Activity of the Eta-Aquariid and Orionid meteor showers

Abstract

Aims. We present a multi-instrumental, multidecadal analysis of the activity of the Eta-Aquariid and Orionid meteor showers for the purpose of constraining models of 1P/Halley's meteoroid streams. Methods. The interannual variability of the showers' peak activity and period of duration is investigated through the compilation of published visual and radar observations prior to 1985 and more recent measurements reported in the International Meteor Organization (IMO) Visual Meteor DataBase, by the IMO Video Meteor Network and by the Canadian Meteor Orbit Radar (CMOR). These techniques probe the range of meteoroid masses from submilligrams to grams. The η-Aquariids and Orionids activity duration, shape, maximum zenithal hourly rates (ZHR) values, and the solar longitude of annual peaks since 1985 are analyzed. When available, annual activity profiles recorded by each detection network were measured and are compared. Results. Observations from the three detection methods show generally good agreement in the showers' shape, activity levels, and annual intensity variations. Both showers display several activity peaks of variable location and strength with time. The η-Aquariids are usually two to three times stronger than the Orionids, but the two showers display occasional outbursts with peaks two to four times their usual activity level. CMOR observations since 2002 seem to support the existence of an ∼12 year cycle in Orionids activity variations; however, additional and longer term radar and optical observations of the shower are required to confirm such periodicity.

Modeling the past and future activity of the Halleyids meteor showers

“…We first compute synthetic intensity profiles (model shower activity as a function of time around the maximum of each shower, each year) from our simulations. This provides a quick analysis of the meteor showers' shape, duration, average activity and year to year variations to compare to the measurements provided in Egal et al (2020). In addition, the simulated radiants and particles' mass and size distributions at Earth can be compared to meteor observations, all of which both constrain and validate the simulations.…”

“…The η-Aquariids occur at the descending node of the comet, while the Orionids occur at the ascending node. Modern observations of the η-Aquariids and Orionids date back to the late 19th century (Egal et al 2020). However, analysis of ancient observations of meteor showers suggests that both showers have been active for at least a millennium, and likely longer (Ahn 2003(Ahn , 2004Imoto and Hasegawa 1958;Zhuang 1977).…”

“…The best weighting solution is determined by calibrating the activity profiles on past observations of the meteor showers. At present, the longest and most consistent continuous monitoring of the Halleyids is provided by the Canadian Meteor Orbit Radar (CMOR), operational since 2002 (Egal et al 2020). Our simulated activity profiles are calibrated to CMOR observations at 29 MHz, first for the η-Aquariid meteor shower (which has more particles) and then refined with the Orionids simulations.…”

“…In this work, we present the second part of our analysis of the Halleyids meteor showers. In Egal et al (2020), we have documented the long-term (∼several decades) activity of the η-Aquariids and Orionids. The showers' activity profiles, shapes, and year to year variations were defined through a compilation of visual meteor observations since 1985, more recent measurements of the Canadian Meteor Orbit Radar (CMOR, cf.…”

“…The purpose of the present work is to apply a new numerical model of meteoroid stream evolution developed in Egal et al (2019) to the Halleyids. In particular, the long term evolution of these streams can now be constrained by the 35 years of observations reported in Egal et al (2020). Through extensive numerical simulations and the application of an adapted weighting solution to the ejected particles (see for e.g., Egal et al 2019), we constrain the model parameters using the η-Aquariids and Orionids intensity profiles and interannual variability since 1985.…”