Physics and Chemistry of the Earth, Part C: Solar, Terrestrial & Planetary Science最新文献

Satellite observations of plasma waves are often analyzed within linear theory of an infinite, homogeneous and magnetized plasma. Important aspects of wave propagation, such as dispersion and polarization, can then be analyzed. However, even for this simplified plasma model, the structure of the eigenmodes is sometimes complex. For instance, several wave modes with different polarization may be allowed at the same frequency. One way of distinguishing between wave modes in real data is by using the polarization information contained in observed frequency spectra to reconstruct the energy density in wave vector space, also called the wave distribution function (WDF). The purpose of this presentation is to show how WDF analysis can be used for identifying wave modes in a case with two overlapping wave modes, and to compare the results obtained with two independently developed methods for reconstructing the WDF. For this purpose Freja observations of waves around the local proton gyrofrequency are analyzed.

Absorption of solar radiation of wavelengths between 175 to 205 nm plays a fundamental role in the photochemistry of the middle atmosphere. Nitric oxide photodissociates in the δ(0-0) and δ(1-0) bands near 191 and 183 nm, respectively, initiating the primary mechanisms for NO_x removal in the middle atmosphere. The spectrally rich Schumann-Runge (S-R) bands of O₂ are the main source of atmospheric opacity at these wavelengths. A re-evaluation of O₂ absorption has been made based on recent advances in understanding of S-R line shapes, leading to differences with conventional approaches assuming Voigt line profiles in line-by-line calculations of the O₂ cross section. The new results are used to examine the impact of O₂ transmission on the photodissociation of NO in the δ(0,0) and δ(1,0) bands.

The application of correlation technique for automatic scaling of ionograms is presented. A method of automatic scaling of critical frequency f₀F2 and MUF(3000) is shown. The ionograms are considered as digital images and the detection process of the traces is performed without using information on polarization. For this reason the method can be applied to ionogram recorded by single antenna systems.

High spatial and temporal resolution observations of auroral forms made by the University of Calgary Portable Auroral Imager are reviewed. Observations include auroral forms with apparent widths of on the order of tens to hundreds of meters and lifetimes of less than a second to several tens of seconds. Included here is a class of multiple auroral arc systems exhibiting a strikingly asymmetric internal topology. It is shown that such systems of multiple linear arcs may be explained by mode conversion of field-line resonance shear Alfvén waves to inertial Alfvén waves. A survey of small-scale, short-lived auroral vortices (curls) occurring on thin auroral forms within the active aurora has also been performed, with some results being reviewed here. The Kelvin-Helmholtz instability as a responsible mechanism is discussed in light of the observationally acquired statistical data. Observations of small-scale “black” auroral arcs and vortices are briefly reviewed as well.

Instantaneous mapping methods for hourly observations were developed within the COST 251 European Action. The hourly maps of foF2 for eclipse day are available on the web page http://www.cbk.waw.pl/rwc/idce.html of the Ionospheric Despatch Centre in Europe. However, the eclipse effect on the ionosphere requires more frequent time scale for the observations than 1 hour. This paper presents the results of maps of foF2, foF1, foE with the use of 5-minute measurements during the eclipse of 11 August 1999. The instantaneous maps are shown be a useful tool to study the effect of the solar eclipse upon the ionosphere.

Shear Alfvén wave dispersion produced by electron inertia, ion gyro-kinetic and electron thermal pressure is modeled using two-fluid MHD and kinetic theory. In a dipolar magnetosphere, dispersion and non-linearity determine the spatial structure, temporal evolution and amplitude of parallel electric fields and large amplitude density fluctuations near to the polar ionosphere. Deep auroral density cavities are found to have a strong influence on auroral electric field generation. Many features of satellite and ground based observations of discrete arcs are predicted using two-fluid MHD, but large parallel electric fields (mV/m) and keV electron precipitation cannot easily be explained. To explain the observed electric fields it is necessary to evaluate the non-local kinetic electron response to standing shear Alfvén waves on dipolar magnetic field lines. It is shown that electron trapping leads to a significant reduction of the collisionless electron conductivity and a large enhancement of parallel electric fields in the 1 – 4 mHz frequency range of observed field line resonances.