COST 75 final seminar on Advanced Weather Radar Systems Contributions of the institute

SIGLEAvailable from TIB Hannover: RR 6341(98) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Influence of propulsion efficiency on contrail formation: theory and experimental validation. Experimental test of the influence of propulsion efficiency on contrail formation

Aircraft cause contrails when flying in an atmosphere colder than a threshold temperature which depends on the overall efficiency #eta# of propulsion of the aircraft/engine combination. Higher #eta# causes contrails at higher ambient temperatures and over a larger range of flight altitudes. The ratio of temperature increase relative to moisture increase in engine plumes is lower for engines with higher #eta#. Thermodynamic arguments are given for this fact and measurements and observations are reported which support the validity of the given criterion. The measurements include contrail observations for identified aircraft flying at ambient temperature and humidity conditions measured with high precision in-situ instruments, measurements of the temperature and humidity increases in an aircraft exhaust plume, and an observation of contrail formation behind two different four-engine jet aircraft with different engines flying wing by wing. The observations show that an altitude range exists in which the aircraft with high efficiency causes contrails while the other aircraft with lower efficiency causes none. Aircraft with more efficient propulsion cause contrails more frequently. The climatic impact depends on the relative importance of increased contrail frequency and reduced carbon dioxide emissions for increased efficiency, and on other parameters, and has not yet been quantified. (orig.)62 refs.SIGLEAvailable from TIB Hannover: RR 6341(139) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

The evaluation of flux aggregation methods using aircraft measurements in the surface layer

The use of the bulk aerodynamic relationship to predict the turbulent flux of momentum, heat or moisture at the surface over heterogeneous terrain may lead to a dependence of the exchange coefficient on averaging scale, i.e. on model grid size. This study investigates the scale dependence of exchange coefficients for momentum and heat transfer in a forest dominated heterogeneous boreal landscape by comparing the results of four different flux aggregation methods with aircraft data in the atmospheric surface layer. We have used a total of 41 aircraft runs (with a length of #approx#60 km each) from 11 flights performed during NOPEX (a NOrthern hemisphere land-surface climate Processes Experiment). We find a different behavior for momentum and scalar transfer. While momentum flux is governed by the roughest elements (in our case forest) in any single grid box (or aircraft run segment), the sensible heat flux is determined by the dominant land cover type. The effective exchange coefficients for momentum transfer appear to be independent of the averaging scale. This implies that an effective roughness length can be used for momentum flux parameterization purposes and standard similarity theory can be used. The effective roughness length for momentum transfer is on the order of 1.5 m. In contrast, the effective exchange coefficient for sensible heat transfer does depend on averaging scale. Therefore, the subgrid scale heterogeneity of the landsurface and the overlying boundary layer must be resolved explicitly in order to predict the correct grid averaged surface heat flux. Sensitivity analysis and comparison with data taken over a warmer and drier land-surface show, that this scale dependence seems to be confined to land surfaces with a surface temperature close to the temperature of the overlying air. This is particularly the case when sub-grid water surfaces are present. (orig.)Available from TIB Hannover: RR 6341(99) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Auswirkung des Flugverkehrs auf klima- und oekologisch relevante Immissionen in der Atmosphaere ueber Europa: Ermittlung optimaler Flughoehen und Flugrouten unter dem Aspekt minimaler Klimawirksamkeit

In this principle study it is demonstrated that flight routes and flight levels can be optimized such that the effects of air traffic on the environment becomes minimal. An adequate ecological penalty function is constructed. It is based on the simplified hypothesis that emissions are harmful only if they are found in the stratosphere 10 days after release. In order to take into account both environmental and economic aspects the ecological penalty function and the economic penalty function are suitably normalized, weighted by 'political' factors, and summed to form the total penalty function. The optimal flight routes and flight levels are then optained by minimizing the line integral over the total penalty function. This procedure is applied in selected case studies. It has been shown that the environmental pollution, according to our criteria, may be clearly reduced without simultaneously increasing the operating costs. (orig.)SIGLEAvailable from TIB Hannover: RN 8908(98-025) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekUmweltbundesamt, Berlin (Germany); Bundesministerium fuer Umwelt, Naturschutz und Reaktorsicherheit, Bonn (Germany)DEGerman

The cloud analysis tool APOLLO Improvements and validations

During its more than twelve years of existence, the 'AVHRR processing scheme over clouds, land and ocean' (APOLLO) has been modified and extended. The intention of this paper is to document the present state of APOLLO and to summarize the experiences gained. The scope of the processing scheme is reviewed and the actual state of the day time and night time algorithms are presented. The reason for the modifications are discussed. Validations of the modifications include comparisons with surface observations, with data from the 'international satellite cloud climatology project' (ISCCP) and with model simulations of the cloud liquid water path. APOLLO is now a robust and versatile cloud analysis tool. It is presently used to establish a cloud climatology in central Europe, based on processing of 15 years of daily AVHRR data. (orig.)29 refs.Available from TIB Hannover: RR 6341(126) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Entwicklung und Betrieb von meteorologischen Sensoren und eines Dropsonden-Messsystems fuer die STRATO 2C Abschlussbericht

As a part of the projected STRATO 2C instrumentation a basic meteorological instrumentation and a dropsonde system was developed and finally installed and tested on other aircraft. The basic instrumentation was projected to consist of sensors detecting temperature, pressure, humidity, wind, and radiation quantities. Sensors like these are normally permanently installed, as the parameters they provide are needed for nearly all scientific flight missions. The sensors have been tested intensively especially regarding their ability to operate properly even in the extended altitude region up to 24 km. After that they have been installed inside a wing pylon of the high altitude research aircraft G-520 T. In a test flight all systems worked without any failure, the temperature data of different sensors agreed quite well, and also the other data appeared to behave as expected. Adding a dropsonde measuring system to the aircraft instrumentation expands the measuring capabilities especially over inaccessible areas, where the network of radiosonde stations on the ground is fragmentary. Dropsondes work like upsondes, which are dropped from an aircraft and descent on a parachute. The receiving station and the data acquisition unit are installed on board the aircraft, therefore no ground stations are needed at all. The system built within the frame of this project has been installed and tested on the DLR meteorological research aircraft Falcon 20, and in the meantime it has been operated successfully in different research projects. (orig.)SIGLEAvailable from TIB Hannover: F99B283+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman

Einsatz und Weiterentwicklung eines Modells zur Prognose der zukuenftigen Entwicklung der stratosphaerischen Ozonschicht Abschlussbericht

In this project first assessments of the future development of the stratospheric ozone layer have been carried out (Dameris et al., 1998c). For that purpose the climate-chemistry model in version ECHAM3/CHEM has been used. During the project the model has been further developed to an interactively coupled system, based on very recent versions of ECHAM and CHEM (ECHAM4.L39) ((DLR)/CHEM). Results of model scenarios of the past and present time have been extensively evaluated against observations (Hein et al., 1999). It is obvious that the model system is able to reproduce well the mean conditions of the atmosphere in its current situation and also the observed changes (trends) during the last decade. Regional differences are found for the recovery of stratospheric ozone in the future scenarios. Particularly in polar latitudes the reformation of the ozone layer is delayed since the greenhouse effect yields a cooling of the lower stratosphere. According to an increased denitrification in the lower stratosphere a more effective chlorine activation is found. (orig.)Im Rahmen dieses Vorhabens wurden erste Abschaetzungen zur zukuenftigen Entwicklung der stratosphaerischen Ozonschicht durchgefuehrt (Dameris et al., 1998c). Dazu wurde das Klima-Chemie-Modell in der Version ECHAM3/CHEM verwendet. Im Verlauf des Projekts wurde das Modell zu einem interaktiv rueckkoppelnden System weiterentwickelt, auf der Grundlage neuester Versionen von ECHAM und CHEM (ECHAM4.L39 (DLR)/CHEM). Ergebnisse von Modellszenarien der Vergangenheit und Gegenwart wurden ausfuehrlich mit Beobachtungen verglichen (Hein et al., 1999). Es zeigt sich, dass das Modellsystem sowohl den gegenwaertigen mittleren Zustand der Atmosphaere gut beschreibt als auch die Veraenderungen waehrend der letzten Jahre (Trends) richtig wiedergibt. Die Ergebnisse der Zukunftsszenarien zeigen, dass es zu einer regional unterschiedlichen Rueckbildung der Ozonschicht kommt. Vor allem in den Polargebieten erholt sich das Ozon nur langsam, da es durch den Treibhauseffekt zu einer Abkuehlung der Stratosphaere kommt. Als Folge einer verstaerkten Denitrifizierung in der unteren Stratosphaere kommt es zu einer effektiveren Chloraktivierung. (orig.)SIGLEAvailable from TIB Hannover: DtF QN1(85,16) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung und Forschung (BMBF), Bonn (Germany)DEGerman

A model-based wind climatology of the eastern Adriatic coast

The results of statistical-dynamical downscaling of a 12-year period of ECMWF reanalysis data were used to elaborate basic climatological wind characteristics (mean windspeed, wind roses) over the Adriatic sea and Croatia in the winter months (December, January, February). The downscaling results are in good agreement with observations of 15 Croatian climate stations. Three major wind regimes with characteristic bimodal frequency distributions of wind direction were identified and spatially separated: Adriatic Sea (NW and SE), coastal stripe (NE and SE), and Croatian inland (SW and NE). The most frequent wind directions reflect the respective spatial occurrence of northeasterly 'bora' winds and southeasterly 'jugo' winds. (orig.)43 refs.Available from TIB Hannover: RR 6341(124) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Regionale Kondensstreifen-Bedeckung aus Satellitendaten und ihr Einfluss auf den Strahlungshaushalt

An operational contrail detection algorithm is applied to day and night overpasses of the Advanced Very High Resolution Radiometer (AVHRR). From the classification results the daytime and nighttime coverage by linear shaped contrails over Western Europa is derived. The annual daytime average for the analyzed region of 0.75% shows a strong annual cycle with 1.0% coverage during winter and 0.4% during summer. The day/night ratio reaches the factor 3. Using the radiance contrasts in the 11 #mu#m channel for contrail and adjacent pixels an average visible optical depth for the observed contrails of 0.1 is derived. This leads to an annual mean top of atmosphere radiative forcing by contrails over Central Europe in the range of 0.03 W/m"2 to 0.08 W/m"2, which is about one magnitude smaller than prior studies suggest. The highest annual mean contrail forcing exceeds 0.12 W/m"2 over Northeastern France, Belgium, Great Britain and Hungary. (orig.)Ein operationelles Kondensstreifen-Erkennungsverfahren wird auf Tag- und Nacht-Ueberfluege des Advanced Very High Resolution Radiometer (AVHRR) angewandt. Aus den Klassifizierungsergebnissen wird die mittaegliche und naechtliche Bedeckung durch linienhafte Kondensstreifen ueber Westeuropa abgeleitet. Das Jahresmittel der Bedeckung am Tag betraegt 0,75% und zeigt einen ausgepraegten Jahresgang mit 1% im Winter und 0,4% im Sommer, sowie einen starken Tag/Nacht-Unterschied mit einer Amplitude von 3. Mit Hilfe von Strahldichtekontrasten im 11 #mu#m Kanal zwischen Kondensstreifen und benachbarten Pixeln wird fuer die erkannten Kondensstreifen eine durchschnittliche optische Dicke im sichtbaren Spektralbereich von 0,1 abgeschaetzt. Daraus ergibt sich am Oberrand der Atmosphaere ein mittlerer auf Kondensstreifen zurueckzufuehrender Strahlungsantrieb zwischen 0,03 W/m"2 und 0,08 W/m"2, was eine Groessenordnung unter den Ergebnissen bisheriger Studien liegt. Die hoechsten Jahresmittel mit mehr als 0,12 W/m"2 werden ueber Nordost-Frankreich, Belgien, Grossbritannien und Ungarn gefunden. (orig.)Available from TIB Hannover: RA 437(2000-26) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Contrail cirrus

Contrails are visible line-shaped clouds forming in the wake of aircraft. Contrails may spread, trigger extensive cirrus cloud formation, and influence the Earth's radiation budget. Contrails form when the relative humidity in the plume of exhaust gases mixing with ambient air temporarily reaches liquid saturation, so that liquid droplets form on cloud-condensation nuclei and soon freeze to ice particles. The condensation nuclei come from soot and chemiions emitted by the engines, from sulfuric acid droplets forming partly on chemiions in the exhaust plume, and from ambient aerosols. Contrails persist and grow in ice-supersaturated air masses in the upper troposphere, where 10 to 20% of all air traffic takes place. The ice water content in persistent contrails grows about exponentially with ambient temperature. Contrail particles are smaller than cirrus particles at least during the first half hour. Contrails may be responsible for degradation in the observability of the solar corona and photosphere. Contrails are visible in satellite data. A recent example shows a contrail of more than 1500 km length. The mean cover of contrails over mid Europe is at least 0.5% on average at noon. The global cover is estimated to be about 0.1% based on such regional satellite data and a global analysis of temperature, humidity, and traffic activity. The contrail cover causes a positive radiative forcing depending mainly on contrail cover and optical depth. Regionally persistent contrails may cause a reduction of the daily temperature range. In order to determine the impact of aerosols and contrails on cirrus cloud properties, midlatitude cirrus properties should be measured and compared between the Northern and Southern Hemisphere. (orig.)111 refs.Available from TIB Hannover: RR 6341(114) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman