A worldwide assessment of the Jenkinson-Collison atmospheric circulation classification and observational uncertainty based on different reanalysis.

Lamb Weather Types (LWT, 1972) are a classical method in synoptic climatology consisting in a subjective classification of atmospheric circulation based on an expert interpretation of sea-level pressure (SLP) fields centered on the British Isles. Jenkinson-Collison (1977) made a subsequent adaptation of the original LWT approach (JC-WT) to obtain an automated, objective method that is also applicable to other locations. In spite of its potential for an objective large-scale circulation typing in extratropical regions of the world, to date, JC-WT has been seldom used in the Southern Hemisphere, which requires a minor modification of its original formulation to this aim. This study sets the grounds for the adoption of the JC-WT classification worldwide by applying it centered in all cells of a 2.5º global grid (excluding a 10º wide equatorial band). We present an open, 6-hourly JC-WT catalogue on this grid for the period 1979-2005 built from five popular reanalysis products (https://doi.org/10.5281/zenodo.5761258). This catalogue is used to evaluate the observational uncertainty linked to the representation of atmospheric circulation in the different reanalyses.

Overall, we find empirical evidence of the suitability of the JC-WT classification for the regional assessment of atmospheric circulation outside the tropics, including the Southern Hemisphere. We also find important differences in the JC-WT representation by different reanalyses in some regions, such as the Tibetan Plateau, the Andes, Greenland and Antarctica, in light of the comparison of their respective occurrences and transition probabilities. These inconsistencies may compromise the robustness of circulation-based model assessments relying on a single reanalysis in these regions.