摘要:

A radar experiment was conducted on August 18, 1978, at Kwajalein Atoll, Marshall Islands, to investigate the spatial relationship of 1‐m equatorial spreadFirregularities to plasma bubbles (localized depletions inFlayer plasma density). East‐west scans were made with Altair, an incoherent scatter radar, to spatially map (1) the backscatter produced by field‐aligned irregularities and (2) the electron density distribution of the backgroundFlayer. Plasma bubbles were spatially mapped for the first time with an incoherent scatter radar. By assuming invariance along the magnetic field lines (over distances of less than 100 km) we show that 1‐m field‐aligned irregularities are directly related to plasm

ISSN:0148-0227    

DOI:10.1029/JA085iA01p00185

年代:1980

数据来源: WILEY

摘要:

Normal type 1 radar echoes obtained from relatively large zenith angles have a power spectrum with a single narrow peak whose Doppler shift corresponds approximately to the acoustic velocity in the medium. On some occasions, however, this single maximum splits into two distinct peaks, separated in phase velocity on one occasion by 270 m/s. This bifurcation is most easily observed at large zenith angles during daytime when a narrow antenna beam is used. It has also been seen in a daytime experiment in which radars at Jicamarca and Huancayo simultaneously probed the same region from two different radar zenith angles. The bifurcation has been observed so far only to the west of Jicamarca, over the Pacific Ocean. This spectral splitting could be caused by vertical electron density gradients, such as those associated with ‘blanketing’ sporadicElayers. A sufficiently sharp (scale lengths of a few hundred meters or less) positive gradient on the underside of the layer and negative gradient on the topside would cause the type 1 velocity to be decreased and increased, respectively, during the day, by amounts as large as those obser

ISSN:0148-0227    

DOI:10.1029/JA085iA01p00191

年代:1980

数据来源: WILEY

摘要:

The spatial extent and duration of the winter anomaly, i.e., anomalous and large enhancement in ionospheric absorption of HF and MF waves occurring on groups of winter days at middle latitudes, are examined on the basis offmindata at 18 stations in USSR, Japan, and North America during the periods November–February in 1971–1972 and 1972–1973, considering thatfminenhancement represents an increased ionospheric absorption of HF and MF waves. The relationship between the phenomena of winter anomaly and geomagnetic storm is also examined. It is found that the winter anomaly occurs simultaneously in an extensive daytime area at middle latitudes, at least in some scattered region over the area, whose longitudinal extent reaches at most ∼100°. The southern boundary of the anomaly seems to be controlled geomagnetically and located below 30° in geomagnetic latitude. Also it is shown that the winter anomaly seems to be associated with geomagnetic storms, mainly sc (sudden commencement) storms, because outstanding enhancements in wave absorption begin usually 1–3 days after the beginning of an individual sc storm and last for more than a few days with decreasing magnitude. It is suggested that the winter anomaly is ascribed to ionization enhancements in the lowerDregion due to precipitating electrons from the outer atmosphere, mainly from the slot region, associated with geomagn

ISSN:0148-0227    

DOI:10.1029/JA085iA01p00197

年代:1980

数据来源: WILEY

摘要:

The relative vibrational population of N2+(B²Σu+) in a rare proton aurora, observed on March 8 (UT), 1978, was twice as high as the values found in almost all nighttime auroras. On the basis of various laboratory measurements the proton aurora observations point to precipitation of ∼1.2‐keV protons, carrying an energy flux of ∼14 ergs cm−2s−1. Simultaneous measurements of N2+1 NG (0, 1), (1, 2), (0, 2), and (1, 3) bands as well as Hβand [O I] 6300‐Å emissions from this rare, low‐energy proton aurora yield Hβ/N2+1 NG (0, 2) ≃ 3 and [O I] 6300/N2+1 NG(0, 1) ≃2.4. The corresponding values in the auroras excited predominantly by electrons are generally low (e.g.,<0.7 and 0.6, respectively). Most of the N2+1 NG emissions from proton auroras are excited by protons (and not hydrogen atoms which constitute the bulk of the charge equilibrated auroral particle bea

ISSN:0148-0227    

DOI:10.1029/JA085iA01p00206

年代:1980

数据来源: WILEY

摘要:

Electron temperature models for the topside ionosphere, which make use of the protonospheric heat flux ϕC, deduced from the experimental electron temperature profiles, are presented for low as well as medium solar activity conditions. The parameter ϕCis found to show inverse correlation with electron concentrationNein the topside ionopshere. This relationship betweenNeand ϕCat 400 km is used to obtain ϕCwhenNeis known. The value of ϕCcan be used to build the electron temperature profile in the topside ionosphere ifTeat some lower height is known. TheTevalue at a lower height, say at 300 km, can be obtained from earlier models based upon empiricalTe‐Nerelationships. The electron temperature obtained from our present models are compared with the measured temperatures and are found to show reasonable agr

ISSN:0148-0227    

DOI:10.1029/JA085iA01p00213

年代:1980

数据来源: WILEY

摘要:

Pulsating auroras of very thin vertical extent have recently been observed. It is shown that if the primary electrons are stopped in a region as thin as that reported, extremely strong electric fields, ac or dc (or both), are implied. This consequence could be tested by in situ measurements. If the stopping is due to dc electric fields, a potential drop of the order of 10 kV or more in a thin region is required. The local field strength, several mV/m, has an order of magnitude comparable to that estimated for so‐called electric double layers. If the stopping were due to ac fields, the rms electric field strength would have to be even larger. Alternatively, the reported thinness of the luminosity distribution might result without a correspondingly abrupt stopping of the primary electrons. Two conceivable mechanisms for this are discussed and shown to be inadequate. However, there is at least one, involving excitation of the N2+Meinel band by keV electrons, that cannot be definitely rejected on the basis of existing observations. This question could, however, be resolved by TV observations using suitably band‐limited filt

ISSN:0148-0227    

DOI:10.1029/JA085iA01p00217

年代:1980

数据来源: WILEY

ISSN:0148-0227    

DOI:10.1029/JA085iA01p00219

年代:1980

数据来源: WILEY

ISSN:0148-0227    

DOI:10.1029/JA085iA01p00221

年代:1980

数据来源: WILEY

ISSN:0148-0227    

DOI:10.1029/JA085iA01p00223

年代:1980

数据来源: WILEY

ISSN:0148-0227    

DOI:10.1029/JA085iA01p00224

年代:1980

数据来源: WILEY