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[1] We present observations of the F-region ionosphere over Arecibo, Puerto Rico (18.34°N, 66.75°W), during the January-February 2008 and January-February 2009 sudden stratospheric warming (SSW) events. For the first period (2008), we have used incoherent scatter radar (ISR) electron density and temperature measurements from the Arecibo Observatory (AO), as well as relative total electron content (TEC) derived from a dual-frequency GPS receiver. For the second event (2009), during which we observed the largest recorded stratospheric warming, we have used the relative GPS TEC. Our analysis indicates that the ionosphere over Arecibo exhibits perturbations after the SSW, the effects are most visible during the daytime. The strongest signatures are observed in the TEC measurements, represented by large enhancements (with respect to non SSW days), particularly during daytime hours. However, the local time dependence of these enhancements is not the same in the two events. In addition, the data show that our results are consistent with the larger than normal daytime vertical drift differences observed at the magnetic equator over Jicamarca. The electron temperature is also affected during the daytime due to changes in electron density, indicating that the electron temperatures is influenced, indirectly, by changes in planetary wave activity in the lower altitudes.Citation: Chau, J. L., N. A. Aponte, E. Cabassa, M. P. Sulzer, L. P. Goncharenko, and S. A. González (2010), Quiet time ionospheric variability over Arecibo during sudden stratospheric warming events,

Here we present North American observations of the 3‐dimensional structure of large‐scale traveling ionospheric disturbances (TIDs) that affected the low‐ and mid‐latitude ionosphere during the stormtime period of October 1–2, 2002. Using TEC data from the American network of dual‐frequency GPS receivers, we are able to examine the effect of the TIDs on the background TEC and thus image their horizontal scales. Incoherent scatter radar data from the Arecibo Observatory give information on the vertical structure of the disturbances. The meridional and zonal structure of the TIDs are explored by computing the TEC perturbation, a method which has a resolution of a fraction of a TEC unit. The technique is effective in mapping the global structure of large‐scale disturbances, as the lower latitude perturbations can be examined at the same time as the higher latitude sources. The method may prove valuable in studying the formation and propagation of TIDs.

Abstract.The fact that the incoherent backscatter spectrum narrows when the radar beam is nearly perpendicular to the magnetic field is well known and has been used at Jicamarca for more than 30 years to measure very accurate line-of-sight velocities. Recently it has become clear that these spectra are narrower than expected. We have explained this effect and also the small change to the spectral shape required at somewhat larger angles to correct the ratio of electron to ion temperature seen in some studies. Coulomb collisions affecting the motion of the electrons are responsible for the additional spectral narrowing. We have carried out very accurate simulations of electron motion resulting in incoherent scatter spectra which are qualitatively similar to spectra resulting from other types of collisions, and to those predicted in an analytic solution for the Coulomb case [Woodman, 1967]. However, we found that the spectrum of the velocity time series in the radar line of sight departs significantly from the nearly Lorentzia. n form expected with simple collisional models. This causes the collisional effects to extend to somewhat shorter scale lengths, or further from perpendicular to the magnetic field than expected. In order to investigate the collisional process more closely, we performed another simulation combining the effects of electron-ion collisions and a simple friction model (Langevin equation) in an adjustable combination. This one showed that the effect of electron-ion collisions alone would result in collisional effects extending several degrees farther from perpendicular to the field than when both kinds of collisions are included. Collisions affecting the speed of the electrons tend to limit the size of the effect at larger angles from perpendicular. Thus the effect of these collisions on the incoherent scatter spectrum cannot be accurately predicted from simple models but depends on the detailed physics of the collisions.