The Unique Behavior of Vertical Velocity in Developing Deep Convection

When daytime tropical convection develops away from mesoscale disturbances, it typically transitions gradually from dry to shallow to deep convection on hourly timescales. The transition is commonly associated with the formation of larger horizontal boundary‐layer structures and an increasing level of cloud organization aloft. This study demonstrates that a spectral analysis of the resolved high‐resolution sub‐cloud flow features allows for a robust identification of dominant length scales and the quantification of their growth rates during the transition. Furthermore, it is shown that temperature, moisture, and horizontal winds develop multiple length scales with the largest ones growing up to several kilometers in magnitude. However, the vertical velocity behaves in a distinct manner developing significantly smaller values, comparable over land and ocean. This indicates stronger inherent limits of vertical velocity to self‐organize by size. When tropical storms form away from big weather systems, they usually go through several stages, starting with shallow clouds and then gradually intensifying until deep clouds with anvils develop. As the transition progresses, larger flow patterns form in the air close to the ground, and the clouds above become more organized. This study found that by looking at high‐resolution modeling data in terms of energy distribution per structure size, we can see how these patterns change and grow over time. It also found that the sizes of temperature, moisture, and horizontal wind patterns are similar to each other and can be several kilometers wide. But the patterns of vertical motion behave differently, staying smaller and not growing as much, whether over land or ocean. This indicates natural limits to how big the structures of vertical air movement can get during the formation of local storms. Simulated transition to deep convection over both land and ocean is analyzed using a novel method based on spectral analysisDominant sub‐cloud length scales for temperature, moisture, and wind grow linearly until the onset of deep convectionNotably, vertical velocity length scale remains at much lower values, indicating a weaker tendency to self‐organize by size Simulated transition to deep convection over both land and ocean is analyzed using a novel method based on spectral analysis Dominant sub‐cloud length scales for temperature, moisture, and wind grow linearly until the onset of deep convection Notably, vertical velocity length scale remains at much lower values, indicating a weaker tendency to self‐organize by size