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Proceedings: 7th Tall Timbers Ecology Conference 1967

The of

E. V. KOMAREK, SR. Tall Timbers Research Station, Tallahassee,

THE PREVALENCE and behavior of lightning fires are of interest to those of us who study the mosaic of plants and animals and attempt to interpret the ecological conditions existing before changes made by man. We at Tall Timbers are particularly interested in those natural processes and principles that underlie the occurrence, abundance, and welfare of the plants and animals that surround us. We are vitally concerned with the ecology of man and his environment. Lightning, and lightning fires assumed a position of great impact on ecosystems before man came to this continent some 20,000 years ago, more or less. As I have discussed many phases of this "fire mosaic" in several previous papers (1962, 1963, 1964, 1965, 1966), let me simply state the obvious: Man did not invent fire or forest fires. They were a part of the long before the coming of man. My personal interest as a fire ecologist is to develop an under­ standing of the many ramifications of fire in nature; its effects on the habitat and on the plants and animals themselves as well. At the same time, however, I wish to point out that as an ecologist I am all too aware that man himself is a creature of his environment -his fire environment if you will. Thus, if man is to be successful in this environment with its great potentiality for fires he must understand the processes that control such an environment. All too

5 E. V. KOMAREK, SR. often we are concerned too much with the final effects instead of the underlying basic patterns of both the living, as well as the chemo-physical world in which we live. It is with these thoughts in mind ~hat I present this paper. Lightning as a cause of forest fires has long been recognized and a rather extensive literature has developed in the past half­ century. Unfortunately, most of the more detailed studies have appeared in publications of specialized interest with limited distribu­ tion. Much of this material is not indexed and has found its way into all too few bibliographies. After some 10 years or more of constant interest in a study of this subject, I still continue to find excellent and thorough scientific studies made many years ago that, in a manner of speaking, have been lost in the literature. This study of the nature of lightning, and lightning fires, is based on 22 years accumulation of data on lightning fires by the U. S. National Forest Service as published in its Annual Fire Reports for the National Forests. In addition, I have reviewed the literature quite extensively in the Library of Congress, the National Agricultural Library, the Library of the American Institute of Electrical Engineers, as well as others. I will incorporate considerable data, particularly from earlier studies in publications that are not easily accessible. First, however, I wish to thank both the U. S. Forest Service and its many workers both in the Washington office and on the forests for their readiness to furnish data. Much time as well as expense was necessary to furnish the information for which I asked. Likewise, members of the staffs of the Environmental Sciences Service Ad­ ministration have been both kind and helpful in furnishing data ranging from to .

LITERATURE REVIEW The U. S. Forest Service has conducted many excellent studies on lightning fires. G. F. Plummer (1912) pointed out the prevalence of lightning and lightning fires in the forests and gave a diagram on "Lightning Zones in Mountain Country." S. B. Show and E. I. Kotok (192 3) recorded much valuable information on lightning fires and in­ cluded a map showing "Lightning Fire Zones in the National Forests

6 THE NATURE OF LIGHTNING FIRES of ." J. A. Larsen and C. C. Delavan (1922) wrote on "For­ est Fires in Montana and Northern Idaho, 1909 to 1919", and included data on lightning-caused fires. H. T. Gisborne (1926) reported on four years of intensive study from 170 lookout stations in 1922 to 1925 inclusive. He pointed out that in a period of 18 years, 39% of the forest fires were caused by lightning in that region and that, " ... for the of 1924 and 1925 the figures are 51 % and 80%, respectively." George W. Alexander (1927) summarized data on thunderstorms and lightning fires in the state of Washington on the basis of Bureau and other records for a 20-year period 1904-1923, in that area. H. T. Gisborne (1931-1932) discussed and presented sound evidence on the nature of lightning fires based on a study of 14,754 lightning fire reports in the forests of Idaho and Montana. He gives an annual average of 824 such fires for the lO-year period, 1919-1928, as against only 379 man-caused or un­ known fires on 23,000,000 acres of land in that region. William G. Morris (1934) reported on a study ". . . based on more than 6,000 systematic reports describing lightning seen by United States Forest Service fire lookouts in Oregon and Washington during the months from 1925-1931, inclusive." Richard E. McArdle and Donald N. Mathews (1934) point out differences in lightning starts in snags and green trees in different areas and stated that over the Pacific Northwest region 42% of the lightning fires started in needles and duff. In this same report William G. Morris reports on lightning fire zones. J. S. Barrows (1954) points out that, ". . .during the 5-year period 1948-1952 over 17,000 lightning fires occurred in the ten Rocky Mountain states. The average an­ nualload of 3,500 lightning fires amounts to 63 % of the total number of fires occurring in the rugged mountain country ranging northward from and New Mexico through Idaho and Montana." Arnold Court (1960) in two papers gives much data on "Lightning Fire Incidence in Northeastern California and on Frequency in Northern California." Donald M. Fuquay (1962) states in a Skyfire Progress Report 1958-1960: During the 20-year period 1939-1958, lightning caused more than 132,000 fires in the 13 western states including Alaska. About 7,500 lightning-caused fires occur annually in the United States.

7 E. V. KOMAREK, SR.

In the western United States, lightning is the most frequent single cause of forest fires; in the Rocky Mountain states, 70 per cent of all forest fires are lightning caused. During one 10-day period in July 1940, the National Forests in western Montana and northern Idaho reported 1,488 lightning fires. Keith Arnold (1964), at our Third Annual Fire Ecology Conference in Tallahassee, presented a paper, "Project Skyfire Lightning Re­ search," and said, What is the lightning fire problem? Consider this; at this very moment some 1,800 thunderstorms are in progress over the 's surface. During the next 20 minutes these storms will produce 60,000 -to- lightning discharges. Some of them will start fires. This sequence occurs 9,000 times each summer in America's forests and grasslands (including Alaska and Hawaii.) During the period 1946-1962, the United States experienced more than 140,000 lightning-caused fires. These studies are all by Forest Service and Weather Bureau personnel. These are exceedingly well conducted scientific investi­ gations and there are many others. There is a great amount of scientific data of the highest quality and of much value in these investigations by foresters and as an ecologist, I certainly feel greatly indebted to them. In contrast, studies by plant and animal ecologists on this vital force in nature are practically non-existant.

LIGHTNING FIRES: 1945 -1966 INCLUSIVE An analysis by myself of the Annual Fire Reports of the National Forests for the 22-year period, 1945-1966, shows that the number of lightning-caused fires continues to be high. In this paper I have only used data relative to fires on federally owned lands. I have presumed that these are the most accurate. In this respect this data is on the conservative side. On the 186,497,010 acres of federally owned lands, 168,632 wild­ fires occurred, during the past 22 years (Fig. 1). This includes all 50 states and Puerto Rico. During this period 64% or 107,160 of these fires were caused by lightning and only 36%, or 61,472 were at­ tributed to man or were from unknown causes. The number of lightning fires ranged from a high incidence of 9,344 in 1961 to a

8 THE NATURE OF LIGHTNING FIRES low incidence of only 2,445 and an average annual figure of 4,871 per year (Fig. 2). The relation of the number of lightning fires to the acres of land in these same national forests is also of interest. In this 22-year period, the relationship of number of lightning fires to acres of land ranged from a high of one fire per 19,958 acres to a low of one fire per 76,276 acres; and an average of one lightning-caused fire per each 38,287 acres, federally owned (Fig. 3). These figures are nearly unbelievable, particularly when it is realized that the 186,487,010 acres of land considered, included millions of acres that can be classified non-flammable such as , areas, bare and certain kinds of deciduous forests where lightning is rarely en­ countered as a forest fire producing agent. Likewise, areas in build­ ings are not excluded. Were it not for the supporting data from the studies already referred to in the literature review and others, they would be unbelievable. This data means that, if the fires were averaged out over this area, each acre would be subjected to at least one lightning fire in less than 50 yt~ars When we consider that the incidence of lightning­ caused fires does vary considerably from year to year, and from region to region, then there must have been lands that before the advent of man, burned over from lightning fires periodically during a very short period of time; a ratio in some areas of nearly every three or four years.

CALIFORNIA LIGHTNING-CAUSED FIRES When we study the figures for lightning-caused fires on California national forests we see a much higher incidence of such fires than the national figure. During the 22-year period, there were 25,055 on 19,370,383 acres of federally owned lands within the California national forests. Of these 69% or 17,056 were caused by lightning and only 31 % or 7,999 by man or from unknown causes (Fig. 4). In 1948, the low year, 21 °lightning fires occurred, and 1961 was a year of high incidence with 1,764 fires of lightning origin (Fig. 5). There was an average of one lightning-caused fire for each 24,927

9 E. V. KOMAREK, SR.

~ WILDFIRES ON U.S. NATIONAL FORESTS

168,632 OWILDFIRES ON 186,487,010 ACRES ..... LAND

107,160 OR 64% CAUSED BY"l LIGHTNING

61,4 72 OR 36 % CAUSED BY i MAN OR? UNKNOWN

22 YEAR PERIOD 1945 - 1966 FIG. 1. Percentage of lightning-set and man-caused fires on all U. S. National Forests for the 22-year period 1945-1966.

107, 160 LIGHTNING FIRES ON U. S. NATIONAL FORESTS

"lLiGHTNING FIRES PER YEAR AVERAGE 4871

LOW INCIDENCE-1948 --- 2445 HIGH INCIDENCE-1966 -- 9344

186,487,010 acres - 50 states 22 year period -1945 -1966 FIG. 2. Incidence of lightning-set fires on all U. S. National Forests for the 22- year period 1945-1966.

10 THE NATURE OF LIGHTNING FIRES

107.160 LIGHTNING FIRES ON U.S. NATIONAL FORESTS

AVERAGE -ONE rt LIGHTNING FIRE PER EACH 38,287 ACRES

LOW INCIDENCE -1948 ONE rt LIGHTNING FIRE PER EACH 76,276 ACRES

HIGH INCIDENCE-1961 ONE 'l'LlGHTNING FIRE PER EACH 19,958 ACRES 186,487,010 acres-50 states - 22 year period 1945 -1966 FIG. 3. Acreage burned by lightning-set fires on all U. S. National Forests for the 22-year period 1945-1966.

WILDFIRES on CALIFORNIA NATIONAL FORESTS

25,055 OWildfires on 19,370,383 acres .....Iand

17,056 or 69" caused by I"'( LIGHTNING only 7,999 or 31" caused by i man or t unknown

22 year period 1945 -1966 FIG. 4. Percentage of lightning-set and man-caused fires on all California National Forests for the 22-year period 1945-1966.

11 E. V. KOMAREK, SR.

17,056 LI GH T N I NG FIR ES on CALIFORNIA NATIONAL FORESTS

'l LIGHTNING FIRES PER YEAR AVERAGE 775

LOW INCIDENCE -1948-- 210

HIGH INCIDENCE-1961 --1,764

19,370,383 acres in 17 National Forests 22 YEAR PERIOD -1945 - 1966 FIG. 5. Incidence of lightning-set fires on all California National Forests for the 22-year period 1945-1966.

17,056 LIGHTNING FIRES ON CALIFORNIA NATIONAL FORESTS

AVERAGE -ONE fJ LIGHTNING FIRE PER EACH 24,927 ACRES PER YEAR

LOW INCIDENCE-1948 ONE 'lLiGHTNING FIRE PER EACH 92,239 ACRES

HIGH INCIDINCE-1961 ONE 'lLiGHTNING FIRE PER EACH 10,981 ACRES

19,370,383 Acres in 17 National Forests 22 YEAR PERIOD -1945 -1966 FIG. 6. Acreage burned by lightning set fires on all California National Forests for the 22-year period 1945-1966.

12 THE NATURE OF LIGHTNING FIRES acres; a low incidence in 1948 of one such fire to each 92,239 acres and a high ratio in 1961 of one lightning fire for each 10,981 acres (Fig. 6). Thus, it is evident that the incidence of lightning-caused fires in the California national forests is higher than that in the na­ tional average; and also that the average ratio of lightning fires per acres of land is larger in California, and that the extremes from low to high incidence lightning years is greater than the national average.

METEOROLOGICAL BASIS FOR FIRE ECOLOGY Since I have presented a paper on "The Meteorological Basis for Fire Ecology" (Komarek, 1967), I shall give only a short review here. All too frequently, we take the weather more or less for granted and do not stop to consider the global patterns of weather that de­ termine our local weather conditions. Thunderstorms, even those that seem rather local, are due to processes of meteorological phe­ nomena, some of which take place far away. To have thunderstorms and consequently lightning, there must be air masses in which certain conditions of and moisture are present. These masses of hot and cold and moist air must meet. Although there are still several theories in regard to the development of lightning, they all are con­ cerned with the friction of drops or within this electrical generator we call the thunderstorm. Now these conditions can he rather limited, in which event only small local thunderstorms will develop. Then again, if a large tongue of moist, warm unstable air flows up from the Gulf of Mexico or from off the Pacific Ocean, particularly the southern or more tropical part of it, and this meets cold air descending from mountain tops or a cold traveling from the north, we have conditions for thunderstorms over a very large region. The length of one such large thunderstorm area has been reported (Climatological Summary 1966) to have extended for 800 miles in California along the Sierra Nevada. Morris (1934) re­ ported, Most of the lightning storms in Washington and Oregon have progressively built up ("moved") for a distance of from 11 to 40 miles. Only a few storms have exceeded 80 miles in length. The lightning fires in western United States have been plotted

13 E. V. KOMAREK, SR.

(Fig. 7) for the entire 22-year period. Note that the greatest fre­ quency of such fires occurs in southern Arizona and then progresses northward through central California and on into Oregon, Wash­ ington' Idaho and Montana. The arrows show the way in which moist, unstable air can come into this region to "trigger" ­ storms. In the previous mentioned paper I have shown several com­ bined weather and lightning-caused fire maps that show this quite clearly. The same patterns as illustrated in 1965 occurred in 1966. The topography of the western states with its mountain chains running largely north and south and with the intervenirtg valleys, lowlands, basins, and plateaus usually "open" on the southern end, so that moist unstable air can easily flow northward, is admirably suited for such thunderstorm development. This to a great extent determines the lightning fire zones as portrayed by Plummer, by Show and Kotok and others. Direction of Travel of Thunderstorms :-There is considerable agreement in all studies made in the West that thunderstorms travel from south and southwest to north and northeast about half of the time, and in some years as much as 67 % of the time. The two maps by Morris (1934) for Washington and Oregon show this quite well. These are composite maps for all the lightning storms reported during the summer seasons of 1929 and 1930. My data assembled from the fire reports of the California national forests show this same direction of travel as shown in this diagram (Fig. 8). Types of Thunderstorms :-There is agreement by all who have studied this subject that conditions for lightning-caused fires are created by three main types of thunderstorms. 1. The small "local "-only a few fires are caused by these. 2. The "general" type storm which occurs over a wide area and literally creates waves of lightning fires for three or more days. 3. The "intermediate" type storm that occurs over a smaller area and then for only a day or two. Nearly all the "peak loads" of lightning fires occur on these waves of "general" type storms which seem to occur somewhat regularly two to four times a month. Furthermore, when these "pulsating" storms occur after a long drought or when they consist of "dry lightning thunderstorms", and if there is any great amount of

14 THE NATURE OF LIGHTNING FIRES

WESlERN LIGHTNING • 250 - 500 FIRES • EACH 500 FIRES .. OVER 5000 FIRES ARROWS REPRESENT MOIST AIR FIG. 7. Number of lighming-set forest fires on western National Forests by Ranger Districts for 22-year period 1945-1966. flammable material in the forest or grassland, they create "fire storm" conditions. And the forest fire fighters cannot .control such fires no how many men and how much equipment is available. Nature must intervene with a change in weather conditions, a large natural barrier or the fire enters a region of low fuel.

15 E. V. KOMAREK, SR.

ASPECT

FIG. 8. Lightning set fires occur largely 011 south to southwest-west slopes in Cali­ fornia National Forests-22-year period 1945-1966.

Other Thunderstorm Characteristics :-There is general agree­ ment, as would be expected, that most of the lightning-caused fires occur in the summer months from June to October, but less frequently also earlier and later in the year. Gisborne's chart on the occurrence of thunderstorms appears to be typical of the far western region. He also has written that, at least in his studies, the so-called dry lightning storm did not produce an appreciably larger number of fires and that the condition of the forest as regards to moisture and fuel content was the most important factor.

16 THE NATURE OF LIGHTNING FIRES

Some studies have been made on the speed with which thunder­ storms move. Gisborne showed that in Washington and Oregon most thunderstorms moved only about six to ten miles per hour. However, from a fire spread viewpoint the generated by the thunderstorm itself are most important. Downdrafts occurring as the thunderstorm moves by, can create winds of forty to fifty miles per hour. Also, as the thunderstorm moves on, a -shift usually occurs. Thus, winds from one direction during or after the strike may push the fire in one direction. When a wind-shift occurs, and this can be a 180 0 shift, the fire then moves on a broad front of many miles in width. This is one of the main reasons that fires started by "general" type thunderstorms are so difficult to control. We have much to learn about the development, movement, ­ ning behavior, and many other characteristics of thunderstorms. The very rapid development of satellite meteorology by the U. S. Weather Bureau and other agencies offers hope that someday we can, not only understand climatic developments such as thunder­ ~torms, but may be then able to predict when and how they occur on a large scale. By photographing from the development and movement of , man for the first time can see such patterns in their entirety. Three of these photographs show three jifferent types of weather development. Figure 9 shows a small :ropical disturbance off the coast of Baja, California, of the type :hat can and does pump moist, unstable air into California and this ::ombined with the hot of the valleys and the cold :emperatures of the mountain ranges produce ideal conditions for :hunderstorm development. Figure 10 shows the pahern of develop­ nent and movement of "mountain waves" traveling down off the Rockies onto the Great Plains. These are not only hazardous to lir travel but can push fires rapidly over large areas. Figure 11 shows :hunderstorm development over a large section of the mountain ranges )f western South America, the Andes, etc. Note the development of he thunderstorms right over the mountains (A), then the maturing )f these (B) and (C) where the line of thunderstorms is dying md is characterized by the long line of eastward streamers. Pictures uch as these and eventually some with even more resolution, taken 760 nautical miles above the surface of the earth every 23 minutes,

17 FIG. 9. Small tropical disturbance off Baja California coast, September 20, 1967. (Photo by ESSA National Environmental Satellite-Environmental Sciences Service Administration)

FIG. 10. Mountain wave east of the Rockies, September 12, 1%7. (Photo by ESSA National Environmental Satellite-Environmental Sciences Service Administration) FIG. 11. Thunderstonn development over the Andes Mountains, South America, August 10, 1967 (Photo by ESSA National Environmental Satellite-Environmental Sciences Service Administration) A. Developing thunderstorms. B. Maturing thun­ derstonns. C. Thunderstonn streamers.

allow to study weather condition~ on a vast scale. As satellites become even more sophisticated with various kinds of re­ mote sensing devices for , temperature, barometric , etc., they will certainly reorganize all our thinking on the of the earth. The putting of these patterns on movie film with a lapse camera shows the actual movements shortened in time such as the motion pictures we commonly see of flower buds slowly opening and turning into flowers. In fact, satellite meteorology even now is gathering far more data than can be communicated or interpreted and an entire new "breed" of meteorologists will have to develop for its understanding.

AREA OF IGNITION-California National Forests, 1966

Topography: The upper third of the mountain slope apparently receives more lightning ignition strikes as shown in Figure 12 and the

19 E. V. KOMAREK, SR. remaining areas receive the rest rather evenly. In a recent study in Canada, Kourtz (1967) has reported that, Sixty percent of the strikes were within the top third of the hills, 19 percent were within the middle third, and 21 percent were within the lower third.

LIGHTNING FIRES Ignition Point

~ 148 MIDDLE" THIRD SLOPE , 130

114 LOWER THIRD SLOPE ~ OTHER FIG. 12. Ignition point by lightning in relation to topography. California National Forests 1966.

Specific Fuel, Point of Origin: Most of the time ignition from a lightning strike occurs in the , rotten-wood and duff; less fre­ quently in snags or spiketop trees, and occasionally in green trees. This may vary considerably from one area to another, (this was reflected in my figures from forest to forest) and is indicated by Morris (1934). Needles and duff on the ground formed the most important kindling material. Live trees were second in importance and dead trees third. In several national forests on the west slope of the Cascades, however, dead trees kindled more fires than any other material. Grass was important only in northeastern Washington.

20 THE NATURE OF LIGHTNING FIRES

Kourtz (1967) writes that, Further analysis revealed that 31.1 percent of all the trees that were ignited by lightning \vere dry snags, and probably only about 5 percent of the trees in the forests of Canada are dry snags. This suggests either that snags attract more lightning or that, when struck, they were more easily ignited than green trees. There seems to be general agreement that most lightning-caused fires are ignited in the litter and duff on the surface of the forest floor, but dead snags, spike-top trees, or even living trees can also be the point of ignition in considerable numbers in some areas. It should be obvious that heavy litter or duff provides an ideal "set" for lightning-caused fires. Fuel Type: In California national forests, by far most of the lightning-caused fires occur in mature forest: A forest in which trees of saleable value occur. Figure 13, however, also shows that fires can be caused in brush, young forest, grass, slash from lumber opera­ tions, chaparral, etc. Cover Type: Figure 13 showing the "cover type" in which light­ ning fires occur is quite interesting. Note that a large percentage of fires occurred in mixed conifer forests while lesser percentages occurred in pine and fir forests. It makes me wonder how much of this mixed conifer forest is natural and how much of it has been created by fire exclusion in a fire type forest, such as the original park-like ponderosa forests. Here in the West in many of the forests, as contrasted to the Southeast, fire exclusion allows a more highly flammable forest to develop than the original fire type forest. Ex­ amples of this might be ponderosa-fir; another, sequoia-white fir and in both instances the fir addition creates more flammable con­ ditions than the original pure sequoia or ponderosa pine. In the southeastern pine forests, fire exclusion permits a build up of hard­ wood understories that in time become less flammable than the original pine forest. But in both the West and Southeast, the fire excluded forest changes to a forest of decidedly less value. Elevation: In regard to the elevations at which lightning-caused fires occur, Morris (1934) writes, It has been a common belief that zones of great lightning fire risk exist at high more frequently than at low altitudes

21 E. V. KOMAREK, SR.

AREA OF STRIKE

FIG. 13. Origin of lightning-set fires by fuel-ignition point, by fuel type, and by cover type. California National Forests, 1966.

because the highest mountains seem more exposed to lightning flashes; but analysis of the altitudinal distribution of lightning fires in the mountains of Oregon and Washington shows that on a given national forest the number of lightning fires per acre at low altitudes is as great as the number at high altitudes if ap­ proximately the same number of lightning storms occur over the two areas and if there is sufficient kindling material. The greater number of lightning fires simply occur at the level containing the greater part of the land surface. To determine this relation­ ship precisely, the area of forest land between 0 and 2,000 feet altitude, 2,000 and 4,000, etc., was planimetered from United States Geological Survey topographic maps of three national forests in different parts of Oregon and Washington. In each case, the number of lightning fires which have occurred at each altitude during the 6-year period was directly proportional to the area of forest land at each altitude. However, apparently lightning fires do occur most frequently on the upper third or top of ridges, small mountain slopes, etc., as shown

22 THE NATURE OF LIGHTNING FIRES by Figure 12. I would like to emphasize here, however, that there can very well be climatic zones where certain atmospheric elements meet that would produce more lightning storms, but not necessarily more lightning fires because of heavier and different fuel characteristics of the forest. Lightning Fire Zones: Several writers have described the possi­ bility of lightning fire zones and Show and Kotok (192 3) illustrate this by a map of the lightning fire zones in the national forests of California. However, Morris (1934) writes: An attempt was made to construct a map showing comparative horizontal zones of lightning fire frequency. The starting points for 5,500 lightning fires which occurred on the national forests of Oregon and Washington were plotted on a single map. At first there appeared to be a few fairly well-defined groupings of these fires, but further analysis showed that there are not zones of consistently repeated fire occurrence. Detailed study of lightning fire maps for individual days indicates why there is little or no consistent zonation of lightning fire occurrence. Usually, the fires set on anyone day are widely scattered throughout the area covered by the storms, which is often 7,500 square miles; but occasionally the storms of a single day set many fires within a small area, giving to that area the appearance of a dangerous fire zone. Several years often elapse before another fire is set in the same locality, even though storms occur over it. Despite what seem to be differences in regard both to elevation and lightning fire zones by various authors, Figure 14 shows that there are relationships between lightning fires and elevation on a broad scale. The differences by writers may be in part due to local observations. This graph, on only a one-year record of fires, does apparently show that lightning fires are at higher elevations in the southern Sierras and at lower elevations in the northern Sierras and northern California. Checks on other years apparently bear out this assumption. I might point out that this graph, in a way, is quite similar to the zonation of various plant communities and forest types as they range from south to north in accord with well established climatic zones. As an example, the ponderosa pine forest is definitely at lower altitude zones in the southern part of its range as contrasted to its northern range. This is in agreement with other climatic factors

23 FIG. 14. Elevation of lightning-set fires in the California National Forests by Forest for one-year period 1966. THE NATURE OF LIGHTNING FIRES

such as temperature. As temperatures are an important part of thunderstorm development it would appear that at least through the summer months thunderstorms probably develop more frequently at certain altitudes depending in mountainous country on , as well as elevation. Daily Time of Lightning Fires: All studies apparently show that although thunderstorms and lightning fires occur at all hours of the day and they predominately occur in the afternoon hours. This is quite evident in Figure 15 showing time of lightning fires on California national forests for 1966.

FIG. 15. Time of ignition of lightning-set fires in California National Forests for 1966.

25 E. V. KOMAREK, SR.

FREQUENCY OF LIGHTNING FIRES The global aspect of weather patterns responsible for lightning fires is discussed in my previous mentioned paper. I have since graphed the data on all the lightning fires and man-caused fires on a continental basis; on a regional basis; on only those fires that oc­ curred in California, and finally on the basis of what appear to be different lightning fire regions in that state. The six graphs show in varying degree four basic trends (Figs. 16-21) .

. 1' II'II!II+ " Ii ]1, lltt lI!"f~i: i ',! !., ! :1 iAlri~1 - . l. -1W+l+~.'H ,. II, ' II" _ !11~ii'f-.; ! !~Ii "1 ,'. j-

FIG. 16. Lightning-set and man-caused fires on all U. S. National Forests annually for the 22-year period 1945-1966.

Trend No.1 I have already mentioned the fact that the summer months are obviously the months of highest lightning fire frequency. However, when the monthly records are analyzed not only for California but on a national basis, such fires do not occur randomly scattered

26 THE NATURE OF LIGHTNING FIRES

m~ il I' ;.1'] fl· Ii . cl t!., II. 11II .111 IIi 1111 If rm ! Ilil .1. T .• ·11' I11I 111~ Iii ·1 wITI;M'Jl ! j.j+t+H+c~Bii J • J.! i I I !' .. rrar.H+++lmT!+H'.+'+ ++11++' ~H+l ~Ii Ii: II111 Ii, ,; : II i !

FIG. 17. Lightning-set fires for the 22-year period 1945-1966 by general regions. Eastern region includes the Southeast.

27 E. V. KOMAREK, SR.

,.. _....

, i'

throughout the summer months. In fact, they occur in what one may call waves or clusters of fires. That is, these fires are ignited on only a few days, relatively speaking, and then only during short periods of from two to five or six days and these periods will occur only two or three times a month. As pointed out in my paper on the meteorological basis for fire ecology, I believe this is part of global weather patterns, not just purely local events. The fluctuation of such fire activity here in California is shown in Figs. 18-21. This periodicity of lightning fires has been well discussed in a number of papers and all investigators are agreed that they occur in this manner. It is also a well-known fact among those who fight such fires.

28 THE NATURE OF LIGHTNING FIRES

Hh;--' iii- ~~'­ -,. ~

... ~_ L-: . , 1.::.1' hit " i: ELf 4 :' - _ -l ..L FIG. 19. Lighming-set and man-caused fires, annually, on the National Forests in the Coast Ranges of California for the 22-year period 1945-1966.

Trend No.2 The number of lightning fires per year have increased or decreased from year to year in a rather periodic or rhythmic manner in two or three year periods. They have not occurred in a randomized pat­ tern. Now is this periodicity due purely to chance, to a periodic waning of lightning activity, or is it related to some other phenomena of the atmosphere? Alexander (192 7) pointed out a similar "see-saw effect" in precipi­ tation with a periodicity of about three years. Gisborne (1922) had previously suggested such a possibility. Larsen and Delavan (1922) reported that this three-year fluctuation was in possible accord with the cycles of sun activity and weather and with sunspot cycles. In this connection I should like to point out that nearly all summer

29 E. V. KOMAREK,. SR.

FIG. 20. Lightning-set and man-caused fires, annually, on the National Forests of the Southern Sierra Nevada (south of Tahoe) for the 22-year period 1945-1966. precipitation, in particular, is caused by thunderstorms as are light­ ning fires. Because thunderstorms are gigantic electric mechanisms and as sunspots are , we may also have a rather rhythmic variation in actual electrical activity, and thus in lightning fires.

Trend No.3 The largest number of lightning-caused fires during this all too short 22-year period occurred in two "peaks" of fire activity; 1950-51 and 1960-61. This period, in length of time, is comparable with the ll-year sunspot cycle, which, however, does vary a year or two from year to year. There is a further hint in older fragmentary records of high fire activity that this same periodicity, varying some­ what from 9 to 11 years, may also be in keeping with present day ideas on sunspot cycles. In fact, the terrific fire period of the 1910's

30 THE NATURE OF LIGHTNING FIRES

FIG. 21. Lightning-set and man-caused fires annually on the National Forests of the Northern Sierra Nevadas and Northern California (north of Tahoe) for the 22-year period 1945-1966. would appear to fit into this category. I am trying to get together such early records as are available on possible lightning fire periods of the past. It would appear to me from this study that the fires of this past summer in Idaho, etc., are but the beginning of a new cycle of intense lightning fire activity which may reach its peak in the next two years. The next sunspot maxima is predicted for 1969. Before going on to the next trend, the fourth, in this discussion I would like to digress to discuss the possible harmonic analysis of lightning fire frequencies for if this is possible it might lead to the prediction of such periods. The possibility of the periodicity of such fires being subject to such a harmonic analysis should be investigated by qualified investigators. May I point out that our present ocean

31 E. V. KOMAREK, SR. tide tables of low and high tides are the result of such a harmonic analysis. Schureman (1941) in the Manual of Harmonic Analysis and Prediction of Tides, points out that, Sir William Thomson (Lord Kelvin) devised the method of reduction of tides by harmonic analysis about the year 1867. The principle upon which the system is based-which is that any periodic motion or oscillation can always be resolved into a sum of a series of simple harmonic motions-is said to have been dis­ covered by Eudoxas as early as 356 B.c. when he explained the apparently irregular motions of the by combinations of uniform circular motions. Horin (1960) discusses in detail such wave-like patterns in rainfall. Sabbagh and Bryson (1962) in An Objective Precipitation Clima­ tology of Canada wrote, Climatologist, in their effort to arrive at the genesis of and to relate climate to associated phenomena, must contend with the problem of establishing the nature of the climate in a precise, ob­ jective manner. This is particularly difficult when both regional and seasonal variations of climatic elements are involved. A method of objectively describing and mapping such variations of space and time is that of harmonic analysis.

They then go on to say, The depiction of the annual march of precipitation over Canada by the harmonic charts reveals the existence of regions having distinct seasonal characteristics of precipitation. It is possible therefore, to identify precipitation regimes. Similar studies and analysis of lightning fires may perhaps show characteristic behavior of thunderstorms, lightning activity, and iden­ tify lightning fire "regimes."

Trend No.4 There appears to be a trend upward in numbers of lightning fires over the entire 22-year period. The same sort of trend has also occurred in man-caused fires. In regard to all fires from whatever cause, Raymond (I 961) presented graphs that showed a steady trend

32 THE NATURE OF LIGHTNING FIRES upwards in the number of all fires in California, a downward trend in the acreage burned, and a very decided trend upward in both manpower and equipment costs. Maclean and Lockman (1967) in "Forest Fire Losses in Canada 1965" pointed out that from 1945 to 1965 fire occurrence increased by about 30 to 35 % and that "about 25 percent of this increase occurred between 1955 and 1965." My graphs also show a rather consistent trend in increased number of man-caused fires, as well as lightning fires, for the 22- year period, not only on a national scale, but particularly so for the California national forests. The increase in numbers of man-caused fires has been attributed to the expanding recreational use of forest land. However, in my opinion, this is not the entire answer for lightning fires have also shown an upward trend. The increased number of both lightning fires and those caused by man appears to be largely due to increased combustibility of the forest. Man appears to always work towards greater uniformity over vast areas, greater conformity within these areas, and then hopes that time will stand still. Unfortunately, these are human attributes for in nature uniformity and conformity are not the rule and certainly time does not stand still. These dynamic processes such as plant succession, variations in climatic conditions, soils, topography are opposed to man's efforts. Lightning fire is one such dynamic process and man must learn to live with this fire environment.

SUMMARY Lightning fires are an integral part of our environment and though they may vary in number in both time and space they are rhythmically in tune with global weather patterns. This periodicity of such fires, monthly, seasonally, yearly, and perhaps even in much longer periods, appears to be subject to a harmonic analysis and if so, then subject to prediction. The original fire mosaic of plants and animals created by the varying frequency and intensity of lightning fires, in both time and space, has been disturbed by man. However, the causative agent, ' lighming and lightning-fires still remains with us and our environ-

33 E. V. KOMAREK, SR. ment can properly be called a "fire environment." That both the number of lightning and man-caused fires are increasing is evident and so the reason must lie in the condition or man's use of those lands. Man, I fear, has been the unknowing agent of our catastrophic fires for both the forest and the lightning long preceeded him.

BIBLIOGRAPHP Alexander, George W. 1923. Weather and the Berkeley fire. Monthly Weather Rev. 51:464--465. --. 1923. Intensive studies of local conditions as an aid to. forecasting fire weather. Monthly Weather Rev. 51 (11) :561-563. ---. 1927. Lightning storms and forest fires in the state of Washington. Monthly Weather Rev. 55:123-129. --. 1928. The frequency and persistence of low relative in the state of Washington. Monthly Weather Rev. 56: 129-136. --. 1930. Fire weather and fire climate. Monthly Weather Rev. Sept. 1930. 370-372 Alexander, William H. 1915. Distribution of thunderstorms in the United States. Monthly Weather Rev. 41:322-326. --. 1924. The distribution of thunderstorms in the United States. Monthly Weather Rev. 52(7) :337-348. --. 1934. The distribution of thunderstorms in the United States. Monthly Weather Rev. 61 (5): 157-158. Alter, Dinsmore. 1927. A study of the possibility of economic value in statistical investigations of rainfall periodicities. Monthly Weather Rev. 55:110-111. Anonymous. 1917. Great thunderstorm of August I, 1917 in Trinity County, Cali­ fornia. Monthly Weather Rev. 39:500. Arnold, R. Keith, and Charles C. Buck. 1954. Blow-up fires-silviculture or weather problems? Jour. of Forestry. Vol. 52. 408-411. Bailey, Harry P. 1966. The climate of southern California. Calif. Nat. Hist. Guides 17. Univ. of Calif. Press, Berkeley and Los Angeles. Beals, E. A. 1916. How the Weather Bureau can help. Monthly Weather Rev. 40: 138-139. --. 1916. Droughts and hot weather. Monthly Weather Rev. 40:135-138. --_. 1923. Discussion of thunderstorms and forest fires in California. Monthly Weather Rev. 51 (4): 180-182~ Beers, Francis, and Dever Colson. 1960. Use of extended range prognoses for fire­ . Monthly Weather Rev. 88(4) :131;-136. Bjerkness, Jr. 1919. On the structure of moving . Geophys. Publ. Vol. I, No.2, pp. 90-99. Brandt, John C. 1966. The sun and stars. McGraw-Hill Co., N. Y. ---, and Paul W. Hodge, 1960. Solar system astrophysics. McGraw Hill, N. Y. Brown, A. A., and A. D. Folweiler. 1953. Fire in the forests of the United States. John S. Swift Co., Inc., St. Louis, Mo. Browning, Keith A., and T. Jujita. 1965. A family outbreak of severe local storms. Air Force Cambridge Res. Lab. Rept. 32. Bedford, Mass. "For additional, extensive references concerning lightning see Komarek, 1964 and 1966.

34 THE NATURE OF LIGHTNING FIRES

Bryson, Reid A. 1957. Some factors in Tucson summer rainfall. Tech. Report. No.4. Univ. of Ariz., Tucson, Ariz. Buck, Charles G. 1950. Fire behavior in relation to factors of environment. Univ. of Calif., Davis, Short Course on Range Improvements Proc. 1950:66-71. Calvert, E. B. 1925. Weather forecasting as an aid in preventing and controlling forest fires. Monthly Weather Rev. 53 (5): 187-190. Campbell, Archibald. 1906. Sonora storms and Sonora of California. Monthly Weather Rev. 32:464-465. Carlin, Albert V. 1952. A case study of the of in planetary waves. MS report, U. S. Weather Bur. Library, Washington, D. C. Carpenter, A. 1919. Convectional clouds induced by forest fires. Monthly Weather Rev. 47(3) :143-144. Chandler, Craig C. 1961. Fire behavior of the basin fire. U. S. Forest Servo Pacific SW Forest & Range Exp. Sta. 84 pp., illus. Church, J. E. 1907. Electric disturbances and perils on mountain tops. Monthly Weather Rev. 33:578-579. Clayton, H. Helm. 1934. World weather and solar activity. Smith. Misc. ColI. 89(15) :52 p. ___. 1940. The 11-year and 27-day solar periods in meteorology. Smith. Misc. ColI. 99(5): 20 p. ---. 1943. Solar relations to weather and life. Clayton Weather Service, Canton, Mass. ---. 1955. Sunspot and geomagnetic 1874-1954. Royal Greenwich Observatory, . Coffin, Harry. 1959. Effect of marine air on the fireclimate in the mountains of southern California. U. S. Forest Serv., Pacific SW Forest & Range Exp. Sta. Tech. Paper 39, 30 pp. illus. Coleman, E. A. 1953. Fire and water in southern California mountains. U. S. Forest Serv. Calif. Forest & Range Exp. Sta. Misc. Paper 3, 7 p. Colson, Dever. 1960. High level thunderstorms of July 31-August 1, 1959. Monthly Weather Rev. 88:279-285. Conroy, Charles C. 1928. Thunderstorms in the Los Angeles district. Monthly Weather Rev. 56:310. Cooper, William S. 1922. The broad-sclerophyll vegetation of California. Carnegie Inst., Washington, D. C. Countryman, C. M. 1956. Fire severity in 1955 on the Klamath National Forest. U. S. Forest Servo Calif. Forest & Range Exp. Sta. Res. Note 103, 7 pp., illus. ---. 1956. Old growth conversion also converts fireclimate. Soc. Amer. Foresters Proc. 1955: 158-160, illus. ---. 1957. California fire-weather severity in 1956. U. S. Forest Servo Calif. Forest & Range Exp. Sta. Res. Note 118, 7 pp. ---, and Dever Colson. 1958. Local wind patterns in Wildcat Canyon. U. S. Forest Servo Calif. Forest & Range Exp. Sta. Tech. Paper 28, 12 pp., illus. --, and M. J. Schroeder. 1958. Prescribed burn fireclimate survey 1-57. U. S. For­ est Servo Calif. Forest & Range Exp. Sta. Tech. Paper 29, 14 pp., illus. ---. 1959. Prescribed burn fire climate survey 2-57. U. S. Forest Servo Pacific SW Forest & Range Exp. Sta. Tech. Paper 31, 18 pp., illus. ---. 1959. Prescribed burn fireclimate survey 3-57. U. S. Forest Serv. Pacific SW Forest & Range Exp. Sta. Tech. Paper 34, 15 pp. 1959. Prescribed burn fire climate survey 4-57. U. S. Forest Servo Pacific SW Forest & Range Exp. Sta. Tech. Paper 35,19 pp.

35 E. V. KOMAREK, SR.

---. 1960. Fire environment-the key to fire behavior. Fifth World Forestry Con­ gress Proc. ---. 1960. Fire environment and silvicultural practice. Soc. Amer. Foresters Proc. 1959: 22-23. Court, Arnold. 1959. Thunderstorm frequency in northern California. Bull. Amer. Meteor. Soc. 41 (8) :406-409. ---. 1960. Lightning fire incidence in northeastern California, 1945-56. U. S. Forest Servo Pacific SW Forest & Range Exp. Sta. Tech. Paper 47, 21 pp. ---. 1960. Thunderstorm frequency in northern California. Amer. Meteor. Soc. 41 (8) :406-409. Covert, Roy N. 1924. Lightning fire losses. Monthly Weather Rev. 52:259-260. Critchfield, H. F. 1966. General climatology. Prentice-Hall. Curry, J. R. (1936). Fire behavior studies on the Shasta Experimental Forest. U. S. Forest Servo Fire Control Notes 1:2-30. ---, and W. L. Fons. 1938. Rate of spread of surface fires in the ponderosa pine type of California. Jour. Agr. Res. 57 (4) :239-267. ---. 194'0. Forest fire behavior studies. Mech. Engin. 62 (3) : 219-225. Dague, Charles 1. 1930. Disastrous fire weather of September, 1929. Monthly Weather Rev. 58: 368-370. ---. 1934. The weather of the Great Tillamook, Ore., fire of August 1933. Monthly Weather Rev. 62:227-231. Dale, Robert F. 1966. of the states-California. Climatography of the United States No. 60-4. 46 pp. Deutsch, Joseph L. 1961. Enroute weather over the United Air Lines System. United Air Lines, Inc., Stapleton Airfield, Denver, Colo. U AL Meteorology Cir. No. 51. Dorsey, N. Ernest. 1927. Lightning. Monthly Weather Rev. 55:268'--270. Dunning, Duncan. 1929. Fire on the foothills; the problem of controlling fires in the marginal brush lands of California. Calif. Countryman 15 (7) :6-16. Espy, James P. 1919. Rain from cumulus clouds over fires. Monthly Weather Rev. 47(3) :145-147. Fergusson, S. P., and C. F. Brooks. 1919. Heights of cumulus clouds forming over fires. Monthly Weather Rev. 47:147-149. Flint, Howard R. 1923. How weather forecasting can aid in forest fire control. Monthly Weather Rev. 51 (11) :567-569. Folweiler, A. D. 1937. Theory and practice of forest fire protection in the United States. La. State Univ. Printed John S. Swift, Co., Inc., St. Louis. Forest Service. Annual fire report for the National Forests, 1945-1966, incl. U. S. Dept. of Agric., Washington, D. C. Foster, Donald S. 1958. Thunderstorm gusts compared with computed downdraft speeds. Monthly Weather Rev. 86:91-94. Franceschini, Guy A. 1959. A probability factor for thunderstorm warnings. Bull. Amer. Meteor. Soc. 41 (1) : 28-30. Frise, Harry A. 1912. Electric induction by clouds during thunderstorms. Monthly Weather Rev. 60:1202. Fuquay, Donald M. 1962. Mountain thunderstorms and forest fires. Weatherwise 15: 149-153 illus. ---, R. G. Baughman, A. R. Taylor, and R. G. Hawe. 1967. Documentation of. lightning discharges and resultant forest fires. U. S. Forest Servo Intermountain Forest & Range Exp. Sta. Res. Note 68, 7 pp. Gast, P. R., and P. W. Stickel. 1929. Solar radiation and relative humidity in rela­ tion to duff moisture and forest fire hazard. Monthly Weather Rev. 57:466-468.

36 THE NATURE OF LIGHTNING FIRES

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37 E. V. KOMAREK, SR.

Joy, George C. 1923. Forest Fire weather in western Washington. Monthly Weather Rev. 51 (11) :564-566. Jurwitz, Louis R. 1937. Thunderstorm frequencies for 6-hour periods at Miles City, Mont. Monthly Weather Rev. 64:237-238. Kerr, D. P. 1951. The summer-dry climate of Georgia Basin, British Columbia. Trans. Roy. Can. lnst. XXXIX pt. 1 p. 28. Keyser, E. M. 1929. Some 1929 fire-weather comparisons. Monthly Weather Rev. 58:365-368. Kiepenheuer, Karl. 1959. The sun. Univ. of Michigan Press, Ann Arbor, Mich. pp. 149-150. Komarek, E. V., Sr. 1964. The natural history of lightning. Proc. Third Ann. Tall Timbers Fire Ecol. Conf. p. 139-183. Tall Timbers Res. Sta., Tallahassee, Fla. ___. 1966. The meteorological basis for fire ecology. Proc. Fifth Ann. Tall Timbers Fire Ecol. Conf. p. 85-125. Tall Timbers Res. Sta. Tallahassee, Fla. Kotok, E. I. 1930. Fire, a problem in American forestry. Sci. Monthly 31:45~52. ___. 1933. Fire, a major ecological factor in the pine region of California. Fifth Pacific Sci. Congo Proc. 1933.4017-4022. Kourtz, P. 1967. Lightning behavior and lightning fires in Canadian forests. Canada Dept. of Forestry & Rural Development. Pub. 1179. Ottawa, Canada. 33 pp. Kraus, John D. 1966. Radio astronomy. McGraw-Hill Book Co., N. Y. 481 p. Larsen, J. A., and C. C. Delavan. 1922. Climate and forest fires in Montana and northern Idaho, 1909 to 1919. Monthly Weather Rev. 49(2) :55-66. ---. 1925. The forest-fire season at different elevations in Idaho. Monthly Weather Rev. 53:60-63. . Lothman, Arvy A. 1938. forecasting for fire control in southern California. Monthly Weather Rev. 66:134-135. McAdie, Alexander. 1910. Sixty years of rainfall in California. Monthly Weather Rev. 36: 1591-1592. ---. 1928. Phenomena preceding lightning. Monthly Weather Rev. 56:219-220. ---. 1929. An unusual lightning flash. Monthly Weather Rev. 57: 197-198. McCarthy, E. F. 1924. Forest fires and storm movement. Monthly Weather Rev. 52: 257-259. McFarland, Byron. 1901. The thunderstorm; a new explanation of one of its phe­ nomena. Monthly Weather Rev. 27:297-298. Maclean, D. L., and M. R. Lockman. 1967. Forest fire losses in Canada, 1965. Canada Dept. of Forestry & Rural Development, O.D.c., Ottawa, Canada. 435.2 (71): 15. Marvin, C. F. 1931. Are meteorological sequences fortuitous? Monthly Weather Rev. 58 (12) :490-492. Means, Lynn L. 1944. The nocturnal maximum occurrence of thunderstorms in the Midwestern states. Misc. Rep. No. 16., Univ. of Chicago, Dept. of Meteor., Chicago, Ill. ---. 1952. On thunderstorm forecasting in the central United States. Monthly Weather Rev. 80(10): 165-189. Morris, William G. 1932. A preliminary report, giving some of the results obtained in a study of lightning storm occurrence and behavior on the national forests of Oregon and vVashington. U. S. Forest Servo Pacific NW Forest Exp. Sta. Res. Note 10, 11 pp. ---. 1934. Fuel inflammability studies. U. S. Forest Servo Pacific NW Forest Exp. Sta. Res. Note 15. p. 14-15. ---. 1934. Lightning storms and fires on the national forests of Oregon and Washington. Monthly Weather Rev. 62. 370--375.

38 THE NATURE OF LIGHTNING FIRES

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39 E. V. KOMAREK, SR.

___. 1961. Down-canyon afternoon winds. Amer. Met. Soc. Bull. 42 (8) :527-542. --.1961. Topometeorology-the local scale. Amer. Met. Soc. Bull. 42(8):590.. Schroeder, Mark J., and C. M. Countryman. ~957. Fire-weather survey can aid prescribed burning. V. S. Forest Servo CalIf. Forest & Range Exp. Sta. Tech. Paper 21, 10 p. 1960. Exploratory fire-climate surveys on prescribed burns. Monthly Weather Rev. 88(4):123-124. Schureman, Paul. 1941. Manual of harmonic analysis and prediction of tides. V. S. Coast and Geodetic Survey, Spec. Publ. No. 98. Government Printing Office, Washington, D. C. Shipley, John F. 1941. Lighming and its symbols. Quart. J. Royal Met. Soc. 67(290): 135-151. London, England. Show, C. V. 1919. Climate and forest fires in northern California. J. of Forestry 17: 965-979. ---. 1923. Lightning and forest fires in California. Monthly Weather Rev. 51 (11): 566-567. ---, and E. I. Kotok. 1923. The occurrence of lightning storms in relation to forest fires in California. Monthly Weather Rev. 51(4) :175-180. ------. 1923. Forest fires in California, 1911-1920; an analytical study. V.SoO.A. Circ. 243,80 p. ------. 1924. The role of fire in the California pine forests. V.SoO.A. Bull. l294. 80 p. ------. 1925. Fire and the forest (California pine region.) V.S.D.A. Circ. 358. 20 p. ------. 1925. Weather conditions and forest fires in California. V.SoO.A. Circ. 354. 24 p. ------. 1929. Cover type and fire control in the National forests of northern California. V.SoO.A. Bull. 1495.35 p. ---. 1931. Meteorology and the forest fire problem. Monthly Weather Rev. November 1931. 432-433. ---, and C. A. Abell, R. L. Deering, P. D. Hanson. 1941. A planning basis for ade­ quate fire control on the southern California national forests. V. S. Forest Servo Fire Control Notes 5 (1): 1-59. Simpson, A. Gael. 1930. Relative hUlnidity and short-period fluctuations in the moisture content of certain forest fuels. Monthly Weather Rev. 58:373-374. Simpson, George C. 1906. . Monthly Weather Rev. 32:16-17. ---. 1916. Some problems of atmospheric electricity. Monthly Weather Rev. 44: 115-122. ---. 1928. The mechanism of a thunderstorm. Monthly Weather Rev. 56:311-3l2. Small, R. T. 1957. The relationship of weather factors to the rate of spread of the Robie Creek fire. Monthly Weather Rev. 85 (1): 1-8. Smith, Alex G. 1967. Radio exploration of the sun. D. Van Nostrand Co., Inc., Princeton, N. J. 159 p. Stevens, W. R. 1934. Meteorological conditions preceding thunderstorms on the national forests. Monthly Weather Rev. 62:366-370. ---. 1935. Meteorological conditions preceding thunderstorms on the national forests. Monthly Weather Rev. 63 (6): 183-184. Sugiura, Masuhisa. 1960. A note on harmonic analysis of geophysical data with special reference to analysis of geomagnetic storms. Geoph. Inst. Rpt, No. 1. Vniv. of Alaska, College, Alaska. Sverdrup, H. V. 1933. Papers in physical oceanography and meteorology. Mass. Inst. of Tech., Cambridge, Mass. 2 (I).

40 THE NATURE OF LIGHTNING FIRES

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41