National Aeronautics andSpace AdministrationIS20George C. Marshall Space Flight CenterMarshall Space Flight Center, Alabama35812

NASA/TP—2008–215249

On the Relationship Between Solar Wind Speed, Geomagnetic Activity, and the Solar Cycle Using Annual ValuesRobert M. Wilson and David H. HathawayMarshall Space Flight Center, Marshall Space Flight Center, Alabama

February 2008

The NASA STI Program…in Profile

Since its founding, NASA has been dedicated to the advancement of aeronautics and space science. The NASA Scientific and Technical Information (STI) Program Office plays a key part in helping NASA maintain this important role.

The NASA STI program operates under the auspices of the Agency Chief Information Officer. It collects, organizes, provides for archiving, and disseminates NASA’s STI. The NASA STI program provides access to the NASA Aeronautics and Space Database and its public interface, the NASA Technical Report Server, thus providing one of the largest collections of aeronautical and space science STI in the world. Results are published in both non-NASA channels and by NASA in the NASA STI Report Series, which includes the following report types:

• TECHNICAL PUBLICATION. Reports of completed research or a major significant phase of research that present the results of NASA programs and include extensive data or theoretical analysis. Includes compilations of significant scientific and technical data and information deemed to be of continuing reference value. NASA’s counterpart of peer-reviewed formal professional papers but has less stringent limitations on manuscript length and extent of graphic presentations.

• TECHNICAL MEMORANDUM. Scientific and technical findings that are preliminary or of specialized interest, e.g., quick release reports, working papers, and bibliographies that contain minimal annotation. Does not contain extensive analysis.

• CONTRACTOR REPORT. Scientific and technical findings by NASA-sponsored contractors and grantees.

• CONFERENCE PUBLICATION. Collected papers from scientific and technical conferences, symposia, seminars, or other meetings sponsored or cosponsored by NASA.

• SPECIAL PUBLICATION. Scientific, technical, or historical information from NASA programs, projects, and missions, often concerned with subjects having substantial public interest.

• TECHNICAL TRANSLATION. English-language translations of foreign scientific and technical material pertinent to NASA’s mission.

Specialized services also include creating custom thesauri, building customized databases, and organizing and publishing research results.

For more information about the NASA STI program, see the following:

• Access the NASA STI program home page at <http://www.sti.nasa.gov>

• E-mail your question via the Internet to <help@sti.nasa.gov>

• Fax your question to the NASA STI Help Desk at 301– 621–0134

• Phone the NASA STI Help Desk at 301– 621–0390

• Write to: NASA STI Help Desk NASA Center for AeroSpace Information 7115 Standard Drive Hanover, MD 21076–1320

�

NASA/TP—2008–215249

On the Relationship Between Solar Wind Speed, Geomagnetic Activity, and the Solar Cycle Using Annual ValuesRobert M. Wilson and David H. HathawayMarshall Space Flight Center, Marshall Space Flight Center, Alabama

February 2008

Nat�onal Aeronaut�cs andSpace Adm�n�strat�on

Marshall Space Fl�ght Center • MSFC, Alabama 35812

��

Ava�lable from:

NASA Center for AeroSpace Informat�on7115 Standard Dr�ve

Hanover, MD 21076 –1320301– 621– 0390

Th�s report �s also ava�lable �n electron�c form at<https://www2.st�.nasa.gov>

���

TABLE OF CONTENTS

1. INTRODUCTION ........................................................................................................................... 1

2. RESULTS AND DISCUSSION ....................................................................................................... 2

3. SUMMARY ..................................................................................................................................... 9

REFERENCES ..................................................................................................................................... 10

�v

v

LIST OF FIGURES

1. Annual var�at�on of (a) sunspot number R and (b) the corrected aa geomagnet�c �ndex for the years 1860–2006. The th�n, vert�cal l�nes mark the sunspot m�n�mum years and the numbers refer to the sunspot cycles 10–23. Not�ce that most cycles have the�r largest aa �ndex after sunspot max�mum (except cycles 12 and 13) and the�r m�n�mum aa �ndex value e�ther �n the sunspot m�n�mum year or the year follow�ng the sunspot m�n�mum year (except cycle 21) . ........................................................ 3

2. Scatterplot of the annual aa �ndex values aga�nst R for the years 1868–2006. Not�ce that all aa �ndex values l�e on or above the l�ne denoted aaR, wh�ch �s used to compute the lead�ng sporad�c component of the aa �ndex (�.e., the solar cycle component) ............................................................................................................................. 4

3. Annual var�at�on of the res�dual or follow�ng recurrent �nterplanetary component of the aa �ndex, computed as aaI = aa – aaR for the years 1868–2006. The th�n, vert�cal l�nes mark the sunspot m�n�mum years; the th�ck, vert�cal l�nes mark the sunspot max�mum years; and the numbers refer to the sunspot cycles 11–23. Pla�nly, the max�mum recurrent component of the aa �ndex usually occurs after sunspot max�mum (except cycles 12 and 13). Not�ce that the largest observed value of the recurrent component (24.3) occurred �n 2003 dur�ng the decl�ne of cycle 23 ............. 4

4. Annual var�at�on of (a) R, (b) aa, (c) aaI, (d) solar w�nd speed v, and (e) number of hours of solar w�nd observat�ons for the years 1950–2006. The th�n and th�ck vert�cal l�nes and the numbers 19–23 have the same mean�ngs as before. See text for deta�ls ......................................................................................................................... 6

5. Scatterplots of (a) aa and (b) aaI versus v for the years 1964–2006. See text for deta�ls ................................................................................................................................ 7

6. Cycl�c var�at�on of (a) <R>, (b) < aa >, (c) < aaI >, and (d) and <v> for cycles 11–23. See text for deta�ls .................................................................................................................. 8

v�

LIST OF ACRONYMS

IP �nterplanetary

PI pred�ct�on �nterval

TP Techn�cal Publ�cat�on

v��

NOMENCLATURE

aa the aa geomagnet�c �ndex

< aa > cycl�c average of aa

aaI res�dual component of the aa �ndex, equal to aa – aaR

< aaI > cycl�c average of aaI

aamax aa �ndex max�mum

aamin aa �ndex m�n�mum

cl confidencelevel

R sunspot number

<R> cycl�c average of R

Rmax sunspot max�mum

Rmin sunspot m�n�mum

r linearcorrelationcoefficient

r2 coefficientofdetermination

se standard error of est�mate

v solar w�nd speed

x �ndependent var�able

y regress�on equat�on

v���

1

TECHNICAL PUBLICATION

ON THE RELATIONSHIP BETWEEN SOLAR WIND SPEED, GEOMAGNETIC ACTIVITY, AND THE SOLAR CYCLE USING ANNUAL VALUES

1. INTRODUCTION

In order to expla�n the late-occurr�ng geomagnet�c peak �n solar cycles, Feynman1 suggested decompos�ng the aa geomagnet�c �ndex �nto two components—one that �s �n phase and correlated d�rectly w�th the sunspot cycle, the lead�ng sporad�c component, and the other that �s out of phase and assoc�-ated w�th �nterplanetary d�sturbances from the Sun, the res�dual or follow�ng recurrent component, wh�ch usually peaks after sunspot max�mum (the except�ons are cycles 12 and 13) just before the next cycle’s sunspot m�n�mum.2–5 Follow�ng Feynman’s approach, Hathaway and W�lson6,7 decomposed the aa geo-magnet�c record and used the late-cycle recurrent peak to forecast the expected s�ze of the next sunspot cycle (cycle 24), us�ng both the observed and adjusted records of the aa �ndex, where the adjusted record �s one that compensates for changes �n the repos�t�on�ng of the magnetometers pr�or to 1957 that are used �n the determ�nat�on of the aa �ndex. (See also Svalgaard, Cl�ver, and Le Sager.8) From the�r stud�es, �t was determ�ned that cycle 24 should be expected to be a cycle of larger than average s�ze, comparable to cycles 21 and 22, the second and th�rd largest cycles of the modern era. (See also D�kpat�, de Toma, and G�lman.9)

It has long been bel�eved that there should be a good correlat�on between geomagnet�c act�v�ty and solar w�nd speed10 and, �ndeed, for per�ods of h�gh coverage, a strong correlat�on has been found.11 Also, �t has been found that a general �ncrease �n the aa �ndex has occurred between 1868 and 2006, where th�s increasehasbeenattributedtoanincreaseinthestrengthofthepolarmagneticfieldoftheSun.12

In th�s Techn�cal Publ�cat�on (TP), the relat�onsh�p between solar w�nd speed, geomagnet�c act�v-�ty (the aa �ndex), and the solar cycle �s reexam�ned us�ng annual averages, where the solar w�nd speed �s determ�ned us�ng the Omn�-merged, 1-hr, 1 AU �nterplanetary (IP) data <http://cdaweb.gsfc.nasa.gov>.13 Thisisthefirstofatwo-partstudyofsolarwindandthegeomagnetic/solarcycle.

2

2. RESULTS AND DISCUSSION

F�gure 1 d�splays the var�at�on of annual averages of (a) sunspot number R and (b) the adjusted aa �ndex for the �nterval 1860 –2006, where the adjusted aa �ndex7 �s merely the observed aa value for the �nterval 1957–2006 and the observed value plus 3 nT for the �nterval 1868–1956. Although Nevan-l�nna and Kataja14 have extended the aa �ndex for two add�t�onal solar cycles (1844 –1867) us�ng hourly decl�nat�on read�ngs at the Hels�nk� magnet�c-meteorolog�cal observatory (1844 –1880), these data have not been used �n th�s TP. The th�n, vert�cal l�nes mark the sunspot m�n�mum years and the numbers refer to sunspot cycles 10–23, where cycle 23 �s the current sunspot cycle that began �n 1996. Wh�le sunspot cyclesusuallyhaveasingle,well-definedpeak(Rmax) that follows sunspot m�n�mum (Rmin) by 3–5 yr when descr�bed us�ng annual averages, the geomagnet�c cycle typ�cally has mult�ple peaks, w�th the larg-est (aamax) usually occurr�ng dur�ng the decl�n�ng port�on of the sunspot cycle (as prev�ously ment�oned, the except�ons are cycles 12 and 13), just pr�or to the sunspot m�n�mum of the follow�ng cycle. Also, the m�n�mum value of the geomagnet�c �ndex (aamin) almost always has occurred �n the year follow�ng the sunspot m�n�mum year. (The except�ons are cycles 14, 15, and 19, wh�ch had aamin and Rmin occurr�ng contemporaneously, and cycle 21, wh�ch had aamin occurr�ng �n 1980, some 4 yr past Rmin and 1 yr past Rmax, although a sl�ghtly larger local m�n�mum value was seen at 1 yr past Rmin; the aamin value for cycle 11 l�kely occurred dur�ng the sunspot m�n�mum year of 1867 and not 1868.)

Fromfigure1,Rmin �s found to have var�ed between 1.4 (cycle 15) and 13.4 (cycle 22), hav�ng a 90% pred�ct�on range of 7 ± 6.7 for the g�ven sample s�ze of 13 cycles. Also, Rmax �s found to have var�ed between 63.5 (cycle 14) and 190.2 (cycle 19), hav�ng a 90% pred�ct�on range of 117.5 ± 70.9. The rat�o (not shown) of Rmax to Rmin for the past 13 solar cycles �s found to have var�ed between 10.38 (cycle 20) and 74.21 (cycle 15), hav�ng a 90% pred�ct�on range of 22.3 ± 31.89. The value of R �n 2006 measured 15.2, a value that l�es just outs�de the 90% pred�ct�on range for Rmin. Hence, the sunspot m�n�mum year for cycle 24 l�kely w�ll occur �n 2007 (the annual average for 2007 has recently been determ�ned to be 7.6, well w�th�n the 90% range for Rmin), or poss�bly 2008 �f cycle 24 turns out to be a slow r�ser.

Likewise, fromfigure 1,aamin (�n the v�c�n�ty of sunspot m�n�mum) �s found to have var�ed between 9 (cycle 14) and 20.2 (cycles 19 and 21; cycle 21 actually had a lower aamin �n 1980 (18.5), well after �ts sunspot m�n�mum year of 1976), hav�ng a 90% pred�ct�on range of 15.2 ± 7.1 for the g�ven sample s�ze of 12 cycles. (Cycle 11 �s not �ncluded s�nce �ts aamin probably occurred �n 1867, before the start of the aa record.) Also, aamax �s found to have var�ed between 20.5 (cycle 14) and 37.1 (cycle 23), w�th all cycles from cycle 18 onward hav�ng an aamax≥30.3.The90%predictionrangeforaamax �s 29.7 ± 8.1. The rat�o (not shown) of aamax to aamin for the past 12 solar cycles �s found to have var�ed between 1.62 (cycle 19) and 2.59 (cycle 12), hav�ng a 90% pred�ct�on range of 2.03 ± 0.6. The value of aa �n 2006 measured 16.2, a value w�th�n the 90% pred�ct�on range for aamin, and the value of aaforthefirst7moof 2007 has averaged 15.6. Exclud�ng cycles 12 and 13, wh�ch had aamax that preceded Rmax by 1 yr, aamax �s found to have occurred after Rmax, on average, by about 3 yr (the range �s 2–6 yr). (Cycles 12 and 13 had sl�ghtly smaller local aamax values after Rmax, by 3 and 1 yr, respect�vely.)

3

1860 1880 1900 1920 1940

Year

1960 1980 2000 2020

1860 1880 1900 1920 1940 1960 1980 2000 2020

10 11 12 13 14 15 16 17 18 19 20 21 22 23

10 11 12 13 14 15 16 17 18 19 20 21 22 23

(a)

(b)

40

30

20

10

0

200

150

100

50

0

aaR

F�gure 1. Annual var�at�on of (a) sunspot number R and (b) the corrected aa geomagnet�c �ndex for the years 1860–2006. The th�n, vert�cal l�nes mark the sunspot m�n�mum years and the numbers refer to the sunspot cycles 10–23. Not�ce that most cycles have the�r largest aa �ndex after sunspot max�mum (except cycles 12 and 13) and the�r m�n�mum aa �ndex value e�ther �n the sunspot m�n�mum year or the year follow�ng the sunspot m�n�mum year (except cycle 21).

F�gure 2 shows the scatterplot of aa versus R for 1868–2006. All aa values are found to l�e e�ther on or above the g�ven d�agonal l�ne aaR = 8.83123 + 0.06254R, where th�s equat�on �s used to compute the lead�ng sporad�c component of the aa �ndex (�.e., the solar cycle component).

F�gure 3 dep�cts the res�dual aaI = aa – aaR, or the follow�ng recurrent �nterplanetary component, hav�ng removed the lead�ng sporad�c component. The res�dual �s bel�eved to be assoc�ated w�th recur-rent h�gh-speed streams from coronal holes, wh�ch typ�cally are at the�r greatest extent after sunspot max�mum.15 Th�n, vert�cal l�nes mark the sunspot m�n�mum years; th�ck, vert�cal l�nes mark the sunspot max�mum years; and the numbers 11–23 aga�n refer to the sunspot cycles. For all cycles, except cycles 12 and 13, the max�mum value of the res�dual, denoted here as (aaI)max, occurs after sunspot max�-mum and ranges �n value between 10.5 (cycle 14) and 24.3 (cycle 23), hav�ng a 90% pred�ct�on range of 16.7 ± 7.4.

4

1868–2006

aaR = 8.83123 + 0.06254R

aaR

40

30

20

10

0

aa

0 20 40 60 80 100 120 140 160 180 200

R

F�gure 2. Scatterplot of the annual aa �ndex values aga�nst R for the years 1868–2006. Not�ce that all aa �ndex values l�e on or above the l�ne denoted aaR, wh�ch �s used to compute the lead�ng sporad�c component of the aa �ndex (�.e., the solar cycle component).

11 12 13 14 15 16 17 18 19 20 21 22 23

30

20

10

0

aal

1860 1880 1900 1920 1940 1960 1980 2000 2020

aal aa – aaR, aaR 8.83123 0.06254R

Year

F�gure 3. Annual var�at�on of the res�dual or follow�ng recurrent �nterplanetary component of the aa �ndex, computed as aaI = aa – aaR for the years 1868–2006. The th�n, vert�cal l�nes mark the sunspot m�n�mum years; the th�ck, vert�cal l�nes mark the sunspot max�mum years; and the numbers refer to the sunspot cycles 11–23. Pla�nly, the max�mum recurrent component of the aa �ndex usually occurs after sunspot max�mum (except cycles 12 and 13). Not�ce that the largest observed value of the recurrent component (24.3) occurred �n 2003 dur�ng the decl�ne of cycle 23.

5

F�gure 4 plots the annual var�at�on of R, aa, aaI, the solar w�nd speed v (�n km s–1), and the number of hours of solar w�nd observat�on (plots (a)–(e), respect�vely) for the �nterval 1950–2006. As before, th�n, vert�cal l�nes mark the sunspot m�n�mum years; th�ck, vert�cal l�nes mark the sunspot max�mum years; and the numbers refer to solar cycles 19–23. Solar w�nd data are ava�lable for 1964–present, adapted here us�ng the Omn�-merged, 1-hr, 1 AU IP data (ava�lable at <http://cdaweb.gsfc.nasa.gov>).13 In part�cu-lar, the annual solar w�nd speed used �n th�s study �s the average of the max�mum and m�n�mum hourly solar w�nd speeds for each day, we�ghted by the number of hours of da�ly observat�on. As an example, on January 1, 1964, solar w�nd speeds were recorded for 12 hr, hav�ng a max�mum of 370 km s–1 and a m�n�mum of 310 km s–1, thereby, �nferr�ng an average of the extremes of 340 km s–1. Observat�ons are ava�lable for 29 of the 31 days of the month cover�ng 558 hr (75% coverage). The average of the da�ly max�mum-m�n�mum averages, we�ghted accord�ng to the number of hours of da�ly observat�on, was 369 km s–1 and th�s value represents the average solar w�nd speed for January 1964. For the rema�nder of the year, the average monthly solar w�nd speed/numbers of hours of observat�on were 352.9/228 (Febru-ary), 0/0 (March–June), 517.5/111 (July), 453.6/159 (August), 463.4/237 (September), 459.8/396 (Octo-ber), 430.7/249 (November), and 396/183 (December). For the year 1964, the average solar w�nd speed was 418.4 km s–1 based on 2,121 hr of observat�on (24.1% coverage), and �t �s th�s solar w�nd speed (and numberofhoursofobservation)thatisplottedinfigure4fortheyear1964.Inspectionoffigure4clearlyshows that the solar w�nd speed v peaks after sunspot max�mum for all observed cycles (cycles 20–23; observat�ons began �n November 1963). Interest�ngly, the h�ghest average solar w�nd speed occurred �n 2003 (542.8 km s–1, based on 8,688 hr of observat�on or 99.2% coverage; coverage �s greatest (>90% coverage) for the years of 1974, 1979–1981, and 1995–present), and the peak �n solar w�nd speed for all cycles (except cycle 23) occurs 2 yr pr�or to the follow�ng cycle’s sunspot m�n�mum year (cycle 23 actu-ally has a secondary peak �n 2005, measur�ng 469.9 km s–1 based on 8,689 hr of observat�on or 99.2% coverage).

F�gure 5 shows the scatterplots of (a) aa versus v and (b) aaI versus v for 1964–2006. Pla�nly, both aa and aaI tend to �ncrease �n value as solar w�nd speed �ncreases. Both correlat�ons are stat�st�cally very significant,withthestrongeronebeingbetweenaaI and v.Theinferredcorrelationhasacoefficientofdeterm�nat�on r2 = 0.748, �mply�ng that nearly 75% of the var�ance can be expla�ned by the �nferred regres-s�on. So, the peaks observed �n the aa and aaI �nd�ces late �n the cycle (after solar max�mum) appear to be d�rectly related to �ncreased solar w�nd speed, wh�ch probably �s the result of h�gh-speed streams from coronal holes.15–21

F�gure 6 dep�cts (a) the cycl�c var�at�on of sunspot number <R>, (b) the aa geomagnet�c �ndex < aa >, (c) the follow�ng recurrent component < aaI >, and (d) the solar w�nd speed <v> for cycles 11–23, where each cycl�c average �s computed from sunspot m�n�mum to subsequent cycle sunspot m�n�mum. (Cycle 23ispresumedtohaveendedin2006onthebasisofannualaverages.)Forthefirstthreeparameters,allreveal a long-term �ncrease over t�me, such that for cycle 24, the next cycle, one �nfers <R> = 82.6 ± 27.6, < aa > = 26 ± 4.3, and < aaI > = 12 ± 2.8, these est�mates be�ng the 90% pred�ct�on �ntervals. Thus, there �s a 95% probab�l�ty that cycle 24 w�ll have <R> ≥ 55, < aa > ≥ 21.7, and < aaI > ≥ 9.2. Because of the close relat�onsh�p between solar w�nd speed and, �n part�cular, aa and aaI(fig.5),thecyclicaverageofsolarw�nd speed �s �nferred to have �ncreased over t�me, as well. (Str�ctly speak�ng, the cycl�c var�at�on of solar w�nd speed <v> �s �ndeterm�nate because of the brev�ty of the solar w�nd record, 1964–present, espec�ally, as compared to the solar/geomagnet�c record, wh�ch �s cons�dered rel�able s�nce the m�d 1800s.)

6

19 20 21 22 23

19 20 21 22 23

19 20 21 22 23

19 20 21 22 23

19 20 21 22 23

9,000

8,000

7,000

6,000

5,000

4,000

3,000

2,000

1,000

0

Num

ber o

f Hou

rs

600

500

400

300

200

v

40

30

20

10

0

aa

200

150

100

50

0

R

30

20

10

0

aal

1950 1960 1970 1980 1990 2000 2010

1950 1960 1970 1980 1990 2000 2010

1950 1960 1970 1980 1990 2000 2010

1950 1960 1970 1980 1990 2000 2010

1950 1960 1970 1980 1990 2000 2010

Year

(a)

(b)

(c)

(d)

(e)

F�gure 4. Annual var�at�on of (a) R, (b) aa, (c) aaI, (d) solar w�nd speed v, and (e) number of hours of solar w�nd observat�ons for the years 1950–2006. The th�n and th�ck vert�cal l�nes and the numbers 19–23 have the same mean�ngs as before. See text for deta�ls.

7

v

(a)

(b)

30

25

20

15

10

5

0

40

35

30

25

20

15

10

5

0

350 400 450 500 550

350 400 450 500 550

aaaa

l

1964–2006

y –45.689 0.125xr 0.865, r 2 0.748se 2.435, cl 99.9%

y –26.347 0.111xr 0.749, r 2 0.561se 3.669, cl 99.9%

1964–2006

y

y

aal aa–aaRaaR 8.83123 0.06254R

F�gure 5. Scatterplots of (a) aa and (b) aaI versus v for the years 1964–2006. See text for deta�ls.

8

450

400

10

0

30

20

10

100

50

0

<v>

<aa l>

<aa>

<R>

11 12 13 14 15 16 17 18 19 20 21 22 23 24

11 12 13 14 15 16 17 18 19 20 21 22 23 24

11 12 13 14 15 16 17 18 19 20 21 22 23 24

11 12 13 14 15 16 17 18 19 20 21 22 23 24

y 2.411 0.399xr 0.718, r 2 0.515se 1.567, cl 99%

aal 24 12 2.8 (90% PI)

y 11.185 0.615xr 0.729, r 2 0.531se 2.386, cl 99%

aa 24 26 4.3 (90% PI)

y –2.001 3.526xr 0.682, r 2 0.465se 15.368, cl 98%

R 24 82.6 27.6 (90% PI)

Cycle

y

y

y

(a)

(b)

(c)

(d)

F�gure 6. Cycl�c var�at�on of (a) <R>, (b) < aa >, (c) < aaI >, and (d) and <v> for cycles 11–23. See text for deta�ls.

9

3. SUMMARY

Th�s study has shown that, on the bas�s of annual averages, solar w�nd speed �s d�rectly related to both the geomagnet�c and solar cycles. H�gher (lower) solar w�nd speed assoc�ates w�th h�gher (lower) values of the aa �ndex, espec�ally for the res�dual or follow�ng recurrent component of the aa �ndex. Because there has been a long-term �ncrease �n the strength of the solar/geomagnet�c cycles over t�me (cycles 11–23), �t �s �nferred that the solar w�nd speed has also exper�enced a long-term �ncrease.

10

REFERENCES

1. Feynman, J.: “Geomagnet�c and Solar W�nd Cycles, 1900–1975,” J. Geophys. Res., Vol. 87, p. 6153, 1982.

2. Allen, C.W.: “Relat�on Between Magnet�c Storms and Solar Act�v�ty,” Mon. Not. R. Astron. Soc., Vol. 104, p. 13, 1944.

3. Saemundsson, Th.: “The Stat�st�cs of Geomagnet�c Storms and Solar Act�v�ty,” Mon. Not. R. Astron. Soc., Vol. 123, p. 299, 1962.

4. Ohl, A.I.: “Phys�cs of the 11-year Var�at�on of Magnet�c D�sturbances,” Geomagn. Aeron., Vol. 11, p. 549, 1971.

5. Sargent, H.H. III: “Recurrent Geomagnet�c Act�v�ty: Ev�dence for Long-L�ved Stab�l�ty �n Solar W�nd Structure,” J. Geophys. Res., Vol. 90, p. 1425, 1985.

6. Hathaway, D.H.; and W�lson, R.M.: “Geomagnet�c Act�v�ty Ind�cates Large Ampl�tude for Sunspot Cycle 24,” Geophys. Res. Lett., Vol. 33, p. L18101, do�:10.1029/2006GL027053, 2006.

7. W�lson, R.M.; and Hathaway, D.H.: “ An Exam�nat�on of Selected Geomagnet�c Ind�ces �n Relat�on to the Sunspot Cycle,” NASA/TP—2006–214711, Marshall Space Fl�ght Center, Alabama, <http://trs.n�s.nasa.gov/arch�ve/00000741>, p. 52, December 2006.

8. Svalgaard, L.; Cl�ver, E.W.; and Le Sager, P.: “IHV: A New Long-Term Geomagnet�c Index,” Adv. Space Res., Vol. 34, p. 436, 2004.

9. D�kpat�, M.; de Toma, G.; and G�lman, P.A.: “Pred�ct�ng the Strength of Solar Cycle 24 Us�ng a Flux-Transport Dynamo-Based Tool,” Geophys. Res. Lett., Vol. 33, p. L05102, do�:10.1029/2005GL025221, 2006.

10. Ch�rkov, N.P.: “Correlat�on of Geomagnet�c Act�v�ty and Solar W�nd Veloc�ty w�th Solar Act�v�ty,” Geomagn Aeron., Vol. 19, p. 143, 1979.

11. Gaz�s, P.R.; Ahluwal�a, H.S.; F�kan�, M.M.; and Xue, S.S.: “Long Term Var�ab�l�ty of the Solar W�nd Speed,” Internat�onal Solar W�nd 8 Conference, NASA Ames Research Center, p. 89, June 1995.

12. Russell, C.T.; and Mull�gan, T.: “ The 22-year Var�at�on of Geomagnet�c Act�v�ty: Impl�cat�ons for the Polar Magnet�c F�eld of the Sun,” Geophys. Res. Lett., Vol. 22, p. 3287, 1995.

13. Coord�nated Data Analys�s Web, <http://cdaweb.gsfc.nasa.gov>, accessed 2007.

11

14. Nevanl�nna, H.; and Kataja, E.: “An Extens�on of the Geomagnet�c Act�v�ty Index Ser�es aa for Two Solar Cycles (1844 –1868),” Geophys. Res. Lett., Vol. 20, p. 2703, 1993.

15. Z�rker, J.B.: “Coronal Holes and H�gh-Speed W�nd Streams,” Rev. Geophys. Sp. Phys., Vol. 15, p. 257, 1977.

16. Watar�, S.; and Watanabe, T.: “The Solar Dr�vers of Geomagnet�c D�sturbances Dur�ng Solar M�n�-mum,” Geophys. Res. Lett., Vol. 25, p. 2489, 1998.

17. Watar�, S.; and Wantanabe, T.: “Geomagnet�c D�sturbances Around the Solar M�n�mum of Cycle 22 and The�r Solar Sources,” Solar Physics with Radio Observations, Proceedings of Nobeyama Sympo-sium 1998, NRO Report 479, p. 199, 1998.

18. R�chardson, I.G.; Cl�ver, E.W.; and Cane, H.V.: “Sources of Geomagnet�c Act�v�ty Over the Solar Cycle: Relat�ve Importance of Coronal Mass Eject�ons, H�gh-Speed Streams and Slow Solar W�nd,” J. Geophys. Res., Vol. 105, p. 18,203, 2000.

19. Rangarajan, G.K.; and Barreto, L.M.: “Long Term Var�ab�l�ty �n Solar W�nd Veloc�ty and IMF Inten-s�ty and the Relat�onsh�p Between Solar W�nd Parameters & Geomagnet�c Act�v�ty,” Earth Planets Space, Vol. 52, p. 121, 2000.

20. R�chardson, I.G.; Cane, H.V.; and Cl�ver, E.W.: “Sources of Geomagnet�c Act�v�ty Dur�ng Nearly Three Solar Cycles (1972–2000),” J. Geophys. Res., Vol. 107, p. 1187, do�:10.1029/2001JA000504, 2002.

21. Tsurutan�, B.T.; Gonzalez, W.D.; Gonzalez, A.L.C.; et al.: “Corotat�ng Solar W�nd Streams, and Recurrent Geomagnet�c Act�v�ty: A Rev�ew,” J. Geophys. Res., Vol. 111, p. A07501, do�:10.1029/2005JA011273, 2006.

12

REPORT DOCUMENTATION PAGE Form Approved

OMB No. 0704-0188

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintain-ing the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operation and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503

1. AGENCY USE ONLY (Leave Blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED

4. TITLE AND SUBTITLE 5. FUNDING NUMBERS

6. AUTHORS

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION REPORT NUMBER

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSORING/MONITORING AGENCY REPORT NUMBER

11. SUPPLEMENTARY NOTES

12a. DISTRIBUTION/AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 words)

14. SUBJECT TERMS 15. NUMBER OF PAGES

16. PRICE CODE

17. SECURITY CLASSIFICATION OF REPORT

18. SECURITY CLASSIFICATION OF THIS PAGE

19. SECURITY CLASSIFICATION OF ABSTRACT

20. LIMITATION OF ABSTRACT

NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89)Prescribed by ANSI Std. 239-18298-102

Unclassified Unclassified Unclassified Unl�m�ted

Robert M. W�lson and Dav�d H. Hathaway

George C. Marshall Space Fl�ght CenterMarshall Space Fl�ght Center, AL 35812

Nat�onal Aeronaut�cs and Space Adm�n�strat�onWash�ngton, DC 20546–0001

PreparedfortheScienceandExplorationVehicleOffice,ScienceandMissionSystemsOffice

Unclassified-UnlimitedSubject Category 92Ava�lab�l�ty: NASA CASI 301–621–0390

The aa �ndex can be decomposed �nto two separate components: the lead�ng sporad�c component due to solar act�v�ty as measured by sunspot number and the res�dual or recurrent component due to �nterplanetary d�sturbances, such as coronal holes. For the �nterval 1964–2006, a h�ghly stat�st�cally �mportant correlat�on (r = 0.749) �s found between annual averages of the aa �ndex and the solar w�nd speed (espec�ally between the res�dual component of aa and the solar w�nd speed, r = 0.865). Because cycl�c averages of aa (and the res�dual component) have trended upward dur�ng cycles 11–23, cycl�c averages of solar w�nd speed are �nferred to have also trended upward.

20

M–1222

Techn�cal Publ�cat�onFebruary 2008

NASA/TP—2008–215249

Sun, sunspot/geomagnet�c cycle, solar w�nd speed

On the Relationship Between Solar Wind Speed, Geomagnetic Activity, and the Solar Cycle Using Annual Values

The NASA STI Program…in Profile

Since its founding, NASA has been dedicated to the advancement of aeronautics and space science. The NASA Scientific and Technical Information (STI) Program Office plays a key part in helping NASA maintain this important role.

The NASA STI program operates under the auspices of the Agency Chief Information Officer. It collects, organizes, provides for archiving, and disseminates NASA’s STI. The NASA STI program provides access to the NASA Aeronautics and Space Database and its public interface, the NASA Technical Report Server, thus providing one of the largest collections of aeronautical and space science STI in the world. Results are published in both non-NASA channels and by NASA in the NASA STI Report Series, which includes the following report types:

• TECHNICAL PUBLICATION. Reports of completed research or a major significant phase of research that present the results of NASA programs and include extensive data or theoretical analysis. Includes compilations of significant scientific and technical data and information deemed to be of continuing reference value. NASA’s counterpart of peer-reviewed formal professional papers but has less stringent limitations on manuscript length and extent of graphic presentations.

• TECHNICAL MEMORANDUM. Scientific and technical findings that are preliminary or of specialized interest, e.g., quick release reports, working papers, and bibliographies that contain minimal annotation. Does not contain extensive analysis.

• CONTRACTOR REPORT. Scientific and technical findings by NASA-sponsored contractors and grantees.

• CONFERENCE PUBLICATION. Collected papers from scientific and technical conferences, symposia, seminars, or other meetings sponsored or cosponsored by NASA.

• SPECIAL PUBLICATION. Scientific, technical, or historical information from NASA programs, projects, and missions, often concerned with subjects having substantial public interest.

• TECHNICAL TRANSLATION. English-language translations of foreign scientific and technical material pertinent to NASA’s mission.

Specialized services also include creating custom thesauri, building customized databases, and organizing and publishing research results.

For more information about the NASA STI program, see the following:

• Access the NASA STI program home page at <http://www.sti.nasa.gov>

• E-mail your question via the Internet to <help@sti.nasa.gov>

• Fax your question to the NASA STI Help Desk at 301– 621–0134

• Phone the NASA STI Help Desk at 301– 621–0390

• Write to: NASA STI Help Desk NASA Center for AeroSpace Information 7115 Standard Drive Hanover, MD 21076–1320

National Aeronautics andSpace AdministrationIS20George C. Marshall Space Flight CenterMarshall Space Flight Center, Alabama35812

NASA/TP—2008–215249

On the Relationship Between Solar Wind Speed, Geomagnetic Activity, and the Solar Cycle Using Annual ValuesRobert M. Wilson and David H. HathawayMarshall Space Flight Center, Marshall Space Flight Center, Alabama

February 2008