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.