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A model is proposed for the formation of lunar mascons which explains persistence of lunar mascons for more than 3 b.y., evidence for the volcanic activity 3.7-3.2 b.y. ago, and negative gravity anomalies surrounding the mascons. It is concluded that mascons have resulted from the perturbations introduced by the giant impacts into an otherwise spherically symmetric Moon; a giant impact enhances the rate of cooling beneath the impact site by introducing releatively low temperature to a deeper part of the Moon through forming a basin and also by removing substantial amount of radioactive material by means of ejecta. On the other hand, it reduces the rate of cooling beneath the surrounding highland by thermal insulation through extensive fracturing and covering by an ejecta blanketing. Consequently, the base of the lithosphere (100 km thick) beneath the highland remelts to a depth of about 80 km and this creates thermal stresses strong enough to open the fractures in the overlying region and to cause magmatization and volcanic activity. Persistence of the molten phase around 100 km depth for about 1 b.y. probably provides further differentiation and an upward concentration of low density material, giving rise to the observed negative gravity rings. On the other hand, the relatively cold lithosphere beneath the basin forms a layer strong enough to support the associated mascon.

It is shown that the sporadicE layer at an equatorial station is not always of the commonly known equatorial (q) type Es. Broadly there occur two types of Es at a station near the magnetic equator,viz., (i) diffuseq type and (ii) multiple or blanketing (b) type. The latter may be of diffuse type or of thin layer type. The Es-b is due to highly dense cloud of ions which are localised, whereas Es-q occurs over an extended area at any time. The effect of counter-electrojet is seen on both the types of Es layers. The disappearance of sporadicE during counter-electrojet is valid for only theq type of Es, but sometimes Es-b may occur during periods of very weak or reversed electrojet. It is suggested that published equatorial Es data should be used with caution unless the type of Es is also indicated. The plausible causes of the sudden disappearance of Es-q on some occasions and the appearance of Es-b during others are suggested.

Computerized cratering-obliteration models are developed for use in interpreting planetary surface histories in terms of the diameter-frequency relations for craters classified by morphology. An application is made to a portion of the lunar uplands, revealing several episodes of blanketing, presumably due to the formation of some of the major basins. Application to Martian craters leads to the following picture of Martian cratering and obliteration history. During a probable period of intense early bombardment, craters were degraded by two processes: a depositional-type process connected with the declining cratering rate, and a process tending to flatten the largest craters (e.g., isostatic adjustment). During late stages of the early bombardment, or subsequent to it, there occurred a major relative episode of obliteration (probably atmosphere related), but it ceased concurrently with the massive (presumably volcanic) resurfacing of the cratered plains. Subsequent resurfacing episodes have occurred in the smooth plain terrains, but obliteration processes have been virtually absent in the low-latitude cratered terrains. Recent global Martian cratering interpretations of Hartmann and Soderblom are compared. Absolute cratering chronologies are only so good as knowledge of the absolute cratering flux on Mars. The crater data of Arvidson, Mutch, and Jones do not confirm the basis, whereby Soderblom requires the dominant Martian crater obliteration process to be coincident in time with the early bombardment. If the asteroidal-cometary impact flux on Mars has averaged five times the lunar flux during post-lunar-mare epochs, then the obliterative episode lasted about half a billion years and occurred about 1.5 × 10 9 yr ago.

A continuous series of backscatter observations at 19 MHz made at Plum Island, Massachusetts, 56°N invariant latitude, over nearly half a solar cycle is utilized to derive occurrence characteristics of ground backscatter propagated by means of F-layer reflection, 1F, as well as those of aspect-sensitive field-aligned echoes from the F layer, FAE(F). Neither field-aligned E-layer echoes nor ground backscatter propagated by means of sporadic E were found to produce any noticeable blanketing of the radar signal for this frequency and radar location. The 1F propagation showed marked sunspot cycle and azimuthal dependence and was strongest in winter and weakest in summer. Under quiet magnetic conditions FAE(F) was primarily a sunset phenomenon, occurring usually at delays of 7 to 10 msec, with a marked sunspot cycle dependence. Some daytime activity was observed at longer delays of 20 to 22 msec which could be explained in terms of F-layer field alignment after one intermediate ground reflection. The occurrence of FAE(F) during magnetic storms showed a seasonal variation in agreement with the well-known storm behavior of f0F2 at these latitudes. In general, however, the occurrence of FAE(F) increased monotonically with increasing magnetic activity until the threshold of KFr = 4 was reached, beyond which the depletion in the F-layer background ionization caused it to decrease, with complete cut-off occurring irrespective of season during very disturbed conditions, KFr ≥ 7. With the aid of ray traces, the occurrence statistics of both 1F and FAE(F) are interpreted and discussed in terms of the geometry of the probing radar, the various factors controlling F-layer propagation, and the extent of the F-layer irregularity region.

The worldwide ionospheric current system predicted by a previously described theory of the auroral electrojets is computed. Tidal air motions are neglected at first, and the high-latitude current system is assumed to be due entirely to the interaction of magnetospheric rotation with the belt of energetic protons trapped in the distorted geomagnetic field. For a given geomagnetic distortion and trapped proton distribution, the computed current system strongly resembles Chapman's idealized Ds, current system, if sufficiently high E-region electron concentrations independent of geographical position are assumed. As the assumed electron concentrations are decreased, however, the intensity of the computed current system is reduced, first in the auroral zone and then at all latitudes; at the same time the phase of the current system is advanced in the polar cap and is retarded at low latitudes. In view of this limitation of the current system by the available electron concentrations, the large disturbance variations observed during an intense geomagnetic storm can be explained by the present theory only if, in addition to an enhancement in the trapped proton density, greatly enhanced E-region electron concentrations are assumed, particularly in the auroral zone. Such enhanced electron concentrations are known to occur when blanketing sporadic E is observed. The observed correlation between blanketing sporadic E and the strength of the electrojet current is thus predicted by the present theory. The interaction of the tidal wind system with the belt of trapped protons is also considered. The resulting auroral electrojet currents oppose the Ds a current system if the usually accepted pattern of upper atmospheric tidal winds is assumed; the existence of a different wind pattern at high latitudes, at least during geomagnetic storms, is a possibility that cannot altogether be excluded, although it appears unlikely. If the majority of energetic particles in the radiation belt were electrons, their interaction with the usually accepted tidal wind pattern would result in the correct phase for the Ds current system; satellite observations indicate, however, that the majority of the energetic particles are protons. The present theory can also account for the generation of meridional static electric fields of the type that, according to a theory of Megill and Carleton, cause midlatitude red arcs.

BLANKETING BY PLASTIC TUBING IS USED TO PREVENT BOND BETWEEN STRAND AND CONCRETE NEAR THE ENDS OF PRETENSIONED PRESTRESSED GIRDERS. TESTS OF FIVE 34-FT. T-BEAMS INDICATED THAT THE BONDED EMBEDMENT LENGTH REQUIRED BY SECTION 2611 OF THE 1963 ACI BUILDING CODE IS INADEQUATE FOR BLANKETED STRAND. TWICE THIS ANCHORAGE LENGTH IS NEEDED TO DEVELOP THE ULTIMATE FLEXURAL AND SHEAR STRENGTH OF GIRDERS WHEN BLANKETING IS USED. /AUTHOR/

Forward-oblique ionograms made on the path from Thule, Greenland, to College, Alaska in 1963–1964 were studied to determine whether HF signals propagating through the auroral curtain were adversely affected by scattering or blanketing effects. The location of the aurora was determined by an HF radar at College. Neither scatter from the auroral curtain nor blanketing by the auroral-E layer was found to significantly affect the 1F forward-oblique propagation mode on the Thule-College path. Higher-order modes and spread signals diminished appreciably at the onset of an auroral disturbance and reappeared with the decay of the disturbance. The disappearance or marked attenuation of the 1F mode on the Thule-College path was almost always found to be caused by an increase in auroral absorption and not by blanketing or scattering effects. Although auroral-E critical frequencies near 65° magnetic latitude were frequently above 5 MHz, they were rarely above 2 MHz between 70° and 72°, indicating the presence of a strong southward gradient in the electron concentration of the auroral-E layer between 65° and 72°. In an earlier paper it was concluded that auroral sporadic E caused the observed cutoff of the ground scatter echo at the range of the auroral curtain. This suggestion is discussed in light of the results presented in this paper.

The Es region as recorded on routine h'f records taken at Brisbane (latitude 27°.5 south, longitude 153°.0 east) between June 1943 and December 1949 has been studied. At all seasons the critical frequency is lowest at dawn. In summer months, the critical frequency reaches a maximum at about 10h and then declines gradually, remaining high until after midnight. In winter, the rise is slower and the maximum critical frequency occurs around 14h, dropping markedly by sunset. In general, a high Es critical frequency is accompanied by blanketing of F echoes up to a comparatively high frequency; but, whereas the occurrence of high critical frequencies shows a summer maximum and a winter sub-maximum, the occurrence of high blanketing frequencies is least frequent in winter. The observations suggest that there are two distinct types of Es common at Brisbane—one formed at greater heights and descending to its final position, the other formed in situ. The first, the predominant type in summer, blankets strongly and has probably a uniform ionization density; but the second, the winter type, blankets little and probably has pronounced lateral irregularities. No evidence of correlation could be found with sunspot numbers, ionospheric storms, or meteor occurrence frequency, and the conclusion is reached that the Brisbane Es is not predominantly of meteor origin. There is some slight evidence of correlation between the constant-height type of Es and F region diffuseness.

Standard measurements of sporadic E blanketing frequencies (ƒbEs, assumed to indicate peak ion densities) during November 1965 from three temperate latitude stations are examined in the light of current theory that predicts two important properties of this variety of sporadic E: (a) that major events consist predominantly of slowly-recombining monatomic ions, probably of meteoric origin, and (b) that these ions converge and accumulate in thin layers through combined effects of the geomagnetic field and the profile of horizontal winds. Two such levels of convergence seem to be indicated by daytime ƒbEs data. The hypothesis of a meteoric origin for the ions suggests that major events of ƒbEs might correlate with the increased meteoric mass arriving during large showers, as shown by radar meteor data. Some evidence of this correlation is shown during the November 1965 Leonid meteor shower.

Two computer programs have been used to compute flux constant model atmospheres, which include the effects of convection as well as line blanketing, for solar type stars. One program computes a model atmosphere and then calculates the integrated radiative flux and convective flux as a function of optical depth. After applying a line-blanketing correction to the fluxes, temperature corrections are calculated and a new model atmosphere computed. A second program computes the line blocking of a model atmosphere as a function of optical depth. The line-blocking data, expressed as a function of the radiative flux computed without allowance for line absorption, is used by the model atmosphere program to allow for line absorption effects. This method of com. puting line-blanketed model atmospheres, the flux-fraction method, does not make the opacity correlation assumption that is inherent in the giant-line method. Model atmospheres have been computed for the Sun, a metal deficient star (STAA/H! = -0.6) and Groombridge 1830 and the colors of these models are discussed. The models do predict the observed variation of ultraviolet excess, delta (U-B), with metal abundance. (auth)

The methods of constructing a model atmosphere and computing its theoretical spectrum are reviewed, attention being directed to the restrictions which are imposed and to the simplifications which are made in representing the interactions between radiation and matter. One important restriction is that it is assumed that Boltzmann's, Saha's and Kirchhoff's laws are valid throughout the atmosphere. However, observation indicates that these relationships are certainly not valid in those parts of the atmosphere where many of the strong lines which are used for classifying O B stars are formed. More accurate theories of line formation are required to predict the strengths and shapes of lines from the lowest levels and from metastable levels or levels connected to the metastable levels by strong transitions in the spectra of the light elements. It is pointed out that the constraints radiative equilibrium and hydrostatic equilibrium do not define sufficiently accurately the parts of the atmosphere where many empirically selected classification lines are formed. Here the motion of the gases seems to play a significant role in determining the shape and strength of the absorption lines. Some examples are given of the differences between the line profiles predicted from blanketed and unblanketed early-type models and it is shown that these differences would not be readily detected from the usually observed spectrum in the range 3500 A to 5000 a. Although line blanketing lowers the effective temperatures of O B models by 2500° to 3000° from the values estimated by means of unblanketed models, the unblanketed models are adequate for interpreting the spectrum between 3500 A and 5000 A and deducing abundances from weak lines.

The paper describes the results of measurement on the variation of reflection co-efficient of the sporadic E echoes and of the statistical study of the variations of amplitude of the same, carried out, over a period of 8 months (March to October, 1952) at the Ionosphere Laboratory of the University of Calcutta. It has been possible from these measurements and studies to discriminate between two types of Es ionisations —thin layer type and ion cloud or blob type—causing the echoes. It was found that there is predominance of different types of ionizations at different hours of day and night. Thus in 78.6% of the cases observed in the early morning hours, the Es ionization was of the cloud or blob type of structure. It is suggested that this type owes its origin to ionization by sporadic meteors which are most frequent in the early morning. During the period of sunrise in the E layer, thin layer type of ionization were found in 83.7% of the cases. Such ionization is probably caused by the production of a sharp ionization density gradient at the bottom of the E layer, due to photo-detachment of electrons from negative ions of 0 and 02 by sun's rays coming from below the horizon. The most common type of Es ionization in the afternoon and evening hours was found to be a mixture of the thin layer and ion cloud types. These owe their origin to travelling ion clouds coming from above. Observations also showed that Es ionization (of the mixed type, with a slight preponderance of the thin layer type) was associated with thunderstorms. Blanketing types of Es are also observed during thunderstorms. Occasionally, some thin layer types of ionizations were also observed in the morning, a few hours after sunrise. The origin of these ionizations seems to be due to some modifications of the E layer structure.

A long term series of absorption observations on up to eight frequencies has been made at Breisach, near Freiburg. Apart from the usual studies a discrimination between deviative (E) and non-deviative (D) absorption has been made. In the investigation those cases where blanketing Es was present have been treated separately. The results for a period of four years have shown: 1. (1) The diurnal variation is mainly due to the non-deviative part; the parameters of the deviative absorption remain nearly constant during daylight hours. 2. (2) An asymmetry exists, evening values being considerably higher than the corresponding morning values. 3. (3) The average diurnal variation (after shifting for the asymmetry) gives different cos χ-laws in summer and winter; the exponent is about 0.8 in summer but only 0.45 in winter. 4. (4) The seasonal variation is largely influenced by systematic height variations of the E-layer. 5. (5) The sunspot cycle variation has shown a positive correlation for both absorption influences. A “saturation” occurs when the average sunspot number number reaches 160.

To assist in the interpretation of ultraviolet continuum observations, we present observational features of a grid of non-grey model atmosphères in strict radiative equilibrium which have effective temperatures in the range 10000 °K to 20000 °K and surface gravities 103 and 104. For three models, we add the blended wings of the higher Balmer and Lyman hydrogen lines and include in an approximate way further effects of line blanketing in the ultraviolet. Finally, we present a preliminary calculation of the effect of departures from L. T. E. on the continuous flux.To examine the validity of the models, we compare the predicted continuous flux and predicted line profiles with the corresponding observed quantities for Vega and Sirius.We consider the question of discrepancies between theory and observations in the ultraviolet from the viewpoint of these new calculations, and find generally good agreement with recent observations made by T. Stecher.

The effect of the intermittent passage of gas bubbles entrained in the sodium coolant on the integrity of the fuel rod cladding is examined for typical conditions of liquid metal fast breeder reactors. The maximum stable size of the bubbles is calculated to be of the order of 0.5 in equivalent spherical diameter. The transient blanketing of the fuel rod due to the passage of the bubbles is studied for two extremely conservative geometrical configurations. The maximum calculated cladding temperature increase during the transient was found to be fairly limited, and the thermal fatigue effect due to the passage of a large number of bubbles was assessed. It appears that even in the most pessimistic conditions the fatigue effect is well below the failure limit. It has been concluded, therefore, that gas bubbles flowing through the core do not endanger the cladding integrity and do not reduce the fuel rod lifetime.

The simultaneous observations of midlatitude sporadic E by rockets and ionosondes are analyzed to compare the rocket-observed maximum plasma frequency in Es with the corresponding ionogram values of ƒbEs, ƒEs, and ƒoEs. The results of the analysis show that (i) the blanketing frequency (ƒbEs) gives the maximum electron concentrations in the Es layers within an error of about 10% on the average, and (ii) both ƒEs and ƒoEs give electron concentration values exceeding the rocket-observed maximum electron concentrations by 40–100% during daytime and by several hundred per cent during nighttime. The deduction of ƒoEs from the observed ƒEs and the identification of ƒoEs with the ordinary ray ‘critical frequency’ of Es are shown to be questionable.

A self-consistent model of the Venus atmosphere that satisfies the multitude of existing observational data is proposed. Its main properties and the line of reasoning are described as follows. The radiative greenhouse effect cannot account for a surface temperature of 570°K. The blanketing must be due to dust; and the main source of energy, wind friction at the surface. The term ‘aeolosphere’ is proposed for the region between the surface and the clouds of Venus, where wind is responsible for grinding and raising the dust as well as for the heating. Self-consistency requires the opacity to be so high as to impose an adiabatic vertical lapse rate. The potential temperature in the aeolosphere must be nearly constant. Horizontal pressure gradients driving the wind are caused by climatic differences near the top of the dust clouds. The dust may consist of calcium and magnesium carbonates with impurities. Pressure estimates from CO2 bands and optical scattering point to the presence of two distinct reflecting layers, the visible cloud level at about 0.6 atm and 340°K, and an upper haze level at 0.08 atm and 234°K. In the visual and near infrared the upper haze is virtually transparent, owing to forward scattering. In the ultraviolet, and in the infrared beyond 1.4 microns, it is opaque. Vertical cross sections of the Venus atmosphere are constructed for 80, 40, and 20 per cent CO2. For 80 per cent CO2 the results are somewhat more consistent, yielding a pressure of 4.3 atm at 570°K at the surface, 22 km below the visible cloud level. Despite uncertainties in the H2O content, its amount is so small as to be nowhere condensable.

We consider some theoretical models of crater destruction to explain not only the exponent −2 of the equilibrium distribution of crater diameters, but also the density coefficient and its regional variations, Destruction of small craters appears to be governed principally by blanketing or filling by ejecta, and the equilibrium density coefficient decreases with increasing size of the largest crater affecting the region studied. Destruction of large craters seems to depend mainly on destruction of a substantial part of the crater wall by a crater of similar or greater diameter. Only certain south polar and far-side continental regions appear to be saturated with craters.

An examination of the ionospheric records at Kodaikanal, which is located almost on the geomagnetic equator, reveals that the sporadic E layer here has some regular features not observed at other latitudes. It occurs in nearly 93 per cent of the half-hourly records during the daytime. Two main types of Es are observed; namely, (1) the patchy type with a well-marked diurnal variation, and (2) the blanketing type which occurs mostly during afternoons. It is found that neither meteoric activity nor thunderstorm activity has any appreciable influence on the formation of either of the two types of Es. No correlation is observed between Es and the geomagnetic field.

Ionosonde data, obtained on blanketing sporadic E at some equatorial stations during the I.G.Y. have been analysed to yield temporal and latitude variations. The results are compared with corresponding ones for the middle latitudes and they are also discussed in the light of the wind-shear mechanism. The main features of the occurrence frequency are (i) the absence of a morning peak in the daily variation, (ii) an equinoctial maximum and a June-solstitial minimum, (iii) and a stronger dependence on the dip angle (or geomagnetic latitude) than on geographic latitude. The latitude variation obtained also suggests that blanketing sporadic E would occur over both the dip and geomagnetic equators.

Attention is drawn to the difficulties encountered at many stations in interpreting absorption measurements made by the classical vertical incidence pulse amplitude method. Results obtained by comparing echo amplitudes of different orders show a serious discrepancy (amounting to 15 db in some instances) from absorption values deduced by different methods. It is generally assumed, to a first approximation, that the ionospheric layers are plane and parallel. It is also assumed that absorption may be measured by comparing the echo amplitudes of the first and second order reflections, or by comparing the amplitude of the first order reflection to a standard value I 0 expected on the basis of zero absorption. Appropriate height corrections are made. A detailed study was made of the numerous amplitude recordings obtained at Domont (near Paris) on 3.4 mc/s from September, 1955 to March, 1957. Results show that the absorption value L 1 (derived by comparing the first and second order echoes returned from the F region) is systematically smaller than the value L 3 (determined by comparing the first order echo amplitude with the standard, zero absorption, value I 0 ). Graphs show that the larger the value of absorption, the greater this discrepancy. The difference is materially reduced when reflections occur from blanketing sporadic E. Moreover, the amplitude records show that second order echoes exhibit a rather long period fading (about 10 minutes), much deeper than that found for the first order echoes. There is no correlation between the fading of the first and second echoes. It also frequently happens that the first order echo amplitude remains almost constant while the second order echo amplitude reaches and even exceeds this value for periods of several minutes. Reflections from sporadic E never display such a phenomenon. It is concluded that ionospheric focusing, when present, affects second order amplitudes much more than anticipated. The effect probably arises from the longer optical path of these echoes compared to that for a first order reflection. Because of this effect, absorption measurements should be made, preferably, by a comparison of the first order amplitudes with the standard constant I 0 .

The majority of British distant-water trawlers use echo sounders for the detection of fish. Previous forms of display have been: ( a ) a recorder producing an intensity-modulated chart of a range annulus (e.g. 60 fathoms) and ( b ) a cathode-ray tube scale-expander showing the range just above the sea bed (5 to 10 fathoms), which is of interest for trawling. In the new equipment the transmitted power has been increased to 8 kW and the transducer is lowered 2 ft below the vessel to reduce “blanketing” by aerated water. The displayed range is locked to the sea-bed echo and is therefore independent of changes in depth due to the sea-bed contour or to vertical movement of the trawler. The locking is done by storing echoes in the range adjacent to the sea bed on a magnetic recording drum. These echoes are observed on a cathode-ray tube, in which the signals are replayed many times while the next pulse is travelling out and back so that the trace appears virtually continuously, and also on a recorder, in which stylus movement is triggered by the sea-bed echo and the stored signals are recorded on electro-sensitive paper. Only the range within 4 fathoms of the sea bed is displayed and this is locked to the sea-bed echo

Sporadic-E (ES) data from Japan were presented to show the temporal variations in sporadic-E blanketing frequency (ƒbES), virtual height (h′ES), and frequency of occurrence. Tidal winds were substituted into the wind-shear theory of ES to calculate electron density profiles and determine the influence of the tidal winds in the asymmetry of the ES occurrence variation. Results showed that the tidal wind model used was not strong enough to significantly influence the formation of molecular ion ES layers, but that the winds did have the proper orientation to accumulate and layer metallic ions in the late afternoon. The role of metallic ions in afternoon ES will have to be established.

The increasingly high flux predicted to the violet of 4500 A by many model solar atmospheres stands in contradiction to the observations. Since one possible cause of the disagreement is that the solar ‘windows’ by which the observed continuum is established might be obscured by line wings, we have made detailed calculations of these narrow spectral regions. With the exception of a few windows affected by the wings of Balmer lines, those redward of the Balmer discontinuity appear free of line blanketing. Even the assumption that the ultraviolet continuum is depressed 5% by unseen lines not included in our calculations leaves substantial disagreements between the models and observations. The discrepancies could perhaps be explained by a veil of weak lines across the ultraviolet spectrum.

The question is raised as to whether multiple erosion surfaces that have been described in a number of recent papers actually exist, and, if so, whether they have been correctly interpreted as products of repeated partial peneplanations. Analysis of the criteria used for determining such surfaces indicates that some are not adequate. Particularly, the use of ridge crests, isolated hills, and spurs as markers of former erosion levels is unsafe. Too little correlation has been made between surface form and rock resistance. Analysis of what happens after an old-age surface is rejuvenated indicates that stream-bed grading is very rapid relative to inter-stream degradation, so that the “treppen” concept of stair-step-like benches with bordering scarps retreating across a region following successive rejuvenations of a master stream cannot ordinarily be valid. Multiple erosion surfaces at small vertical intervals are difficult to explain as products of sub-aerial erosion working toward intermittently lowered base levels, but they are entirely expectable results of another process that has been given too little attention. Progressive burial of surfaces planed by the waves of an intermittently advancing sea, or of pediment surfaces bordering a mountain range in an arid land, followed by uplift and stripping of the blanketing sediments, is not only a competent cause of the production of multiple surfaces but so inevitably leads to their production that such an explanation should receive first consideration where multiple surfaces can be definitely proven. Application of this principle to the interpretation of the physiography of the Front Range of the Rocky Mountains is suggested.

In the temperate zones, it is known that ƒ0Es and ƒbEs are insensitive to gain changes of the ionosonde used to measure them even when ƒbEs is much less than ƒ0Es. Such insensitivity may be accounted for if the sporadic-E layer has a peak electron density which varies rapidly horizontally such that the corresponding critical frequencies within an area of the order of the first Fresnel zone have a normal “Gaussian” distribution with standard deviation Δƒ. If the mean critical frequency ƒM, then ƒ0Es is a little greater than ƒM + 3.1 Δƒ and ƒbEs, a little less than ƒM − 1.2 Δƒ. Thus the blanketing frequency is a better measure of the mean peak electron density in the sporadic-E layer than is the critical frequency.

Heat-transfer coefficients are presented for water flowing vertically in thin rectangular channels (0.1 × 2.5 in.) 18 and 36 in. long and heated electrically around the entire periphery. The range of variables covered is: 65 to 200 psia pressure, 90 to 200 F sub-cooling, and 4 to 50 fps water velocity. Heat-transfer correlations are given for data along the narrow and wide faces of the rectangular test section. Burnout data also are reported with steam blanketing occurring first at the corner of the test section. The proposed correlating equation, valid at the narrow face of the test section, gives values considerably lower than those obtained in a circular pipe.

From station's observations much information on top-frequencyfEs, less on blanketing frequencyfbEs is obtained. The results must be interpretated in statistical terms. Time- and distance-correlation functions are established. Daily, seasonal and geographic regularities are discussed. A sharp maximum exists at the magnetic equator but only for the top-frequency. No well defined influence of the solar cycle has been found, only a very weak one of lunar tides. Apart the routine evaluation observations of the variation of the reflection coefficient with frequency have been made. In temperate latitudes in about 1/3 of all cases there is no partial reflection; in the other cases local variations of electron concentration up to 1:2 are found, higher values are rare. At low latitudes the variation may be more important. This is found by a qualitative classification of ionograms of different stations. Such classification has been made for transparency, scatter, angle of incidence and layer developpement. Diffuse echoes exist often near the magnetic equator.Es is always vertically sounded at temperate latitudes. In most cases the ionization originates as a thin layer of constant altitude. Transitory phenomena coming downwards are responsible for «E2s» in daytine. It appears that a cumulo-cirrus-cloud layer is a good model forEs-ionization. An atmospheric ionization process using stored energy from dissociation or ion existence seems to be most probable.

The presence of suspended solids and ferric chloride in solution are shown to have a deleterious effect on the performance of a biological film reactor. This effect is thought to result from a blanketing of a fraction of the liquid-micro-organism interface preventing it from taking part in the mass transfer process. In the former case the blanketing occurs as a result of entrapment of the solids on the surface of the gelatinous mass and in the second case by adsorption.

It is important to separate the D and E layer contributions, respectively, when interpreting results obtained by the usual determination of the apparent reflection coefficient. One criterion which can be used is the different frequency variation of both non-deviative and deviative absorption. Hitherto, for deviative absorption, a one parametric formula depending upon the E layer critical frequency has been used. This procedure failed when blanketing Es was present; for a fixed frequency, a higher reflection coefficient was obtained than for even the thick, normal E layer. With a thin layer model for sporadic E, a new formula has been obtained which depends upon two parameters, f o E and the cusp frequency, f r . One and a half years' data for noon were reduced on this basis. Results may be described in terms of a parameter B (characterizing the non-deviative absorption) and a parameter C (essentially proportional to the product of collision frequency and half thickness of the E layer). A greater seasonal variation was found for C than for B. The summer maximum of absorption was found to arise from deviative absorption. During summer the E layer occurs at lower altitudes; i.e. in a region of higher collissional frequency. The value of B is nearly constant from February through August and appears to have its minimum in November. The well known winter anomaly is an effect of non-deviative absorption and has its maximum during January. The daily variation has been checked using three days of observation each month. For the parameter C, the daily variation was small, so that the maximum of absorption near noon is essentially an effect of non-deviative absorption. Another interesting result was noted during SID periods: the value B became very large whereas C remained unchanged. The day to day dispersion of absorption is not greater than that of other ionospheric characteristics. The quartile dispersion is ±10 per cent for B and ± 14 per cent for C. Again, the variability of conditions in the E region is rather large in comparison to those of the D region.

Hourly measurements of the blanketing frequency of sporadic E(ƒbEs) made during the years 1958 through 1965 have been analyzed for lunar daily variations. The data, which came from ten stations, were analyzed by the Chapman-Miller method. Both seasonal and yearly average lunar variations were obtained. The lunar semidiurnal oscillations in ƒbEs ranged from 0.01 to 0.04 MHz, with maximums occurring from 7 to 9 hours lunar time. The amplitude of the lunar tide in ƒbEs is an order of magnitude less than the lunar variations of ƒ0Es. Since ƒbEs is close to the plasma frequency of Es, the oscillation in ƒbEs represents a lunar variation in the electron density of Es layers, whereas the significance of the lunar variation of ƒ0Es is not clear. The phases of the lunar tides in ƒbEs, ƒ0Es, and h′Es are found to be nearly the same. Two sources of lunar influence on Es electron density are considered (1) wind shears in the lunar tide acting to augment or decrease the wind shears responsible for E8, and (2) interaction of E8 with electrostatic fields associated with the lunar current system.

An in-depth study of blanketing sporadic E (Es) layers at temperate latitudes has been carried out with the purpose of clearly establishing many pertinent details of their temporal and latitudinal variations. A new method of analysis has been used in which blanketing Es layers have been separated into four groups according to their intensity, which is defined in terms of the ratio (ƒbEs/ƒoE). From an analysis of eight-years' (1958–1965) data of hourly ƒbEs, values at ten stations, it has been possible to establish, for the first time, that (1) Es layers of different intensities show different daytime variations with regard to their occurrence, and (2) there is a clear-cut change from higher to lower midlatitudes in the pattern of these daytime variations. It is shown that the daytime Es occurrence does not go through two maxima at all latitudes and in all seasons. The seasonal and solar cycle variations in the average ƒbEs and in the percentage occurrence of Es layers in each group are also shown. The ƒbEs values of intense Es layers show a marked decrease with decreasing solar activity, and this indicates the existence of solar cycle variation in the neutral wind shears and possibly in other relevant parameters in the E region. On the other hand, the occurrence of ‘intense’ and ‘moderately strong’ Es layers shows an increase with decreasing solar activity. Both features are shown to be consistent with the conclusions of wind-shear theory. A careful analysis of the Es variations with geographic latitude and with H (the horizontal component of geomagnetic field) has produced no unambiguous evidence for the dependence of Es occurrence or ƒbEs on H; and the inability of the present analysis to bring out this theoretically predicted dependence is attributed to the possibility that significant variations of neutral wind shears with latitude and geographic location can easily obscure the dependence on H. It is shown that the abnormally high incidence of ‘intense’ Es layers at Kokubunji is a purely summertime phenomenon. It is pointed out that this high incidence at Kokubunji cannot be explained in terms of the large H value alone, but the occurrence of very strong wind shears at this station has to be assumed. It is emphasized that much self-restraint is needed against making simplistic statements about the observed morphological characteristics of sporadic E.

THE ULTRAVIOLET excess 6(&B) relative to the Hyades main sequence stars can be used to determine metal abundances of stars in the range 0.4 I B-VI 1.0. The blanketing lines or blanketing vectors for dwarf stars in the two-colour diagram are given by SANDAGE and EGGEN and by WILDEY et al. ‘*) The resulting differences A(U-B) and A(&I/) between observed colours and colours of a star with the same effective temperature T, on the Hyades sequence can then be calibrated in terms of the metal abundance u (WALLERSTEIN and CARLSON, BASCHEK,(~) WALLERUEIN@‘). Recently DEUTSCH and CONTI@) pointed out that a change in microturbulence velocities { from 0 to 2.6 km/set affects the U.V. excess up to 0.06 mag. Hence small excesses must not indicate an effect of low metal abundances alone. An additional scatter in the ultraviolet excesses is introduced if slightly evolved stars are mixed with main sequence stars. This effect and observations of colours of globular cluster stars make it desirable to give a theoretical interpretation of the influence of the surface gravity g on the UBI/ colours, thus allowing to apply the blanketing vector procedure also to subgiants and giants. Model atmospheres have been constructed for two values of surface gravity, g, and go/100 roughly corresponding to luminosity classes V and III, in the range of T, from 6250 to 5000°K. A scaled solar T(r) relation (HOLWEGER”‘) was used for all models since differences in line intensities due to the g-effect are relatively small. In fairly good approximation the influence of g and of tl on the colours can be treated separately. The back-warming effect has to be taken into account only once and is already included in the tables of Wildey et al. (equivalent to a change of T, from a star with solar metal abundance to a low metal-abundance star). The colour is written

The importance in the blanketing effect of the wings of strong lines broadened by collisions is evaluated. It is found that in stars of spectral types F5-K5 the cumulative absorption by a group of lines is due half to the center of the lines and half to the wings. For the same stars it is evaluated the influence of the collisional broadening on the computed color indices (U-B), (B-V).

The parameters controlling the development of a simple model of the E and F regions of the ionosphere are discussed. Uses of such models in scientific investigations and engineering applications are given. A computer model is described that will provide estimates of the electron and ion densities in middle latitudes as a function of latitude, longitude, altitude, season, time, and solar activity. Statistical parameters for midlatitude blanketing sporadic E are presented. An analytic expression is used for the CIRA 1965 neutral atmospheric models. The F1 region is treated using a photoequilibrium model with three ionic constituents and 62 ionizing radiation groups. The F2 layer uses theoretical models arranged to fit boundary conditions of NmF2, HmF2 and the electron density at 1000 km. Values of NmF2 are obtained by using the CCIR atlas of ionospheric characteristics. The midlatitude sporadic E layer is treated by presenting three parameters of the layer: the probability of observing sporadic E with a blanketing frequency greater than 0.5 MHz, the average peak electron density when sporadic E is observed, and the standard deviation (assuming log normal distributions for the peak electron density). The restrictions on the model and the availability of data on suitable boundary conditions are discussed. Suggestions for further development of models of the ionosphere are given.

The daytime measurements of the velocities and other fading characteristics of equatorial Es and blanketing Es irregularities in the frequency range 4–6 MHz are presented for Ibadan. The modes of signal returns by the two groups of Es are discussed. The experimental results suggest that the equatorial Es irregularities observed in the 4-6 MHz frequency range at Ibadan are of a similar nature to those observed at 50 MHz at Huancayo during a weak electrojet. A tentative inference from the equatorial Es results is that the magnitudes of equatorial Es velocities may be independent of the relative strength of electrojet intensity.

A careful survey of quarter-hourly ionograms for the year 1969 has shown that blanketing layer type ionization irregularities occur on many occasions in the E-region of the ionosphere over Trivandrum (dip ∼ 0.6°S). It is shown that horizontal shears of horizontal neutral winds are the most likely sources of such layer type irregularities at the magnetic equator. The horizontal wind shears of required magnitude are shown to be provided by internal gravity waves of short period. The rarity of Es-layer occurrence is attributed to the stringent requirements on the amplitude and wave vector orientation of the relevant gravity waves generating the Es-layers.

Polarization measurements on high frequency radio waves (2–8 Mc/s) reflected from blanketing and semi-transparent types of E s show that the blanketing type of E s reflects both the magnetoionic components, while the semi-transparent type reflects in general more of the extraordinary than the ordinary component, the X -magnetoionic component alone being reflected on a good number of occasions.

Corrections are given which transform the Tables of the solar radiation data (Labs and Neckel, 1968) into the ‘International Practical Temperature Scale of 1968’. Additionally, for the adjustment of the data of the ‘true continuum’ and the corresponding line blanketing as well, the veiled line effect mentioned first by Carbon et al. (1968), but studied in more detail by Holweger (1970a), has been considered also. The corresponding corrections of the solar irradiance result in an improved value of the spectrophotometric solar constant: S = 1.947 cal cm-2 min-1 or 0.1358 W cm-2. Two Tables presenting the ‘highest (window-) intensities’ and the corrected irradiance data have been added.

The blanketing type sporadic- E which frequently occurs with a high penetration frequency near the magnetic dip equator is explained as a thin layer of enhanced ionisation. It is shown that this enhancement could occur where the dip angle is greater than zero but less than a few degrees, and the electric intensity has a small component directed towards the equator. The variations in the horizontal intensity and the declination of the earth's magnetic field recorded at Addis Ababa (dip angle = 1.42°) appear to be consistent with this pattern of the electric intensity. It is shown how the occurrence of this type of layer would modify the scattering from wavelike irregularities arising from a two-stream or other plasma instability.

Sharply delineated closed depressions, one-half to tens of kilometers across, with 400 meters estimated maximum depth, are locally abundant in the south polar region. They indent the surface of a massive homogeneous blanket that mantles the cratered bedrock surface. Some pits extend through the blanket exposing the underlying rock floor, and, where the blanket is thin (50–100 meters), its extensive removal exposes large ares of exhumed rock floor producing a terrain described as etched. The blanketing material is speculatively interpreted to be an eolian sedimentary deposit containing a mixture of fine particulate matter, possibly including volcanic ash, and particles of frozen volatiles, principally CO_2and H_2O. Fields of dunes, groups of linear grooves and flutes, and an unusual scoured topography on the surface of layered blanketing material suggest strong wind action. For this reason, deflation by wind, aided by ablation (evaporation) of included frozen volatiles, is regarded as the most likely mechanism for producing the south polar pits and etched terrain. Pitted and etched terrains and the deposits into which they are cut suggest that the south polar region, and presumably the north polar area as well, have experienced alternating episodes of eolian deposition and erosion.

The characteristics of midlatitude sporadic-E layers are observed using rocket payloads incorporating a probe and a propagation experiment. Layers below 120 km show evidence of preferred altitudes. The slopes of layers are within 1 deg of horizontal. The horizontal dimensions are deduced to be several hundred kilometers. Individual profiles of daytime layers show a range of shapes ranging from triangular to rectangular. The plasma frequency derived from the peak electron density in the layer is found to agree with the blanketing frequency given by the local ionosphere sounder.