磁層頂的位置和形狀主要取決於太陽風的動壓和地球磁層內的磁壓平衡。本篇文章為了討論磁層頂內側磁場與地球磁偶極場的比值，我們使用了THEMIS任務中的五顆衛星的資料。利用五顆衛星擁有相同酬載的優點當作我們觀測資料的來源。經過資料處理之後我們發現日側磁層頂內側磁場與地球磁偶極場的比值與靜止平衡距離在南向行星際磁場（Southward IMF）的時候會呈現正比的關係。此外在北向行星際磁場的時候，磁層頂內側磁場會隨著靜止平衡距離的-2.6次方而變化；在南向行星際磁場的時候，磁層頂內側磁場會隨著靜止平衡距離的-1.9次方而變化。這有別於地球磁偶極場隨著靜止平衡距離的-3.0次方而改變，藉由磁層頂內側磁場與靜止平衡距離之間的關係可以得到一個最佳的方程式。 The pressure is balanced at the magnetopause where separates the shocked solar wind and the compressed geomagnetic field. In this research, we use the magnetic fields from five THEMIS probes and the theoretical dipole magnetic field model to calculate the ratio of the compressed geomagnetic field just inside the magnetopause to the dipole magnetic field. Here we find that the ratio is linearly proportional to the subsolar standoff distance. Additionally, we also research the relation between the compressed geomagnetic field and the subsolar distance. Here we also find that the compressed geomagnetic field varies with the subsolar distance in a power law of -2.6 (-1.9) on the Northward (Southward) IMF, which is different from that estimated from the dipole magnetic field (-3.0). Furthermore, this relation can be turned into a function of the compressed geomagnetic field in terms of the subsolar distance.
