Wolfgang Priester

Time-Dependent Structure of the Upper Atmosphere

Abstract The physical properties of the upper atmosphere are determined mainly by heat conduction, the heat sources and the barometric law. An analysis of the integro-differential equation which describes these physical processes has been carried out. It is found that heating of the thermosphere due to absorption of the solar extreme ultraviolet (EUV) radiation alone cannot explain the observed diurnal variation of density and temperature, since it would yield a maximum of these properties at about 17h local time, instead of 14h where it is observed. Secondly, if the EUV flux is adjusted to give the observed average temperature, then the diurnal variation in density would be much too large compared with the observed amplitude. Thirdly, it would require an extremely high efficiency for the conversion of EUV radiation into heat, if we compare the required flux with Hintereggers measurements of the EUV flux. Thus, it is necessary to have another heat source in addition to the heating due to absorption of EU...

Of the Diurnal Variation of the Upper Atmosphere

Abstract The diurnal variation of the upper atmosphere as revealed from satellite drag measurements has been further investigated on the basis of a simultaneous integration of the heat conduction equation and the hydrostatic law. In addition to the beat source due to absorption of solar extreme ultraviolet radiation and the hypothetical “second heat source,” the heating due to absorption of solar radiation in the Schumann-Runge range by oxygen molecules has been included. Furthermore, the effects of time-dependent variations in the boundary conditions on the phase and amplitude of the diurnal variation in the upper thermosphere and exosphere have been investigated. Also the effects of lateral heat conduction and lateral convective heat transport on the diurnal variation of density and temperature are discussed. The main purpose of the paper is to investigate several possibilities which could be thought to eliminate the requirement for the “second heat source.” It is shown that neither the inclusion of abs...

Vacuum energy in a Friedmann-Lematre cosmos

The age of our Galaxy has been derived from two different sets of Th/U ratio measurements in meteorites to be 20.8 (+ 2, 4 ) or (17.6 +4)109 years [28, 27]. This implies a lower limit for the age of the universe of 14.10 9 years if we accept the method as reliable cosmic chronometer. A consequence of this is that solutions of the Einstein-Friedmann equations with zero cosmological constant A are only possible if the present Hubble parameter H 0 < 7 0 k m s l M p c 1 (see Fig. 4 of Par t I of our review [2]). On the other hand derivations of the Hubble parameter from observations span a range from 50 (+ 10, 7 ) E24] to 100 ( 1 0 ) kms -1 Mpc -1 [4]. At the Patras meeting of the International Astronomical Union the value of 75 was favoured. The acceptance of this value would imply that solutions of the Friedmann equations require values of the cosmological constant A which correspond to an equivalent constant vacuum density P~>Po, where Po is the present matter density of the universe. This situation has prompted us to reinvestigate solutions of the cosmological equations with nonzero A, An average value of the present density of the baryonic matter po,B = 0 . 5 . 1 0 3 ~ -3 has been derived from the primordial 4He and 2H abundances. This value is independent of the special choice of the Hubble parameter. Quantum field theory permits to interpret A as vacuum energy density C 4 ,%=pvc 2 -A (1) 8riG

On the Semiannual Variation of the Upper Atmosphere

Abstract Several possible mechanisms are investigated which could be invoked to explain the observed semiannual density variation in the thermosphere and exosphere. A variation of the height of the mixtopause leads to a large density variation for heights above 700 km. Below that height, however, the density is essentially invariant to this process. This invariance is to some degree caused by the neglect of downward heat transport by eddy diffusion at the bottom of the thermosphere. The limitations of using the simple mixtopause scheme in this context are discussed. Another mechanism can be ruled out on the grounds that it fails to explain the observed amplitude at a height of 200 km. This mechanism is a small permanent heat flux conducted into the lower exosphere from above. A variation of this flux by 3×10−2 erg cm−2 sec−1 would yield a sufficiently large density variation only for heights above 300 km. The recent observations at heights below 200 km indicate that the temperature and density at the bott...

The observational discrimination of Friedmann-Lemaître models

AbstractIt is the purpose of this paper to illustrate the interrelation between the problems of the ‘missing mass’, the galactic age and the cosmological constant A (or its equivalent quantum vacuum densityρv).The inflationary picture of the early universe predicts that our present universe should have a very nearlyEuclidean metric. If we accept this concept, one would have to discriminate between two rather extreme Euclidean cosmological models:(1)The standard model with ∧=0 and a densityρc = 3H028πG. There are difficulties ifH0≥5- km s−1 Mpc−1 and the galactic aget0≥14×109 years.(2)The Euclidean Friedmann-Lemaître models with ∧>0, i.e., Δgt;0, i.e.,ρv=ρc −ρo, whereρo is the present matter density, including the nonrelativistic dark matter. Hereρv ‘competes’ with the missing mass. Measurements of apparent diameters of galaxies up to redshifts of 2 will permit one to discriminate between the models provided that size evolution of galaxies can be determined or neglected (see Figure 3).

The structure of the thermosphere and its variations.

The diurnal variation of the thermosphere is the key feature for a theoretical understanding of the entire thermospheric structure and of its energy balance (heating processes, heat loss, conduction and convection). Earlier attempts (1962) at calculating the diurnal variation failed to yield the diurnal maximum of density and temperature at the observed local time of 1400. In these attempts no horizontal interaction was included. Recent calculations of the horizontal wind system, which is set up by the pressure gradients of the atmospheric bulge, have shown that winds of the order of 100–200 m sec−1 in the altitude range from 200 to 400 km can provide a large horizontal energy transport. It is not yet possible to decide, however, whether horizontal advection alone is sufficient to remove the whole discrepancy between the calculated time of the diurnal maximum (1700 local time) and the observed time (1400).

75 Jahre Theorie des expandierenden Kosmos: Friedmann Modelle und der “Einstein–Limit”

AbstractDie geschichtliche Entwicklung der kosmologischen Modelle für den homogen–isotropen Kosmos, beginnend mit Alexander Friedmanns epochalen Arbeiten (1922 und 1924) bis zur heutigen Diskussion aktueller Modelle wird dargestellt. Eine kardinale Rolle spielt die offene Frage: Besteht die Materie des Kosmos zum weit überwiegenden Teil aus nicht–baryonischer (sog. exotischer) Dunkel–Materie oder reicht die gesamte baryonische Materie aus, die aus den bekannten Atomen und Molekülen besteht, um die Entwicklung des Kosmos zu verstehen. Auch von der normalen (baryonischen) Materie im Kosmos ist nur ein geringer Anteil (etwa 20

Vergleich zwischen den Luftdichteschwankungen und der solaren 20 cm-Strahlung. Solare und tageszeitliche Effekte

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Kurzfristige Störungen beim Auftreten starker geomagnetischer Stürme

5 Prozent) in leuchtenden Objekten (Sterne, Gas, Staub) direkt beobachtbar. Im Abschnitt 3 wird der “Einstein–Limit” für die kosmologische Konstante erläutert und eine leicht einsichtige Herleitung des Zahlenwertes gegeben.

Modell der Hochatmosphäre für schwache, mittlere und starke Sonnenaktivität. Tageszeitliche Schwankungen von Dichte und Temperatur

In der Abbildung 1 wurde neben dem zeitlichen Verlauf der Luftdichten ϱ* fur die Hohen 208 bzw. 210 km, 260, 350 und 660 km uber der Zeitskala vom 1. Nov. 1957 bis 31. Juli 1959 die Variation der solaren 20 cm-Strahlung nach den Messungen am Heinrich-Hertz-Institut fur Schwingungsforschung Berlin-Adlershof eingezeichnet.