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Comparison of geomagnetic storms and trough development at solar activity maximum and minimum
COMPARISON OF GEOMAGNETIC STORMS AND TROUGH DEVELOPMENT AT SOLAR ACTIVITY MAXIMUM AND MINIMUM Laboratory
DAVID D. WOODBRIDGE for Environmental and Solar Studies, Florida Institute of Technology, Melbourne, Florida 32901, U.S.A. (Received infinalform
2 March 1971)
Abstract-Geomagnetic storms have long been found to be related to solar storms. However, the effects of solar activity within the lower atmosphere have been postulated but not as yet confirmed. A positive correlation was found between trough development at 300 mb and geomagnetic storms during the 1956-57 solar activity maxima in a study performed at the High Altitude Observatory of the University of Colorado. Similar studies performed at the Army Ballistic Missile Agency and at Florida Institute of Technology have also shown positive correlations between geomagnetic storms and subsequent trough development. A comparison of the results of these investigations into a possible solar weather effect are presented. INTRODUCTION
Approximately a decade ago, a series of works by the author and others (Woodbridge et al., 1958, 1959; Macdonald and Roberts, 1960, 1961), led to the surprising conclusion that increases of geomagnetic activity were followed, in a statistically significant way, by deepening of troughs in the large scale atmospheric circulation at the 300 mb level. Winter troughs that first formed within or moved into the Alaska-Aleutians area two to four days after a geomagnetic disturbance displayed, some days later at their fullest development, a greater cyclonic curvature than troughs appearing in the same region at other times during the winter half-year. The results implied a causal relationship between geomagnetic disturbances, which are associated with solar corpuscular emission, and subsequent meteorological phenomena at lower stratospheric or upper tropospheric levels. The earlier authors were unable to identify any plausible physical mechanism to explain their findings, nor has subsequent work cast further light on physical explanations. It is of interest, however, that other authors in this field, such as Mustel (1970), persistently offer findings purporting to exhibit influences on weather by aurora1 or geomagnetic activity associated with solar corpuscular emission. The results, for the most part, are inconclusive and sometimes quite confusing. If the effects are real they are of great significance, particularly since they appear, in most instances, to exhibit themselves at a lag of approximately a week, by which time most large-scale circulation forecasting techniques have fallen to zero skill. A mechanism acting at this large lag time could be of great theoretical and practical value. Because of the importance of the earlier results, the author decided to repeat the older analyses with precisely the techniques used before, but using the newer meteorological and geomagnetic data that have accumulated in the intervening years. The results from this study appear to substantiate, in totally independent fashion, the older work of the author (Woodbridge et al., 1958, 1959) and of Macdonald and Roberts (1960, 1961). This being so, the author believes that additional work is highly merited, but that further researches should focus upon more meaningful physical parameters of the circulation, which can now be easily derived using large computers. Further work should also be directed toward development of a physical explanation for the observed associations. Some specific recommendations are given in the last part of this paper. 821
822
DAVID
D. WOODBRIDGE
METHOD
OF AX=TSIS
The prime purpose of the analysis undertaken by the author in the present study, has been to repeat precisely the methods of the studies carried out earlier at the High Altitude Observatory. In those studies, low pressure troughs showing in the large scale circulation at the 300 mb level were characterized by means of a trough index developed by Woodbridge et al. (1957). The index was designed to measure the cyclonic curvature in the troughs, and it consisted of a dimensionless number involving the ratio of the trough depth to width. Measurements were made at two height contours (30,400 ft and 29,200 ft height contours). The trough indexing procedure has been described in detail earlier by Woodbridge et al. (1959). Daily maps of the 300 mb level for the western half of the Northern Hemisphere were supplied by the Department of Transport of Canada. In the earlier study, as in the present, each trough was tabulated from the first day that it formed or moved into the grid area north of 50” latitude between the longitudes 12O”W and 180”. Trough indices were measured at two contour heights for each day of the observable life of the trough, and the values of the two heights were averaged to give a single index for each trough for each day. The troughs generally migrated eastwards through the map system, and reached a maximum trough index value on some date of their migration. The maximum value of the index, irrespective of the date of its occurrence, was used to characterize the fully developed size of the trough. No distinction was made between troughs that migrated into the grid area from farther west, and those that developed within the area. All identifiable troughs were analyzed for winter half-years: 1 October-31 March, inclusive. The troughs were then divided into three size classes of approximately equal number, based on the value of the maximum trough index. In the earlier study approximately 46 troughs could be identified in each of the winter half-years 1956-57, 1957-58. In the present study a total of 99 troughs were identified in the two winter half-years 1964-65 and 1965-66. The objective of the earlier study was to examine the distribution of trough indices into the large, medium and small index values dependent upon whether the date of first appearance of a trough within the grid area was preceded by a geomagnetic disturbance of notable magnitude. Surprisingly, the studies showed that there was a statistically significant tendency for troughs that were preceded by geomagnetic storms to attain a larger size at maturity. The earlier studies identified geomagnetic storms by slightly different criteria than those available now. This should not introduce any difficulties, however. In the earlier studies the geomagnetic indices used were generally based on the geomagnetic activity observed at Cheltenham, Maryland by the Central Radio Propagation Laboratory (now a part of the The geomagnetic index criteria National Oceanic and Atmospheric Administration). were designed to identify the principal periods of marked disturbance during each winter half-year. For the present study we adopted the following criteria for a geomagnetic storm zero-day: it was a day on which the planetary geomagnetic index A,* was 15 or larger, and had first reached this value through a one-day rise of the A, value of greater than Il. * A, index is the average daily planetary index of the magnetic activity on a linear scale. It is the average value of a 3-hourly index which is defined as one-half the average gamma range of the most disturbed of the three force components at stations throughout the world.
GEOMAGNETIC
STORMS
AND TROUGH
823
DEVELOPMENl-
RESULTS The results of our present analysis are shown in three ways, all identical in principle with those used in the earlier studies we sought to confirm. The first result is shown in the contingency table, Table 1. TABLE 1. DATA FROM 19%1966
Large I, > 0.7 Geomagnetic disturbonce No geomagnetic disturbance
Total
Medium 0.7 > It > 0.5
15(7) -!(12) 19
X2 test with two degree of freedom:
STUDY
Small I, < 0.5
13(17)
5(9)
26(22)
36(32)
39
41
Total
99
P < lo-*.
In Table 1, the trough index class frequencies for the large, medium, and small maximum values are separated into two groups: (1) trough maxima preceded, three or four days before, by a geomagnetic zero-day meeting the criteria described above and (2) trough maxima not preceded by geomagnetic disturbances meeting our criteria. In parentheses after each class frequency in the table is the frequency to be expected on the assumption that the troughs are randomly distributed relative to the occurrence of geomagnetic disturbance. It is clear that a significant positive association exists between troughs with large indices at maximum development, and the occurrence of a geomagnetic storm three to four days before the trough’s first appearance in the Gulf of Alaska region. A X2 analysis, with two degrees of freedom, shows that a result as far as this from random is to be expected with a probability less than lo- 5. The similar table from the earlier study is reproduced as Table 2. TABLE 2. DATA FROM 1956-1957 STUDY
Large If > 0.7 Geomagnetic disturbance No geomagnetic disturbance Total
Medium 0.7 > zt > 0.5
Small zt < 0.5
Total 16
9(6) 14
X2 test with two degree of freedom:
12
17(15)
30
20
46
P < 0.002.
The present study shows an even stronger association of large trough values with magnetic disturbance than did the earlier work. A second method of studying the association is given in Fig. 1 which presents the results of a superposed epoch analysis of the large trough frequencies from the analysis of the large trough frequencies from the present study, versus the geomagnetic zero dates of this study. Figure 1 presents the frequencies of occurrence of large troughs distributed according to the number of days that elapsed between the geomagnetic storm and the trough’s first appearance in the Gulf of Alaska area for the 1964-65 and 1965-66 data. A clear peak is evident on the third and fourth days after the geomagnetic zero dates. For comparison,
DAVID
824 I I
I
D. WOODBRIDGE
-
Large troughs (1,>0,7) AAp>ll as Zero day.
usin(
__--
Large troughs CIYO.7) random Zero day
usinc
I
.
(Combined data,
1964-M;
I I I I
I I I
I I I
Days
FIG.].
DISTRIBUTION OF OCCURRENCES OF LARGE TROUGHS WITHIN THE GULF OF ALASKA RELATIVETO THE OCCURRENCES OEGEO,MAGNETIC STORMS DURING THE 1964-67LmNTERs.
The dash line indicates distribution of occurrences of troughs using a random ‘zero day’ rather than the occurrences of a geomagnetic storm. l
-
LarCe troughs (1)0.7) using AAQI I as Zero day
---
Large troughs (1,20.7) using ramdom Zero day
/I
(Combined 1957-58)
data,
1956-57;
Days
FIG. 2. DISIXIBIJTIOSOF OCCURRENCES OF LARGE TROUGHS WITHIN THE GULF OF ALASKA RELAT~VETOTHEOCCURRENCESOFGEO.UAGNE~CSTOR~MSDUR~NGTHE 1956-53 WINTERS. The dash line indicates distribution of occurrences of troughs using a random ‘zero day’ rather
than the occurrences
of a geomagnetic
storm.
GEOMAGNETIC
STORMS
AND TROUGH
825
DEVELOPMENT
O-8
1964-65; a6-
*\ /
.-•
1965-W
-
Primary troughs associated wth large risv of geomagnetic index&Ap&lI
---
Troughs not associated with
\
FIGS. 3 aad 4,
DEVELOPMENT HISTORY OF TROUGHS ASSOCIATED WITH GEWWNFEIC CO~ARWTO~OSENOTASSOCLAIEDUTTHGEOMAGNEnCSIT)~.
STORMS AS
r 1956-57; -
Primary troughs associated with forge rise of geomagnetic index AAp> I I
----
Troughs not ossoclated with geomagnetic disturbance
0.6
II
ISS-58
0.4
IO Days of development Erc.
4.
1956-195s.
the dashed figure shows a superposed epoch analysis of the same large troughs using as zero dates the same number of days, but choosing them at random through the half-year. The absence of a peak of significant proportions lends credence to the association of large troughs with geomagnetic key dates. Far comparison, the sirpilar Ggure from the earlier study is given in Fig. 2. Once again, the new data confirm the earlier results. A finaf analysis of the data, for comparison with tfre earlier studies, is given in Fig. 3 and Fig. 4.
826
DAVID
D. WOODBRIDGE
Figure 3 shows the average values of the trough index of the new study to be compared with Fig. 4 which shows the previous study. Both figures show the trough index as a function of the number of days from the hrst identification of the trough in the Gulf of Alaska area. The solid curves in these figures present the data for troughs preceded three to four days earlier by a geomagnetic disturbance meeting our criteria. The dashed curves represent all other troughs. Clearly the maxima show markedly larger average values for the troughs preceded by geomagnetic activity. The average size maximizes at about six days after first recognition of the troughs, or about nine or ten days after the apparently associated geomagnetic disturbance. CONCLUSIONS
No physical explanation of these associations is given in this paper, nor is the author aware of any satisfactory mechanism to explain the results. The independent confirmation gives some urgency to more sophisticated studies of the trough behavior, and its apparent association with geomagnetic activity of a type very probably associated with sporadic solar activity. The energy changes available as a result of variable solar activity are small, and most of the marked atmospheric effects of solar activity are at the ionospheric levels, and not in the lower stratosphere, where these associations are found. The trough index used in these two sets of studies is a somewhat unsatisfactory quantity to interpret physically. Clearly a re-analysis is merited using more objectively derived and more meaningful parameters of the circulation. It would be useful, perhaps, to carry out such a study identifying as the circulation parameter the change in absolute vorticity associated with each trough in its day-to-day development. Or perhaps one could look at the value of the curvature term in the vorticity calculation on a day-to-day basis. Analyses of this sort should be relatively easy with modern computer techniques. In addition, a search should be made for unique properties of the dynamics of the trough development for troughs found to be associated with geomagnetic activity. Perhaps their development will reveal idiosyncrasies that will give a clue to the nature of their apparent connection with the Sun and with geomagnetic activity. Acknowle@ements-The author wishes to thank the Canadain Department of Transport for supplying the 300 mb maps that have been used through this study, and Dr. Walter Orr Roberts, President of the University Corporation for Atmospheric Research for his suggestions and encouragements through the years. Thanks also go to Mrs. Priscilla Cooper for her assistance in the statistical analyses. This research was performed under National Science Foundation grants: GA818 and GP4767. REFERENCES N. J. and ROBERTS,W. 0. (1960). J.geophy. Res. 65,524-534. MACDONALD, N. J. and ROBERTS,W. 0. (1961). J. Meteorol. 18, 116118. MUSTEL, E. R. (1970). Internat. Commission Solar-Terrestriul Phys. Leningad. USSR. (Astronomical Council, Academy of Sciences, USSR, Center for Hydrometeorology.) WOODBRIDGE,D. D. and MACDONALD, N. J. (1959). Science 129,638-639. WOODBRIDGE,D. D., MACDONALD, N. J. and POHRTE,T. W. (1958). J. Meteorol. 15,247-248. WOODBRIDGE,D. D., MACDONALD, N. J. and POURTE, T. W. (1959). J.geophys. Res. 64,3. WOODBRIDGE,D. D., POHIITE,T. W. and MACDONALD, N. J. (1957). Tech. Rep. No. 3. High Altitude Observatory, Institute for Solar-Terrestrial Res. MACDONALD,
DAVID D. WOODBRIDGE for Environmental and Solar Studies, Florida Institute of Technology, Melbourne, Florida 32901, U.S.A. (Received infinalform
2 March 1971)
Abstract-Geomagnetic storms have long been found to be related to solar storms. However, the effects of solar activity within the lower atmosphere have been postulated but not as yet confirmed. A positive correlation was found between trough development at 300 mb and geomagnetic storms during the 1956-57 solar activity maxima in a study performed at the High Altitude Observatory of the University of Colorado. Similar studies performed at the Army Ballistic Missile Agency and at Florida Institute of Technology have also shown positive correlations between geomagnetic storms and subsequent trough development. A comparison of the results of these investigations into a possible solar weather effect are presented. INTRODUCTION
Approximately a decade ago, a series of works by the author and others (Woodbridge et al., 1958, 1959; Macdonald and Roberts, 1960, 1961), led to the surprising conclusion that increases of geomagnetic activity were followed, in a statistically significant way, by deepening of troughs in the large scale atmospheric circulation at the 300 mb level. Winter troughs that first formed within or moved into the Alaska-Aleutians area two to four days after a geomagnetic disturbance displayed, some days later at their fullest development, a greater cyclonic curvature than troughs appearing in the same region at other times during the winter half-year. The results implied a causal relationship between geomagnetic disturbances, which are associated with solar corpuscular emission, and subsequent meteorological phenomena at lower stratospheric or upper tropospheric levels. The earlier authors were unable to identify any plausible physical mechanism to explain their findings, nor has subsequent work cast further light on physical explanations. It is of interest, however, that other authors in this field, such as Mustel (1970), persistently offer findings purporting to exhibit influences on weather by aurora1 or geomagnetic activity associated with solar corpuscular emission. The results, for the most part, are inconclusive and sometimes quite confusing. If the effects are real they are of great significance, particularly since they appear, in most instances, to exhibit themselves at a lag of approximately a week, by which time most large-scale circulation forecasting techniques have fallen to zero skill. A mechanism acting at this large lag time could be of great theoretical and practical value. Because of the importance of the earlier results, the author decided to repeat the older analyses with precisely the techniques used before, but using the newer meteorological and geomagnetic data that have accumulated in the intervening years. The results from this study appear to substantiate, in totally independent fashion, the older work of the author (Woodbridge et al., 1958, 1959) and of Macdonald and Roberts (1960, 1961). This being so, the author believes that additional work is highly merited, but that further researches should focus upon more meaningful physical parameters of the circulation, which can now be easily derived using large computers. Further work should also be directed toward development of a physical explanation for the observed associations. Some specific recommendations are given in the last part of this paper. 821
822
DAVID
D. WOODBRIDGE
METHOD
OF AX=TSIS
The prime purpose of the analysis undertaken by the author in the present study, has been to repeat precisely the methods of the studies carried out earlier at the High Altitude Observatory. In those studies, low pressure troughs showing in the large scale circulation at the 300 mb level were characterized by means of a trough index developed by Woodbridge et al. (1957). The index was designed to measure the cyclonic curvature in the troughs, and it consisted of a dimensionless number involving the ratio of the trough depth to width. Measurements were made at two height contours (30,400 ft and 29,200 ft height contours). The trough indexing procedure has been described in detail earlier by Woodbridge et al. (1959). Daily maps of the 300 mb level for the western half of the Northern Hemisphere were supplied by the Department of Transport of Canada. In the earlier study, as in the present, each trough was tabulated from the first day that it formed or moved into the grid area north of 50” latitude between the longitudes 12O”W and 180”. Trough indices were measured at two contour heights for each day of the observable life of the trough, and the values of the two heights were averaged to give a single index for each trough for each day. The troughs generally migrated eastwards through the map system, and reached a maximum trough index value on some date of their migration. The maximum value of the index, irrespective of the date of its occurrence, was used to characterize the fully developed size of the trough. No distinction was made between troughs that migrated into the grid area from farther west, and those that developed within the area. All identifiable troughs were analyzed for winter half-years: 1 October-31 March, inclusive. The troughs were then divided into three size classes of approximately equal number, based on the value of the maximum trough index. In the earlier study approximately 46 troughs could be identified in each of the winter half-years 1956-57, 1957-58. In the present study a total of 99 troughs were identified in the two winter half-years 1964-65 and 1965-66. The objective of the earlier study was to examine the distribution of trough indices into the large, medium and small index values dependent upon whether the date of first appearance of a trough within the grid area was preceded by a geomagnetic disturbance of notable magnitude. Surprisingly, the studies showed that there was a statistically significant tendency for troughs that were preceded by geomagnetic storms to attain a larger size at maturity. The earlier studies identified geomagnetic storms by slightly different criteria than those available now. This should not introduce any difficulties, however. In the earlier studies the geomagnetic indices used were generally based on the geomagnetic activity observed at Cheltenham, Maryland by the Central Radio Propagation Laboratory (now a part of the The geomagnetic index criteria National Oceanic and Atmospheric Administration). were designed to identify the principal periods of marked disturbance during each winter half-year. For the present study we adopted the following criteria for a geomagnetic storm zero-day: it was a day on which the planetary geomagnetic index A,* was 15 or larger, and had first reached this value through a one-day rise of the A, value of greater than Il. * A, index is the average daily planetary index of the magnetic activity on a linear scale. It is the average value of a 3-hourly index which is defined as one-half the average gamma range of the most disturbed of the three force components at stations throughout the world.
GEOMAGNETIC
STORMS
AND TROUGH
823
DEVELOPMENl-
RESULTS The results of our present analysis are shown in three ways, all identical in principle with those used in the earlier studies we sought to confirm. The first result is shown in the contingency table, Table 1. TABLE 1. DATA FROM 19%1966
Large I, > 0.7 Geomagnetic disturbonce No geomagnetic disturbance
Total
Medium 0.7 > It > 0.5
15(7) -!(12) 19
X2 test with two degree of freedom:
STUDY
Small I, < 0.5
13(17)
5(9)
26(22)
36(32)
39
41
Total
99
P < lo-*.
In Table 1, the trough index class frequencies for the large, medium, and small maximum values are separated into two groups: (1) trough maxima preceded, three or four days before, by a geomagnetic zero-day meeting the criteria described above and (2) trough maxima not preceded by geomagnetic disturbances meeting our criteria. In parentheses after each class frequency in the table is the frequency to be expected on the assumption that the troughs are randomly distributed relative to the occurrence of geomagnetic disturbance. It is clear that a significant positive association exists between troughs with large indices at maximum development, and the occurrence of a geomagnetic storm three to four days before the trough’s first appearance in the Gulf of Alaska region. A X2 analysis, with two degrees of freedom, shows that a result as far as this from random is to be expected with a probability less than lo- 5. The similar table from the earlier study is reproduced as Table 2. TABLE 2. DATA FROM 1956-1957 STUDY
Large If > 0.7 Geomagnetic disturbance No geomagnetic disturbance Total
Medium 0.7 > zt > 0.5
Small zt < 0.5
Total 16
9(6) 14
X2 test with two degree of freedom:
12
17(15)
30
20
46
P < 0.002.
The present study shows an even stronger association of large trough values with magnetic disturbance than did the earlier work. A second method of studying the association is given in Fig. 1 which presents the results of a superposed epoch analysis of the large trough frequencies from the analysis of the large trough frequencies from the present study, versus the geomagnetic zero dates of this study. Figure 1 presents the frequencies of occurrence of large troughs distributed according to the number of days that elapsed between the geomagnetic storm and the trough’s first appearance in the Gulf of Alaska area for the 1964-65 and 1965-66 data. A clear peak is evident on the third and fourth days after the geomagnetic zero dates. For comparison,
DAVID
824 I I
I
D. WOODBRIDGE
-
Large troughs (1,>0,7) AAp>ll as Zero day.
usin(
__--
Large troughs CIYO.7) random Zero day
usinc
I
.
(Combined data,
1964-M;
I I I I
I I I
I I I
Days
FIG.].
DISTRIBUTION OF OCCURRENCES OF LARGE TROUGHS WITHIN THE GULF OF ALASKA RELATIVETO THE OCCURRENCES OEGEO,MAGNETIC STORMS DURING THE 1964-67LmNTERs.
The dash line indicates distribution of occurrences of troughs using a random ‘zero day’ rather than the occurrences of a geomagnetic storm. l
-
LarCe troughs (1)0.7) using AAQI I as Zero day
---
Large troughs (1,20.7) using ramdom Zero day
/I
(Combined 1957-58)
data,
1956-57;
Days
FIG. 2. DISIXIBIJTIOSOF OCCURRENCES OF LARGE TROUGHS WITHIN THE GULF OF ALASKA RELAT~VETOTHEOCCURRENCESOFGEO.UAGNE~CSTOR~MSDUR~NGTHE 1956-53 WINTERS. The dash line indicates distribution of occurrences of troughs using a random ‘zero day’ rather
than the occurrences
of a geomagnetic
storm.
GEOMAGNETIC
STORMS
AND TROUGH
825
DEVELOPMENT
O-8
1964-65; a6-
*\ /
.-•
1965-W
-
Primary troughs associated wth large risv of geomagnetic index&Ap&lI
---
Troughs not associated with
\
FIGS. 3 aad 4,
DEVELOPMENT HISTORY OF TROUGHS ASSOCIATED WITH GEWWNFEIC CO~ARWTO~OSENOTASSOCLAIEDUTTHGEOMAGNEnCSIT)~.
STORMS AS
r 1956-57; -
Primary troughs associated with forge rise of geomagnetic index AAp> I I
----
Troughs not ossoclated with geomagnetic disturbance
0.6
II
ISS-58
0.4
IO Days of development Erc.
4.
1956-195s.
the dashed figure shows a superposed epoch analysis of the same large troughs using as zero dates the same number of days, but choosing them at random through the half-year. The absence of a peak of significant proportions lends credence to the association of large troughs with geomagnetic key dates. Far comparison, the sirpilar Ggure from the earlier study is given in Fig. 2. Once again, the new data confirm the earlier results. A finaf analysis of the data, for comparison with tfre earlier studies, is given in Fig. 3 and Fig. 4.
826
DAVID
D. WOODBRIDGE
Figure 3 shows the average values of the trough index of the new study to be compared with Fig. 4 which shows the previous study. Both figures show the trough index as a function of the number of days from the hrst identification of the trough in the Gulf of Alaska area. The solid curves in these figures present the data for troughs preceded three to four days earlier by a geomagnetic disturbance meeting our criteria. The dashed curves represent all other troughs. Clearly the maxima show markedly larger average values for the troughs preceded by geomagnetic activity. The average size maximizes at about six days after first recognition of the troughs, or about nine or ten days after the apparently associated geomagnetic disturbance. CONCLUSIONS
No physical explanation of these associations is given in this paper, nor is the author aware of any satisfactory mechanism to explain the results. The independent confirmation gives some urgency to more sophisticated studies of the trough behavior, and its apparent association with geomagnetic activity of a type very probably associated with sporadic solar activity. The energy changes available as a result of variable solar activity are small, and most of the marked atmospheric effects of solar activity are at the ionospheric levels, and not in the lower stratosphere, where these associations are found. The trough index used in these two sets of studies is a somewhat unsatisfactory quantity to interpret physically. Clearly a re-analysis is merited using more objectively derived and more meaningful parameters of the circulation. It would be useful, perhaps, to carry out such a study identifying as the circulation parameter the change in absolute vorticity associated with each trough in its day-to-day development. Or perhaps one could look at the value of the curvature term in the vorticity calculation on a day-to-day basis. Analyses of this sort should be relatively easy with modern computer techniques. In addition, a search should be made for unique properties of the dynamics of the trough development for troughs found to be associated with geomagnetic activity. Perhaps their development will reveal idiosyncrasies that will give a clue to the nature of their apparent connection with the Sun and with geomagnetic activity. Acknowle@ements-The author wishes to thank the Canadain Department of Transport for supplying the 300 mb maps that have been used through this study, and Dr. Walter Orr Roberts, President of the University Corporation for Atmospheric Research for his suggestions and encouragements through the years. Thanks also go to Mrs. Priscilla Cooper for her assistance in the statistical analyses. This research was performed under National Science Foundation grants: GA818 and GP4767. REFERENCES N. J. and ROBERTS,W. 0. (1960). J.geophy. Res. 65,524-534. MACDONALD, N. J. and ROBERTS,W. 0. (1961). J. Meteorol. 18, 116118. MUSTEL, E. R. (1970). Internat. Commission Solar-Terrestriul Phys. Leningad. USSR. (Astronomical Council, Academy of Sciences, USSR, Center for Hydrometeorology.) WOODBRIDGE,D. D. and MACDONALD, N. J. (1959). Science 129,638-639. WOODBRIDGE,D. D., MACDONALD, N. J. and POHRTE,T. W. (1958). J. Meteorol. 15,247-248. WOODBRIDGE,D. D., MACDONALD, N. J. and POURTE, T. W. (1959). J.geophys. Res. 64,3. WOODBRIDGE,D. D., POHIITE,T. W. and MACDONALD, N. J. (1957). Tech. Rep. No. 3. High Altitude Observatory, Institute for Solar-Terrestrial Res. MACDONALD,