Variations of the nighttime thermospheric mass density at low and middle latitudes

[1] The latitudinal structure of the nighttime thermospheric mass density at 385 km has been investigated using observations made by the accelerometer onboard the CHAMP satellite between 2002 and 2007. The nighttime thermospheric mass density had a clear latitudinal variation. There was a local density peak around the geographic equator and two minima at about ±30°. This nighttime equatorial mass anomaly (NEMA) was opposite to the latitudinal variations of the daytime ionospheric equatorial anomaly and thermospheric mass density anomaly as both have minima at the magnetic dip equator and maxima around ±20° in magnetic latitudes. This anomalous behavior of the nighttime thermospheric mass density had strong local time, seasonal, hemispheric, and solar cycle dependences. The largest crest-to-trough ratio between the peak density at the equator and the minima at the anomaly latitudes (±30°) occurred between 0000 and 0200 local time. The NEMA appeared to be more pronounced during solstice seasons. It was also stronger during solar minimum than during solar maximum. In addition, under the same geophysical conditions, the empirical NRLMSISE-00 model shows similar but much weaker nighttime mass density anomaly features at low and middle latitudes. A high-resolution National Center for Atmospheric Research-Thermosphere Ionosphere Mesosphere Energetics Global Circulation Model (TIMEGCM) simulation reproduced most of the observed latitudinal variations of the nighttime mass density as well as the thermospheric midnight temperature maximum (MTM). Model results suggest that superposition of diurnal and semidiurnal migrating tides of modes up to wave number 6 is the likely cause of both the NEMA and MTM phenomena.

[1]  Jeffrey M. Forbes,et al.  Migrating and nonmigrating semidiurnal tides in the upper atmosphere excited by tropospheric latent heat release: MIGRATING AND NONMIGRATING SEMIDIURNAL TIDES , 2003 .

[2]  Joseph E. Salah,et al.  A global thermospheric model based on mass spectrometer and incoherent scatter data MSIS, 1. N2 density and temperature , 1977 .

[3]  D. Drob,et al.  Nrlmsise-00 Empirical Model of the Atmosphere: Statistical Comparisons and Scientific Issues , 2002 .

[4]  N. Spencer,et al.  On the horizontal distribution of the equatorial thermospheric midnight temperature maximum and its seasonal variation , 1982 .

[5]  Jeffrey M. Forbes,et al.  Migrating and nonmigrating diurnal tides in the middle and upper atmosphere excited by tropospheric latent heat release , 2002 .

[6]  Jeffrey M. Forbes,et al.  Global thermospheric neutral density and wind response to the severe 2003 geomagnetic storms from CHAMP accelerometer data , 2005 .

[7]  B. Reinisch,et al.  Modeling the low-latitude thermosphere and ionosphere , 2002 .

[8]  Wenbin Wang,et al.  Seasonal and latitudinal differences of the saturation effect between ionospheric NmF2 and solar activity indices , 2009 .

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

[10]  Thomas N. Woods,et al.  Effects of solar variability on thermosphere density from CHAMP accelerometer data , 2007 .

[11]  L. Jacchia,et al.  Thermospheric temperature, density, and composition: New models , 1977 .

[12]  P. Richards,et al.  EUVAC: A solar EUV Flux Model for aeronomic calculations , 1994 .

[13]  Hermann Lühr,et al.  Solar and magnetospheric forcing of the low latitude thermospheric mass density as observed by CHAMP , 2009 .

[14]  A.-M. Mainguy,et al.  Synthesis of flight results of the Cactus accelerometer for accelerations below 10−9g , 1979 .

[15]  Hitoshi Fujiwara,et al.  Solar terminator wave and its relation to the atmospheric tide , 2009 .

[16]  Dieter Bilitza,et al.  Solar-terrestrial models and application software , 1990 .

[17]  R. Lindzen.  Turbulence and stress owing to gravity wave and tidal breakdown , 1981 .

[18]  C. Fesen.  Simulations of the low‐latitude midnight temperature maximum , 1996 .

[19]  S. Bruinsma,et al.  A solar terminator wave in thermosphere neutral densities measured by the CHAMP satellite , 2008 .

[20]  M. Mendillo,et al.  The current state of investigations regarding the thermospheric midnight temperature maximum (MTM) , 2002 .

[21]  T. Fuller‐Rowell,et al.  Midnight temperature maximum (MTM) in Whole Atmosphere Model (WAM) simulations , 2009 .

[22]  Hermann Lühr,et al.  A solar terminator wave in thermospheric wind and density simultaneously observed by CHAMP , 2009 .

[23]  Hermann Lühr,et al.  Global distribution of the thermospheric total mass density derived from CHAMP , 2004 .

[24]  R. Roble,et al.  Connections between deep tropical clouds and the Earth's ionosphere , 2007 .

[25]  Raymond G. Roble,et al.  A thermosphere/ionosphere general circulation model with coupled electrodynamics , 1992 .

[26]  A. Hedin,et al.  A revised thermospheric model based on mass spectrometer and incoherent scatter data - MSIS-83 , 1983 .

[27]  N. Spencer,et al.  An equatorial temperature and wind anomaly (ETWA) , 1991 .

[28]  Libo Liu,et al.  Solar activity variations of nighttime ionospheric peak electron density , 2006 .

[29]  M. Iredell,et al.  Midnight density and temperature maxima, and thermospheric dynamics in Whole Atmosphere Model simulations , 2010 .

[30]  Raymond G. Roble,et al.  A coupled thermosphere/ionosphere general circulation model , 1988 .

[31]  A. Hedin,et al.  Magnetic control of the near equatorial neutral thermosphere , 1973 .

[32]  C. Reigber,et al.  CHAMP mission status , 2002 .

[33]  L. Jacchia,et al.  Diurnal and seasonal latitudinal variations in the upper atmosphere , 1968 .

[34]  Dale N. Anderson,et al.  Dynamics of the low-latitude thermosphere: Quiet and disturbed conditions , 1997 .

[35]  M. Faivre,et al.  New results on equatorial thermospheric winds and the midnight temperature maximum , 2008 .

[36]  Larry J. Paxton,et al.  Control of equatorial ionospheric morphology by atmospheric tides , 2006 .

[37]  B. K. Ching,et al.  Ion gauge measurements of latitudinal density variations at night , 1974 .

[38]  Jann‐Yenq Liu,et al.  Plausible effect of atmospheric tides on the equatorial ionosphere observed by the FORMOSAT‐3/COSMIC: Three‐dimensional electron density structures , 2007 .

[39]  A. Hedin,et al.  Empirical model of global thermospheric temperature and composition based on data from the OGO-6 quadrupole mass spectrometer , 1974 .

[40]  T. Fuller‐Rowell,et al.  Dynamic and energetic coupling in the equatorial ionosphere and thermosphere , 2003 .

[41]  Hermann Lühr,et al.  Climatology of the equatorial thermospheric mass density anomaly , 2007 .

[42]  M. D. Burrage,et al.  GSWM-98: Results for migrating solar tides , 1999 .

[43]  A. Hedin.  MSIS‐86 Thermospheric Model , 1987 .

[44]  H. Hinteregger,et al.  Observational, reference and model data on solar EUV, from measurements on AE-E , 1981 .

[45]  F. Barlier,et al.  Densities from the CACTUS accelerometer as an external test of the validity of the thermospheric models , 1981 .

[46]  Richard Biancale,et al.  Atmospheric densities derived from CHAMP/STAR accelerometer observations , 2004 .

[47]  R. Nerem,et al.  Interannual and latitudinal variability of the thermosphere density annual harmonics , 2008 .