Prediction of the number of cloud droplets in the ECHAM GCM

In this paper a prognostic equation for the number of cloud droplets (CDNC) is introduced into the ECHAM general circulation model. The initial CDNC is based on the mechanistic model of Chuang and Penner [1995], providing a more realistical prediction of CDNC than the empirical method previously used. Cloud droplet nucleation is parameterized as a function of total aerosol number concentration, updraft velocity, and a shape parameter, which takes the aerosol composition and size distribution into account. The total number of aerosol particles is obtained as the sum of marine sulfate aerosols produced from dimethyl sulfide, hydrophylic organic and black carbon, submicron dust, and sea-salt aerosols. Anthropogenic sulfate aerosols only add mass to the preexisting aerosols but do not form new particles. The simulated annual mean liquid water path, column CDNC, and effective radius agree well with observations, as does the frequency distributions of column CDNC for clouds over oceans and the variations of cloud optical depth with effective radius

Experimental Evaluation of a Low Emissions High Performance Duct Burner for Variable Cycle Engines (VCE)

An evaluation was conducted with a three stage Vorbix duct burner to determine the performance and emissions characteristics of the concept and to refine the configuration to provide acceptable durability and operational characteristics for its use in the variable cycle engine (VCE) testbed program. The tests were conducted at representative takeoff, transonic climb, and supersonic cruise inlet conditions for the VSCE-502B study engine. The test stand, the emissions sampling and analysis equipment, and the supporting flow visualization rigs are described. The performance parameters including the fuel-air ratio, the combustion efficiency/exit temperature, thrust efficiency, and gaseous emissions calculations are defined. The test procedures are reviewed and the results are discussed

Paired Comparisons Analysis: An Axiomatic Approach to Rankings in Tournaments

In this paper we present an axiomatic analysis of several ranking methods for tournaments. We find that two of them exhibit a very good behaviour with respect to the set of properties under consideration. One of them is the maximum likelihood ranking, the most common method in statistics and psychology. The other one is a new ranking method introduced in this paper: recursive Buchholz. One of the most widely studied methods in social choice, the fair bets ranking, also performs quite well, but fails to satisfy some arguably important properties.Tournament;ranking;paired comparisons;fair bets;maximum likelihood

Analytical evaluation of the impact of broad specification fuels on high bypass turbofan engine combustors

The impact of the use of broad specification fuels on the design, performance durability, emissions and operational characteristics of combustors for commercial aircraft gas turbine engines was assessed. Single stage, vorbix and lean premixed prevaporized combustors, in the JT9D and an advanced energy efficient engine cycle were evaluated when operating on Jet A and ERBS (Experimental Referee Broad Specification) fuels. Design modifications, based on criteria evolved from a literature survey, were introduced and their effectiveness at offsetting projected deficiencies resulting from the use of ERBS was estimated. The results indicate that the use of a broad specification fuel such as ERBS, will necessitate significant technology improvements and redesign if deteriorated performance, durability and emissions are to be avoided. Higher radiant heat loads are projected to seriously compromise liner life while the reduced thermal stability of ERBS will require revisions to the engine-airframe fuel system to reduce the thermal stress on the fuel. Smoke and emissions output are projected to increase with the use of broad specification fuels. While the basic geometry of the single stage and vorbix combustors are compatible with the use of ERBS, extensive redesign of the front end of the lean premixed prevaporized burner will be required to achieve satisfactory operation and optimum emissions

A Light-Independent Magnetic Compass in the Leatherback Sea Turtle

Diverse animals can orient to the earth's magnetic field (1-6), but the mechanism or mechanisms undrlying magnetic field detection have not been determined. Behavioral (7-9) amd neurophysiological (10-12) results suggest that the transduction process underlying magnetic compass orientation in vertebrates is light-dependent, a finding consistent with theoretical models proposing that magnetoreception involves a modulation of the response of retinal photoreceptors to light (13, 14). We report, however, that leatherback sea turtle (Dermochelys coriacea) hatchlings orient to the geomagnetic field in complete darkness. Thus, light-dependence is not a universal feature of vertebrate magnetic compasses

Why are salinity anomalies of great importance for long-term climate variability ? Analysis of simple climate models

We analyze the sensitivity of the ocean’s thermohaline circulation using ideal- ized models of the North Atlantic. The nonlinear Stommel (1961) box model is solved exactly. Using the analytical solution of a coupled atmosphere-ocean version of Stommel’s model, we derive the critical salinity perturbation, nec- essary to induce a break down of the thermohaline circulation . We find that the glacial oceanic circulation with a weaker meridional overturning is more sensitive than the present one. The model reveals furthermore that the optimal perturbation affecting long-term climate variability is by high lat- itude haline forcing, although this perturbation has little resemblence with the most unstable mode of the system and the leading EOF. The linear stage of the forecast error growth is analyzed in the box model. The amplification of the forecast error ellipsoide is largest for high latitude haline forcing, associated with maximum energy growth on times less than a decade. Sensitivity experiments with a more sophisticated coupled model reveal the basic mechanisms involved in the thermohaline circulation’s re- sponse to sea surface salinity perturbations. The results qualitatively agree with those of the analytical model, although different mechanisms are re- sponsible for the sensitivity. Our results are useful for the interpretation of paleoclimatic records and interdecadal climate variability

Impact of sulfate aerosols on albedo and lifetime of clouds: A sensitivity study with the ECHAM4 GCM

A coupled sulfur chemistry-cloud microphysics scheme (COUPL) is used to study the impact of sulfate aerosols on cloud lifetime and albedo. The cloud microphysics scheme includes precipitation formation, which depends on the cloud droplet number concentration (CDNC) and on the liquid water content. On the basis of different observational data sets, CDNC is proportional to the sulfate aerosol mass, which is calculated by the model. Cloud cover is a function of relative humidity only. Additional sensitivity experiments with another cloud cover parameterization (COUPL-CC), which also depends on cloud water, and with a different autoconversion rate of cloud droplets (COUPL-CC-Aut) are conducted to investigate the range of the indirect effect due to uncertainties in cloud physics. For each experiment, two simulations, one using present-day and one using preindustrial sulfur emissions are carried out. The increase in liquid water path, cloud cover, and shortwave cloud forcing due to anthropogenic sulfur emissions depends crucially upon the parameterization of cloud cover and autoconversion of cloud droplets. In COUPL the liquid water path increases by 17 and cloud cover increases by 1 because of anthropogenic sulfur emissions, yielding an increase in shortwave cloud forcing of-1.4 W m-2. In COUPL-CC the liquid water path increases by 32, cloud cover increases by 3 and thus shortwave cloud forcing increases by -4.8 W m-2. This large effect is caused by the strong dependence of cloud cover on cloud water and of the autoconversion rate on CDNC, cloud water, and cloud cover. Choosing a different autoconversion rate (COUPL-CC-Aut) with a reduced dependence on CDNC and cloud water results in an increase of liquid water path by only 11 and of cloud cover by 1 , and the increase in shortwave cloud forcing amounts to -2.2 W m-2. These results clearly show that the uncertainties linked to the indirect aerosol effect are higher than was previously suggested. Copyright 1997 by the American Geophysical Union