Ionospheric Climatology

Studies of ionospheric climatology have been conducted using large data sets of ISR observations, with focusing on the morphology and effect of the ionospheric densities, dynamics and thermal status. This research addresess general, synthetic, averaged and large spatial scale ionospheric features, in contrast to specific ionospheric andspace weather eventr. These results establish an important background climatology upon which weather effects can be better identified and elucidated. Some of those specific topics are:

Plasma temperature climatology
Annual and semiannual variations
Ionospheric Variability
Long-term Trends

Plasma temperature climatology

Incoherent Scatter Radar Model Ionospheric plasma temperature variations have recently been studied based on incoherent scatter radar (ISR) observations at Millstone Hill, a sub-auroral midlatitude site in North America, and at Saint Santin, a typical midlatitude site in Europe with a geographic latitude slightly higher but an apex latitude 14 degrees lower than Millstone. This study indicates a complicated response of electron temperature on solar activity, which varies with local time (daytime or nighttime) and season and is strongly associated with the background electron density. An enhanced solar EUV flux gives rise to more photoelectrons which in turn elevate plasma temperatures by heating processes (proportional to Ne); meanwhile, the increased electron density due to the enhanced EUV flux leads to an enhanced electron cooling rate through Coulomb collisions (proportional to Ne^2), which may lead to a lower Te. The actual response of Te to a change in solar EUV is the result of, in addition to effects of heat conduction at high altitudes, these two competing processes.

Annual and semiannual variations

Annual The annual variation of ionospheric electron density Ne is largely caused by the annual change of solar zenith angle and of the neutral composition. Prior studies based on ionosonde and TEC data and theoretical modeling have indicated the variation of annual changes with longitude and latitude. ISR data at Shigaraki showed the variation with height in the F region. Our studies use long-term ISR databases from a variety of latitudes and longitudes covering an appropriate altitude range to address ionospheric annual/semiannual changes seen in multiple parameters at different latitudes and longitudes. The study shows how the month-by-month variation of Ne evolves, when the latitude increases, from a regular annual change with Ne in summer greater than in winter to an annual change with "winter anomaly", and from a strong annual component to a strong semiannual component. Examining annual Ti variations, it is found that at high latitudes Ti is highest in summer, at Millstone, however, the maximum occurs in later spring and earlier summer (May), suggesting an equinoctial asymmetry.

Ionospheric Variability

From October 4 to November 4, 2002, a 32 consecutive day incoherent scatter radar (ISR) campaign was conducted by the EISCAT Svalbard Radar (ESR) and the Millstone Hill Radar. [see here for the 2002 30-day run ] This experiment, which was the longest ever attempted by incoherent scatter radars provided a unique opportunity to study many important ionosphere-thermosphere phenomena, e.g., the ionospheric variability and long-lasting space weather events. The global neutral atmosphere was simultaneously monitored by the TIMED spacecraft in a 625 km circular orbit above Earth. The Global Ultraviolet Imager (GUVI) instrument onboard the spacecraft produces far-ultraviolet imaging spectrograms of photons emitted from the upper atmosphere, providing dayside neutral composition information. The day-to-day variability under quiet magnetic conditions in electron density, ion temperature and electron temperature, respectively, changed with local time and height. Midnight through dawn was the period of largest variability. Quasiperiodic Ne oscillations were present with periods > 1 day. Some of these oscillations were correlated with changes in the neutral composition originating from geomagnetic activity, which altered the global atmospheric circulation. However, the wave-type oscillation of Ne exhibits a downward phase progression which persists up to 600 km and prevails until a large storm appears to impose an upward phase progression.

References

Zhang, S.-R., J. M. Holt, A. P. van Eyken, M. McCready, C. Amory-Mazaudier, S. Fukao, and M. Sulzer, Ionospheric local model and climatology from long-term databases of multiple incoherent scatter radars, Geophys. Res. Lett., 32, L20102, doi:10.1029/2005GL023603.PDF

Zhang, S.-R., J. M. Holt, P. J. Erickson, F. D. Lind, J. C. Foster, A. P. van Eyken, Y. Zhang, L. J. Paxton, W. C. Rideout, L. P. Goncharenko, and G. R. Campbell, October 2002 30-day Incoherent Scatter Radar Experiments at Millstone Hill and Svalbard and Simultaneous GUVI/TIMED Observations, Geophys. Res. Lett., 32, L01108, doi:10.1029/2004GL020732, 2005 ( PDF, 2 5Mb)

Lei, J., L. Liu, W. Wan, and S.-R. Zhang, Variations of eletron density based on long-term incoherent scatter radar and ionosonde measurements over Millstone Hill, Radio Science, 40, RS2008, doi:10.1029/2004RS003106, 2005.( PDF )

Zhang, S.-R., J. M. Holt, A. M. Zalucha, and C. Amory-Mazaudier, Mid-latitude ionospheric plasma temperature climatology and empirical model based on Saint Santin incoherent scatter radar data from 1966-1987, J. Geophys. Res., 109, A11311, doi:10.1029/2004JA010709, 2004. (Full Paper: PDF)

Zhang, S.-R. and J. M. Holt, Ionospheric temperature variations during 1976-2001 over Millstone Hill, Adv. Space Res., 33, 963-969, 2004. DOI 10.1016/j.asr.2003.07.012 (Full Paper: PDF file )

Lei, Jiuhou; Liu, Libo; Wan, Weixing; Zhang, Shun-Rong; Holt, John M., A statistical study of ionospheric profile parameters derived from Millstone Hill incoherent scatter radar measurements Geophys. Res. Lett., Vol. 31, No. 14, L14804, 10.1029/2004GL020578, 2004. (Full Paper: PDF file )

Holt, J. M., S.-R. Zhang, and M. J. Buonsanto, Regional and local ionospheric models based on Millstone Hill incoherent scatter radar data, Geophys. Res. Lett., 29(8), 10.1029/2002GL014678, 2002

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