1. UNIVERSITY OF BASILICATA CNR-IMAA (Consiglio Nazionale delle Ricerche Istituto di Metodologie per l’Analisi Ambientale) Tito Scalo (PZ) Analysis and interpretation of lidar and radar data for the characterization of aerosol-cloud interactions Marco Rosoldi marco.rosoldi@imaa.cnr.it PhD in Methods and Technologies for Environmental Monitoring Potenza

2. Motivation 7th Atmospheric Measurement Summer School, 9-21 September 2012, Isle of Arran, Scotland Arosols affect the Earth’s radiation budget and climate by :  direct effects due to their interaction with radiation  indirect effects due to their interaction with clouds Observations of aerosol and cloud properties and the study of aerosol-cloud interactions are strongly needed in order to better quantify aerosol indirect effects on climate From: IPCC 4th AR There is a great interest in aerosol indirect effects because they have not yet been accurately evaluated and parameterized in weather and climate models. Indeed there are large uncertainties in estimates of aerosol radiative forcing (the radiative forcing is the quantity used to assess the direct and indirect effects of atmospheric constituents on the Earth’s radiation budget)

3. Lidar and radar Lidar (light detection and ranging) and radar (radio detection and ranging) are two active remote sensing techniques which allow to obtain the vertical profiles of the properties of atmospheric constituents, such as aerosols, water vapor and clouds. They can employ ground-based or satellite sensors 7th Atmospheric Measurement Summer School, 9-21 September 2012, Isle of Arran, Scotland (= height) The essential difference between the two techniques is that the lidar transmits and receives light pulses (λ = 250 - 1100nm), which are strongly attenuated by clouds, while the radar transmits and receives microwave pulses (λ = 1 - 100mm) which can pass through clouds. So, unlike the lidar, the radar can work in presence of dense clouds and bad weather conditions. Satellite lidar Ground-based lidars

4. Instruments Transmission: 355,532 and 1064nm Detection: 355,532 and 1064nm (elastic backscattering) 387 and 607nm (Raman backscattering from N 2 ) 407nm (Raman backscattering from H 2 O) Ka-band Doppler radar Multi-wavelength Raman lidar T ransmission/Detection: ν = 35.5GHz, λ=8.45mm 7th Atmospheric Measurement Summer School, 9-21 September 2012, Isle of Arran, Scotland

5. Methodology: analysis of lidar signals The lidar signals, properly processed, allow to obtain the vertical profiles of: 1)aerosol optical properties :  exctintion coefficient α directly dependent on the concentration of aerosol particles (the higher the concentration, the higher the coefficient)  backscattering coefficient β directly dependent on the concentration of aerosol particles  lidar ratio LR = α/β which gives information about the type of aerosol particles  particle depolarization ratio which gives information about the shape of aerosol particles  Angstrom exponents which indicate how α and β vary with wavelength. The Angström exponents are inversely related to the average size of the particles in aerosol (the smaller the particles, the higher the exponents) 2)water vapor content in the atmosphere:  water vapor mixing ratio WVMR  relative humidity RH 7th Atmospheric Measurement Summer School, 9-21 September 2012, Isle of Arran, Scotland

6. Examples 7th Atmospheric Measurement Summer School, 9-21 September 2012, Isle of Arran, Scotland Vertical profiles of aerosol backscattering coefficient at 355, 532 and 1064 nm, aerosol extinction coefficient at 355 and 532 nm, lidar ratio at 355 and 532 nm, and corresponding Angstrom exponents. The profiles have been obtained from lidar signals acquired in the day and time interval indicated and have a vertical resolution ranging within 360 and 540m. Vertical profile of WVMR obtained from lidar measurements of 27/05/2010 from 23:31 to 23:40 UTC and calibrated using a co-located simultaneous radio-sounding profile (on the left); time series of WVMR profiles obtained from measurements of 27-28/05/2010 from 23:31 to 01:15 UTC with a vertical resolution ranging within 90 and 360 m and a time resolution of 10 minutes(on the right). low dependece of α and β on the wavelength clouds between 5.5 and 6.5 km of altitude mineral aerosol between 3 and 5 Km of altitude

7. 7th Atmospheric Measurement Summer School, 9-21 September 2012, Isle of Arran, Scotland Methodology: analysis of radar signals The radar signals, properly processed, allow to obtain the vertical profiles of:  Radar reflectivity factor Ze which is directly related to the concentration and size (Ze  D 6 ) of cloud constituents (water droplets and ice crystals)  Linear Depolarization Ratio which gives information about the shape of cloud particles  Doppler velocity that is the vertical velocity of cloud particles Furthermore, from radar reflectivity factor measurements supported by lidar and microwave radiometer measurements, it is possible to obtain:  cloud geometrical depth (cloud base and top) and the vertical profiles of:  Liquid Water Content in clouds which is the mass of liquid water per unit volume in clouds  Ice Water Content in clouds which is the mass of ice water per unit volume in clouds  Effective radius which is the average radius of cloud particles

8. 7th Atmospheric Measurement Summer School, 9-21 September 2012, Isle of Arran, Scotland Time series of vertical profiles of the radar reflectivity factor, the linear depolarization ratio and the Doppler velocity obtained from the radar signals acquired april 23, 2009. The profiles have a vertical resolution of 30 m and a time resolution of 10 s. Time series of vertical profiles of ice and liquid water concentration in clouds calculated from radar, lidar and microwave radiometer observations of the April 23,2009, using Cloudnet retrieval scheme. (vertical resolution: 30 m, time resolution: 10 s). Examples the higher the reflectivity factor, the higher the concentration and /or size of cloud particles the lower the depolarization ratio, the more the shape of the particles is close to the spherical shape for Doppler velocity, the plus and minus signs respectively represent velocities directed upwards and downwards

9. 7th Atmospheric Measurement Summer School, 9-21 September 2012, Isle of Arran, Scotland Objectives  analyze simultaneous and co-locate lidar and radar measurements in order to select a large dataset of cases characterized by aerosol layers in free troposphere (FT) in presence of liquid or mixed phase clouds  study correlations between the aerosol properties and the water vapor content in presence of aerosol layers in FT  study correlations between the macroscopic and microphysical properties of clouds and the aerosol properties in the cloud base region provide a statistical study about the properties of aerosols, water vapor and clouds and their mutual relationships. Such a study might be useful to improve the evaluation and parameterization of aerosol indirect effects in weather and climate models

10. 7th Atmospheric Measurement Summer School, 9-21 September 2012, Isle of Arran, Scotland