arXiv subjects

Josef Ludescher

Publications and source records attributed to Josef Ludescher.

12 recordsLinked to original sources

arXiv2026

Climate network and complexity based ENSO forecast for 2026

The El Niño Southern Oscillation (ENSO) is the dominant driver of interannual global climate variability and can lead to extreme weather events such as droughts or flooding. Recently, we have developed several statistical approaches for early ENSO forecasting, in particular, its El Niño phase. The climate network-based approach allows forecasting the onset of an El Niño event or its absence about 1 year ahead [1]. The complexity-based approach allows additionally to forecast the magnitude of an upcoming El Niño event in the calendar year before the onset [2]. Additionally, we have developed methods for forecasting the type (Eastern Pacific or Central Pacific) of an El Niño [3] and for probabilistic forecasting of La Niña and neutral events [4], also by the end of the calendar year before the event. Here we present the forecasts of these methods for 2026. The climate network and the complexity-based approach do not provide concurring signals for this year. The combined forecast indicates that a neutral event is more likely than an El Niño. If an El Niño develops in 2026, the complexity-based approach predicts a weaker event with a magnitude of $0.84\pm0.36$°C.

physics.ao-ph↗

arXiv2022

Teleconnections among Tipping Elements in the Earth System

Tipping elements of the Earth system may shift abruptly and irreversibly from one state to another at tipping points, resulting in a growing threat to our society. Yet, it is not fully clear how to assess and quantify the influence of a tipping element and how to explore the teleconnections between different tipping elements. To fill this knowledge gap, we propose a climate network approach to quantitatively analyze the global impacts of a prominent tipping element, the Amazon Rainforest Area (ARA). We find that regions, such as, the Tibetan Plateau (TP) and West Antarctic ice sheet, are characterized by higher network weighted links and exhibit strong correlations with the ARA. We then identify a teleconnection propagation path between the ARA and the TP. This path is robust under climate change as simulated by various climate models of CMIP5 and CMIP6. In addition, we detect early warning signals for critical transition in the snow cover extent on the Tibetan Plateau by applying critical slowing down indicators, lag-1 autocorrelation and detrended fluctuation analysis. We find that the snow cover of the TP has been losing stability since 2008, revealing that the TP is operating like a tipping element and approaching a potential tipping point. We further uncover that various climate extremes between the ARA and the TP are significantly synchronized under climate change. Our framework provides new insights into how tipping elements are linked to each other and into the potential predictability of cascading tipping dynamics.

physics.soc-ph↗

arXiv2022

Climate network and complexity based El Niño forecast for 2022

The El Niño Southern Oscillation (ENSO) is the most important driver of interannual global climate variability and can trigger extreme weather events and disasters in various parts of the globe. Recently, we have developed two approaches for the early forecasting of El Niño. The climate network-based approach allows forecasting the onset of an El Niño event about 1 year ahead. The complexity-based approach allows additionally to forecast the magnitude of an upcoming El Niño event in the calendar year before. Here we communicate the forecasts of both methods for 2022.

physics.ao-ph↗

arXiv2020

Statistical physics approaches to the complex Earth system

Global climate change, extreme climate events, earthquakes and their accompanying natural disasters pose significant risks to humanity. Yet due to the nonlinear feedbacks, strategic interactions and complex structure of the Earth system, the understanding and in particular the predicting of such disruptive events represent formidable challenges for both scientific and policy communities. During the past years, the emergence and evolution of Earth system science has attracted much attention and produced new concepts and frameworks. Especially, novel statistical physics and complex networks-based techniques have been developed and implemented to substantially advance our knowledge for a better understanding of the Earth system, including climate extreme events, earthquakes and Earth geometric relief features, leading to substantially improved predictive performances. We present here a comprehensive review on the recent scientific progress in the development and application of how combined statistical physics and complex systems science approaches such as, critical phenomena, network theory, percolation, tipping points analysis, as well as entropy can be applied to complex Earth systems (climate, earthquakes, etc.). Notably, these integrating tools and approaches provide new insights and perspectives for understanding the dynamics of the Earth systems. The overall aim of this review is to offer readers the knowledge on how statistical physics approaches can be useful in the field of Earth system science.

physics.soc-ph↗

arXiv2020

Network-based Approach and Climate Change Benefits for Forecasting the Amount of Indian Monsoon Rainfall

The Indian summer monsoon rainfall (ISMR) has a decisive influence on India's agricultural output and economy. Extreme deviations from the normal seasonal amount of rainfall can cause severe droughts or floods, affecting Indian food production and security. Despite the development of sophisticated statistical and dynamical climate models, a long-term and reliable prediction of the ISMR has remained a challenging problem. Towards achieving this goal, here we construct a series of dynamical and physical climate networks based on the global near surface air temperature field. We uncover that some characteristics of the directed and weighted climate networks can serve as efficient long-term predictors for ISMR forecasting. The developed prediction method produces a forecast skill of 0.5 with a 5-month lead-time in advance by using the previous calendar year's data. The skill of our ISMR forecast, is comparable to the current state-of-the-art models, however, with quite a short (i.e., within one month) lead-time. We discuss the underlying mechanism of our predictor and associate it with network-delayed-ENSO and ENSO-monsoon connections. Moreover, our approach allows predicting the all India rainfall, as well as forecasting the different Indian homogeneous regions' rainfall, which is crucial for agriculture in India. We reveal that global warming affects the climate network by enhancing cross-equatorial teleconnections between Southwest Atlantic, Western part of the Indian Ocean, and North Asia-Pacific with significant impacts on the precipitation in India. We find a hotspots area in the mid-latitude South Atlantic, which is the basis for our predictor. Remarkably, the significant warming trend in this area yields an improvement of the prediction skill.

physics.ao-ph↗

arXiv2020

Very early warning signal for El Niño in 2020 with a 4 in 5 likelihood

The El Niño Southern Oscillation (ENSO) is the most important driver of climate variability and can trigger extreme weather events and disasters in various parts of the globe. Recently we have developed a network approach, which allows forecasting an El Niño event about 1 year ahead. Here we communicate that since 2012 this network approach, which does not involve any fit parameter, correctly predicted the absence of El Niño events in 2012, 2013 and 2017 as well as the onset of the large El Niño event that started in 2014 and ended in 2016. Our model also correctly forecasted the onset of the last El Niño event in 2018. In September 2019, the model indicated the return of El Niño in 2020 with an 80% probability.

physics.ao-ph↗

arXiv2019

Complexity based approach for El Nino magnitude forecasting before the "spring predictability barrier"

The El Nino Southern Oscillation (ENSO) is one of the most prominent interannual climate phenomena. An early and reliable ENSO forecasting remains a crucial goal, due to its serious implications for economy, society, and ecosystem. Despite the development of various dynamical and statistical prediction models in the recent decades, the ``spring predictability barrier'' (SPB) remains a great challenge for long (over 6-month) lead-time forecasting. To overcome this barrier, here we develop an analysis tool, the System Sample Entropy (SysSampEn), to measure the complexity (disorder) of the system composed of temperature anomaly time series in the Nino 3.4 region. When applying this tool to several near surface air-temperature and sea surface temperature datasets, we find that in all datasets a strong positive correlation exists between the magnitude of El Nino and the previous calendar year's SysSampEn (complexity). We show that this correlation allows to forecast the magnitude of an El Nino with a prediction horizon of 1 year and high accuracy (i.e., Root Mean Square Error $=0.23^\circ C$ for the average of the individual datasets forecasts). For the on-going 2018 El Nino event, our method forecasts a weak El Nino with a magnitude of $1.11\pm 0.23^\circ C$. Our framework presented here not only facilitates a long--term forecasting of the El Nino magnitude but can potentially also be used as a measure for the complexity of other natural or engineering complex systems.

physics.ao-ph↗

arXiv2014

The significance of trends in long-term correlated records

We study the distribution $P(x;α,L)$ of the relative trend $x$ in long-term correlated records of length $L$ that are characterized by a Hurst-exponent $α$ between 0.5 and 1.5 obtained by DFA2. The relative trend $x$ is the ratio between the strength of the trend $Δ$ in the record measured by linear regression, and the standard deviation $σ$ around the regression line. We consider $L$ between 400 and 2200, which is the typical length scale of monthly local and annual reconstructed global climate records. Extending previous work by Lennartz and Bunde \cite{Lennartz2011} we show explicitely that $P$ follows the student-t distribution $P\propto [1+(x/a)^2/l]^{-(l+1)/2}$, where the scaling parameter $a$ depends on both $L$ and $α$, while the effective length $l$ depends, for $α$ below 1.15, only on the record length $L$. From $P$ we can derive an analytical expression for the trend significance $S(x;α, L)=\int_{-x}^x P(x';α,L)dx'$ and the border lines of the $95\%$ percent significance interval. We show that the results are nearly independent of the distribution of the data in the record, holding for Gaussian data as well as for highly skewed non-Gaussian data. For an application, we use our methodology to estimate the significance of Central West Antarctic warming.

physics.data-an↗

arXiv2013

Improved El Niño-Forecasting by Cooperativity Detection

Although anomalous episodical warming of the eastern equatorial Pacific, dubbed El Niño by Peruvian fishermen, has major (and occasionally devastating) impacts around the globe, robust forecasting is still limited to about six months ahead. A significant extension of the pre-warming time would be instrumental for avoiding some of the worst damages such as harvest failures in developing countries. Here we introduce a novel avenue towards El Niño-prediction based on network methods inspecting emerging teleconnections. Our approach starts from the evidence that a large-scale cooperative mode - linking the El Niño-basin (equatorial Pacific corridor) and the rest of the ocean - builds up in the calendar year before the warming event. On this basis, we can develop an efficient 12 months-forecasting scheme, i.e., achieve some doubling of the early-warning period. Our method is based on high-quality observational data as available since 1950 and yields hit rates above 0.5, while false-alarm rates are below 0.1.

physics.ao-ph↗

arXiv2009

Spatial Wilson loop in continuum, deconfining SU(2) Yang-Mills thermodynamics

The uniquess of the effective actions describing 4D SU(2) and SU(3) continuum, infinite-volume Yang-Mills thermodynamics in their deconfining and preconfining phases is made explicit. Subsequently, the spatial string tension is computed in the approach proposed by Korthals-Altes. This SU(2) calculation is based on a particular, effective two-loop correction to the pressure needed for the extraction of the hypothetic number density of isolated and screened magnetic monopoles or antimonopoles in the deconfining phase. By exponentiating the exchange of the tree-level massless but one-loop dressed mode within a quadratic spatial contour of side-length $L$ in the effective theory we demonstrate that for $L\to\infty$ the Wilson loop exhibits {\sl perimeter} law. This is in contrast to a rigorous {\sl lattice} result subject to the Wilson action and for this action valid at sufficiently high temperature. In the framework of the effective theory there is, however, a regime for small (spatially unresolved) $L$ were the exponent of the spatial Wilson loop possesses curvature as a function of $L$.

hep-th↗

arXiv2009

Thermal photon dispersion law and modified black-body spectra

Based on the postulate that photon propagation is governed by an SU(2) gauge principle we numerically compute the one-loop dispersion for thermalized photon propagation on the radiatively induced mass shell. Formerly, the dispersion was addressed by assuming $p^2=0$. While this approximation turns out to be excellent for temperatures $\le 2 T_{\tiny{CMB}}$ the exact result exhibits a much faster (power-like) shrinking of the gap in the black-body spectral intensity with rising temperature. Our previous statements on anomalous large-angle CMB temperature-temperature correlations, obtained in the approximation $p^2=0$, remain valid.

hep-th↗

arXiv2009

CMB dipole revisited

We re-evaluate the build-up of a horizon-sized temperature profile of amplitude $δT/T \sim 10^{-3}$ at $z\sim 1$ in light of an improved determination of the black-body anomaly, based on a pure SU(2) Yang-Mills theory, and the correction of a mistake in deriving the evolution equation for $δT$. Our present results for the temperature profiles hardly are distinguishable from those published previously.

hep-th↗