Meteoric smoke particle properties derived using dual-beam Arecibo UHF observations of D-region spectra during different seasons

We present a seasonal study of the presence and characteristics of meteoric smoke particles (MSPs) in the D-region plasma derived from observations using the Gregorian and line feeds of the 430 MHz dual-beam Arecibo Observatory (AO) incoherent scatter radar (ISR) in Puerto Rico ( 18 ∘ N , 67 ∘ W ) . MSPs are the product of re-condensation of ablated meteoric material and are believed to be the condensation nuclei for the formation of ice particles in the polar mesopause region. These CNs can then be responsible for the formation of polar mesospheric clouds (PMCs), noctilucent clouds (NLCs) and polar mesospheric summer echoes (PMSEs). For this work, we simultaneously employed both AO antenna feeds to define two radar beams inclined 15 ∘ east and west of zenith ( Janches et al., 2006). Because of the non-vertical pointing, the sampled spectra are Doppler shifted due to the rapidly changing neutral dynamics of the MLT region. We correct this effect by removing the Doppler shift using the radial velocities estimated every ∼ 2 min and then integrate the corrected spectra for longer periods to enhance signal-to-noise ratio (SNR) and better investigate the variability of MSP properties. We determine MSP radii and number densities utilizing a method similar to the one developed by Strelnikova et al. (2007) in which the autocorrelation function (ACF) is approximated as the sum of two exponential decays, i.e., the power spectrum is approximated as the sum of two Lorentzians. This method, which assumes mono-disperse particles, allows us to determine mean particle properties in the 80–95 km altitude range during the hours of 10–14 AO LT when the detected SNR from the D-region is highest. Results from this work show MSP radii approximately 0.6–1.5 nm is size depending on altitude and season. Also, MSP densities as a function of altitude and season are determined with the aid of the IRI model resulting in values on the order of 10 2 – 10 4 per cubic centimeter. Our error analysis shows that spectral broadening from atmospheric sources such as neutral turbulence induced by gravity wave vertical variance, and non-zero vertical winds results in < 10 % change in derived MSP radii. Also, since our dataset covers different seasons, we investigate a potential correlation between the seasonal variations of the derived MSPs properties with that of the meteoric input function (MIF) in the MLT above Arecibo.