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- ItemSporadic Ca and Ca+ layers at mid-latitudes: Simultaneous observations and implications for their formation(München : European Geopyhsical Union, 2001) Gerding, M.; Alpers, M.; Höffner, J.; von Zahn, U.We report on the observations of 188 sporadic layers of either Ca atoms and/or Ca ions that we have observed during 112 nights of lidar soundings of Ca, and 58 nights of Ca+ soundings, at Kühlungsborn, Germany (54° N, 12° E). The Ca+ soundings have been performed simultaneously and in a common volume with the Ca soundings by two separate lidars. Correlations between sporadic neutral and ionized metal layers are demonstrated through four case studies. A systematic study of the variations of occurrence of sporadic Ca and Ca+ layers reveals that neutral and ionized Ca layers are not as closely correlated as expected earlier: (a) The altitude distribution shows the simultaneous occurrence of both sporadic Ca and Ca+ layers to be most likely only in the narrow altitude range between 90 and 95 km. Above that region, in the lower thermosphere, the sporadic ion layers are much more frequent than atom layers. Below 90 km only very few sporadic layers have been observed; (b) The seasonal variation of sporadic Ca layers exhibits a minimum of occurrence in summer, while sporadic Ca+ layers do not show a significant seasonal variation (only the dense Ca+ layers appear to have a maximum in summer). At mid-latitudes sporadic Ca layers are more frequent than sporadic layers of other atmospheric metals like Na or K. For the explanation of our observations new formation mechanisms are discussed.
- ItemOn the longitudinal structure of the transient day-to-day variation of the semidiurnal tide in the mid-latitude lower thermosphere - I. Winter season(München : European Geopyhsical Union, 2001) Merzlyakov, E.G.; Portnyagin, Yu.I.; Jacobi, C.; Mitchell, N.J.; Muller, H.G.; Manson, A.H.; Fachrutdinova, A.N.; Singer, W.; Hoffmann, P.The longitudinal structure of the day-to-day variations of semidiurnal tide amplitudes is analysed based on coordinated mesosphere/lower thermosphere wind measurements at several stations during three winter campaigns. Possible excitation sources of these variations are discussed. Special attention is given to a nonlinear interaction between the semidiurnal tide and the day-to-day mean wind variations. Data processing includes the S-transform analysis which takes into account transient behaviour of secondary waves. It is shown that strong tidal modulations appear during a stratospheric warming and may be caused by aperiodic mean wind variations during this event.
- ItemThree years of routine Raman lidar measurements of tropospheric aerosols: Backscattering, extinction, and residual layer height(Göttingen : Copernicus GmbH, 2002) Schneider, J.; Eixmann, R.We have performed a three-year series of routine lidar measurements at preselected times. The measurements were performed between 1 December 1997, and 30 November 2000, at Kühlungsborn, Germany (54°07′N, 11°46′E). Using a Rayleigh/Mie/Raman lidar system, we measured the aerosol backscatter coefficients at three wavelengths and the extinction coefficient at one wavelength. The present data analysis focuses on after-sunset Raman measurements obtained on cloud-free days. Aerosol backscatter profiles are available for altitudes above 100 m, while the majority of the extinction measurements has been restricted to heights above the residual layer. The residual layer shows an annual cycle with its maximum height in summer (2000 m) and minimum height in winter (850 m). The backscatter coefficients in the residual layer were found to be about 10 times higher than above. The mean aerosol optical depth above the residual layer and below 5 km is 0.3(±1.0) × 10-2 in summer, and 1.5(±1.0) × 10-2 in winter, which almost is negligible compared to values measured in during daytime in the planetary boundary layer. A cluster analysis of the backward trajectories yielded two major directions of air mass origin above the residual layer and 4 major directions inside. A marked difference between the aerosol properties dependent on the air mass origin could be found for air masses originating from the west and travelling at high wind speeds. Comparing the measured spectral dependence of the backscatter coefficients with data from the Global Aerosol Data Set, we found a general agreement, but only a few conclusions with respect to the aerosol type could be drawn due to the high variability of the measured backscatter coefficients.
- ItemGravitational lensing in astronomy(Berlin : Springer, 1998) Wambsganss, J.Deflection of light by gravity was predicted by General Relativity and observationally confirmed in 1919. In the following decades, various aspects of the gravitational lens effect were explored theoretically. Among them were: the possibility of multiple or ring-like images of background sources, the use of lensing as a gravitational telescope on very faint and distant objects, and the possibility of determining Hubble's constant with lensing. It is only relatively recently, (after the discovery of the first doubly imaged quasar in 1979), that gravitational lensing has became an observational science. Today lensing is a booming part of astrophysics. In addition to multiply-imaged quasars, a number of other aspects of lensing have been discovered: For example, giant luminous arcs, quasar microlensing, Einstein rings, galactic microlensing events, arclets, and weak gravitational lensing. At present, literally hundreds of individual gravitational lens phenomena are known. Although still in its childhood, lensing has established itself as a very useful astrophysical tool with some remarkable successes. It has contributed significant new results in areas as different as the cosmological distance scale, the large scale matter distribution in the universe, mass and mass distribution of galaxy clusters, the physics of quasars, dark matter in galaxy halos, and galaxy structure. Looking at these successes in the recent past we predict an even more luminous future for gravitational lensing.
- ItemCoherent motion of low frequency vibrations in ultrafast excited state proton transfer(Routledge : Taylor and Francis Inc., 1999) Pfeiffer, M.; Chudoba, C.; Lau, A.; Lenz, K.; Elsaesser, T.Photoexcitation of internal proton transfer in the tinuvin molecule causes the excitation of some low frequency vibrational modes which oscillate with high amplitudes in a coherent manner over 700 fs. Such effect is observed for the first time applying two color pump/probe measurement with 25 fs pulses. Based on resonance Raman spectra a normal coordinate analysis of the modes is performed. It is shown that the nuclear movement given by the normal vibration of one of the modes serves to open up a barrierfree proton transfer path.
- ItemResonance Raman and optical dephasing study of HITCI(Routledge : Taylor and Francis Inc., 1999) Kummrow, A.; Ashworth, S.H.; Lenz, K.Line shape analysis based on resonance Raman spectra of HITCI is used to determine the details of the vibrational part of the line broadening function. Forced Light Scattering with 20 fs pulses from a Ti: sapphire laser measured optical dephasing probing with an Ar+ laser. The observed response is well described by the line broadening function derived from the fluorescence line shape.
- ItemModification of Newton's law of gravity at very large distances(Amsterdam : Elsevier, 2002) Kirillov, A.A.; Turaev, D.We discuss a Modified Field Theory (MOFT) in which the number of fields can vary. It is shown that when the number of fields is conserved MOFT reduces to the standard field theory but interaction constants undergo an additional renormalization and acquire a dependence on spatial scales. In particular, the renormalization of the gravitational constant leads to the deviation of the law of gravity from the Newton's law in some range of scales rmin < r < rmax, in which the gravitational potential shows essentially logarithmic ∼ ln r (instead of 1/r) behavior. In this range, the renormalized value of the gravitational constant G increases and at scales r > rmax acquires a new constant value G′ ∼ Grmax/rmin. From the dynamical standpoint this looks as if every point source is surrounded with a halo of dark matter. It is also shown that if the maximal scale rmax is absent, the homogeneity of the dark matter in the Universe is consistent with a fractal distribution of baryons in space, in which the luminous matter is located on thin two-dimensional surfaces separated by empty regions of ever growing size.
- ItemSol-gel niobium pentoxide coatings: Applications to photovoltaic energy conversion and electrochromism(London : Hindawi Publishing Corporation, 2002) Aegerter, M.A.; Schmitt, M.; Guo, Y.In the last decade the sol-gel process became a promising method to synthesize materials in form of coatings, nanoscale powders and porous systems. Several products or devices made with such a process already exist on the market. This paper briefly reviews the state of the art in the development of electrochromic coatings and devices and nanocrystalline solar cells achieved during the last decade using sol-gel derived pure and doped niobium pentoxide.
- ItemMolecular dynamics investigated by temporally two-dimensional coherent Raman spectroscopy(Routledge : Taylor and Francis Inc., 1999) Lau, A.; Pfeiffer, M.; Kozich, V.; Kummrow, A.A six-wave set-up is described to determine molecular dynamics in the condensed phase. Applying two independent time delays between excitation and probe pulses additional information on the dynamics should be obtainable. We show experimentally that such investigations can be carried out with noisy light having intensity fluctuations in the femtosecond region. As first result we found a fast relaxation time in neat nitrobenzene of 100 fs, becoming even faster in mixtures with low viscosity liquids. Switching on a Raman resonance yields a longer relaxation time, which could be explained by an additional contribution by that vibration.
- ItemAbsolute density measurements in the middle atmosphere(München : European Geopyhsical Union, 2002) Rapp, M.; Gumbel, J.; Lübken, F.-J.In the last ten years a total of 25 sounding rockets employing ionization gauges have been launched at high latitudes ( ~ 70° N) to measure total atmospheric density and its small scale fluctuations in an altitude range between 70 and 110 km. While the determination of small scale fluctuations is unambiguous, the total density analysis has been complicated in the past by aerodynamical disturbances leading to densities inside the sensor which are enhanced compared to atmospheric values. Here, we present the results of both Monte Carlo simulations and wind tunnel measurements to quantify this aerodynamical effect. The comparison of the resulting ‘ram-factor’ profiles with empirically determined density ratios of ionization gauge measurements and falling sphere measurements provides excellent agreement. This demonstrates both the need, but also the possibility, to correct aerodynamical influences on measurements from sounding rockets. We have determined a total of 20 density profiles of the mesosphere-lower-thermosphere (MLT) region. Grouping these profiles according to season, a listing of mean density profiles is included in the paper. A comparison with density profiles taken from the reference atmospheres CIRA86 and MSIS90 results in differences of up to 40%. This reflects that current reference atmospheres are a significant potential error source for the determination of mixing ratios of, for example, trace gas constituents in the MLT region.