Coronal magnetic fields from microwave polarization observations     

C. E. Alissandrakis  F. Borgioli  F. Chiuderi Drago  M. Hagyard  K. Shibasaki 《Solar physics》1996,167(1-2):167-179

The solar active region (AR) 7530 was observed at 6 cm on July 3 and 4, 1993 with the Westerbork Synthesis Radio Telescope, using a multi-channel receiver with very narrow bandwidth. We compare the radio data with Yohkoh SXT observations and with the magnetic field extrapolated from the Marshall vector magnetograms in the force-free and current-free approximations. The comparison with soft X-rays shows that, although a general agreement exists between the shape of the radio intensity map and the X-ray loops, the brightness temperature, T _b, obtained using the parameters derived from the SXT is much lower than that observed. The comparison with the extrapolated photospheric fields shows instead that they account very well for the observed T _b above the main sunspots, if gyroresonance emission is assumed. In the observation of July 4 an inversion and strong suppression of the circular polarization was clearly present above different portions of the AR, which indicates that particular relationships exist between the electron density and the magnetic field in the region where the corresponding lines of sight cross the field quasi-perpendicularly. The extrapolated magnetic field at a much higher level ( 10¹⁰ cm), satisfies the constraints required by the wave propagation theory all over the AR. However, a rather low electron density is derived.  相似文献   

Nonlinear wave coupling in type IV solar radio bursts     

Claudio Chiuderi  Riccardo Giachetti  Hans Rosenberg 《Solar physics》1973,33(1):225-238

In order to explain a fine structure of parallel ridges in stationary type IV continua, the emission due to the coupling of electrostatic upper hybrid waves and Bernstein waves at the sum frequency of the upper hybrid and harmonics of the gyro frequency has been calculated. If the energy density of these electrostatic waves is of the order of 10^-3 times the thermal energy density, then the observed zebra pattern can be emitted by a region with a diameter of 10³ km.  相似文献   

Energy balance in the prominence-corona transition region     

C. Chiuderi  F. Chiuderi Drago 《Solar physics》1991,132(1):81-94

The prominence-corona transition region can be observed both at UV and radio wavelengths. The physical parameters needed to explain one set of observations are, however, in disagreement with those consistent with the other one. A solution of the problem is proposed, based on the proper consideration of the dependence of the thermal conduction on the angle between the magnetic field and the direction of the local temperature gradient.  相似文献   

Current confinement in solar coronal loops     

Claudio Chiuderi  Giorgio Einaudi 《Solar physics》1981,73(1):89-103

In this paper solar coronal loops are regarded as regions of localized current flows. The main purpose is to investigate the consequences of current confinement rather than to produce a model. The physical and observational basis for this assumption are presented as well as the connection with previous studies on loop structure. A proper choice of the current profile allows us to treat quantitatively the equilibrium structure of the loops and their MHD and resistive stability properties. Regions of absolute stability against ideal kink modes are found. Explicit growth rates for the tearing-mode instability are computed. The possible relevance of other resistive effects is also discussed and the crucial importance of the small-scale geometry of the magnetic field outlined.  相似文献   

Neutrino reactions in strong magnetic field     

V. Canuto  C. Chiuderi  C. K. Chou  L. Fassio-Canuto 《Astrophysics and Space Science》1974,28(1):145-161

We present the energy losses due to several neutrinos processes: (1) synchrotron neutrinos, (2) pair annihilation neutrinos, (3) plasmon neutrinos, and (4) photoneutrinos in the presence of a superstrong magnetic field. Numerical results are tabulated and illustrated for several values of densities and temperatures. In the low density regime (10⁷ g cm^–3) the presence of a magnetic field decreases the luminosity, whereas the opposite is true at higher densities. This last effect is however almost entirely due to the existence of a new process the synchrotron neutrinos that disappear whenH0. Even though the overall effect can only be quantitatively ascertain after a complete cooling computation is performed, one should however expect a much lower temperature for neutron star surface than the one computed in theH=0 case.  相似文献   

Brightness distribution at λ = 3 and 21 cm near the solar north pole     

Chiuderi Drago  Franca  Patriarchi  Patrizio 《Solar physics》1974,37(2):403-408

The brightness distribution of the Sun near the north pole at = 3 and 21 cm is obtained using the results of the partial eclipse of February 25, 1971. The solution obtained by expanding B (r) in orthogonal polynomials does not show any brightening at either frequency, but a sensible darkening. If this result is explained by the presence of spicules, the coronal emission must be negligible with respect to the emission coming from the transition region. This is possible, at = 21 cm, only if we assume the presence of a coronal hole near the pole.  相似文献   

On the radio optical depth of the layer where the temperature equals the brightness temperature     

Franca Chiuderi Drago 《Solar physics》1972,27(1):132-136

It is usually believed that the radio optical depth of the layer h* where the temperature equals the brightness temperature is independent of the frequency. This assumption is criticized from the theoretical point of view and the behaviour of (h*) as a function of the frequency v is computed for two different solar models.  相似文献   

Plasmon neutrinos emission in a strong magnetic field     

V. Canuto  C. Chiuderi  C. K. Chou 《Astrophysics and Space Science》1970,9(3):453-460

The decay of a longitudinal plasmon into two neutrinos is studied in the presence of a strong magnetic field. Contrary to the transverse case, for longitudinal plasmons the existence of a new mode, entirely dependent on the magnetic field, greatly enhances the energy loss at high densities. Denoting byQ _HandQ ₀the neutrino energy losses with and without magnetic field respectively, the situation is as follows: atH10¹¹ G andT10⁹K,Q ₀10⁵ Q _Hfor <10¹¹g cm^–3, WhileQ _H10¹⁰ Q ₀for >10¹¹g cm^–3. A second physically interesting feature is the anisotropic character of the energy loss which is highly peaked along the field lines, giving rise to a shorter cooling time in that direction than in any other.  相似文献   

σ-Coordinates hydrodynamic numerical model for coastal and ocean three-dimensional circulation     

M. Drago  L. Iovenitti 《Ocean Engineering》2000,27(10):607

A three-dimensional finite-difference hydrodynamic model has been developed using σ-coordinate for the vertical dimension. An explicit scheme for temporal integration and a staggered grid for spatial discretization have been adopted. The model has been tested against analytical or literature cases for wind and tide induced circulation. Results are in good agreement both with analytical solutions under idealised conditions and with results from the model of Shankar et al. (1996).  相似文献   

Quiescent radio emission of RS CVn binary systems     

F. Chiuderi Drago  K. -L. Klein 《Astrophysics and Space Science》1990,170(1-2):81-84

It is shown that the quiescent radio emission observed in some RS Vc binary systems cannot be ascribed to the same thermal electrons population responsible for the X-ray emission. An alternative explanation to account for the observed correlation between X-ray and radio luminosity is suggested.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.  相似文献