Category: Publications2024

Publications that published in 2024

A multi-scenario analysis of climate impacts on plankton and fish stocks in northern seas

Sandø, A.B., Hjøllo, S.S., Hansen, C., Skogen, M.D., Hordoir, R., Sundby,S. 2024: A multi-scenario analysis of climate impacts on plankton and fish stocks in northern seas. https://doi.org/10.1111/faf.12834

Summary: Globally, impacts of climate change display an increasingly negative development of marine biomass, but there is large regional variability. In this analysis of future climate change on stock productivity proxies for the North Sea, the Norwegian Sea, and the Barents Sea, we have provided calculations of accumulated directional effects as a function of climate exposure and sensitivity attributes. Based on modelled changes in physical and biogeochemical variables from three scenarios and knowledge of 13 different stocks’ habitats and response to climate variations, climate exposures have been weighted, and corresponding directions these have on the stocks have been decided. SSP1-2.6 gives mostly a weak cooling in all regions with almost negligible impacts on all stocks. SSP2-4.5 and SSP5-8.5 both provide warmer conditions in the long term but are significantly different in the last 30 years of the century when the SSP5-8.5 warming is much stronger. The results show that it is the current stocks of cod and Calanus finmarchicusin the North Sea, and polar cod and capelin in the Barents Sea that will be most negatively affected by strong warming. Stocks that can migrate north into the northern seas such as hake in the Norwegian Sea, or stocks that are near the middle of the preferred temperature range such as mackerel and herring in the Norwegian Sea and cod and Calanus finmarchicus in the Barents Sea, are the winners in a warmer climate. The highly different impacts between the three scenarios show that multiple scenario studies of this kind matter.

Link to publication. You are most welcome to contact us or the corresponding author(s) directly, if you have questions.

Probabilistic models for harmful algae: application to the Norwegian coast

Silva, E., Brajard, J., Counillon, F., Pettersson, L.H., Naustvoll, L. 2024: Probabilistic models for harmful algae: application to the Norwegian coast. Environmental Data Science. https://doi.org/10.1017/eds.2024.11

Summary: We have developed probabilistic models to estimate the likelihood of harmful algae presence and outbreaks along the Norwegian coast, which can help optimization of the national monitoring program and the planning of mitigation actions. We employ support vector machines to calibrate probabilistic models for estimating the presence and harmful abundance (HA) of eight toxic algae found along the Norwegian coast, including Alexandrium spp., Alexandrium tamarense, Dinophysis acuta, Dinophysis acuminata, Dinophysis norvegica, Pseudo-nitzschia spp., Protoceratium reticulatum, and Azadinium spinosum. The inputs are sea surface temperature, photosynthetically active radiation, mixed layer depth, and sea surface salinity. The probabilistic models are trained with data from 2006 to 2013 and tested with data from 2014 to 2019. The presence models demonstrate good statistical performance across all taxa, with R (observed presence frequency vs. predicted probability) ranging from 0.69 to 0.98 and root mean squared error ranging from 0.84% to 7.84%. Predicting the probability of HA is more challenging, and the HA models only reach skill with four taxa (Alexandrium spp., A. tamarense, D. acuta, and A. spinosum). There are large differences in seasonal and geographical variability and sensitivity to the model input of different taxa, which are presented and discussed. The models estimate geographical regions and periods with relatively higher risk of toxic species presence and HA, and might optimize the harmful algae monitoring. The method can be extended to other regions as it relies only on remote sensing and model data as input and running national programs of toxic algae monitoring.

Link to publication. You are most welcome to contact us or the corresponding author(s) directly, if you have questions.

A simple statistical post-processing scheme for enhancing the skill of seasonal SST predictions in the tropics

Richter, I., Ratnam, J.V., Martineau, P., Oettli, P., Doi, T., Ogata, T., Kataoka, T., Counillon, F. 2024: A simple statistical post-processing scheme for enhancing the skill of seasonal SST predictions in the tropics. Monthly Weather Review. https://doi.org/10.1175/MWR-D-23-0266.1

Summary: The prediction of year-to-year climate variability patterns, such as El Niño, offers potential benefits to society by aiding mitigation and adaptation efforts. Current prediction systems, however, may still have substantial room for improvement due to systematic model errors and due to imperfect initialization of the oceanic state at the start of predictions. Here we develop a statistical correction scheme to improve prediction skill after forecasts have been completed. The scheme shows some moderate success in improving the skill for predicting El Niño and similar climate patterns in seven prediction systems. Our results not only indicate a potential for improving prediction skill after the fact but also point to the importance of improving the way prediction systems are initialized.

Link to publication. You are most welcome to contact us or the corresponding author(s) directly, if you have questions.

Causal links between sea-ice variability in the Barents-Kara Seas and oceanic and atmospheric drivers

Dörr, J., Årthun, M., Docquier, D., Li, C., Eldevik, T. 2024: Causal links between sea-ice variability in the Barents-Kara Seas and oceanic and atmospheric drivers. Geophysical Research Letters. https://doi.org/10.1029/2024GL108195

Summary: The sea ice in the Barents and Kara Seas (BKS) is melting due to Arctic warming, but this is overlaid by large natural variability. This variability is caused by variations in the ocean and the atmosphere, but it is not clear which is more important in which parts of the region. We use a relatively new method that allows us to quantify cause-effect relationships between sea ice and atmospheric and oceanic drivers. We find that in the north of the BKS, the atmosphere has the biggest impact, in the central and northeastern parts, it is the heat from the ocean, and in the south, it is the local sea temperature. We also find that wind patterns over the Nordic Seas affect how much oceanic heat comes into the Barents Sea, and that, in turn, affects the sea ice. Looking ahead, as the ice is expected to melt more in the future, the atmosphere is likely to become more important in driving sea ice variability in the BKS. This study helps us better understand how the ocean and atmosphere work together to influence the yearly changes in sea ice in this region.

Link to publication. You are most welcome to contact us or the corresponding author(s) directly, if you have questions.

Projecting spring consecutive rainfall events in the Three Gorges Reservoir based on triple-nested dynamical downscaling

Zheng, Y. X., S. L. Li, N. Keenlyside, S. P. He, Suo, L.L. 2024: Projecting spring consecutive rainfall events in the Three Gorges Reservoir based on triple-nested dynamical downscaling. Adv. Atmos. Sci. https://doi.org/10.1007/s00376-023-3118-2

Summary: Spring consecutive rainfall events (CREs) are key triggers of geological hazards in the Three Gorges Reservoir area (TGR), China. However, previous projections of CREs based on the direct outputs of global climate models (GCMs) are subject to considerable uncertainties, largely caused by their coarse resolution. This study applies a triple-nested WRF (Weather Research and Forecasting) model dynamical downscaling, driven by a GCM, MIROC6 (Model for Interdisciplinary Research on Climate, version 6), to improve the historical simulation and reduce the uncertainties in the future projection of CREs in the TGR. Results indicate that WRF has better performances in reproducing the observed rainfall in terms of the daily probability distribution, monthly evolution and duration of rainfall events, demonstrating the ability of WRF in simulating CREs. Thus, the triple-nested WRF is applied to project the future changes of CREs under the middle-of-the-road and fossil-fueled development scenarios. It is indicated that light and moderate rainfall and the duration of continuous rainfall spells will decrease in the TGR, leading to a decrease in the frequency of CREs. Meanwhile, the duration, rainfall amount, and intensity of CREs is projected to regional increase in the central-west TGR. These results are inconsistent with the raw projection of MIROC6. Observational diagnosis implies that CREs are mainly contributed by the vertical moisture advection. Such a synoptic contribution is captured well by WRF, which is not the case in MIROC6, indicating larger uncertainties in the CREs projected by MIROC6.

Link to publication. You are most welcome to contact us or the corresponding author(s) directly, if you have questions.

Intercomparison of initialization methods for Seasonal-to-Decadal Climate Predictions with the NorCPM

Garcia-Oliva, L., Counillon, F., Bethke, I., Keenlyside, N. 2024: Intercomparison of initialization methods for Seasonal-to-Decadal Climate Predictions with the NorCPM. Clim Dyn. https://doi.org/10.1007/s00382-024-07170-w

Summary: Initialization is essential for accurate seasonal-to-decadal (S2D) climate predictions. The initialization schemes used differ on the component initialized, the Data Assimilation method, or the technique. We compare five popular schemes within NorCPM following the same experimental protocol: reanalysis from 1980 to 2010 and seasonal and decadal predictions initialized from the reanalysis. We compare atmospheric initialization—Newtonian relaxation (nudging)—against ocean initialization—Ensemble Kalman Filter—(ODA). On the atmosphere, we explore the benefit of full-field (NudF-UVT) or anomaly (NudA-UVT) nudging of horizontal winds and temperature (U, V, and T) observations. The scheme NudA-UV nudges horizontal winds to disentangle the role of wind-driven variability. The ODA+NudA-UV scheme is a first attempt at joint initialization of ocean and atmospheric components in NorCPM. During the reanalysis, atmospheric nudging improves the synchronization of the atmosphere and land components with the observed data. Conversely, ODA is more effective at synchronizing the ocean component with observations. The atmospheric nudging schemes are better at reproducing specific events, such as the rapid North Atlantic subpolar gyre shift. An abrupt climatological change using the NudA-UV scheme demonstrates that energy conservation is crucial when only assimilating winds. ODA outperforms atmospheric-initialized versions for S2D global predictions, while atmospheric nudging is preferable for accurately initializing phenomena in specific regions, with the technique’s benefit depending on the prediction’s temporal scale. For instance, atmospheric full-field initialization benefits the tropical Atlantic Niño at 1-month lead time, and atmospheric anomaly initialization benefits longer lead times, reducing hindcast drift. Combining atmosphere and ocean initialization yields sub-optimal results, as sustaining the ensemble’s reliability—required for ODA’s performance—is challenging with atmospheric nudging.

Link to publication. You are most welcome to contact us or the corresponding author(s) directly, if you have questions.

The Role of Ocean Heat Content on the Madden–Julian Oscillation (PhD thesis)

Ashneel Chandra (2024-03-19): The Role of Ocean Heat Content on the Madden–Julian Oscillation. PhD thesis, University of Bergen, Bergen, Norway. https://hdl.handle.net/11250/3124162

Summary: The overall goal of this dissertation is to understand the role of upper ocean heat content (OHC) and equatorial ocean dynamics on the Madden-Julian Oscillation (MJO). While the response of the ocean to atmospheric forcing on intraseasonal timescales has been studied extensively, the feedback of OHC on the MJO has not been systematically investigated. Recently, a new line of research has emerged that highlights the interaction between ocean dynamics, OHC, and the MJO in the Indian Ocean (IO) basin. In the IO, synchronization between oceanic equatorial waves and the MJO is possible because of the basin-scale, the propagation speed of oceanic equatorial waves, and the timescale of MJO variability. In a series of three papers, this thesis aims to contribute to understanding the variability and interactions between the MJO, equatorial ocean dynamics, and OHC in the IO basin.

Link to publication. You are most welcome to contact us or the corresponding author(s) directly, if you have questions.

Present and future drivers of Arctic sea ice variability (PhD thesis)

Jacob Dörr (2024-03-07): Present and future drivers of Arctic sea ice variability. PhD thesis, University of Bergen, Bergen, Norway. https://hdl.handle.net/11250/3124162

Summary: The long-term decline of the Arctic sea-ice cover is overlaid by substantial interannual to decadal internal variability. This variability is a major source of uncertainty in projections over the next decades, including the timing of a seasonally ice-free Arctic. Understanding the mechanisms of internal variability and how they modify the evolution of the sea-ice cover will enable better predictions, and help to constrain future projections of the sea-ice cover. As the Arctic becomes ice-free in summer, future sea-ice loss and variability will be largest in winter. Winter sea-ice variability is currently strongest in the Barents Sea, but as the ice edge retreats, more central regions of the Arctic Ocean will see increased sea-ice variability, where the mechanisms and drivers might be different. This thesis advances our understanding of the present and future atmospheric and oceanic drivers of winter sea-ice variability, and how internal variability has modified the observed changes in the summer and winter sea-ice cover.

Link to publication. You are most welcome to contact us or the corresponding author(s) directly, if you have questions.

Nonstationarity in the NAO–Gulf Stream SST Front Interaction

Famooss Paolini, L., Omrani, N.-E., Bellucci, A., Athanasiadis, P.J., Ruggieri, P., Patrizio, C.R., Keenlyside, N. 2024: Nonstationarity in the NAO–Gulf Stream SST front interaction. J Clim. https://doi.org/10.1175/JCLI-D-23-0476.1

Summary: The interaction between the North Atlantic Oscillation (NAO) and the latitudinal shifts of the Gulf Stream sea surface temperature front (GSF) has been the subject of extensive investigations. There are indications of nonstationarity in this interaction, but differences in the methodologies used in previous studies make it difficult to draw consistent conclusions. Furthermore, there is a lack of consensus on the key mechanisms underlying the response of the GSF to the NAO. This study assesses the possible nonstationarity in the NAO–GSF interaction and the mechanisms underlying this interaction during 1950–2020, using reanalysis data. Results show that the NAO and GSF indices covary on the decadal time scale but only during 1972–2018. A secondary peak in the NAO–GSF covariability emerges on multiannual time scales but only during 2005–15. The nonstationarity in the decadal NAO–GSF covariability is also manifested in variations in their lead–lag relationship. Indeed, the NAO tends to lead the GSF shifts by 3 years during 1972–90 and by 2 years during 1990–2018. The response of the GSF to the NAO at the decadal time scale can be interpreted as the joint effect of the fast response of wind-driven oceanic circulation, the response of deep oceanic circulation, and the propagation of Rossby waves. However, there is evidence of Rossby wave propagation only during 1972–90. Here it is suggested that the nonstationarity of Rossby wave propagation caused the time lag between the NAO and the GSF shifts on the decadal time scale to differ between the two time periods.

Link to publication. You are most welcome to contact us or the corresponding author(s) directly, if you have questions.

Recent Ventures in Interdisciplinary Arctic Research: The ARCPATH Project

Ogilvie, A.E., King, L.A., Keenlyside, N., Counillon, F., Daviđsdóttir, B., Einarsson, N., Gulev, S., Fan, K., Koenigk, T., McGoodwin, J.R. and Rasmusson, M.H. 2024: Recent Ventures in Interdisciplinary Arctic Research: The ARCPATH Project. Adv. Atmos. Sci. https://doi.org/10.1007/s00376-023-3333-x

Summary: This paper celebrates Professor Yongqi GAO’s significant achievement in the field of interdisciplinary studies within the context of his final research project Arctic Climate Predictions: Pathways to Resilient Sustainable Societies – ARCPATH (https://www.svs.is/en/projects/finished-projects/arcpath). The disciplines represented in the project are related to climatology, anthropology, marine biology, economics, and the broad spectrum of social-ecological studies. Team members were drawn from the Nordic countries, Russia, China, the United States, and Canada. The project was transdisciplinary as well as interdisciplinary as it included collaboration with local knowledge holders. ARCPATH made significant contributions to Arctic research through an improved understanding of the mechanisms that drive climate variability in the Arctic. In tandem with this research, a combination of historical investigations and social, economic, and marine biological fieldwork was carried out for the project study areas of Iceland, Greenland, Norway, and the surrounding seas, with a focus on the joint use of ocean and sea-ice data as well as social-ecological drivers. ARCPATH was able to provide an improved framework for predicting the near-term variation of Arctic climate on spatial scales relevant to society, as well as evaluating possible related changes in socioeconomic realms. In summary, through the integration of information from several different disciplines and research approaches, ARCPATH served to create new and valuable knowledge on crucial issues, thus providing new pathways to action for Arctic communities.

Link to publication. You are most welcome to contact us or the corresponding author(s) directly, if you have questions.