Research – Complex Systems Modelling – a research group at UiT

The Complex Systems Modelling group at UiT comprises the university’s statisticians and applied mathematicians, together with climate modelers and plasma physicists. The group is devoted to interdisciplinary efforts to analysis and modeling of complex physical, biological, and socio-economic systems. Our approach is to study complex systems through a combination of data analysis and modeling. We apply a broad spectrum of statistical methods, ranging from classical time series analysis to big-data methodology. And on the modeling side, we have expertise in dynamical systems, stochastic modeling, partial differential equations, fluid dynamics, and GCM climate modeling. The group is currently researching mathematical and statistical methods in climate science, fusion energy, linear and non-linear optics, and modern medical and epidemiological statistics. The group is a central part of the Faculty of Science and Technology’s thematic effort, The Dynamics of the Climate in the Arctic, where we collaborate closely with the Department of Geosciences. We are also hosting the newly established Aurora Center for Nonlinear Dynamics and Complex Systems Modeling (DYNAMO).

The Complex Earth System

♦ Rypdal, Martin wibe; Fredriksen, Hege-Beate; Myrvoll-Nilsen, Eirik; Rypdal, Kristoffer; Sørbye, Sigrunn Holbek. Emergent scale invariance and climate sensitivity. Climate 2018; Volum 6 (4). ISSN 2225-1154.s 1 – 15.s doi: 10.3390/cli6040093.

♦ Rypdal, Martin wibe; Fredriksen, Hege-Beate; Rypdal, Kristoffer; Steene, Rebekka. Emergent constraints on climate sensitivity. Nature 2018; Volum 563 (7729). ISSN 0028-0836.s E4 – E5.s doi: 10.1038/s41586-018-0639-4.

♦ Fredriksen, Hege-Beate; Rypdal, Martin wibe. Long-range persistence in global surface temperatures explained by linear multibox energy balance models. Journal of Climate 2017; Volum 30 (18). ISSN 0894-8755.s 7157 – 7168.s doi: 10.1175/JCLI-D-16-0877.1.

♦ Rypdal, Martin wibe. Early-warning signals for the onsets of Greenland interstadials and the younger dryas-preboreal transition. Journal of Climate 2016; Volum 29 (11). ISSN 0894-8755.s 4047 – 4056.s doi: 10.1175/JCLI-D-15-0828.1.

♦ Løvsletten, Ola; Rypdal, Martin wibe. Statistics of Regional Surface Temperatures after 1900: Long-Range versus Short-Range Dependence and Significance of Warming Trends. Journal of Climate 2016; Volum 29 (11). ISSN 0894-8755.s 4057 – 4068.s doi: 10.1175/JCLI-D-15-0437.1.

♦ Rypdal, Martin wibe; Rypdal, Kristoffer. Late Quaternary temperature variability described as abrupt transitions on a 1/f noise background. Earth System Dynamics 2016; Volum 7. ISSN 2190-4979.s 281 – 293.s doi: 10.5194/esd-7-281-2016.

♦ Rypdal, Kristoffer; Rypdal, Martin wibe; Fredriksen, Hege-Beate. Spatiotemporal long-range persistence in earth’s temperature field: Analysis of stochastic-diffusive energy balance models. Journal of Climate 2015; Volum 28 (21). ISSN 0894-8755.s 8379 – 8395.s doi: 10.1175/JCLI-D-15-0183.1.

♦ Rypdal, Martin wibe; Rypdal, Kristoffer. Long-memory effects in linear response models of Earth’s temperature and implications for future global warming. Journal of Climate 2014; Volum 27 (14). ISSN 0894-8755.s 5240 – 5258.s doi: 10.1175/JCLI-D-13-00296.1.

Complex fusion plasmas

Selected publications:

♦ Theodorsen, Audun; Garcia, Odd Erik. Probability distribution functions for intermittent scrape-off layer plasma fluctuations. Plasma Physics and Controlled Fusion 2018; Volum 60 (3). ISSN 0741-3335.s 1 – 14.s doi: 10.1088/1361-6587/aa9f9c.

♦ Theodorsen, Audun; Garcia, Odd Erik. Level crossings and excess times due to a superposition of uncorrelated exponential pulses. Physical review. E 2018; Volum 97 (1). ISSN 2470-0045.s 1 – 18.s doi: 10.1103/PhysRevE.97.012110.

♦ Kube, Ralph; Garcia, Odd Erik; Theodorsen, Audun; Brunner, Daniel; Kuang, Adam; LaBombard, Brian; Terry, James L. Intermittent electron density and temperature fluctuations and associated fluxes in the Alcator C-Mod scrape-off layer. Plasma Physics and Controlled Fusion 2018; Volum 60 (6). ISSN 0741-3335.s 1 – 16.s doi: 10.1088/1361-6587/aab726.

♦ Garcia, Odd Erik; Kube, Ralph; Theodorsen, Audun; Labombard, B; Terry, J.L. Intermittent fluctuations in the Alcator C-Mod scrape-off layer for ohmic and high confinement mode plasmas. Physics of Plasmas 2018; Volum 25 (5). ISSN 1070-664X.s doi: 10.1063/1.5018709.

♦ Garcia, Odd Erik; Theodorsen, Audun. Intermittent fluctuations due to uncorrelated Lorentzian pulses. Physics of Plasmas 2018; Volum 25 (1). ISSN 1070-664X.s doi: 10.1063/1.5020555.

♦ Garcia, Odd Erik; Theodorsen, Audun. Auto-correlation function and frequency spectrum due to a super-position of uncorrelated exponential pulses. Physics of Plasmas 2017; Volum 24 (3). ISSN 1070-664X.s 1 – 13.s doi: 10.1063/1.4978955.

♦ Theodorsen, Audun; Garcia, Odd Erik; Kube, Ralph; LaBombard, Brian; Terry, Jim L. Relationship between frequency power spectra and intermittent, large-amplitude bursts in the Alcator C-Mod scrape-off layer. Nuclear Fusion 2017; Volum 57 (11). ISSN 0029-5515.s 1 – 7.s doi: 10.1088/1741-4326/aa7e4c.

♦ Theodorsen, Audun; Garcia, Odd Erik; Rypdal, Martin Wibe. Statistical properties of a filtered Poisson process with additive random noise: distributions, correlations and moment estimation. Physica Scripta 2017; Volum 92 (5). ISSN 0031-8949.s doi: 10.1088/1402-4896/aa694c.

♦ Garcia, Odd Erik; Theodorsen, Audun. Power law spectra and intermittent fluctuations due to uncorrelated Lorentzian pulses. Physics of Plasmas 2017; Volum 24 (2). ISSN 1070-664X.s 1 – 5.s doi: 10.1063/1.4975645.

Climate dynamics

Selected publications:

♦ Naakka, Tuomas; Nygård, Tiina; Vihma, Timo; Sedlar, Joseph; Graversen, Rune. Atmospheric moisture transport between mid-latitudes and the Arctic: Regional, seasonal and vertical distributions. International Journal of Climatology 2019; Volum 39 (6). ISSN 0899-8418.s 2862 – 2879.s doi: 10.1002/joc.5988.

♦ Graversen, Rune; Burtu, Mattias. Arctic amplification enhanced by latent energy transport of atmospheric planetary waves. Quarterly Journal of the Royal Meteorological Society 2016; Volum 142 (698). ISSN 0035-9009.s 2046 – 2054.s doi: 10.1002/qj.2802.

♦ Fritzner, Sindre Markus; Graversen, Rune; Christensen, Kai Håkon; Rostosky, Philip; Wang, Keguang. Impact of assimilating sea ice concentration, sea ice thickness and snow depth in a coupled ocean-sea ice modelling system. The Cryosphere 2019; Volum 13 (2). ISSN 1994-0416.s 491 – 509.s doi: 10.5194/tc-13-491-2019.

♦ Stoll, Patrick; Graversen, Rune; Noer, Gunnar; Hodges, Kevin I. An objective global climatology of polar lows based on reanalysis data. Quarterly Journal of the Royal Meteorological Society 2018; Volum 144 (716). ISSN 0035-9009.s 2099 – 2117.s doi: 10.1002/qj.3309.

♦ Graversen, Rune; Langen, Peter; Mauritsen, Thorsten. Polar Amplification in CCSM4: Contributions from the Lapse Rate and Surface Albedo Feedbacks. Journal of Climate 2014; Volum 27. ISSN 0894-8755.s 4433 – 4450.s doi: 10.1175/JCLI-D-13-00551.1.

Statistics and analytics

Selected publications:

♦ Sørbye, S. H., Illian, J. B., Simpson, D. P., Burslem, D. and Rue, H. Careful prior specification avoids incautious inference for log-Gaussian Cox point processes. Journal of the Royal Statistical Society, Series C, 2018. doi:10.1111/rssc.12321.

♦ Sørbye, S. H.; Myrvoll-Nilsen, Eirik; Rue, Håvard. An approximate fractional Gaussian noise model with O(n) computational cost. Statistics and computing 2018. doi: 10.1007/s11222-018-9843-1.

♦ Sørbye, Sigrunn Holbek; Rue, Håvard. Fractional Gaussian noise: Prior specification and model comparison. Environmetrics 2017; Volum 29 (5-6). ISSN 1180-4009.s 1 – 12.s doi: 10.1002/env.2457.

♦ Sørbye, Sigrunn Holbek; Rue, Håvard. Penalised Complexity Priors for Stationary Autoregressive Processes. Journal of Time Series Analysis 2017; Volum 38 (6). ISSN 0143-9782.s 923 – 935.s doi: 10.1111/jtsa.12242.

♦ Rue, Håvard; Riebler, Andrea Ingeborg; Sørbye, Sigrunn Holbek; Illian, Janine B.; Simpson, Daniel Peter; Lindgren, Finn Kristian. Bayesian Computing with INLA: A Review. Annual Review of Statistics and Its Application 2017; Volum 4. ISSN 2326-8298.s 395 – 421.s doi: 10.1146/annurev-statistics-060116-054045.

♦ Løvsletten, Ola. Consistency of detrended fluctuation analysis. Physical Review E. Statistical, Nonlinear, and Soft Matter Physics 2017; Volum 96:012141 (1). ISSN 1063-651X.s 1 – |10.s doi: 10.1103/PhysRevE.96.012141.

Ecology and epidemiology

Selected publications:

♦ Rypdal M. and G. Sugihara, Inter-outbreak stability reflects the size of the susceptible pool and forecasts magnitudes of seasonal epidemics, Nature Communications 10, 2374, 2019, doi: 10.1038/s41467-019-10099-y

♦ Rypdal, Martin wibe; Rypdal, Veronika Gjertsen; Burney, Jennifer A.; Cayan, Daniel; Bainto, Emelia; Skochko, Shannon; Tremoulet, Adriana H.; Creamean, Jessie; Shimizu, Chisato; Kim, Ji-Hoon; Burns, Jane C. Clustering and climate associations of Kawasaki Disease in San Diego County suggest environmental triggers. Scientific Reports 2018; Volum 8:16140. ISSN 2045-2322.s 1 – 9.s doi: 10.1038/s41598-018-33124-4.

♦ Rypdal, Veronika Gjertsen; Arnstad, Ellen Dalen; Aalto, Kristiina; Berntson, Lillemor; Ekelund, Maria; Fasth, Anders; Glerup, Mia; Herlin, Troels; Nielsen, Susan; Peltoniemi, Suvi; Zak, Marek; Rygg, Marite; Rypdal, Martin Wibe; Nordal, Ellen Berit. Predicting unfavorable long-term outcome in juvenile idiopathic arthritis: Results from the Nordic cohort study. Arthritis Research & Therapy 2018; Volum 20 (91). ISSN 1478-6362.s doi: 10.1186/s13075-018-1571-6.

♦ Ytterstad E, Frailty in Survival Analysis of Widowhood Mortality, Journal of Probability and Statistics, 2018, 2378798, 2018. (Link to paper)

Linear and non-linear optics

Selected publications:

♦ Jakobsen, Per; Mansuripur, Masud; Kolesik, Miroslav. Leaky-mode expansion of the electromagnetic field inside dispersive spherical cavity. Journal of Mathematical Physics 2018; 59 (3). ISSN 0022-2488.s doi: 10.1063/1.5006956.

♦ Juhász, David; Kolesik, Miro; Jakobsen, Per. Convergence and completeness for square-well Stark resonant state expansions. Journal of Mathematical Physics 2018; 59 (11). ISSN 0022-2488.s 113501-1 – 113501-17.s doi: 10.1063/1.5042523.

♦ Jakobsen, Per. Exact formula for the high harmonic response of a strongly driven two-level system. Physica Scripta 2015; Volum 90 (2). ISSN 0031-8949.s doi: 10.1088/0031-8949/90/2/025501.

♦ Jakobsen, Per. Bidirectional pulse propagation equation for extreme nonlinear optics. Physica Scripta 2014; Volum 89 (9). ISSN 0031-8949.s doi: 10.1088/0031-8949/89/9/095502.

♦ Kolesik, Miroslav; Brown, Jeremy M.; Teleki, Aba; Jakobsen, Per; Moloney, Jeremy V.; Wright, Ewan M. Metastable electronic states and nonlinear response for high-intensity optical pulses. Optica 2014; Volum 1 (5). ISSN 2334-2536.s 323 – 331.s doi: 10.1364/OPTICA.1.000323.

♦ Bahl, Anand; Teleki, Aba; Jakobsen, Per; Wright, Ewan; Kolesik, Miroslav. Reflectionless Beam Propagation on a Piecewise Linear Complex Domain. Journal of Lightwave Technology 2014; Volum 32 (22). ISSN 0733-8724.s 4272 – 4278.s doi: 10.1109/JLT.2014.2354631.

♦ Jakobsen, Per; Moloney, J. V. The effect of longitudinal electric field components on the propagation of intense ultrashort optical pulses. Physica D : Non-linear Phenomena 2012; Volum 241 (19). ISSN 0167-2789.s 1603 – 1611.s doi: 10.1016/j.physd.2012.06.004.

Dynamical systems and complexity theory

Selected publications:

♦ Rypdal, Kristoffer; Kozelov, Boris V; Ratynskaia, Svetlana; Klumov, B.; Knapek, C.; Rypdal, Martin wibe. Scale-free vortex cascade emerging from random forcing in a strongly coupled system. New Journal of Physics 2008; Volum 10. ISSN 1367-2630.s 093018 – .s doi: 10.1088/1367-2630/10/9/093018.

♦ Rypdal, Kristoffer; Klumov, B.; Kozelov, Boris; Kube, Ralph; Rypdal, Martin wibe. Exploring the Analogy Between Freezing of a 2D Yukawa Liquid and 2D Decaying Turbulence in Fluids. AIP Conference Proceedings 2011; Volum 1397 (1). ISSN 0094-243X.s 72 – 77.s doi: 10.1063/1.3659743.

♦ Rypdal, Martin wibe; Rypdal, Kristoffer. A stochastic theory for temporal fluctuations in self-organized critical systems. New Journal of Physics 2008; Volum 10. ISSN 1367-2630.s 123010/1 – 11.s doi: 10.1088/1367-2630/10/12/123010.

♦ Rypdal, Martin wibe; Rypdal, Kristoffer. Modeling temporal fluctuations in avalanching systems. Physical Review E. Statistical, Nonlinear, and Soft Matter Physics 2008; Volum 78. ISSN 1063-651X.s 051127/1 – 11.s doi: 10.1103/PhysRevE.78.051127.

♦ Rypdal, Kristoffer; Rypdal, Martin wibe; Zivkovic, Tatjana; Kozelov, Boris V. Complexity in astro and geospace systems: the turbulence versus SOC controversy. AIP Conference Proceedings 2007; Volum 932. ISSN 0094-243X.s 203 – 208.

♦ Kruglikov, Boris Serafimovich; Rypdal, Martin Wibe. Entropy via multiplicity. Discrete and Continuous Dynamical Systems 2006; Volum 16. ISSN 1078-0947.s 395 – 410.

♦ Kruglikov, Boris Serafimovich; Rypdal, Martin Wibe. Dynamics and entropy in the Zhang model of self-organized criticality. Journal of statistical physics 2006; Volum 122. ISSN 0022-4715.

♦ Kruglikov, Boris Serafimovich; Rypdal, Martin Wibe. A piece-wise affine contracting map with positive entropy. Discrete and Continuous Dynamical Systems 2006; Volum 16. ISSN 1078-0947.s 393 – 394.

Space physics

Selected publications:

♦ Garcia, Odd Erik; Pecseli, Hans. Models for electrostatic drift waves with density variations along magnetic field lines. Geophysical Research Letters 2013; Volum 40 (21). ISSN 0094-8276.s 5565 – 5569.s doi: 10.1002/2013GL057802.

♦ Rypdal, Martin wibe; Rypdal, Kristoffer. Is there long-range memory in solar activity on timescales shorter than the sunspot period?. Journal of Geophysical Research – Space Physics 2012; Volum 117. ISSN 2169-9380.s doi: 10.1029/2011JA017283.

♦ Rypdal, Martin wibe; Rypdal, Kristoffer. Discerning a linkage between solar wind turbulence and ionospheric dissipation by a method of confined multifractal motions. Journal of Geophysical Research – Space Physics 2011; Volum 226. ISSN 2169-9380.s A02202 – .s doi: 10.1029/2010JA015907.

♦ Rypdal, Martin wibe; Rypdal, Kristoffer. Stochastic modeling of the AE index and its relation to fluctuations in B-z of the IMF on time scales shorter than substorm duration. Journal of Geophysical Research – Space Physics 2010; Volum 115. ISSN 2169-9380.s doi: 10.1029/2010JA015463.

♦ Rypdal, Martin wibe; Rypdal, Kristoffer. Testing Hypotheses about Sun-Climate Complexity Linking. Physical Review Letters 2010; Volum 104 (12). ISSN 0031-9007.s doi: 10.1103/PhysRevLett.104.128501.

♦ Hall, Chris; Rypdal, Kristoffer; Rypdal, Martin wibe. The E region at 69 degrees N, 19 degrees E: Trends, significances, and detectability. Journal of Geophysical Research – Space Physics 2011; Volum 116. ISSN 2169-9380.s A05309 – .s doi: 10.1029/2011JA016431.

Complex market dynamics

Selected publications:

♦ Løvsletten, Ola; Rypdal, Martin wibe. Approximated maximum likelihood estimation in multifractal random walks. Physical Review E. Statistical, Nonlinear, and Soft Matter Physics 2012; Volum 85 (4). ISSN 1063-651X.s doi: 10.1103/PhysRevE.85.046705.

♦ Rypdal, Martin wibe; Sirnes, Espen; Løvsletten, Ola; Rypdal, Kristoffer. Assessing market uncertainty by means of a time-varying intermittency parameter for asset price fluctuations. Physica A: Statistical Mechanics and its Applications 2013. ISSN 0378-4371.

♦ Rypdal, Martin wibe; Løvsletten, Ola. Modeling electricity spot prices using mean-reverting multifractal processes. Physica A: Statistical Mechanics and its Applications 2013; Volum 392 (1). ISSN 0378-4371.s 194 – 207.s doi: 10.1016/j.physa.2012.08.004.

Scientific computing

Selected publications:

♦ Kilen, Isak Ragnvald; Jakobsen, Per. Computing the Casimir force using regularized boundary integral equations. Physica Scripta 2014; 89 (11). ISSN 0031-8949.s doi: 10.1088/0031-8949/89/11/115205.

♦ Jakobsen, Per. Calculating optical forces using the boundary integral method. Physica Scripta 2009; 80 (3). ISSN 0031-8949.s doi: 10.1088/0031-8949/80/03/035401.