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Neutral Density During the Recent Solar
Minimum
Contributions from
Solar, Geomagnetic Activity, and Anthropogenic
Rodney Viereck
NOAA Space Weather Prediction Center
Drag Data provided by John Emmert
NRL
MURI Workshop, Boulder
October 2010
400 km Neutral Density Derived from Satellite Drag
(thanks to John Emmert, NRL)
-13
1.5x10
Density (4 day running avg.)
Density (365 day running avg.)
3
Density (gm/cm )
-13
1.0x10
-14
5.0x10
0.0
1970
1975
1980
1985
1990
Year
1995
2000
2005
2010
Drag Density at Solar Minima
(log plot)
Density (4 day running avg.)
Density (365 day running avg.)
-13
3
Density (gm/cm )
10
-14
10
9.397x10
-15
8.49x10
7.44x10
-15
-15
4.578x10
-15
-15
10
1970
1975
1980
1985
1990
Year
1995
2000
2005
2010
Thermospheric Drivers
60
220
200
50
180
160
40
140
120
30
100
20
60
Ap
F10
80
40
10
20
0
F10
Ap
CO2
-20
-40
-60
0
-10
-80
-100
-20
1970
1975
1980
1985
1990
1995
2000
2005
700
680
660
640
620
600
580
560
540
520
500
480
460
440
420
400
380
360
340
320
300
CO2 (ppmv)
Solar EUV (F10), Geomagnetic Storms (Ap), Climate Change(CO2)
2010
Year
October 2010
Viereck: MURI 2010
4
Drag Density vs MSIS Density
(again thanks to John Emmert)
MSIS only has Solar (F10) and Geomagnetic (Ap) inputs (no climate change)
Drag Density (365 day running avg.)
MSIS Density (365 day running avg.)
-13
3
Density (gm/cm )
10
-14
10
9.397x10
-15
-0.44x10
-15
-0.96x10
-15
-1.27x10
-15
Delta: Difference between MSIS and Observed Neutral Density
-15
10
1970
1975
1980
1985
1990
Year
1995
2000
2005
2010
Estimating the Anthropogenic Contribution
3.00E-015
2.80E-015
2.60E-015
2.40E-015
2.20E-015
2.00E-015
1.60E-015
1.40E-015
1.20E-015
Correction
Polynomial Fit
2.00E-015
1.00E-015
1.80E-015
8.00E-016
6.00E-016
4.00E-016
330 335 340 345 350 355 360 365 370 375 380 385 390 395 400
Mauna Loa CO2 Density
Density offset (delta) vs CO2 data. (fitting a line to only the
first three minima)
Density Correction for CO2
Delta
1.80E-015
1.60E-015
1.40E-015
1.20E-015
1.00E-015
8.00E-016
6.00E-016
4.00E-016
1975
1980
1985
1990
1995
2000
2005
2010
Date
Extrapolating the correction to the full extent if the time series
Note: This is about twice the rate of Roble’s estimate
Subtracting the Anthropogenic Correction
3
Densit (gm/cm )
1E-13
Drag
MSIS
MSIS-CO2
1E-14
1970
1975
1980
1985
1990
Year
1995
2000
2005
2010
Detailed Plot of the Observations vs MSIS
(With and without the CO2 correction)
2E-14
1.8E-14
1.6E-14
1.4E-14
3
Densit (gm/cm )
1.2E-14
1E-14
Minimum
Values
8E-15
7.11E-15
6E-15
4E-15
1970
Note the excellent fit during
the first three minima
Drag
MSIS
MSIS-CO2
1975
1980
5.20E-15
4.57E-15
Note the improved fit
during the last minimum
1985
1990
Year
1995
2000
2005
2010
Solar Irradiance
Observations vs Proxies
Mg II index solar min to
min variation is about right
(7% of max-min)
0.290
SEM 304
SEM 304 (365 Day Running Avg.)
F10 solar min to min
variation is too small
(2.3% of max-min)
300
Daily F10
F10 (365 Day Running Avg)
250
SEM 304 (Photons/cm2/sec)
3.50E+010
3.00E+010
0.280
0.275
0.270
2.50E+010
0.265
0.2632
1996
1.50E+010
1.17E10
9.42E9
F10
5.00E+009
1996
150
1998
2000
2002
2004
Year
100
71
68
50
2000
2002
2004
Year
2006
2008
1998
2000
2002
2004
Year
1.00E+010
1998
0.2644
2.00E+010
200
1996
Daily MgII Index
Mg II (365 Day Running Avg)
0.285
Mg II Index (Ratio)
SEM 304 solar min to
min variation is too large
(14% of max-min)
2010
2006
2008
2010
2006
2008
2010
Solar Data and Proxies Scaled to F10
F10
Mgfit
SEMfit
220
200
180
F10
160
140
120
100
80
60
Fitting SEM 304 and Mg II to
F10 at the last minimum
40
1970
1975
1980
1985
1990
Year
1995
2000
2005
2010
MSIS Results Using the Three Solar Inputs
(Corrected for CO2)
Neutral Density
1E-13
1E-14
Drag
MSIS With Mg II - CO2
MSIS With SEM - CO2
MSIS With F10 - CO2
1970
1975
1980
1985
1990
Year
1995
2000
2005
2010
MSIS Results Using the Three Solar Inputs
(Details)
2E-14
1.8E-14
1.6E-14
1.4E-14
Neutral Density
1.2E-14
1E-14
8E-15
6E-15
Mg II Index provides the best fit
to the observed density
4E-15
1970
Drag
MSIS With Mg II - CO2
MSIS With SEM - CO2
MSIS With F10 - CO2
1975
1980
1985
1990
Year
1995
2000
2005
2010
Relative Magnitude of the Density Changes
Modeled density changes for each input while holding the other two constant
3
Density (gm/cm )
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%
1E-14
1970
1975
1980
1985
1990
1995
2000
2005
2010
Year
March 2008
Viereck: SDO and Space Weather
13
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