English
norskBlar i forfatter "Graversen, Rune"
Viser treff 1-20 av 21
-
Assessment of High‐Resolution Dynamical and Machine Learning Models for Prediction of Sea Ice Concentration in a Regional Application
(Journal article; Tidsskriftartikkel, 2020-10-17)In this study, the potential for sea ice concentration prediction using machine‐learning methods is investigated. Three different sea ice prediction models are compared: one high‐resolution dynamical assimilative model and two statistical machine‐learning models. The properties of all three models are explored, and the quality of their forecasts is compared. The dynamical model is a state‐of‐the‐art ... -
Assimilation of high-resolution ice charts in a coupled ocean-sea-ice model
(Journal article; Tidsskriftartikkel, 2019)In this study, we show assimilation results from a coupled ocean sea-ice model. The model has a horizontal resolution of 2.5 km. In the assimilation system, we assimilate high-resolution ice charts, structured on a 1 km grid. We compare the assimilation of passive microwave observations with the assimilation of ice charts. It is shown that the ice charts have a larger impact on the assimilation ... -
Comparison between a multi-variate nudging method and the ensemble Kalman filter for sea-ice data assimilation
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-04-25)Increasing ship traffic and human activity in the Arctic has led to a growing demand for accurate Arctic weather forecast. High-quality forecasts obtained by models are dependent on accurate initial states achieved by assimilation of observations. In this study, a multi-variate nudging (MVN) method for assimilation of sea-ice variables is introduced. The MVN assimilation method includes procedures ... -
Effect of seasonal mesoscale and microscale meteorological conditions in Ny-Ålesund on results of monitoring of long-range transported pollution
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-09-06)Ny-Ålesund is an international research settlement where the thermodynamics and chemical composition of the air are monitored. The present work investigates the effects of micrometeorological conditions, mesoscale dynamics and local air pollution on the data collected at two different locations around the village. Daily filter measurements of sulphur dioxide and non-sea salt sulphate from the temporary ... -
Effects of the tropospheric large-scale circulation on European winter temperatures during the period of amplified Arctic warming
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-07-08)We investigate factors influencing European winter (DJFM) air temperatures for the period 1979–2015 with the focus on changes during the recent period of rapid Arctic warming (1998–2015). We employ meteorological reanalyses analysed with a combination of correlation analysis, two pattern clustering techniques, and backtrajectory airmass identification. In all five selected European regions, severe ... -
Estimating Radiative Forcing With a Nonconstant Feedback Parameter and Linear Response
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-12-06)A new algorithm is proposed for estimating time-evolving global forcing in climate models. The method is a further development of the work of Forster et al. (2013), <a href=https://doi.org/10.1002/jgrd.50174>https://doi.org/10.1002/jgrd.50174</a>, taking into account the non-constancy of the global feedbacks. We assume that the non-constancy of this global feedback can be explained as a time-scale ... -
Estimating Remaining Carbon Budgets Using Temperature Responses Informed by CMIP6
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-07-12)A remaining carbon budget (RCB) estimates how much CO2 we can emit and still reach a specific temperature target. The RCB concept is attractive since it easily communicates to the public and policymakers, but RCBs are also subject to uncertainties. The expected warming levels for a given carbon budget has a wide uncertainty range, which increases with less ambitious targets, i.e., with higher CO2 ... -
Evaluating CM-SAF solar radiation CLARA-A1 and CLARA-A2 datasets in Scandinavia
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-05-26)Estimating/retrieving solar radiation through satellite-based remote sensing provides larger spatial coverage compared to other methods. Accurate estimates of incoming solar radiation is important when planning new solar energy installations. In addition, these estimates are also used in climate studies. Geostationary satellites are ideal for estimating solar radiation but cannot be used for high ... -
Evaluation of Six Atmospheric Reanalyses over Arctic Sea Ice from Winter to Early Summer
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-06-19)This study evaluates the performance of six atmospheric reanalyses (ERA-Interim, ERA5, JRA-55, CFSv2, MERRA-2, and ASRv2) over Arctic sea ice from winter to early summer. The reanalyses are evaluated using observations from the Norwegian Young Sea Ice campaign (N-ICE2015), a 5-month ice drift in pack ice north of Svalbard. N-ICE2015 observations include surface meteorology, vertical profiles from ... -
High-resolution polar low winds obtained from unsupervised sar wind retrieval
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-11-18)High-resolution sea surface observations by spaceborne synthetic aperture radar (SAR) instruments are sorely neglected resources for meteorological applications in polar regions. Such radar observations provide information about wind speed and direction based on wind-induced roughness of the sea surface. The increasing coverage of SAR observations in polar regions calls for the development of ... -
Impact of assimilating sea ice concentration, sea ice thickness and snow depth in a coupled ocean-sea ice modelling system
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-02-08)The accuracy of the initial state is very important for the quality of a forecast, and data assimilation is crucial for obtaining the best-possible initial state. For many years, sea-ice concentration was the only parameter used for assimilation into numerical sea-ice models. Sea-ice concentration can easily be observed by satellites, and satellite observations provide a full Arctic coverage. During ... -
Influence of seasonal mesoscale and microscale meteorological conditions in Svalbard on results of monitoring of long-range transported pollution [poster]
(Conference object; Konferansebidrag, 2018)The Zeppelin Observatory is an atmospheric monitoring station located on the northwest coast of Spitzbergen island, in the Svalbard archipelago. The station provides background air composition, meteorological and climatological data for numerous research projects. The observatory is located on a mountain ridge in a region with complex topography that affects local atmospheric circulation ... -
Magnitude of extreme heat waves in present climate and their projection in a warming world
(Journal article; Tidsskriftartikkel; Peer reviewed, 2014)An extreme heat wave occurred in Russia in the summer of 2010. It had serious impacts on humans and natural ecosystems, it was the strongest recorded globally in recent decades and exceeded in amplitude and spatial extent the previous hottest European summer in 2003. Earlier studies have not succeeded in comparing the magnitude of heat waves across continents and in time. This study introduces a new ... -
Modelled and observed sea-spray icing in Arctic-Norwegian waters
(Peer reviewed; Journal article; Tidsskriftsartikkel, 2016-11-15)Hazardous marine icing is a major concern for ships operating in Arctic waters during freezing conditions. Sea spray generated by the interaction between a ship and ocean waves is the most important water source in these dangerous icing events. Although there exist several data sets with observations of ice accretion in conjunction with meteorological and oceanographic parameters, these data sets ... -
An objective global climatology of polar lows based on reanalysis data
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-04-16)Here we present an objective global climatology of polar lows. In order to obtain objective detection criteria, the efficacy of several parameters for separating polar lows from other cyclones has been compared. The comparison and the climatology are based on the ERA‐Interim reanalysis from 1979 ‐ 2016 and the high‐resolution Arctic System Reanalysis from 2000 ‐ 2012. The most effective parameters ... -
On the Role of the Atmospheric Energy Transport in 2xCO2-Induced Polar Amplification in CESM1
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-06-12)A doubling of the atmospheric CO<sub>2</sub> content leads to global warming that is amplified in the polar regions. The CO<sub>2</sub> forcing also leads to a change of the atmospheric energy transport. This transport change affects the local warming induced by the CO<sub>2</sub> forcing. Using the Community Earth System Model (CESM), the direct response to the transport change is investigated. ... -
Polar Lows - Moist Baroclinic Cyclones in Four Different Vertical Wind Shear Environments
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-01-15)Polar lows are intense mesoscale cyclones that develop in polar marine air masses. Motivated by the large variety of their proposed intensification mechanisms, cloud structure, and ambient sub-synoptic environment, we use self-organising maps to classify polar lows. The method is applied to 370 polar lows in the north-eastern Atlantic, which were obtained by matching mesoscale cyclones from ... -
Poleward energy transport: is the standard definition physically relevant at all time scales?
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-05-17)Poleward energy transport in the atmosphere and oceans constitutes an important branch of the global energy budget, and its role in the climate system has been the subject of many studies. In the atmosphere, the transport is affected by “eddies” and large scale meridional cells, both with zero net mass transport across latitude circles, but also partly by processes associated with a net transport ... -
Spectral Decomposition and Extremes of Atmospheric Meridional Energy Transport in the Northern Hemisphere Midlatitudes
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-07-03)The atmospheric meridional energy transport in the Northern Hemisphere midlatitudes is mainly accomplished by planetary and synoptic waves. A decomposition into wave components highlights the strong seasonal dependence of the transport, with both the total transport and the contributions from planetary and synoptic waves peaking in winter. In both winter and summer months, poleward transport extremes ... -
Summers with low Arctic sea ice linked to persistence of spring atmospheric circulation patterns
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-05-30)The declining trend of Arctic September sea ice constitutes a significant change in the Arctic climate system. Large yearto-year variations are superimposed on this sea–ice trend, with the largest variability observed in the eastern Arctic Ocean. Knowledge of the processes important for this variability may lead to an improved understanding of seasonal and long-term changes. Previous studies suggest ...
