The Effect of IMF By on Thermospheric Composition at High and Middle Latitudes

The strength and orientation of the interplanetary magnetic field (IMF) has a strong effect on the high-latitude plasma convection pattern, thereby influencing the speed and direction of polar thermospheric winds. The possibility of similar IMF control over the compositional response of the thermosphere during geomagnetic disturbances has not been fully investigated. This study finds that the y-component of the IMF (IMF By) exerts significant control over the development and subsequent equatorward transport of composition disturbances during periods of heightened geomagnetic activity. This is determined using the NCAR-TIMEGCM to simulate the thermospheric conditions during the first three weeks far-ultraviolet (FUV) imaging operations of the Dynamics Explorer 1 (DE-1) mission in 1981. The images reveal changes in the relative thermospheric column abundance of O vs. N2 (ΣO/N2). These changes are reproduced by the model, incorporating variable IMF strength and orientation as inputs. It is found that simple reversal of IMF By leads to subsequent changes in ΣO/N2 at middle latitudes by as much as 30%. This is a manifestation of the effect identified in the companion to this report [Crowley et al., this issue]. The study confirms the hypothesis of Immel et al. [1997] that IMF-By effects on middle-latitude thermospheric composition are important, though more complex than expected. Contrary to previous predictions, early morning local times are shown to be more likely to suffer large decreases in ΣO/N2 when By is negative. However, the overall magnitude of high-latitude Joule heating is found to be greater when By is positive.

[1]  S. E. Pryse,et al.  First direct evidence of meso-scale variability on ion-neutral dynamics using co-located tristatic FPIs and EISCAT radar in Northern Scandinavia , 2005 .

[2]  Robert R. Meier,et al.  Initial observations with the Global Ultraviolet Imager (GUVI) in the NASA TIMED satellite mission , 2003 .

[3]  R. Walterscheid,et al.  Spin‐up circulation of high‐latitude ion drag‐driven gyres , 2003 .

[4]  John D. Craven,et al.  Six days of thermospheric‐ionospheric weather over the Northern Hemisphere in late September 1981 , 2001 .

[5]  G. Crowley,et al.  Dayside enhancements of thermospheric O/N2 following magnetic storm onset , 2001 .

[6]  G. Crowley,et al.  Quantification of high latitude electric field variability , 2001 .

[7]  D. Drob,et al.  Atomic oxygen in the thermosphere during the July 13, 1982, solar proton event deduced from far ultraviolet images , 1999 .

[8]  J. Craven,et al.  Influence of IMF By on large-scale decreases of O column density at middle latitudes , 1997 .

[9]  J. Craven,et al.  A Survey of Large-Scale Variations in Thermospheric Oxygen Column Density with Magnetic Activity as Inferred from Observations of the FUV Dayglow , 1997 .

[10]  Timothy Fuller-Rowell,et al.  On the importance of E‐field variability for Joule heating in the high‐latitude thermosphere , 1995 .

[11]  J. Craven,et al.  Interpretation of Dynamics Explorer far UV images of the quiet time thermosphere , 1995 .

[12]  Raymond G. Roble,et al.  A thermosphere-ionosphere-mesosphere-electrodynamics general circulation model (time-GCM): Equinox solar cycle minimum simulations (30–500 km) , 1994 .

[13]  Timothy Fuller-Rowell,et al.  Height-integrated Pedersen and Hall conductivity patterns inferred from the TIROS-NOAA satellite data , 1987 .

[14]  R. W. Spiro,et al.  A model of the high‐latitude ionospheric convection pattern , 1982 .

[15]  John D. Craven,et al.  Global auroral imaging instrumentation for the Dynamics Explorer mission. , 1981 .

[16]  G. W. Prölss.  Magnetic storm associated perturbations of the upper atmosphere: Recent results obtained by satellite‐borne gas analyzers , 1980 .

[17]  E. Smith,et al.  The ISEE-C Vector Helium Magnetometer , 1978, IEEE Transactions on Geoscience Electronics.

[18]  R. Meier.  Depressions in the far-ultraviolet airglow over the poles , 1970 .

[19]  L. Jacchia,et al.  Corpuscular Radiation and the Acceleration of Artificial Satellites , 1959, Nature.

[20]  Jeffrey P. Thayer,et al.  Height-resolved Joule heating rates in the high-latitude E region , 1998 .

[21]  G. W. Prölss,et al.  Perturbations of the FUV dayglow and ionospheric storm effects , 1998 .

[22]  Bernard Pinty,et al.  National Center for Atmospheric Research, Boulder, Colorado , 1990 .

[23]  M. Smith,et al.  A theoretical and empirical study of the response of the high latitude thermosphere to the sense of the "Y" component of the interplanetary magnetic field , 1986 .