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
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 T
z 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 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
z
z z z H H
Geomag activity
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 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
z
z 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
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 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.
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