Browsing by Author "Zhou, Qihou"

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    A study on meteor head echo using a probabilistic detection model at Jicamarca
    (American Geophysical Union, 2020-01) Li, Yanlin; Zhou, Qihou; Scott, Mark; Milla, Marco
    A coded long pulse is applied to the Jicamarca 50 MHz high power large aperture radar to study meteor head echoes. We develop a probabilistic detection model, which finds 25% more meteors than the commonly used signal‐to‐noise threshold method. The long code and the probabilistic approach allow us to detect over 180 meteors per minute during the dawn hours, which is several times higher than reported previously. The typical mass of the meteoroids is estimated to be about 10−9 kg, slightly smaller than other sensitive very‐high‐frequency and ultrahigh‐frequency high power large aperture radars except the Arecibo radar. The high sensitivity allows us to observe numerous meteors in the presence of the strongest equatorial electrojet. We report and discuss the characteristics of meteor flux rate, ablation height, and velocity with a constant noise power for the first time for the Jicamarca radar. The highest average detection height is found to be near 2 a.m., instead of near 6 a.m. when the largest average velocity is observed. This is likely due to the combination of the relative large atmospheric velocity and the substantial atmospheric entry angles around 2 a.m. The observed characteristics suggest that many meteors are detected 8° off zenith despite that the full beam width is only 2.4°.
    Palabras clave:Meteor detectionMeteor scienceRadar
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    The August 2011 URSI World Day campaign: Initial results
    (Elsevier, 2015-11) Immel, Thomas J.; Liu, Guiping; England, Scott L.; Goncharenko, Larisa P.; Erickson, Phillip J.; Lyashenko, Mykhaylo V.; Milla, Marco; Chau Chong Shing, Jorge Luis; Frey, Harald U.; Mende, Stephen B.; Zhou, Qihou; Stromme, Anja; Paxton, Larry J.
    During a 10-day URSI World Day observational campaign beginning on August 1, 2011, an isolated, major geomagnetic storm occurred. On August 5, Kp reached values of 8− and Dst dropped to −113 nT. The occurrence of this isolated storm in the middle of a 10-day URSI World Day campaign provides and unprecedented opportunity to observe the coupling of solar wind energy into the magnetosphere and to evaluate the varied effects that occur in the coupled magnetosphere–ionosphere–thermosphere system. Dramatic changes in the ionosphere are seen at every one of the active radar stations, extending from Greenland down to equatorial Peru in the American sector and at middle latitudes in Ukraine. Data from TIMED and THEMIS are shown to support initial interpretations of the observations, where we focus on processes in the middle latitude afternoon sector during main phase, and the formation of a dense equatorial ionosphere during storm recovery. The combined measurements strongly suggest that the changes in ionospheric conditions observed after the main storm phase can be attributed in large part to changes in the stormtime thermosphere. This is through the generation of disturbance dynamo winds and also global neutral composition changes that either reduce or enhance plasma densities in a manner that depends mainly upon latitude. Unlike larger storms with possibly more sustained forcing, this storm exhibits minimal effects of persistent meridional stormtime wind drag, and little penetration of solar wind electric potentials to low latitudes. It is, therefore, an outstanding example of an impulsive event that exhibits longer-term effects through modification of the background atmosphere.
    Palabras clave:IonosphereRadarThermosphere