Comparison of contrail predictions with observations

This paper presents examples of comparison of modelled contrail cirrus properties with observed cirrus and contrail properties as obtained during the Mid-Latitude Cirrus Experiment (ML-CIRRUS) in March/April 2014. ML-CIRRUS was performed by more than 14 partner institutions (universities and research institutes), mainly from Germany, under coordination by DLR (see Voigt et al., EGU, 2015). During the ML-CIRRUS mission, 13 scientific mission flights have been performed with the High Altitude and Long Range research aircraft HALO at altitudes up to 13.8 km between 26 March and 15 April 2014 over Europe and the eastern part of the North Atlantic, often in high density air traffic regions. HALO was instrumented with about 3 tons of in-situ instruments for meteorology, gases, aerosols and cloud properties, with a high spectral resolution lidar and with other remote sensing instruments. Most of the measurement data are now available in the HALO data bank, though some still preliminary. A subset of the results has been presented at the EGU in Vienna in April 2015 (e.g., presentation by Christiane Voigt and the whole ML-CIRRUS team). The model results are obtained from simulations with the Contrail Cirrus Prediction tool (CoCiP) which has been developed to simulate and predict the properties of a large ensemble of contrails as a function of given air traffic and meteorology (Schumann, GMD, 2012). This paper will show that contrails cirrus is, to some degree, predictable on time scales of several days. A metric to measure the accuracy of the predictions is difficult to specify and will depend on the information that is needed from such predictions. Hence, the degree of agreement or disagreement between models and observations is hard to specify quantitatively. The main prerequisites for accurate predictions are accurate meteorological forecast fields (relative humidity, horizontal and vertical wind, temperature, cirrus ice water content, and top-of-the-atmosphere shortwave and longwave radiances), and accurate and detailed air traffic information (aircraft types and route waypoint sequences during the 24 h before the observations). For ML-CIRRUS, the model is driven with ECMWF IFS forecast and analysis data (1-h time resolution, 0.5° horizontal resolution, in the ML-CIRRUS domain 60°W-20°E, 20°N-70°N). For forecast, historical data are used from ACCRI (see Wilkerson et al., ACP, 2010; Schumann and Graf, 2013)). For analyses, traffic data were collected from various sources (including data from the Deutsche Flugsicherung, Flightradar24, Eurocontrol and VOLPE/FAA). Unfortunately, none of these data sources cover the whole ML-CIRRUS-domain uniformly. The paper will show that the measurements give insight in the validity of various model properties, in particular in respect to plume dilution, ice water content and ice crystal number concentrations

Contrail Cirrus Forecasts for the ML-CIRRUS Experiment and Some Comparison Results

In order to test and possibly improve contrail models, high-quality observations are needed to which multi-parameter model output can be compared. The mid-latitude cirrus experiment ML-CIRRUS was performed (see Voigt et al., this conference) with a suite of in-situ and Lidar instruments for airborne measurements on the research aircraft HALO. Before and during the mission, CoCiP was run daily to provide 3-days forecasts of contrail cover using operational ECMWF forecasts and historical traffic data. CoCiP forecast output was made available in an internet tool twice a day for experiment planning. The one-day and two-day contrail forecasts often showed only small differences. Still, most recent forecast and detailed satellite observations results were transmitted via satellite link to the crew for onboard campaign optimization. After the campaign, a data base of realistic air traffic data has been setup from various sources and CoCiP was rerun with improved ECMWF-NWP data (at one-hour time resolution). The model results are included in the HALO mission data bank and the results are available for comparison to in-situ data. The data are useful for identifying aircraft and other sources for measured air properties. The joint analysis of observations and model result has basically just started. Preliminary results from comparisons with lidar-measured extinction profiles, in-situ measured humidity and nitrogen oxides, and with meteorological observations (wind, temperature etc.) illustrate the expected gain in insight. The contrail forecasts have been checked by comparison to available data including satellite data and HALO observations. During the campaign, it became obvious that predicted contrail cirrus cover compared qualitatively mostly well with what was found when HALO reached predicted cirrus regions. Still considerable case-by-case differences occur, both between predicted and observed meteorology and predicted and observed contrail properties. As expected, nature is far more variable than a model can predict. The observed optical properties of cirrus and contrails vary far more in time and space than predicted. Local values were often far higher or lower than mean values. A one-to-one correlation between local observations and model results is not to be expected. This inhomogeneity may have consequences for the climate impact of aviation induced cloud changes

Porous aerosol in degassing plumes of Mt. Etna and Mt. Stromboli

Aerosols of the volcanic degassing plumes from Mt. Etna and Mt. Stromboli were probed with in situ instruments on board the Deutsches Zentrum für Luft- und Raumfahrt research aircraft Falcon during the contrail, volcano, and cirrus experiment CONCERT in September 2011. Aerosol properties were analyzed using angular-scattering intensities and particle size distributions measured simultaneously with the Polar Nephelometer and the Forward Scattering Spectrometer probes (FSSP series 100 and 300), respectively. Aerosols of degassing plumes are characterized by low values of the asymmetry parameter (between 0.6 and 0.75); the effective diameter was within the range of 1.5– 2.8 μm and the maximal diameter was lower than 20 μm. A principal component analysis applied to the Polar Nephelometer data indicates that scattering features of volcanic aerosols of different crater origins are clearly distinctive from angular-scattering intensities of cirrus and contrails. Retrievals of aerosol properties revealed that the particles were “optically spherical” and the estimated values of the real part of the refractive index are within the interval from 1.35 to 1.38. The interpretation of these results leads to the conclusion that the degassing plume aerosols were porous with air voids. Our estimates suggest that aerosol particles contained about 18 to 35% of air voids in terms of the total volume

ML-CIRRUS: The Airborne Experiment on Natural Cirrus and Contrail Cirrus with the High-Altitude Long-Range Research Aircraft HALO

The Midlatitude Cirrus experiment (ML-CIRRUS) deployed the High Altitude and Long Range Research Aircraft (HALO) to obtain new insights into nucleation, life cycle, and climate impact of natural cirrus and aircraft-induced contrail cirrus. Direct observations of cirrus properties and their variability are still incomplete, currently limiting our understanding of the clouds’ impact on climate. Also, dynamical effects on clouds and feedbacks are not adequately represented in today’s weather prediction models.Here, we present the rationale, objectives, and selected scientific highlights of ML-CIRRUS using the G-550 aircraft of the German atmospheric science community. The first combined in situ–remote sensing cloud mission with HALO united state-of-the-art cloud probes, a lidar and novel ice residual, aerosol, trace gas, and radiation instrumentation. The aircraft observations were accompanied by remote sensing from satellite and ground and by numerical simulations.In spring 2014, HALO performed 16 flights above Europe with a focus on anthropogenic contrail cirrus and midlatitude cirrus induced by frontal systems including warm conveyor belts and other dynamical regimes (jet streams, mountain waves, and convection). Highlights from ML-CIRRUS include 1) new observations of microphysical and radiative cirrus properties and their variability in meteorological regimes typical for midlatitudes, 2) insights into occurrence of in situ–formed and lifted liquid-origin cirrus, 3) validation of cloud forecasts and satellite products, 4) assessment of contrail predictability, and 5) direct observations of contrail cirrus and their distinction from natural cirrus. Hence, ML-CIRRUS provides a comprehensive dataset on cirrus in the densely populated European midlatitudes with the scope to enhance our understanding of cirrus clouds and their role for climate and weather