In-situ observations of young contrails – overview and selected results from the CONCERT campaign

Lineshaped contrails were detected with the research aircraft Falcon during the CONCERT – CONtrail and Cirrus ExpeRimenT – campaign in October/November 2008. The Falcon was equipped with a set of instruments to measure the particle size distribution, shape, extinction and chemical composition as well as trace gas mixing ratios of sulfur dioxide (SO<sub>2</sub>), reactive nitrogen and halogen species (NO, NO<sub>y</sub>, HNO<sub>3</sub>, HONO, HCl), ozone (O<sub>3</sub>) and carbon monoxide (CO). During 12 mission flights over Europe, numerous contrails, cirrus clouds and a volcanic aerosol layer were probed at altitudes between 8.5 and 11.6 km and at temperatures above 213 K. 22 contrails from 11 different aircraft were observed near and below ice saturation. The observed NO mixing ratios, ice crystal and soot number densities are compared to a process based contrail model. On 19 November 2008 the contrail from a CRJ-2 aircraft was penetrated in 10.1 km altitude at a temperature of 221 K. The contrail had mean ice crystal number densities of 125 cm<sup>−3</sup> with effective radii <i>r</i><sub>eff</sub> of 2.6 μm. The presence of particles with <i>r</i>>50 μm in the less than 2 min old contrail suggests that natural cirrus crystals were entrained in the contrail. Mean HONO/NO (HONO/NO<sub>y</sub>) ratios of 0.037 (0.024) and the fuel sulfur conversion efficiency to H<sub>2</sub>SO<sub>4</sub> (ε<sub><i>S</i>↓</sub>) of 2.9 % observed in the CRJ-2 contrail are in the range of previous measurements in the gaseous aircraft exhaust. On 31 October 2010 aviation NO emissions could have contributed by more than 40% to the regional scale NO levels in the mid-latitude lowest stratosphere. The CONCERT observations help to better quantify the climate impact from contrails and will be used to investigate the chemical processing of trace gases on contrails

Aviation effects on already-existing cirrus clouds.

Determining the effects of the formation of contrails within natural cirrus clouds has proven to be challenging. Quantifying any such effects is necessary if we are to properly account for the influence of aviation on climate. Here we quantify the effect of aircraft on the optical thickness of already-existing cirrus clouds by matching actual aircraft flight tracks to satellite lidar measurements. We show that there is a systematic, statistically significant increase in normalized cirrus cloud optical thickness inside mid-latitude flight tracks compared with adjacent areas immediately outside the tracks

Deformation induced martensite formation in metastable austenitic steel during in situ fatigue loading in a scanning electron microscope

Aim of the study is to identify quantitatively the influence of deformation-induced phase transformation on the fatigue damage of a metastable austenitic steel during loading in the high cycle fatigue regime. Cyclic deformation tests were carried out in situ in a scanning electron microscope (SEM) in combination with automated electron backscatter diffraction (EBSD) used for phase analysis and crystallographic orientation mapping. The in situ experiments were supported by ex situ cycling in a servohydraulic testing machine. The examined metastable austenitic steel (AISI 304L) transforms diffusion less from the fcc austenite lattice to the bcc α´ martensite lattice either spontaneously at very low temperatures or at room temperature when a critical value of monotonic or accumulated cyclic plastic strain is exceeded. The experiments showed that already after some initial 10,000 cycles of fatigue loading at stress amplitudes close to the fatigue limit a nucleation of martensite occurs as needles near activated slip systems as a consequence of localized plastic deformation. Once first microstructurally short cracks have nucleated, strong martensitic transformation occurs within the plastic zone ahead of the crack tip. Due to the higher specific volume the martensite is considered to shield the crack tip, i.e., transformation-induced crack closure takes place. The role of deformation-induced phase transformation on (i) crack initiation and (ii) the mechanism of fatigue microcrack propagation is discussed in detail in the present paper

The effect of the embrittlement on the fatigue limit and crack propagation in a duplex stainless steel during high cycle fatigue

In order to evaluate the effects that the “475° embrittlement” produces on the fatigue life during high-cycle fatigue, stress-controlled cyclic loading tests were conducted on a standard duplex stainless steel in two different heat treatment conditions (homogenized and embrittled). Transmission (TEM) and scanning electron microscopy (SEM) in combination with automated electron back-scattered diffraction (EBSD) techniques were carried out to analyze the surface damage as well as the initiation and propagation of fatigue cracks. These studies have revealed that the fatigue limit of the embrittled samples is substantially larger than that of the conventional samples at 107 cycles in the homogenized condition. Finally, an existing numerical short-crack propagation model was adapted using the stereological values obtained by EBSD to reproduce the propagation of microstructural fatigue cracks in the homogenized and embrittled conditions.Fil: Marinelli, María Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Física de Rosario (i); Argentina. University of Applied Sciences; AlemaniaFil: Krupp, U.. University of Applied Sciences; AlemaniaFil: Kübbeler, M.. University of Siegen. Institute of Mechanics and Control Engineering-Mechatronics; AlemaniaFil: Hereñu, Silvina Andrea Noemi. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Física de Rosario (i); ArgentinaFil: Alvarez, Iris. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Física de Rosario (i); Argentin

Thin and subvisible cirrus and contrails in a subsaturated environment

The frequency of occurrence of cirrus clouds and contrails, their life time, ice crystal size spectra and thus their radiative properties depend strongly on the ambient distribution of the relative humidity with respect to ice (RHice). Ice clouds do not form below a certain supersaturation and both cirrus and contrails need at least saturation conditions to persist over a longer period. Under subsaturated conditions, cirrus and contrails should dissipate. During the mid-latitude aircraft experiment CONCERT 2008 (CONtrail and Cirrus ExpeRimenT), RHice and ice crystals were measured in cirrus and contrails. Here, we present results from 2.3/1.7 h of observation in cirrus/contrails during 6 flights. Thin and subvisible cirrus with contrails mbedded therein have been detected frequently in a subsaturated environment. Nevertheless, ice crystals up to radii of 50 μm and larger, but with low number densities were often observed inside the contrails as well as in the cirrus. Analysis of the meteorological situation indicates that the crystals in the contrails were entrained from the thin/subvisible cirrus clouds, which emerged in frontal systems with low updrafts. From model simulations of cirrus evaporation times it follows that such thin/subvisible cirrus can exist for time periods of a couple of hours and longer in a subsaturated environment and thus may represent a considerable part of the cirrus coverage