Abstract
Abstract. Non-specular meteor trail echoes are radar reflections from plasma instabilities that are caused by field-aligned irregularities. Meteor simulations are examined to show that these plasma instabilities, and thus the associated meteor trail echo, strongly depend on the meteoroid properties and the characteristics of the atmosphere in which the meteoroid is embedded. The effects of neutral winds, as a function of altitude, are analyzed to understand how their amplitude variability impacts the temporal–space signatures of non-specular meteor trail echoes present in very high-frequency (VHF) radar observations. It is found that amplitudes of the total horizontal neutral wind smaller than 0.6 m s−1 do not provide the right physical conditions to enable the genesis of non-specular meteor echoes. It is also found that a 0.0316 µg meteoroid traveling at 35 km s−1 can be seen as a meteor trail echo if the amplitudes of horizontal neutral winds are stronger than 15 m s−1. In contrast, a 0.316 µg meteoroid, traveling at the same speed, requires horizontal winds stronger than 1 m s−1 to be visible as a meteor trail echo. The neutral velocity threshold illustrates how simulations show that no trail echo is created below a critical wind value. This critical wind value is not mapped directly to radar observations, but it is used to shed light on the physics of meteor trails and improve their modeling. The meteor simulations also indicate that time delays on the order of hundreds of milliseconds or longer, between head echoes and non-specular echoes, which are present in VHF backscatter radar maps, can be a consequence of very dense plasma trails being affected by weak horizontal neutral winds that are smaller than 1 m s−1.
Highlights
Day and night, meteoroids smaller than a grain of sand penetrate the Earth’s upper atmosphere and generate meteor plasma trails at altitudes between 70 and 140 km
We have just described two scenarios that can manifest themselves when neutral wind amplitudes are close to a critical value that is needed to sustain meteor plasma instabilities, which in turn will create non-specular meteor reflections. These results indicate that the impact of neutral winds on trail evolution is a plausible and complementary explanation of the characteristics exhibited by very high-frequency (VHF) radar reflections such as those reported in Close et al (2004), Malhotra et al (2007), Dyrud et al (2007), Malhotra and Mathews (2009), and Sugar et al (2010)
We extend the outcomes of our simulations to analyze head echoes and non-specular meteor echoes detected with the Jicamarca VHF radar during the ηAquarids campaign (Chau and Galindo, 2008)
Summary
Meteoroids smaller than a grain of sand penetrate the Earth’s upper atmosphere and generate meteor plasma trails at altitudes between 70 and 140 km. For more than 2 decades, scientists have studied two new types of radar meteor reflections. These reflections are known as meteor head echoes and non-specular trails, typically observed with high-power and large-aperture (HPLA) radars. Non-specular meteor echoes are radar reflections from meteor plasma instabilities that are generated from field-aligned irregularities (FAIs); i.e., non-specular meteor echoes are detected when pointed perpendicularly to the Earth’s magnetic field B (Chapin and Kudeki, 1994; Zhou et al, 2001; Oppenheim et al, 2001, 2003, 2014; Dyrud et al, 2002; Chau et al, 2014; Oppenheim and Dimant, 2015; Dimant and Oppenheim, 2017a, b; Sugar et al, 2018, 2019). Our goal is to understand how a realistic vertical wind profile will influence echo structures routinely seen in VHF range–time–intensity
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