Abstract: A new model was presented in a three dimensional geographic coodinate system to describe the linear growth of R-T instability so that the effects of magnetic inclination and declination were taken into accont. It is an generalization of former theories from equatorial to mid-latitude regions. From this model one can see the influence of magnetic strength, inclination and declination. Due to the magnetic effects, the occurrence rate of the instability is not symmetric in longitudes even at the magnetic equator. Some occurrence peaks or valleys will appear in certain places around the world.

Key words: Spread-F, geographic three-dimensional model, global characteristics

摘要： 从三维地理坐标系出发建立模型，考虑了地磁倾角和偏角的影响，研究Spread-F现象的全球分布特点，是对以前的研究从赤道地区向中、低纬度地区的推广。从该三维模型中可以看到地磁场的大小和位型的影响(包括磁倾角和磁偏角的效应)。由于地磁位型的不同，发生率的分布并不具有经度对称性，即使在磁赤道附近也如此。在某些特殊的经度和纬度地区，会达到发生率的峰值。

关键词: Spread-F, 地理三维Spread-F模型, Spread-F的全球特征