Neutral Density During the Recent Solar Minimum

Contributions from Solar, Geomagnetic Activity, and Anthropogenic

Rodney ViereckNOAA Space Weather Prediction Center

Drag Data provided by John EmmertNRL

MURI Workshop, BoulderOctober 2010

400 km Neutral Density Derived from Satellite Drag(thanks to John Emmert, NRL)

1970 1975 1980 1985 1990 1995 2000 2005 2010

0.0

5.0x10-14

1.0x10-13

1.5x10-13

D

ensi

ty (g

m/c

m3 )

Year

Density (4 day running avg.) Density (365 day running avg.)

Drag Density at Solar Minima(log plot)

1970 1975 1980 1985 1990 1995 2000 2005 201010-15

10-14

10-13

7.44x10-158.49x10-15

4.578x10-15

D

ensi

ty (g

m/c

m3 )

Year

Density (4 day running avg.) Density (365 day running avg.)

9.397x10-15

Thermospheric DriversSolar EUV (F10), Geomagnetic Storms (Ap), Climate Change(CO2)

October 2010 Viereck: MURI 2010 4

1970 1975 1980 1985 1990 1995 2000 2005 2010-100-80-60-40-20

020406080

100120140160180200220

F1

0

Year

F10

-20

-10

0

10

20

30

40

50

60

Ap

Ap

300320340360380400420440460480500520540560580600620640660680700

CO2

CO

2 (ppm

v)

Drag Density vs MSIS Density(again thanks to John Emmert)

1970 1975 1980 1985 1990 1995 2000 2005 201010-15

10-14

10-13

-0.96x10-15-0.44x10-15 -1.27x10-15

D

ensi

ty (g

m/c

m3 )

Year

Drag Density (365 day running avg.) MSIS Density (365 day running avg.)

9.397x10-15

Delta: Difference between MSIS and Observed Neutral Density

MSIS only has Solar (F10) and Geomagnetic (Ap) inputs (no climate change)

Estimating the Anthropogenic Contribution

1975 1980 1985 1990 1995 2000 2005 2010

4.00E-016

6.00E-016

8.00E-016

1.00E-015

1.20E-015

1.40E-015

1.60E-015

1.80E-015

2.00E-015 Correction Polynomial Fit

Den

sity

Cor

rect

ion

for C

O2

Date

330 335 340 345 350 355 360 365 370 375 380 385 390 395 400

4.00E-016

6.00E-016

8.00E-016

1.00E-015

1.20E-015

1.40E-015

1.60E-015

1.80E-015

2.00E-015

2.20E-015

2.40E-015

2.60E-015

2.80E-015

3.00E-015

Del

ta

Mauna Loa CO2 Density

Density offset (delta) vs CO2 data. (fitting a line to only the first three minima)

Extrapolating the correction to the full extent if the time seriesNote: This is about twice the rate of Roble’s estimate

Subtracting the Anthropogenic Correction

1970 1975 1980 1985 1990 1995 2000 2005 2010

1E-14

1E-13

D

ensi

t (gm

/cm

3 )

Year

Drag MSIS MSIS-CO2

Detailed Plot of the Observations vs MSIS(With and without the CO2 correction)

1970 1975 1980 1985 1990 1995 2000 2005 2010

4E-15

6E-15

8E-15

1E-14

1.2E-14

1.4E-14

1.6E-141.8E-14

2E-14

4.57E-15

5.20E-15

D

ensi

t (gm

/cm

3 )

Year

Drag MSIS MSIS-CO2

7.11E-15

Note the excellent fit during the first three minima

Note the improved fit during the last minimum

Minimum Values

Solar IrradianceObservations vs Proxies

1996 1998 2000 2002 2004 2006 2008 2010

0.265

0.270

0.275

0.280

0.285

0.290

Daily MgII Index Mg II (365 Day Running Avg)

0.2632

Mg

II In

dex

(Rat

io)

Year

0.2644

F10 solar min to min variation is too small (2.3% of max-min)

1996 1998 2000 2002 2004 2006 2008 201050

100

150

200

250

300 Daily F10 F10 (365 Day Running Avg)

68

F10

Year

71

SEM 304 solar min to min variation is too large (14% of max-min)

1996 1998 2000 2002 2004 2006 2008 20105.00E+009

1.00E+010

1.50E+010

2.00E+010

2.50E+010

3.00E+010

3.50E+010

1.17E10

SEM 304 SEM 304 (365 Day Running Avg.)

SE

M 3

04 (P

hoto

ns/c

m2/

sec)

Year

9.42E9

Mg II index solar min to min variation is about right (7% of max-min)

Solar Data and Proxies Scaled to F10

1970 1975 1980 1985 1990 1995 2000 2005 201040

60

80

100

120

140

160

180

200

220

F1

0

Year

F10 Mgfit SEMfit

Fitting SEM 304 and Mg II to F10 at the last minimum

MSIS Results Using the Three Solar Inputs(Corrected for CO2)

1970 1975 1980 1985 1990 1995 2000 2005 2010

1E-14

1E-13

N

eutra

l Den

sity

Year

Drag MSIS With Mg II - CO2 MSIS With SEM - CO2 MSIS With F10 - CO2

MSIS Results Using the Three Solar Inputs(Details)

Mg II Index provides the best fit to the observed density

1970 1975 1980 1985 1990 1995 2000 2005 2010

4E-15

6E-15

8E-15

1E-14

1.2E-14

1.4E-14

1.6E-141.8E-14

2E-14

N

eutra

l Den

sity

Year

Drag MSIS With Mg II - CO2 MSIS With SEM - CO2 MSIS With F10 - CO2

Relative Magnitude of the Density ChangesModeled density changes for each input while holding the other two constant

March 2008 Viereck: SDO and Space Weather 13

1970 1975 1980 1985 1990 1995 2000 2005 2010

1E-14

Den

sity

(gm

/cm

3 )

Year

CO2 Solar Geomag

Relative Contributions of the change from(1996 to 2009)Solar 1.49E-15 = 48%Geomag 1.03E-15 = 33%Anthro 0.61E-15 = 19%

Conclusions

• Neutral density at 400 km shows a decrease during the last solar minimum– Significantly lower than previous three minima

• Both F10 and Ap are also significantly lower during this most recent solar minimum.– Still can’t account for the observed decrease (using MSIS).

• Adjusting for Anthropogenic (CO2) forcing and climate change accounts for some of the remaining difference– Still some density drop that cannot be accounted for• Using the SOHO SEM 304 data instead of F10 provides too

much of a decrease in the neutral density• Using the Mg II Index instead of F10 provides a more accurate

estimate of the density during this last solar minimum.– Solar 1.49E-15 = 48%– Geomag 1.03E-15 = 33%– Anthro 0.61E-15 = 19%

March 2008 Viereck: SDO and Space Weather 14