DATE:

Friday, November 6, 2020

TIME:

3:30 PM

LOCATION:

Virtual Zoom Conference

SPEAKER:

Dr. Bo-Wen Shen, Mathematics and Statistics, San Diego State University

ABSTRACT:

Over 50 years since Lorenz√¢¬Ä¬ôs 1963 study and a follow-up presentation in 1972, the statement “weather is chaotic√¢¬Ä¬ô√¢¬Ä¬ô has been well accepted. Such a view turns our attention from regularity associated with Laplace√¢¬Ä¬ôs view of determinism to irregularity associated with chaos. In contrast to single type chaotic solutions, recent studies using a generalized Lorenz model (GLM, Shen 2019a; Shen et al. 2019) have focused on the coexistence of chaotic and regular solutions that appear within the same model using the same modeling configurations but different initial conditions. The results, with attractor coexistence, suggest that the entirety of weather possesses a dual nature of chaos and order with distinct predictability (e.g., Shen et al. 2020). The refined view on the dual nature of weather is neither too optimistic nor pessimistic as compared to the Laplacian view of deterministic predictability that is unlimited and the Lorenz view of deterministic chaos with finite predictability. The refined view may unify our theoretical understanding of different predictability within various types of solutions of Lorenz models and recent numerical simulations of advanced global weather/climate models that can simulate large-scale tropical systems (e.g., African easterly waves and Madden-Julian Oscillations) beyond two weeks (e.g., Shen 2019b; Judt 2020).

In this study, based on the GLM, we discuss the following two mechanisms that may enable or modulate two kinds of attractor coexistence and, thus, contribute to distinct predictability: (1) the aggregated negative feedback of small-scale convective processes that can produce stable non-trivial equilibrium points and, thus, enable the appearance of stable steady-state solutions and their coexistence with chaotic or nonlinear oscillatory solutions, referred to as the 1st and 2nd kinds of attractor coexistence; and (2) the modulation of large-scale time varying forcing (heating) that can determine (or modulate) the alternative appearance of two kinds of attractor coexistence. Based on our results, we then discuss new opportunities and challenges in predictability research with the aim of improving predictions at extended-range time scales, as well as sub-seasonal to seasonal time scales.

HOST:

Jose Castillo

VIDEO: