The Weather of the European Atlantic Seaboard During October 1805: An Exercise in Historical Climatology

Several thousand ships' logbooks havesurvived from the eighteenth and nineteenth centuries.They provide a valuable source of climaticinformation. This paper takes the Battle of Trafalgaras an example of how this source can be used toprovide a better knowledge and understanding ofweather and climate from those distant times. Thereliability of the non-instrumental climatic recordsof the logbooks is confirmed and a simple statisticalmeasure is used to quantify their degree ofconsistency. Reconstructions of daily weather patternsare made and a zonal index is calculated to representthe circulation patterns of the region. The movementsof pressure systems are plotted and indicate that thezonal index was negative (air pressure increasing fromsouth to north) for most of the month. The storm thatfollowed the battle is identified as one of notableseverity. This extreme behaviour is interpreted withinthe context of longer-term aspects of the contemporaryclimate.