Abstract
Abstract The dependence of the storm-time amplitude on longitude and latitude was analyzed by statistically investigating great magnetic storms observed at different observatories. First, we compared the storm-time ranges observed at Beijing Observatory (BJI) and San Juan Observatory (SJG) to reveal their longitudinal dependence. It was found that the difference between BJI and SJG could be fitted by the 4-order Fourier series approximation, and the storm-time H ranges at dawn were less than those at dusk. Second, we carried out a case study of two typical storms, and analyzed the focused local time when peak storm-time H ranges occurred. The results confirmed the above conclusion. Third, a statistical study was conducted for all magnetic storms observed at the 120°E magnetic chain in eastern China for 1995–2004 to reveal the latitudinal dependence of storm-time ranges. It was found the relationship depended on the activity of analyzed storms and became complicated for giant storms with Dst ≤ −300 nT.
Highlights
A magnetic storm is a global geomagnetic field disturbance characterized by a distinct decrease in the horizontal (H ) component of the magnetic field at mid and low latitudes
The dependence of magnetic storms on local time and latitude is analyzed in this paper
Statistical analysis for 21 great storms with Dst ≤ −100 nT from 1998 to 2000 shows that the storm-time H amplitude was obviously different between Beijing Observatory (BJI) and SJG
Summary
A magnetic storm is a global geomagnetic field disturbance characterized by a distinct decrease in the horizontal (H ) component of the magnetic field at mid and low latitudes. The strength of a magnetic storm is usually measured by the Dst index, which is derived from hourly values of the H component of the geomagnetic field recorded at four low-latitude stations. The derivation of the Dst index is based on the assumption that the geomagnetic variation caused by the ring current is axially symmetrical and has no longitudinal/local time dependence. 2. Data Preparation The geomagnetic field disturbance recorded by a ground station depends on its location relative to the sun. Data Preparation The geomagnetic field disturbance recorded by a ground station depends on its location relative to the sun For those stations located at the same latitude, the dependence of the recorded storm-time amplitude on longitude is that on local time. It is important to choose stations located approximately at the same latitude to study the dependence of the storm-time H and D amplitudes on longitude.
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