Lutz Hirsch

A multisensor approach toward a better understanding of snowfall microphysics : The TOSCA Project

The Towards an Optimal estimation based Snow Characterization Algorithm (TOSCA) project addresses possible novel measurement synergies for deriving snowfall microphysical parameters from the ground by combining the unique information obtained from a suite of ground-based sensors: microwave radiometers (22–150 GHz), 24- and 36-GHz radar, lidar, and in situ optical disdrometer methods. During the winter of 2008/09, such instruments were deployed at the Environmental Research Station Schneefernerhaus (UFS; at 2650 m MSL) at the Zugspitze Mountain in Germany for deriving microphysical properties of snowfall. This contribution gives an overview of the measurements carried out and discusses the potential for the developments of synergetic retrieval algorithms for deriving snow water content within the vertical column. The identification of potentially valuable ground-based instrument synergy for the retrieval of snowfall parameters from the surface will also be of importance for the development of new space-bor...

The Barbados Cloud Observatory — anchoring investigations of clouds and circulation on the edge of the ITCZ

AbstractClouds over the ocean, particularly throughout the tropics, are poorly understood and drive much of the uncertainty in model-based projections of climate change. In early 2010, the Max Planck Institute for Meteorology and the Caribbean Institute for Meteorology and Hydrology established the Barbados Cloud Observatory (BCO) on the windward edge of Barbados. At 13°N the BCO samples the seasonal migration of the intertropical convergence zone (ITCZ), from the well-developed winter trades dominated by shallow cumulus to the transition to deep convection as the ITCZ migrates northward during boreal summer. The BCO is also well situated to observe the remote meteorological impact of Saharan dust and biomass burning. In its first six years of operation, and through complementary intensive observing periods using the German High Altitude and Long Range Research Aircraft (HALO), the BCO has become a cornerstone of efforts to understand the relationship between cloudiness, circulation, and climate change.

EUREC 4 A: A Field Campaign to Elucidate the Couplings Between Clouds, Convection and Circulation

Trade-wind cumuli constitute the cloud type with the highest frequency of occurrence on Earth, and it has been shown that their sensitivity to changing environmental conditions will critically influence the magnitude and pace of future global warming. Research over the last decade has pointed out the importance of the interplay between clouds, convection and circulation in controling this sensitivity. Numerical models represent this interplay in diverse ways, which translates into different responses of trade-cumuli to climate perturbations. Climate models predict that the area covered by shallow cumuli at cloud base is very sensitive to changes in environmental conditions, while process models suggest the opposite. To understand and resolve this contradiction, we propose to organize a field campaign aimed at quantifying the physical properties of trade-cumuli (e.g., cloud fraction and water content) as a function of the large-scale environment. Beyond a better understanding of clouds-circulation coupling processes, the campaign will provide a reference data set that may be used as a benchmark for advancing the modelling and the satellite remote sensing of clouds and circulation. It will also be an opportunity for complementary investigations such as evaluating model convective parameterizations or studying the role of ocean mesoscale eddies in air–sea interactions and convective organization.

The Signature of Aerosols and Meteorology in Long-Term Cloud Radar Observations of Trade Wind Cumuli

AbstractThe signature of aerosols and meteorology on the development of precipitation from shallow cumuli in the trades is investigated with ground-based lidar and radar remote sensing. The measurements are taken from a cloud observatory recently established on the windward shore of Barbados. Cloud microphysical development is explored through an analysis of the radar echo of shallow cumuli before the development of active precipitation. The increase of reflectivity with height (Z gradient) depends on the amount of cloud water, which varies with meteorology, and cloud droplet number concentration N, which varies with the aerosol. Clouds with a large Z gradient have a higher tendency to form precipitation than clouds with a small Z gradient. Under similar meteorological conditions, the Z gradient is expected to be large in an environment with few aerosols and small in an environment with many aerosols. The aerosol environment is defined using three methods, but only one (based on the Raman lidar linear-dep...

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.

Calibration of a 35-GHz Airborne Cloud Radar: Lessons Learned and Intercomparisons with 94-GHz Cloud Radars

and Intercomparisons with 94-GHz Cloud Radars Florian Ewald1, Silke Groß1, Martin Hagen1, Lutz Hirsch2, Julien Delanoë3, and Matthias Bauer-Pfundstein4 1Deutsches Zentrum für Luft und Raumfahrt, Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany 2Max Planck Institute for Meteorology, Hamburg, Germany 3LATMOS/UVSQ/IPSL/CNRS, Guyancourt, France 4Metek GmbH, Elmshorn, Germany Correspondence to: Florian Ewald (florian.ewald@dlr.de)

Multiple receiver wind profiling techniques for the boundary layer in the presence of hydro‐meteors

A UHF boundary layer wind profiler has been operated in a multiple receiver mode. The data sets collected are used to estimate the horizontal wind using different multiple receiver analysis techniques performed in the time and frequency domains. Those results are also compared with simultaneous Doppler beam swinging measurements. The particularity of the data sets used for this inter-comparison is that they were recorded while hydro-meteors were present in the boundary layer. The large mean fall speed and the broad fall velocity distribution of rain drops causes a much more rapid decay of diffraction patterns than in the case of scattering by snow flakes or micro turbulence. Therefore, analysis methods which do not account for the effect of the decay of the diffraction patterns show an over-estimation of the wind velocity, and do so in a different way whether snow or rain is present. To the contrary, algorithms that account for the effect of diffraction pattern decay appear to reasonably estimate the actual horizontal wind and compare well with the Doppler measurements.