Climatology of Size, Shape, and Intensity of Precipitation Features over Great Britain and Ireland

Abstract

Abstract A climatology of precipitation features (or objects) from the Great Britain and Ireland radar-derived precipitation mosaic from 2006 to 2015 is constructed, with features defined as contiguous areas of nonzero precipitation rates. Over the 10 years, there are 54 811 747 nonunique precipitating features over 100 km2 in area, with a median precipitation feature area of 249 km2, median major axis length of 29.2 km, median aspect ratio of 2.0:1, median feature mean precipitation rate of 0.49 mm h−1, and median feature maximum precipitation rate of 2.4 mm h−1. Small-scale precipitating systems are most common, but larger systems exceeding 10 000 km2 contribute close to 70% of the annual precipitation across the study region. Precipitation feature characteristics are sensitive to changes in annual and diurnal environment, with feature intensities peaking during the afternoon in summer and the largest precipitation features occurring during winter. Precipitation intensities less than 5 mm h−1 comprise 97.3% of all precipitation occurrences and contribute 83.6% of the total precipitation over land. Banded precipitation features (defined as precipitation features with aspect ratio at least 3:1 and major axis length at least 100 km) comprise 3% of all precipitation features by occurrence, but contribute 23.7% of the total precipitation. Mesoscale banded features (defined as banded precipitation features with major axis length at least 100 km and total area not exceeding 10 000 km2) and mesoscale convective banded features (defined as banded precipitation features with at least 100 km2 of precipitation rates exceeding 10 mm h−1) are most prevalent in southwestern England, with mesoscale convective banded features contributing up to 2% of precipitation.