Post on 14-Jan-2016
description
Atmospheric structure from lidar and radarJens Bösenberg
1. Motivation2. Layer structure3. Water vapour profiling4. Turbulence structure5. Cloud profiling6. Precipitation7. Conclusion and outlook
Motivation
Improve prediction of weather and climate
Improve understanding of atmospheric processes on all relevant scales
Improve data sets:accurate and validated climatology of relevant parameters, 4-D coveragehorizontal and vertical transport of relevant parameters
Improve observational capabilities:global satellite imagery plus high quality reference stationsnew instrumentation for transport studies
Motivation
Rationale for the Global Water Vapor Project (GVaP ) of GEWEX:
Objectives:...improving predictions of weather, seasonal and interannual climate variability, and
long-term climate changes ... ...understanding and predicting water vapor variability, forcing and feedback in the
Earth's weather and climate ...
Data requirements:... establish an accurate and validated water vapor climatology on the relevant time and space scales;
... identify the horizontal and vertical fluxes of water vapor and the processes that control those fluxes and the associated phase changes of atmospheric water; ...
Instrument requirements:Global observations from satellites plus high quality reference stations.New instrumentation for transport studies.
Applications requiring „new“ instrumentation
•Water vapour:-Reference stations: continuous high quality profiling.-Transport studies: high resolution profiling.
•Clouds:-3-D structure, multi-level cloud systems.-Microphysical properties.
•Precipitation:-3-D structure-Replacement of insufficient conventional measuring networks.
•Aerosol:-Systematic observations of the vertical distribution.-Systematic retrievals of optical properties.
Instruments and retrieved parameters:
Backscatter lidar: Layer structure, geometrical properties
Raman lidar: Aerosol extinction, (water vapour)
DIAL: Water vapour
Doppler lidar: Vertical wind
RASS: Wind vector, temperature
Cloud radar: Cloud structure, phase, vertical velocity
Common features: high resolution, high accuracy, highly specific
aerosol
water vapour
AFWEX2000ARM/CART, Oklahoma
Single parameters do not reveal the full structure!
aerosol
water vapour
•Very good agreement between 3 advanced lidars and sonde•Raman lidar shows best resolution (during night time!)•Ground based DIAL and Raman show similar statistical errors•Airborne DIAL is better at greater altitudes, but shows less precision and resolution at lower altitudes
AFWEX2000:Intercomparison of water vapour profiling at the ARM/CART site
Comparison of mean profiles
Water vapour DistributionGotland, 13/09/96Resolution:10 s temporal60m vertical
Ka-band cloud radar:
Investigation of meso- to microscale cloud parameters with high resolution
-Boundaries of multilayer cloud systems-Internal dynamic processes/structures-Microphysics of cloud droplets
Reflectivity, dBz
Linear depolarisation ratio, dB
Vertical velocity, m/s
Application of Ka-band radar:
Statistics of typical cloud parameters
Number of cloud layers Cloud thickness
Application of Ka-band radar
Validation of satellite retrievals, cloud top temperature
MODIS retrievals:C. RathkeInst. Für WeltraumforschungFU Berlin
Resolution temporal 0.1 s, vertical 30m, beam diameter 30 m, measurement at 2860m, bright band at 2400m
High resolution necessary to separate different cloud particle fractions!
•Doppler lidar with heterodyne detection • „laboratory setup“ under field conditions•One week continuous measurement•Operation in heavy precipitation
•Penetration through rain•Penetration through snowfall•Penetration into cloud
Structure of snowfallStructure of rainfallLocation of melting layerFall speed of precipitation
Common view:•Lidar is a fair-weather instrument only•Lidar is unstable, works for short periods only
Lidar „sees“ smaller particles than radar
Summary
Active remote sensing provides high resolution data on the vertical distribution of:
-Aerosol-Water vapour, (Ozone)-Wind (vector)-Cloud microphysics and structure-Precipitation
•Some techniques are fully operational (radar, RASS)•Some are used in routine applications (backscatter lidar, Raman lidar)•Some need further technical development (DIAL, Doppler lidar), but perspectives are promising for operational application.•Some need further development of methodology to improve the interpretation of results (cloud radar).
Outlook
Great progress has be made towards operational use of advanced lidar and radar methods which will be appliedfor monitoring as well as for dedicated process studies.
Combination of ground-based active remote sensing, passive satellite imagery, and data assimilation into models is very promising for high quality global monitoring.