency. All effects are related to the position of the day–night interface and occur in the observer's local time. The range of amplitude modulations in a non-uniform cavity is of ± (10–15)% relative to the average amplitude.

The nightscape of the Arctic winter shapes the diving behavior of a marine predator

Predator–prey interactions in marine ecosystems are dynamically influenced by light, as demonstrated by diel vertical migrations of low-trophic level organisms. At high latitudes, the long winter nights can provide foraging opportunities for marine predators targeting vertically migrating prey closer to the surface at night. However, there is limited documentation of such diel patterns in marine predators under extreme light regimes. To address this, we recorded the diving behavior of 17 harbour porpoises just south of the Arctic circle in West Greenland, from summer to winter. Unlike classical diel vertical migration, the porpoises dove 24–37% deeper at night and the frequency of deep dives (> 100 m) increased tenfold as they entered the darkest months. The daily mean depth was negatively correlated with daylength, suggesting an increased diving activity when approaching the polar night. Our findings suggest a light-mediated strategy in which harbour porpoises would either target (i) benthic prey, (ii) pelagic prey migrating seasonally towards the seafloor, or (iii) vertically migrating prey that may be otherwise inaccessible in deeper waters at night, therefore maximizing feeding activity during extended periods of darkness. Extreme light regimes observed at high latitudes are therefore critical in structuring pelagic communities and food webs.

DNA metabarcoding reveals a diverse, omnivorous diet of Arctic amphipods during the polar night, with jellyfish and fish as major prey

IntroductionCurrently, Arctic marine ecosystems are witnessing the most rapid physical changes worldwide, leading to shifts in pelagic and benthic communities and food web structure, concomitant with the introduction of boreal species. Gelatinous zooplankton or jellyfish represent one particular group of which several boreal species are prone to undergo significant poleward range expansions and population increases in the Arctic in the course of the ongoing changes. Historically, jellyfish were considered a trophic dead-end, but an increasing number of studies using modern tools have highlighted their role as major prey items in marine food webs. In this study, we aimed to verify the role of jellyfish and other metazoans as food sources in the Arctic polar night food web, when pelagic resources are limited.MethodsWe identified the diet of different bentho-pelagic amphipod species in the Atlantifying Kongsfjorden (West Svalbard) during the polar night. We regularly sampled lysianassoid and gammarid amphipods using baited traps and hand nets over a period of one month during the polar night and identified their diet spectrum by applying DNA metabarcoding (COI) to their stomach contents.ResultsWe demonstrate that all investigated species are omnivorous. Fish species including polar cod and snailfish, likely in the shape of carrion, played an important role in the diet of the scavengers Orchomenella minuta and Anonyx sarsi. Predation and potential scavenging on jellyfish contributed to the diet of all four investigated species, particularly for the species Gammarus setosus and G. oceanicus, as evidenced by high read abundances and high frequencies of occurrence. Besides jellyfish, crustaceans and macroalgae were important components of the diet of the two Gammarus species.DiscussionThe diverse jellyfish community present in Kongsfjorden in the polar night is clearly being utilized as a food source, either through pelagic feeding or feeding on jelly-falls, albeit to a different extent in the local amphipod community. These findings provide novel insights into the Arctic food web during the polar night and represent the first evidence of feeding on natural (non-experimental) jelly-falls.

Shortwave and longwave components of the surface radiation budget measured at the Thule High Arctic Atmospheric Observatory, Northern Greenland

Abstract. The Arctic climate is influenced by the interaction of shortwave (SW) and longwave (LW) radiation with the atmosphere and the surface. The comprehensive evolution of the Surface Radiative Fluxes (SRF) on different time scales is of paramount importance to understanding the complex mechanisms governing the Arctic climate. However, only a few sites located in the Arctic region provide long-term time series of SRF allowing for capturing of the seasonality of atmospheric and surface parameters and for carrying out validation of satellite products and/or reanalyses. This paper presents the daily and monthly SRF record collected at the Thule High Arctic Atmospheric Observatory (THAAO, 76.5∘ N, 68.8∘ W), in North-Western Greenland. The downwelling components of the SW (DSI) and the LW (DLI) irradiances have been measured at THAAO since 2009, whereas the collection of the upwelling SW (USI) and LW (ULI) irradiance was started in 2016, together with additional measurements, such as meteorological parameters and column water vapour. The datasets of DSI (Meloni et al., 2022a; https://doi.org/10.13127/thaao/dsi), USI (Meloni et al., 2022b; https://doi.org/10.13127/thaao/usi), DLI (Meloni et al., 2022c; https://doi.org/10.13127/thaao/dli), ULI (Meloni et al., 2022d; https://doi.org/10.13127/thaao/uli), and near-surface air temperature (Muscari et al., 2018; https://doi.org/10.13127/thaao/met), can be accessed through the THAAO web site (https://www.thuleatmos-it.it/data, last access: 16 January 2024). The DSI is absent (solar zenith angle ≥90∘) from 29 October to 13 February, assuming maxima in June (monthly mean of 277.0 Wm−2), when it is about half of the total incoming irradiance. The USI maximum occurs in May (132.4 Wm−2) owing to the combination of moderately high DSI values and high albedo. The shortwave surface albedo (A) assumes an average of 0.16 during summer, when the surface is free of snow. Differently, during months of snow-covered surface, when solar radiation allows A to be estimated, its values are greater than 0.6. A large interannual variability is observed in May and September, months characterized by rapidly changing surface conditions, having a link with air temperature anomalies. The DLI and ULI maxima occur in July and August, and the minima in February and March. ULI is always larger than DLI and shows a wider annual cycle. ULI is well described by a fourth-order polynomial fit to the air temperature (R2>0.99 for monthly data and R2>0.97 for daily data). The Surface Radiation Budget (SRB) is positive from April to August, when absorption of solar radiation exceeds the infrared net cooling, with a maximum value of 153.2 Wm−2 in June. From November to February, during the polar night, the LW net flux varies between −34.5 and −43.0 Wm−2. In March and September, the negative LW net flux overcomes the positive SW contribution, producing a negative SRB. The THAAO measurements show clear evidence of the influence of several regional weather/climate events, that appear strongly linked with SRF anomalies. These anomalies were found, for example, during summer 2012, when a large ice melting event took place over Greenland, and during winter 2019–2020, which was extraordinarily cold in the Arctic region.

Global 500 m seamless dataset (2000–2022) of land surface reflectance generated from MODIS products

Abstract. The Moderate Resolution Imaging Spectroradiometer (MODIS) is widely utilized for retrieving land surface reflectance to reflect plant conditions, detect ecosystem phenology, monitor forest fires, and constrain terrestrial energy budgets. However, the state-of-the-art MODIS surface reflectance products suffer from temporal and spatial gaps due to atmospheric conditions (e.g. clouds and aerosols), limiting their use in ecological, agricultural, and environmental studies. Therefore, there is a need for reconstructing spatiotemporally seamless (i.e. gap-filled) surface reflectance data from MODIS products, which is difficult due to the intrinsic inconsistency of observations resulting from various sun/view geometry and the prolonged missing values resulting from polar night or heavy cloud coverage, especially in monsoon season. We built a framework for generating the global 500 m daily seamless data cubes (SDC500) based on MODIS surface reflectance dataset, which contains the generation of a land-cover-based a priori database, bidirectional reflectance distribution function (BRDF) correction, outlier detection, gap filling, and smoothing. The first global spatiotemporally seamless land surface reflectance at 500 m resolution was produced, covering the period from 2000 to 2022. Preliminary evaluation of the dataset at 12 sites worldwide with different land cover demonstrated its robust performance. The quantitative assessment shows that the SDC500 gap-filling results have a root-mean-square error (RMSE) of 0.0496 and a mean absolute error (MAE) of 0.0430. The SDC500 BRDF correction results showed an RMSE of 0.056 and a bias of −0.0085 when compared with MODIS nadir BRDF-adjusted reflectance (NBAR) products, indicating the acceptable accuracy of both products. From a temporal perspective, the SDC500 eliminates abnormal fluctuations while retaining the useful localized feature of rapid disturbances. From a spatial perspective, the SDC500 shows satisfactory spatial continuity. In conclusion, the SDC500 is a well-processed global daily surface reflectance product, which can serve as the fundamental input for large-scale ecological, agricultural, and environmental applications and quantitative remote sensing studies. The SDC500 is available at http://data.starcloud.pcl.ac.cn/resource/27 (Liang et al., 2023b) or https://doi.org/10.12436/SDC500.27.20230701 (Liang et al., 2023a).

ИССЛЕДОВАНИЕ ПСИХИЧЕСКОЙ РАБОТОСПОСОБНОСТИ И ГРУППОВОЙ ДИНАМИКИ В АВТОНОМНЫХ УСЛОВИЯХ ЗИМОВКИ НА СТАНЦИИ «ВОСТОК»

The paper deals with the investigation of psychic performance and group dynamics during Russian Antarctic expedition RAE66. Eight winterers were tested 7 times with the use of the cognitive Master-Test. Group dynamics was assessed by sociometry and cohesion diagnostics on the basis of common goals and values. Psychophysiological status was assessed weekly using the actigraphy and HR data, and questionnaires. At the end of the polar day and in early autumn, it was the mood that went down first (autumn and winter), then accuracy of sensorimotor reactions degraded (winter) and mistakes in a simple math test became more frequent (winter and spring). On the contrary, performance of short-term memory tests improved in winter and spring. Motor activity reduced during the first half of the expedition and started increasing gradually at the beginning of the polar night. Though the sleeping time was normally from 7 to 8.5 hours, sleep quality subjectively changed during the wintering it correlated with physical activity and consequent changes of heart rate variability (stress) and blood oxygen saturation. The latter remained low throughout the period of life on station Vostok in comparison to measurements made on the ship. Cohesion was high but for some slackening by the third quarter of wintering; at the end of wintering cohesion grew strong again. The sociometric status of winterers varied with intensity of negative emotions.

Biophilic analogous patterns for light-responsive architecture during polar night: Examining the photobiological effects of electrical lighting on surface colour configuration

This paper investigates occupants' photobiological responses of biophilic analogous patterns such as electrical lighting and surface colour configuration during dark periods in northern architecture. Biophilic design establishes that the integration of nature-inspired architectural strategies could positively impact occupants’ photobiological responses to enhance well-being in locations with limited daylight access. Photobiological responses are indicated on image-forming (IF) and non-image forming (NIF) effects. IF relates to visual outcomes, reflected on vision and visual tasks, and measured in photopic units. NIF relates to non-visual outcomes such as the biological process of circadian clock stimulation and measured in melanopic units. Limited research addresses the impact of electrical lighting combined with surface colour (SC) configurations to optimize minimum lighting requirements at photopic and melanopic levels in an architectural setting. This research therefore examines eight surface colour configurations tested under three different luminaire positions set at warm, warm-white, and white correlated colour temperature (CCT). The variables generated 72 scenarios, which were captured through high dynamic range images (HDRi), analyzed, and post-processed to display false colour maps and values of illuminance, melanopic-Equivalent Daylight Illuminance (melanopic-EDI) and spatial colour temperature. Results demonstrate the spatial diversification generated by electrical lighting to different visual tasks and circadian stimulation over a day. The study also proved that several coloured surfaces and luminaire settings can generate similar photopic and melanopic lighting conditions despite their perceived spatial colour temperature. This research highlights the photobiological adjustment of biophilic coloured lighting ambiances provided by electrical systems in northern latitudes compromised by extreme photoperiod.

Solar influences on the Earth’s atmosphere: solved and unsolved questions

Solar influences on the Earth’s atmosphere: solved and unsolved questions

Evaluation of methods to determine the surface mixing layer height of the atmospheric boundary layer in the central Arctic during polar night and transition to polar day in cloudless and cloudy conditions

Abstract. This study evaluates methods to derive the surface mixing layer (SML) height of the Arctic atmospheric boundary layer (ABL) using in situ measurements inside the Arctic ABL during winter and the transition period to spring. An instrumental payload carried by a tethered balloon was used for the measurements between December 2019 and May 2020 during the year-long Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. Vertically highly resolved (centimeter scale) in situ profile measurements of mean and turbulent parameters were obtained, reaching from the sea ice to several hundred meters above ground. Two typical conditions of the Arctic ABL over sea ice were identified: cloudless situations with a shallow surface-based inversion and cloudy conditions with an elevated inversion. Both conditions are associated with significantly different SML heights whose determination as accurately as possible is of great importance for many applications. We used the measured turbulence profile data to define a reference of the SML height. With this reference, a more precise critical bulk Richardson number of 0.12 was derived, which allows an extension of the SML height determination to regular radiosoundings. Furthermore, we have tested the applicability of the Monin–Obukhov similarity theory to derive SML heights based on measured turbulent surface fluxes. The application of the different approaches and their advantages and disadvantages are discussed.

Equilibrium Climate after Spectral and Bolometric Irradiance Reduction in Grand Solar Minimum Simulations

In this study, we use the Whole Atmosphere Community Climate Model, forced by present-day atmospheric composition and coupled to a Slab Ocean Model, to simulate the state of the climate under grand solar minimum forcing scenarios. Idealized experiments prescribe time-invariant solar irradiance reductions that are either uniform (percentage-wise) across the total solar radiation spectrum (TOTC) or spectrally localized in the ultraviolet (UV) band (SCUV). We compare the equilibrium condition of these experiments with the equilibrium condition of a control simulation, forced by perpetual solar maximum conditions. In SCUV, we observe large stratospheric cooling due to ozone reduction. In both the Northern Hemisphere (NH) and the Southern Hemisphere (SH), this is accompanied by a weakening of the polar night jet during the cold season. In TOTC, dynamically induced polar stratospheric cooling is observed in the transition seasons over the NH, without any ozone deficit. The global temperature cooling values, compared with the control climate, are 0.55±0.03 K in TOTC and 0.39±0.03 K in SCUV. The reductions in total meridional heat transport outside of the subtropics are similar in the two experiments, especially in the SH. Despite substantial differences in stratospheric forcing, similarities exist between the two experiments, such as cloudiness; meridional heating transport in the SH; and strong cooling in the NH during wintertime, although this cooling affects two different regions, namely, North America in TOTC and the Euro–Asian continent in SCUV.

Hypometabolism to survive the long polar night and subsequent successful return to light in the diatom Fragilariopsis cylindrus.

Diatoms, the main eukaryotic phytoplankton of the polar marine regions, are essential for the maintenance of food chains specific to Arctic and Antarctic ecosystems, and are experiencing major disturbances under current climate change. As such, it is fundamental to understand the physiological mechanisms and associated molecular basis of their endurance during the long polar night. Here, using the polar diatom Fragilariopsis cylindrus, we report an integrative analysis combining transcriptomic, microscopic and biochemical approaches to shed light on the strategies used to survive the polar night. We reveal that in prolonged darkness, diatom cells enter a state of quiescence with reduced metabolic and transcriptional activity, during which no cell division occurs. We propose that minimal energy is provided by respiration and degradation of protein, carbohydrate and lipid stores and that homeostasis is maintained by autophagy in prolonged darkness. We also report internal structural changes that manifest the morphological acclimation of cells to darkness, including the appearance of a large vacuole. Our results further show that immediately following a return to light, diatom cells are able to use photoprotective mechanisms and rapidly resume photosynthesis, demonstrating the remarkable robustness of polar diatoms to prolonged darkness at low temperature.

Model-informed classification of broadband acoustic backscatter from zooplankton in an in situ mesocosm

Abstract Classification of zooplankton to species with broadband echosounder data could increase the taxonomic resolution of acoustic surveys and reduce the dependence on net and trawl samples for ‘ground truthing’. Supervised classification with broadband echosounder data is limited by the acquisition of validated data required to train machine learning algorithms (‘classifiers’). We tested the hypothesis that acoustic scattering models could be used to train classifiers for remote classification of zooplankton. Three classifiers were trained with data from scattering models of four Arctic zooplankton groups (copepods, euphausiids, chaetognaths, and hydrozoans). We evaluated classifier predictions against observations of a mixed zooplankton community in a submerged purpose-built mesocosm (12 m3) insonified with broadband transmissions (185–255 kHz). The mesocosm was deployed from a wharf in Ny-Ålesund, Svalbard, during the Arctic polar night in January 2022. We detected 7722 tracked single targets, which were used to evaluate the classifier predictions of measured zooplankton targets. The classifiers could differentiate copepods from the other groups reasonably well, but they could not differentiate euphausiids, chaetognaths, and hydrozoans reliably due to the similarities in their modelled target spectra. We recommend that model-informed classification of zooplankton from broadband acoustic signals be used with caution until a better understanding of in situ target spectra variability is gained.

МЕТОДОЛОГИЧЕСКИЕ ПРИНЦИПЫ ЛЕЧЕНИЯ ХЕЙЛИТОВ НА КРАЙНЕМ СЕВЕРЕ

When studying exogenous factors of the Far North that negatively affect human health, it was established: the impact of not only low temperatures, traumatic aerodynamic conditions, and a deficiency of ultraviolet radiation, but also geomagnetic field tension, microelement shifts in the composition of soil and water, and fluctuations in atmospheric pressure levels. A special role for carrying out therapeutic and diagnostic measures is played by the fact that the entire territory located beyond the Arctic Circle belongs to zones with a significant deficiency of the biologically active part of the solar spectrum of ultraviolet radiation. This leads to disruption of photoperiodicity due to the change of polar day and polar night, disruption of biological rhythms, and a decrease in reserve capabilities for regulating homeostasis. The fact that a person lives in a long-term deficiency of ultraviolet radiation affects all biological processes occurring in the body; it plays a special role in the occurrence and development of some forms of cheilitis. The study involved 37 patients aged 18 to 55 years with a diagnosis of chronic recurrent fissure of the lip, meteorological cheilitis, dry form of exfoliative cheilitis, symptomatic atopic cheilitis. After a thorough history, review of patient medical records, and dental examination, serum vitamin D and E levels were measured in all patients before treatment. The best results in treatment were achieved by prescribing combined ointments based on glucocorticoids and antibacterial/antifungal components in combination with physiotherapeutic procedures.