[1] In this paper, we present a modeling and observational study of the micrometeor input function with a focus on understanding how each of the extraterrestrial sporadic meteoroid sources contributes to the observed meteoric flux in the Mesosphere and Lower Thermosphere (MLT) atmospheric region. For this purpose, we expand the model presented by Janches et al. (2006) using a Monte Carlo technique and incorporating: 1) a widely accepted global mass flux, which is divided into different proportions among the known sporadic meteoroid sources as the initial input above Earth's atmosphere; 2) contemporary knowledge on the source's velocity and radiant distributions; and 3) the full integration of the canonical meteor equations that describe the meteoroid entry and ablation physics. In addition, we constrain the initial input through a comparison of our modeled results with meteor observations obtained with the 430 MHz High Power and Large Aperture (HPLA) Arecibo radar in Puerto Rico that covers all seasons. The predicted meteor rates and velocity distributions are in excellent agreement with the observed ones without the need for any additional normalization factor. Our results indicate that although the Earth's Apex centered radiant source, which is characterized by high geocentric speeds ($55 km/s), appears to be $33% of the meteoroids in the Solar System at 1 AU, it accounts for $60% of the meteors observed by the Arecibo HPLA radar in the atmosphere. The remaining 40% of observed meteors originate mostly from the Helion and Anti-Helion sources, with a very small, but constant during the day, contribution of the South and North Toroidal sources. These results also suggest that particles smaller than $10 À3 mg with slow velocities (<30 km/s) will not significantly ablate and never become observable meteors. The motivation of this effort is to construct a new and more precise MIF model needed for the subsequent modeling of the atmospheric phenomena related to the meteoric flux.Citation: Fentzke, J. T., and D. Janches (2008), A semi-empirical model of the contribution from sporadic meteoroid sources on the meteor input function in the MLT observed at Arecibo,

[1] This paper presents a case study of the day-to-day variability in the midlatitude upper atmospheric ion temperature (~200-400 km) with a focus on variability resulting from meteorological forcing. The data are obtained by the Millstone Hill incoherent scatter radar (42.6 N, 288.5 E) on 18-31 January 2010, in coincidence with a major sudden stratospheric warming. We elucidate oscillations in ion temperature with both tidal periods (~8 h and~12 h) and non-tidal periods (>24 h) by analyzing residuals between the observed temperatures and those expected from an empirical model. We present the spatial-temporal development of periodicities in ion temperature and discuss to what degree these periodicities might be related to the sudden stratospheric warming event. The spectral location and temporal evolution of periodicities with~9.9-12.9 h and~6.2-7.9 h suggest that they are related to the semidiurnal (12 h) and terdiurnal (8 h

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[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.