GRAVITY-WAVE MODULATION OF GRADIENT DRIFT INSTABILITIES IN MIDLATITUDE SPORADIC-E IRREGULARITIES

被引:190
作者
WOODMAN, RF [1 ]
YAMAMOTO, M [1 ]
FUKAO, S [1 ]
机构
[1] KYOTO UNIV,CTR RADIO ATMOSPHER SCI,UJI,KYOTO 611,JAPAN
关键词
D O I
10.1029/91GL01159
中图分类号
P [天文学、地球科学];
学科分类号
07 ;
摘要
Recent E region VHF backscatter echoes observed by the MU radar at mid-latitudes show quasi-periodic striations with a fairly constant range vs. time tilt in a RTI display. These features are explained in terms of gravity waves with frequencies close to the Brunt-Vaisala frequency which modulate the shape of sporadic E layers. The conditions of instability, when the magnetic field has a significant dip angle, is revised. Differing from previous work, we argue that conditions of local gradient drift instability are not sufficient and one has to consider the integrated properties of each magnetic filed tube. Stratified sporadic E layers are stable using this new criteria, unless they are distorted to produce unstable integrated gradients. Gravity waves with phase fronts parallel to the magnetic dip angle are capable of producing such distortion, imposing its own temporal and spatial periodicity on the echoes.
引用
收藏
页码:1197 / 1200
页数:4
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