Study of the diurnal variation at high latitudes and of its dependence on the conditions of the Interplanetary Magnetic Field
3 July 2008, 14.30 pm | Manuela Pietrolungo | Conference Room Rome | Headquarters | Young researchers seminars Section Rome 2
We carried out a statistical analysis of the diurnal variation examined at Observatories located at high latitudes in positions different from the polar cap considering the different seasons of Lloyd and the different conditions of the Interplanetary Magnetic Field (IMF).
The diurnal variation (24-hour period and its harmonics) is generated in the polar cap by two different systems of electric currents: Sq° (extrapolation of the Sq at medium latitude driven by the ionospheric dynamo) and the Spq of polar cap, connected to field-aligned currents flowing along the geomagnetic field lines from the magnetosphere to the ionosphere. The S systempq it is generated by external sources related to processes in the magnetosphere and its interactions with the IMF. It is believed to be the primary source of diurnal variation at high latitudes, especially during the local winter when the ionospheric ionization of the polar cap, caused by solar radiation, is greatly reduced.
The analysis was carried out for the years 2005-2006 using data from the Italian-French Observatory of the Concordia Station (geographical latitude 75.1°S, corrected geomagnetic latitude 88.9°S) and showed the dependence of the diurnal variation on the components of the IMF bz and By (parallel to the axial dipole and along the east-west direction). In particular, certain conditions of Bz correspond to different contributions to the diurnal variation, while certain conditions of By produce a temporal displacement of the diurnal variation, indicating an asymmetry with respect to the midday meridian.
For the year 2006 the analysis was also extended to the Italian Mario Zucchelli Geomagnetic Observatory (previously Terra Nova Bay, geographic latitude 74.7°S, corrected geomagnetic latitude 80.0°S) and to the French Dumont D'Urville Observatory (66.7° S, 80.4°S), together with DMC. The three stations are located two by two at the same correct geographic and geomagnetic latitude; in this way a position allows to identify if the geographical or geomagnetic reference system is more suitable to describe the phenomenon observed at high latitudes. It has been found that the characteristics of the diurnal variation even at high latitudes essentially depend on the geographical coordinates (and therefore LT) of the stations within the polar cap, suggesting that mid-latitude ionospheric currents are the primary source for the diurnal variation. Furthermore, the 24-h variation has a characteristic pattern, but its amplitude strongly depends on the season, the global geomagnetic activity and the electric current system of the region. polar cap Spq.
The diurnal variation analysis was extended to three Canadian Arctic geomagnetic observatories: Resolute Bay (RES; 74.7°N, 83.0°N), Cambridge Bay (CBB; 62.2°N, 77.0°N) and Alert (ALE, 82.5°N). N,87.2°N). The results show that for the X component the diurnal variation is similar for all stations, while for the Y component it is inverse in the two hemispheres. Furthermore, the structure of the diurnal variation is completely different at CBB, which is the station at the lowest geomagnetic latitude, closest to the auroral oval.
In-depth articles:
Cafarella, L., D. Di Mauro, S. Lepidi, A. Meloni, M. Pietrolungo, L. Santarelli, and JJ Schott - Daily variation at Concordia station (Antarctica) and its dependence on IMF conditions, Annales Geophysicae, 25, 2045-2051, 2007.
Lepidi, S., L. Cafarella, P. Francia, A. Meloni, P. Palangio, and JJ Schott - Low frequency geomagnetic field variations at Dome C (Antarctic), Annales Geophysicae, 21, 923-932, 2003.
Vennerstrom, S., T. Moretto, L. Rastatter, and J. Raeder - Field-aligned currents during northward interplanetary magnetic field: Morphology and causes, Journal of Geophysical Research, 110, A06205, doi:10.1029/2004JA010802, 2005.
The diurnal variation (24-hour period and its harmonics) is generated in the polar cap by two different systems of electric currents: Sq° (extrapolation of the Sq at medium latitude driven by the ionospheric dynamo) and the Spq of polar cap, connected to field-aligned currents flowing along the geomagnetic field lines from the magnetosphere to the ionosphere. The S systempq it is generated by external sources related to processes in the magnetosphere and its interactions with the IMF. It is believed to be the primary source of diurnal variation at high latitudes, especially during the local winter when the ionospheric ionization of the polar cap, caused by solar radiation, is greatly reduced.
The analysis was carried out for the years 2005-2006 using data from the Italian-French Observatory of the Concordia Station (geographical latitude 75.1°S, corrected geomagnetic latitude 88.9°S) and showed the dependence of the diurnal variation on the components of the IMF bz and By (parallel to the axial dipole and along the east-west direction). In particular, certain conditions of Bz correspond to different contributions to the diurnal variation, while certain conditions of By produce a temporal displacement of the diurnal variation, indicating an asymmetry with respect to the midday meridian.
For the year 2006 the analysis was also extended to the Italian Mario Zucchelli Geomagnetic Observatory (previously Terra Nova Bay, geographic latitude 74.7°S, corrected geomagnetic latitude 80.0°S) and to the French Dumont D'Urville Observatory (66.7° S, 80.4°S), together with DMC. The three stations are located two by two at the same correct geographic and geomagnetic latitude; in this way a position allows to identify if the geographical or geomagnetic reference system is more suitable to describe the phenomenon observed at high latitudes. It has been found that the characteristics of the diurnal variation even at high latitudes essentially depend on the geographical coordinates (and therefore LT) of the stations within the polar cap, suggesting that mid-latitude ionospheric currents are the primary source for the diurnal variation. Furthermore, the 24-h variation has a characteristic pattern, but its amplitude strongly depends on the season, the global geomagnetic activity and the electric current system of the region. polar cap Spq.
The diurnal variation analysis was extended to three Canadian Arctic geomagnetic observatories: Resolute Bay (RES; 74.7°N, 83.0°N), Cambridge Bay (CBB; 62.2°N, 77.0°N) and Alert (ALE, 82.5°N). N,87.2°N). The results show that for the X component the diurnal variation is similar for all stations, while for the Y component it is inverse in the two hemispheres. Furthermore, the structure of the diurnal variation is completely different at CBB, which is the station at the lowest geomagnetic latitude, closest to the auroral oval.
In-depth articles:
Cafarella, L., D. Di Mauro, S. Lepidi, A. Meloni, M. Pietrolungo, L. Santarelli, and JJ Schott - Daily variation at Concordia station (Antarctica) and its dependence on IMF conditions, Annales Geophysicae, 25, 2045-2051, 2007.
Lepidi, S., L. Cafarella, P. Francia, A. Meloni, P. Palangio, and JJ Schott - Low frequency geomagnetic field variations at Dome C (Antarctic), Annales Geophysicae, 21, 923-932, 2003.
Vennerstrom, S., T. Moretto, L. Rastatter, and J. Raeder - Field-aligned currents during northward interplanetary magnetic field: Morphology and causes, Journal of Geophysical Research, 110, A06205, doi:10.1029/2004JA010802, 2005.