Observations In Polar Regions Research Articles

Monitoring the Spatiotemporal Dynamics of Arctic Winter Snow/Ice with Moonlight Remote Sensing: Systematic Evaluation in Svalbard

Accurate monitoring of the spatiotemporal dynamics of snow and ice is essential for under-standing and predicting the impacts of climate change on Arctic ecosystems and their feedback on global climate. Traditional optical and Synthetic Aperture Radar (SAR) remote sensing still have limitations in the long-time series observation of polar regions. Although several studies have demonstrated the potential of moonlight remote sensing for mapping polar snow/ice covers, systematic evaluation on applying moonlight remote sensing to monitoring spatiotemporal dynamics of polar snow/ice covers, especially during polar night periods is highly demanded. Here we present a systematic assessment in Svalbard, Norway and using data taken from the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi National Polar-orbiting Partnership (SNPP) Day/Night Band (DNB) sensor to monitor the spatiotemporal dynamics of snow/ice covers during dark Arctic winters when no solar illumination available for months. We successfully revealed the spatiotemporal dynamics of snow/ice covers from 2012 to 2022 during polar night/winter periods, using the VIIRS/DNB time series data and the object-oriented Random Forests (RF) algorithm, achieving the average accuracy and kappa coefficient of 96.27% and 0.93, respectively. Our findings indicate that the polar snow/ice covers show seasonal and inter-seasonal dynamics, thus requiring more frequent observations. Our results confirm and realize the potential of moonlight remote sensing for continuous monitoring of snow/ice in the Arctic region and together with other types of remote sensing data, moonlight remote sensing will be a very useful tool for polar studies and climate change.

High Gas-Phase Methanesulfonic Acid Production in the OH-Initiated Oxidation of Dimethyl Sulfide at Low Temperatures.

Dimethyl sulfide (DMS) influences climate via cloud condensation nuclei (CCN) formation resulting from its oxidation products (mainly methanesulfonic acid, MSA, and sulfuric acid, H2SO4). Despite their importance, accurate prediction of MSA and H2SO4 from DMS oxidation remains challenging. With comprehensive experiments carried out in the Cosmics Leaving Outdoor Droplets (CLOUD) chamber at CERN, we show that decreasing the temperature from +25 to −10 °C enhances the gas-phase MSA production by an order of magnitude from OH-initiated DMS oxidation, while H2SO4 production is modestly affected. This leads to a gas-phase H2SO4-to-MSA ratio (H2SO4/MSA) smaller than one at low temperatures, consistent with field observations in polar regions. With an updated DMS oxidation mechanism, we find that methanesulfinic acid, CH3S(O)OH, MSIA, forms large amounts of MSA. Overall, our results reveal that MSA yields are a factor of 2–10 higher than those predicted by the widely used Master Chemical Mechanism (MCMv3.3.1), and the NOx effect is less significant than that of temperature. Our updated mechanism explains the high MSA production rates observed in field observations, especially at low temperatures, thus, substantiating the greater importance of MSA in the natural sulfur cycle and natural CCN formation. Our mechanism will improve the interpretation of present-day and historical gas-phase H2SO4/MSA measurements.

Version 1 of a sea ice module for the physics-based, detailed, multi-layer SNOWPACK model

Abstract. Sea ice is an important component of the global climate system. The presence of a snowpack covering sea ice can strongly modify the thermodynamic behavior of the sea ice, due to the low thermal conductivity and high albedo of snow. The snowpack can be stratified and change properties (density, water content, grain size and shape) throughout the seasons. Melting snow provides freshwater which can form melt ponds or cause flushing of salt out of the underlying sea ice, while flooding of the snow layer by saline ocean water can strongly impact both the ice mass balance and the freezing point of the snow. To capture the complex dynamics from the snowpack, we introduce modifications to the physics-based, multi-layer SNOWPACK model to simulate the snow–sea-ice system. Adaptations to the model thermodynamics and a description of water and salt transport through the snow–sea-ice system by coupling the transport equation to the Richards equation were added. These modifications allow the snow microstructure descriptions developed in the SNOWPACK model to be applied to sea ice conditions as well. Here, we drive the model with data from snow and ice mass-balance buoys installed in the Weddell Sea in Antarctica. The model is able to simulate the temporal evolution of snow density, grain size and shape, and snow wetness. The model simulations show abundant depth hoar layers and melt layers, as well as superimposed ice formation due to flooding and percolation. Gravity drainage of dense brine is underestimated as convective processes are so far neglected. Furthermore, with increasing model complexity, detailed forcing data for the simulations are required, which are difficult to acquire due to limited observations in polar regions.

Observing Polar Regions from Space: Comparison between Highly Elliptical Orbit and Medium Earth Orbit Constellations

AbstractContinuous observation of polar regions from space remains an important unsolved technical challenge of great interest for the international meteorological community. This capacity would allow achieving global continuous coverage once combined with the geostationary (GEO) satellite network. From a practical point of view, continuous coverage of polar regions with a small number of spacecraft can be obtained from a constellation of satellites either in highly elliptical orbits (HEO) or in medium Earth orbits (MEO). The study compares HEO and MEO satellite constellations for their capacity to provide continuous imaging of polar regions as function of the viewing zenith angle (VZA) and evaluates the corresponding latitude limits that ensure sufficient overlap with GEO imagery. Earlier studies assumed the latitude boundary of 60° and the VZA range 70°–85° depending on the space mission focus: meteorological purposes or communications. From the detailed analysis of meteorological retrieval requirements, this study suggests that the overlap of the GEO and polar observing systems (HEO or MEO) should occur down to the latitude band 45°–50° with a maximum VZA ranging between 60° and 64°. This coverage requirement can be met with two sets of three-satellite HEO constellations (one for each polar area) or a six-satellite MEO constellation. The 12-h Molniya and 14-, 15-, and 16-h HEO systems have been analyzed and determined to meet these revised requirements. The study demonstrates that the six-satellite 24-h MEO system can provide a suitable solution, which is also beneficial from the point of view of ionizing radiation and image acquisition geometry. Among the HEO systems, the 16-h HEO has some advantages relative to other HEO systems from the point of view of spatial coverage and space radiation.

How Does Ground Clutter Affect CloudSat Snowfall Retrievals Over Ice Sheets?

CloudSat has provided the first spaceborne snowfall observations in polar regions. Nevertheless, CloudSat retrievals may be affected by ground clutter even if the snowfall rate at the surface is estimated from the reflectivity measured at about 1200 m above land/ice surface. In this study, the impact of ground clutter contamination on CloudSat snowfall retrievals over the Antarctic and Greenland ice sheets is investigated. Our results suggest that ground clutter affects CloudSat snowfall observations over some areas, particularly over complex terrain such as mountain ranges and fjords. Over these areas, the snowfall rates deduced from CloudSat observations can be, therefore, significantly overestimated. This has implications when developing snowfall climatologies from CloudSat products.

Optimising assimilation of sea ice concentration in an Earth system model with a multicategory sea ice model

A data assimilation method capable of constraining the sea ice of an Earth system model in a dynamically consistent manner has the potential to enhance the accuracy of climate reconstructions and predictions. Finding such a method is challenging because the sea ice dynamics is highly non-linear, and sea ice variables are strongly non-Gaussian distributed and tightly coupled to the rest of the Earth system – particularly thermodynamically with the ocean. We investigate key practical implementations for assimilating sea ice concentration – the predominant source of observations in polar regions – with the Norwegian Climate Prediction Model that combines the Norwegian Earth System Model with the Ensemble Kalman Filter. The performances of the different configurations are investigated by conducting 10-year reanalyses in a perfect model framework. First, we find that with a flow-dependent assimilation method, strongly coupled ocean–sea ice assimilation outperforms weakly coupled (sea ice only) assimilation. An attempt to prescribe the covariance between the ocean temperature and the sea ice concentration performed poorly. Extending the ocean updates below the mixed layer is slightly beneficial for the Arctic hydrography. Second, we find that solving the analysis for the multicategory instead of the aggregated ice state variables greatly reduces the errors in the ice state. Updating the ice volumes induces a weak drift in the bias for the thick ice category that relates to the postprocessing of unphysical thicknesses. Preserving the ice thicknesses for each category during the assimilation mitigates the drift without degrading the performance. The robustness and reliability of the optimal setting is demonstrated for a 20-year reanalysis. The error of sea ice concentration reduces by 50% (65%), sea ice thickness by 25% (35%), sea surface temperature by 33% (23%) and sea surface salinity by 11% (25%) in the Arctic (Antarctic) compared to a reference run without assimilation.

Design and implementation of a Cube satellite mission for Antarctic glacier and sea ice observation

The research for global climate changes calls for high quality satellite data and imageries regarding the Polar Regions. In recent years, the emerging Earth-Observation micro/nano satellite technology provides new data sources for polar region observations. The STU-2A, also named TW-1A, is such a nano satellite designed for polar region observation activities. It is a 3U CubeSat of 2.9 kg with a size of 30 × 10 × 10 cm carrying an Earth observation camera, launched into a Sun Synchronous Orbit (SSO) at 481 km with an inclination of 97.3°, on September 25, 2015. During the Antarctic summer of 2015/16, it has acquired visible-light true color images with a resolution of 94 m, covering different sea and coastal regions including Amundsen Sea, Ross Sea and Vincennes Bay. These images were used to analyze the change of glacier and sea ice, compared and calibrated with reference to the publically available MODIS images with a resolution of 250 m. As the camera was specially designed for the Polar regions which have an environment of low solar elevation angle and high surface reflectance, it eliminates the oversaturation problem of the MODIS sensors and can provide high quality images. Based on data analysis and assessment, it is confirmed that this satellite data can meet the demand of glacier and sea ice observation. This paper presents the Cubesat system design and configuration, the payload camera design, and its application in Antarctic glacier and sea ice observation.

DATA ASSIMILATION IN A SOLAR DYNAMO MODEL USING ENSEMBLE KALMAN FILTERS: SENSITIVITY AND ROBUSTNESS IN RECONSTRUCTION OF MERIDIONAL FLOW SPEED

ABSTRACT We implement an Ensemble Kalman Filter procedure using the Data Assimilation Research Testbed for assimilating “synthetic” meridional flow-speed data in a Babcock–Leighton-type flux-transport solar dynamo model. By performing several “observing system simulation experiments,” we reconstruct time variation in meridional flow speed and analyze sensitivity and robustness of reconstruction. Using 192 ensemble members including 10 observations, each with 4% error, we find that flow speed is reconstructed best if observations of near-surface poloidal fields from low latitudes and tachocline toroidal fields from midlatitudes are assimilated. If observations include a mixture of poloidal and toroidal fields from different latitude locations, reconstruction is reasonably good for error in low-latitude data, even if observational error in polar region data becomes 200%, but deteriorates when observational error increases in low- and midlatitude data. Solar polar region observations are known to contain larger errors than those in low latitudes; our forward operator (a flux-transport dynamo model here) can sustain larger errors in polar region data, but is more sensitive to errors in low-latitude data. An optimal reconstruction is obtained if an assimilation interval of 15 days is used; 10- and 20-day assimilation intervals also give reasonably good results. Assimilation intervals days do not produce faithful reconstructions of flow speed, because the system requires a minimum time to develop dynamics to respond to flow variations. Reconstruction also deteriorates if an assimilation interval days is used, because the system’s inherent memory interferes with its short-term dynamics during a substantially long run without updating.

A Depolarization Ratio Anomaly Detector to Identify Icebergs in Sea Ice Using Dual-Polarization SAR Images

Icebergs represent hazards to maritime traffic and offshore operations. Satellite synthetic aperture radar (SAR) is very valuable for the observation of polar regions, and extensive work was already carried out on detection and tracking of large icebergs. However, the identification of small icebergs is still challenging especially when these are embedded in sea ice. In this paper, a new detector is proposed based on incoherent dual-polarization SAR images. The algorithm considers the limited extension of small icebergs, which are supposed to have a stronger cross-polarization and higher cross- over copolarization ratio compared to the surrounding sea or sea ice background. The new detector is tested with two satellite systems. First, RADARSAT-2 quad-polarimetric images are analyzed to evaluate the effects of high-resolution data. Subsequently, a more exhaustive analysis is carried out using dual-polarization ground-detected Sentinel-1a extra wide swath images acquired over the time span of two months. The test areas are in the east coast of Greenland, where several icebergs have been observed. A quantitative analysis and a comparison with a detector using only the cross-polarization channel are carried out, exploiting grounded icebergs as test targets. The proposed methodology improves the contrast between icebergs and sea ice clutter by up to 75 times. This returns an improved probability of detection.

Sea Ice Observations in Polar Regions: Evolution of Technologies in Remote Sensing

Evolution of remote sensing sensors technologies is presented, with emphasis on its suitability in observing the polar regions. The extent of influence of polar regions on the global climate and vice versa is the spearhead of climate change research. The extensive cover of sea ice has major impacts on the atmosphere, oceans, and terrestrial and marine ecosystems of the polar regions in particular and teleconnection on other processes elsewhere. Sea ice covers vast areas of the polar oceans, ranging from ~18 × 106 km2 to ~23 × 106 km2, combined for the Northern and Southern Hemispheres. However, both polar regions are witnessing contrasting rather contradicting effects of climate change. The Arctic sea ice extent is declining at a rate of 0.53 × 106 km2·decade–1, whereasAntarcticaexhibits a positive trend at the rate of 0.167 × 106 km2·decade–1. This work reviews literature published in the field of sea ice remote sensing, to evaluate and access success and failures of different sensors to observe physical features of sea ice. The chronological development series of different sensors on different satellite systems, sensor specifications and datasets are examined and how they have evolved to meet the growing needs of users is outlined. Different remote sensing technology and observational methods and their suitability to observe specific sea ice property are also discussed. A pattern has emerged, which shows that microwave sensors are inherently superior to visible and infrared in monitoring seasonal and annual changes in sea ice. Degree of successes achieved through remote sensing techniques by various investigators has been compared. Some technologies appear to work better under certain conditions than others, and it is now well accepted that there is no algorithm that is ideal globally. Contribution of Indian remote sensing satellites is also reviewed in the context of polar research. This review suggests different primary datasets for further research on sea ice features (sea ice extent, ice type, sea ice thickness, etc.). This work also examines past achievements and how far these capabilities have evolved and tap into current state of art/direction of sensor technologies. Effective monitoring and syntheses of past few decades of research pinpoint useful datasets for sea ice monitoring, thereby avoiding wastage of resources to find practical datasets to monitor these physically inaccessible regions.

Influence of high-latitude geomagnetic pulsations on recordings of broadband force-balanced seismic sensors

Abstract. Seismic broadband sensors with electromagnetic feedback are sensitive to variations of surrounding magnetic field, including variations of geomagnetic field. Usually, the influence of the geomagnetic field on recordings of such seismometers is ignored. It might be justified for seismic observations at middle and low latitudes. The problem is of high importance, however, for observations in Polar Regions (above 60° geomagnetic latitude), where magnitudes of natural magnetic disturbances may be two or even three orders larger. In our study we investigate the effect of ultra-low frequency (ULF) magnetic disturbances, known as geomagnetic pulsations, on the STS-2 seismic broadband sensors. The pulsations have their sources and, respectively, maximal amplitudes in the region of the auroral ovals, which surround the magnetic poles in both hemispheres at geomagnetic latitude (GMLAT) between 60° and 80°. To investigate sensitivity of the STS-2 seismometer to geomagnetic pulsations, we compared the recordings of permanent seismic stations in northern Finland to the data of the magnetometers of the IMAGE network located in the same area. Our results show that temporary variations of magnetic field with periods of 40–150 s corresponding to regular Pc4 and irregular Pi2 pulsations are seen very well in recordings of the STS-2 seismometers. Therefore, these pulsations may create a serious problem for interpretation of seismic observations in the vicinity of the auroral oval. Moreover, the shape of Pi2 magnetic disturbances and their periods resemble the waveforms of glacial seismic events reported originally by Ekström (2003). The problem may be treated, however, if combined analysis of recordings of co-located seismic and magnetic instruments is used.

Evaluation of the sea ice simulation in a new coupled atmosphere‐ocean climate model (HadGEM1)

A rapid increase in the variety, quality, and quantity of observations in polar regions is leading to a significant improvement in the understanding of sea ice dynamic and thermodynamic processes and their representation in global climate models. We assess the simulation of sea ice in the new Hadley Centre Global Environmental Model (HadGEM1) against the latest available observations. The HadGEM1 sea ice component uses elastic‐viscous‐plastic dynamics, multiple ice thickness categories, and zero‐layer thermodynamics. The model evaluation is focused on the mean state of the key variables of ice concentration, thickness, velocity, and albedo. The model shows good agreement with observational data sets. The variability of the ice forced by the North Atlantic Oscillation is also found to agree with observations.

Water detection on atmosphereless celestial bodies: Alternative explanations of the observations

Alternative explanations are proposed for the results of the three types of remote sensing experiments in which water ice is supposed to be found on the surfaces of atmosphereless celestial bodies: (1) measurements of hydrogen content by the neutron spectrometer on Lunar Prospector, (2) observations of the absorption bands near 3 μm in reflectance spectra of asteroids, and (3) radar observations of polar regions of Mercury. Calculations have shown that in the first two types of observations solar wind protons chemically trapped by oxygen atoms in hydroxyl groups or other radiation defects in oxygen‐bearing particles on the surfaces of atmosphereless bodies can be mistaken for water. Higher hydrogen content in the lunar polar regions, especially in polar craters, as compared to equatorial zones can be due to sharp decrease of escape probability with temperature. Spots of high hydrogen content in equatorial zones of the Moon can be explained by variations of degassing rates in different materials. Solar wind origin of OH groups may account for 3‐μm absorption by asteroids of M and E classes thought to be differentiated. Strong, highly depolarized radar echoes from polar and lower latitude craters of Mercury can be explained by decrease of the dielectric loss of silicate material with temperature, which solves the problems of delivery and thermal stability of low‐loss material on Mercury surface, being consistent with the observed regional variations of radar brightness. The possibilities considered in the paper should be taken into account in interpretation of the observations aimed on search of water.

The modern atmospheric background dust load: Recognition in central Asian snowpack, and compositional constraints

Dusts in strata of snowpack in the Alai‐Pamir range, Kirghizstan, Central Asia, have chemical compositions that are in the same restricted range as those of the dusts found in snowpacks at three other locations: central south Greenland, the St. Elias range (Alaska), and coastal Antarctica, where special‐type local dust sources certainly cannot dominate. This similarity at the four widely separated sites appears to indicate that there is a modern atmospheric background dust that is the same on a regional, hemispheric, or global scale. The common compositional range is that of average crustal rock, or of moderately ferromagnesian volcanic rock. It is not that of carbonate, nor highly siliciceous rocks. Previously, the existence of an atmospheric background dust has been postulated only on the basis of its particle size distribution, and only from observations in polar regions. The present study partially determines the chemical composition of the background dust, and confirms its existence in snowpack at four localities worldwide, including the center of the earth's largest continent where dusts of local source have considerable influence.

A balloon borne interferometer in the upper stratosphere with long flight duration capability: An alternative to a space-based interferometer

We propose an interferometer with 12 telescopes of 30 cm aperture fixed on a light rigid structure with a 20 meter diameter. This is to be transported in the upper stratosphere by an open free balloon with long a flight duration capability, and will be lofted for observations in polar regions. This interferometer would give access to a spectal band between the far ultraviolet and millimeter wavelengths with an angular resolution of 5 milliarcseconds in the visible. Its performance would be equivalent to that of a similar sized space-based interferometer. Moreover, the proposed instrument is more attractive than space projects for baselines smaller than 100 meters due to its lower cost and easier accessibility. For the development of future space-based interferometers, balloon-borne experiments will also provide an ideal test bed.

Albert Paddock Crary, 1911-1987

... Known as the "father" of the American Antarctic science program and, earlier, a leading researcher in the Arctic, Crary conducted a broad range of scientific observations in Polar regions, incidentally becoming the first person to have set foot on both North and South Poles. [He has been described as] ... "the leading light in glaciology in Antarctica during the IGY, "an outstanding scientist and a great friend," "an indispensable man," as "an exceptional man because of his ability to combine his genius as a scientific explorer with his qualities as a human being." ... [And according to Dr. Charles R. Bentley,] "Bert Crary was the man who, more than any other, was responsible for the introduction of solid geophysical techniques into both north and south polar studies. Both by his leadership and by his personality, he was an inspiration to two generations of polar scientists."

Radio observations of polar regions

Radio observations of polar regions

Some suggestions for auroral and magnetic observations in polar regions

The frequency of the occurrence of aurorae has been found to increase rapidly with the magnetic latitude of the observing station, reaching a maximum zone about 23° from the north, or south, magnetic pole and decreasing at higher latitudes. Records from antarctic expeditions, notably those of Sir Douglas Mawson, show that strong auroral displays are usually most frequent in the evening hours before midnight at all latitudes above 60° south, that the frequency of the‐quiet aurorae are a maximum before midnight for magnetic latitudes below 67°, and that the maximum shifts to the early morning hours at magnetic latitudes above 67°; at certain stations in the very high latitudes there were two maxima, one in the evening and one in the morning. The records from the arctic regions, which are less complete than those from the antarctic, show much the same diurnal distribution of the aurorae. In general it seems that the geographical distribution of the various types of aurorae, as arches, glows, streamers, etc., is roughly known for latitudes above the zone of maximum auroral frequency, but is not so well known at lower latitudes. Detailed observations in the lower latitudes, as well as at the higher latitudes, might be of value. If such records are obtained it is to be hoped that they will be published in full. A complete report would be of immeasurably greater value to the development of a theoretical explanation than a summary or an abbreviated outline.