Daily near-surface large-scale atmospheric circulation patterns over the wider Caribbean

The day-to-day variability of the atmospheric circulation over the Caribbean region is investigated in this work through the extraction of frequently occurring atmospheric circulation types. A two-stage cluster analysis technique using Ward's agglomerative algorithm followed by the k-means algorithm was applied to daily circulation defined by the NCEP/DOE reanalysis wind components at the 850 hPa level for the period 1979-2010. Seven atmospheric circulation types (CTs) were extracted. The daily circulation types are distinguished through the extension and location of the well-known quasi-stationary Atlantic and Pacific anticyclones. However, three of the circulation types show a third anticyclonic feature, a Gulf of Mexico anticyclone which is not observed on monthly scales because it is transient with a mean lifetime of 2-3 days and rarely occurs in the July-September period. Other notable characteristics include the decrease in annual frequency of a circulation type defined by the transient Gulf of Mexico anticyclone, a neutral area over the Greater Antilles islands and weaker than average easterly winds. In addition, a second type with south-easterly winds throughout the Caribbean increases in annual frequency. This latter type also had events lasting as long as 85 days. The monthly frequency of the CTs that prevail during the dry season is correlated with several Atlantic and Pacific based teleconnections. The resulting daily atmospheric circulation types in this work comprise the first atmospheric circulation catalogue, of many to come, for the Caribbean region and may be useful in statistical-dynamical downscaling applications to explain the variability of surface weather variables such as wind speeds.