4,813 research outputs found
Colombian Purchasing Power Parity Analysed Using a Framework of Multivariate Cointegration
This paper tests for purchasing power parity (PPP)between Colombia and its main trading partners using the Johansen framework of multivariate cointegration. The tests shows that PPP does not hold in the strong sense, but a clear purchasing power relationschip is, nevertheless, shown to exist. The model is, furthermore, shown to have significant forecasting power. It outperforms a random walk in out-of sample forecasting on the 12 and 24 month horizont but not on the 3 and 6-month horizon.
Magneto--Acoustic Energetics Study of the Seismically Active Flare of 15 February 2011
Multi--wavelength studies of energetic solar flares with seismic emissions
have revealed interesting common features between them. We studied the first
GOES X--class flare of the 24th solar cycle, as detected by the Solar Dynamics
Observatory (SDO). For context, seismic activity from this flare
(SOL2011-02-15T01:55-X2.2, in NOAA AR 11158) has been reported in the
literature (Kosovichev, 2011; Zharkov et al., 2011). Based on Dopplergram data
from the Helioseismic and Magnetic Imager (HMI), we applied standard methods of
local helioseismology in order to identify the seismic sources in this event.
RHESSI hard X-ray data are used to check the correlation between the location
of the seismic sources and the particle precipitation sites in during the
flare. Using HMI magnetogram data, the temporal profile of fluctuations in the
photospheric line-of-sight magnetic field is used to estimate the magnetic
field change in the region where the seismic signal was observed. This leads to
an estimate of the work done by the Lorentz-force transient on the photosphere
of the source region. In this instance this is found to be a significant
fraction of the acoustic energy in the attendant seismic emission, suggesting
that Lorentz forces can contribute significantly to the generation of
sunquakes. However, there are regions in which the signature of the
Lorentz-force is much stronger, but from which no significant acoustic emission
emanates.Comment: Submitted to Solar Physic
Magnetic field variations and the seismicity of solar active regions
Dynamical changes in the solar corona have proven to be very important in
inducing seismic waves into the photosphere. Different mechanisms for their
generation have been proposed. In this work, we explore the magnetic field
forces as plausible mechanisms to generate sunquakes as proposed by Hudson,
Fisher and Welsch. We present a spatial and temporal analysis of the
line-of-sight magnetic field variations induced by the seismically active 2003
October 29 and 2005 January 15 solar flares and compare these results with
other supporting observations.Comment: 4 pages, 4 figures, letter, Accepted in February by MNRA
Desequilibrios nominales y reales del tipo de cambio en Colombia
La estimaciĂłn de los desequilibrios nominales y reales del tipo de cambio(TC) en Colombia se construye a partir de dos componentes: el permanenteasociado con una tendencia estocástica (no estacionaria) y el transitoriovinculado con el ciclo (estacionario). La separaciĂłn entre lo permanente ylo transitorio se realiza a partir de las relaciones de largo plazo entre el TCnominal (real) y sus determinantes fundamentales. El nivel de equilibrio dela TC nominal (real) se obtiene como el componente permanente, segĂşn lametodologĂa de common trends", aplicada a la TC nominal y a susdeterminantes fundamentales, mientras que el componente transitorio secalcula por residuo y se asocia al desequilibrio. El ejercicio se lleva a cabopara diferentes frecuencias (anual y trimestral) y perĂodos de informaciĂłn y se usan variosmodelos de determinaciĂłn del TC nominal y real."tasa de cambio real, equilibrio de la tasa de cambio real.
A statistical correlation of sunquakes based on their seismic and white-light emission
Several mechanisms have been proposed to explain the transient seismic emission, i.e. “sunquakes,” from some solar flares. Some theories associate high-energy electrons and/or white-light emission with sunquakes. High-energy charged particles and their subsequent heating of the photosphere and/or chromosphere could induce acoustic waves in the solar interior. We carried out a correlative study of solar flares with emission in hard X-rays, enhanced continuum emission at 6173 Å, and transient seismic emission. We selected those flares observed by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) with a considerable flux above 50 keV between 1 January 2010 and 26 June 2014. We then used data from the Helioseismic and Magnetic Imager onboard the Solar Dynamic Observatory to search for excess visible-continuum emission and new sunquakes not previously reported. We found a total of 18 sunquakes out of 75 flares investigated. All of the sunquakes were associated with an enhancement of the visible continuum during the flare. Finally, we calculated a coefficient of correlation for a set of dichotomic variables related to these observations. We found a strong correlation between two of the standard helioseismic detection techniques, and between sunquakes and visible-continuum enhancements. We discuss the phenomenological connectivity between these physical quantities and the observational difficulties of detecting seismic signals and excess continuum radiation
Seismic Emissions from a Highly Impulsive M6.7 Solar Flare
On 10 March 2001 the active region NOAA 9368 produced an unusually impulsive
solar flare in close proximity to the solar limb. This flare has previously
been studied in great detail, with observations classifying it as a type 1
white-light flare with a very hard spectrum in hard X-rays. The flare was also
associated with a type II radio burst and coronal mass ejection. The flare
emission characteristics appeared to closely correspond with previous instances
of seismic emission from acoustically active flares. Using standard local
helioseismic methods, we identified the seismic signatures produced by the
flare that, to date, is the least energetic (in soft X-rays) of the flares
known to have generated a detectable acoustic transient. Holographic analysis
of the flare shows a compact acoustic source strongly correlated with the
impulsive hard X-ray, visible continuum, and radio emission. Time-distance
diagrams of the seismic waves emanating from the flare region also show faint
signatures, mainly in the eastern sector of the active region. The strong
spatial coincidence between the seismic source and the impulsive visible
continuum emission reinforces the theory that a substantial component of the
seismic emission seen is a result of sudden heating of the low photosphere
associated with the observed visible continuum emission. Furthermore, the
low-altitude magnetic loop structure inferred from potential--field
extrapolations in the flaring region suggests that there is a significant
inverse correlation between the seismicity of a flare and the height of the
magnetic loops that conduct the particle beams from the corona.Comment: 16 pages, 7 figures, Solar Physics Topical Issue: SOHO 19/GONG 2007
"Seismology of Magnetic Activity", Accepte
- …