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Publications (10 of 13) Show all publications
Molinder, J., Körnich, H., Olsson, E. & Hessling, P. (2019). The Use of Uncertainty Quantification for the Empirical Modeling of Wind Turbine Icing. Journal of Applied Meteorology and Climatology, 58(9), 2019-2032
Open this publication in new window or tab >>The Use of Uncertainty Quantification for the Empirical Modeling of Wind Turbine Icing
2019 (English)In: Journal of Applied Meteorology and Climatology, ISSN 1558-8424, E-ISSN 1558-8432, Vol. 58, no 9, p. 2019-2032Article in journal (Refereed) Published
Abstract [en]

A novel uncertainty quantification method is used to evaluate the impact of uncertainties of parameters within the icing model in the modeling chain for icing-related wind power production loss forecasts. As a first step, uncertain parameters in the icing model were identified from the literature and personal communications. These parameters are the median volume diameter of the hydrometeors, the sticking efficiency for snow and graupel, the Nusselt number, the shedding factor, and the wind erosion factor. The sensitivity of these parameters on icing-related wind power production losses is examined. An icing model ensemble representing the estimated parameter uncertainties is designed using so-called deterministic sampling and is run for two periods over a total of 29 weeks. Deterministic sampling allows an exact representation of the uncertainty and, in future applications, further calibration of these parameters. Also, the number of required ensemble members is reduced drastically relative to the commonly used random-sampling method, thus enabling faster delivery and a more flexible system. The results from random and deterministic sampling are compared and agree very well, confirming the usefulness of deterministic sampling. The ensemble mean of the nine-member icing model ensemble generated with deterministic sampling is shown to improve the forecast skill relative to one single forecast for the winter periods. In addition, the ensemble spread provides valuable information as compared with a single forecast in terms of forecasting uncertainty. However, addressing uncertainties in the icing model alone underestimates the forecast uncertainty, thus stressing the need for a fully probabilistic approach in the modeling chain for wind power forecasts in a cold climate.

National Category
Meteorology and Atmospheric Sciences
Research subject
Meteorology
Identifiers
urn:nbn:se:smhi:diva-5444 (URN)10.1175/JAMC-D-18-0160.1 (DOI)000484447400001 ()
Available from: 2019-10-14 Created: 2019-10-14 Last updated: 2019-10-14Bibliographically approved
Amorim, J. H., Asker, C., Belusic, D., Carvalho, A., Engardt, M., Gidhagen, L., . . . Baklanov, A. (2018). Integrated Urban Services for European cities: the Stockholm case. WMO Bulletin, 67(2), 33-40
Open this publication in new window or tab >>Integrated Urban Services for European cities: the Stockholm case
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2018 (English)In: WMO Bulletin, ISSN 0042-9767, Vol. 67, no 2, p. 33-40Article in journal (Refereed) Published
Place, publisher, year, edition, pages
The World Meteorological Organization, 2018
National Category
Environmental Sciences
Research subject
Environment
Identifiers
urn:nbn:se:smhi:diva-5183 (URN)
Available from: 2019-04-15 Created: 2019-04-15 Last updated: 2019-04-15Bibliographically approved
Molinder, J., Körnich, H., Olsson, E., Bergstrom, H. & Sjoblom, A. (2018). Probabilistic forecasting of wind power production losses in cold climates: a case study. Wind Energy Science, 3(2), 667-680
Open this publication in new window or tab >>Probabilistic forecasting of wind power production losses in cold climates: a case study
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2018 (English)In: Wind Energy Science, ISSN 2213-3968, E-ISSN 2366-7443, Vol. 3, no 2, p. 667-680Article in journal (Refereed) Published
National Category
Meteorology and Atmospheric Sciences
Research subject
Meteorology
Identifiers
urn:nbn:se:smhi:diva-4995 (URN)10.5194/wes-3-667-2018 (DOI)000446813300001 ()
Available from: 2018-10-23 Created: 2018-10-23 Last updated: 2018-10-23Bibliographically approved
Berntell, E., Zhang, Q., Chafik, L. & Körnich, H. (2018). Representation of Multidecadal Sahel Rainfall Variability in 20th Century Reanalyses. Scientific Reports, 8, Article ID 10937.
Open this publication in new window or tab >>Representation of Multidecadal Sahel Rainfall Variability in 20th Century Reanalyses
2018 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 10937Article in journal (Refereed) Published
National Category
Meteorology and Atmospheric Sciences
Research subject
Meteorology
Identifiers
urn:nbn:se:smhi:diva-4797 (URN)10.1038/s41598-018-29217-9 (DOI)000439101600036 ()30026485 (PubMedID)
Available from: 2018-08-07 Created: 2018-08-07 Last updated: 2018-08-07Bibliographically approved
Olsson, J., Pers, C., Bengtsson, L., Pechlivanidis, I., Berg, P. & Körnich, H. (2017). Distance-dependent depth-duration analysis in high-resolution hydro-meteorological ensemble forecasting: A case study in Malmo City, Sweden. Environmental Modelling & Software, 93, 381-397
Open this publication in new window or tab >>Distance-dependent depth-duration analysis in high-resolution hydro-meteorological ensemble forecasting: A case study in Malmo City, Sweden
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2017 (English)In: Environmental Modelling & Software, ISSN 1364-8152, E-ISSN 1873-6726, Vol. 93, p. 381-397Article in journal (Refereed) Published
National Category
Oceanography, Hydrology and Water Resources
Research subject
Hydrology
Identifiers
urn:nbn:se:smhi:diva-4135 (URN)10.1016/j.envsoft.2017.03.025 (DOI)000403512500026 ()
Available from: 2017-08-08 Created: 2017-08-08 Last updated: 2018-01-13Bibliographically approved
Bengtsson, L. & Körnich, H. (2016). Impact of a stochastic parametrization of cumulus convection, using cellular automata, in a mesoscale ensemble prediction system. Quarterly Journal of the Royal Meteorological Society, 142(695), 1150-1159
Open this publication in new window or tab >>Impact of a stochastic parametrization of cumulus convection, using cellular automata, in a mesoscale ensemble prediction system
2016 (English)In: Quarterly Journal of the Royal Meteorological Society, ISSN 0035-9009, E-ISSN 1477-870X, Vol. 142, no 695, p. 1150-1159Article in journal (Refereed) Published
Abstract [en]

A stochastic parametrization for deep convection, based on cellular automata, has been evaluated in the high-resolution (2.5 km) ensemble prediction system Hirlam Aladin Regional Mesoscale Operational NWP Ensemble Prediction System (HarmonEPS). We studied whether such a stochastic physical parametrization, whilst implemented in a deterministic forecast model, can have an impact on the performance of the uncertainty estimates given by an ensemble prediction system. Various feedback mechanisms in the parametrization were studied with respect to ensemble spread and skill, in both subgrid and resolved precipitation fields. It was found that the stochastic parametrization improves the model skill in general, by reducing a positive bias in precipitation. This reduction in bias, however, led to a reduction in ensemble spread of precipitation. Overall, scores that measure the accuracy and reliability of probabilistic predictions indicate that the net impact (improved skill, degraded spread) of the ensemble prediction system is improved for 6 h accumulated precipitation with the stochastic parametrization and is rather neutral for other quantities examined.

National Category
Meteorology and Atmospheric Sciences
Research subject
Meteorology
Identifiers
urn:nbn:se:smhi:diva-2029 (URN)10.1002/qj.2720 (DOI)000372951300051 ()
Available from: 2016-05-03 Created: 2016-05-02 Last updated: 2017-11-30Bibliographically approved
Megner, L., Tan, D. G., Körnich, H., Isaksen, L., Horanyi, A., Stoffelen, A. & Marseille, G.-J. -. (2015). Linearity aspects of the ensemble of data assimilations technique. Quarterly Journal of the Royal Meteorological Society, 141(687), 426-432
Open this publication in new window or tab >>Linearity aspects of the ensemble of data assimilations technique
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2015 (English)In: Quarterly Journal of the Royal Meteorological Society, ISSN 0035-9009, E-ISSN 1477-870X, Vol. 141, no 687, p. 426-432Article in journal (Refereed) Published
Abstract [en]

We examine the linearity of the Ensemble of Data Assimilations (EDA) technique with respect to the amplitude of the applied observation perturbations. We provide explicit examples to assess the linear relationship between such modifications of the observing system and the resulting changes in the EDA ensemble spread. The results demonstrate that, for a state-of-the-art numerical weather prediction (NWP) system, such linearity between the applied observation perturbations and the EDA ensemble spread holds well for temporal and spatial regimes relevant to global medium-range weather prediction: specifically, for forecast lead-times of up to approximately 5 days, in the vertical throughout the troposphere up to the lower and middle stratosphere and for broad horizontal scales.

National Category
Meteorology and Atmospheric Sciences
Research subject
Meteorology
Identifiers
urn:nbn:se:smhi:diva-1992 (URN)10.1002/qj.2362 (DOI)000353413500007 ()
Available from: 2016-04-25 Created: 2016-03-03 Last updated: 2017-11-30Bibliographically approved
Schlutow, M., Becker, E. & Körnich, H. (2014). Positive definite and mass conserving tracer transport in spectral GCMs. Journal of Geophysical Research - Atmospheres, 119(20), 11562-11577
Open this publication in new window or tab >>Positive definite and mass conserving tracer transport in spectral GCMs
2014 (English)In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 119, no 20, p. 11562-11577Article in journal (Refereed) Published
Abstract [en]

A new scheme that solves the advection-diffusion equation for tracers in a spectral General Circulation Model (GCM) is presented. The main ideas are (1) using a monotonic and smooth functional of the tracer as prognostic variable to ensure positive definite concentrations and continuity of all derivatives and (2) defining an adjustable tracer-mass correction as a multiplication of the tracer in grid space, giving rise to an efficient correction in spectral space. Common standard benchmark tests for two-dimensional horizontal advection using deformational wind fields show that the new scheme is accurate and essentially not diffusive. A three-dimensional test is proposed in order to validate vertical transport. Additionally to standard error norms and global tracer mass, the entropy of mixing is introduced as another conservation constraint and utilized to determine the strength of the mass correction which is a free parameter. The transport scheme is applied in a mechanistic spectral GCM from the surface to the lower thermosphere. It is extended such that the mass correction takes the diffusion and other nonconservative effects explicitly into account. By this method we estimate the mean age of air along with its dependence on the turbulent horizontal Schmidt number.

Keywords
tracer transport, subgrid-scale diffusion, spectral method
National Category
Meteorology and Atmospheric Sciences
Research subject
Meteorology
Identifiers
urn:nbn:se:smhi:diva-101 (URN)10.1002/2014JD021661 (DOI)000345298100006 ()
Available from: 2015-04-14 Created: 2015-03-26 Last updated: 2017-12-04Bibliographically approved
Chen, H. W., Zhang, Q., Körnich, H. & Chen, D. (2013). A robust mode of climate variability in the Arctic: The Barents Oscillation. Geophysical Research Letters, 40(11), 2856-2861
Open this publication in new window or tab >>A robust mode of climate variability in the Arctic: The Barents Oscillation
2013 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 40, no 11, p. 2856-2861Article in journal (Refereed) Published
Abstract [en]

The Barents Oscillation (BO) is an anomalous wintertime atmospheric circulation pattern in the Northern Hemisphere that has been linked to the meridional flow over the Nordic Seas. There are speculations that the BO has important implications for the Arctic climate; however, it has also been suggested that the pattern is an artifact of Empirical Orthogonal Function (EOF) analysis due to an eastward shift of the Arctic Oscillation/North Atlantic Oscillation (AO/NAO). In this study, EOF analyses are performed to show that a robust pattern resembling the BO can be found during different time periods, even when the AO/NAO is relatively stationary. This BO has a high and stable temporal correlation with the geostrophic zonal wind over the Barents Sea, while the contribution from the AO/NAO is small. The surface air temperature anomalies over the Barents Sea are closely associated with this mode of climate variability.

Keywords
Barents Oscillation, Arctic Oscillation, North Atlantic Oscillation, Arctic climate variability, Barents Sea, Empirical Orthogonal Function
National Category
Meteorology and Atmospheric Sciences
Research subject
Meteorology
Identifiers
urn:nbn:se:smhi:diva-373 (URN)10.1002/grl.50551 (DOI)000321261600069 ()
Available from: 2015-04-10 Created: 2015-03-31 Last updated: 2017-12-04Bibliographically approved
Sundqvist, H. S., Holmgren, K., Fohlmeister, J., Zhang, Q., Bar Matthews, M., Spoetl, C. & Körnich, H. (2013). Evidence of a large cooling between 1690 and 1740 AD in southern Africa. Scientific Reports, 3, Article ID 1767.
Open this publication in new window or tab >>Evidence of a large cooling between 1690 and 1740 AD in southern Africa
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2013 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 3, article id 1767Article in journal (Refereed) Published
Abstract [en]

A 350-year-long, well-dated delta O-18 stalagmite record from the summer rainfall region in South Africa is positively correlated with regional air surface temperatures at interannual time scales. The coldest period documented in this record occurred between 1690 and 1740, slightly lagging the Maunder Minimum (1645-1710). A temperature reconstruction, based on the correlation between regional surface temperatures and the stalagmite delta O-18 variations, indicates that parts of this period could have been as much as 1.4 degrees C colder than today. Significant cycles of 22, 11 and 4.8 years demonstrate that the solar magnetic and the El Nino-Southern Oscillation cycle could be important drivers of multidecadal to interannual climate variability in this region. The observation that the most important driver of stalagmite delta O-18 on interannual time scales from this subtropical region is regional surface temperature cautions against deterministic interpretations of delta O-18 variations in low-latitude stalagmites as mainly driven by the amount of precipitation.

National Category
Meteorology and Atmospheric Sciences
Research subject
Meteorology
Identifiers
urn:nbn:se:smhi:diva-378 (URN)10.1038/srep01767 (DOI)000318334000004 ()
Available from: 2015-04-07 Created: 2015-03-31 Last updated: 2017-12-04Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-0524-6440

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