NADIR – MURI – Oct 2008 1

NADIR – MURI – Oct 2008 2

The ESA Study aims to address all issues regarding derivation of absolute Air Density from Precision Satellite Accelerometers:-

Preparation for the ESA Swarm Mission:

Three Spacecraft with coordinated orbits;

Each Spacecraft carries a precision accelerometer (etc).

ISSUES:

• Drag Coefficient: function of shape, orbit, atmospheric temp / composition?

• Exact Spacecraft Area and Mass?

• Correction for the in-track thermospheric wind component

• Unknown effects / influences due to attitude control systems etc

NADIR – MURI – Oct 2008 3

NADIR – MURI – Oct 2008 4

NADIR – MURI – Oct 2008 5

NADIR – MURI – Oct 2008 6

CHAMP

NADIR – MURI – Oct 2008 7

CHAMP Geometry

CHAMP area from X-direction (front)

CH-ITDID-0001 0.7425 m2

Reference GFZ Panels 0.4701 m2 -37%

Bruinsma & Biancale Panels 0.6366 m2 -14%

ANGARA 0.7944 m2 +7%

These differences are very important for absolute density!!

CHAMP

NADIR – MURI – Oct 2008 8

NADIR – MURI – Oct 2008 9

NADIR – MURI – Oct 2008 10

NADIR – MURI – Oct 2008 11

NADIR – MURI – Oct 2008 12

NADIR – MURI – Oct 2008 13

CHAMP - Bias

NADIR – MURI – Oct 2008 14

GRACE

NADIR – MURI – Oct 2008 15

GRACE

NADIR – MURI – Oct 2008 16

GRACE

NADIR – MURI – Oct 2008 17

Cross-Wind Corrections

NADIR – MURI – Oct 2008 18

NADIR – MURI – Oct 2008 19

CHAMP

NADIR – MURI – Oct 2008 20

CHAMP

NADIR – MURI – Oct 2008 21

GRACE

NADIR – MURI – Oct 2008 22

NADIR – MURI – Oct 2008 23

CHAMP vs CTIP - Density

NADIR – MURI – Oct 2008 24

CHAMP vs CTIP – Zonal Wind

NADIR – MURI – Oct 2008 25

CHAMP vs CTIP - Temperature

NADIR – MURI – Oct 2008 26

Wind Issues – I – Magneto-torquer Effect

NADIR – MURI – Oct 2008 27

Wind Issues – I – Magneto-torquer Effect

NADIR – MURI – Oct 2008 28

Physical Drag Coefficients for four compact shapes at Solar Minimum

Note: Cd for CHAMP, GRACE and Swarm are all “way off the right side”

Summary Taken From Moe and Moe, 2008 (COSPAR)

Density Issues – I – Coefficient of Drag

NADIR – MURI – Oct 2008 29

Summary Taken From Moe and Moe, 2008 (COSPAR)

Percentage by which the Jacchia Model (J70 etc) Densities are too High

Altitude Solar Minimum (km) Solar Maximum (km)

150 4

200 7 6

250 10 8

300 13 9

350 10

400 12

500 12

Density Issues – I – Coefficient of Drag

NADIR – MURI – Oct 2008 30

Summary[13] Densities at about 400 km altitude derived from satellite orbital decay using the high-accuracy Special Perturbations technique indicate an unmodeled long-term decrease of 1.7% per decade over the period 1970–2000.

Based on the linear extrapolation assumptions, our results agree with findings of theoretical simulations by Roble and Dickinson [1989], Rishbeth and Roble [1992], and Akmaev [2003] to within +0.3% to 0.8% per decade.

Our results indicate that the overall cooling from 1970 through 2000 is about 3.2% per decade less than that derived by Keating for three solar minimum conditions alone and 1.1% per decade less than that of Emmert et al. [2004] over a period similar to ours.

Detection of a long-term decrease in thermospheric neutral density:Frank A. Marcos, John O. Wise, Michael J. Kendra, Neil J. Grossbard, and Bruce R. Bowman.

Density Issues – II – Decadal Changes

NADIR – MURI – Oct 2008 31

IMF dependence of high latitude thermospheric wind pattern derived from CHAMP cross-track accelerometer data and the corresponding magnetospheric convection from Cluster EDI (COSPAR 2008 – C13 July 2008)

Matthias Förster 1 , Stein E. Haaland 2,3 , Stefanie Rentz 1 , and Huixin Liu 41 Helmholtz Zentrum Potsdam, Deutsches GeoForschungsZentrum (GFZ), Germany, mfo@gfzpotsdam.de2 Max Planck Institute for Extraterrestrial Physics, Garching, Germany and at: 3. Department of Physics, University of Bergen, Norway, 4 Hokkaido University, Div. of Earth and Planet. Science, Sapporo, Japan

Abstract:

Neutral thermospheric wind pattern at high latitudes obtained from crosstrack acceleration measurements of the CHAMP satellite above both North and South polar regions are statistically analyzed in their dependence on the Interplanetary Magnetic Field (IMF) direction in the GSM yz plane (clock angle). We compare this dependency with magnetospheric convection pattern using 1minaverages of Cluster/EDI electric drift observations and the same IMF and solar wind sorting conditions. The spatially distributed Cluster/EDI measurements are mapped to a the common reference level at ionospheric F-region heights in a magnetic latitude/MLT grid. We obtained both regular thermospheric wind and plasma drift pattern according to the various IMF conditions. The IMFdependency shows some similarity with the corresponding high latitude plasma convection insofar that the largerscale convection cells, in particular the roundshaped dusk cell for IMF By+ (By) conditions at the Northern (Southern) Hemisphere, leave their marks on the dominant general transpolar wind circulation from the dayside to the nightside. The direction of the transpolar circulation is generally deflected toward a duskward flow, in particular in the evening to nighttime sector. The degree of deflection correlates with the IMF clock angle. It is larger for IMF By+ than for By and is systematically larger (about 5 deg) and appear less structured at the Southern Hemisphere compared with the Northern. Thermospheric cross-polar wind amplitudes are largest for IMF Bz/By conditions (corresponding to sector 5) at the Northern Hemisphere, but for IMF Bz/ By+ conditions (sector 3) at the Southern because the magnetospheric convection is in favour of largest wind accelerations over the polar cap under these conditions. The overall variance of the thermospheric wind magnitude at Southern high latitudes is larger than for the Northern. This is probably due to a larger “stirring effect” at the Southern Hemisphere because of the larger distance between the geographic and geomagnetic frameworks.

CHAMP

NADIR – MURI – Oct 2008 32

CHAMP Winds – North Polar Region

NADIR – MURI – Oct 2008 33

CHAMP Winds – Hemispheric Comparison

NADIR – MURI – Oct 2008 34

CHAMP Winds – North Polar Region

NADIR – MURI – Oct 2008 35

CHAMP Winds – North Polar Region

NADIR – MURI – Oct 2008 36

Conclusions

Large scale clockwise circulation vortices at the dusk side are dominant features forIMF By+ conditions in the Northern, and By- in the Southern Hemisphere.

The dawn cell is not favoured for thermospheric wind response of plasma circulationdue to counteracting Coriolis and centrifugal forces.

Largest magnitudes of crosspolar upper thermospheric winds occur for IMF Bz/By (sector 5) at the Northern, and Bz/By+ (sector 3) at Southern Hemisphere.

Larger standard deviations of the wind amplitudes at the Southern Hemisphere incomparison with the Northern (“stirring effect”).

The “pressure valve” effect for the neutral wind is manifested also in smaller angularvariations of wind vector directions under these asymmetric conditions.

CHAMP – Winds - Summary

NADIR – MURI – Oct 2008 37

There will be a Swarm Science Meeting at:

DFG-Potsdam (near Berlin, Germany):

Most probably from 24-26 June 2009.

It is also planned to hold a ½ day Meeting of the

CIRA Working Group in conjunction with this Meeting

Please notify me if interested in attending the Meeting.

INIVITATION – CIRA W.G. Meeting

NADIR – MURI – Oct 2008 38

COSPAR 2008 Montréal, July 2008References:Haaland, S. E.; Paschmann, G.; Förster, M.; Quinn, J. M.; Torbert, R. B.; McIlwain, C. E.; Vaith, H.; PuhlQuinn, P. A.; Kletzing, C. A. (2007):High latitude plasma convection from Cluster EDI measurements: method and IMF dependence,Annales Geophysicae, 25, 239253.Förster, M.; Paschmann, G.; Haaland, S. E.; Quinn, J. M.; Torbert, R. B.; Vaith, H.; Kletzing, C. A. (2007): High latitude plasma convection from Cluster EDI: variances and solar wind correlations, Annales Geophysicae, 25, 7, 16911707.Förster, M.; Rentz, S.; Köhler, W.; Liu, H.; Haaland, S. E. (2008): IMF dependence of high latitude thermospheric wind pattern derived from CHAMP cross track measurements, Annales Geophysicae, 26, 6, 15811595.

CHAMP