Comparing the diurnal variations in the SuperMAG auroral electrojet indices SML and SMU
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Diurnal variations of the SuperMAG auroral electrojet indices (SML and SMU) were examined for the period of 1980–2010, and the differences between SML and SMU were especially analyzed. The diurnal variation of SML with a maximum at around 1100 UT has a prenoon-postnoon asymmetry. At solstices, the diurnal variation of SML is much stronger than that at equinoxes. For the SMU, two maxima are recorded in the diurnal variation with the bigger one at 1700 UT and the smaller one at 0400 UT. The seasonal variations are not obvious in the UT variation characteristics of SMU although the intensity of SMU is changed remarkably season by season. For both SML and SMU, the contributing stations are located at higher geomagnetic latitude around 1600 UT and at lower geomagnetic latitude around 0400 UT. These results indicate that: (1) the SML is mostly controlled by the convection electric field. Its diurnal variation is mainly correlated with the equinoctial and R-M hypothesis; (2) the SMU is largely controlled by the ionospheric conductance. Its diurnal variation is tightly correlated with the solar radiation.
KeywordsAuroral electrojet SuperMAG Diurnal variation SML index SMU index
This work was supported by the National Basic Research Program of China (2014CB845903, 2011CB811404), the National Natural Science Foundation of China (41104110), the Ocean Public Welfare Scientific Research Project, State Oceanic Administration, China (201005017), and the Program of Chinese Academy of Sciences (ZDYZ2012-1).
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