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Combined airborne lidar measurments of moisture transport and cirrus properties: HALO-LIDAR

Fachliche Zuordnung Physik und Chemie der Atmosphäre
Förderung Förderung von 2010 bis 2015
Projektkennung Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 179422122
 
Erstellungsjahr 2016

Zusammenfassung der Projektergebnisse

Humidity in and around cirrus clouds: Radiative effects of cirrus clouds are a major uncertainty in determining the climate cloud feedback. The variability of cirrus on different spatial scales is another major issue which complicates modelling of their radiative properties. Aerosol and water vapour measurements were performed with the DLR lidar system WALES in 2010 during the first mission with the new German research aircraft HALO. ECMWF temperature analyses are used to derive relative humidity inside and outside of cirrus clouds from the lidar water vapour observations. Comparisons with in situ measurements of humidity on the research aircraft Falcon flying inside the cirrus clouds confirm the high accuracy of the WALES system. The study shows the advantages of lidar cross sections to provide additional information about the vertical structure of the complex humidity field, also allowing for simultaneous statistical analyses in different cloud layers. Combined with accurate temperature measurements, the lidar observations have a great potential for detailed statistical cirrus cloud and related humidity studies. Future HALO missions will benefit from the findings and techniques developed here. HSRL aerosol classification: To better understand the effects of aerosols on the climate system it is important to obtain highly accurate information on the aerosol optical properties (e.g., extinction coefficient, single scattering albedo and phase function) as well as on their temporal and spatial distribution. The high spectral resolution lidar (HSRL) method based on an iodine absorption filter and a frequency doubled pulsed Nd:YAG laser, developed at DLR, has the capability to directly measure the extinction and backscatter coefficients of aerosols and clouds. Airborne HSRL data from four different field experiments are used in the frame of this project to build up an aerosol classification. The method is based on HSRL measurements of a set of intensive aerosol properties, in particular the lidar ratio, the particle linear depolarization ratio and the color ratio of backscatter. Applied to the HSRL measurements on ESA’s EarthCARE mission it will provide the climate relevant properties extinction coefficient and aerosol optical depth, together with the global, verticallyresolved distribution of aerosols and clouds. Statistical characterization of humidity variability: The distribution of water vapour in the atmosphere shows variability on all spatial scales. An accurate representation of cloud processes in climate models with limited resolution relies on a statistical description of the unresolved structures. A compact description that can describe intermittent variability on many scales is multifractal scaling based on structure functions of different orders. This analysis method was applied to airborne water vapour lidar measurements from a number of field campaigns in midlatitude, polar and subtropical latitudes. The humidity was found to be characterized by two universal regimes, consisting of convective and nonconvective air masses. A comparison of the observations numerical simulations showed that a model with sufficient resolution can reproduce the observed statistics in both regimes, while the simple statistical model provided by multifractal scaling can be used in the development of improved parameterizations for models with coarser resolution.

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