Analyzing the Instabilities in the Venus Atmosphere Using Bred Vectors

Abstract

Barotropic, baroclinic, and Rossby‐Kelvin instabilities exist in the Venus atmosphere, as revealed by previous studies using numerical models. This study aims to deepen our understanding of the instabilities in the Venus atmosphere using the breeding of growing modes (BGM) method for the first time. We conducted a 1‐year model simulation as the control run. First, we conducted identical twin experiments in which random perturbations were added to the control run at the initial time, and they grew freely. Perturbations in the upper layer (UL, 70–100 km altitudes) grow faster at the beginning but saturate earlier at a low value compared to those in the lower layer (LL, 40–70 km altitudes). Next, we implemented the BGM method and conducted multiple breeding cycle experiments with different rescaling amplitudes and intervals, the two parameters of the BGM method. The bred vectors (BVs) from these experiments identified instabilities in various regions. With large rescaling amplitudes, the structure and amplitude of the BVs in the LL closely resembled the deviations in the control run, indicating the growth of BVs due to barotropic, baroclinic, and Rossby‐Kelvin instabilities. Composite mean analysis shows larger BV amplitudes in the morning hemisphere at the 60–70 km altitudes in the mid‐latitudes, indicating enhanced baroclinic instability by the thermal tide. Finally, we estimated the intrinsic predictability related to baroclinic instability for Venus is >1 month, which would be longer than that for the Earth of ∼2 weeks.