Analogy of multiday sequences of atmospheric circulation favoring large rainfall accumulation over the French Alps

We propose in this article an analogy approach for characterizing the similarity between daily atmospheric state sequences—in our case large‐scale geopotential height fields. The similarity is measured using two indices—the persistence and the singularity. The persistence of a sequence is defined through the average distance between its consecutive states. Its singularity is the average distance between its states and their closest analogues. We apply these indices to geopotential heights over Western Europe in view of characterizing the sequences yielding record rainfall accumulations over several days in the Northern French Alps, more specifically in the Isère River catchment at Grenoble. We show that these indices remarkably stratify the heaviness of rainfall sequences in the region. We find that the less singular and the more persistent the atmospheric state sequence, the wetter the rainfall sequence. Although the persistence of atmospheric states leading to extremes was expected, their low singularity might be a feature of the Northern French Alps, which usually experiences roughly westerly winds triggering orographically enhanced precipitation. Relying on some choices that may be improvable, our study opens the door to future research on the characterization of the atmospheric state sequences favoring regional climate extremes based on analogy.