摘要:

Protons in the one to hundreds of kev energy range precipitate into the atmosphere in the auroral zone. Limited rocket and satellite measurements suggest total nighttime fluxes of the order of 107cm−2sec−1sterad−1for energies ≳10 kev, with about 1% of this flux above 100 kev, and perhaps 10−3% above 500 kev, as being reasonable but not necessarily average. The proton flux below 10 kev may exceed the flux above 10 kev by as much as a factor of 10 or even 100. Daytime fluxes appear to be less than nighttime fluxes. Various pitch‐angle distributions have been reported, and there is some suggestion that the proton flux at high pitch angles increases with decreasing proton energies. The region of precipitation is normally a broad (3°–7° of latitude) diffuse zone that locates on the equatorward side of the region of electron precipitation. Protons undergo charge‐exchange interactions in the atmosphere, forming neutral hydrogen atoms in excited states in sufficient quantity to give readily detectable Balmer series emissions (Hα, Hβ, and Hγ) on the ground. The Hβ intensity is typically less than 100 R, and the Balmer decrement Hα/Hβ is about 3. This proton precipitation also results in the excitation of various oxygen and nitrogen emission, such as λ3914, λ4709 N2+, and λ5577 O I, and theoretical ratios of the intensities of these emissions to the Hβ intensity in an aurora excited entirely by protons are 5‐20, 0.3‐1.0, and 4‐12, respectively. Strong visual auroras cannot be excited entirely by protons.The Balmer emissions are radiated by moving hydrogen atoms, and thus the radiation is Doppler‐shifted. The magnetic‐zenith profile commonly shows about a 6‐A Doppler shift of the profile peak, whereas the magnetic‐horizon profile is unshifted; the proton pitch‐angle distribution results in a Doppler broadening of both profiles. The shape of the hydrogen line profiles reflects the energy and pitch‐angle distributions of the incident protons, as well as the energy dependence of the charge‐exchange cross sections involved. Theoretical interpretation of measured line profiles in terms of simplified models of proton precipitation has led to dubious conclusions. There is little or no dependence of the occurrence of hydrogen auroras on the presence of stronger, visual (electron‐excited) auroras, though visual auroras may frequently be superimposed on the broader, diffuse zone of hydrogen emission. There is little evidence for rapid variations in hydrogen intensities similar to the pulsations often observed in electron‐excited emissions, though longer period (∼minutes) variations have been reported. The zone of hydrogen emission locates equatorward of quiet visual arcs and moves to lower latitudes before midnight and back poleward again after midnight, and it often expands poleward in association with auroral breakup events. The zone appears to widen and move equatorward during increased magnetic activity.Other effects of proton precipitation include ‘r’ typeEsionization and possibly certain types of radio auroras. Polar‐glow auroras are associated with higher‐energy proton events (though the main excitation could be due to lower‐energy particles). Low‐energy proton precipitation may cause appreciable heating of the upper atmosphere and may excite certain high‐altitude red arcs at both midlatitudes and high latitudes. Auroral protons may also repr

ISSN:8755-1209    

DOI:10.1029/RG005i003p00207

年代:1967

数据来源: WILEY

摘要:

A proven prediction of longshore current velocity is not available, and reliable data on longshore currents are lacking over a significant range of possible flows. Theoretical studies have been based on over‐simplified models, and empirical predictions have been hampered by lack of data. The empirically modified, momentum‐flux theory now accepted as the best prediction is based on an untenable assumption and supported by inappropriate data. Regardless of their validity, however, all six of the testable equations agree fairly well with at least one of six sets of published data, and two agree with both of the better sets of data. These two equations may be used as empirical guides for velocity prediction in the absence of a proven theory. The best prospect for a generally valid velocity prediction appears to be an empirical correlation based on reliable d

ISSN:8755-1209    

DOI:10.1029/RG005i003p00287

年代:1967

数据来源: WILEY

摘要:

The current status of laboratory measurements of ion‐molecule reactions of ionospheric relevance is reviewed. Rate constants for the atmospheric loss reactions of He+, O+, and N2+appear to be established to within about a factor of 2 at 300°K. The laboratory rate constants for O+and N2+ion loss are compatible with quiet midlatitudeE‐ andF‐region requirements. The He+loss reactions appear to be higher than is compatible with some He+concentrations observed; however, the laboratory rate constants have been measured by so many investigators that they are unlikely to be seriously in error. In theDregion, on the other hand, many of the important reactions are as yet unmeasured. Measurements of the relevant negative ion reactions with neutrals have only recently been started. No in situ atmospheric negative ion composition studies have as yet been carried out to guide the laboratory investigations. Many positive ion reactions of importance in theDregion (as well as in sporadicElayers) remain to be measured. Finally, very little information concerning reactions of excited state ions with neutrals has been obtained. This will be important for certain disturbed ionospheric conditions and possibly for a precise analysis of normal ionospheric conditions, when this is m

ISSN:8755-1209    

DOI:10.1029/RG005i003p00305

年代:1967

数据来源: WILEY