Andreas Schäfler

ML-CIRRUS - The airborne experiment on natural cirrus and contrail cirrus with the high-altitude long-range research aircraft HALO

AbstractThe 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 f...

The Saharan aerosol long-range transport and aerosol-cloud-interaction experiment. Overview and Selected Highlights

AbstractNorth Africa is the world’s largest source of dust, a large part of which is transported across the Atlantic to the Caribbean and beyond where it can impact radiation and clouds. Many aspects of this transport and its climate effects remain speculative. The Saharan Aerosol Long-Range Transport and Aerosol–Cloud-Interaction Experiment (SALTRACE; www.pa.op.dlr.de/saltrace) linked ground-based and airborne measurements with remote sensing and modeling techniques to address these issues in a program that took place in 2013/14. Specific objectives were to 1) characterize the chemical, microphysical, and optical properties of dust in the Caribbean, 2) quantify the impact of physical and chemical changes (“aging”) on the radiation budget and cloud microphysical processes, 3) investigate the meteorological context of transatlantic dust transport, and 4) assess the roles of removal processes during transport.SALTRACE was a German-led initiative involving scientists from Europe, Cabo Verde, the Caribbean, a...

Quantifying Emerging Local Anthropogenic Emissions in the Arctic Region: The ACCESS Aircraft Campaign Experiment

AbstractArctic sea ice has decreased dramatically in the past few decades and the Arctic is increasingly open to transit shipping and natural resource extraction. However, large knowledge gaps exist regarding composition and impacts of emissions associated with these activities. Arctic hydrocarbon extraction is currently under development owing to the large oil and gas reserves in the region. Transit shipping through the Arctic as an alternative to the traditional shipping routes is currently underway. These activities are expected to increase emissions of air pollutants and climate forcers (e.g., aerosols, ozone) in the Arctic troposphere significantly in the future. The authors present the first measurements of these activities off the coast of Norway taken in summer 2012 as part of the European Arctic Climate Change, Economy, and Society (ACCESS) project. The objectives include quantifying the impact that anthropogenic activities will have on regional air pollution and understanding the connections to ...

Tropospheric Water Vapor Transport as Determined from Airborne Lidar Measurements

AbstractThe first collocated measurements during THORPEX (The Observing System Research and Predictability Experiment) regional campaign in Europe in 2007 were performed by a novel four-wavelength differential absorption lidar and a scanning 2-μm Doppler wind lidar on board the research aircraft Falcon of the Deutsches Zentrum fur Luft- und Raumfahrt (DLR). One mission that was characterized by exceptionally high data coverage (47% for the specific humidity q and 63% for the horizontal wind speed υh) was selected to calculate the advective transport of atmospheric moisture qυh along a 1600-km section in the warm sector of an extratropical cyclone. The observations are compared with special 1-hourly model data calculated by the ECMWF integrated forecast system. Along the cross section, the model underestimates the wind speed on average by −2.8% (−0.6 m s−1) and overestimates the moisture at dry layers and in the boundary layer, which results in a wet bias of 17.1% (0.2 g kg−1). Nevertheless, the ECMWF mode...

The North Atlantic Waveguide and Downstream Impact Experiment

Multi-aircraft and ground-based observations were made over the North Atlantic in fall 2016 to investigate the importance of diabatic processes for midlatitude weather. The North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX) explored the impact of diabatic processes on disturbances of the jet stream and their influence on downstream high-impact weather through the deployment of four research aircraft, each with a sophisticated set of remote-sensing and in situ instruments, and coordinated with a suite of ground-based measurements. A total of 49 research flights were performed, including, for the first time, coordinated flights of the four aircraft; the German High Altitude and LOng Range Research Aircraft (HALO), the Deutsches Zentrum fur Luft- und Raumfahrt (DLR) Dassault Falcon 20, the French Service des Avions Francais Instrumentes pour la Recherche en Environnement (SAFIRE) Falcon 20, and the British Facility for Airborne Atmospheric Measurements (FAAM) BAe 146. The observation period from 17 Sep to 22 Oct 2016 with frequently occurring extratropical and tropical cyclones was ideal to investigate midlatitude weather over the North Atlantic. NAWDEX featured three sequences of upstream triggers of waveguide disturbances, their dynamic interaction with the jet stream, subsequent development, and eventual downstream weather impact on Europe. Examples are presented to highlight the wealth of phenomena that were sampled, the comprehensive coverage and the multi-faceted nature of the measurements. This unique dataset forms the basis for future case studies and detailed evaluations of weather and climate predictions to improve our understanding of diabatic influences on Rossby waves and downstream impact of weather systems affecting Europe.

Detection and Analysis of Water Vapor Transport by Airborne Lidars

Water vapor, a minor constituent of the earths atmosphere, plays a major role in the radiation budget and the water cycle with important implications for weather and climate. Due to the heterogeneous distribution of its sources, evaporation, and sinks, condensation and precipitation, and due to the complexity of atmospheric motion and mixing, its distribution in the atmosphere is highly variable. Despite the high relevance of this trace gas, its variability challenges accurate measurements of its concentration. Advanced airborne lidar instruments aid to better observe water vapor and its transport in the atmosphere, in view of an improved understanding of atmospheric processes that are key to weather and climate research. The combination of a water vapor differential absorption lidar and a heterodyne detection Doppler wind lidar on an aircraft is new and allows to measure vertical profiles of the latent heat flux in a convective boundary layer and to portray the small- to large-scale humidity transport and variability along the aircraft flight track with high accuracy and spatial resolution.

Detection and analysis of water vapor transport

Water vapor, though a minor constituent of Earth’s atmosphere, plays a major role in the atmospheric radiation budget and the global water cycle. Atmospheric water vapor concentrations are highly variable due to the complex interplay between their sources (evaporation) and sinks (condensation and precipitation) in combination with transport and mixing. They strongly decrease with temperature and thus with altitude. Accurate measurement of water vapor is essential for better understanding its transport and cloud formation in the atmosphere and their impact on both weather and climate. To this end the institute develops and deploys lidars and in situ hygrometers onboard aircraft.

Airborne lidar observations of water vapor transport

Water vapor, a minor constituent of the earths atmosphere, plays a major role in the radiation budget and the water cycle with important implications for weather and climate. Due to the heterogeneous distribution of its sources, evaporation, and sinks, condensation and precipitation, and due to the complexity of atmospheric motion and mixing, its distribution is highly variable. Despite the relevance of this trace gas, its variability and instrumental shortcomings impede accurate measurements of its concentration. Advanced airborne lidar instruments aid to better observe water vapor and its transport in the atmosphere, in view of an improved understanding of the related key implications. The combination of a water vapor differential absorption lidar and a heterodyne detection Doppler wind lidar on an aircraft allows to measure vertical profiles of the latent heat flux in a convective boundary layer and to portray the small-to meso-scale humidity transport and variability beneath the aircraft with high accuracy and spatial resolution, in the frame of dedicated meteorological process studies.

Water vapour and wind profiles from collocated airborne lidars during COPS 2007

Tropospheric profiles of water vapour and wind were measured with differential absorption lidar (DIAL) and heterodyne detection wind lidar collocated onboard the DLR Falcon research aircraft during the Convective and Orographicallyinduced Precipitation Study (COPS; www.cops2007.de) over Southwest Germany in summer 2007. This international field campaign aimed at refining observational and modelling efforts to improve the forecast skill of convective precipitation over complex terrain in the summer season. The DIAL, a completely new system with four wavelengths (each 50 Hz, 40 mJ) at 935 nm, was installed nadir-viewing. The 2-micron wind lidar was operated either in scanning mode at 20 degrees off-nadir for 3d-wind profiles or in nadir-viewing mode for high resolution vertical wind measurements. The unique combination of both lidars enables the measurement of both horizontal (humidity advection) and vertical (latent heat) fluxes of water vapour that play an eminent role in precipitation forecast and convection initiation. The wind lidars spatial resolution is 100 m in the vertical and 150 m (vertical wind, boundary layer) to 12 km (3d-wind profiles, whole troposphere) in the horizontal. The DIAL horizontal and vertical resolution ranges from 150 m in the boundary layer to 500 m in the upper troposphere. This high spatial resolution permits the investigation of smallscale processes such as turbulent humidity transport in the convective boundary layer or orographically-induced flow perturbations. Likewise, meso- and synoptic scale processes, e.g. upper level potential vorticity streamers were sampled by flying extended legs across Western Europe.