摘要:

Results obtained at Ithaca, N.Y., concerning radio reflections from the aurora by both pulse and continuous‐wave transmissions are described. At 104 Mc/sec, radar reflections show the following properties: (i) They occur only during auroras having ray structure; (ii) the radar must be directed roughly normal to the rays; (iii) echoes are complex, indicating contributions from many scattering elements mutually interfering in more or less random phase. At various frequencies, from 2.4 to 144 Mc/sec, measurements of fading show that auroral reflections fade at a rate roughly proportional to frequency; rates are between one and two powers of ten faster than would be expected for a quiet ionosphere.These observations are interpreted as indicating that radio reflections from auroras arise by scattering from numerous auroral columns of ionization, somewhat like meteor trails, having the magnetic zenith as radiant. The fading is principally due to a wind‐like motion of the auroral columns, much faster than is customary for meteor trails, and apparently much faster than can actually be observed for meteor trails occurring during auroral disturbances. Visual observations of the fine structure of rays with high‐power field‐glasses and by photometric analysis show that rays often consist of a large number of fine streaks, each of which extends only part of the length of the ray and lasts only about a second. It is tempting to associate these visual auroral streaks with the auroral ionization trails that are required to explain radio reflections from the aurora.Alternative interpretations suggested by other workers are considered, especially that by Harang and Landmark [11]. Reasons are given for rejecting these interpretations in favor of that described above.Although practically all of the auroral echoes observed at Ithaca are interpreted as coming fromE‐region levels, reasons are given why auroral echoes fromF‐region levels may be seen, especially by radars in lowe

ISSN:0148-0227    

DOI:10.1029/JZ060i001p00001

年代:1955

数据来源: WILEY

摘要:

The role of ionic diffusion in placing free electrical charge on droplets falling in the atmosphere is considered. Experimentally verified expressions for the diffusion of ions onto droplets are shown to account for the sign and magnitude of the free charge observed on light rain and mist. In the lower atmosphere, such droplets are normally positive and carry a specific free charge approximating 1 esu/gm. The observed variability of the electrical conductivity of the atmosphere suggests that diffusion may occasionally transfer large negative as well as positive charges to the falling drops.

ISSN:0148-0227    

DOI:10.1029/JZ060i001p00023

年代:1955

数据来源: WILEY

摘要:

World‐wide sudden commencements which appear during the night hours at College, Alaska, are found to occur most frequently during the onset, or decreasingHstage, of negative bays. As this stage of magnetic disturbance accompanies a distinct change from homogeneous to rayed aurora, it is suggested that s.s.c.'s have an atmospheric source which is related to sudden changes in auroral activit

ISSN:0148-0227    

DOI:10.1029/JZ060i001p00029

年代:1955

数据来源: WILEY

摘要:

A qualitative hypothesis is given that attributes recurrent “M‐region” geomagnetic disturbances to the arrival at the earth of solar corpuscles that have been gathered into beams by the deflecting action of coronal‐region fields, presumably magnetic, associated with centers of heightened solar activity. The hypothesis identifies the source of solar corpuscles that producesM‐region magnetic disturbances with “quiet areas” of the solar surface. A related hypothesis associates non‐recurrent magnetic storms, the greatest ones, with a different solar corpuscular source, found in the activ

ISSN:0148-0227    

DOI:10.1029/JZ060i001p00033

年代:1955

数据来源: WILEY

摘要:

An increase in the ionization near the ground due to the fall‐out from a radioactive cloud formed by a nuclear explosion will increase the conductivity and lower the potential gradient in the lower atmosphere. Records of atmospheric conductivity and potential gradient from the Tucson Magnetic Observatory are compared with records of the deposition of atomic debris on the ground following the Nevada tests. The observed changes are not inconsistent with values computed from theoretical considerations. Most of the effects are confined to a very shallow layer, within a few meters of the groun

ISSN:0148-0227    

DOI:10.1029/JZ060i001p00045

年代:1955

数据来源: WILEY

摘要:

Observations of backscatter on 13.7 Mc over a southeasterly path from Sterling, Virginia, revealed the existence of meteor‐trail reflections just ahead of the main body of the backscatter, demonstrating that the latter was from the ground in these instances. The existence of apparent two‐hop backscatter without the appearance of one‐hop was noted in a number of cases. Possible reasons for this behavior are disc

ISSN:0148-0227    

DOI:10.1029/JZ060i001p00053

年代:1955

数据来源: WILEY

摘要:

In the course of a fixed‐frequency ionospheric study, employing a pulse‐triggered transmitter operating on 3.5 Mc/s and three spaced‐receivers, the transmission delay was continuously recorded. Aside from a vertical‐incidence transmission, two oblique transmissions were thus available with 62 and 109 km as base lines, the latter being correspondingly oriented in an approximate west‐east and northwest‐southeast direction.An analysis of the echoes from theF‐region was made for the period between August 1952 and December 1953. Successive irregularities observed simultaneously on three records displayed frequently consistent time‐displacements. Assuming the midpoints of the transmissions to be characteristic and preferred areas for the reflection of the h.f.‐pulses, the time‐displacements were interpreted as being due to a mechanical motion of theF‐region. Direction and speed of this movement were thus obtained, and semiannual and annual periods of these compo

ISSN:0148-0227    

DOI:10.1029/JZ060i001p00057

年代:1955

数据来源: WILEY

摘要:

Annual variations of the horizontal intensity (Hforce) were computed for a number of stations, using values for magnetically quiet days where available. These are expressed in terms of Fourier components. Differences found between one pair of stations suggest that the annual variation arises from local as well as world‐wide influence

ISSN:0148-0227    

DOI:10.1029/JZ060i001p00071

年代:1955

数据来源: WILEY

摘要:

The theory of the self‐absorption of resonance photons within a luminescent airglow layer is developed and expressions obtained analogous to the Van Rhijn equation for the variation of intensity as a function of zenith angle. The measured flux is shown to be a function ofL0/T, whereL0is the vertical thickness in atoms/cm2andTthe absolute temperature of the layer. The attenuation at large zenith angles in the case of the sodiumDlines is shown to be large enough whenL0is between 1 and 2×1010cm−2andTbetween 160° and 220° to cause a layer at 70 km to simulate a non‐absorbing (Van Rhijn) layer between 200 and 300 km. If self‐absorption is important, it is shown that the ratio ofD1toD2intensity should vary with zenith angle and different apparent heights found for the two components. Accurate measurements ofL0andTare shown to be necessary for even good approximate height deductions where resonance radiation (for example, Na and OI) is

ISSN:0148-0227    

DOI:10.1029/JZ060i001p00075

年代:1955

数据来源: WILEY

摘要:

The kinematic viscosity η/ρ approaches infinity as the density ρ approaches zero, since the results of kinetic theory show that the molecular viscosity η is independent of density. The elementary viscosity derivations use a linear velocity profile which implies near infinite streaming velocities as the density becomes small. The streaming velocities must be finite, and the velocity profile must have an upper and a lower limit in the atmosphere. It is shown that the viscous stress must approach zero with decreasing density when the velocity profile is bounded. Either the velocity gradients or the corrected viscosity coefficients become small in the higher atmosphere. The viscous effect depends on a length scale representative of the wind shear and is a maximum in the lowerF‐region for scales comparable to those representative of the air currents studied in synoptic meteor

ISSN:0148-0227    

DOI:10.1029/JZ060i001p00087

年代:1955

数据来源: WILEY