Polar Night Conditions Research Articles

Impact of climate change on the kelp Laminaria digitata – simulated Arctic winter warming

The Arctic is seasonally exposed to long periods of low temperatures and complete darkness. Consequently, perennial primary producers have to apply strategies to maximize energy efficiency. Global warming is occurring in the Arctic faster than the rest of the globe. The highest amplitude of temperature rise occurs during Polar Night. To determine the stress resistance of the ecosystem-engineering kelp Laminaria digitata against Arctic winter warming, non-meristematic discs of adult sporophytes from Porsangerfjorden (Finnmark, Norway) were kept in total darkness at 0°C and 5°C over a period of three months. Physiological variables, namely maximum quantum yield of photosynthesis (Fv/Fm) and dry weight, as well as underlying biochemical variables including pigments, storage carbohydrates, total carbon and total nitrogen were monitored throughout the experiment. Although all samples remained in generally good condition with Fv/Fm values above 0.6, L. digitata performed better at 0°C than at 5°C. Depletion of metabolic products resulted in a constant decrease of dry weight over time. A strong decrease in mannitol and laminarin was observed, with greater reductions at 5°C than at 0°C. However, the total carbon content did not change, indicating that the sporophytes were not suffering from “starvation stress” during the long period of darkness. A decline was also observed in the accessory pigments and the pool of xanthophyll cycle pigments, particularly at 5°C. Our results indicate that L. digitata has a more active metabolism, but a lower physiological and biochemical performance at higher temperatures in the Arctic winter. Obviously, L. digitata is well adapted to Arctic Polar Night conditions, regardless of having its distributional center at lower latitudes. Despite a reduced vitality at higher temperatures, a serious decline in Arctic populations of L. digitata due to winter warming is not expected for the near future.

Satellite mapping of air temperature under polar night conditions

ABSTRACT A novel satellite technique for air temperature mapping with a spatial resolution of ~100 m was proposed for the town of Apatity, the Kola Peninsula (Russia), taken as a case study. The main idea behind this novel technique is to find the statistical relationships between the land surface temperatures in each point of the study area, observed by multiple infrared thermal satellite imagery, and the time series of air temperatures recorded by World Meteorological Organization (WMO) weather station. Fourteen scenes of infrared thermal spectral band of the Landsat satellites for the period 2014–2019 were used, as well as the long-term time series of air temperature from the weather station and the results of air temperature observations carried out by the network of loggers. For calm weather conditions, according to the ground truth, the error of air temperature mapping was σ = 1.5°C, and the precision was estimated as δ = 1.0°C. An analysis of the compiled air temperature map showed that, under polar night conditions, the air temperature on the hilltops was by 10–18°C higher than in the lowlands. It was concluded that, for economic reasons, as well as for the reasons of population health protection in the Arctic, it would be advisable to plan the placement of new cities on the hills. Each of these new areas should be designed in a “semi-isolated” manner in order to minimize the time needed by the local people for crossing the lowlands between the nearby districts. A characteristic feature of modern megalopolises is their internal structure formed by the growing primary settlements that can be considered as nuclei interlinked by transportation routes. Thus, the new Arctic cities can be called “Arctic megalopolises” because of their internal structure that is specific to megalopolises.

СПУТНИКОВЫЙ МОНИТОРИНГ ОЗОНОСФЕРЫ

The importance of controlling total ozone (TO) and surface ultraviolet irradiance is a reason for continuous monitoring of the ozonosphere using various ground-based and satellite methods and instruments. The global monitoring of TO has been carried out with the Russian instrument IKFS-2 on the Meteor-M No. 2 satellite since 2015. These measurements are conducted during the whole day and in polar night conditions. The developed algorithm based on using artificial neural networks and OMI satellite instrument measurements is periodically updated and allows determining TO with an average total error of 3-5%. The IKFS-2 measurements can be used for analyzing spatial and temporal (seasonal, interannual) variations in ozone, its long-term trends, verifying modern numerical stratospheric models, studying ozone anomalies, etc. The examples of analyzing TO in autumn-spring periods and TO anomalies in winter and spring of 2020 are given. They clearly demonstrate advantages of satellite TO measurements with the thermal radiation method.

Windows with Variable Thermal Protection for Buildings in the Far North

A window is, first, an element of daylighting and visual comfort, but, in addition, the window can be an element of an air-conditioning system. In a building with natural ventilation, the outside air inflow is conducted, as a rule, through leaks in the fillings of window openings or through window elements – vents, transoms. The window is also an element of the building’s thermal protection. It gets special significance in buildings built in the climatic conditions of the Russian Far North. This region is characterized by a very short duration or even complete absence of solar time in winter (in the polar night conditions). In these conditions, the role of the window as an element of daylighting and visual comfort is turned off. The task of increasing the heat-shielding characteristics of windows becomes essential. In the Far North, a window can have the same thermal protection as a wall with proper design solutions. In temperate climate conditions, it is possible to increase the thermal protection of windows in public buildings during the period when the building is not in use: at night, on weekends and holidays. The paper provides an overview of new technologies for changing the optical properties and heat-shielding characteristics of windows, depending on changes in climatic conditions, time of day and people’s preferences, and discusses the possibilities of increasing the energy efficiency of buildings in the Far North conditions using windows with variable heat protection, as well as new designs of “smart windows”.

Early Jurassic palaeopolar marine reptiles of Siberia

AbstractMarine reptile occurrences are rare in the Lower Jurassic Series outside of Europe. Here we describe diverse marine reptile faunas from the Lower Jurassic Series (Pliensbachian and Toarcian stages, including the Toarcian–Aalenian boundary interval) of Eastern Siberia. The taxonomic composition of Toarcian marine reptile assemblages of Siberia highlight their cosmopolitan nature, with the presence of taxa previously known nearly exclusively from coeval strata of Europe, such as ichthyosaurians Temnodontosaurus and Stenopterygius, microcleidid plesiosaurians (including the genus Microcleidus), rhomaleosaurids and basal pliosaurids. The palaeogeographic reconstruction places these faunas to the palaeopolar region, north of the 80th northern parallel and up to the palaeo north pole (upper value within the 95% confidence interval for some of the localities). The materials include remains of both mature and juvenile (or even infant, judging by their very small size and poor ossification) animals, indicating a possibility that these polar seas may serve as a breeding area. The diversity and abundance of plesiosaurians and ichthyosaurians, along with a lack of thalattosuchian remains (considering their wide distribution elsewhere at low latitudes), is an additional argument that plesiosaurians and neoichthyosaurians were able to live and reproduce in a polar environment. There is no certainty whether these animals lived in polar seas permanently, or whether they were taking seasonal migrations. However, given the polar night conditions at high latitudes, the latter seems more plausible, and both these scenarios are further indirect evidence that these groups likely had a high metabolism.

Линейно-угловые построения в закрытой местности с использованием спутниковой геодезической аппаратуры

Invisibility between points can occur due to dense building location, terrain irregularities, intensive construction, and under polar night conditions. Forest thickets (the distance between the trunks up to 5 m, the closeness of the crowns start at 0,5 m) and undergrowth require cutting and clearing glades; terrain elevations, dense building setting, traffic flows and construction machines complicate the development of geodetic reference networks, the implementation of detailed surveys and construction layout. In the absence of visibility when the sides of the geodetic network make 200–500 m, it is recommended that two or more GPS receivers should work simultaneously under the same weather conditions, which compensates for errors at receiving radio signals, except for multipath and noise. With synchronous operation of the receivers, accurate coordinates and orientations for the upcoming electronic geodetic surveys are at mutually visible neighboring points obtained even without post-processing. Simultaneous GPS measurements enable finding the distance between them and horizontal angles in a closed area over the nearest points of the base and moving antennas in the building network for geodetic planning justification of detailed surveys and construction layout.

Daily Dynamics of Lipids and Fatty Acids and the Activity of Enzymes of Energy and Carbohydrate Metabolism in Young Fish of the Daubed Shanny Leptoclinus maculates (Fries, 1838) at Different Stages of Development in Polar Night Conditions

Daily Dynamics of Lipids and Fatty Acids and the Activity of Enzymes of Energy and Carbohydrate Metabolism in Young Fish of the Daubed Shanny Leptoclinus maculates (Fries, 1838) at Different Stages of Development in Polar Night Conditions

Modeling of Surface Temperature for Near-Earth Asteroid 2016HO3

On April 18, 2019, the China National Space Administration (CNSA) published the plan of asteroid exploration, which would select the near-earth asteroid 2016HO3 as one of its targets. On this paper, the parameters of 2016HO3 for thermal environment analysis were discussed. By investigating the current international observation data, the environmental parameters of 2016HO3 are obtained preliminarily. Then the near-Earth asteroid thermal model(NEATM) and asteroid thermal physics model (TPM) were used to model and analyze the surface temperature of 2016HO3, and the upper boulder of the temperature was 412 K. Considering the spinning effect, the day and night temperature difference at different locations was simulated and analyzed, and the temperature analysis method under the polar night conditions was proposed, then the maximum temperature difference at any position was determined to be about 30 K. Last on the basis of TPM, by the idea of the average illumination during the rotation period, the temperature analysis method of the polar night was proposed, and lower limit of temperature of 2016HO3 was achieved.

Generation of waves by jet-stream instabilities in winter polar stratosphere/mesosphere

In the paper we investigate the manifestation of large-scale and middle-scale atmospheric irregularities observed on stratosphere/mesosphere heights. We consider typical patterns of circulation in stratosphere and lower mesosphere which are formed due to a difference of air potential energy between equatorial and polar latitudes, especially in polar night conditions. On the base of ECMWF Era Interim reanalysis data we consider the dynamics of midlatitude winter jet-streams which transfer heat from low latitudes to polar region and which develop due to equator/pole baroclinic instabilities. We consider typical patterns of general circulation in stratosphere/lower mesosphere and reasons for creation of flaky structure of polar stratosphere. Also we analyze conditions that are favorable for splitting of winter circumpolar vortex during sudden stratosphere warming events and role of phase difference tides in this process. The analysis of vertical structure of the stratosphere wind shows the presence of regions with significant shear of horizontal velocity which favors for inducing of shear-layer instability that appears as gravity wave on boundary surface. During powerful sudden stratosphere warming events the main jet-stream can amplify these gravity waves to very high amplitudes that causes wave overturning and releasing of wave energy into the heat due to the cascade breakdown and turbulence. For the dynamics observed in reanalysis data we consider physical mechanisms responsible for observed phenomena.

Impact of early food input on the Arctic benthos activities during the polar night

In Arctic areas where benthic primary production does not occur or is not sufficient, the benthos depends on episodic events of food inputs from overlying waters, in particular spring ice algal and phytoplankton blooms. Climate change is expected to lead to earlier ice melts and subsequently to earlier spring blooms and food inputs to the benthos. The goal of the present study was to characterize benthic community structure and activities during the polar night in Rijpfjorden, a high Arctic fjord from Svalbard, and to assess experimentally how earlier climate-induced food inputs can impact these benthic activities. Two concentrations of freeze-dried phytoplankton were added to intact sediment cores, while additional control cores did not receive food addition. Sediment oxygen demand (SOD), nutrient fluxes, bioturbation coefficients (as indicator of benthic activities) and contents of organic matter and pigments in sediments were measured at the beginning of the experiment and 9 days after the addition. In the initial polar night conditions, SOD was ~4.2 mmol O2 m−2 d−1, bioturbation coefficients were null for biodiffusion and 1.08 y−1 for bioadvection, and benthic biomass was 1.36 g 0.1 m−2. In the cores with food addition, the phytoplankton added was quickly consumed, and after 9 days, SOD and bioturbation were higher in the food treatments compared with the control cores, both being higher with higher food concentration. This study documented a clear and quick response in benthic activities following the food input, suggesting that in winter/early spring, Arctic benthos may depend on early food inputs for its activities. Climate-induced changes in food supply to the seafloor could have drastic consequences for the benthic ecosystem functioning.

10.1007/s11478-008-2010-7

The results of model studying the mechanism of formation of large-scale disturbances in the thermosphere under the action of short-period waves propagating from the middle atmosphere are presented. The region of the solar terminator is considered as a source of such waves. The calculation results for the summer conditions in the Northern Hemisphere indicate that such an energy source, local in the space and time, results in the formation of large-scale inhomogeneities at altitudes of 120–160 km. A disturbance of these inhomogeneities is caused by the nonlinear and dissipative processes accompanying HF propagation in the terminator region. Large-scale disturbances have a quasistationary character and are localized near the morning and evening terminators. Vortex motions around the pole at altitudes of 140–160 km are formed at nigh latitudes of the winter hemisphere under the polar night conditions.

Spatio-temporal observations of the tertiary ozone maximum

Abstract. We present spatio-temporal distributions of the tertiary ozone maximum (TOM), based on GOMOS (Global Ozone Monitoring by Occultation of Stars) ozone measurements in 2002–2006. The tertiary ozone maximum is typically observed in the high-latitude winter mesosphere at an altitude of ~72 km. Although the explanation for this phenomenon has been found recently – low concentrations of odd-hydrogen cause the subsequent decrease in odd-oxygen losses – models have had significant deviations from existing observations until recently. Good coverage of polar night regions by GOMOS data has allowed for the first time to obtain spatial and temporal observational distributions of night-time ozone mixing ratio in the mesosphere. The distributions obtained from GOMOS data have specific features, which are variable from year to year. In particular, due to a long lifetime of ozone in polar night conditions, the downward transport of polar air by the meridional circulation is clearly observed in the tertiary ozone maximum time series. Although the maximum tertiary ozone mixing ratio is achieved close to the polar night terminator (as predicted by the theory), TOM can be observed also at very high latitudes, not only in the beginning and at the end, but also in the middle of winter. We have compared the observational spatio-temporal distributions of the tertiary ozone maximum with that obtained using WACCM (Whole Atmosphere Community Climate Model) and found that the specific features are reproduced satisfactorily by the model. Since ozone in the mesosphere is very sensitive to HOx concentrations, energetic particle precipitation can significantly modify the shape of the ozone profiles. In particular, GOMOS observations have shown that the tertiary ozone maximum was temporarily destroyed during the January 2005 and December 2006 solar proton events as a result of the HOx enhancement from the increased ionization.

Model studying the effect of the solar terminator on the thermospheric parameters

The results of model studying the mechanism of formation of large-scale disturbances in the thermosphere under the action of short-period waves propagating from the middle atmosphere are presented. The region of the solar terminator is considered as a source of such waves. The calculation results for the summer conditions in the Northern Hemisphere indicate that such an energy source, local in the space and time, results in the formation of large-scale inhomogeneities at altitudes of 120–160 km. A disturbance of these inhomogeneities is caused by the nonlinear and dissipative processes accompanying HF propagation in the terminator region. Large-scale disturbances have a quasistationary character and are localized near the morning and evening terminators. Vortex motions around the pole at altitudes of 140–160 km are formed at nigh latitudes of the winter hemisphere under the polar night conditions.

Study of the spatio-temporal distribution of stratospheric ozone from millimeter-waves observations for middle and high latitudes

We present the results of simultaneous ozonospheric millimeter-wave observations performed from the Earth’s surface at the middle and high latitudes of the Northern hemisphere in cold seasons of 2002–2005. The observed spatial and temporal variations in the ozone content are described. The features of the vertical ozone distribution inside and outside the polar stratospheric vortex are considered. It is concluded that radiophysical methods are efficient for studying the evolution of the ozonospheric especially under the polar-night conditions.

Validation of MIPAS-ENVISAT NO<sub>2</sub> operational data

Abstract. The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) instrument was launched aboard the environmental satellite ENVISAT into its sun-synchronous orbit on 1 March 2002. The short-lived species NO2 is one of the key target products of MIPAS that are operationally retrieved from limb emission spectra measured in the stratosphere and mesosphere. Within the MIPAS validation activities, a large number of independent observations from balloons, satellites and ground-based stations have been compared to European Space Agency (ESA) version 4.61 operational NO2 data comprising the time period from July 2002 until March 2004 where MIPAS measured with full spectral resolution. Comparisons between MIPAS and balloon-borne observations carried out in 2002 and 2003 in the Arctic, at mid-latitudes, and in the tropics show a very good agreement below 40 km altitude with a mean deviation of roughly 3%, virtually without any significant bias. The comparison to ACE satellite observations exhibits only a small negative bias of MIPAS which appears not to be significant. The independent satellite instruments HALOE, SAGE II, and POAM III confirm in common for the spring-summer time period a negative bias of MIPAS in the Arctic and a positive bias in the Antarctic middle and upper stratosphere exceeding frequently the combined systematic error limits. In contrast to the ESA operational processor, the IMK/IAA retrieval code allows accurate inference of NO2 volume mixing ratios under consideration of all important non-LTE processes. Large differences between both retrieval results appear especially at higher altitudes, above about 50 to 55 km. These differences might be explained at least partly by non-LTE under polar winter conditions but not at mid-latitudes. Below this altitude region mean differences between both processors remain within 5% (during night) and up to 10% (during day) under undisturbed (September 2002) conditions and up to 40% under perturbed polar night conditions (February and March 2004). The intercomparison of ground-based NDACC observations shows no significant bias between the FTIR measurements in Kiruna (68° N) and MIPAS in summer 2003 but larger deviations in autumn and winter. The mean deviation over the whole comparison period remains within 10%. A mean negative bias of 15% for MIPAS daytime and 8% for nighttime observations has been determined for UV-vis comparisons over Harestua (60° N). Results of a pole-to-pole comparison of ground-based DOAS/UV-visible sunrise and MIPAS mid-morning column data has shown that the mean agreement in 2003 falls within the accuracy limit of the comparison method. Altogether, it can be indicated that MIPAS NO2 profiles yield valuable information on the vertical distribution of NO2 in the lower and middle stratosphere (below about 45 km) during day and night with an overall accuracy of about 10–20% and a precision of typically 5–15% such that the data are useful for scientific studies. In cases where extremely high NO2 occurs in the mesosphere (polar winter) retrieval results in the lower and middle stratosphere are less accurate than under undisturbed atmospheric conditions.

Behavior of mesospheric ozone under nearly polar night conditions

The spatio-temporal behavior of the ozone mixing ratio in the upper mesosphere/mesopause region under nearly polar night conditions is one phenomenon not completely understood and reproduced by models thus far. On the basis of a sophisticated 3D-model of the dynamics and chemistry of the middle atmosphere (0–150 km) particularly designed to investigate the extended mesopause region, we examine the spatio-temporal structure of this phenomenon and discuss it in terms of chemistry. The most marked feature is a pronounced ozone maximum around 72 km, also called the tertiary ozone maximum, and a large decrease of the mixing ratios around 80 km. This feature was also found by means of ground-based microwave measurements in middle latitude at Lindau (51.66 °N) and high latitude at ALOMAR (69.29 °N) during the night in the winter season. It was, however, absent during the daytime hours. The calculations brought evidence that the enhanced ozone values occur in a latitudinal band close to the polar night terminator. It is confined both to a height range approximately between 66 and 77 km and to a certain latitudinal range which alters with the season according to the change of the polar night terminator. For a constant latitude there are two annual maxima of the ozone mixing ratio that occur nearly symmetrically about the winter solstice. These maxima are more widely separated at higher latitudes. The theoretical analysis of this phenomenon showed that while ozone is formed under nearly grazing incidence conditions the radiation that dissociates water vapor is almost completely absorbed. This means that the formation of hydrogen radicals that destroy odd oxygen is significantly reduced but there is still some atomic oxygen production that permits ozone formation during the short twilight periods close to the polar night terminator. The loss of the accumulated ozone takes place partly through the Chapman reactions of a pure oxygen system and partly through catalytic reactions, including HO x radicals that result from O( 1D) oxidation of the even hydrogens H 2 and H 2O and a residual photolysis of H 2O. The O( 1D) oxidation is important because the ozone dissociation rate is only slightly reduced for grazing incidence conditions in that region. Within the region of the large ozone decrease near 80 km the chemistry is marked by a steady increase of atomic hydrogen entailing a decrease of ozone and HO 2. The poleward directed meridional wind also transports ozone into the polar night.

On the spatiotemporal behavior of ozone within the upper mesosphere/mesopause region under nearly polar night conditions

The spatiotemporal behavior of the ozone mixing ratio in the upper mesosphere/mesopause region under nearly polar night conditions is one of the phenomena not completely understood and reproduced by models thus far. We examine this issue using an advanced three‐dimensional model of the dynamics and chemistry of the middle atmosphere (0–150 km) particularly designed to investigate the spatiotemporal structure of this phenomenon in the extended mesopause region. The most marked features of the modeling results are a pronounced ozone maximum around 72 km occurring close to the polar night terminator and a strong drop of the mixing ratio above ∼80 km. These features were also found by means of ground‐based microwave measurements in high latitude at the Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR, 69.29°N, 16.03°E) and even at the moderate latitude of Lindau (51.66°N, 10.13°E) during the night in the winter season but less marked there. They were absent at both stations during the daytime hours. The calculations suggest that the stronger enhanced ozone values occur in a latitudinal band of approximately 15° in the vicinity of the polar night terminator. During nighttime, enhanced values reach into midlatitudes. The effect is confined both to a height interval approximately between 66 and 76 km and to a certain latitudinal range which alters with season according to the change of the polar night terminator. We discuss the model results in terms of chemistry for nearly grazing incidence conditions of the solar insolation and in context with advective transport.

Numerical simulation of the winter polar wave clouds observed by Mars Global Surveyor Mars Orbiter Laser Altimeter

In 1998, the Mars Orbiter Laser Altimeter revealed the presence of isolated or quasi-periodic thick clouds during the martian polar night. They are believed to be composed of CO 2 ice particles and to be tilted against the wind direction, a feature characteristic of vertically propagating orographic gravity waves. To support that interpretation, we present here numerical simulations with a two-dimensional anelastic model of stratified shear flow that includes simple CO 2 ice microphysics. In some of the simulations presented, the orography is an idealized trough, with dimensions characteristic of the many troughs that shape the Mars polar cap. In others, it is near the real orography. In the polar night conditions, our model shows that gravity waves over the north polar cap are strong enough to induce adiabatic cooling below the CO 2 frost point. From this cooling, airborne heterogeneous nucleation of CO 2 ice particles occurs from the ground up to the altitude of the polar thermal inversion. Although the model predicts that clouds can be present above 15 km, only low altitude clouds can backscatter the Laser beams of MOLA at a detectable level. Accordingly, the shape of the Laser echoes is related to the shape of the clouds at low level, but do not necessarily coincide with the top of the clouds. The model helps to interpret the cloud patterns observed by MOLA. Above an isolated orographic trough, an isolated extended sloping cloud tilted against the wind is obtained. The model shows that the observed quasi-periodic clouds are due to the succession of small-scale topographic features, rather than to the presence of resonant trapped lee waves. Indeed, the CO 2 condensation greatly damps the buoyancy force, essential for the maintenance of gravity waves far from their sources. Simulations with realistic topography profiles show the cloud response is sensitive to the wind direction. When the wind is directed upslope of the polar cap, on the one hand, a large scale cloud, modulated by small-scale waves, forms just above the ground. On the other hand, when the wind is directed downslope, air is globally warmed, and periodic ice clouds induced by small-scale orography form at altitudes higher than 3–5 km above the ground. In both cases, a good agreement between the simulated echoes and the observed one is obtained. According to our model, we conclude that the observed clouds are quasi-stationary clouds made of moving ice particles that successively grow and sublimate by crossing cold and warm phases of orographic gravity waves generated by the successive polar troughs. We also find that the rate of ice precipitation is relatively weak, except when there is a large scale air dynamical cooling.

Zur Fernerkundung der Erdatmosphäre mittels Infrarotspektrometrie: Rekonstruktionstheorie und Anwendung

Remote sensing retrieval theory covers the methodology used to infer information on unknown parameters of the object under investigation from indirect remote measurements. Application of infrared spectrometry of the atmosphere leads to the inverse solution of the atmospheric radiative transfer equation. Its successful inversion depends on (1) a suitable forward model for simulation of atmospheric radiative transfer (2) the appropiate definition of the retrieval parameter vector, (3) an optimized vector containing the measurements, (4) the appropriate formulation of a constraint, and (5) a tool for stable numeric inversion. Experiments with limb emission spectrometers as well as uplooking emission and absorption spectrometers serve as examples for discussion of application of relevant retrieval schemes. With respect to retrieval theory, the following progress is reported and the following findings were gained: An optimized radiative transfer model for application within a retrieval program was developed. This model is both accurate and efficient. It includes all radiative processes relevant to application to atmospheric infrared spectrometry, including refraction, absorption, emission, scattering, line-coupling and non-local thermodynamic equilibrium. Objective selection of spectral gridpoints used for data analysis reduces the retrieval error and reduces computer resources needed. The more spectral data are considered, the more information is used for the retrieval of the target parameter. This is counterbalanced by the fact that radiance at the considered gridpoints depend on further parameters which may be uncertain and thus contribute to the error budget. Tentative retrieval of all these parameters from the measurement leads to an impracticable large number of unknowns. Therefore, an objective method for an optimized selection of spectral data was developed. It was shown that for limb measurements of medium spectral resolution the unconstrained solution of the inverse problem is instable if the vertical profile of the target parameter is represented on a discrete level model instead of a discrete layer model. Regularization is needed for level models, while retrieval of parameters represented by layers typically are stable. Solvability of ill-posed inversion problems in the context of remote sensing retrieval problems by implicit or explicit regularization was demonstrated. For explicit regularization in particular a smoothing constraint was investigated and considered useful. Implicit regularization we understand is the reduction of the size of the parameter vector by appropriate discrete representation of vertical profiles of atmospheric state parameters. It was shown that the global fit analysis of a limb sequence of spectra is not at all always superior over sequential onion peeling analysis, as commonly believed. In particular in the case of medium spectral resolution measurements the advantage of gobal fit with respect to accuracy disappears and the efficiency of onion peeling becomes significant. Methods developed were applied to the following experiments: The MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) balloon-borne instrument; these were the first high spectral resolution limb emission measurements in a winter polar vortex. Vertical profiles of some trace gases relevant to ozone research were retrieved under polar night conditions for the first time. The MIPAS aircraft instrument; the MIPAS-FT (Aircraft Transall) instrument recorded the first scientifically useful high resolution spectroscopic measurements under positive elevation angles. These allowed retrieval of zenith column amounts of atmospheric constituents sampled along the flight trajectory independent of solar illumination.

Air‐sea interactions over Terra Nova Bay during winter: Simulation with a coupled atmosphere‐polynya model

A preliminary simulation of the Terra Nova Bay polynya has been performed with a coupled atmosphere–polynya model. The atmospheric model is a hydrostatic primitive equations model that has been validated previously by a simulation of the strong katabatic winds observed in that area. The polynya model includes a representation of the free drift of frazil ice and simple sea‐ice dynamics and thermodynamics. Two and three‐dimensional experiments have been performed under polar night conditions. Two‐dimensional experiments show that an open (warm) water area influences significantly the atmospheric circulation in the antarctic coastal zone: an additional ice‐breeze effect is simulated and is responsible for the strenghthening of the katabatic winds near the coast. Because of the important temperature difference between the continental air and the ice‐free ocean (up to 40°C), strong surface heat fluxes are simulated over the polynya. Finally, a three‐dimensional experiment has been performed. The integration domain includes Terra Nova Bay. The polynya observed in that region is well simulated. It is found that heat losses from the polynya surface are stronger than previously thought but are probably constrained by the idealized representation of frazil ice, which is assumed to be uniform in each grid box. This stresses the need for having a better knowledge of frazil ice evolution in large polynyas.