SOURCES: Daily data of wind direction over the English Channel based on direct marine observations derived from Royal Navy ships' logbooks (1685-1870) and ICOADS v3.0 (1750-2014) datasets. DESCRIPTION: The SI is the Directional Indices (DIs) that give a measure of the southerly flow. It is an instrumental-based monthly index defined as the proportion of southerly days per month (in % with respect to the total number of available days for each month) over the English Channel. A southerly day is defined as a day with prevailing wind from the south (wind blowing from the [135, 225)N sector). When only one daily observation was available, the day was classified from the wind direction of that single observation. If several observations per day were available over the English Channel, a southerly wind day was said to occur when at least a percentage of 37% of the total number of observations of that day corresponded to westerly wind.DATA:SI: Southerly Index (% of days in a month with southerly wind direction with respect to the total number of available (i.e., non missing) days in the month)No: Number of available days (i.e., with at least one wind observation) in a month (in % with respect to the total number of days in the month). Months with no wind direction observation at all in the full month are labeled as missing (-99.9)IMPORTANT NOTE: Please, note that the SI is herein provided regardless the number of observations. Some months have a low number of observations (No < 50 %)