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. Thus the

Unauthenticated | Downloaded 10/08/21 12:25 AM UTC TABLE II. Correlation Coefficients between Latitude of Sunspots and Inter- diurnal Changes of Barometric Pressure at New Haven (Based on 12 pairs of averages for calendar months, 1877-1935). Date in Relation to ABC barometric Northern solar Southern solar Both solar changes hemisphere hemisphere hemispheres -2. Second rotation before -.34 -.56* -.40 -1. First rotation before -.48 -.50* -.69* 0. Same rotation -.64* -.65* -.79** + 1. First rotation after -.76** -.57* -.78** + 2. Second rotation after -.51 -.52* -.54*

•Probably significant. ** Mathematically significant. January sections of the lines in FIG. are related in such a way that the 1 and 2 represent solar conditions in nature (sign) of the relationship 5 different months ranging from the changes regularly from season to November before high or low baro- season. In much of FIG. 1 (based on metric variability to the March there- TABLE V at end of this article), but after. The lowest diagram in each only in the upper parts of FIG. 2 column illustrates average solar con- (TABLE VI), the lines cross irregu- ditions during the two or three rota- larly according to the first type of tions which appear to be of special relationship. In no part of either significance (rotations 0 and 1, except figure does one line remain constantly on the right of FIG. 1). In both figures above the other as required by the the sun's northern hemisphere is on second type of relationship. In some the left, the southern hemisphere in parts of FIG. 1 and in most of FIG. 2, the middle, and the two combined on the lines symmetrically fluctuate in the right. In combining the two hem- opposite directions, thus indicating ispheres the average latitudes have a relationship which changes from simply been added together and div- season to season according to the third ided by two with no attempt at of the preceding alternatives. weighting according to the area of the Some idea of the degree of connec- sunspots. tion between sunspot areas and baro- In studying FIG. 1 and 2 the first metric variations can be obtained point to note is the degree to which from correlation coefficients between each diagram agrees with one of the the average values of these two fac- following alternatives: (1) the solid tors during the 12 calendar months. and dotted lines cross irregularly; (2) Such coefficients are given in Table 1. one line remains consistently above or Being based on only 12 pairs of num- below the other; (3) the lines are bers they must, of course, be used arranged in a definite inverse pattern with caution, but they give a general such that where one is high, the other idea of the degree of accordance or is low. The first alternative provides divergence between the solar and ter- no evidence of a relationship between restrial data. According to R. A. barometric variability and solar activ- Fisher (TABLE V. A. in Statistical ity. The second indicates that through- Methods for Research Workers) a out the year a given solar condition is correlation coefficient above .50 is associated with a definite barometric probably significant when there are tendency. The third affords evidence only 12 pairs of variates. A coeffi- that solar and barometric conditions cient of .70 or more is almost certainly

Unauthenticated | Downloaded 10/08/21 12:25 AM UTC significant, for it indicates less than that for the present we can merely one chance in a hundred that the say that a connection between the apparent relationship is due to acci- area of sunspots and interdiurnal dent. In Column A of the table (rep- changes of atmospheric pressure is resented graphically on the left of suggested but not proved. FIG. 1) there is no reliable indication COMPARISON WITH LATITUDE OF of any correlation between the area of spots in the sun's northern hemi- SUNSPOTS sphere and the amount of interdiurnal The evidence as to the relation of variability of atmospheric pressure at barometric variability to the latitude New Haven, the highest coefficient of sunspots is more conclusive than being only -.35. The sun's southern that as to their area. Before dis- hemisphere (column B) shows a dif- cussing this, however, we must explain ferent picture. The coefficients rise our treatment of solar rotations dur- from practically zero, when baro- ing which the absence of spots leaves metric variability is compared with doubt as to the latitude of maximum sunspot areas during the second solar turbulence in the solar atmosphere. rotation previous to the observed Among the 790 solar rotations from barometric conditions, to -.74 when 187i7 to 1935 there were 68 of this barometric variability is compared kind for the northern hemisphere with sunspot areas at the same time. and 55 for the southern. Three pos- Then the coefficients drop off again. sibilities present themselves: (1) to Column C shows that when the en- omit such rotations; (2) to count tire area of sunspots in both solar their latitude as zero; or (3) to esti- hemispheres is compared with baro- mate the latitude of greatest solar metric variability, the coefficients are spot activity on the basis of preceding intermediate between those when the and following rotations. We have two solar hemispheres are kept sep- followed the last method. Rotations arate. The regular rise and fall of without spots normally occur between the coefficients in column B, and the those with unusually high or unusu- fact that the coefficients for both rota- ally low latitudes. In such cases we tions 0 and + 1 are large enough to have assumed that during a rotation be significant suggests that the area with no spots the sun's atmosphere is of sunspots in the sun's southern most active in the average latitude hemisphere may be correlated with of the preceding and following rota- the variability of the barometer at tions which have spots. Sometimes, New Haven. If so, the diagrams for however, we have cases such as an rotations 0 and -f- 1 in the central average latitude of 2.7° followed by column of FIG. 1 suggest that in mid- a rotation with no spots and then by winter an abundance of spots in the one with 22.7°, to use an actual ex- sun's southern hemisphere is corre- ample. In the middle rotation the lated with low barometric variability. latitude of greatest solar activity is The diagram for rotation + 1 sug- so doubtful that 15 such cases in the gests an opposite condition in sum- northern hemisphere and 20 in the mer, and so does that for rotation 0 southern have been omitted. This on the right of FIG. 1. The irregu- method gives more systematic results larity of FIG. 1, as a whole, however, than either of the others. The re- and the small size of the sample and sults appear in TABLE VI at the end of the correlation coefficients in Col- of this paper. umn C of TABLE 1 seem to indicate From TABLE VI it is possible to cal-

Unauthenticated | Downloaded 10/08/21 12:25 AM UTC TABLE III. Interdiurnal Changes of Barometric Pressure at New Haven, 1877-1935, at Different Phases of the Sunspot Cycle. A B Number of Average Sunspot Phase Solar Rotations Barometric Variability I. Few or no spots 205 10.77 II. Increasing spots 186 10.50 III. Many Spots 217 10.78 VI. Decreasing spots 190 10.72 culate TABLE II which shows the cor- nection with the sunspots of April relation coefficients between the lati- and May than with those of February tude of sunspots at times of high and and January. Thus to a certain ex- low barometric variability. Here, just tent "the cart seems to come before as in Table I, the coefficients are based the horse." If this relationship should on 12 pairs of averages representing prove to be widespread, it might mean calendar months. Most of them, being that the atmospheric turbulence of above .50, are probably significant. both the earth and the sun is influ- Three rise high enough to be conclu- enced by some third factor, perhaps sively significant. All are negative. some unobserved solar condition, These facts suggest that sunspots in which stirs up both atmospheres, but relatively high solar latitudes affect produces its maximum manifestation the earth's atmosphere in an opposite more quickly in the small and shallow way from those in low latitudes, but atmosphere of the earth than in the the effects vary systematically in a more extensive and vastly deeper at- cycle of six months. When the lati- mosphere of the sun. tudes of the northern and southern The chief feature of the present spots are averaged (column C, TABLE investigation is the way in which the II), four out of five coefficients rise solid and dotted lines show pronounced above those for the two hemispheres opposition in most of the 18 diagrams separately. Moreover, the coefficients of FIG. 2. The opposition is imperfect rise steadily from rotation —2 until at the top of the middle and right rotation 0 is reached, that is, until hand columns, but comes surprisingly barometric changes are compared with near to perfect lower down in rota- the sunspot latitudes which occur at tions 0 and + 1. Another feature of the same time. Such facts suggest a FIG. 2 is the clarity with which it real and significant relationship. shows that we are dealing with a re- Another interesting relationship is lationship which has a double annual suggested by the fact that the coeffi- cycle. Each curve has two maxima cient (-.78) for rotation + 1 in col- and two minima during the year. In umn C is practically the same as for midwinter and again in early summer rotation 0 (-.79), while the one for high barometric variability is asso- rotation + 2 (-.54) is greater than ciated with high latitude of sunspots, for rotation -2 (-.40). Expressed and low variability with low latitude. in calendar months for the sake of In the early Spring and Autumn the clearness, the barometric variability opposite relationship prevails. Such of March, for example, although con- a condition seems to demand some nected more closely with the sunspots cause in addition to ordinary seasonal of that same month than with those conditions such as contrasts in tem- of any other, seems to have more con- perature.

Unauthenticated | Downloaded 10/08/21 12:25 AM UTC TABLE IV. Correlation Coefficients showing Contrast between Solar Lati- tude and Distance from Center of Sun's Visible Disk.

B Periods with high Periods with great vs. vs. low latitude slight distance of spots of sunspots from center of solar disk

Rotation -2 .19 .25 Rotation -1 -.07 -.34 Rotation 0 .05 -.37 Rotation + 1 .16 -.42 Rotation + 2 .39 -.10 Although the reality of the double Haven, is small. Only in October does annual cycle seems certain, the mag- the coefficient (-.32) rise to 4 times nitude of the terrestrial effect is a the probable error, but inasmuch as different matter. Some idea of this we are dealing with sixty pairs of can be gained from FIG. 3., which variables this is mathematically signi- ficant. It is about what we should expect from data with the many im- perfections described on an earlier page. It should be noted, however, that FIG. 3 faithfully reflects the double annual cycle which is so con- spicuous in FIG. 2. Among the many questions to which FIG. 3. Correlation coefficients between baro- metric variability at New Haven and latitude the preceding facts give rise, we shall of sunspots, 1877-1935. try to answer only two. The first is shows the correlation coefficients whether our results are due to the month by month between barometric successive phases of the sunspot cycle. variability and the latitude of sun- A sunspot cycle begins with spots in spots. The coefficient for each month high latitudes and ends with spots is based on somewhat more than 60 near the equator. TABLE III shows pairs of data. The solid curve por- that when seasonal differences are trays the coefficients when the mean eliminated, the average interdiurnal latitudes of the spots in the two hemi- change of barometric pressure at New spheres are averaged. The dotted line Haven during four nearly equal is similar except that the mean lati- phases of the sunspot cycle is approx- tude of each hemisphere is weighted imately the same. The actual differ- according to the area of the sunspots. ence between phases II and III is The fact that the solid line is the only twice the probable difference. smoother of the two suggests that Hence it is doubtful whether the latitude rather than area is the im- phases of the sunspot cycle have any portant factor. A more detailed anal- definite relation to the semi-annual ysis of individual groups of spots ac- cycle of FIG. 2, although it is true that cording to their latitude might show spots occur in high latitudes chiefly barometric relationships stronger than in the early part of the cycle. This have yet been detected. On the basis seems puzzling until one recalls that of the data now available, however, the relationship of barometric var- the correlation between sunspot lati- iability and sunspot latitude varies tude and the barometric variability from season to season. When the of a single station, such as New whole year is averaged together, the

Unauthenticated | Downloaded 10/08/21 12:25 AM UTC TABLE V. Average Area of Sunspots Part I. When Barometric Variability at New Haven, 1877-1935, is 5% or more Above Normal Sun's northern Sun's southern Month Number of hemisphere hemisphere rotations Date of rotations Date of rotations -2 -1 0 1 2 -2 -1 0 1 2 Jan. 29 289 278 190 165 185 203 210 230 241 208 Feb. 26 272 336 298 336 268 263 294 284 353 397 Mar 29 274 286 282 233 241 334 336 284 296 297 Apr. 23 306 238 262 225 256 406 351 384 288 338 May 25 297 300 260 300 299 236 263 280 372 328 June 23 207 210 272 184 192 263 207 245 320 286 July 25 342 339 409 240 359 306 324 308 340 320 Aug 27 394 236 340 254 234 365 382 408 341 272 Sept. 26 293 299 330 262 383 328 366 301 295 274, Oct. 23 374 405 333 359 425 325 342 252 266 342 Nov. 28 416 360 346 313 295 238 221 243 295 280 Dec. 24 199 213 330 261 284 197 173 229 311 387 Average: 305 292 304 261 285 289 289 287 310 311 Part II. When Barometric Variability at New Haven, 1877-1935, is 5% or more Below Normal Jan. 24 298 277 299 319 321 296 342 366 427 268 Feb. 23 295 234 192 201 224 184 248 370 167 162 Mar. 27 334 265 344 256 268 398 415 254 273 280 Apr. 29 228 271 233 276 420 314 211 258 283 323 May 29 153 152 172 201 172 260 214 189 275 294 June 27 244 259 316 348 290 336 323 310 264 251 July 28 216 276 156 329 326 251 163 290 260 274 Aug. 32 262 292 298 272 313 258 258 223 284 222 Sept. 25 253 306 335 411 326 229 220 296 234 300 Oct. 29 281 256 346 402 308 241 328 275 320 320 Nov. 26 245 256 244 273 238 295 284 292 305 314 Dec. 28 364 344 260 349 239 328 374 404 369 384 Average: 264 266 266 303 287 283 282 294 288 281 conditions observed in March and the solar rotations beginning in each October largely cancel those of June calendar month (about 65 in number and December. except in February) we have selected The second question was raised by the 25 showing the highest average Dr. Charles F. Brooks on reading the latitude of the sunspots in one solar first draft of this article. He inquired hemisphere or the other, and the 25 whether the significant solar condition showing the lowest similar average. is the actual latitude of the sunspots, In many cases the spots in both solar or their distance from the center of hemispheres agree in placing a given the sun's visible disk. A final test of rotation in one or the other of these this seems to require that we go back two groups. Sometimes only one to the original data for individual solar hemisphere shows spots at a groups of sunspots. This involves so distance such as to put the rotation much work that it is not now feasible. in one group or the other. These rota- Therefore a preliminary exploratory tions are included except in a few method has been employed. Among instances when a rotation falls into

Unauthenticated | Downloaded 10/08/21 12:25 AM UTC TABLE VI. Average Latitude of Sunspots, 1877-1935 Part. I. When Interdiurnal Changes of Barometric Pressure at New Haven, Conn., average at least 5% above the seasonal normal

Sun's northern Sun's southern Number of hemisphere hemisphere Month rotations Date of rotations Date of rotations -2 -1 0 + 1 + 2 -2 -1 0 + 1 + 2 Jan. 27 to 29 13.9° 14.9° 14.8° 14 5° 14.6° 15.4° 14.3° 13.6° 15.1° 16.3C Feb. 25 to 26 13.8 14.1 13,3 13,6 13.6 13.5 13.9 15.4 13.8 15.1 Mar. 28 to 29 11.9 12.7 12.6 12.8 12.6 11.8 13.9 12.1 12.6 13.0 April 22 to 23 13.2 12.9 13.6 13.7 12.6 13.9 14.6 13.8 15.8 14.1 May 24 to 25 14.3 14.7 14.1 14.5 13.8 13.9 15.4 15.2 14.4 14.0 June 22 to 23 13.9 14.3 15.4 15.2 14.7 13.6 12,8 12.8 15.4 15.0 July 23 to 25 14.4 14,1 13.0 13.4 12.9 13.8 13.7 16.2 15.1 14.2 Aug. 27 13.0 12.6 14.1 13.6 12.3 15.5 15.8 15.3 14.3 12.5 Sept. 24 to 26 12.5 12.5 12.3 12.5 13,6 14.0 13.8 13.1 13.4 13.9 Oct. 23 13.8 14.1 12.4 12.3 13.1 13.9 13.5 12.9 12.8 14.2 Nov. 27 to 28 13.8 13.5 14.5 14.4 13.4 15.2 15.2 16.0 16.0 15.0 Dec. 23 to 24 14.4 15,0 15.4 14.6 13.8 14.9 15.0 14.0 13.5 14.1 Average: 13.6 13.8 13.8 13.8 13.4 14.1 14.3 14.2 14.4 14.3 Part II. When Interdiurnal Changes of Barometric Pressure at New Haven, Conn., average at least 5% below seasonal normal Jan. 22 to 23 12.4° 12.4° 11.6° 10.5° 12.1° 10.2° 11.8° 13.0° 13.2° 11.5° Feb. 22 to 23 13.8 13.9 13.0 14.1 13.6 13.5 13.6 14.3 15.8 13.9 Mar. 27 14.7 14.8 15.2 14.1 12.9 15.3 14.5 15.6 14.8 14.9 April 28 to 29 11.9 12.8 12.5 12.4 13.9 13.2 13.7 14.71 14.5 14.3 May 28 to 29 12.1 11.4 11.2 11.6 11.5 13.1 12.5 12.5 12.0 14.0 June 26 to 27 12.9 12.8 12.4 12.0 12.3 14.9 14.5 14.3 14.4 14.6 July 26 to 28 13.6 12.9 12.6 13.9 14.4 15.3 15.2 13.6 13.8 13.8 Aug. 31 to 32 12.8 12.9 13.3 13.9 13.8 14.0 13.8 14.6 13.7 14.2 Sept. 24 to 25 13.9 15.6 15.4 13.6 15.0 16.0 15.5 15.2 14.9 14.7 Oct. 28 to 29 14.9 15.2 14.6 16.7 14.7 15.2 15.8 16.5 16.6 15.1 Nov. 25 to 26 12.8 13.2 13.4 13.2 12.7 13.0 13.0 12.8 12.4 10.7 Dec 27 to 28 13.3 13.6 13.2 13.1 13.6 15.1 14.9 14.5 13.8 14.3 Average: 13.3 13.5 13.2 13.3 13.4 14.1 14.1 14.3 14.2 13.8 both the high and the low groups age interdiurnal variability of atmo- because the spots of a new cycle are spheric pressure is computed. This in high latitudes on one side of the supplies data for ten pairs of curves solar equator and those of an old cycle like those of FIG. 1 and 2. Five of are in low latitudes on the other side. these, representing rotations - 2 to The elimination of such rotations + 2, provide a comparison between leaves from 21 to 25 in each monthly the curves for barometric variabil- group. The next step is precisely the ity associated with high and low solar same except that the average lati- latitudes. These show only a hint of tudinal distance of the spots from the the double annual period seen in FIG. center of the sun's visible disk is sub- 2. For example, in the lower part of stituted for latitude. Thus for each FIG. 4 the curves for barometric vari- calendar month we obtain four groups ability at times of high and low sun- of solar rotations based on the posi- spot latitudes (rotations 0 and +1) tion of sunspots on the sun's surface. are in opposition only from April to For each of these groups the aver- July, and approach agreement the

Unauthenticated | Downloaded 10/08/21 12:25 AM UTC 398 BULLETIN AMERICAN METEOROLOGICAL SOCIETY [Vol. 23 rest of the time. The other five pairs the times when they would be expected of curves, the ones associated with if we are dealing with a real relation- distance from the center of the sun's ship. Then, too, the double annual disk, show the double annual period period shown in FIG. 4 must not be quite clearly, as appears in the upper overlooked. From all these facts it part of FIG. 4. Nevertheless, the op- seems probable that, in spite of the preliminary nature of the method here employed, the distance of sun- spots from the center of the sun's disk is responsible for the semi-annual cycle in the relationship between sun- spots and interdiurnal barometric variability at New Haven. The causes of the correlation be- tween barometric variability and the distance of sunspots from the center of the sun's visible disk are obscure. The presence of the double annual cycle seems to force us to choose be- tween two alternatives. The cause FIG. 4. Interdiurnal barometric variability may be found either in some condition compared with latitude of sunspots (Below) and distance of sunspots from center of sun's which has a cycle of six months, or visible disk (Above). in two conditions, each with a cycle position of the two curves is not so of a year, but with opposite seasonal perfect as in the central curves of phases. The search for a 6-month FIG. 2. The whole matter is summed cycle which offers even the slightest up in TABLE IV which gives the cor- hope of explaining the solar-terres- relation coefficients between the trial correlation here described has monthly barometric variabilities asso- thus far proved fruitless. There are, ciated with high as compared with low however, two annual cycles whose sea- latitude of sunspots (column A), and sonal incidence agrees with the double those associated with relatively great cycle shown in FIG. 2. They arise compared with slight distance of from the inclination of the axes of spots from the center of the solar disk the earth and the sun to the plane in (column B). which the earth rotates around the sun. Noteworthy in this table are the small and irregular values of the co- The earth's southern pole is most efficients in column A. They seem to inclined toward the sun in December have no significance. Another point and the northern pole in June. At is regular downward change in the those times, or immediately there- coefficients of column B from a small after, high latitude of sunspots, or plus value to minus values which in- relatively great distance from the crease in size until rotation + 1 is center of the sun's disk, is associated reached and then drop toward zero. with high barometric variability. On Although no one coefficient is large the other hand, on March 5 the sun's enough to be mathematically signifi- south pole points most nearly to the cant, those for rotations -1, 0, and earth, while in early September the + 1 are decidedly larger than the cor- north solar pole has its maximum responding figures in column A. More- earthward inclination. At those times over, the highest coefficients come at high latitude of sunspots is associated

Unauthenticated | Downloaded 10/08/21 12:25 AM UTC with low barometric variability. It spots. On page 296, Clough speaks seems impossible that any thermal as follows concerning correlations be- effect of the sun upon barometric vari- tween half-yearly means of tempera- ability could vary in such a way as ture at St. Paul and solar latitude of to produce a double seasonal cycle sunspots from 1875 to 1923. "The conforming to the inclination of the maximum coefficients, ± 0.60, with axes of both the earth and the sun. a probable error of ± .06, are far It is likewise difficult to frame an greater than any coefficient yet ob- electro-magnetic hypothesis as to how tained by correlating solar and me- this could happen, but the probabil- teorological data. In view of these ities seem to us to lie in that direc- high coefficients, it cannot be doubted tion. that a real relation exists between the mean latitude of sunspots and the temperature at St. Paul". Inciden- Added in proof: tally it may be noted that on page 29 After this paper was in the hands of "Earth and Sun" (New Haven, of the printer the September number 1923), the present author showed that of this BULLETIN (Vol. 23, pp. 292- the correlation between yearly storm- 298) was received. An article there iness in the main storm track area of published by H. W. Clough "On the North America and the yearly sunspot Interpretation of the Results of numbers from 1889 to 1918 is ±0.61 Periodogram Analysis and of Self- ± .07. This coefficient is slightly Correlation" affords an interesting larger than the one just published by confirmation of the conclusion that Clough, but is not based on so large terrestrial weather is related to sun- a number of cases.

Typhoons in 1939 & 1940 in the are included in a single volume, with China Sea (The Energy of Ty- a paper on The energy of typhoons. phoons).—From 1926 to 1938, Fr. E. The paper is opened with a reprint Gherzi, S.J., Director of the Zi-Ka- of a portion of the poem, "The cy- Wei Observatory, Shanghai issued an- clone," by Townsend Allen, 1902 nual summaries of typhoons in the (pubd. in Mon. Weather Rev., 1902, Far East, with maps of their courses, v. 30, p. 270); its main point, how- and often with some discussion of ever, is a computation of the energy typhoon problems. These discussions of the typhoon of Sept. 13-16, 1928, have been: Where do the typhoons based on the precipitation over an develop? (1927), Distribution of area of 47,303 sq. km (13,774 sq. mi.), rclouds in a typhoon (1930), Some by J. S. Groodin. The data are given data about typhoon centre (1931), in detail on two fold-in plates, for Note on the swell of cyclones (1932), the 30 stations and the areas they Typhoons and "fronts" (1933), Set represent, for each of the days of the caused by tropical cyclones (1934), storm. The mean rainfall was 173 Air masses acting over China etc. mm (6.8 in.), in the precipitation of (1935), The "pumping" of typhoons which the latent heat liberated was (1936), The hurricane wave (1937), equivalent in energy to 6 million The steering of typhoons (1938). H. P. per hour per sq. km.—C. F. B. Now the typhoons of 1939 and 1940

Unauthenticated | Downloaded 10/08/21 12:25 AM UTC