Deriving Lamb weather types suited to regional climate studies: A case study on the synoptic origins of precipitation over Ireland

Abstract

The Lamb weather type (LWT) categorization system is one of the best known procedures for summarizing the synoptic circulations that regulate daily weather. Traditionally, it is applied to daily sea level pressure, centred on a domain over the British Isles (BI), which is classed into one of 27 types (or 7 main types). The available register of LWTBI extends to the mid‐19th century and has provided a valuable context for understanding the reasons for temporal and spatial variations in recorded weather elements, especially precipitation. Much of what is known of the synoptic origins of precipitation in Ireland has been based on the LWTBI, although it lies in the western part of this domain. While the original classification was based on manual assessment of weather maps, numerical methods can now be employed to objectively classify a pressure field into a LWT. As a result, it is possible to redefine the region of interest. In this study we applied the objective method to a new domain centred on Ireland (LWTIR). The article compares the catalogue of LWT created for the new domain with that available for the original domain; while the overall synoptic climatology does not change, the sequence of LWT classes differs considerably. As a result, the interpretation of the synoptic origins of precipitation over Ireland is modified and this directs research to new areas of enquiry. This new LWT register that is focused on Ireland provides a more useful context for studying Irish climate and demonstrates the value of the objective method.