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

THE WEATHER OF THE EUROPEAN ATLANTIC SEABOARD DURINGOCTOBER 1805: AN EXERCISE IN HISTORICAL CLIMATOLOGY

DENNIS WHEELERGeography Department, University of Sunderland, SR1 3SD, U.K.

Abstract. Several thousand ships’ logbooks have survived from the eighteenth and nineteenthcenturies. They provide a valuable source of climatic information. This paper takes the Battle ofTrafalgar as an example of how this source can be used to provide a better knowledge and under-standing of weather and climate from those distant times. The reliability of the non-instrumentalclimatic records of the logbooks is confirmed and a simple statistical measure is used to quantifytheir degree of consistency. Reconstructions of daily weather patterns are made and a zonal index iscalculated to represent the circulation patterns of the region. The movements of pressure systems areplotted and indicate that the zonal index was negative (air pressure increasing from south to north)for most of the month. The storm that followed the battle is identified as one of notable severity.This extreme behaviour is interpreted within the context of longer-term aspects of the contemporaryclimate.

1. Introduction

The late Hubert Lamb drew attention to the value of ships’ logs as a source ofclimatological information when he observed “. . . this is a vast treasure trove wait-ing to be used” (Lamb, 1995, p. 89). But Lamb merely echoes the much earliersentiments of Francis Beaufort who wrote to his brother-in-law Richard Edgeworthin 1809, stating “. . . there are from 2 to 8 logbooks deposited every year in theNavy Office; those logbooks give the wind and weather every hour . . . what betterdata could a patient meteorological philosopher desire?” (Friendly, 1977). The truevalue of this information needs, however, to be assayed with caution. This paperundertakes such a task through the medium of one of the most memorable settingsof English history – the Battle of Trafalgar.

The author has already published a number of items concerned with the weatherof this period (Wheeler, 1985, 1987, 1995a). The recent discovery of a hithertounknown diary of climatological observations made at Cádiz in the early nineteenthcentury provides a more complete picture of the contemporary conditions. Thelogbooks, together with the multiplicity of additional items that describe the con-ditions of the time, provide an important opportunity for the cross-checking of datasources and confirmation (or otherwise) of their reliability for climatic research.

Climatic Change48: 361–385, 2001.© 2001Kluwer Academic Publishers. Printed in the Netherlands.

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2. The Historical Events

The Battle of Trafalgar, although engaged in October 1805, continues to interesthistorians and the general public alike to whom it represents a signal victory inthe British campaign to defeat the Republican aspirations of post-RevolutionaryFrance. It is not however the purpose of this paper to review the historical eventssurrounding the Battle. The political intrigues of the day are discussed in Desbrière(1933), Warner (1966) and Bennett (1977). It needs only to be observed that Britishstrategy depended upon dominion of the seas in the manner described by Mahan(1890) and, to British strategists, the most effective means of ensuring this was tobring the French fleets to a decisive action and thereby to render them impotent bycomprehensive defeat. Nelson, who had passed the previous two years attemptingto achieve this very objective, had earlier in 1805 fruitlessly pursued the Frenchand Spanish, hereafter referred to as the Combined Fleet, under the command ofAdmiral Pierre Villeneuve across the Atlantic to the West Indies and back again.The Combined Fleet had found eventual refuge in Cádiz. By this time Nelson,unaware of the Combined Fleet’s exact position, was taking leave at his home justoutside London. On 2 September he received word of their whereabouts. Within afew days he set sail from Portsmouth in HMSVictory. On the 25th, with his fleetgrowing daily as vessels were directed by the Admiralty to his assistance, Nelsonsighted Cádiz where he was to remain until the issue of battle had been resolvedon 21 October. The following is an account and interpretation of the weather of theeastern North Atlantic seaboard during that critical period.

3. The Data Sources

The study is given fresh detail by the discovery of a weather diary found in thearchives of the Spanish Royal Navy’s Observatory in San Fernando, 7 km fromCádiz (Wheeler, 1992a). The diary (anonymous, undated) embraces the period1799 to 1812 but contains many gaps. Fortunately, the period from January 1805 toDecember 1808 is complete with observations made twice daily (at 8 in the morn-ing and 2 in the afternoon) of air pressure, temperature, wind direction, wind forceand the state of the weather. These observations are henceforward referred to asthe Cádiz data. The diary’s author provides also a helpful list of instruments whichconsisted of a barometer manufactured by the French instrument maker Mégnié(units in Paris feet) with an attached thermometer (reading degrees Réaumer) and afree standing thermometer of Dolland manufacture (reading in degrees Fahrenheit).A copy of the page for October 1805 appears in Figure 1.

The wind strength was recorded on a scale comparable to the four-point systemthen popular in England and employed the categoriescalma (calm), flox or flojo(light winds),frescaor fresquita(fresh) andrecargada(usually abbreviated torec:strong winds). The state of the weather again uses a consistent, if limited, list of

THE WEATHER OF THE EUROPEAN ATLANTIC DURING OCTOBER 1805 363

Figure 1.Sample page of the Cadiz Weather Diary for October 1805.

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descriptions which includednublado(cloudy), lluvioso (rainy), toldad (overcast),clara (clear) anddespejado(cloud-free).

The majority of the information comes, however, from the logbooks of theBritish Fleet. The data that they contained were of great importance for navigationand officers made note of prevailing weather and the sea conditions to assist indetermining the ship’s speed, direction and location. At each of the day’s threewatches an entry was made of wind force and direction together with any otherweather information deemed important. The state of the sea, fog, thunder, precipi-tation and any severe or unusual conditions would all fall under this heading. Windwas recorded on a thirty-two point compass but, with only a very few exceptions,no instrumental records were kept at this time. The general character of Englishlogbooks has been reviewed by Oliver and Kington (1970).

A sample of English logbooks was drawn to meet two purposes. The first ofthese was to include logbooks of vessels from the same fleets in which independentobservers were making simultaneous records in a limited geographic area. Fromthis sub-sample it would be possible to determine the consistency with which thelogbook weather notes were prepared. Two such fleets were active in the regionat this time. The Channel Fleet was then on blockade duty off Brest (Brittany),while in the Gulf of Cádiz off south-west Spain was Nelson’s squadron. The secondrequirement of the sample was to cover a wide area of the European Atlantic Sea-board. This could only be met by also including the logbooks of single vessels onunattached duty in the waters between and around the two principal fleets. Vesselsserving in the areas required to complete the spatial coherence of the sample werefound by consultingSteels’ Navy Listfor 1805 that includes each ship’s attachmentor designated port for the year. By this means vessels were identified serving in theIrish Sea, the English Channel, Bay of Biscay and the Atlantic waters to the westof the main theatres of action. Additional information was derived from diaries ofland-based observers in the British Isles. These sources, and the data they contain,are itemised in Table I. The geography of the study area is summarised in Figure 2.

4. Data Source Reliability

Two issues arise in respect of data reliability. These can be summarised thus:1. How reliable were the recording officers when describing the weather con-

ditions that they encountered? In particular, with what consistency did differentobservers record the same weather events?

2. How consistently were terms used? For example was the description ‘strongbreezes’ equally understood by the observers of two centuries past? And, of similarimportance, are those interpretations consistent with those of today?

In respect of point 1, Wheeler (1988) has reported on the results of a practicalexperiment, which indicated that reliable estimates of wind force and direction canbe made from the deck of sailing ships even by relatively untrained crews. There


Figure 2.The geography of the study area and the general disposition of the two English fleets andvessels whose logs were consulted. The routes of those vessels not on permanent attachment arealso shown: 1 – HMSHeron; 2 – HMSAfrica; 3 – HMSAeolus; 4 – HMSWeazle. The land-basedobservatories are also shown.

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TABLE I

List of sites and details of land-based observations

Location Wind Wind Temp. Pressure Weather Frequency

direction force

Cadiz X X X X X 2× daily

Goodwood Ho., Sussex X X X X X 3× daily

Syon Ho., Middlesex X X X X daily

Derby X X X 3× daily

Newcastle-upon-Tyne X X X X 3× daily

Ednam, Tweed Valley X X X X daily

Pitlochrya X X daily

X Indicates that these observations were taken.a The precise location of this site is questionable but lies in the Pitlochry–Perth area.

are no reasons to doubt that a similar conclusion applies to earlier records made byexperienced and professional officers particularly when it is recalled that such datawere used for the important purpose of navigation.

The vocabulary of early nineteenth century mariners needs also to be con-sidered. In 1806 Francis Beaufort proposed his first wind force scale, a variantof which persists in use to the present day. However, Beaufort merely formalisedand adopted terms that had by then entered common usage. Indeed Beaufort’s ownlogbooks use this unofficial vocabulary, a practice which he doubtless acquired, asall junior officers then did, under the tutelage of the ship’s master or captain. Bythis tradition of oral transmission the system was perpetuated, to be eventually pre-served by Beaufort. Thus, and although it was to be several years before the RoyalNavy formally adopted the Beaufort scheme, the terms then employed almost cer-tainly equate to their present-day definitions. This view is supported by Wheeler(1995b) who has used contemporary documents to confirm the Beaufort terms. Thevocabulary of the sample of logbooks is summarised in Table II and a referencedlist of those logbooks that were consulted is provided at the conclusion of the paper.Usage is concentrated in the Beaufort force 4 and 5 classes.Strong breezesseemhowever to be under-represented but this may be a result of the small sample size orinaccurate conversions of wind force terms to actual speeds.Gentle breezes, a termnow included in the Beaufort Scale, appears not to have enjoyed wide currency twohundred years ago. The absence ofwhole gale, stormandhurricaneentries, on theother hand, reflects the lack of such extreme conditions during the study period.Chenoweth (in press) has, in similar fashion, identified Beaufort forces 4 and 5 asbeing those most frequently noted on logbooks from this period. He has howeverargued that logbook estimates differ from the real wind speeds, but by less thanthe range of one unit of the Beaufort Scale. For the purposes of this case studysuch disagreements do not represent a major problem. The sub-sample of thirteen


TABLE II

List of terms used in the sample Royal Navy logs examined in the present paper. These termsare matched with those later specified in the official Admiralty Memorandum of 1838 when theBeaufort Scale was officially adopted. The percentages are based on a sample size of 567 diaryentries

Terms used in the logs Beaufort’s 1838 terms Beaufort’s original scale Percentage

incidence

in sample

Calm Calm 0 2.5

Little windsa 1.9

Light airs Light airs 1 12.2

Light breeze Light breeze 2 13.6

Did not appear in sample Gentle breeze 3 0

Moderate breeze Moderate breeze 4 27.2

Fresh breeze Fresh breeze 5 22.8

Strong breeze Strong breeze 6 4.6

Did not appear in sample Moderate gale 7 0

Fresh gale Fresh gale 8 6.8

Strong gale Strong gale 9 8.3

Did not appear in sample Whole gale 10 0

Did not appear in sample Storm 11 0

Did not appear in sample Hurricane 12 0

a This term was found only in the logbook of HMSCaptain(ADM51/1525).

vessels operating in the Gulf of Cádiz also provided an opportunity of determiningthe consistency of records. The three categories of weather elements (wind force,wind direction and weather) were abstracted for each of the days 1–30 October.The statistical mode for each day for each element was judged to represent the‘real’ conditions and the percentage of entries that used that same term was noted.Figure 3 shows how the three respective percentages varied from day to day. Theoverall consistency was high and the mean percentage of observations that werein agreement were 69.8 for wind direction, 66.1 for weather and 67.3 for winddirection. Only on the day of battle did the figures fall well below these averages.Furthermore, in the case of the ordinal-scale data of wind force and direction, thevast majority of the residual observations were in the adjacent classes.

In addition to the terms used to denote wind force there existed categories todescribe the weather. Of those that were later adopted by Beaufort the currentsample yieldedhazy, cloudy, clear, rain, squally, fair, fog(sometimesfoggy), thun-der, lightning, showers, hail, drizzleandsmall rain. Other terms, seemingly popularbut which Beaufort did not include, for understandable reasons of definition, weremoderate, pleasantandfine.

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Figure 3.Consistency of ship logbook records. The three categories of wind direction, wind forceand weather are plotted as percentages of their respective total number of observations and are here‘stacked’ into daily bars the lengths of which are proportional to the sum of the three independentpercentages.

TABLE III

Frequency of matches between Cadiz wind forces and the modal value determinedfrom Royal Navy vessels in the nearby open waters of the Gulf of Cadiz

Beaufort scale/ Calms to Light Moderate Fresh and Moderate

Cadiz term light airs breezes breezes strong breezes and above

Force 0–1 2 4 5/6 7+

Calma 1 0 0 0 0

Flojo 0 5 4 0 0

Fresquita 0 5 3 6 1

Recargada 0 0 0 2 2

The sub-sample of Nelson’s fleet was also used to verify the interpretationof the wind force terms in the Cádiz diary. The diary observations for each daywere compared with the corresponding modal force noted from the logbooks. Theresults, summarised in Table III, not only confirm the scale order but also allow anapproximate conversion to equivalent ranges on the Beaufort scale. The termcalmacovers winds from force 0 to 1,flojo from 2 to 4,fresquita5 and 6 andrecargada7 and above.


Although standardised instrumental readings from land-based sites had to wait afurther half century, a considerable body of data could be called upon in addition tothe Cádiz diary. The daily records from a number of British sites (Table I) provideda means of extending the latitudinal range of the study. This was important fromthe point of view of barometric data particularly as no marine records have beenlocated for this period and area. The five sets of barometric observations werereduced to present day standards, i.e., for gravity, temperature and altitude. Theheights of all the barometers could be estimated to within 5 m, while that of theSan Fernando Observatory is known to the nearest metre. In all cases the dailycabinet temperatures are recorded.

The British series’ reveal the same trends but that for Syon house (in the ThamesValley to the west of London) is, by a margin of approximately 5 millibars, consist-ently the lowest (Figure 4b). As a result the observations from the other southernsite at Goodwood Hose (on the Sussex coastline) were preferred. The reliabilityof the Spanish records was less easily confirmed there being no correspondingnetwork of nearby sites; the Gibraltar barometric series does not start until 1821while the contemporary Madrid record does not provide a suitable comparison be-cause of the local, thermally-driven pressure patterns that characterise the climateof the centre of Iberia. Instead the gridded monthly barometric reconstructions(U.S. Department of Energy, 1987) for 1805 and more recent times were used withcontemporary site-specific data for Cádiz to detect any remaining inconsistenciesor need for further corrections. This check revealed that the Mégnié barometer wasunder-recording by 3.5 mb and this final correction was applied to the data beforethey were used for analysis.

5. The Weather of the Month

October 1805 was an anomalous month from a number of climatological pointsof view. Data from Cádiz must be viewed with caution (Wheeler, 1995c) but itis probable that temperatures were 1.5 degrees Celsius above the prevailing meanfor the period (1805–1816 data only are available). While the Central EnglandTemperatures series (Manley, 1974) reveals the month to have been unusually coldin that region where the daily mean of 8.2◦C was 1.5 degrees Celsius below the1805–1816 average. The precipitation characteristics were similarly unusual. TheCádiz rainfall record begins in this year (Wheeler, 1992b) and the October total of96.2 mm was twice the mean for the period 1805 to 1839. In England and Wales,in contrast, the October 1805 precipitation was 51.1 mm, just 56 percent of thelong-term mean (1805–1835).

A daily portrayal of the month’s temperature and air pressure are shown inFigures 4a,b. The temperature trends were similar between the British sites withthe two northern locations of Newcastle-upon-Tyne and Ednam being, not unex-pectedly, cooler than the others. The air pressure trends differ to an even lesser

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Figure 4.Daily plot of (a) temperatures and (b) corrected air pressure for sites during October 1805.


Figure 5.Daily corrected mean air pressure of the British sites and for Cadiz during October 1805.The differences (Cadiz – British mean, the latter calculated excluding the questionable Syon houseseries) between the two are also shown. The five phases into which the month has been divided aredetermined by the character of the latter. Phase 3 is positive, phases 1 and 4 are negative and phases 2and 5 are neutral.

degree. Moreover as Cádiz and the most northerly British sites are separated bytwenty degrees of latitude an index of zonality can be derived based on the dailyair pressure differences between the two regions. Figure 5 depicts the five phasesinto which the month can divided using this measure; a negative index (pressureincreasing northwards) prevailed from the 1st to 8th and again from the 18th to27th, a neutral position (no significant or persistent gradient) prevailed between8th and 12th and again between 27th and 31st. What today would be regarded asthe ‘normal’ position, with the pressure decreasing from south to north across themid-latitudes, prevailed only between the 12th and 18th. These five phases can nowbe viewed in more detail.

Phase 1: 1–8 October. At the start of the month the British Isles was undersettled, anticyclonic conditions. Land stations experienced light to variable windsfrom between south-east and north-east. The Ednam (southern Scotland) observernoted ‘small’ rain on the 3rd and fog on the 5th. Elsewhere the weather was amixture of cloudy, fine and clear conditions. Temperatures were steady during thisperiod and the highest for the month. Newcastle’s and Ednam’s pressure values

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were slightly higher than elsewhere which, together with the evidence of an easterlyair flow, suggests high pressure to the north of Britain.

The logbooks of the Channel Fleet indicate more unsettled weather with easterlygales around the 2nd but winds falling to fresh to moderate breeze strength by the4th although staying in the east. HMSFoudroyant, then moored in Cawsand Bay (apopular mooring on the south Devonshire coast), also noted easterlies at this timebut with a force that varied between fresh breezes and gales; the latter again occur-ring on the 2nd. This evidence is corroborated by that from the log of HMSAfrica(south of the Lizard, Cornwall) with easterly gales and a ‘heavy swell from E’ onthe 2nd. The logbook of HMSCaptain, south of Cape Clear (southern Ireland),notes easterlies at fresh breeze strength. Further to the south the winds were morewesterly in nature. The sloop HMSHeron, sailing in the area 48◦N 20◦W, notessoutherly to south-westerly winds, reaching gale force on the 3rd and 4th decliningrapidly on the 5th. HMSWarrior was at 50◦N 10◦W to the west of the Isles ofScilly and her logbook also records fresh to moderate south-westerlies (but nogales) during the first week of October. This pattern suggests that two low pressuresystems followed a route through the English Channel. Both centres intensified thepressure gradient against the anticyclone to the north producing easterly gales onthe 2nd and the 4th. Neither system appears however as a strong element on theland-based barometer records, possibly as a result of the anticyclone sustainingits grip and deflecting the low pressure centres on paths to the south. Figure 6asummarises these conclusions in map form for one day of this phase.

Air pressure, although lower over the Gulf of Cádiz was rising slowly andwas accompanied by much more settled weather than in the English Channel.Winds were mostly light airs and light breezes (70 percent of log entries) andthe weather a mixture of cloudy, hazy and fine conditions. On the 1st and 2ndthe winds were west to south-west but then settled into an easterly flow. Mostvessels noted occasional cloud cover while the log of the frigate HMSSirius, thenmoored at Gibraltar, notes squalls on the 1st. Changeable conditions, light windswith cloud were recorded in the Cádiz diary on the 1st and rain on the 2nd. Skieswere cloudless on the 5th and 6th. This pattern of light and shifting winds, of settledweather but with references to occasional outbreaks of more unstable squally ele-ments supports a hypothesis of a period during which the quasi-permanent Azoresanticyclone was weakly developed over south-west Iberia with its principal axispossibly displaced to the north.

Nelson’s strategy was based on ‘open blockade’, keeping the main fleet at adistance of over fifty miles, out of site of Cádiz and giving encouragement for Vil-leneuve to venture forth. After his arrival, Nelson dispatched a squadron of frigatesto keep close watch on the activities in Cádiz. To maintain communications withthe frigates he stationed larger vessels at intervals to transmit flag signals using therecently-developed Home-Popham signal book. This was the most rapid means ofsending messages then available but required clear conditions for them to be easilyread any distance beyond a few miles or so. The prevailing settled weather was


Figure 6.Synoptic reconstructions for (a) 4 October 1805, (b) 10 October 1805, (c) 16 October 1805,and (d) 21 October 1805.

therefore vital to Nelson. Equally importantly on what would be a lee-shore, therewere no conditions severe enough to disperse the fleet or drive it to the security ofGibraltar. With minor fluctuations, these advantageous conditions persisted untilthe day of Battle.

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Period 2 (8–12 October).This period is distinguished in Figure 5 by a conver-gence of the British and Cádiz pressure traces and by a sharp fluctuation around the10th in the former when a rapidly-moving depression replaced the high pressuresystem that characterised the first phase. Conditions over Britain were cloudy withwidespread light rain and variable, but often easterly, winds. The winds becamewesterly to north-westerly only on the 11th with fresher weather, marking thenorth-eastward passage of a filling depression and the arrival of polar air. Therewas an accompanying sharp fall in temperature over northern Britain.

Cyclonic weather was dominant on 10th with easterly winds over southern Bri-tain and the English Channel. The logbooks of the Channel fleet also record fresheasterlies. HMSFoudroyantwas still in Cawsand Bay with easterly gales on the9th. HMSTriton (at Waterford, southern Ireland) noted fresh south-easterlies withshowers on the 10th. HMSCaptain, 60 miles east of Brest, recorded no gales butwinds were here westerly with squalls. It can be seen in Figure 4b that the greatestfalls in pressure were at Goodwood House (close to the south coast in the countyof Sussex) and Syon House (to the west of London in the Thames valley). Theevidence again points to a cyclonic system passing through the English Channel,its centre to the north of Brittany but to the south of the British Isles. In the absenceof any anticyclonic element to the north this system extended its influence widelyacross the British Isles before taking a north-eastward route across the North Sea.

Elsewhere the sloop HMSAeolusnoted fresh breezes from the north-west whenlying north of Cape Finisterre (Spain). This same circulation prevailed as far southas latitude 42◦ N where HMSAfrica, then off the Portuguese coast (Figure 1),experienced fresh breezes from the north-west on the 8th, 9th and 10th rising brieflyto gale force on 11th with squalls. This deterioration may have marked the passageof the depression’s trailing cold front. Figure 6b summarises these observations ina synoptic chart for the 10th.

Air pressure fell slightly over the Bay of Cádiz at this time, the result of atemporary weakening of the high pressure ridge. The logs note a correspondingdeterioration in the weather with a greater frequency of squalls, rain and cloudyconditions. The Cádiz diary records rain on the morning of the 11th; this may againindicate the passage of the trailing cold front. The falling barometer at Cádiz around8th (Figure 5) was however to have a dramatic effect on the officers of the Frenchand Spanish fleets when Villeneuve held a council for his officers. Orders had beenreceived from Napoleon that the Combined Fleet should sail to the Mediterraneanto support military activities in that theatre. The officers were well aware of thethreat posed by the English fleet and saw no advantage in an avoidable engagementand the fleet remained in harbour. There is a popular, though apocryphal beliefthat Admiral Gravina (the Spanish C-in-C) offered the practical observation thatsailing would be ill-advised at this time; “Do you not see, sir, that the barometeris falling?”. Whereupon Villeneuve retorted “It is not the glass, but the courageof certain persons that is falling”. Swords are said to have been drawn. But suchofficial papers as have survived cannot support this colourful reconstruction. This


uncertainty notwithstanding, Villeneuve’s reports stated that north-easterly galesprevented his sailing at this time. Although no ships in the Gulf of Cádiz notedanything in excess of fresh breeze strength theAfrica’s record of gales off Lisbonmay give substance to Villeneuve’s caution.

Period 3 (12–18 October). This is the only time when the zonal index was pos-itive. Figure 5 shows a recovery of pressure and stabilising of conditions in the Bayof Cádiz following the frontal disturbances around the 11th. Equally significant isthe fall of pressure over the British Isles following the passage of a high pressureridge on the 12th. The winds were north-westerly backing to westerly as the ridgecrossed the area. Clear skies and nocturnal heat loss on the 12th brought frosts tosouthern Britain but conditions became cloudier thereafter with rain and showersnoted in most diaries as another depression approached from the west. Rain wasmost widespread on the 15th and 17th at which time the air pressure had fallen toits lowest for the month over the British Isles. HMSWarrior, then to the immediatewest of the Brittany coast, recorded gales and squalls late on the 16th. The nearbyHMS Captainnoted gales the 15th followed by squalls and rain. These outburstsmarked the passage of fronts in the, by then, occluding system. Winds were ex-clusively from the western quarter over southern England but were northerly overthe Midlands, northern England and Scotland where snow fell on the hills on the18th. The Ednam and Newcastle records reveal a fall in temperature over thisperiod (Figure 4a) in a region now subjected to the polar airstreams in the wakeof the passing depression. In the English Channel the same change in the synopticconditions manifest itself in more settled weather, with declining wind forces andthe cessation of rain and showers. By this time air pressure was beginning to makea significant recovery following the protracted period of low pressure that suggeststhis to have been a slow-moving system.

Once again the westerly circulation extended beyond the south coast of Eng-land. The Channel Squadron experienced westerly to north-westerly winds ofvariable strength. Gale force winds with squalls prevailed on the 14th and 15thbacking to southerly on the 16th. The logbook of HMSAeolus, then to the westof Iberia at 42◦N 10◦W, indicates that the circulation reached even those distantwaters where winds were westerly from the 15th with rain on the 17th.

In contrast off Cádiz the Azores anticyclone remained dominant and neithergales nor severe weather were noted. Most logbooks recorded light westerlies ornorth-westerlies at this time with cloudy skies and occasional rain. In the moresheltered waters of the Strait of Gibraltar HMSQueen’slogbook records lightwesterlies. The Cádiz diary notes cloudless conditions of 14th and 15th giving wayto cloud, light rain and squalls on the 16th and again on 17th with winds from thewest. A general recovery to more settled, drier conditions over the British Isles andsurrounding seas occurred on 18th as pressure increased abruptly in the northernlatitudes. The synoptic situation on 16th is reconstructed in Figure 6c.

Period 4 (18–27 October). This period marked the change of the zonal indexwith a return to a negative phase (Figure 5). Air pressure continued to rise over

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the British Isles as an anticyclone intensified and, possibly, approached from thenorth-west to bring the settled weather noted above. Over the Gulf of Cádiz thefall in pressure is perceptible from 20th before descending steadily to the lowestOctober levels of 996.4 mb (corrected) on the 25th. The records from the Britishdiaries make increasingly frequent reference to fine, bright and frosty weather. Fog,the result of a temperature inversion over the Thames valley, was recorded at SyonHouse. Winds were light under the anticyclonic conditions, but adopted an east tonorth-easterly character from the 20th. Northern sites recorded calms from the 19thto 22nd and the centre of anticyclonic activity might thus have been located closeto central Scotland. The fall in temperatures was pronounced for both Newcastleand Ednam and resulted from nocturnal heat loss under clear skies.

Off Cádiz settled conditions characterised the 18th and 19th with light windsshifting from east to west under partially cloudy skies. Although the weather hereremained settled important changes were about to take place. These were first notedin the logbook of HMSAeoluswhich lay at 42◦N 10◦W on the 21st. She had beenin a westerly air stream since 18th with often cloudy conditions but late on the 21stwinds rose to gale force with rain and thunder.

By unfortunate coincidence this was the period chosen by Villeneuve to put tosea. He had already received his orders to sail, and was aware that five English shipshad been dispatched to Gibraltar, and that Admiral Rosily was on his way fromMadrid to replace him. This was his final opportunity and at 5.15 in the afternoonon the 18th the flag signal was flown instructing the Combined Fleet to unmoor.Winds which in the harbour had been north-west went round to a more advantage-ous south-easterly but remained light. Nelson’s private journal noted “Fine weather,wind easterly . . . the enemy cannot have finer weather to set sail”.

By next morning, with only some of the Combined Fleet out of port, the airpressure had risen slightly and the winds fell away. The French frigateThemiscould make no headway against the prevailing current while another frigate,Her-mione, had to be towed by rowing boats. But at 10 am the wind freshened fromthe south-south-west allowing the remainder of the fleet to get beyond the narrowsby 1 pm. The English fleet also noted the same rise of wind on the 19th. Theprogress of the Combined Fleet was slow and Nelson considered the possibilitythat Villeneuve may turn back to Cádiz even at this late stage. He did not, and inthe continuing south-westerly airstream the two fleets maintained their watchfuldistance throughout the 20th. The day was not without its meteorological eventshowever. The midday entries for all English logbooks note squally conditions andheavy rain with strong breezes. Thomas Webb, master of HMSAgamemnon, re-cords the event as a ‘fresh gale’ which caused considerable damage to his vessel.Nelson, in his private diary, describes “fresh gales and heavy rain”. In attemptingto work to the west in order to have sufficient seaway to pass through the Straitof Gibraltar, several of the Combined Fleet suffered minor damage. Rain alsoappears as a record in the Cádiz diary for 20th. By dusk however the conditionshad subsided. The consistency of record, and the abrupt, short-lived character of


this event suggests a line squall of the type common in these seas (MeteorologicalOffice, 1978). This disturbance appears not to have had sufficient vigour to carryit over the high ground immediately inland of the Spanish coast and there are norecords of strong breezes or gales in Gibraltar until the 24th.

On the morning of the 21st the winds had dropped to light south-westerly butwith an ominous swell from the west. At this stage the English fleet was ten miles tothe west and to windward of the Combined Fleet which was moving slowly towardsthe Strait of Gibraltar and within sight of Cape Trafalgar. Nelson’s plan was toengage the enemy in two columns and the signal was made for the fleet to forminto two groups, one to the north under Nelson, the other to the south under Vice-Admiral Cuthbert Collingwood. Fearful that they might slip away, the English fleetput on all sail to close with the enemy. At 8 o’clock Villeneuve ordered his fleet toput about to the north and form in traditional line ahead. In the light winds and withthe limitations of the raw crews this manoeuvre was as protracted as it was difficult.The task was, nonetheless, accomplished. The light winds and heavy swell ensuredthat neither fleet could make rapid progress, and the logbooks suggest speeds of oneor two knots only. Battle commenced at noon with Collingwood’sRoyal Sovereignbeing first to breach the enemy line. Nelson’s squadron engaged forty minutes laterand so began one of the bloodiest and one of the last major battles of the age ofsail.

Throughout the engagement the handling of the ships, difficult enough as aresult of damaged rigging, sheets and sails, was rendered all but impossible in thelight winds, the ships drifting rather than directing themselves through a shroud ofobscuring gunsmoke. Aware of the storm presaged by the swell, and of the hazardoffered by a lee shore, one of Nelson’s last, anxious commands had been for hisfleet to anchor at close of day. In the event few ships could do so, their anchors andropes having been shot away.

Winds remained light throughout the 21st with the swell persisting to night-fall. At midnight the winds were moderate and the sky cloudy but by 8 am onthe 22nd the gales and rain that had earlier struck HMSAeoluswere recorded inalmost every logbook. Some, e.g.,Royal Sovereign, noted thunder and lightning– suggesting severe instability. The weather now embarked on a spell of acutelyunsettled conditions that continued to the month’s end and which were to providea challenge to the English fleet as serious as that offered by the enemy.

This general description of conditions, combined with the anticyclonic, ‘block-ing’ situation over the British Isles, indicates the presence of a cut-off low overthe region that sustained itself for a period of some six or seven days bringingtypically unsettled and wet weather to this now exposed region. This system mayhave developed as early as 20th before drifting south-eastwards into the Gulf ofCádiz. The record of HMSHeron is helpful in this respect. This vessel was sailingsouth-westwards from Britain. Between the 19th and 22nd, when at 41◦ N 40◦W,she lay in the grip of strong northerly gales. These subsided on the 23rd as thevessel continued her south-westwards passage. These gales were probably those on

378 DENNIS WHEELER

the western side of the developing cut-off low that continued on its south-eastwardroute. It seems probable that this system, in common with most of its kind, movedslowly and remained beneath the cold pool of a quasi-stationary meridional trough.Off Cape Trafalgar south-westerly gales persisted through the 23rd but subsidedon the 24th with most logs noting only strong to fresh breezes. On land the Cádizweather book provides evidence of rain all day on the 20th, 22nd, 23rd and 24thwith showers finally clearing only on the 29th. Winds were mostly from the south-west and were recorded asrecargada(Beaufort force 7 or higher – see Table III)everyday between the 23rd and 26th. The respite offered by conditions on the 24thwas nevertheless short-lived and strong gales are recorded with great consistency(91 percent of sampled logbooks) on the 25th and 26th. By the 27th the stormhad abated but fresh breezes from the south-west persisted until the month’s endalthough some logs noted fresh gales as late as the 30th.

The full effects of the storm did not, however, range much further south or east.HMS Queen, sent to revictual in Gibraltar, recorded no gales, but did note ‘constantrain’ on the 23rd. While HMSWeazle, an armed brig that had been off Cádiz onthe 19th, was to be found to the east of Gibraltar on the 22nd where calms and lightairs were recorded. Gales appear in her logbook following only on a return passagethrough the Strait of Gibraltar on the 24th.

The record of the Channel squadron and other vessels helps to clarify develop-ments on the northern side of the weather system. Both HMSCaptainand HMSFoudroyant(still on blockade east of Brest) noted gales as early as the 21st, risingto strong gales from the 23rd to 27th all, significantly, from the south-east. Thefrigate HMS Triton, in Waterford Harbour, experienced winds rising from lightbreezes from the south-east on 18th to reach strong breeze force with rain on 26th.While HMS Aeolus(off the Portuguese coast) found herself negotiating south-easterly gales on the 25th, northerlies on the 26th and south-westerlies again onthe 27th. This variability suggests that the centre of cyclonic activity was nearby.Drawing on this evidence Figure 6d summarises the synoptic conditions on the dayof battle.

While the storm continued over the Gulf of Cádiz and the Bay of Biscay changeswere taking place over the British Isles. By the 24th the easterly circulation on thenorthern flanks of the depression had extended to embrace southern England withrain in many areas and a recovery of temperatures as high pressure was replacedby the milder cyclonic air streams. Air pressure fell steadily throughout the 23rdto 25th (Figure 5) as the system extended its range. The same poor weather did notreach Scotland until the 26th where the weakening grip of the anticyclone persisted.Wet, windy and easterly weather was widespread across England until the 30thwhen the records show a change of wind to the north-west with fresher and drierconditions accompanied by a sharp rise in air pressure.

Period 5 (27–31 October).Pressure increased steadily at Cádiz over this period.There was also a rapid rise of air pressure over Britain on the 31st. During thisphase the English fleet endeavoured to keep well away from the lee shore of Cape


Figure 7. Victory towed into Gibraltar 28th October 1805. An oil painting by Clarkson Stanfield R.A.completed in 1853. When first exhibited Lieutenant Paul Harris Nicholas’ epigraph began “Disabledships continued to arrive for several days bringing with them the fury of the late gale”. Whilst doubtwas cast by contemporaries over the accuracy with which HMSVictory was represented, the condi-tions of both sea and sky are consistent with the evidence for the day.Reproduced by kind permissionof Lord Somerleyton.

Trafalgar whilst simultaneously repairing the damage and maintaining control ofthe prize vessels captured during the battle. Most of the fleet were able to takeadvantage of the more settled conditions and reached the fastness of Gibraltarby the month’s end but without most of the prizes of captured enemy ships. Theconditions portrayed in Figure 7 may be an accurate representation of the weatherof the time with choppy, but not fierce, seas and much cloud.

6. Interpretation of Weather Events

The severity of the storm is difficult to gauge. Impressions were doubtless colouredby the state of the crews and condition of the vessels. That the gale reached force10, even 11, is however highly probable. In a letter written by Henry Walker onHMS Bellerophonto his mother he states “. . . a storm came on such as I havenever witnessed, and for the four following days we had a much severer struggleagainst the elements than the enemy”. But Walker was a relatively inexperiencedmidshipman. More significantly, the seasoned Captain Henry Blackwood in a letterto his wife wrote “Wed. 23rd . . . it has blown a hurricane . . . ”. The term ‘hurricane’

380 DENNIS WHEELER

TABLE IV

Percentage of wind observations from each direction for the monthOctober 1805. Calms have been excluded from these data andcalculations. Data are based on the modal classes for each day

Sation N NE E SE S SW W NW

Channel fleet 0 7 21 42 10 7 7 7

Cadiz fleet 3 10 7 13 0 43 10 13

was, in those days, commonly used to describe all violent winds, tropical andotherwise.

The most probable interpretation of events is that they were brought about bythe development of a cut-off low. These are not unusual to the immediate westof Iberia and they are recognised as a ‘synoptic type’ by the U.K. MeteorologicalOffice (1978) and by the Spanish Instituto Nacional de Meteorología (Font Tullot,1983). The timing was typical of such developments and the October–Novemberperiod is when they are most frequent with the two months accounting for overone-quarter of their present-day annual incidence. The distinctive features of thiscut-off low were its duration (in excess of seven days), intensity (force 9 or above)and geographic range (extending across 15 degrees of latitude). Indeed it should benoted that no close analogue has been found in the meteorological record of thisarea from 1950 onwards (Wheeler, 1987).

Cut-off lows require a cold pool aloft with marked meridionality in the upperwesterlies. Instability would be a necessary consequence of this arrangement (Boy-den, 1963) and the contemporary records of thunder and lightning support thisinterpretation. In addition the synoptic pattern for the period with the ‘blocking’high over the British Isles and a deep low over the Gulf of Cádiz supports anysuggestion of meridionality. Cut off lows also produce some of the heaviest falls ofrain in southern and Mediterranean Spain. It is unfortunate that daily rainfall datafrom Cádiz are not available. However the month’s total was well above normal andof the eleven ‘rain days’ in the record, eight occurred after the 21st and probablyprovided a corresponding proportion of the month’s total. The logbook entries alsoindicate the same 11 rain days at sea.

It is also important to set these events in a wider contemporary time frame.The year falls within the Little Ice Age and Lamb (1977 and 1995) has offeredcogent arguments to support the hypothesis that this period was one characterisedby more marked meriodonality in the upper westerlies than has occurred in most ofthe twentieth century. He has also shown (Lamb, 1991) that during the early yearsof the nineteenth century the incidence of south-westerly days was the lowest since1300 AD, with an annual frequency of only a little over fifty in contrast to thepresent day frequency of nearly 100. Table IV summarises the wind directions


Figure 8.Ten-year running means of October air pressure differences between grid squares 65◦ N10◦W and 40◦ N 10◦W.

experienced by the two fleets and the dominance of easterlies observed by theChannel Fleet conforms to Lamb’s suggestion and again hints at low-zonality/high-meridionality in the mid-latitude circulations. Only the vessels of Nelson’s fleet, farto the south, experienced more westerly weather. Closer attention reveals a morecomplex picture however. The gridded barometric data set cited above confirmsthe low zonality of the month’s overall circulation and the pressure differencebetween grids 40◦ N 10◦W and 65◦N 10◦W was just 0.2 mb. On only three otheroccasions in the period 1780 to 1880 did the October difference fall below this;1785 (–0.4 mb, i.e., the month’s average air pressure was higher to the north),1864 (–8.0 mb) and 1876 (0.0 mb). The following century (1880–1980) provided,on the other hand, eight Octobers with a smaller pressure differences. It might beconcluded on this basis that conditions of October 1805 were, in contradiction toLamb’s speculations, anomalous. This apparent disagreement is partly resolved byreference to Figure 8 that reveals the period 1800 to 1825 to have been charac-terised throughout by small pressure differences between to two areas. October1805 differed, it would appear, only in degree, rather than kind, from this longerterm tendency. The later years show more frequent departures of this type but onlywithin a more variable setting.

This system’s extreme behaviour may be seen in other aspects. No reliable datahave been assembled for the early nineteenth century but in recent times gales in thesea areas off-shore of Cádiz represent only 2 percent of all observations. Similarlythe minimum air pressures of 994 mb fall within the current lowest 5 percentilepoints on the pressure cumulative frequency distributions (U.S. Navy, 1974). The

382 DENNIS WHEELER

duration of the gales was also exceptional and only about 10 percent of cut-off lowspersist for seven days or longer (U.K. Meteorological Office, 1978). This furtherevidence of possible extreme behaviour perhaps explains why, as noted above, norecent analogue for such conditions has been found.

7. Conclusion

Studies of this nature serve many purposes. On the one hand they lend a climato-logical perspective to historical events. More importantly, they provide a means ofdetermining the nature of past climates within a fine temporal scale of one to threedays and a spatial resolution that whilst depending on logbook availability can,in the correct circumstances, go down to less than 100 km. Kington (1988) hasalready produced a series of daily maps for the 1780s making limited use of log-book material. Although logbooks lack the statistical detail of instrumental recordsit has been shown that they provide nonetheless a reliable means of determiningwind, weather and, by inference, pressure patterns across oceanic areas. Statisticalmeasures confirm the consistency of logbook evidence. Persuasive evidence of thesource’s scientific value is provided by the mutual agreement of different sourcesand the unequivocal manner in which the data are accommodated within the dailysynoptic reconstructions. Only rarely do individual observations fail to fit withinthe broad synoptic reconstruction.

In this particular example the extent in space and time of an individual, if not-able, storm has been estimated and its intensity gauged with sufficient reliability toset it against present-day and contemporary conditions. Future undertakings couldwell be directed to extending such short-period studies over longer spans of timethereby establishing a picture of the evolving nature of climate and climatic changeat the annual and decadal scales. Such a major programme of work would do muchto improve our knowledge of climatic change in the immediate pre-instrumentalperiod. The fact that such information reliably describes the conditions over theoceans adds significance to future endeavours in this field given the relative povertyof data from those areas. Two hundred years later, we might recall the words ofBeaufort cited in the introduction – that the ‘meteorological philosopher’ will findmuch of value in the study of logbooks.

Acknowledgements

The author acknowledges with gratitude the financial support provided by theRoyal Meteorological Society for the preparation of a copy of the Cádiz weatherdiary. Thanks are also extended to Dr. Francisco González, the archivist at theReal Observatorio de la Marina, San Fernando, Cádiz, and John Kington, ClimaticResearch Unit, University of East Anglia, Norwich, for reading an early draft of


the paper. The author also acknowledges the informative and helpful comments ofMichael Chenoweth and John Walsh who reviewed the initial submission of thispaper toClimatic Change.

Appendix A

TABLE A.I

The logbooks of the following vessels were consulted in the preparation of this paper. All items arein the care of the Public Records Office, Kew, Surrey, U.K.

Vessel Reference number Sailing area Details of vessel

Achillea ADM51/1535 Bay of Cadiz Ship-of-the-line 74 guns

Aeolus ADM51/1576 Bay of Biscay Frigate 32 guns

Africaa ADM51/1518 Eng. Channel – Bay of Cadiz Ship-of-the-line 64 guns

Britanniaa ADM51/1552 Bay of Cadiz Ship-of-the-line 100 guns

Captain ADM51/1525 English Channel Ship-of-the-line 74 guns

Conquerera ADM51/1529 Bay of Cadiz Ship-of-the-line 74 guns

Excellent ADM51/1558 English Channel Ship-of-the-line 74 guns

Foudroyant ADM51/1475 English Channel Ship-of-the-line 74 guns

Heron ADM51/1576 Atlantic Ocean Armed sloop

Naiada ADM51/1518 Straits of Gibraltar Frigate 38 guns

Polyphemusa ADM51/1544 Bay of Cadiz Ship-of-the-line 64 guns

Princea ADM51/1543 Bay of Cadiz Ship-of-the-line 98 guns

Queen ADM51/1540 Bay of Cadiz Ship-of-the-line 98 guns

Royal Sovereigna ADM51/4494 Bay of Cadiz Ship-of-the-line 100 guns

Seahorse ADM51/1582 Valetta Harbour, Malta Frigate 32 guns

Siriusa ADM51/1595 Bay of Cadiz Frigate 32 guns

Triton ADM51/1557 Waterford Harbour, Ireland Frigate 36 guns

Victorya ADM51/4514 Bay of Cadiz Ship-of-the-line 100 guns

Victoryb ADM52/3711 Bay of Cadiz Ship-of-the-line 100 guns

Warrior ADM51/1543 English Channel Ship-of-the-line 74 guns

Weazle ADM51/1493 Straits of Gibraltar Armed brig

a Indicates that this vessel was present at the Battle of Trafalgar.b This logbook is that of the Master of HMSVictory. All other log are those of the respective ship’scaptains.

384 DENNIS WHEELER

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(Received 7 July 1998; in revised form 31 January 2000)

Documents

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