High resolution analysis of rainfall intermittency at mid-latitude using disdrometer decade-long data

This study analyzes rainfall structure using an unusually long record of continuous 1-minute disdrometer observations, comprising 11 years (2013–2023) of data from a Thies Clima disdrometer near Rome, Italy. We identify rainfall events based on minimum inter-event times (MITs), calculating rain rate, mass-weighted mean diameter (Dm[jls-end-space/]), as well as stratiform and convective precipitation classification. After cleaning erroneous data, seasonal analysis shows autumn had the highest rainfall with the majority of medium sized drops, winter featured prolonged light rain with smaller drops, while summer recorded the least rainfall but with the highest intensity and largest drops. The differences in drop sizes and rain types across seasons are crucial, as stratiform clouds, linked to steady rain, were more common in autumn and winter, whereas convective clouds, associated with intense, short-duration rain, dominated summer. The study focuses on rainfall intermittency, defined by the abrupt onset or interruptions of rainfall events. Intermittency was measured using the intermittency fraction (IFr), which indicates the proportion of dry time within a given period. Time Averaged Rainfall Intermittency (TARI) estimates IFr over fixed intervals, while Intra-Event Rainfall Intermittency (IERI) does so dynamically between consecutive fixed-length dry periods, also called MIT. Both methods, applied across multiple categories, produced consistent results, validating each other. A diurnal analysis of IFr (15-minute TARI-based) reveals significant seasonal differences, peaking between 9 AM and 2 PM. In summer, sharp peaks occur before noon, followed by a rapid decline in the afternoon, whereas winter maintains a more consistent IFr throughout the day. These seasonal differences remain robust with increasing durations in TARI from 15-minutes to 1 day. Overall, the longest wet spell lasted 19.4 h, while the longest dry spell was 534.4 h. IERI across various MITs shows higher IFr values at shorter MITs, particularly during the summer. These results highlight disdrometers’ vital necessity during hazard-prone seasons, causing flash floods and erosion.