Propagation of interplanetary shock waves by observations of type II solar radio bursts on IMP-6

A new interpretation of the low frequency type II solar radio bursts of 30 June 1971, and 7–8 August 1972 observed with IMP-6 satellite (Malitson et al., 1973a,b) is suggested. The analysis is carried out for two models of the electron density distribution in the interplanetary medium taking into account that N ~ 3.5 cm^?3 at a distance of 1 a.u. It is assumed that the frequency of the radio emission corresponds to the average electron density behind the shock front which exceeds the undisturbed electron density by the factor of 3. The radio data indicate essential deceleration of the shock waves during propagation from the Sun up to 1 a.u. The characteristics of the shock waves obtained from the type II bursts agree with the results of the in situ observations.     

Type III radio bursts in the outer corona

Type III solar radio bursts observed from 3.0 to 0.45 MHz with the ATS-II satellite over the period April–October 1967 have been analyzed to derive two alternative models of active region streamers in the outer solar corona. Assuming that the bursts correspond to radiation near the electron plasma frequency, pressure equilibrium arguments lead to streamer Model I in which the streamer electron temperature derived from collision damping time falls off much more rapidly than in the average corona and the electron density is as much as 25 times the average coronal density at heights of 10 to 50 solar radii (R ). In Model II the streamer electron temperature is assumed to equal the average coronal temperature, giving a density enhancement which decreases from a factor of 10 close to the Sun to less than a factor of two at large distances (> 1/4 AU). When the burst frequency drift is interpreted as resulting from the outward motion of a disturbance that stimulates the radio emission, Model I gives a constant velocity of about 0.35c for the exciting disturbance as it moves to large distances, while with Model II, there is a decrease in the velocity to less than 0.2c beyond 10 R .     

Determination and analysis of coronal hole radio spectra

Solar radio maps obtained by our group and others over a wide wavelength range (millimeter to meter) and over a considerable time span (1973–1978) have allowed us to compute the radio spectrum of an average coronal hole, i.e., the brightness temperature inside a coronal hole normalized by the brightness temperature of the quiet Sun outside the coronal hole measured at several different radio wavelengths. This radio spectrum can be used to obtain the changes of the quiet Sun atmosphere inside coronal holes and also as an additional check for coronal hole profiles obtained by other methods. Using a standard solar atmosphere and a computer program which included ray tracing, we have tried to reproduce the observed radio spectrum by computing brightness temperatures at many different wavelengths for a long series of modifications in the electron density, neutral particle density and temperature profiles of the standard solar atmosphere. This analysis indicates that inside an average coronal hole the following changes occur: the upper chromosphere expands by about 20% and its electron density and temperature decrease by about 10%. The transition zone experiences the largest change, expanding by a factor of about 6, its electron density decreases by a similar factor, and its temperature decreases by about 50%. Finally in the corona the electron density decreases by about 20% and the temperature by about 15%.     

Type III solar radio burst storms observed at low frequencies

The analysis of a storm of type III solar radio bursts observed in August 1968 between 5 and 0.2 MHz by the RAE-1 satellite has yielded the storm morphology, a possible relation to meter and decameter storms, and an average exciter speed of 0.37 c between 10 and 40 R (Fainberg and Stone, 1970a, b). A continuation of the analysis, based on the apparent dependence of burst drift rate on heliographic longitude of the associated active region, now provides a distance scale between plasma levels in the streamer, an upper limit to the scale size of coronal streamer density inhomogeneities, and an estimate of the solar wind speed. By fixing one level the distance scale is utilized to determine the electron density distribution along the streamer between 10 and 40 R . The streamer density is found to be 16 times that expected for the solar minimum quiet solar wind. An upper limit to the scale size of streamer density inhomogeneities is estimated to be of the order of 1 or 2 solar radii over the same height range. From the progressive delay of the central meridian passage (CMP) of the lower frequency emission, a streamer curvature is inferred which in turn implies an average solar wind speed of 380 km/sec between 14 and 36 R within the streamer.     

Decay of a highly eccentric satellite

The re-entry phase of a highly eccentric satellite is discussed. Numerical simulations allowing the prediction of the exact date of re-entry of a highly eccentric satellite are exposed.It is shown that under very particular circumstances the life of the satellite can be extended by a few days. The number of final revolutions of the rapidly contracting orbit depends critically on the air density between 70 km and 100 km.Re-entry of the European scientific satellite HEOS-1 predicted for 28 October, 1975 is near such a situation.     

火星电离层无线电掩星探测仿真研究

对中俄联合火星星-星电离层掩星技术体制进行了分析和介绍,采用三维射线追踪方法对电离层掩星事件的电波观测值进行了模拟计算,并利用模拟的掩星观测数据进行了电子密度廓线反演,结果说明仿真算法可靠.利用仿真的方法,分别对掩星电波相位观测误差和卫星轨道误差等带来的反演误差进行了个例计算和分析,结果得到:5%周的相位测量误差对白天电离层掩星探测结果的影响可以忽略,而夜间电子密度测量的绝对误差小于4×108 m-3;卫星轨道误差对掩星的主要影响是导致电离层高度抬升或下降.结果表明,中俄联合火星电离层掩星探测技术体制先进,可望获得高精度的电子密度廓线;其技术体制也可以用于月球电离层环境的探测.     

Electron temperature models of the thermosphere to 1100 km based on ESRO-4 measurements

Measurements of thermospheric electron temperatures at altitudes in the range 250–1100 km, made with a Langmuir probe carried on the polar-orbiting satellite ESRO-4, have been used to derive model functions of electron temperature in terms of altitude, magnetic latitude and local time for the periods November 1972 to June 1973 and March to October 1973. The technique used to compute the coefficients of the model functions is described, and the model electron temperatures are compared with those obtained from similar instruments on the Ariel-1 satellite in 1962 and the ESRO-1A satellite in 1968–1969, and from ground-based observatories. The models reproduce the major features of topside electron distributions viz. mid-day temperatures exceeding midnight temperatures by about 500 K, dawn enhancement leading to peak temperatures greater than mid-day values particularly around 50° magnetic latitude, and temperatures increasing with altitude at all latitudes and with latitude at all altitudes. The daytime mid-latitude temperature is used to complete a series of observations by various techniques over a solar cycle and thereby to confirm the sense and degree of solar cycle control on the thermospheric electron temperature predicted by theoretical considerations.     

Lower ionosphere electron densities from rocket measurements employing LF radio propagation and DC probe techniques

Electron densities throughout the D- and E-regions of the ionosphere have been measured during two rocket flights from Woomera, Australia; one in the daytime and one at night. The detailed distributions have a height resolution of much better than a km over the majority of the height range which was 66–175 km on the day flight and 83–184 km at night. This resolution has enabled sharp changes in electron density to be observed such as those associated with positive ion changes near 85 km (Reid 1970) and with sporadic-E layers.The detail and large dynamic range in electron density (10² to 3 × 10⁵ cm^?3) were achieved by combining the data from an LF radio propagation experiment with those from a probe experiment. The radio equipment allowed measurement of both the phase and amplitude of the wavefield above a ground transmitter. The method of deducing electron density from the phase velocity of the penetrating component of the wavefield is explained in detail. A comparison of the probe current and electron density has shown that the ratio between them varies slowly with height.     

The evening diffuse radio aurora,field-aligned currents and particle precipitation

The relationship of the afternoon/evening diffuse radio aurora, proton and electron precipitation and field-aligned currents is studied with data from the auroral radar at Slope Point, New Zealand, and the ISIS 2 satellite. It is shown that there is a very close association between the radio aurora and (primarily downward) field-aligned currents, which confirms and extends previous work, but that there is no clear relation with either proton or electron precipitation.     

Comet plasma densities deduced from refraction of occulted radio sources

Eighty MHz observations of the occultation of the radio source Culgoora-1 0300 + 16 by the plasma tail of Comet Kohoutek (1973f) were made in February/March 1974 with the Culgoora radioheliograph. No detectable source broadening or change in flux density was observed, but the results showed a 2' arc anomaly in the observed position. This is greater than can be attributed to ionospheric refraction or experimental error. We suggest that it arose from refraction in the plasma tail of the comet. Similar observations of the occulation of the radio source Culgoora-1 2313-14 by the plasma tail of Comet West (1975n) were made at Culgoora in February 1976. These results were inconclusive but did suggest that the cometary plasma may have had some influence on the observed source position. The results are used to derive, from simple models, the distribution of electron density in comet tails. Peak electron densities of approximately 2 to 5 × 10⁴ cm^?3 and density gradients of ～0.05 cm^?3 km^?1 are indicated.     

Interplanetary baseline observations of type III solar radio bursts

Simultaneous observations of type III radio bursts from spacecraft separated by 0.43 AU have been made using the solar orbiters HELIOS-A and HELIOS-B. The burst beginning at 19:22 UT on March 28, 1976 has been located from the intersection of the source directions measured at each spacecraft, and from burst arrival time differences. The source positions range from 0.03 AU from the Sun at 3000 kHz to 0.08 AU at 585 kHz. The electron density along the burst trajectory, and the exciter velocity (=0.13c) were determined directly, without the need to assume a density model as has been done with single-spacecraft observations. The separation of HELIOS-A and -B has also provided the first measurements of burst directivity at low frequencies. For the March 28 burst the intensity observed from near the source longitude (HELIOS-B) was 3–10 dB greater than that from 60° west of the source (HELIOS-A).     

Variations in air density,satellite drag coefficient and atmospheric rotation rate from analysis of the orbit of 1966-92D

Variations in air density, the satellite drag coefficient, and the atmospheric rotation rate at 60°S lat and 120–130 km height during the period September 1968–June 1969 have been determined from analysis of the high-eccentricity orbit of the 4th Molyniya 1 upper-stage rocket body, 1966-92D. The results show good correlation between density increases and strong geomagnetic activity, although solar flares of equal geomagnetic index value do not consistently produce density changes of equal magnitude. A 30 per cent semi-annual variation was observed, but there was no indication of the 50 per cent lower thermosphere seasonal-latitudinal variation that was predicted from the CIRA 1972 atmosphere. The satellite drag coefficient was observed to begin decreasing with height at an altitude where the molecular mean free path, λ, was twice the satellite's length. The coefficient decreased to a value approaching 1.0 as the satellite's perigee height fell below the altitude where λ was one-half the length. A mean atmospheric rotation rate of 1.1 ± 0.1 Earth rot/day was obtained for the last 20 days of decay. However, variations were observed with west-to-east wind speeds of ?100 m/sec measured for a local time of 13 hr.     

The radio luminosity of pulsars and the distribution of interstellar electron density

The radio luminosities of pulsars are given as functions of their period and the time variation of the period. The parameters of that dependence are calculated and independent distances are determined for pulsars. The average electron densities toward the pulsars are determined from the known dispersion measures. The results obtained are used to study the large-scale electron density distribution in the Galaxy. The distribution maximum lies in the vicinity of the Sagittarius spiral arm. The electron density falls off exponentially in the regions between spiral arms. This revised version was published online in July 2006 with corrections to the Cover Date.     

Topside ionosphere disturbance effects during different phases of two successive magnetic storms in september, 1963

Using the data obtained by means of the Alouette-1 satellite, the distribution of electron density in the region of the F2-layer maximum and topside ionosphere during different phases of two successive magnetic storms on September 13 and 16,1963 have been studied. The middle latitudes at local near noon and midnight hours have been considered mainly. It is shown that the daytime topside electron density at some altitudes did not change during the main phases of the two magnetic storms. The electron density decreases below these levels and increases above. During the recovery phases of both magnetic storms the increase in electron density remains at all altitudes from h_mF2 to 1000 km.     

Extragalactic MeV γ-ray emission from cocoons of young radio galaxies

Strong γ-ray emission from cocoons of young radio galaxies is predicted for the first time. Considering the process of adiabatic injection of the shock dissipation energy and mass of the relativistic jet in active nuclei into the cocoon, while assuming thermalizing electron plasma interactions, we find that the thermal electron temperature of the cocoon is typically predicted to be of the order of ∼ MeV, and is determined only by the bulk Lorentz factor of the relativistic jet. Together with the time-dependent dynamics of the cocoon expansion, we find that young cocoons can yield thermal bremsstrahlung emissions at energies ∼MeV.     

Structure in the solar corona from radio scintillation measurements

Since the 1950s, a wide variety of radio observations based on scattering by electron density fluctuations in the solar wind has provided much of our information on density fluctuations and solar wind speed near the source region of the solar wind. This paper reviews recent progress in the understanding of the nature of these density fluctuations and their relationship to features on the Sun. The results include the first measurements of fine-scale structure within coronal streamers and evidence for structure in solar wind speed in the inner corona.     

Coronal line-width variations

Line-width measurements of the coronal ion Siviii confirm earlier observations which show an increase in the non-thermal velocity above the solar limb. The present data, taken at the equatorial limb, show an increase from 24 km s^-1 at the limb to 28 km s^-1 some 25000 km above the limb. The electron density as measured from the Siviii line pair shows a decrease from 3.5 × 10⁸ cm^-3 to 1.8 × 10⁸ cm^-3 over the same distance. These data imply that the non-thermal velocity is inversely proportional to the quadratic root of the electron density, in excellent agreement with that predicted for undamped radially propagating Alfvén waves.     

An auroral F-region study using in situ measurements by the Atmosphere Explorer-C satellite

On 14 July 1974 the Atmosphere Explorer-C satellite flew through an aurora at F-region altitudes just after local midnight. The effects of the particle influx are clearly evident in the ion densities, the 6300 Å airglow, and the electron and ion temperatures. This event provided an opportunity to study the agreement between the observed ion densities and those calculated from photochemical theory using in situ measurements of such atmospheric parameters as the neutral densities and the differential electron energy spectra obtained along the satellite track. Good agreement is obtained for the ions O₂⁺, NO⁺ and N₂⁺ using photochemical theory and measured rate constants and electron impact cross sections. Atomic nitrogen densities are calculated from the observed [NO⁺]/[O₂⁺] ratio. In the region of most intense electron fluxes (20 erg cm⁻² sec⁻¹) at 280 km, the N density is found to be between 2 and 7 × 10⁷ cm⁻³. The resulting N densities are found to account for approx. 60% of the production of N⁺ through electron impact on N and the resonant charge exchange of O⁺(²P) with N(⁴S). This reaction also provides a significant source of O(¹S) in the aurora at F-region altitudes. In the region of intense fast electron influx, the reaction with atomic nitrogen is found to be the main loss of O⁺(²P).     

The source and structure of the jovian radiation belt

The radio emission from Jupiter at 10, 21 cm wavelength has been measured with a spatial resolution of the order of 1 Jupiter radius. This may be analytically reduced to the emission per cubic centimeter of source at each measured frequency. The theoretically predicted synchrotron emission of electrons as a function of frequency, magnetic field and electron energy can then be compared to the observed source emissivity to obtain the number density and ‘temperature’ of the electrons. Present observations taken at different epochs are not sufficiently reliable to infer peak energies within an order of magnitude. Nevertheless the present results indicate that electrons diffuse in rapidly (in a time of the order of months) conserving the first adiabatic invariant and reach a peak energy at about 2 Jupiter radii. The electron energy decreases rapidly nearer the planet because of energy lost to radiation in the large magnetic field close to the planet.     

Reconstruction of ion and electron density profiles from space-based measurements of the upper electron content

Presented is a new method for retrieving the topside electron density distribution from space-based observations of the total electron content. By assuming an adequate topside density distribution, the profile reconstruction technique utilizes ionosonde and oxygen-hydrogen ion transition level measurements for uniquely determining the unknown ion scale heights and the corresponding ion and electron density profiles. The method is tested on actual measurements from the CHAMP satellite. Important applications are envisaged, such as developing and evaluating empirical and theoretical ionosphere-plasmasphere models.