Popular Science Monthly/Volume 80/February 1912/The Value of Non-Instrumental Weather Observations
| THE VALUE OF NON-INSTRUMENTAL WEATHER OBSERVATIONS |
HARVARD UNIVERSITY
MUCH emphasis has been laid—and lightly—upon the necessity, in climatological studies, of systematic observations, carefully checked, punctually recorded and extending throughout many years, of properly exposed standard meteorological instruments. Upon such observations the scientific study of the world's climatology must be based. Without them everything remains vague; no real comparison of climates is possible; no detailed investigations of climate in relation to health, to crops, to industry, can be undertaken. Our conviction has become fixed that unless we can keep such a series of standard records, with a considerable and expensive instrumental equipment, it is not worth while to attempt any meteorological observations whatever. This is far from being the case. There is a very considerable series of observations—non-instrumental, unsystematic, irregular, "haphazard" if you will—which any one with ordinary intelligence and with a real interest in weather conditions may undertake. Such a diversion will add greatly to the interest of our humdrum every-day life, and will develop from day to day, in a surprising way, powers of observation which we were unconscious of possessing. Obviously, when such non-instrumental observations can be made at regular hours, at one place, they lead to a more compact and complete result than when they are made at odd times, in different places, as during a journey.
During the past summer, while recovering from a recent illness and therefore not wishing to burden myself with routine instrumental observations, I have found great satisfaction among the New Hampshire hills in working out day after day the local meteorological conditions. I have tried to banish from my mind altogether my previous knowledge of the climate of the region as a whole, and of the meteorological phenomena of mountain districts in particular. Thus, open-minded and unprejudiced, as far as possible, I have gradually worked out the essential elements of a local, non-instrumental climatology—an undertaking which has given me great interest, and I frankly confess has added not a little to my general store of climatological knowledge.
During the excessive heat of the first part of July (1911) it was comforting to note[1] that the maximum temperatures up in the New Hampshire hills averaged 3°–5° lower than at the Weather Bureau station in Boston, and that the nocturnal minima in the clearer air and at the higher altitude of my hillside were also several degrees lower than the disagreeably high minima of the city. The very regular occurrence of marked up-slope and down-slope ("mountain and valley") winds on all fine days; the increasing wind velocity towards noon and in the early afternoon, with calm mornings and evenings ("diurnal variation in wind velocity"), on these same days; the wonderful growth of cumulus clouds on the surrounding mountains and in relation to them; the development of cloud banners, cloud caps and cloud cascades; the effect of the general topography upon the local wind direction; the development of low-lying valley fogs at night, their gradual rise as fracto-stratus clouds and their dissipation under the morning sun; the marked difference, in relation to exposure to the cool nocturnal downhill breeze and to valley fogs, which neighboring house-sites exemplified; the apparent development of small local thunderstorms over the near-by mountains, while the larger thunderstorms came across these same mountains unaffected by the topography—these were a few of the many things which my very casual observations emphasized. Apart from these special subjects the general sequence of the larger weather changes resulting from cyclonic and anticyclonic controls was, of course, noted. So distinctly worth while has this simple and far from burdensome undertaking proved that I heartily recommend others to try it, but let it be repeated that real interest will come only if all previous meteorological knowledge of the region is, so far as possible, banished from the mind. And let me warn every one that he must beware lest his meteorological explanations run counter to the general traditions of the community. The location of most of the abandoned farmhouses in the region where I spent the summer, on the hillsides or even hill-tops, seemed to me to be most naturally explained on the theory that they were placed there in order that they might be above the cold and frost and fogs of the valley bottoms. One of my neighbors, who firmly believed that these houses were placed on the hill-slopes so that their original owners might have early warning of the approach of Indians, has upbraided me with shattering all the old and romantic traditions of the place. Let me suggest, further, that a very simple study of the value, as prognostics, of many weather proverbs will prove an interesting occupation. Weather proverbs are good, and bad, and indifferent. Most of them are bad, that is, do not work at all. A large number are indifferent, that is, work both ways. Comparatively few are really good. It is well worth while to select a few of the best known proverbs and keep careful written record of the times that each one "hits," and also of the times that each one "misses." Most people count the "hits" and disregard the "misses." If such a record be kept, the wheat will be separated from the chaff, but a week or a month of record, while long enough to bring out much of interest, is far too short a time for purposes of scientific comparison of relative values.
Travelers, even when passing rapidly through a country on the railroad, and, still better, when moving more slowly on horseback or on foot, usually have opportunities for making simple non-instrumental observations which will add greatly to the interest of their journey, and which, if the region is comparatively little known, may really be of considerable importance. I have long felt that what I have termed "car-window climatology" deserves far more attention than it has received. In my own experience when traveling in South America under conditions which usually made it impossible to carry any instrument except a sling psychrometer, it was found feasible, when journeying on horse or mule back, on the Brazilian "trolley," or in the train, to collect facts which added greatly to my understanding of the climatology of the regions passed through; made the trips alive and interesting, and helped to hasten the passage of many weary hours. Some of these observations, indeed, it has seemed worth while to publish. There are many observations which an intelligent traveler can make, even from a car-window, although a slower method of progression is, of course, to be preferred in such a study. "Wind velocity may be reasonably accurately estimated, after a little practise, by noting the effect of the wind in blowing trees, or in producing waves of different sizes in lakes or on rivers. The prevailing wind direction can often be very accurately determined by observing the slant of wind-blown trees, or again, by taking note of the effects of wave action on the leeward side of a lake or pond. Vegetation always furnishes a general criterion in regard to temperature and rainfall. When trees shed their leaves we infer a season of cold or it may be of drought. The occurrence of frost may be detected both by seeing it, and by noting its effects. The altitude reached by frost may likewise be observed. The direction of rainy or snowy winds may be discovered by observing on which side trees are wet. Whether or not hail, or snow, or sleet, or frozen rain, or gales, or heavy rains, or fog, occur in a region is observable, so far as the period of his visit is concerned, by any traveler. Forest and prairie fires indicate droughts, or dry seasons. Tornadoes and high gales, may be detected many years after their occurrence by the damage they did to trees. Whether or not a river is subject to floods may usually be determined by such hurried observations as can be made from a car-window, by noting the mud deposited by former floods on the trunks of trees, or by seeing the banks and neighboring fields actually overflowed. The condition of the roads, whether dusty or muddy, indicates in a general way the occurrence or lack of recent rainfalls. And thus, through a long list, we might go on. Non-instrumental, even irregular and scattering observations of meteorological conditions, and of their effects, are well worth while, if intelligently made. Such observations should be more generally undertaken.
During the short semi-vacation of the past summer I have found much interest in reading the "Journals" of the Lewis and Clark Expedition "to the sources of the Missouri, across the Rocky Mountains, down the Columbia River to the Pacific in 1804–06" What struck me particularly was the remarkably clear picture which I gained of the climatic conditions of the then unknown country through which, amid great hardships and many dangers, this famous expedition passed. The leader of the expedition was charged by the President with reporting upon very many matters besides meteorology.[2] Yet, in spite of the many difficulties of the journey, and with only one instrument — a thermometer — which was unfortunately broken before the end of the trip, the observing eye of Captain Lewis was able to note a variety of meteorological and climatic facts which give a vivid picture and emphasize, in a striking manner, the kind and the value of simple weather observations which any intelligent traveler can take.[3] In view of the many hardships of the journey, it is surprising to see how few gaps there are in the record, which covers the period January 1, 1804—September 30, 1805. Between May 14 and September 18, 1804, there comes the only considerable gap, with the significant comment: "The party were then just beginning the ascent of the Missouri, and it is probable that amongst the many other important things which engrossed their attention this was omitted." The tables give date, and thermometer, weather and wind direction at sunrise and 4 p.m.; also the rise and fall of rivers, in inches and feet.
The thermometer readings have, perhaps, less value than might be expected, partly because they could not be continued throughout the expedition, partly because they were made but twice a day, and partly because it is unlikely that the instrument was always well exposed.[4] The highest temperature noted was 92° (July 31 and August 4, 4 p.m., 1805), and the lowest was –45° (sunrise December 17, 1804). Clearly the expedition passed through a country of large annual and diurnal ranges of temperature (east of the Rocky Mountains). The summer afternoon temperature rose to 70°–80°, and even 90°, while in winter the sunrise readings were as low as –20°, –30° and even –40°. The diurnal ranges are noted as having been extremely large among the mountains, and on one day a difference of 59° was noted between sunrise and 4 p.m. The prevailing summer type of weather was fine, warm or even hot days, with cooler evenings and nights; not infrequent thunder-storms, moderate to high winds, especially in the afternoons. The southerly winds are so often referred to that we have little hesitation in concluding that this is the prevailing direction in summer on the Great Plains, and we see at once, in our mind's eye, that great sweep of southerly and southeasterly winds, across the region west of the Mississippi River—the continental inflow of summer, in response to the pressure-gradient between the Gulf of Mexico and the interior of the continent. These winds are frequently described as of high velocity during the daytime, blowing the sand from sand-bars and river-banks. Within the past quarter-century these same winds have been harnessed for the service of man, and they are to-day driving hundreds of windmills on the Great Plains for pumping water for stock and for irrigation, for sawing wood and for grinding corn and wheat. Captain Lewis observed that "the winds blow with astonishing violence in this open country." We have learned since that their velocities are not only high, comparable with those along the seaboard, but that they are also very uniformly distributed through the year, and are "usable" for windmill purposes to a remarkable degree. But no more striking illustration of the wind velocities on the plains has ever been given than Captain Lewis's description of the occasion when one of his boats, which was being transported on wheels, was blown along by the wind, the boat's sails being set! Surely this account emphasizes the analogy between the winds of the ocean and the winds of the Plains. Both sweep over a surface of little friction. Both attain high velocities in consequence.
The frequent occurrence of rain in May and June emphasizes the season of maximum precipitation (the "Missouri Type" of Gen. A. W. Greely) which has since proved of such immense economic benefit over this great region, for on the whole the most rain falls when it is most needed for agriculture. A different seasonal distribution of precipitation would banish agriculture from thousands of acres of land which are to-day giving our farmers good crop returns. The fact did not escape the watchful eye of Captain Lewis that the rainfall of the warmer months over the region which he crossed is essentially spasmodic and "patchy" in character, i. e., is of the shower or thunderstorm type, as contrasted with the more general and widespread rains and clouds of the large storms which characterize the winter months over the country as a whole. It is this very peculiarity of "patchiness" of the warm-season rains which renders them disappointing to the farmers whose crops are suffering from drought. A half-hour shower, covering perhaps a very small portion of a state, is a terribly exasperating occurrence to those whose lands are "screaming for water," but are outside of the limited area covered by the rain. Further, the fact that there is "very little rain or snow either winter or summer," is a sufficient emphasis on the general decrease in the rainfall to the west of the Mississippi River, which is so marked a feature on our mean annual rainfall maps. Captain Lewis paid particular attention to thunderstorms, in which, probably because of their violence, he seems to have been much interested. On April 1, 1805, he wrote, "I have observed that all thunder clouds in the western part of the continent proceed from the westerly quarter, as they do in the Atlantic states." This is perhaps the first specific mention of this important meteorological fact. On May 18, 1805, the record states: "We have had scarcely any thunder and lightning; the clouds are generally white, and accompanied with wind only." This we may take to indicate that the season of maximum thunderstorm activity had not begun, the clouds were doubtless our typical summer cumulus clouds, which, being best developed when the wind is strongest, i. e., in the warmer hours, are often called "wind clouds." A thunderstorm which occurred on June 27, 1805, receives special mention. This storm lasted two hours and a half, and was accompanied by hail about the size of pigeons' eggs, which covered the ground to the depth of 11⁄2 inches. Some of the hail-stones rebounded from the ground to a height of 10 or 12 feet. Several of the men were knocked down and bruised; some got under the canoe for protection, and others covered their heads. One hail-stone weighed 3 ounces and measured 7 inches in circumference. The stones were generally round, and perfectly solid. Captain Lewis adds: "I am convinced that if one of these had struck a man on his naked head it would certainly have fractured his skull." On July 6, 1805, another thunderstorm brought hail which covered the ground and was near the size of musket balls. One blackbird was seen to be killed by the hail, and Captain Lewis was "astonished that more have not suffered in a similar manner."
Our general understanding of the essential climatic characteristics of the country through which the expedition passed, already reasonably accurate although only in outline, becomes clearer as we pick out other details which are noted in the journals. "The air is remarkably dry and pure in this open country. . . . The atmosphere is more transparent than I ever observed it in any country through which I have passed," Captain Lewis says, thereby bringing out very clearly one of the great climatic advantages of the region. The rapid evaporation, which has its disadvantages as well as merits, was frequently observed. Thus (September 23, 1804) on one occasion "in 36 hours 2 spoonfuls of water evaporated in a saucer," and elsewhere in the "Journals" we note that the rapidity with which Captain Lewis's ink dried up was recorded as furnishing a striking illustration of the dryness of the air. Surely that gives us a hint as to what can be done by a traveler who is alive to what is going on around him. The difficulty of making any accurate estimate of distances in the air of the mountain country, so much drier and purer than that to which he had been accustomed, struck Captain Lewis forcibly. Similar difficulty has been experienced by many persons whose eyes have become trained to estimate distances in turbid air near sea-level, and find, on mountain tops, that their whole scale of distances must be revised in order to allow for the greater clearness of the mountain air. Although the winter was spent on the Pacific coast, there was no lack of opportunity to observe frost and cold on the Plains and northern plateaus. Frost we find recorded as "white," "hard," "very hard." The thickness of ice frozen in a day is often recorded. On October 18, 1804, we note that water in vessels exposed to the air was frozen, as was "the clay near the water edge." And on another occasion (April 15, 1805) "the earth at the depth of about 3 feet is not yet thawed, which we discover by the banks falling in and disclosing a strata of frozen earth." It was recorded that snow fell on the mountains while rain fell at lower levels—a common phenomenon resulting from the lower temperatures aloft. The occurrence of nocturnal radiation fogs; the prevalence of cold northwesterly winds in the colder months (as contrasted with the warm southerly and south-easterly winds of summer); the depth of snowfall; the appearance of auroras, and of haloes and other optical phenomena; the migrations of birds; the coming of rains with northwesterly winds (this being a combination which is not very common in the eastern United States, but occurs more frequently in the west)—these are a few of the many instructive observations which have been picked out in a rather haphazard way from the very rich harvest in the "Journals." The occurrence of a heavy dew near the Falls of the Missouri is attributed to the greater dampness of the air in that place resulting from the spray produced by the falls. This reminds one of the reported appearance of dews in the vicinity of desert oases, and of the tradition that travelers across deserts have often been assured of their approach to an oasis when they have observed that dew forms at night. The frequent firing of the grass on the Great Plains by the Indians is often referred to, but there is no reference to the possible effects of this custom upon the treelessness of the region.
The winter time which was spent by the Lewis and Clark Expedition on the Pacific coast, at the mouth of the Columbia River, gave Captain Lewis abundant opportunity to observe the meteorological and climatic peculiarities of that region, and to contrast them with those with which he had become familiar in the east. "The loss of my thermometer I most sincerely regret," he wrote on January 3, 1806. "I am confident that the climate here is much warmer than in the same parallel of latitude on the Atlantic Ocean, though how many degrees it is now out of my power to determine." A few days later we read, "Weather perfectly temperate. I never experienced a winter so warm as the present has been," and note is made of the fact that the Coast Indians wore, and needed, less clothing than those east of the mountains. Clouds, and heavy rains and gales—much changeable stormy weather and very little sunshine—made such an impression that Captain Lewis wrote, "The vicissitudes of the weather happen two, three or more times in half a day." The early part of the winter was so mild that, as already noted, it could not fail to attract attention for that reason. There being no ice, meat was smoked in order to save it, and even that method was by no means uniformly successful. Later on, however, we find frequent mention of greater cold, of snow and of "hail" (frozen rain?). On January 28, 1806, a vessel of water was exposed in order that the thickness of ice might be measured. Unfortunately, the water was only two inches deep, and it froze to the bottom. "How much more it might have frozen had the vessel been deeper is therefore out of my power to decide," was Captain Lewis's interesting and critical comment. It is clearly stated that the winds from the land were cold and clear, while those obliquely along the coast or off the ocean brought warm, damp, cloudy and rainy weather. Thus a significant climatic control received early and explicit recognition. Later in the winter (March 6) this earlier statement was qualified as follows: "Easterly winds which have heretofore given us the only fair weather we have enjoyed seem now to have lost their influence in this respect." The strongest winds came from the southwest. There is further an interesting statement to the effect that a certain harbor was not protected against southerly and southeasterly winds, but as these seemed to be winter winds the harbor would doubtless be safe in summer. The explanation, which could not be given in Captain Lewis's time, is to-day found in the frequency of strong southerly winds during the cyclonic storm season (winter) of the Pacific coast. If any one can read Captain Lewis's weather record for the northern Pacific coast without gaining from it a vivid idea of the cloudiness, the heavy rainfall, the high winds, the small amount of sunshine and withal the mildness of the winter of the particular district which the expedition encamped, he must be a hopelessly unappreciative and unintelligent person.
In looking over what I have written on the weather records of the Lewis and Clark Expedition, I realize that I have failed to bring out, with any of the clearness which it was my hope to secure, the climatic picture which Captain Lewis makes so distinct and so interesting. In spite of the deficiencies in my presentation, I hope, nevertheless, that I have to some extent succeeded in emphasizing the value of non-instrumental meteorological observations.
- ↑ A sling thermometer was used in this case.
- ↑ President Jefferson instructed Captain Lewis to report upon climate as follows: "Climate, as characterized by the thermometer, by the proportion of rainy, cloudy and clear days; by lightning, hail, snow, ice; by the access and recess of frost, by the winds prevailing at different seasons; the dates at which particular plants put forth, or lose their flower or leaf; times of appearance of particular birds, reptiles or insects."
- ↑ Captain Lewis's scheme of notation of weather was as follows :
f, fair weather. c, cloudy. r, rain. s, snow. h, hail. t, thunder. l, lightning. a, after, as f a r means fair after rain which has intervened since the last observation. c a s, cloudy after snow intervening. c a r s, cloudy after rain and snow. - ↑ It should be noted, however, that at the beginning of the table of observations, where the first data are given, for "Duboes, "January 1, 1804, it is stated: "Thermometer on the north side of a tree in the woods." This surely indicates careful attention to exposure, when possible.