06.11.2024, 14:00 - 16:00
– Campus Golm, Building 9, Room 2.22 and via Zoom
Institutskolloquium
Graphon Models for Inhomogeneous Random Graphs
Olga Klopp (Paris), Nicolas Verzelen (Montpellier)
Elena Saggioro (University of Reading, UK)
The coupling between stratospheric and tropospheric dynamics is currently a topic of major interest [1,2]. In the context of the Southern Hemisphere (SH) summertime, reanalysis data seem to suggested that the stratospheric polar vortex acts as an organizing influence on the variability of the tropospheric zonal-mean circulation [3, 4, 5].
In order to test this potentially causal influence, which is currently quantified in terms of lagged cross-correlations, a novel inference technique based on Time-Series Bayesian Causal Networks [6,7,8] is adopted. Comparisons of a causal measure with the standard lagged cross-correlation analysis shows how the latter leads to highly biased results, if interpreted as a diagnostic for influence. In fact, cross-correlation is strongly affected by autocorrelation of individual time-series [9], which are particularly relevant for the stratospheric index.
The causal framework nonetheless supports the conclusion of a downward stratospheric influence during the spring-to-summer transition, which can be interpreted as a source of statistical predictability relevant to inform optimal model set up for seasonal forecasting.
References:
[1] J. Kidston et al., Nature Geoscience 8.6 (May 2015), pp. 433–440.
[2] O. P. Tripathi et al. , Quarterly Journal of the Royal Meteorological Society 141.689 (Oct. 2014), pp. 987–1003.
[3] R. X. Black et al. , Journal of the Atmospheric Sciences 64.8 (Aug. 2007), pp. 2968–2974.
[4] N. J. Byrne et al. , Journal of Climate 30.18 (Sept. 2017), pp. 7125–7139.
[5] N. J. Byrne et al. , Journal of Climate 31.9 (May 2018), pp. 3467–3483.
[6] I. Ebert-Uphoff et al. , Journal of Climate 25.17 (Sept. 2012), pp. 5648–5665.
[7] J. Runge et al, Physical Review Letters 108.25 (June 2012).
[8] J. Runge., Chaos 28.7 (July 2018), p. 075310.
[9] J. Runge et al., Journal of Climate 27.2 (Jan. 2014), pp. 720–739.
Invited by Sebastian Reich