Altitude Response of Thermosphere Mass Density to Geomagnetic Activity in the Recent Solar Minimum Jeffrey P. Thayer, Xianjing Lui, and Jiuhou Lei MURI NADIR Meeting 25–26 October 2011

A Compressed Thermosphere Leads to a Greater % Change in Density Response Given the Same Energy Input – Preconditioning by EUV Flux Relative changes in thermosphere density response to geomagnetic forcing is stronger under low EUV conditions Absolute Density at 400 km Relative Perturbations Quiet A Active B C P 2 P 1 Satellite altitude Altitude h

In 2008, the Solar EUV Flux was at an Extreme Minimum with Little Change over the Year While 38 CIRS were Catalogued!! Density - 400km altitude Solar wind density IMF Bx Geomagnetic Activity Index Solar wind speed IMF Bz IMF |B|

Classical CIR The interplanetary conditions for different types of geomagnetic activity are indicated by numbers: (1) geomagnetic quiet, (2) a storm initial phase, (3) a magnetic storm main phase, and (4) the storm extended ‘‘recovery’’ phase. Tsurutani, B. T., et al. (2006), Corotating solar wind streams and recurrent geomagnetic activity: A review, J. Geophys. Res., 111, A07S01, doi: /2005JA Superposed Epoch Analysis of 29 CIR/HSS in 2008

Thermospheric response to CIRs globally Calm Lei, J., J. P. Thayer, W. Wang, and R. L. McPherron (2011), Impact of CIR storms on thermosphere density variability during the solar minimum of 2008, Sol. Phys., doi: /s y. Superposed-Epoch Analysis of CHAMP Thermosphere Density in 2008

Altitude Response of Mass Density using CHAMP and GRACE Measurements CHAMP Satellite – GFZ Potsdam Inclination 87.3  LifetimeJuly, 2000-September 2010 Nominal Orbit Altitude~400 km GRACE Satellite – NASA / DLR Inclination 88.9  LifetimeMarch 2002-present Nominal Orbit Altitude~500 km

NADIR 7 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: /2010JA

A0A0 QuietActive CHAMP altitude Altitude h A1A1 Altitude Response in Thermosphere Mass Density to Geomagnetic Activity GRACE altitude B0B0 B1B1

NADIR 9 Geomagnetic Activity Dec 2008 During a CHAMP and GRACE Common Local Time Orbits Quiet Time: December 9-11, 2008 = 67 = 15 Active Time: December 5 – 7, 2008 = 68 = 2

NADIR 10 Thermosphere Mass Density Ratio (Active/Quiet) for Dec 2008 HSS Event: Thermosphere Composition Effect GRACE Normalized to 476 km CHAMP Normalized to 332 km MSIS Density Ratio

MSIS VS. CHAMP and GRACE Observations December 2008 Active time densityQuiet time density

NADIR 12 Mg II Correction to F10.7 Index at Solar Minimum Solomon, S. C., L. Qian, L. V. Didkovsky, R. A. Viereck, and T. N. Woods (2011), Causes of low thermospheric density during the 2007–2009 solar minimum, J. Geophys. Res., 116, A00H07, doi: /2011JA

CHAMP and GRACE Densities with Adjusted F10.7 based on Mg II During the Active Period of the Geomagnetic Storm During the active time, a good MSIS representation is achieved by lowering f10.7 by 11. Before After

Original Values GRACE Densities with MSIS adjusted for F10.7, Ap, and Helium Density Adjust F Adjust F10.7 – 14, Ap+2 Adjust F10.7 – 14, Ap+2, 30% increase in Helium

CHAMP Densities with MSIS adjusted input values of F10.7, Ap, and Helium same as for GRACE Original Values Adjust F Adjust F10.7 – 14, Ap+2 Adjust F10.7 – 14, Ap+2, 30% increase in Helium

Quiet Time Mass Density at GRACE Altitudes is Significantly Impacted by the Presence of Helium

NADIR 17 Mass Density Response as a Function of Altitude in Winter High latitudes is significantly lessened at GRACE Altitudes by Helium

NADIR 18 Latitude Dependence in Altitude Response to December 2008 Geomagnetic Activity

Thermosphere Mass Density During CIR/HSS Events Recurrent geomagnetic activity enabled isolation of CIR/HSS processes on the preconditioned solar minimum state of the thermosphere. Response at CHAMP Altitudes:  The recurrent geomagnetic activity and constant EUV flux in 2008 enabled a superposed epoch analysis that demonstrated the typical global thermosphere response at 400 km to CIR/HSS events was on average a 75% increase with recovery taking a week or more. Integrated effect rivals CMEs but also demonstrated significant variability

Cont’d Response at GRACE Altitudes:  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 mass density response to geomagnetic activity in the contracted winter hemisphere is lessened by the presence of helium leading to strongly varying mass density response with altitude.  F10.7 input to MSIS during December 2008 required a downward adjustment (concomitant with Mg II index) to adequately represent mass density observations and subsequently the modeled drag coefficient requires reevaluation to account for the significant presence of helium. Need information of composition to adequately describe the thermosphere density response to geomagnetic activity