A numerical study of aircraft wake induced ice cloud formation

Numerical simulations of ice cloud formation in the wake of an aircraft flying at cruise altitude have been performed. The engine exhaust has been excluded from the simulations in order to study cloud formation due to aerodynamic effects. The ice is formed via homogeneous freezing nucleation of ambient haze droplets in the upwelling limbs of the vortex pair behind the aircraft. Properties of wake ice clouds are compared with properties of contrails obtained with in situ measurements and recent simulations. In particular, we find that aerodynamically induced ice clouds are similar in microphysical and radiative respects to contrails that are formed from the nucleation of exhaust particles. The results show that significant fractions of contrails as young as 2 to 5 minutes may originate from aerodynamic effects and not only from nucleation of the exhaust particles. (orig.)Available from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Understanding regime support in new democracies Does politics really matter more than economics?

'Fuer die neuen Demokratien in Mittel- und Osteuropa ist es wichtig, die Unterstuetzung der Bevoelkerung zu haben. Doch welche gesellschaftlichen Bedingungen Politikzufriedenheit am staerksten foerdern, darueber gibt es anhaltende Debatten. Sind die politischen Ertraege der Transformation, wie Freiheiten und Demokratie, ausschlaggebend? Oder ist es die wirtschaftliche Situation? Mit Hilfe verschiedener Umfragedaten wird in diesem Beitrag eine Antwort auf die Frage versucht: 'Was zaehlt mehr: Politik oder Oekonomie?' Eine Makroanalyse, die viele Laender einschliesst, zeigt, dass die Bewertung des neuen politischen Systems durch die Bevoelkerung mit der demokratischen Entwicklung eines Landes zusammenhaengt - doch mit der wirtschaftlichen und sozialen Situation ergeben sich staerkere Zusammenhaenge. In einer Mikroanalyse von zwei Laendern wird nachgewiesen, dass in Ostdeutschland die Demokratiezufriedenheit vor allem davon abhaengt, ob Freiheiten und Buergerrechte als realisiert gelten. In Ungarn dagegen bestimmt die persoenliche wirtschaftliche Lage weitgehend die Bewertung. Die Ergebnisse bestaetigen nicht die vorherrschende Auffassung, dass in post-sozialistischen Gesellschaften die Politik generell mehr zaehlt als die Oekonomie. Zudem sollten bei der Untersuchung der Legitimitaet postkommunistischer Regime weitere Outputdimensionen wie soziale Sicherung, soziale Gerechtigkeit und oeffentliche Sicherheit beruecksichtigt werden.' (Autorenreferat)'It is essential that the new democracies of post-communist Central and Eastern Europe enjoy the full support of their citizenry. Among social scientists there is an ongoing debate about which conditions ensure mass support. Is political output, like individual freedom, or economic output, like citizens' financial situation, a more potent force in generating approval for the newly established democratic institutions? In this paper we explore the question 'what matters more: politics or economics?' by means of various survey data. A macro-analysis of many countries reveals that political support is correlated with democratic development, but also - and more strongly -with economic and social conditions. A micro-analysis of two countries reveals that while in East Germany the perception of guaranteed liberties contributes most to satisfaction with democracy, in Hungary the personal economic situation is most influential. The results do not confirm the view that politics are the most important factor for mass support in all post-communist counties. Furthermore we argue that it is fruitful to take into account other domains of regime performance like social security, social justice and protection.' (author's abstract)German title: Unterstuetzung der Regierungen durch die Bevoelkerung in den neuen Demokratien; was zaehlt mehr: politische Realitaet oder Oekonomie?Available from http://skylla.wz-berlin.de/pdf/2000/iii00-403.pdf / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Boundary layer budgets over the NOPEX area

The regional budgets of sensible heat and moisture are estimated for two days during NOPEX '94 by means of aircraft measurements. A box flight pattern is analysed for the 13 and 14 June. We perform a scale analysis in order to identify the main transporting scales of the turbulent fluxes and to investigate the mesoscale variability of the sensible heat and moisture flux. The example of a mesoscale moisture front indicates the importance of subgrid mesoscale variability. The turbulent fluxes of sensible heat and moisture are affected significantly by the mesoscale variability. This mesoscale variability is usually subgrid in numerical models and therefore must be parameterized. The source of the mesoscale moisture variability appears to be related to a cold front. Mesoscale flux divergence is explicitly included into the budget of sensible heat and moisture. The average vertical mesoscale flux divergence is small compared to the turbulent flux for the two cases investigated. however, the vertical mesoscale flux can locally be large. The budgets indicate the importance of horizontal advection for the NOPEX region. The time evolution of sensible heat and moisture during 14 June appears dominated by large scale horizontal advection. A comparison between the area-averaged surface flux from aircraft data and surface flux stations for the 13 June is not conclusive because of fractional cloud cover. For the 14 June (a strong wind case), there is a disagreement between surface fluxes based on aircraft data and data from surface flux stations which appears to be related with the strong mesoscale moisture variability. (orig.)32 refs.Available from TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

In situ observations of particles in jet aircraft exhausts and contrails for different sulfur containing fuels

The impact of sulfur oxides on particle formation and contrails is investigated in the exhaust plume of a twin-engine jet aircraft. Different fuels were used with sulfur mass fractions of 170 and 5500 ppm in the fuel, one lower than average, the other above the specification limit of standard Jet-A1 fuel. During various phases of the same flight, the two engines burnt either high or low sulfur fuel or different fuels in the two engines. Besides visual, photo and video observations from close distance, in situ measurements were made within the plumes at plume ages of 20 to 30 s, at altitudes between 9 and 9.5 km, and temperatures between -49 and -55 C. The data include particle number densities for particles larger than 7 nm, 18 nm, 120 nm, and 1 #mu#m in diameter, together with wind, temperature and humidity measurements. The observations show visible and measurable differences between contrails caused by the different sulfur levels. At ambient temperatures 5 K below the threshold temperature for contrail onset, the plume became visible about 10 m after the engine exit for high sulfur content, but 15 m after the engine exit for low sulfur content. The higher sulfur emission caused a larger optical thickness of the contrail shortly after onset, with slightly brown colored contrail when observed with the sun in the back, and more contrast when viewed against the sun. The high-sulfur contrail grew more quickly but also evaporated earlier than the low-sulfur contrail. (orig./KW)Available from TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Near field measurements on contrail properties from fuels with different sulfur content

Microphysical properties of jet engine exhaust aerosol and contrails were studied in the near field of the emitting aircraft for different fuel sulfur contents. Measurements were performed behind the research aircraft ATTAS of DLR and an Airbus A310-300 using fuels with different sulfur contents of 6 ppm and 2700 ppm. The major differences in accumulation mode aerosol and microphysical contrail properties between the used aircraft were an increased number concentration of both the accumulation mode aerosol and the contrail particles in the Airbus A310-300 plume compared to the ATTAS plume. Part of the difference in contrail particles may be caused by different ambient conditions, but the major differences are assumed to be caused by different engine properties. (orig.)Available from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman