Modeling the temporal and geographical variability of the micrometeor mass input in the upper atmosphere using HPLA radar measurements

Janches, D.1 and Fentzke, J.2

1 NWRA./CoRA Div., Boulder, USA
2 University of Colorado, Boulder, USA

It is now widely accepted that microgram extraterrestrial particles from the sporadic background are the major contributors of metals in the Mesosphere/Lower Thermosphere (MLT). It is also well established that this material gives rise to the upper atmospheric metallic and ion layers observed by radars and lidars. In addition, micrometeoroids are believed to be an important source for condensation nuclei (CN), the existence of which is a prerequisite for the formation of NLC particles in the polar mesopause region. In order to understand how this flux gives rise to these atmospheric phenomena, accurate knowledge of the global meteoric input function (MIF) is critical. This function accounts for the annual and diurnal variations of meteor rates, global distribution, directionality, and velocity and mass distributions. Estimates of most of these parameters are still under investigation. In this talk, we present results of a detailed model of the diurnal, seasonal and geographical variability of the micrometeoric activity in the upper atmosphere. The principal goal of this effort is to construct a new and more precise sporadic MIF needed for the subsequent modeling of the atmospheric chemistry of meteoric material and the origin and formation of metal layers in the MLT. The model is constructed based on meteor radar observations obtained with the 430 MHz dual-beam Arecibo (AO) radar in Puerto Rico, the 50 MHz Jicamarca (JRO) radar in Peru and the 1.29 GHz Sondrestrom radar in Greenland, thus utilizing almost the entire NSF ISR chain. The model uses Monte Carlo simulation techniques and includes an accepted mass flux provided by six main known meteor sources (i.e. orbital families of dust) and a detailed modeling of the meteoroid atmospheric entry physics. The results indicate, that although the Earth’s Apex centered source, composed of dust from long period comets, is required to be only about ~33% of dust in the Solar System at 1 AU, it accounts for 60 to 70% of the actual dust which enters the atmosphere. These particles are mostly characterized by very high geocentric speeds (~55 km/sec) since they are in retrograde orbits. The reminding 30% of meteoroids entering the atmosphere originate mostly from the Helion and Ant-helion sources. The results of the model are in excellent agreement with observed diurnal curves obtained at different seasons and locations. Based on these results, we calculate the micrometeor global, diurnal and seasonal input in the upper atmosphere.