Monthly wind directional indices based on ships logbooks observations, WI

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 WI is the Directional Indices (DIs) that give a measure of the westerly flow. It is an instrumental-based monthly index defined as the proportion of westerly days per month (in % with respect to the total number of available days for each month) over the English Channel. A westerly day is defined as a day with prevailing wind from the east (wind blowing from the [225, 315)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 westerly wind day was said to occur when at least a percentage of 45% of the total number of observations of that day corresponded to westerly wind. DATA: WI: Westerly Index (% of days in a month with westerly 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 WI is herein provided regardless the number of observations. Some months have a low number of observations (No < 50 %)