Daily variation at three Antarctic geomagnetic observatories within the polar cap

Abstract

Abstract. In this work we present a statistical analysis of the diurnal variation as observed at three Antarctic observatories located at different positions within the polar cap during the year 2006. Data used for the analysis are from the Italian geomagnetic observatory at Mario Zucchelli Station (formerly Terra Nova Bay, geographic latitude 74.7 • S, corrected geomagnetic latitude 80.0 • S), from the French-Italian observatory at Concordia Station (75.1 • S, 88.9 • S) and from the French observatory at Dumont D'Urville (66.7 • S, 80.4 • S), which are located in pairs at the same geographic and corrected geomagnetic latitude; such a position allows to distinguish whether the geographic or the geomagnetic reference system is better suitable to describe the observed phenomena at so high latitudes. The peculiarities of the daily variation as observed during this year and its relation with the observatory location and magnetospheric and interplanetary conditions were analysed. Data were also studied taking into account different Lloyd seasons. The results indicate that the 24-h variation is quite persistent, but its amplitude strongly depends on season and global geomagnetic activity: indeed, it almost vanishes during local winter for quiet geomagnetic conditions; this reduction is more evident at the stations closer to the geographic pole, where the solar radiation reduction during winter is more dramatic. The Interplanetary Magnetic Field orientation has been found to be important in that the north-south and the east-west components control the amplitude and the diurnal pattern of the variation, respectively.

On the terms of geomagnetic daily variation in Antarctica

“…The difference between our results and those proposed by Pietrolungo et al (2008) is due to the different approach used in the data analysis. The superposed epoch analysis, which has been applied by Pietrolungo et al (2008) to reconstruct the average diurnal variation along X and Y components of the geomagnetic field, does not allow recognizing the different contributions of the ionospheric-magnetospheric current systems to the daily changes of the geomagnetic field.…”

“…Indeed, taking into account the relationship between LT and MLT at TNB geomagnetic observatory (LT=MLT+19), the φ 1 X is characterized by a minimum around 14:00 LT while the φ 1 Y function is characterized by negative values in the range 00:00<LT<14:00 with a minimum around LT=09:00 and by positive values in the range 14:00<LT<24:00 with a maximum around LT=18:30. Our patterns are consequently equal to those reported by Pietrolungo et al (2008). These patterns of the X and Y components might resemble the S 0 q current system at high latitude in the Southern Hemisphere.…”

“…These results, which are well in agreement with the current systems present at high latitude, show some differences with respect to the results recently presented by Pietrolungo et al (2008). Indeed, the authors, using data coming from three different geomagnetic observatories all located within the Antarctic polar cap, have suggested that the contribution of the S p q polar electric current systems to the diurnal variation is not relevant and that the mid latitude ionospheric currents are the main source of the daily variation also at high latitudes, at least during a period of solar minimum.…”

“…The superposed epoch analysis, which has been applied by Pietrolungo et al (2008) to reconstruct the average diurnal variation along X and Y components of the geomagnetic field, does not allow recognizing the different contributions of the ionospheric-magnetospheric current systems to the daily changes of the geomagnetic field. This method, indeed, gives only an average trend of daily variation where the different contributions are contained all together.…”

“…For this reason, to compare our results with those obtained using different methods of analysis, it is important to use the same reference system. TNB geomagnetic observatory is generally located inside the polar cap quite close to the auroral oval but, under particular geomagnetic conditions and for a particular range of MLTs, it may be placed under the southern polar cups (Pietrolungo et al, 2008) and thus the geomagnetic variations in this condition may be heavily influenced by local cusp phenomena, mainly related to field aligned currents (Matsushita and Xu, 1982;Campbell, 1997). The structure of the geomagnetic daily variation is consequently quite complex in this part of the world and the use of the Natural Orthogonal Component analysis (Jackson et al, 1991;Golovkov et al, 1992;Xu and Kamide, 2004) can be a tool extremely useful to reveal simple patterns within it.…”