The Arctic climate system includes numerous highly interactive small-scale physical processes in the atmosphere, sea ice, and ocean. During and since the International Polar Year 2007–2009, ...significant advances have been made in understanding these processes. Here, these recent advances are reviewed, synthesized, and discussed. In atmospheric physics, the primary advances have been in cloud physics, radiative transfer, mesoscale cyclones, coastal, and fjordic processes as well as in boundary layer processes and surface fluxes. In sea ice and its snow cover, advances have been made in understanding of the surface albedo and its relationships with snow properties, the internal structure of sea ice, the heat and salt transfer in ice, the formation of superimposed ice and snow ice, and the small-scale dynamics of sea ice. For the ocean, significant advances have been related to exchange processes at the ice–ocean interface, diapycnal mixing, double-diffusive convection, tidal currents and diurnal resonance. Despite this recent progress, some of these small-scale physical processes are still not sufficiently understood: these include wave–turbulence interactions in the atmosphere and ocean, the exchange of heat and salt at the ice–ocean interface, and the mechanical weakening of sea ice. Many other processes are reasonably well understood as stand-alone processes but the challenge is to understand their interactions with and impacts and feedbacks on other processes. Uncertainty in the parameterization of small-scale processes continues to be among the greatest challenges facing climate modelling, particularly in high latitudes. Further improvements in parameterization require new year-round field campaigns on the Arctic sea ice, closely combined with satellite remote sensing studies and numerical model experiments.
The maximum effect of open leads within sea ice on the near‐surface atmospheric temperature is estimated using a 1D atmospheric model coupled with a thermodynamic snow/sea ice model. The study is ...restricted to clear‐sky conditions during polar night. The model is initialized with a typical wintertime atmospheric temperature profile. Results are analyzed at different integration times corresponding to different fetches over the fractured sea ice as a function of wind speed and sea ice concentration A. The results demonstrate that for A > 90% small changes in the sea ice fraction have a strong effect on the near‐surface temperature. A change by 1% causes a temperature signal of up to 3.5 K. A threshold value of about 4 m s−1 for the 10‐m wind speed divides the air‐ice interaction process into a weak‐wind and strong‐wind regime.
Abstract
Background
It has been shown previously that a relevant proportion of childhood cancer survivors suffers from late effects, which are often directly related to the cancer itself or its ...therapy, resulting in particular follow-up needs, additionally burdening healthcare systems. Being diagnosed with cancer at a vulnerable stage of development, this group of cancer survivors is at comparatively higher risk of relapse or subsequent cancer. Although national and international follow-up guidelines based on treatment modalities have been developed, their implementation seems to leave room for improvement. Additionally, they lack a sufficient consideration of the survivors’ psychosocial needs, affecting their adherence to them. The aim of the VersKiK study is to provide representative information on late effects in childhood and adolescence cancer survivors in Germany. The main research objectives are: (1) to describe the state of follow-up care among survivors after a cancer diagnosis in childhood or adolescence; (2) to quantify the occurrence of late effects among this group of survivors; (3) to examine the adherence to selected audiological and cardiological follow-up guidelines and to identify factors affecting it; (4) to explore actual follow-up needs of paediatric cancer survivors; (5) to review selected follow-up guidelines with the aim to improve and expand them.
Methods
VersKiK is designed as a mixed-methods non-interventional study. We will use claims data from statutory health insurance companies in combination with individually linked population-based registry data from the German Childhood Cancer Registry (GCCR). This data base will permit us to quantify diagnoses and procedures in comparison to the general population as well as the adherence to existing follow-up guidelines. Additional information will be obtained through interviews with childhood and adolescence cancer survivors and their informal caregivers, as well as in focus groups with healthcare professionals.
Discussion
The present study aims to research the actual needs of individuals after cancer diagnosis and treatment in childhood or adolescence – physical, psychological and organisational – in order to improve existing follow-up guidelines. These improvements might further positively affect not only actual care provided to paediatric cancer survivors, but also benefit healthcare systems in general while decreasing consequent medical visits in this group of patients.
Trial registration
Registered at German Clinical Trial Register (ID: DRKS00025960 and DRKS00026092).
Sea ice leads play an important role in energy exchange between the ocean and atmosphere in polar regions, and therefore must be considered in weather and climate models. As sea ice leads are not ...explicitly resolved in such models, lead‐averaged surface heat flux is of considerable interest for the parameterization of energy exchange. Measurements and numerical studies have established that the lead‐averaged surface heat flux depends not only on meteorological parameters, but also on lead width. Nonetheless, few studies to date have investigated the dependency of surface heat flux on lead width. Most findings on that dependency are based on observations with lead widths smaller than a few hundred meters, but leads can have widths from a few meters to several kilometers. In this parameter study, we present the results of three series of large‐eddy simulations of turbulent exchange processes above leads. We varied the lead width and air temperature, as well as the roughness length. As this study focused on conditions without background wind, ice‐breeze circulation occurred, and was the main driver of the adjustment of surface heat flux. A previous large‐eddy simulation study with uncommonly large roughness length found that lead‐averaged surface heat flux exhibited a distinct maximum at lead widths of about 3 km, while our results show the largest heat fluxes for the smallest leads simulated (lead width of 50 m). At more realistic roughness lengths, we observed monotonously increasing heat fluxes with increasing lead width. Further, new scaling laws for the ice‐breeze circulation are proposed.
Plain Language Summary
In polar sea ice, often channel‐like openings appear due to ocean and atmosphere currents. These openings are like open windows, where huge amount of heat is transported from ocean to atmosphere. The width of the leads range from a few meters up to more than 10 km. Leads cover only a small area of the polar sea ice, but play an important role in the climate system. Generally, the amount of heat transport depends on wind speed and temperature of air and water. Further, measurements and computational model studies have indicated, that the efficiency of heat transport depends strongly on the width of a lead. Nonetheless, few studies to date have investigated the dependency on lead width. Most findings on that are based on observations for leads smaller than a few hundred meters. In this study, we present results of computer simulations with a so‐called large eddy simulation model, which captures the small scale turbulent processes explicitly. We varied the lead width from 50 m to 25 km for the special meteorological conditions without background wind and found remarkably different results compared to a former study on that topic with same type of computational model.
Key Points
Large eddy simulation study on the convection above sea ice leads of variable width under zero background wind conditions
Lead averaged surface heat flux depends strongly on lead width and is controlled by ice breeze circulation
Our findings differ remarkably from results of a former large eddy simulations study on that topic
An analytical model describing the evolution of a convective atmospheric boundary layer in marine cold-air outbreaks in the Arctic is presented. The novelty of the model is a detailed description of ...the baroclinicity associated with the boundary-layer growth and heating. Ekman friction is also taken into account. Thereby, the model describes the evolution of mixed-layer wind components over the ocean. It is shown theoretically that baroclinicity leads either to deceleration or to acceleration of the flow over the ocean, which depends on the direction of the large-scale flow relative to the orientation of the ice edge. Acceleration of the flow leads to a formation of a low-level jet strongly affecting the surface fluxes of heat and momentum. Baroclinicity and the magnitude of the low-level jet are strongest close to the ice edge being proportional to the ocean-ice temperature difference and decays further downwind. Horizontal decay of the low-level jet strength is governed by the airmass transformation length scale which is estimated to be in the order of 500-1000 km for typical cold-air outbreaks. The model solutions are shown to be in good agreement with aircraft observations over the Fram Strait and results of a numerical nonhydrostatic model.
Turbulent heat transport over inhomogeneous surfaces with sharp temperature discontinuities is investigated with a focus on the flow over leads in sea ice. The main goal consists in the development ...of a turbulence closure for a microscale atmospheric model resolving the integrated effect of plumes emanated from leads, but not the individual convective eddies. To this end, 10 runs are carried out with a large eddy simulation (LES) model simulating the flow over leads for springtime atmospheric conditions with near‐neutral inflow and a strong capping inversion. It is found that leads contribute to the stabilizing of the polar atmospheric boundary layer (ABL) and that strong countergradient fluxes of heat exist outside a core region of the plumes. These findings form the basis for the development of the new closure. It uses a new scaling with the internal ABL height and the characteristic vertical velocity for the plume region as the main governing parameters. Results of a microscale model obtained with the new closure agree well with the LES for variable meteorological forcing in case of lead orthogonal flow and for a fixed ABL height and lead width. The good agreement concerns especially the plume inclination, temperature, and heat fluxes as well as the relative contributions of gradient and countergradient transport of heat. A future more general closure should account, for example, for variable lead widths and wind directions. Results of the microscale model could be used to derive a future parameterization of the lead effect in large‐scale models.
An analysis of Special Sensor Microwave/Imager (SSM/I) satellite data reveals that the Whaler's Bay polynya north of Svalbard was considerably larger in the three winters from 2012 to 2014 compared ...to the previous 20 years. This increased polynya size leads to strong atmospheric convection during cold air outbreaks in a region north of Svalbard that was typically ice-covered in the last decades. The change in ice cover can strongly influence local temperature conditions. Dropsonde measurements from March 2013 show that the unusual ice conditions generate extreme convective boundary layer heights that are larger than the regional values reported in previous studies.
Weather prediction and climate simulations need reliable parameterizations of turbulent fluxes in the stable surface layer. Especially in these conditions, the uncertainties of such parametrizations ...are still large. Most of them rely on the Monin‐Obukhov similarity theory (MOST), for which universal stability functions (SFs) represent important ingredients. The SFs are nonlinear, if so, a numerical iteration of the MOST equations is required. Moreover, presently available SFs are significantly different at large stability. To simplify the calculations, a non‐iterative parametrization of fluxes is derived and corresponding bulk transfer coefficients for momentum and heat for a package of five pairs of state‐of‐the‐art SFs are proposed. For the first time, a parametrization of the related transfer coefficients is derived in a universal framework for all package members. The new parametrizations provide a basis for a cheap systematic study of the impact of surface layer turbulent fluxes in weather prediction and climate models.
Plain Language Summary
Results of weather forecast, present‐day climate simulations, and future climate projections depend among other factors on the interaction between the atmosphere and the underlying sea‐ice, the land, and the ocean. In numerical weather prediction and climate models, some of these interactions are accounted for by transport coefficients describing the turbulent exchange of momentum, heat, and humidity. Currently used transfer coefficients have, however, large uncertainties in flow regimes being typical for cold nights and seasons, but especially in the polar regions. Furthermore, their determination is numerically complex. It is obvious that progress could be achieved when the transfer coefficients would be given by simple mathematical formula in frames of an economic computational scheme. Such a new universal, so‐called non‐iterative parametrization scheme is derived for a package of transfer coefficients. The derivation is based on the Monin‐Obukhov similarity theory, which is well accepted in the scientific community. The new scheme provides a basis for a cheap systematic study of the impact of near‐surface turbulence and of the related transports of momentum, heat, and humidity in models.
Key Points
A non‐iterative universal parameterization of surface layer turbulent fluxes is derived using Monin‐Obukhov similarity theory
Bulk transfer coefficients are given, which are based on five pairs of state‐of‐the‐art surface layer stability functions
The new parametrizations provide a basis for a cheap study of the impact of surface layer turbulent fluxes in numerical weather prediction and climate models
The influence of spatial surface temperature changes over the Arctic Ocean on the 2-m air temperature variability is estimated using backward trajectories based on ERA-Interim and JRA25 wind fields. ...They are initiated at Alert, Barrow and at the Tara drifting station. Three different methods are used. The first one compares mean ice surface temperatures along the trajectories to the observed 2-m air temperatures at the stations. The second one correlates the observed temperatures to air temperatures obtained using a simple Lagrangian box model that only includes the effect of sensible heat fluxes. For the third method, mean sensible heat fluxes from the model are correlated with the difference of the air temperatures at the model starting point and the observed temperatures at the stations. The calculations are based on MODIS ice surface temperatures and four different sets of ice concentration derived from SSM/I (Special Sensor Microwave Imager) and AMSR-E (Advanced Microwave Scanning Radiometer for EOS) data. Under nearly cloud-free conditions, up to 90% of the 2-m air temperature variance can be explained for Alert, and 70% for Barrow, using these methods. The differences are attributed to the different ice conditions, which are characterized by high ice concentration around Alert and lower ice concentration near Barrow. These results are robust for the different sets of reanalyses and ice concentration data. Trajectories based on 10-m wind fields from both reanalyses show large spatial differences in the Central Arctic, leading to differences in the correlations between modeled and observed 2-m air temperatures. They are most pronounced at Tara, where explained variances amount to 70% using JRA and 80% using ERA. The results also suggest that near-surface temperatures at a given site are influenced by the variability of surface temperatures in a domain of about 200 km radius around the site.
Leads are elongated channels in sea ice which play an important role for the heat and moisture exchange between the polar ocean and atmosphere. The aircraft campaign STABLE aimed to improve our ...current understanding of the formation of convective plumes over leads and their impact on the polar atmospheric boundary layer. It was carried out over the pack ice in the northern Fram Strait in March 2013. We present case studies of the boundary layer modification and turbulent fluxes over four wide leads, which differed strongly with respect to lead characteristics and environmental conditions. The observed near‐surface sensible heat fluxes ranged from 15 to 180 W m−2. The leads also induced an increase of the near‐surface temperature of up to 3.2 °C and a humidity increase of up to 0.2 g kg−1. In one of the cases, large entrainment fluxes exceeding 30% of the surface fluxes were observed. Vertical profiles of turbulent sensible heat and momentum fluxes were nonlinear downstream of the leads with a distinct flux maximum in the core of the convective plumes. In two cases, the plumes also strongly affected the wind field within the atmospheric boundary layer. Low‐level jets that existed in those cases in the region upstream of the leads disappeared in the plume region. Finally, it is shown that large errors can occur when flux measurements are derived from lead orthogonal flight legs only. Therefore, complex flight patterns, as presented in this study, are necessary to accurately determine the energy fluxes in the environment of leads.
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