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 dzz H

; ;P TM

M P TH H HdM dz d dz dT dz

1 1 1B

A

z

p Tz M

dzH H H

ln lnlnB

A

zB

A z

z Mg d M d T dzz RT dz dz

Hd dz

Density Scale Height

NADIR 3

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 Tz z z H H H RT dz dz

Feb 20071 29

NADIR 5

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

NADIR 6

C/G Ratio Comparison of MSIS to ObservationsFeb 2007

NADIR 7

Summer / Winter CHAMP to GRACE Ratio: February 2007

Observations

MSIS

Feb 20071 29

NADIR 8

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

zz z z H H

Geomag activity

NADIR 9

C/G Ratio: December 2008

NADIR 10

C/G Ratio Comparison of MSIS to ObservationsDec 2008

NADIR 11

Summer / WinterCHAMP to GRACERatio: Dec. 2008

Observations

MSIS

NADIR 12

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

NADIR 14

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

zz z z H H

Geomag activity

NADIR 15

Oxygen – Helium Transition Dynamics Impacts the Mass Density with Height

Mean Molecular WeightScale Height

Mean Molecular Weight

NADIR 16

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

NADIR 19

Helium – Oxygen Ratio at GRACE Altitudes

NADIR 20

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.

NADIR 21

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

PHdM d dTdP dz

M dz dz T dzM TH H H

dM dz d dz dT dz

HH H H H

H H H

z dz dzz H H H H

z Mg d M d T dzz RT dz dz

NADIR 23

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