P. Francia

Geomagnetic response at low latitude to continuous solar wind pressure variations during northward interplanetary magnetic field

A study of the geomagnetic field response to a series of continuous solar wind pressure variations has been performed at a low-latitude station during interplanetary events characterized by stable northward magnetic field conditions. The geomagnetic field H component responds well to the solar wind pressure changes on a timescale of few minutes. The amplitude of the geomagnetic field response is found to depend on local time, showing greater values around local noon and midnight.

Geomagnetic field variations at low and high latitude during the January 10–11, 1997 magnetic cloud

On Jan. 10–11, 1997 a wide magnetic cloud reached the Earth triggering intense geomagnetic activity. Observations performed at low and very high latitude show that the same features appear simultaneously in correspondence to different changes in the solar wind conditions. In particular, highly polarized modes are simultaneously observed at the same discrete frequencies after the passage of the high density solar wind region following the cloud. SIs and ULF waves polarization are also examined in a wide latitudinal and longitudinal extent.

Geomagnetic sudden impulses at low latitude during northward interplanetary magnetic field conditions

A statistical analysis of geomagnetic sudden impulses has been performed for data acquired at a low-latitude station during northward interplanetary magnetic field conditions. The local time dependence of the ground response, characterized by very low values in the morning with respect to the afternoon and night sectors and by a clear maximum just after local noon, is very similar to that observed at auroral latitudes, suggesting that signatures of auroral ionospheric currents might be observed also at low latitude. The sense of polarization of the sudden impulses shows a clear reversal from counterclockwise to clockwise a few hours after local noon, consistent with the results obtained for low-frequency geomagnetic fluctuations at the same station. In some cases a transient response (overshoot) is clearly observed; its amplitude is greater when the corrected Dst index is more negative, that is, when the ring current intensity is stronger; moreover, it tends to occur within 1-2 hours after the closest interplanetary magnetic field northward turning. These results seem to indicate that at our station overshoots characterize sudden impulses occurring a short time after periods with high magnetospheric activity. Since the local field line is embedded in the plasmasphere, the overshoot might tentatively be interpreted in terms of an overcompression of the plasmasphere which, after periods with high magnetospheric activity, is less dense and more elastic.

Signatures of the ULF geomagnetic activity in the surface air temperature in Antarctica

The variations of the Pc5 and Pc1-2 ULF power and surface air temperature measured at Terra Nova Bay in Antarctica have been analyzed during the late declining phase of solar cycle 23 (2007–2008), in comparison with the simultaneous variations of the solar wind speed. The analysis focused on time scales of several days, which characterize the evolution of the solar wind stream structure. The temperature variations appear clearly during the local winters, while they are strongly reduced in the sunlit summers. During the local winters, the Pc5 and Pc1-2 power and the temperature variations are significantly correlated, with the temperature delayed by a few days with respect to the ULF power. A time-frequency analysis revealed common signals in the temperature and ULF power at periodicities related to the Suns rotation period (~27, 13.5, and 9 days), which, in the same time intervals, characterize the solar wind speed and geomagnetic activity.

ULF geomagnetic and polar cap potential signatures in the temperature and zonal wind reanalysis data in Antarctica

In the present study we investigated the possible coupling between geomagnetic activity and the low atmosphere dynamics in the polar cap. We compared daily values of the ERA-Interim temperature and zonal wind over Antarctica, with the daily geomagnetic ULF power, in the Pc5 (1–7 mHz), Pc1, and Pc2 (100 mHz–1 Hz) frequency ranges, at Terra Nova Bay (Antarctica, corrected geomagnetic latitude λ ~ 80°S) and with solar wind data during 2007, in correspondence to the last declining phase of the solar cycle 23. We found a high and statistically significant correspondence of temperature and zonal wind fluctuations in the stratosphere and troposphere with geomagnetic ULF power fluctuations at the ~27 day periodicity, with a substantial reduction at the tropopause height. A similar, clear relationship between the meteorological parameters and the polar cap potential difference was also observed. The results suggest that the changes in the atmospheric conductivity, due to energetic electrons precipitation driven by the ULF waves, as well as the high latitude potential variations, both associated to high geomagnetic activity, can affect the atmospheric dynamics.

Recurrent flares in active region NOAA 11283

The authors wish to thank the referee for his/her very useful comments and suggestions, which led to a sounder version of the article. This research work has received funding from the European Commissions Seventh Framework Programme under the grant agreements No. 284461 (eHEROES project), No. 312495 (SOLARNET project), No. 606862 (F-Chroma project). This research work is partly supported by the Italian MIUR-PRIN grant 2012P2HRCR on The active Sun and its effects on Space and Earth climate and by Space Weather Italian COmmunity (SWICO) Research Program. The research by the KSU astronomy unit – A.E. and A.S.K. – was supported by King Saud University, Deanship of Scientific Research, College of Science Research Center.

Scaling characteristics of SEGMA magnetic field data around the Mw 6.3 Aquila earthquake

We apply detrended fluctuation analysis (DFA) on fluxgate and search-coil data in ULF range (scales 10–90 s or 0.1–0.011 Hz) for the months January–April 2009 available from the South European GeoMagnetic Array stations: Castello Tesino (CST), Ranchio (RNC), and L’Aquila (AQU) in Italy; Nagycenk (NCK) in Hungary; and Panagyuriste (PAG) in Bulgaria. DFA is a data processing method that allows for the detection of scaling behaviors in observational time series even in the presence of non-stationarities. The H and Z magnetic field components at night hours (00-03 UT, 01–04 LT) and their variations at the stations CST, AQU, NCK, and PAG have been examined and their scaling characteristics are analyzed depending on geomagnetic and local conditions. As expected, the scaling exponents are found to increase when the Kp index increases, indicating a good correlation with geomagnetic activity. The scaling exponent reveals also local changes (at L’Aquila), which include an increase for the Z (vertical) component, followed by a considerable decrease for the X (horizontal) component in the midst of February 2009. Attempts are made to explain this unique feature with artificial and/or natural sources including the enhanced earthquake activity in the months January–April 2009 at the L’Aquila district.

The propagation of ULF waves from the Earth's foreshock region to ground: the case study of 15 February 2009

A long-duration upstream ultralow frequency (ULF) wave event was detected on 15 February 2009 by Cluster satellites, close to the bow shock nose. A clear wave activity was identified when the interplanetary magnetic field orientation was favorable to the local generation. We examined the wave properties in both the solar wind and the spacecraft frame during a selected time interval and found that foreshock waves were essentially Alfven waves propagating at a small angle with respect to the interplanetary magnetic field. A comparison of Cluster observations with those on the ground, in the polar cap and at low-latitude stations, confirms the results of previous studies, indicating that upstream waves can reach different ground regions along different paths.

Some Aspects of the Low Latitude Geomagnetic Response under Different Solar Wind Conditions

We review some aspects of low latitudes (L≤2) geomagnetic field variations associated with magnetospheric pulsations as well as with continuous and impulsive variations of the solar wind (SW) pressure.

ULF geomagnetic activity effects on tropospheric temperature, specific humidity, and cloud cover in Antarctica, during 2003–2010

In the present study we investigated the possible relationship between the ULF geomagnetic activity and the variations of several atmospheric parameters. In particular, we compared the ULF activity in the Pc1-2 frequency band (100 mHz - 5 Hz), computed from geomagnetic field measurements at Terra Nova Bay in Antarctica, with the tropospheric temperature T, specific humidity Q and cloud cover (HCC, MCC and LCC) obtained from re-analysis dataset. The statistical analysis was conducted during the years 2003-2010, using correlation and Superposed Epoch Analysis approaches. The results show that the atmospheric parameters significantly change following the increase of geomagnetic activity within 2 days. These changes are evident in particular when the interplanetary magnetic field Bz component is oriented southward (Bz 0). We suggest that both the precipitation of electrons induced by Pc1-2 activity, and the intensification of the polar cap potential difference, modulating the microphysical processes in the clouds, can affect the atmosphere conditions.