Theoretical models for MHD turbulence in the solar wind

The in situ measurements of velocity, magnetic field, density and temperature fluctuations performed in the solar wind have greatly improved our knowledge of MHD turbulence not only from the point of view of space physics but also from the more general point of view of plasma physics. These fluctuations which extend over a wide range of frequencies (about 5 decades), a fact which seems to be the signature of turbulent nonlinear energy cascade, display, mainly in the trailing edge of high-speed streams, a number of features characteristic of a self-organized situation: i) a high degree of correlation between magnetic and velocity field fluctuations, ii) a very low level of fluctuations in mass density and magnetic-field intensity, iii) a considerable anisotropy revealed by minimum variance analysis of the magnetic-field correlation tensor. Many fundamental processes in plasma physics, which were largely unknown or not understood before their observations in the solar wind, have been explained, by building up analytical models or performing numerical simulations. We discuss the most recent analytical theories and numerical simulations and outline the limits implicit in any analysis which consider the low-frequency solar-wind fluctuations as a superposition of linear modes. The characterization of low-frequency fluctuations during Alfv´enic periods, which results from the models discussed, is finally presented

Nonlinear evolution of the parametric instability: numerical predictions versus observations in the heliosphere

International audienceLow-frequency turbulence in the solar wind is characterized by a high degree of Alfvénicity close to the Sun. Cross-helicity, which is a measure of Alfvénic correlation, tends to decrease with increasing distance from the Sun at high latitudes as well as in slow-speed streams at low latitudes. In the latter case, large scale inhomogeneities (velocity shears, the heliospheric current sheet) are present, which are sources of decorrelation; yet at high latitudes, the wind is much more homogeneous, and a possible evolution mechanism is represented by the parametric instability. The parametric decay of an circularly polarized broadband Alfvén wave is then investigated, as a source of decorrelation. The time evolution is followed by numerically integrating the full set of nonlinear MHD equations, up to instability saturation. We find that, for ~ 1, the final cross-helicity is ~ 0.5, corresponding to a partial depletion of the initial correlation. Compressive fluctuations at a moderate level are also present. Most of the spectrum is dominated by forward propagating Alfvénic fluctuations, while backscattered fluctuations dominate large scales. With increasing time, the spectra of Elsässer variables tend to approach each other. Some results concerning quantities measured in the high-latitude wind are reviewed, and a qualitative agreement with the results of the numerical model is found

Dissipation of Alfven waves in compressible inhomogeneous media

In weakly dissipative media governed by the magnetohydrodynamics (MHD) equations, any efficient mechanism of energy dissipation requires the formation of small scales. Using numerical simulations, we study the properties of Alfv´en waves propagating in a compressible inhomegeneous medium, with an inhomogeneity transverse to the direction of wave propagation. Two dynamical effects, energy pinching and phase mixing, are responsible for the small-scales formation, similarly to the incompressible case. Moreover, compressive perturbations, slow waves and a static entropy wave are generated; the former are subject to steepening and form shock waves, which efficiently dissipate their energy, regardless of the Reynolds number. Rough estimates show that the dissipation times are consistent with those required to dissipate Alfv´en waves of photospheric origin inside the solar corona

On the probability distribution function of small scale interplanetary magnetic field fluctuations

In spite of a large number of papers dedicated to study MHD turbulence in the solar wind there are still some simple questions which have never been sufficiently addressed like: a)do we really know how the magnetic field vector orientation fluctuates in space? b) what is the statistics followed by the orientation of the vector itself? c) does the statistics change as the wind expands into the interplanetary space? A better understanding of these points can help us to better characterize the nature of interplanetary fluctuations and can provide useful hints to investigators who try to numerically simulate MHD turbulence. This work follows a recent paper presented by the same authors. This work follows a recent paper presented by some of the authors which shows that these fluctuations might resemble a sort of random walk governed by a Truncated Leevy Flight statistics. However, the limited statistics used in that paper did not allow final conclusions but only speculative hypotheses. In this work we aim to address the same problem using a more robust statistics which on one hand forces us not to consider velocity fluctuations but, on the other hand allows us to establish the nature of the governing statistics of magnetic fluctuations with more confidence. In addition, we show how features similar to those found in the present statistical analysis for the fast speed streams of solar wind, are qualitatively recovered in numerical simulations of the parametric instability. This might offer an alternative viewpoint for interpreting the questions raised above.Comment: 25pag, 20 jpg small size figures. In press on "ANnales Geophysicae" (September 2004

Absolute frequency measurement of molecular transitions by a direct link to a comb generated around 3-µm

A 3-microm continuous-wave difference-frequency source is directly referenced to a mid-infrared optical frequency comb synthesizer by measuring their beat-note signal by a fast HgCdTe detector. Absolute frequency metrology of molecular vibration spectra is demonstrated by locking the 3-microm coherent radiation to the nearest comb tooth and tuning the comb mode spacing across the Doppler-broadened absorption profile of a CH(4) ro-vibrational transition

Hubungan Karakteristik Pemilik Anjing Dengan Upaya Pencegahan Rabies Di Puskesmas Tobelo Kabupaten Halmahera Utara

: Rabies is a viral disease of the nervous system that could attack all type of warm-blooded animals ( especially dogs), and humans. Character is a personality that's affected by motivation, which induces need to execute something. The prevention of rabies not only depends on animal problems, but also human problems. The success of rabies termination depends on the level of understanding about the rabies disease and awareness of the society. Objective to analyze the characteristic relationship between dog owner and the effort of rabies prevention in Puskesmas Tobelo, region of South Halmahera. Research Design : descriptive analytical by using approach of cross sectional and sampling technic usingpurposive sampling with total of50 samples. Results: Using chi-square test on Fisher exact with mean value α = 0.05 or 95 % and found value of P (age of dog owners 0.023, goal keeping dogs 0,000, breed of dog 0,005 and the origin of the dog 0,000). ConclusionThere are characteristic relationship between dog owner and the effort of rabies prevention in Tobelo Puskesmas, region of South Halmahera. Advice : Give more motivation to the dog owner in preventing rabies

Hubungan Konflik Peran Ganda Perawat Wanita Sebagai Care Giver Dengan Stres Kerja Di Ruangan Rawat Inap Rumah Sakit Jiwa Prof. Dr.v. L. Ratumbuysang Provinsi Sulawesi Utara

: conflict dual role of nurses a form is work-family conflict. In women who work them faced with many choices posed by the changing role that also have a role as a woman who must work to support the family finances, which carried the dual role as a nurse in the ward nursing care giver often lead to conflict. The research objective is to identify the conflict of dual role in female nurses as care giver, Work stress on the nurses, and the dual role of relationship conflict and work stress on female nurses in Psychiatric Hospital Prof. Dr. V. L. Ratumbuysang North Sulawesi province. The research design was observational Analytical, using cross sectional approach. The sampling technique used purposive sampling, with a sample of 44 nurses. The results using the Fisher exact test found significant value is 0,001 with 1,800 eustress opportunities. Conclusions The results showed no relationship conflicts dual role as a care giver female nurses with work stress in Psychiatric Hospital Prof. Dr. V. L. Ratumbuysang. Suggestion The result is expected to be split between the nurse's work problems with family problems by not bringing work home problems and also did not bring up problems at home into the workplace

Intermittency in MHD turbulence and coronal nanoflares modelling

High resolution numerical simulations, solar wind data analysis, and measurements at the edges of laboratory plasma devices have allowed for a huge progress in our understanding of MHD turbulence. The high resolution of solar wind measurements has allowed to characterize the intermittency observed at small scales. We are now able to set up a consistent and convincing view of the main properties of MHD turbulence, which in turn constitutes an extremely efficient tool in understanding the behaviour of turbulent plasmas, like those in solar corona, where in situ observations are not available. Using this knowledge a model to describe injection, due to foot-point motions, storage and dissipation of MHD turbulence in coronal loops, is built where we assume strong longitudinal magnetic field, low beta and high aspect ratio, which allows us to use the set of reduced MHD equations (RMHD). The model is based on a shell technique in the wave vector space orthogonal to the strong magnetic field, while the dependence on the longitudinal coordinate is preserved. Numerical simulations show that injected energy is efficiently stored in the loop where a significant level of magnetic and velocity fluctuations is obtained. Nonlinear interactions give rise to an energy cascade towards smaller scales where energy is dissipated in an intermittent fashion. Due to the strong longitudinal magnetic field, dissipative structures propagate along the loop, with the typical speed of the Alfvén waves. The statistical analysis on the intermittent dissipative events compares well with all observed properties of nanoflare emission statistics. Moreover the recent observations of non thermal velocity measurements during flare occurrence are well described by the numerical results of the simulation model. All these results naturally emerge from the model dynamical evolution without any need of an ad-hoc hypothesis