Variability and Predictability of a reduced-order land atmosphere coupled model

TL;DR

This paper investigates the predictability and variability of atmospheric flow regimes using a simplified coupled land-atmosphere model, revealing how surface friction influences regime transitions, stability, and predictability durations.

Contribution

It introduces a comprehensive analysis of flow regimes and their predictability in a reduced-order coupled model, highlighting the effects of surface friction and model resolution on regime dynamics.

Findings

Presence of zonal, blocking, and transition regimes under low surface friction.

Increased surface friction leads to two regimes and reduced predictability (~2 days).

Zonal patterns have longer predictability horizons than blocking or transition patterns.

Abstract

This study delves into the predictability of atmospheric blocking, zonal, and transition patterns utilizing a simplified coupled model. Initially, we comprehensively scrutinize the model's responses to environmental parameters like solar radiation, surface friction, and atmosphere-ground heat exchange. Subsequently, employing Gaussian mixture clustering, we successfully delineate distinct blocking, zonal, and transition flow regimes, unveiling their dependencies on surface friction. To gauge predictability and persistence, we compute the averaged local Lyapunov exponents for each regime. Our investigation uncovers the presence of zonal, blocking, and transition regimes, particularly under conditions of reduced surface friction. As surface friction increases further, the system transitions to a state characterized by two blocking regimes and a transition regime. Intriguingly, periodic behavior emerges under specific surface friction values, returning to patterns observed under low friction coefficients. Model resolution increase impacts the system in a way that only two regimes are then obtained with the clustering: the transition phase disappears and the predictability drops to roughly 2 days for both of the remaining regimes. In accordance with previous research findings, our study underscores that when all three regimes coexist, zonal patterns exhibit a more extended predictability horizon compared to blocking patterns. Remarkably, transition patterns exhibit reduced predictability when coexisting with the other regimes. In addition, within a specified range of surface friction values where two blocking regimes are found, it is observed that blocked atmospheric situations in the west of the applied topography are marked by instabilities and reduced predictability in contrast to the blockings appearing on the eastern side of the topography.