Solar Disturbances and Interdiurnal Variations of Atmospheric Pressure* ELLSWORTH HUNTINGTON Yale University, New Haven, Ct. SUMMARY relation between disturbances of the The conclusion is that interdiurnal variabil- solar and terrestrial atmospheres a ity of atmospheric pressure at New Haven comparison between interdiurnal vari- appears to show a mathematically significant ations of atmospheric pressure and correlation with the position of sunspots on the disk of the sun as seen from the earth. those aspects of sunspots which are The correlation indicates a double annual cycle readily available in the data published in which high latitude of spots is associated by the Greenwich Observatory has with high barometric variability in summer- been undertaken at Yale University. and winter at about the time of the solstices and with low barometric variability in the The first station to be studied, New spring and fall near the time when one or Haven, Conn., gives such surprising the other axis of the sun points most nearly and interesting results that it seems to the earth. Whether the relationship thus advisable to publish them in prelim- suggested is thermal or electrical, or whether inary form in the hope that other in- it has any causal connection with the axes of either the earth or the sun, we do not know. vestigators may join in the work. The important fact is that this first investiga- This is the more desirable in view of tion of the latitude of sunspots in relation to the large amount of tabulation re- barometric variability suggests that a hidden, quired for even a single station. and perhaps hitherto unrecognized factor, manifested in the form of the latitudinal loca- The necessary barometric data can tion of sunspots, is somehow imposed upon be obtained only by going to the the terrestrial factors which lead to interdiur- original daily records. From these nal changes of barometric pressure. we have taken the change in pressure from a given hour in the morning to NE OF THE FUNDAMENTAL prob- the same hour the next day. From lems of meteorology is the cause monthly averages of such data for 59 Oof short-lived variations in at- years (1877-1935) the normal curve mospheric pressure, such as those of seasonal fluctuations in interdiurnal from one day to the next. The com- variability of pressure has been monly accepted explanation is that drawn. The daily barometric data they are purely terrestrial in origin, have also been tabulated by successive and are due to disturbances of the solar rotation periods each of approx- equilibrium or steady state of the imately 27 days to render them com- general atmospheric circulation. Many parable with the Greenwich solar investigators, however, believe that a data. Then the average barometric solar factor also plays a part. Varia- variability for each solar rotation tions in solar activity, associated pre- has been expressed as a percentage of sumably with disturbances of the the normal for the middle day of the sun's atmosphere, are supposed to re- particular rotation, thus eliminating enforce the terrestrial disturbances, seasonal differences, and facilitating and thereby alter the distribution of direct comparison with sunspots. heat on the earth's surface. In order The Greenwich data enable us to to determine whether there is any cor- compare the terrestrial phenomena with the area of sunspots on each side *The author wishes to express his gratitude for valuable suggestions received from Dr. of the solar equator and with the lati- Charles F. Brooks of the Blue Hill Observatory, tude of the spots in each solar hemi- Dr. Chester Bliss of the Connecticut Agricul- tural Experiment Station, Dr. Dirk Brouwer sphere. Such comparisons show that of the Yale Astronomical Observatory, and Mr. R. G. Stone, Editor. the barometric variability at New Unauthenticated | Downloaded 10/08/21 12:25 AM UTC Haven has an inconclusive correlation we could not expect a perfect correla- with the area of sunspots, but a clear- tion between atmospheric turbulence cut and systematic correlation with and the solar conditions during any their latitude. The vital factor, how- one solar rotation. If we should find ever, appears to be not latitude itself, that barometric variability follows but the closely allied condition of solar activity with a lag of only a few angular distance from the center of days, this would not alter the possi- the sun's visible disk. bility that atmospheric pressure may The latitudinal relation varies from be influenced by other solar conditions season to season, as might be expected, which occurred many months earlier. but this variation takes the unusual When variations in the solar constant, form of a double cycle during the year. for example, alter the temperature of In summer and again in winter high tropical oceans, the poleward flow of latitude of sunspots in either solar warm water in ocean currents may hemisphere is associated with high alter the barometric conditions in barometric variability, while low lati- higher latitudes six months or a year tude or nearness to the center of the later. Then, too, even if interdiurnal sun's visible disk is associated with low barometric fluctuations at any given barometric variability. In spring and station are closely parallel to solar fall, the opposite conditions prevail, variations, the solar influence is cer- high latitude of spots being associated tainly modified by a highly complex with low barometric variability, and series of terrestrial incidents which low latitude with high variability. involve many irregular delays. Hence a high correlation between sunspots A minor, but perhaps significant and atmospheric pressure is not to be feature is that barometric variability expected. The most that we can seems to be related somewhat more reasonably look for is hints which will closely to the sunspots of the succeed- guide further study. Moreover, the ing rotations than to those of preced- present study is merely exploratory. ing rotations, although the main rela- Nevertheless, it suggests that with tionship is to the spots of the rota- more elaborate methods and a larger tion during which the barometric body of data great and hitherto un- changes occur. This suggests that expected results may be obtained. the solar areas where spots are about to break out may influence the earth's In the main part of this study, we atmosphere before the spots are actu- begin with the earth and inquire what ally seen, as well as after the spots conditions prevail on the sun when become visible. specified conditions of barometric vari- Here a word of warning is neces- ability prevail upon the earth. The sary because sunspots and interdi- results are summed up in FIG. 1 and 2, urnal changes of barometric pressure representing seasonal fluctuations in are very imperfect measures of at- the area and latitude of sunspots. mospheric turbulence (solar and ter- Solid lines represent solar conditions restrial, resp.). They are presumably associated with high barometric vari- still more imperfect as indicators of ability, and dotted lines with low. the underlying processes which lead Each solid line is based on 308 solar to such turbulence. Even if we had rotations (about 25 for each calendar data for atmospheric turbulence all month) during which the interdiurnal over the world, and had also a perfect changes of barometric pressure at measure of all solar conditions which New Haven averaged at least 5% might influence the earth's atmosphere more than the seasonal normal. Each Unauthenticated | Downloaded 10/08/21 12:25 AM UTC FIG. 1. Area of Sunspots, during periods with high (solid lines) and low (dotted lines) barometric variability at New Haven, Conn., 1877-1935. Solid lines based on about 25 rotations beginning in each month and having at least 5% more than the normal seasonal changes in interdiurnal variability of Baro- metric Pressure; dotted lines at least 5% less than seasonal normal. TABLE I. Correlation Coefficients between Area of Sunspots and Interdiur- nal Changes of Barometric Pressure (Based on 12 pairs of averages for calen- dar months, 1877>-1935) Date in Relation to A B C barometric Northern solar Southern solar Both solar changes hemisphere hemisphere hemispheres -2. Second rotation before -.34 .05 -.35 -1. First rotation before -.35 -.42 -.42 0. Same rotation .01 -.41 + 1. First rotation after .01 -^64* — .60* 4- 2. Second rotation after .01 -.08 .08 •Probably significant. ••Mathematically significant. Unauthenticated | Downloaded 10/08/21 12:25 AM UTC FIG. 2. Latitude of sunspots during periods with high (solid lines) and low (dotted lines) barometric variability at New Haven, Conn., 1877-1935. Solid lines based on about 25 rotations beginning in each month and having at least 5% more than the normal seasonal changes in interdiurnal variability of barometric pressure; dotted lines at least 5% less than seasonal normal. Solar rotations having no sunspots and no convincing evidence of the probable latitude of maximum solar activity are omitted. dotted line is based on 327 rotations TABLES IV and V at the end of this with a barometric variability at least article and are used in computing the 5% below the normal. Rotations with correlation coefficients shortly to be a variability of less than 5% from the described. normal are omitted, 155 of them. In In both figures the upper set of dia- order to make the main trends stand grams labelled "Rotation -2" repre- out more clearly, the monthly aver- sents solar conditions during the sec- ages forming the basis of all the ond solar rotation before the one when curves in FIG. 1 and 2 are smoothed the barometric variations occur, and by the formula (a -f 2 b + c) /4 =b . so on to + 2, representing the second The unsmoothed data are given in solar rotation thereafter.