History.—The mariner who frequents the areas adjacent to the shores of Southern California during the fall and winter months is certain, sooner or later, to experience one or more of the violent and destructive storms known locally as “Santa Anas.”
There appears to be considerable controversy regarding the derivation of the name Santa Ana. One writer avers that the name was bestowed by the early Spaniards in recollection of one of the first storms observed by them which occurred on St. Ana’s day. Another version attributes the name to the fact that these winds are most severe when they have passed through the Santa Ana Canyon. Although a doubtful honor, there are those who claim that the name was applied as a compliment to the city of Santa Ana which is located near the western end of the Santa Ana Canyon and through which locality these storms usually pass. Another version has it that the term came into use and had its beginning in the days when General Santa Ana was at the head of the Mexican Army operating in Southern California. On his many spectacular tours of this country, the general always rode at the head of a fast riding squadron of cavalry whose swiftly moving horses naturally stirred up great clouds of dust which were plainly visible from afar as they ascended into the air. This in time came to be associated with the arrival of the general and his cavalcade of riders. Anyone observing the approach of one of these storms today will be struck with the aptness of this explanation. Still another version is to the effect that the name was originally “Santana,” which word in the language of the Mexican Indians signified “Big Wind.” One more ingenious explanation accounts for the name by recalling that the early Indians termed the wind the “Wind of the Evil Spirits” because of its well-known drying qualities, which dried up the leaves, berries, and nuts. When the white men arrived they translated this term to the “Wind of Satan” which in time became conventionalized into “Santana Wind.”
General description.—The Santa Ana or desert storm is of particular interest to the officers serving on vessels of the United States Fleet which habitually operate in the areas where these winds attain their greatest violence. The area utilized for anchorage purposes in the Los Angeles- Long Beach area is well protected from seaward by the San Pedro breakwater and the new Long Beach breakwater now under construction, but vessels at anchor here are at the mercy of the Santa Ana which blows from the north or northeast. Little or nothing has been written to inform the mariner as to the cause and effect of these storms or to instruct him as to the warnings, visible or otherwise, that may apprise him of their approach. The Coast and Geodetic Coast Pilot dismisses these storms with the following short sentence:
The “Santa Ana,” a local and exceptional wind of considerable strength from the eastward, is the only wind dangerous to vessels anchored inside the breakwater. With such a wind all small vessels should seek shelter in the inner harbor, but large vessels with good ground tackle will have no difficulty in holding on.
During the height of these storms battleships and other heavy craft have frequently dragged their anchors, while smaller craft have parted their cables or have been swept from their moorings and become stranded on the inner side of the breakwater or upon the sands of Cabrillo Beach. The captain of a mine sweeper that has been set against the breakwater or the captain of a battleship that has dragged its anchors in one of these gales with gusts of over 60 m.p.h. will read the paragraph from the Coast Pilot with a somewhat critical eye.
Dana, in his Two Years Before the Mast, mentions the Santa Ana as follows:
Saturday February 13, 1836. We were called up at midnight to slip for a violent northeaster, for this miserable hole of San Pedro is thought unsafe in almost every wind.
On this occasion his vessel, the brig Pilgrim, was forced to seek the lee of Catalina Island and was absent from its anchorage for three days. On another occasion the Pilgrim experienced a gale commencing on November 16, 1835, when this vessel was off Point Conception. Every sail was stripped from the yards and torn to shreds. The sailors were familiar with the gales and storms of the North Atlantic where such gales are accompanied by clouds and rain. They now marveled at the cloudless sky and lack of rain. To be driven before a howling gale for more than a week with bright sunshine by day and clear starlit skies by night was indeed a novel experience. The Pilgrim was blown half way to Hawaii in this gale and required twenty days for the passage from Santa Barbara to San Francisco.
Meteorological data.—The meteorological conditions attending the formation of a Santa Ana are of the greatest interest to the mariner and to the weather observer.
The normal movement of the air currents over the middle southern California coastal plain is from the ocean inland. Whenever a strong area of high barometric pressure moves into or develops over the plateau region, the barometric gradient will indicate winds from the east or northeast. The lows, in their normal progress across the Western United States, occasionally lag over southern California and southern Arizona, or to the westward, causing a semi-permanent area of low pressure there. The remnant of the semi-permanent low pressure area normally centered near Yuma in the summer months will now be found either to the southwest of San Diego or else to be nonexistent. With such a pressure distribution the skies over southern California are usually clear and brilliant for a day or more before the Santa Ana develops.
Frequently the high-pressure area of the plateau region just referred to “stagnates,” or remains practically stationary for several days, generally decreasing in magnitude. This high may be joined by the inflow of another high causing a semi-permanent area of high pressure. Since the velocity of the wind is dependent upon and proportional to the pressure gradient, it is apparent that, under the conditions just described, the direction of the wind will be from the north or northeast, towards the coast line.
When winds blow from either of these directions they bring air from the elevated land areas of Nevada and northern Arizona. When air from higher levels descends because it is heavier than surrounding air masses, the pressure upon it increases constantly and it suffers compression and work is performed upon the air by the surrounding pressure. As this air descends from the plateau region to the sea level (about 5,000 feet) it is warmed by compression sometimes as much as 27°F. The humidity in the desert areas is normally quite low and after this mechanical warming process the resulting humidity in the coastal areas will be found to be as low or probably lower than can be found in any other part of the world. Comparison of psychrometer readings have indicated a relative humidity as low as 3 per cent at Pomona. Relative humidities of 22 per cent have been observed 15 miles off the coast and at only 8 feet above the surface.
The mariner has no tables at hand with which to determine the values of such low relative humidities. The compilers of Bowditch evidently did not consider it probable that the mariner would ever encounter such low humidities in his voyages around the world, at least, the Bowditch table of relative humidity, paragraph 63, is of no value during the progress of a Santa Ana storm.
The air moving outward from the high-pressure area in Nevada and northern Arizona is blocked on the south by the San Gabriel and San Bernardino Mountain ranges and wherever there is an opening in these ranges the desert air streams through it. When the difference in the barometric pressure between Nevada and southern California is only moderate (0.16 -0.40 inches) these desert winds are usually confined to rather narrow belts extending from the mouths of the passes to the ocean by the lowest and least obstructed routes. They pour through the Cajon Pass and sometimes through the San Gorgonio Pass into the Great Valley of southern California through the Soledad Canyon into the Santa Clara and San Fernando valleys.
The air stream which issues from the Cajon Pass under these conditions is of the greatest interest and importance to mariners. The Cajon Pass lies between the San Gabriel and San Bernardino Mountain ranges, extending roughly north and south, turning towards the southeast near its southern extremity. It is a V-shaped notch about 17 miles long and quite narrow, extending from the Mojave Desert on the north to the Great Valley of southern California on the south. The slope from the summit of the pass northeastward to the Mojave Desert is gradual, the summit being only slightly higher than the general level of the desert beyond it. The fall from the summit to the southward, however, is more abrupt, averaging about 115 feet to the mile. The approach to the pass from the desert side is shaped like a great V with sides formed by the mountains which converge at its entrance.
The desert winds are seldom felt on the floor of the pass, but appear to remain at some elevation above the ground. When one observes them from the San Bernardino Mountains the first dust clouds appear about a half mile south of the southern end of the pass.
The air streams from Cajon Pass usually maintain their identity in a remarkable manner. They move out over the valley floor, swing towards the southwest, and either follow the Santa Ana Canyon or move directly over the low mountains south of the Santa Ana Canyon and then follow a well-defined path over the almost level plains of Orange County and reach the coast line somewhere in the vicinity of Newport. When one is going eastward in the open country some 7 miles south of Cajon Pass, with light to gentle variable winds, one often passes abruptly into an air stream with a velocity of from 30 to 35 m.p.h. which is moving in a southwest direction. The eastern limits of this air stream are usually just as well defined and one passes from a near gale into a region of relative calm within the space of half a mile. The width of the air stream under these conditions is usually about 5 miles. This same air current is often encountered in the open plains 15 miles or so to the southwestward with its velocity and width substantially unchanged and with relatively calm air on either side of it. The air stream may shift its position slightly from time to time but appears to change but little in width or velocity. Sometimes it spreads out somewhat after passing the Santa Ana Mountains, but usually follows a well-defined path to the ocean. It often comes over the south foothills at the western entrance to Santa Ana Canyon, appearing in such cases to come down the hillside in strong gusts directly along the ground.
When steep barometric gradients are present between Nevada and southern California with pressure differences of 0.45-0.70 inches, and especially when a low-pressure area is present over Lower California, the desert winds may come directly over the mountain ranges. If the gradient winds are north, the sections directly south of the San Gabriel Mountains, which extend east and west, usually are not affected, but the wind is likely to appear at the surface about 10 miles south of the mountains. Under such conditions slow eddy currents carry dust into the districts near the mountains which make it appear locally that a west wind of about 6 m.p.h. or less is causing a dust which blots out the sun and limits visibility to about 500 feet.
Coast line affected.—The localities at which the Santa Ana will reach the coast line are, as could be expected, places where the land is low and is connected with the mountains to the eastward by means of a valley which will permit a drainage of the air from the mountains to the sea. In addition to the Long Beach area already referred to, the Tia Juana Valley is also one of these. Places like San Diego which are protected by hills or mountains from strong winds from the northeast or east seldom feel more than slight effects of a Santa Ana. A gale with winds of from 40-60 m.p.h. may be blowing in the vicinity of San Pedro while at the same time a light wind of from 4 to 6 m.p.h. will be blowing at San Diego.
Time of occurrence.—The Santa Ana winds may occur in almost any month of the year, but those that occur during the summer months are usually of minor intensity. They do, however, cause exceptionally high temperatures with corresponding low humidity and consequent fire hazard.
The most destructive Santa Anas occur during the late fall and the winter months When the temperatures in Nevada and northern Arizona are very low. These storms are most frequent during the night or early morning hours. Several reasons may be given for this. Under clear skies at night, the ground loses considerable heat by radiation to space and the air in contact with the ground is cooled greatly. Thus the air on the sides of the mountains, being much cooler and therefore denser, starts flowing down the mountain to the valley. Since the normal wind due to the pressure gradient is also from the high lands to the sea, the gravity effect of the cold air rushing down to the sea is added to the effect of the normal pressure gradient, thus resulting in a stronger wind. On the contrary, during the forenoon, after the sun is fairly high, the intense heating over the land near the coast, especially under the clear skies which now prevail, tends to establish a sea breeze from the west or southwest, and thus opposed to the gradient wind. As a net result of this heating, either there is a much lighter wind from the land, or, as so often is the case, the sea breeze effect is able to reverse the pressure gradient wind near the coast.
This re-enforcement of the desert winds by the mountain wind effect is usually slight and of very minor importance. It is believed that any possible tendency for the desert winds to reach a maximum intensity during the late forenoon is due principally to the fact that the great reservoir of cold air over the plateau region reaches its lowest temperature about sunrise. As a general rule, during the progress of these winds in winter, there is not sufficient difference in temperature between the sea air and that over the coastal plain to cause a tendency towards a sea breeze. Moreover, considering all of these winds which have occurred during the last 15 years, the tendency toward a late forenoon maximum intensity is not any too well recorded. In a great many instances they have blown with great fury throughout the night, and died out suddenly and completely shortly before sunrise.
However, it should be noted that the strong winds from north or northeast may also occur during the warmest part of the day if the pressure gradient is steep enough. As an example, in the storm of November 22, 1930, when the barometric pressure in the center of the high situated at Yellowstone, Wyoming, reached the phenomenal value of 31.02 inches, the pressure gradient towards the coast was steep enough to cause northeast winds accompanied by strong gusts of 60 m.p.h. at the Glendale Airport between 1230 and 1600.
Effects of the Santa Ana.—The time of arrival of the Santa Ana along the coast line is a period of danger to shipping when anchored near the coast. The winds may reach a velocity at times in excess of 60 m.p.h. and frequently appear in strong gusts rather than as a steady blow. These winds do not usually persist with their maximum velocity for periods greatly in excess of an hour, yet there may be more than one period of maximum intensity with as much as a 9-hour interval between. However, weather records have registered Santa Ana storms which have blown with great violence for periods of 24 hours or longer.
These strong winds in their passage through the canyons and passes stir up vast quantities of sand and dust which constitute one of the chief menaces attending this phenomenon. In fact, as previously noted, their approach is usually accompanied by a wall of dust advancing from the northeast, sometimes extending from the surface to an altitude of 5,000 feet. The sand and dust is often blown with such force that automobiles in its path have been known to be stripped of their paint in a few minutes by the sand blasting effect. Cars are frequently stopped by sand being blown into and choking the carburetors.
The excessively low humidity results in much personal discomfort to humanity, causing dryness of the skin and drying up of the nasal secretions. When accompanied by a sand storm as is usually the case, the discomfort is increased by inflammation of the eyes and nose due to the irritation caused by the alkaline dust particles. The housewife has particular cause to dread the approach of one of these sand storms as the fine particles penetrate to every nook and corner. A freshly painted ship’s topsides presents a drab and dusty appearance after receiving a coating of this pulverized sand and dust.
Another phenomenon accompanying the Santa Ana is the electrostatic effect. During the progress of the desert wind frictional electrical charges, due to the extreme dryness of the air, are noticed on nearly every object that is insulated from the ground.
Moving automobiles often gather a heavy charge of static electricity on the body varnish, which, when one on the ground reaches for the door in entering, passes into the hand with an audible snap and with consequent shock. Persons unfamiliar with the character of these electrical discharges often assume that the electrical system of the car is out of order and waste much effort in a search for the seat of the trouble. Many disastrous explosions of gasoline have been caused by these electrical discharges.
Airplane pilots have reported that the wind velocity was undiminished at an altitude of over 5,000 feet and that the dust in the air was as great at this elevation as near the ground. Heavy dust has been observed as much as 75 miles from the shore and a great number of butterflies have been seen from 35 to 50 miles offshore.
Preliminary indications.—The excessively low humidity accompanying these desert storms is one of the best warnings to the mariner that a Santa Ana condition is prevailing, and therefore it behooves the mariner to pay strict attention to the wet-dry bulb thermometers. Whenever the difference between the readings of these two thermometers approaches 8°-10°F., it may be considered that the Santa Ana condition exists. However, this must not be considered to be an infallible indication. There are many occasions when the relative humidity will reach low values due to the fact that the wind is coming from the hot, dry desert country, usually from the north or northeast, but at the same time the barometric gradient plus temperature differences is not sufficiently steep to cause the Santa Ana winds to attain dangerous force.
The onset of the most violent of these winds often is remarkably sudden and in such cases the relative humidity may not indicate any marked decrease until the first strong gusts have arrived. This was the experience in the case of the Santa Ana of January 11, 1933, when vessels at San Pedro recorded fog at midnight January 10-11 and a Santa Ana wind of gale force by 0400.
An additional warning will usually be noted by the observation of a very high visibility for some hours before the Santa Ana arrives at the coast line. This is due to and accompanies the excessively low humidity with resultant lack of haze, mist, and fog. Unlike the blows with which the mariner is familiar in other parts of the world, the Santa Ana announces its onset with few or none of the usual warnings. The barometer is well-nigh useless when its readings are taken alone and it maintains its readings with little variation although a gale of hurricane force may spring up, blow for hours, and cease.
Shortly before the arrival of the Santa Ana on the coast its approach may be observed by a dark brown dust cloud approaching from the northeast. This will often give from 10 to 30 minutes warning and is always one of the positive indications that a Santa Ana is approaching.
Predictions.—All the preliminary warnings noted above are good for but a short time prior to the onset of the blow. However, the mariner has at his command a far more accurate indication and one which will enable him to foretell with considerable accuracy the possibility of there being one of these blows.
The U. S. Weather Bureau issues daily (Sundays and holidays included) bulletins containing weather reports, forecasts, and warnings for the benefit of mariners in the eastern waters of the Pacific Ocean and in the states bordering on that ocean. These bulletins are broadcast from U. S. Naval Radio Station NPG at San Francisco twice daily at 0730 and 1930.
This weather bulletin is divided into two parts. The first part consists of a summary of general atmospheric pressure distribution over land and sea, including the location of high and low areas and the barometer readings at their centers, wind and weather forecasts for Pacific offshore areas, and storm warnings for those areas. The second part consists of surface weather conditions at a selected list of land stations, being based upon observations taken at 0100 and 1300 G.C.T. except as indicated.
This is then followed by a list of ship’5 observer reports from a selected list of vessels situated in the Pacific Ocean taken at 0000 and 1200 G.C.T. These ship reports are transmitted in the International Code for Radio Weather Reports from Ships. This code is described in Weather Bureau Bulletin No. 1046. An explanation of this service is given in Weather Bureau Circular #2 Radio, (first edition, November 1, 1933).
From the data transmitted in the Major Marine Bulletin, a weather map may be constructed on board ship with the blank meteorological charts furnished by the Hydrographic Office for that purpose. (The Radio Weather Maps, North Pacific, issued by the Weather Bureau will probably be found to be more satisfactory for this purpose. These maps are bound into pamphlets of 50 copies each and indicate the various cities from which the observations are received.)
The process of plotting or constructing such a weather chart from radio data received on board ships together with codes used is fully described in H. O. No. 205, Radio Aids to Navigation.
Reference to the completed weather map constructed by means of the coded data referred to will afford much useful information. In addition to giving the location of the high and low it will indicate the barometric gradient and probable direction of the wind. When a Santa Ana condition is prevalent, the location of the high will be found to be more definitely fixed than is the case with the low. The Fenter of the low will be found to be rather indefinite as to longitude.
The existence of a low, well defined or not, will not always be observed before the onset of a Santa Ana, for the Santa Ana often occurs without the presence of well-defined low west of the Mississippi River. It has been noted in the past that the greater number of Santa Anas have been caused by an intensive high area alone, accompanied by a steep barometric gradient. The presence of a low area to the south or southwest of the coast line will naturally increase the velocity of the wind.
A study of the meteorological conditions attending the formation and development of a number of Santa Anas has indicated that many of the strongest blows were preceded or accompanied by temperatures in the Imperial Valley which were above normal. It is to be expected that such high temperatures in the Imperial Valley would favor the development of a small low-pressure area or trough in this vicinity. In this event, the intensity of a Santa Ana which was caused by a high-pressure area to the northward, would be somewhat intensified. However, it is by no means certain that such high temperatures in the Imperial Valley are to any great degree responsible for the development of a Santa Ana.
The Santa Ana of January 11, 1933.— One of the worst and most destructive Santa Anas that has been experienced in many years occurred during the morning of January 11, 1933. This blow piled a tangled mass of wreckage on Cabrillo Beach, the San Pedro breakwater, and Terminal Island, among these being 11 U. S. Navy motor boats and motor launches. A navy lighter broke loose from her moorings and after fouling several yachts at anchor drifted against Cabrillo Beach pier and partially wrecked it. Damage in excess of $1,000,000 was caused in Los Angeles and Oranges Counties, about $100,000 being done in the vicinity of San Pedro. Oil derricks were demolished, citrus trees blown down, and buildings unroofed. Many plate glass windows in the harbor area were blown in. While this gale was raging in the harbor, the city of Los Angeles, 25 miles away, was experiencing a mild breeze of not over 12 m.p.h. Incidentally, the city engineer of Los Angeles estimates that a total of 14,000,000 tons of dust was deposited over Los Angeles County during the progress of this storm. One officer was swept from a cruiser and drowned as he attempted to secure a small boat alongside. This gale reached a maximum velocity of 80 m.p.h. at Riverside and 64 m.p.h. as observed on the U.S.S. Augusta anchored at San Pedro. The maximum intensity was noted at about 0400, January 11. The general direction of blow was observed to be from NE. by E.
The accompanying weather map (Fig. 1) for the morning of January 11 will illustrate most of the points which have been previously described. It will be noted that the center of the high is located near Winnemucca, Nevada, with a barometric pressure of 30.70 inches, while the center of the low, though not as localized as the high, is situated to the southwest of San Diego. A steep barometric gradient of about 0.60 inch is noted from the general direction of the high to the vicinity of Los Angeles. Low temperatures of 8°F. are noted in the vicinity of the high while temperatures of around 62°F. are noted at Los Angeles Harbor. The barometer alone, however, indicated nothing out of the ordinary, being 30.20 inches at Los Angeles Harbor as compared to an average January pressure of 30.05 inches.
This blow commenced about midnight January 10-11, and reached a maximum intensity of 64 m.p.h. at about 0400, January 11. Dying down during the forenoon, the wind had dropped to 5 m.p.h. by 1600 that day.
The Santa Ana of December 24, 1924.—Figure 2 also will illustrate most of the points which have already been described. It shows the distribution of the air pressure over the western portion of the United States on December 24,1924, at the height of the most damaging wind which had been experienced in this area for many years- The barometer reading at Winnemucca, Nevada, is 30.94 inches with a temperature of 2°F. At Los Angeles, California, the barometer reading is 30.26 inches, more than a half inch lower. This excessively steep gradient resulted in a wind of very high velocity causing much damage to shipping in the harbor district.
Figure 3 indicates the meteorological conditions on January 10-11 during the period covered by the Santa Ana storm of that date. Note the relative humidity curve which indicated nearly maximum at midnight, dropping rapidly to 18 per cent at noon. Also observe the steady and gradual rise of the barometric pressure free from the usual violent fluctuations accompanying such blow in other parts of the world.
Note.—The writer wishes to express his appreciation and thanks to Mr. Floyd D. Young, meteorologist of the U. S. Weather Bureau at Pomona, California, for the valuable meteorological data supplied by him and his constructive criticisms of the original draft of this article.