摘要:

The electromagnetic scattering properties of a medium bounded by a plane surface and whose (scalar) dielectric constant is the sum of a nonrandom part assumed to vary only with depth and a small random part are investigated by means of an approximate, first‐order perturbation method. It is shown that the equivalent dielectric constant to be used in calculating the average reflected power in the specular direction is a function of depth even in the case where the nonrandom part of the dielectric constant is independent of depth. Further, the equivalent dielectric constant is shown to be a tensor. Nonspecular scattering is also considere

ISSN:0048-6604    

DOI:10.1029/RS009i005p00509

年代:1974

数据来源: WILEY

摘要:

The continuity equation of electron density is solved for the conditions of theF2region at low latitude along 69°W meridian in the equinox of high solar activity. The transport term includes the electromagnetic drift observed at Jicamarca, the plasma diffusion, the vertical motion due to thermal expansion and contraction, and the neutral wind for which the direction reversal in the morning is rather late. The large‐scale irregularity which forms a bifurcatedF2layer is generated at the geomagnetic equator and travels as far as 15° latitude with a speed of about 10 km min−1. Other features of this bifurcation and the probable mechanism of its formation are described. The height of maximum electron density is strongly controlled by the electromagnetic drift at very low latitude from 0700 to midnight. The computation also shows that the large postsunset peak ofNmF2at a subtropical region is caused by the rapid sunset increase of upward drift at the equator. The late reversal of neutral wind favors the observed diurnal pattern ofNmF2. Other effects of neutral wind and that of loss rate on the low latitude ionosphere are disc

ISSN:0048-6604    

DOI:10.1029/RS009i005p00519

年代:1974

数据来源: WILEY

摘要:

A horizontal electric dipole antenna at the ground operating at ULF can excite hydromagnetic TE waves in the hydromagnetic waveguide centered at theF2ionization maximum. Propagation in the waveguide accompanied by leakage into the earth‐ionosphere cavity provides a mechanism by which magnetic fluctuations may be transmitted to ground receivers some thousands of kilometers from the transmitter. At ULF, the optimum direction for this mode of operation is broadside to the dipole. Under favorable ionospheric conditions, a dipole 30 km in length and driven at a peak current of 500 amp could produce a ground signal of the order of a milligamma at a distance of 2000 k

ISSN:0048-6604    

DOI:10.1029/RS009i005p00533

年代:1974

数据来源: WILEY

摘要:

Near‐field patterns of a short electric dipole antenna were measured in the magnetospheric plasma by an instrument aboard the polar orbiting satellite OV1‐20S. The most common antenna pattern observed at the fixed operating frequency, 300 kHz, was a dominantly biconic pattern with major axis parallel to the geomagnetic field. The measured cone angles are in reasonable agreement with those predicted by warm plasma theory.There was no discernible systematic asymmetry in these angles such as could be attributed to field‐aligned currents in the plasma or to the motion of the satellite throu

ISSN:0048-6604    

DOI:10.1029/RS009i005p00541

年代:1974

数据来源: WILEY

摘要:

The nonlinear impedance of a satellite‐borne, electric dipole antenna was measured at ELF/VLF at drive voltages between 10 mv and 100 v peak‐to‐peak. The magnitude of the impedance is in general agreement with the predictions of theoretical models of plasma‐clad antennas. At low voltages the phase angle of the impedance is in agreement with linear sheath models, i.e., at low densities the current leads the voltage and as the density increases the phase angle approaches zero. However, at high drive voltages the current lags the voltage. Above 10 v p‐p the phase angle often exceed

ISSN:0048-6604    

DOI:10.1029/RS009i005p00547

年代:1974

数据来源: WILEY

摘要:

The multiple‐scattering technique is extended to include the effects of simple collisions and a vertical magnetic field on the impulse response of a stratified cold plasma. In this case as in the free‐electron case it is possible to formulate a multiple‐scattering integral for thenth scattered field in terms of the (n– 1)th scattered field. The total response is the sum over all orders of scatter. By an appropriate convolution process it is possible to find thenth scattered field in the presence of collisions and a magnetic field from the corresponding scatter for the free‐electron case. This method is used to find the response of an infinite region of exponentially increasing electron density and a half space of uniform electron density in the presence of collisions and a magne

ISSN:0048-6604    

DOI:10.1029/RS009i005p00559

年代:1974

数据来源: WILEY

摘要:

The transmission of VHF electromagnetic waves in a curved mine tunnel is analyzed using an idealized model in a cylindrical geometry. The tunnel cross section is assumed to be rectangular and the broad curved walls are imperfectly reflecting. The computations of the modal characteristics are facilitated by using a modified Airy function approximation of the rigorous cylindrical wave functions. The results indicated that the curvature of such tunnels will seriously increase the attenuation of the dominant low‐order modes that are used for communication

ISSN:0048-6604    

DOI:10.1029/RS009i005p00567

年代:1974

数据来源: WILEY