No abstract

Interplanetary shock parameters are analyzed for solar maximum (year 2000) and solar minimum (years 1995-1996) activity. Fast forward shocks are the most usual type of shock observed in the interplanetary medium near Earth's orbit, and they are 88% of the identified shocks in 2000 and 60% in 1995-1996. Average plasma and magnetic field parameters for upstream and downstream sides of the shocks were calculated, and the parameter variations through the shock were determined. Applications of the Rankine-Hugoniot equations were made, obtaining shock speeds and Alfvenic Mach number. Static and dynamic pressures variations through the shocks were also calculated. Every parameter have larger variation through the shock in solar maximum than in solar minimum, with exception of the proton density. The intensity of shocks relative to the interplanetary medium, quantified by the Alfvenic Mach Number, is observed to be similar in solar maximum and minimum. It could be explained because, during solar maximum, in despite of the higher shock speeds, the Alfvenic speed of the interplanetary medium is higher than in solar minimum. I IntroductionThe interplanetary medium has a very low particle density, of about 5 Ñ ¿ , and it has a collisional mean free path of about 1 Astronomical Unit(AU) or ½ ½¼ Ñ[1]. Thus the occurrence of particle collisions is very sporadic. However, the interplanetary space is transiently disturbed by collisionless shock waves. In these shocks, the role that particle collisions make in ordinary shocks, is performed by long range Coulombian forces [1][2][3][4]. These Coulombian forces can have this very important role because the interplanetary medium is ceaseless permeated by the solar wind, a plasma resulting of the solar corona expansion and that carries with it the solar magnetic field through the solar system [1,5] Shock waves detected near the Earth's orbit, 1 AU, are mainly caused by interplanetary remnants of solar ejecta, although some types of shocks could be generated by interaction regions between slow and high speed solar wind streams [5]. Solar ejecta are coronal material expelled from the Sun, the coronal mass ejections [1,6-10] which propagate through the interplanetary medium. A shock occurs when the relative speed between a high speed stream and the background solar wind is higher than the characteristic speed of the medium (Alfvenic, magnetossonic) [1,2,3,5].Interplanetary structures can be geoeffective, causing magnetic storms, especially if an intense and long duration southward component of the magnetic field is present [6,11,12]. Because shock waves have a larger spatial extent than the interplanetary structures, it is usual that spacecrafts near Earth's orbit measure only the shock. However, the shock itself can have geoeffective effects, especially sudden impulses -increase in the H component of the geomagnetic field observed in low and mid latitudes stations, due to the intensification of Chapman-Ferraro current in the magnetopause, and magnetohydrodynamics waves and micropulsat...

No abstract

In this work we apply the wavelet transform to the Pelotas (southern Brazil) total annual rainfall series . Classical, wavelet and cross-wavelet analyses were performed in the El Niño Southern Oscillation (ENSO), Quasi-Biennial Oscillation (QBO), sunspot number (Rz) and Pelotas rainfall time series. Classical spectral analysis for Pelotas has shown a large number of short periods -between 2.2-5.6 years (yr) and periods at 8.9, 11.7 and 24.9 yr. Further, we have found that the Pelotas rainfall wavelet spectrum shows the most significant periodicities around 2-8 yr, but they have an intermittent character. Cross-wavelet spectrum showed that: rainfall and QBO series are correlated at 2-3 yr (QBO) scales and this cross-power is continuous along the time series interval; rainfall and SOI have higher cross-power around 4-8 yr, but this signal is sporadic; rainfall and sunspot number (Rz) showed higher cross-power around the 11-yr solar cycle period, but this crosspower is sporadically high and low; finally, the rainfall cross-spectrum with the double sunspot number (Rz22) revealed a high cross-power around 20-22 yr which is more persistent in duration, compared to the 11-yr period. These wavelet results are compared with classical spectral analysis and with previous work results. We concluded that the phenomenon that influences most of Pelotas rainfall variability is ENSO, but only a minor part of the variance (∼30%) can be described by a simple multi-linear dependence on solar/ ENSO/QBO phenomena, this result could imply that non-linear coupling among sun and internal climatic variability (QBO, ENSO) has an important role in the local/regional climate variations.

No abstract