1,445 research outputs found
A Carrington-like geomagnetic storm observed in the 21st century
In September 1859 the Colaba observatory measured the most extreme
geomagnetic disturbance ever recorded at low latitudes related to solar
activity: the Carrington storm. This paper describes a geomagnetic disturbance
case with a profile extraordinarily similar to the disturbance of the
Carrington event at Colaba: the event on 29 October 2003 at Tihany magnetic
observatory in Hungary. The analysis of the H-field at different locations
during the "Carrington-like" event leads to a re-interpretation of the 1859
event. The major conclusions of the paper are the following: (a) the global Dst
or SYM-H, as indices based on averaging, missed the largest geomagnetic
disturbance in the 29 October 2003 event and might have missed the 1859
disturbance, since the large spike in the horizontal component (H) of
terrestrial magnetic field depends strongly on magnetic local time (MLT); (b)
the main cause of the large drop in H recorded at Colaba during the Carrington
storm was not the ring current but field-aligned currents (FACs), and (c) the
very local signatures of the H-spike imply that a Carrington-like event can
occur more often than expected.Comment: 18 pages, 2 figures, accepted for publication in SWS
Supergranular-scale magnetic flux emergence beneath an unstable filament
Here we report evidence of a large solar filament eruption on 2013, September
29. This smooth eruption, which passed without any previous flare, formed after
a two-ribbon flare and a coronal mass ejection towards Earth. The coronal mass
ejection generated a moderate geomagnetic storm on 2013, October 2 with very
serious localized effects. The whole event passed unnoticed to flare-warning
systems.
We have conducted multi-wavelength analyses of the Solar Dynamics Observatory
through Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager
(HMI) data. The AIA data on 304, 193, 211, and 94 \AA sample the transition
region and the corona, respectively, while HMI provides photospheric
magnetograms, continuum, and linear polarization data, in addition to the fully
inverted data provided by HMI.
[...]
We have observed a supergranular-sized emergence close to a large filament in
the boundary of the active region NOAA11850. Filament dynamics and magnetogram
results suggest that the magnetic flux emergence takes place in the
photospheric level below the filament. Reconnection occurs underneath the
filament between the dipped lines that support the filament and the
supergranular emergence. The very smooth ascent is probably caused by this
emergence and torus instability may play a fundamental role, which is helped by
the emergence.Comment: 9 pages, 6 figures, online material at Journa
Pietra di Langa. ContinuitĂ e discontinuitĂ nelle culture costruttive e nel paesaggio
La pietra come ruolo storico e potenzialitĂ di innovazione e costruzione nell'attenzione alle culture del territorio della Lang
An investigation of customer order flow in the foreign exchange market
This paper examines the effect that heterogeneous customer orders flows have on exchange rates by using a new, and the largest, proprietary dataset of weekly net order flow segmented by customer type across nine of the most liquid currency pairs. We make several contributions. Firstly, we investigate the extent to which customer order flow can help to explain exchange rate movements over and above the influence of macro-economic variables. Secondly, we address the issue of whether order flows contain (private) information which explain exchange rates changes. Thirdly, we look at the usefulness of order flow in forecasting exchange rate movements at longer horizons than those generally considered in the micro-structure literature. Finally we address the question of whether the out-of-sample exchange rate forecasts generated by order flows can be employed profitably in the foreign exchange markets
Changes in Structural, Morphological and Optical Features of Differently Synthetized C3N4-ZnO Heterostructures: An Experimental Approach
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