The Impact of Composition on the Thermosphere Mass Density during Geomagnetic Activity

Jeffrey P. Thayer, Xianjing Lui, Jiuhou Lei, Marcin Pilinski and Alan Burns

Thanks to Eric Sutton for the analyzed CHAMP and GRACE data

Thayer, J. P., X. Liu, J. Lei, M. Pilinski, and A. G. Burns (2012), The impact of helium on thermosphere mass density response to geomagnetic activity during the recent solar minimum, J. Geophys. Res., 117, A07315, doi:10.1029/2012JA017832.

MURI NADIR Meeting 25–26 September 2012

NADIR 2

Mass Density Response with Altitude to Geomagnetic Activity

Quiet

A

Active

B C

P2

P1

Satellite altitudeAlti

tude

h

D

1 1( ), ( )T t m t0 0( ), ( )T t m t

ah

qh

lnB

A

zB

A z

z dz

z H

; ;P TM

M P TH H H

dM dz d dz dT dz

1 1 1B

A

z

p Tz M

dzH H H

ln lnln

B

A

zB

A z

z Mg d M d Tdz

z RT dz dz

Hd dz

Density Scale Height

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Occasions of Common Local Time Passes of CHAMP and GRACE Satellites

Bruinsma, S. L., and J. M. Forbes (2010), Anomalous behavior of the thermosphere during solar minimum observed by CHAMP and GRACE, J. Geophys. Res., 115, A11323, doi:10.1029/2010JA015605.

NADIR 4

CHAMP to GRACE Ratio: February 2007

1 1 1 1 ln lnln C

G C G p TM

z Mg d M d T

z z z H H H RT dz dz

Feb 20071 29

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Latitude-time plot of the natural logarithm of the MSIS mass density ratio normalized by the altitude difference for CHAMP and GRACE satellites over a 29 day period starting from February 1, 2007.

MSIS C/G Ratio Feb 2007

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C/G Ratio Comparison of MSIS to ObservationsFeb 2007

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Summer / Winter CHAMP to GRACE Ratio: February 2007

Observations

MSIS

Feb 20071 29

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MSIS C/G Ratio Behavior with Geomagnetic Activity: Feb 2007

Summer:• C/G ratio driven by pressure

scale height whose response to geomagnetic activity is related to temperature changes

Winter:• Pressure scale height is

invariant with geomagnetic activity as temperature increases are offset by increase in molecular weight.

• Molecular weight scale height is responsible for the wintertime C/G exceeding summer and for the wintertime response to geomagnetic activity.

1 1 1ln C

G C G p M

z

z z z H H

Geomag activity

NADIR 9

C/G Ratio: December 2008

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C/G Ratio Comparison of MSIS to ObservationsDec 2008

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Summer / WinterCHAMP to GRACERatio: Dec. 2008

Observations

MSIS

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Adjusted MSIS by reducing F10.7 and increasing Helium concentration by 30% above 50N

CHAMP and GRACE mass density estimates (red line) versus geographic latitude averaged over December 9-10, 2008. Adjusted MSIS mass density estimates after reducing F10.7 index by 14 sfu and increasing ap by 2 (black line), further adjustment by increasing helium by 30% above 50 °N (black dashed line), and excluding helium in the estimate of MSIS mass density after F10.7 and ap adjustment (black dash-dot line). Error bars on GRACE density represent the statistical error of the mean after two-day averaging.

NADIR 13

Summer / WinterCHAMP to GRACERatio: Dec. 2008

Observations

Adjusted MSIS

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MSIS C/G Ratio Behavior with Geomagnetic Activity: Dec. 2008

Summer:• C/G ratio driven by pressure

scale height whose response to geomagnetic activity is related to temperature and molecular weight changes

Winter:• Pressure scale height change is

now dominated by the molecular weight change being greater than the temperature change with geomagnetic activity.

• Molecular weight scale decreases with geomagnetic activity – opposite to the pressure scale height effect.

1 1 1ln C

G C G p M

z

z z z H H

Geomag activity

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Oxygen – Helium Transition Dynamics Impacts the Mass Density with Height

Mean Molecular WeightScale Height

Mean Molecular Weight

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MSIS Molecular Weight Scale Height

Composition Effects on Thermosphere Mass Density During Geomagnetic Activity

The February 2007 data represented typical solar minimum

conditions while the December 2008 data represented extreme

solar minimum conditions. The CHAMP-to-GRACE mass density ratio for both solstice periods

indicates the dynamics of the oxygen – helium transition region is

playing a role in describing the mass density ratio structure and

response to geomagnetic activity in the winter hemisphere. The description of the C/G mass density ratio in terms of the sum of

the reciprocal pressure scale height and the reciprocal molecular

weight scale height, or equivalently proportional to the ratio in mean

molecular weight to temperature plus the vertical gradient of the

logarithmic mean molecular weight, provided insight to the observed

behavior

Cont’d

Significant concentrations of helium exist at GRACE altitudes (472

km) during quiet geomagnetic activity in the winter hemisphere at

solstice in 2008, i.e., the wintertime helium bulge The dynamics of the oxygen-helium transition height will prove very

important in evaluating the latitudinal thermosphere mass density

response at GRACE altitudes as it resides above the satellite in the

summer polar regions (750 km in December 2008) and below the

satellite in the winter hemisphere (400 km in December 2008)

Need information of composition with height to adequately describe the thermosphere density response to geomagnetic activity

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Helium – Oxygen Ratio at GRACE Altitudes

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CDxA as a Function of He/O Ratio

GRACE panel model CDxA as a function of He/O ratio at two values of atmospheric temperature and angle of attack.

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Figure A2. MSIS outputs for December 9th 2008, sampled along the GRACE orbit.

Altitude Response in Thermosphere Mass Density to Geomagnetic Activity Depends on Composition

0 0

0

0

0

11 1 1

; ;

1 1 1 1 11 1 1

1 1 1ln

ln lnln

p

TM

pp TM

TM

z z

p Tz z M

z

z

PH

dM d dTdP dzM dz dz T dz

M TH H H

dM dz d dz dT dz

HH H H H

H H H

z dzdz

z H H H H

z Mg d M d Tdz

z RT dz dz

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Figure 9. The adjusted MSIS oxygen-helium transition altitude for the month of December, 2008.