The Local Time and Altitude Dependences of Long‐Lived Nonspecular Meteor Echoes With Weak Magnetic Aspect Sensitivity at Low Latitudes

Abstract

AbstractLong‐lived nonspecular meteor echoes backscattered from meteor trail nonfield‐aligned irregularities (NFAIs) were observed sporadically at high latitudes. In this study, we employ the observations by the all‐sky radar of Meteor and ionospheric Irregularity Observation System (MIOS) at Ledong (18.4°N, 109°E) in October 2018, January, April, and July 2019, to investigate the occurrences of meteor trail NFAIs at low latitudes. A deep learning method was developed to identify long‐lived meteor echo events with durations of more than 5 s. The long‐lived echo events with triangular shape (a typical feature of nonspecular echo) in radar range‐time intensity maps were manually distinguished from those with nontriangular shape. Based on the cutoff magnetic aspect angle 12° of nonspecular meteor echoes from field‐aligned irregularities (FAIs), the local time and altitude dependences of meteor NFAIs producing long‐lived nonspecular echoes are investigated. A total of 846 meteor events due to the backscatters of NFAIs were observed. These events peak around the morning hours, with the beginning (end) altitudes up to (down to) 120 km (∼80 km). Their mean heights are about 2–6 km higher than specular meteor echoes. The occurrence of NFAI echoes peaks on certain days that is likely associated with meteor showers. The ratio of the observed NFAI echo to specular echo events is, on average, less than 1‰. Possible factors responsible for the NFAIs at low latitudes are discussed based on the current understanding of meteor dust trail.