SAN DIEGO, CAL. By Mr. FORD A. CARPENTER, Observer, Weather Bureau. Four elements enter into a consideration of the climate of San Diego. Named according to their importance, they are as follows: (1) Distance from the northern storm tracks, and the southern storms of the lower California coast; (2) proximity to the ocean on the west; (3) the mountains in the east; and (4) the great Colorado Desert still farther east. The number of the northern areas of low pressure sufficiently great and moving far enough south to exert an influence at the latitude of San Diego are comparatively few; not one-tenth of these "lows" have an appreciable effect on the climate. The storms from the south (Sonoras," as they are locally known) have but little energy, and probably average two a year. As is the case in all marine climates, the ocean exerts by far the most powerful effect. This is noticed in the slight daily variation in temperature and the absence of either cold or hot weather. The average daily change in temperature from day to day is 2 degrees, and the extremes in temperature from a record of thirty years are 101 and 329. The temperature has exceeded 90° nineteen times in thirty years, or on an average of about twice every three years. Four times in the history of the station has the temperature touched 32, but has never fallen lower. Four killing frosts have occurred in San Diego since the establishment of the station, but aside from blackening tender shoots and killing delicate flowers, no damage was done. The desert winds are responsible for temperatures above 90°, and they are therefore accompanied by extremely low humidity. Records of humidity below 10 per cent are not uncommon during the two or three hours' duration of the desert wind. Three per cent is the lowest relative humidity ever recorded at this station. As the sea breeze is stronger than the desert wind, the highest point reached, whenever the temperature is above 90°, usually occurs about 11 a. m. At this time the sea breeze overcomes the land breeze and the temperature drops to the normal. Nothing so clearly illustrates the strictly local character of the climate of San Diego as the humidity. While the mean annual relative humidity is 78 per cent at the Weather Bureau station, 2 miles north and at an increase of 200 feet in elevation, the humidity decreases 15 per cent. Five miles away, and at an elevation of 300 feet, there is a further decrease of 5 per cent. The temperature is of course proportionately higher. The maximum amount of sunshine occurs in November and the minimum in May and June, the winters being usually bright and warm and the summers cloudy and cool. The photographic sunshine recorder was installed in 1890, and this ten years' record shows an average of four days each year without sunshine. There is a difference of about 1 mile an hour in the average hourly velocity of the wind between the summer and the winter months; the mean annual hourly velocity is 5 miles. While the wind blows from every point of the compass during a normal day, the land breeze is very light, averaging about 3 miles per hour, reaching its lowest velocity just before the sea breeze starts in. The records show that there is an average velocity of from 6 to 9 miles from 10 a. m. to 6 p. m. During the summer a velocity of 6 miles is attained at 9 a. m., increasing to 10 miles at 2 p. m., reaching 6 miles at 7 p. m. The winter months have about five hours of wind over 6 miles, beginning shortly after noon. Winds from 25 to 30 miles per hour occur infrequently, the average annual number being two. Winds of from 31 to 40 miles have an average of less than one a year. The highest velocity ever attained was 40 miles from the northwest, in February, 1878. The record of meteorological observations began in July, 1849, and was made entirely by officials of the Government. The Army and Coast Survey kept up the record until the establishment of this station by the Signal Service, November 1, 1871. Since this date the location of the observing office has been changed a number of times, but the different places have all been within a radius of a few blocks. The office is now in the Keating building, corner Fifth and F streets. The instruments have elevations as follows: Thermometer, 94 feet; rain gauge, 86 feet: anemometer, 102 feet. 1176-Bull. L—03——6 MEAN MONTHLY AND ANNUAL TEMPERATURE (DEGREES FAHRENHEIT). Jan. Feb. Mar. Apr. May. June. July. Aug. Sept. Oct. Nov. Dec. Annual. 1852. 53.1 1853. 53.8 1854. 1855. 52.6 56.2 1856. 51.0 53.5 56.2 60.0 1857. 52.4 53.6 58.8 62.6 55.9 55.0 57.6 61.2 67.1 73.2 72.5 73.6 65.0 57.3 51.9 62.0 69.6 63.5 58.6 53.1 61.1 68.4 66.6 65.1 64.5 68.8 70.8 64.6 66.5 66.2 65.7 64.5 59.2 54.6 60.6 58.2 61.7 62.6 64.6 63.8 60.8 61.8 62.0 60.2 60.6 58.4 60.5 61.9 61.0 60.5 60.1 62.0 65.11 67.2 70.0 68.0 63.9 59.2 55.6 61.4 1872. 1873. 1874. 1875. 1876. 1877 1878. 1879. 1880. 1881. 1882. 1883. 1884. 1885. 1886. 1887. 1888. 1889. 1890. 1891. 1892. 1893. 1894. 1895. 1896. 1897. 1898. 1899. 1900. 1901. སྤྲ£རྫེསྐྱརྩཕ ྤཕ་རྩ༅་༅སྤྲ་རྫ་ཕཕརྩ་རྩ་ཕྱ་ ༄༅་རྩ 59 82 58 58: 81 54 8456 82 56 86 57 83 59 58 54 55 82 57 89 62 80 56 89 58 83 85 60 54 60 55 54 53 90 52 54 5-4 8 59 58 76 Z Z R R 84 54 56 81 51 55 93 53 72 56 60 87 47 74 42 68 35 88 47 76 42 79 40 80 47 77 40 76 40 85 50 82 44 74 36 80 53 75 46 52 83 46 49 91 46 50 14 40 40 82 73 41 69 40 79 47 72 32 71 43 83 78 45 85 38: 79 34 78 46 36 [From 1875 to 1900, 9,496 days, there were 9,181 days of temperature not above 80° or below 40°.] |