[1] We present a study of the climatology of thermospheric neutral wind (TNW) meridional and zonal components measured with the 630.0 nm nightglow Fabry-Perot interferometer at the Arecibo Observatory from 1980 to 2010. We show and discuss the solar and geomagnetic dependencies as well as the long-term trend of the TNW components and their variation over time and season. A main result of this study was the detection of a substantial seasonal and local time dependence of the response of the TNW to solar and geomagnetic activity. In addition, we found that there is a long-term trend in the thermospheric neutral wind, which can be of a larger magnitude than the variation found in the seasonal, solar cycle, and geomagnetic activity influences. A major signature of this trend over the last 30 years was an increase in the meridional northward component up to 1.4 m s À1 yr À1 before midnight local time during the summer.

[1] This work presents the results of a local empirical model that describes the behavior of the ionospheric F 2 region peak. The model was developed using nearly 25 years of incoherent scatter radar (ISR) measurements made at the Arecibo Observatory (AO) between 1985 and 2009. The model describes the variability of the F 2 peak frequency ( f o F 2 ) and F 2 peak height (h m F 2 ) as a function of local time, season, and solar activity for quiet-to-moderate geomagnetic activity conditions (Kp < 4+). Our results show that the solar activity control of h m F 2 and f o F 2 over Arecibo can be better described by a new proxy of the solar flux (F 107P ), which is presented here. The variation of h m F 2 parameter with F 107P is virtually linear, and only a small saturation of the f o F 2 parameter is observed at the highest levels of solar flux. The winter anomaly and asymmetries in the variation of the modeled parameters between equinoxes were detected during the analyses and have been taken into account by the AO model. Comparisons of ISR data with international reference ionosphere (IRI) model predictions indicate that both CCIR and URSI modes overestimate f o F 2 during the daytime and underestimate it at night. As expected, this underestimation is not observed in the AO model. Our analyses also show that the h m F 2 parameter predicted by the IRI modes shows a saturation point, which causes h m F 2 to be underestimated at high solar activity. The underestimation increases with higher levels of solar activity. Finally, we also found that IRI predictions of the seasonal variability of f o F 2 and h m F 2 over Arecibo can be improved by using a small correction that varies with solar activity and local time.Citation: Brum, C. G. M., F. S. Rodrigues, P. T. dos Santos, A. C. Matta, N. Aponte, S. A. Gonzalez, and E. Robles (2011), A modeling study of f o F 2 and h m F 2 parameters measured by the Arecibo incoherent scatter radar and comparison with IRI model predictions for solar cycles 21, 22, and 23,

[1] Previously, ion vector velocity measurements at Arecibo required the rotation of the antenna (a 360°r otation takes about 15 minutes) in order to accumulate enough information from different directions. In addition, a least-squares fitting method or a more sophisticated inversion technique is necessary to determine horizontal velocities. This study reports the first instantaneous longduration F region vector velocity measurements in the magnetic meridian plane using the dual-beam system. This configuration is suitable for measuring the eastward electric field and deriving the meridional neutral wind with very high time resolution. The first results of this experiment presented here seem to show evidence for a gravity wave driven plasma process. Citation: Aponte, N., M. J. Nicolls,

Since 1980, we have observed the thermospheric neutral wind at the Arecibo Observatory using a Fabry‐Perot interferometer to measure the O(1D) 630 nm emission. Burnside and Tepley (1989) examined the first 8 years of this extended data set and found that there were no significant or systematic solar cycle influences on the magnitude or direction of the neutral wind field, nor on its horizontal gradients. Such affects have been observed previously at other locations around the globe, and their absence at Arecibo may have been due to the limited data set. Thus, we have extended the period of acquisition and analysis of our neutral wind measurements to include nearly three complete solar cycles (or approximately 30 years) and will present our results within the framework of the earlier work. While the earlier conclusion that no major systematic solar cycle influence on the neutral winds at Arecibo generally remains intact, we did find a slight increase in wind magnitude and a gradual, yet consistent rotation of the thermospheric neutral wind vector from a general southeast to a more eastward flow during 30 years of observation. We explain the magnitude and directional variations in terms of long‐term changes in the density and temperature of the upper atmosphere and their possible dissimilar influences on each wind component that appear as a rotation of the neutral wind vector.

[1] Thermospheric neutral winds can be the most important driver when modeling ionospheric densities and temperatures. Several papers in this special edition show interesting features of the neutral winds behavior during the last 30 years at the Arecibo Observatory (18.3°N, 66.75°W; ∼28.25°dip latitude) using Fabry-Perot Interferometer (FPI) data. A neutral wind vector that changes its direction, becoming more dominantly eastward over the years and a meridional neutral wind component that decreases in magnitude, were found. The main goal of this work is to look for similar evidence of long-term trends in the radar derived winds that might support these recent discoveries and explore the associated ionospheric parameter measurements to look for the effects of these changing winds on the ionosphere. With this purpose in mind, Incoherent Scatter Radar (ISR) measurements of the F region vector drifts are used to derive the corresponding meridional thermospheric neutral wind along the magnetic field over Arecibo during 20 years. Major findings include a decreasing long-term trend (lowering) of the height where the F2-layer peak density occurs (hmF2), which could be related with a more increased downward flux of the ionosphere. A slight decrease in the peak density of the F2-layer (NmF2) after local midnight also was found during the period studied. The meridional wind along the magnetic field derived from ISR data also revealed a long-term trend, becoming more northward during the period studied, with a maximum variation between 02:30UT and 05:30UT.Citation: Santos, P. T., C. G. M. Brum, C. A. Tepley, N. Aponte, S. A. González, and E. Robles (2011), Using incoherent scatter radar to investigate the neutral wind long-term trend over Arecibo,