Seasonal and longitudinal variations of the solar quiet (Sq) current system during solar minimum determined by CHAMP satellite magnetic field observations

Abstract. Ground-based ionosonde and magnetic-field observations on the equatorial station Huancayo, ESRO4 neutral-composition measurements, and theoretical model calculations were used to analyze disturbed E×B vertical plasma drift during the phase of solar minimum in 1973. Vertical drifts calculated for disturbed days do not show the systematic decrease often mentioned in publications, and demonstrate strong dependence on IMF-Bz changes. It is confirmed with the help of our drift calculations that Bz turnings to a northward direction result in a decrease (up to reversal) of normal Sq (eastward during daytime and westward at nighttime) in the zonal component of electric field. Southward Bz excursions enhance normal Ey both in daytime and nighttime hours. Model predictions of Ey\\'s reaction to IMF-Bz changes are discussed.

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OGO-A magnetic field observations

Journal of Geophysical Research Atmospheres ◽

10.1029/jz072i021p05417 ◽

1967 ◽

Vol 72 (21) ◽

pp. 5417-5471 ◽

Cited By ~ 245

Author(s):

J. P. Heppner ◽

M. Sugiura ◽

T. L. Skillman ◽

B. G. Ledley ◽

M. Campbell

Keyword(s):

Magnetic Field ◽

Field Observations

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3-D magnetic field and current system in the heliosphere

Space Science Reviews ◽

10.1007/bf00170795 ◽

1996 ◽

Vol 78 (1-2) ◽

pp. 85-94 ◽

Cited By ~ 47

Author(s):

Haruichi Washimi ◽

Takashi Tanaka

Keyword(s):

Magnetic Field ◽

Current System

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DECLINE AND RECOVERY OF THE INTERPLANETARY MAGNETIC FIELD DURING THE PROTRACTED SOLAR MINIMUM

The Astrophysical Journal ◽

10.1088/0004-637x/775/1/59 ◽

2013 ◽

Vol 775 (1) ◽

pp. 59 ◽

Cited By ~ 21

Author(s):

Charles W. Smith ◽

Nathan A. Schwadron ◽

Craig E. DeForest

Keyword(s):

Magnetic Field ◽

Interplanetary Magnetic Field ◽

Solar Minimum

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Azimuthal magnetic fields in Saturn’s magnetosphere: effects associated with plasma sub-corotation and the magnetopause-tail current system

Annales Geophysicae ◽

10.5194/angeo-21-1709-2003 ◽

2003 ◽

Vol 21 (8) ◽

pp. 1709-1722 ◽

Cited By ~ 29

Author(s):

E. J. Bunce ◽

S. W. H. Cowley ◽

J. A. Wild

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Magnetic Fields ◽

Current System ◽

Heavy Ion ◽

Local Times ◽

Dynamical Process ◽

Tail Current ◽

Field Lines ◽

Inner Region

Abstract. We calculate the azimuthal magnetic fields expected to be present in Saturn’s magnetosphere associated with two physical effects, and compare them with the fields observed during the flybys of the two Voyager spacecraft. The first effect is associated with the magnetosphere-ionosphere coupling currents which result from the sub-corotation of the magnetospheric plasma. This is calculated from empirical models of the plasma flow and magnetic field based on Voyager data, with the effective Pedersen conductivity of Saturn’s ionosphere being treated as an essentially free parameter. This mechanism results in a ‘lagging’ field configuration at all local times. The second effect is due to the day-night asymmetric confinement of the magnetosphere by the solar wind (i.e. the magnetopause and tail current system), which we have estimated empirically by scaling a model of the Earth’s magnetosphere to Saturn. This effect produces ‘leading’ fields in the dusk magnetosphere, and ‘lagging’ fields at dawn. Our results show that the azimuthal fields observed in the inner regions can be reasonably well accounted for by plasma sub-corotation, given a value of the effective ionospheric Pedersen conductivity of ~ 1–2 mho. This statement applies to field lines mapping to the equator within ~ 8 RS (1 RS is taken to be 60 330 km) of the planet on the dayside inbound passes, where the plasma distribution is dominated by a thin equatorial heavy-ion plasma sheet, and to field lines mapping to the equator within ~ 15 RS on the dawn side outbound passes. The contributions of the magnetopause-tail currents are estimated to be much smaller than the observed fields in these regions. If, however, we assume that the azimuthal fields observed in these regions are not due to sub-corotation but to some other process, then the above effective conductivities define an upper limit, such that values above ~ 2 mho can definitely be ruled out. Outside of this inner region the spacecraft observed both ‘lagging’ and ‘leading’ fields in the post-noon dayside magnetosphere during the inbound passes, with ‘leading’ fields being observed both adjacent to the magnetopause and in the ring current region, and ‘lagging’ fields being observed between. The observed ‘lagging’ fields are consistent in magnitude with the sub-corotation effect with an effective ionospheric conductivity of ~ 1–2 mho, while the ‘leading’ fields are considerably larger than those estimated for the magnetopause-tail currents, and appear to be indicative of the presence of another dynamical process. No ‘leading’ fields were observed outside the inner region on the dawn side outbound passes, with the azimuthal fields first falling below those expected for sub-corotation, before increasing, to exceed these values at radial distances beyond ~ 15–20 RS , where the effect of the magnetopause-tail currents becomes significant. As a by-product, our investigation also indicates that modification and scaling of terrestrial magnetic field models may represent a useful approach to modelling the three-dimensional magnetic field at Saturn.Key words. Magnetospheric physics (current systems; magnetosphere-ionosphere interactions; solar wind-magnetosphere interactions)

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An empirical model (CH-Therm-2018) of the thermospheric mass density derived from CHAMP

10.5194/angeo-2018-25 ◽

2018 ◽

Cited By ~ 1

Author(s):

Chao Xiong ◽

Hermann Lühr ◽

Michael Schmidt ◽

Mathis Bloßfeld ◽

Sergei Rudenko

Keyword(s):

Empirical Model ◽

Solar Minimum ◽

Mass Density ◽

Precise Orbit Determination ◽

Wave Pattern ◽

Magnetic Activity ◽

Low Earth Orbit ◽

Naval Research ◽

Champ Satellite ◽

Incoherent Scatter

Abstract. Thermospheric drag is the major non-gravitational perturbation acting on Low Earth Orbit (LEO) satellites at altitudes up to 1000 km. The drag depends on the thermospheric density, which is a key parameter in the planning of LEO missions, e.g. their lifetime, collision avoidance, precise orbit determination, as well as orbit and re-entry prediction. In this study, we present an empirical model, named CH-Therm-2018, of the thermospheric mass density derived from 9-year (from August 2000 to July 2009) accelerometer measurements at altitude from 460 to 310 km, from the CHAllenging Minisatellite Payload (CHAMP) satellite. The CHAMP dataset is divided into two 5-year periods with 1-year overlap (from August 2000 to July 2005 and from August 2004 to July 2009), to represent the high-to-moderate and moderate-to-low solar activity conditions, respectively. The CH-Therm-2018 model is a function of seven key parameters, including the height, solar flux index, season (day of year), magnetic local time, geographic latitude and longitude, as well as magnetic activity represented by the solar wind merging electric field. Predictions of the CH-Therm-2018 model agree well with the CHAMP observations (disagreements within ±20 %), and show different features of thermospheric mass density during solar activities, e.g. the March-September equinox asymmetry and the longitudinal wave pattern. We compare the CH-Therm-2018 predictions with the Naval Research Laboratory Mass Spectrometer Incoherent Scatter Radar Extended (NRLMSISE-00) model. The result shows that CH-Therm-2018 better predicts the density evolution during the last solar minimum (2008-2009) than the NRLMSISE-00 model. By comparing the Satellite Laser Ranging (SLR) observations of the ANDE-Pollux satellites during August-September 2009, we estimate 6-h scaling factors of thermospheric mass density and obtain a median value of 1.27 ± 0.60, indicating that our model, on average, slightly underestimates the thermospheric mass density at solar minimum.

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