Journal Article 1 Mention
Deterministic Nonperiodic Flow
Edward N. Lorenz•1963
Top 6% · 94th Percentile
19,618 citations · Numerical Analysis
Open Access

TLDR

A system can follow fixed rules yet become impossible to predict far ahead because tiny starting differences grow into major changes. This helps explain why long-range weather forecasts have limits.

Summary

1 Study Aim

The authors investigate whether finite sets of deterministic ordinary nonlinear differential equations (fixed-rule equations describing changing quantities) can produce nonperiodic behavior. They focus on forced dissipative hydrodynamic flow (fluid motion that receives energy but loses it). The study also examines what these results imply for very-long-range weather prediction. The study asks whether fixed rules can still produce behavior that cannot be predicted far ahead.

2 Study Design

The paper analyzes solutions of finite equation systems as trajectories in phase space (a map showing every possible system state). It considers systems with bounded solutions, meaning their values remain within limits. The authors examine their stability and numerical solutions (computer-generated approximations). They then solve a simple system representing cellular convection (organized rising and sinking fluid motion) numerically. The study compares all solutions from this model and assesses their relevance to weather prediction. No observational sample or human participants are used. The research uses mathematical analysis and computer calculations on simplified fluid-flow models.

3 Findings

The study reveals that nonperiodic solutions (motions that do not repeat) are ordinarily unstable, meaning tiny changes can grow substantially. Therefore, slightly different starting states may produce very different later states. The authors also show that systems with bounded solutions have bounded numerical solutions. In the cellular-convection model, every solution is unstable, and almost all are nonperiodic. The research uses these results to examine the feasibility of very-long-range weather prediction, showing why small uncertainties in starting conditions can limit such forecasts. Tiny differences at the beginning can make long-range outcomes differ greatly, limiting far-ahead weather forecasts.

Abstract

Finite systems of deterministic ordinary nonlinear differential equations may be designed to represent forced dissipative hydrodynamic flow. Solutions of these equations can be identified with trajectories in phase space. For those systems with bounded solutions, it is found that nonperiodic solutions are ordinarily unstable with respect to small modifications, so that slightly differing initial states can evolve into considerably different states. Systems with bounded solutions are shown to possess bounded numerical solutions. A simple system representing cellular convection is solved numerically. All of the solutions are found to be unstable, and almost all of them are nonperiodic. The feasibility of very-long-range weather prediction is examined in the light of these results.

Referenced In