摘要:

Observations of the solar ultraviolet irradiance during 1979 (solar maximum) by the Solar Backscatter Ultraviolet Experiment on the Nimbus 7 satellite have established that the irradiance at wavelengths between 200 and 300 nm is modulated by solar rotation. This short‐term variability, which is of the order of 3% at 200 nm and 1% at 250 nm, is associated with the evolution and rotation on the solar disc of plage areas which are enhanced in ultraviolet emission. By using ground‐based Ca II K observations of the fraction of the disc covered by plage during 1979, the intensity ratios for plage to quiet sun emission at these wavelengths have been derived. During the 11‐year solar cycle the number of plage regions on the solar disc increases. There is also an accumulation of active network arising from the remnants of decayed magnetic features. A three‐component model of the solar irradiance is used to estimate the temporal behavior of the ultraviolet emission between 200 and 300 nm, resulting from changes throughout the solar cycle in the active features on the disc. These calculations suggest that for solar cycle 21 the flux variability at 200 nm is 25%, decreasing to 10% at wavelengths between 210 and 250 nm, and to 2% at 300 nm. Ultraviolet flux variability of this magnitude corresponds to an average increase in the total solar irradiance from 1976 to 1979 of about 0.05%. For comparison, the average reduction in the total solar irradiance from 1976 to 1979 due to sunspot blocking is 0.07%. Because of the enhanced ultraviolet emission from solar active features, the variability of the total solar irradiance during cycle 21 is predicted to be less than is calculated by models which consider only the effects of sunspot blocking. This result is consistent with the need for an added faculae brightening term in total solar irradiance

ISSN:0148-0227    

DOI:10.1029/JA089iA01p00001

年代:1984

数据来源: WILEY

摘要:

The result of a study on the application of an improved statistical prediction method for estimating the intermediate‐term (months) and long‐term (years) behavior of solar flux is discussed. The study indicates that better predictions, in a chi square sense, are possible by selecting sets of the solar flux data such that each set (cycle) starts and ends at the maxima (or minima) for the data base and initialization point of the procedure. Then one applies a Lagrangian least‐squares statistical technique. Evidence is also presented to support the existence of an aperiodic variation in the periods as well as the ampli

ISSN:0148-0227    

DOI:10.1029/JA089iA01p00011

年代:1984

数据来源: WILEY

摘要:

Measurements of the galactic cosmic ray intensity for energiesE>2 GeV andE>60 MeV near earth and forE>60 MeV at 5

ISSN:0148-0227    

DOI:10.1029/JA089iA01p00017

年代:1984

数据来源: WILEY

摘要:

The linear and quasi‐linear theory of perturbations in finite‐β, collisionless plasmas that incorporate a sheared velocity flow is developed. A simple, one‐dimensional magnetic field geometry is assumed to adequately represent solar wind conditions near the sun, i.e., atR≈ 0.3 AU. Two modes are examined in detail: an ion‐acoustic mode (finite‐β stabilized) and a compressional Alfvén mode (finite‐β threshold, high‐β stabilization). The role played by equilibrium temperature anisotropies, in the linear stability of these modes, is also presented. From the quasi‐linear theory, the effects of waves on the state of temperature components (parallel and perpendicular to the magnetic field) of the solar wind is determined: qualitative agreement with the observed anisotropies of electrons and ions is obtained. The quasi‐linear temperature changes are also shown to result in saturatio

ISSN:0148-0227    

DOI:10.1029/JA089iA01p00027

年代:1984

数据来源: WILEY

摘要:

Pioneer 11 high time resolution, ∼1‐minute observations within ±3 hours of corotating interaction region shock waves of proton intensities, pitch angle distributions, and crude differential energy spectra of the range of 0.6 ≤ Ep≤ 3.4 MeV are presented. The principal result is the evidence for the persistent flow of particles away from the shocks. The observations are found to be in good agreement with the hypothesis of local interplanetary shock acce

ISSN:0148-0227    

DOI:10.1029/JA089iA01p00037

年代:1984

数据来源: WILEY

摘要:

We present the first analysis of Pioneer Venus Orbiter plasma, electric field, and magnetic field observations in the Venus tail. We have studied the first season of Pioneer Venus Orbiter tail passage (approximately June 1979) in order to determine the main plasma and field configuration in this region at this time and to ascertain some of the basic physical processes. Our analysis shows that the boundary of the Venusian tail is often characterized by changing plasma distributions and enhanced plasma wave activity. We use summary plasma probe parameters to argue that the waves are Doppler‐shifted ion acoustic oscillations. In the magnetotail region there is generally an exclusion of high‐density plasma, but when plasma is detected, the distributions often appear to be non‐Maxwellian at the highest time resolution, and these distorted distribution functions are generally accompanied by enhanced plasma wave signals and magnetic field reversals indicative of electric currents. On the basis of our analyses of the high‐resolution plasma and wave observations for orbit 189, we identify a different time from that previously defined on the basis of the magnetic field data for the spacecraft entrance into the magnetotail. The wave activity in the Venus tail appears similar to the broadband noise identified in the earth's tail, but at Venus the levels are usually

ISSN:0148-0227    

DOI:10.1029/JA089iA01p00047

年代:1984

数据来源: WILEY

摘要:

During the outbound leg of its passage through the Jovian magnetosphere in July 1979, the Voyager 2 spacecraft observed>50 traversals of the magnetotail current sheet during a 10‐day period at distances between 30 and 130RJ. Detailed study of these and Voyager 1 outbound data show that the magnetic structure near and within the current sheet was variable with time and distance from Jupiter, but generally corresponded to one of the following four types: (1) simple rotation of field across the sheet, with either a southward or a northward directed field component normal to the sheet; (2) field having a southward component in a broad region near the sheet, but northward in a restricted region at the sheet itself; (3) a clear bipolar variation of the sheet‐normal field component as the sheet was crossed (i.e., the field became northward and then southward, or vice versa, in crossing the sheet); (4) large‐amplitude fluctuations in all field components near and in the sheet, with alternating northward and southward polarities. Considering Voyager 1 and 2 observations together, twice as many of type 1 signatures were seen as types 2 and 4, which occurred approximately in equal numbers, whereas type 3's were only half as frequent as the latter types. These magnetic structures are all morphologically similar to those observed at the current sheet in the earth's magnetotail at different times. While type 1 and 2 structures are indicative of a simple, static current sheet geometry, types 3 and 4 provide evidence for a more complex and dynamic internal sheet structure at the times of those traversals, suggesting a loop geometry and fine structure consistent with occurrence of the tearing mode instability. Except for one case, both type 1 signatures with southward components and type 2 signatures were found to occur exclusively in the near‐Jupiter region of the magnetotail. Beyond a downtail distance of ∼70RJ, type 1 variations tended to have northward components, and types 3 and 4 were observed more frequently than other types. This suggests that there may have existed a quasi‐stationary crosstail neutral line near 70RJdown the tail at the time of the Voy

ISSN:0148-0227    

DOI:10.1029/JA089iA01p00057

年代:1984

数据来源: WILEY

摘要:

Dual‐wavelength radio observations during the occultations of Voyagers 1 and 2 provided 3.6‐cm and 13‐cm data on Saturn's ionospheric irregularities at two locations. Spectra of the weak fluctuations in amplitude and phase can be interpreted using the theory for scattering from a power law spectrum of anisotropic irregularities embedded in a thin screen. Comparisons of measured scintillation spectra with the theory produced least squares solutions for four parameters which characterize the ionospheric irregularities: (1) the axial ratio, (2) the orientation, (3) the power law exponent of the spatial spectrum, and (4) the magnitude of the spatial variations in electron density. Scattering was observed from irregularities of approximate size 2–60 km; these lower and upper limits result from noise limitations and the method of analysis, respectively, and do not represent either an inner or outer scale. Within this range of length scales, the three‐dimensional spatial spectrum obeys an inverse power law with exponent near 3.5, and the fractional variations in electron density are about 10–20%. All observed irregularities appear to be anisotropic with axial ratios greater than 4∶1. Magnetic field orientations in Saturn's ionosphere were inferred from the direction of alignment of the anisotropic irregularities. When used as a test of Saturnian magnetic field models, the occultation measurements generally confirm the accuracy of the model predictions but also suggest that a small adjustment of model parameters might improve the field r

ISSN:0148-0227    

DOI:10.1029/JA089iA01p00065

年代:1984

数据来源: WILEY

摘要:

Analyses of the wide band plasma wave data obtained by Voyager 1 and 2 at Jupiter and Saturn have revealed electrostatic bursts similar to those recently discovered at earth in association with whistler mode chorus. In all three magnetospheres the bursts are characterized by sporadic emissions near or slightly below the electron plasma frequency with bandwidths ranging from 10% to more than 50% of the center frequency. The events found at Jupiter occur in the middle magnetosphere during both the dayside as well as the early morning passes. At Saturn the bursts occurred in the outer regions of the magnetosphere during the dayside pass. In each of the events analyzed, evidence exists for modulation of the electrostatic bursts by a low‐frequency wave, presumably chorus. One of the observations gained at Jupiter includes the detection of a low‐frequency band at the proper frequency for chorus. Detailed waveform analysis confirms that this band does, indeed, modulate the electrostatic bursts. On the basis of the present understanding of the terrestrial observations, it is believed that the electrostatic bursts are generated by an electron beam trapped in Landau resonance with the cho

ISSN:0148-0227    

DOI:10.1029/JA089iA01p00075

年代:1984

数据来源: WILEY

摘要:

The diurnal variation of the vertical structure of Titan's thermosphere is calculated through simultaneous solution of the equations of heat transfer and hydrostatic equilibrium. The temperature and density profiles are found above the mesopause. The dynamical response of the thermosphere to heating is for the most part neglected. Nevertheless, we are able to draw some interesting qualitative and quantitative conclusions regarding the vertical structure. Heating of the upper thermosphere occurs primarily through absorption of solar Lyman α radiation by methane, with an additional amount of heating (≲20%) due to low‐energy magnetospheric electron precipitation. The heat is conducted downward to the mesopause, where it is removed by IR cooling due principally to acetylene. The mesopause is found to occur where the density is 2.2×1012cm−3(736 km), and has a temperature of ∼110 K. The exospheric temperature is unlikely to exceed 225 K in the course of a Titan day. The diurnally averaged exospheric temperature is in the range 187–197 K depending on the amount of magnetospheric electron heating that is included in the model. The amplitude of the diurnal variation is found to be ≲28 K. We find that the vertical extent of the hydrogen cloud is too large to be explained in terms of simple thermal escape of hydrogen from a ∼225‐K exosphere, and we conclude that other processes must be important for populating or heating

ISSN:0148-0227    

DOI:10.1029/JA089iA01p00085

年代:1984

数据来源: WILEY