Scale interactions of deep convection in the Sahel: Exploring ring patterns in lagged cross-correlations of rainfall

Spatio-temporal patterns in rainfall are evidence of sub-daily scale interactions in convection in the West African Sahel. Radial normalization of two-dimensional conditional probability maps reveals a ring-like structure in rainfall probabilities surrounding previous rainfall, in both satellite observations and regional climate models. These results support a growing body of evidence that scale interactions in tropical convection can provide predictability on short timescales. Additionally, a km-scale model is shown to represent the spatio-temporal structure of the patterns better compared with the same model at 25 km with parameterized convection. These evaluations indicate the potential for creation or enhancement of statistical prediction tools using model data alongside observations. The mechanism for the patterns is investigated in the km-scale model output, and associations are explored with both convectively generated gravity waves and evaporatively driven cold pools. The area inside the ring-like structure, where the probability of new convection is lower, is associated with a cold and divergent anomaly characteristic of a cold pool. Amplitudes of anomalous mid-level ascent prior to the pattern forming correlate well with amplitudes of the radially normalized probabilities three hours later, suggestive of potential wave-driven enhancement of rainfall probability.