Saharan Mineral Dust Experiment (SAMUM) 2006: Vertical profiles of Dust Particle Properties from Airborne in situ and Lidar Observations

Transcription

1 Saharan Mineral Dust Experiment (SAMUM) 2006: Vertical profiles of Dust Particle Properties from Airborne in situ and Lidar Observations Andreas Petzold, Bernadett Weinzierl, Michael Esselborn, Katharina Rasp, Markus Fiebig, Frank Wagner, Aki Virkkula Institute of Atmospheric Physics, DLR University of Evora, Portugal; Finnish Meteorological Institute, Helsinki, Finland Perugia Mineral Dust Workshop, 9-11 July 2007

2 The SAMUM Consortium 6λ LIDAR profiles, sun photometry funding agency chemical composition dust size distritrubition (ground site) Satellite retrievals of dust propertes from MERIS vertical distribution of dust properties (optical, microphys., chem.) from airborne in-situ and HSRL data chemical composition (ground site) Satellite retrievals of dust properties, local contact LIDAR depolarisation and backscatter, sun photometry 2

3 SAMUM 2006 Tenerife Izana Observatory AOT, Lidar, ground site ENVISAT MSG Ouarzazate Partenavia IfT Lidar, MIM Lidar AOT Casablanca Zagora DLR Falcon ground site, MIM Lidar AOT 3

4 SAMUM Airborne Instrumentation Nukleationsmode Aitken Mode Akkumulationsmode Grobpartikelmode NUC AITK ACC COARSE / DUST dn / d log Dp / cm Technique condensation µm CPSA/CPC deposition µm electrical mobility CPC + DS lightscattering µm DMA µm PCASP 100-X µm FSSP 300 size-resolved particle volatility µm spectral absorption coefficient FSSP 100-ER Dp / µm DLR IPA Aerosol Instrumentation - full coverage of the relevant particle size spectrum (D = µm) - high time resolution (5 s) - multi-λ aerosol absorption & particle volatility refractive index 4

5 SAMUM Airborne Instrumentation Airborne nadir-looking HSR LIDAR Parameter Backscatter coefficient Extinction coefficient LIDAR ratio Optical depth of elevated dust layers Depolarization ratio Water vapour Wavelength λ, nm 532, 925, , ,

6 Data Analysis Scheme 4 4 PSAP-Signal Inversion erfolgreich Inversion nicht erfolgreich CPC + PCASP CPC + GRIMM FSSP σ abs URBAN, Mm σ abs DUST, Mm -3 dn / d log Dp, cm 2 10 PSAP - Signal, 1/Mm λ, Wellenlänge nm, nm Dp, µm Size distribution from multiple instruments 3λ-PSAP 700 Å - exponent for σap by 3λ absorption data Aerosol - optical model PM = α [ SiO2, AS ] + β Fe2O3 + γ [ BC, abs. mineral ] σ ep, σ sp, σ ap, σ bp, ω 0, mixing state, vol. fraction 6

7 Our favourite animal 7

8 Our favourite animal - the SAMUM Crocodile 8

9 19 May Dust Vertical Distribution wind dir / deg a, DESCENT OZT 11:12:16-12:12:21 FSSP < Dp < 1 µm 1 < Dp < 3 µm Dp > 3 µm altitude / km ASL altitude / km ASL theta / K N / scm -3 #060519a, OZT Backscatter Dust layer extents across the entire boundary layer. Turbulent mixing of the dust layer -> homogeneous distribution of dust. 9

10 10 Dust Vertical Distribution b) 1 < D p < 3 µm a) 0.4 < D p < 1 µm c) D p > 3 µm altitude / km ASL dust filaments sharp upper boundary of the dust layer Ouarzazate: 1150 m ASL N ambient / cm-3 black line: median grey shaded: 10- and 90- percentile values 10

11 Dust Microphysical Properties dn / dlogdp / (scm -3 ) upper dust, ZAG 11:26:37-11:35: m ASL RH ~ 26 % dn (dlog D p ) -1 / cm D p / µm Dp / µm N CMD GSD Mode1: Mode2: Mode3: Mode4:

12 Dust Microphysical Properties dn / dlogdp / (scm -3 ) upper dust, ZAG 11:26:37-11:35: m ASL RH ~ 26 % dn (dlog D p ) -1 / cm -3 frequency dust, Σ = Dp / µm D p / µm Deff (data) / µm N CMD GSD Mode1: Mode2: Mode3: Mode4: Refractive index coated ACC m mean, 532nm = i DUST m mean, 532nm = i Effective Diameter µm 12

13 Closure of Optical Properties of Dust σ ep (in-situ) / km HSRL: σ ep from direct high spectral resolution lidar measurements (no assumptions). in situ: σ ep from size distributions and refractive index σ ep (532 nm) σ ep (355 nm) 1:1 line σ ep (HSRL, IfT-lidar) / km 13

14 Closure of Optical Properties of Dust σ ep (in-situ) / km High correlation between in situ and HSRL σ ep. SD parameterisation matches observations better than 95%. Effect of particle nonsphericity < - 5%. Mie model applicable to σ ep calculation σ ep (532 nm) σ ep (355 nm) 1:1 line σ ep (HSRL, IfT-lidar) / km 14

15 Refractive Index of Dust (VIS) N å ap n(450 nm) k(450nm) n(700 nm) k(700nm) Hem Vol-% Kao Vol-% Quarz Vol-% Episode Episode Episode 3 a Episode 3 b Episode 3 c å ap =-[ln(σap/σap)]/ ln[467nm/660nm] 15

16 Variability of Dust Optical Properties Rückwärtstrajektorien back trajectories, 75 h L6 L4 L3 L5 L7 L3 L4 L5 L6 L7 L8 L3, L6 Two-layer structure h > 2500 m: å ap < 4 h < 2500 m: å ap > 6 L4, L5 h [m] å ap Differences in å ap and D eff can be assigned to different source regions. 16

17 What does SAMUM deliver? (1) Complete characterisation of dust optical properties from airborne HSRL / backscatter lidar application. (2) Extensive data set on aerosol microphysical, optical and chemical properties of pure dust from the northern Sahara. (3) Dust properties: - å (σ ep ) 0 - å(σ ap ) = D eff = µm - n (530 nm) = k (450) = k (660) = particle depolarisation 30% - lidar ratio = (55) sr (4) Dust properties depend significantly on the source region. 17

18 Acknowledgement The SAMUM activities presented here received funding through the following contracts DFG Research Group SAMUM ESA ESTEC Contract No. ESTEC 19429/06/NL/AR EUFAR Research Project DARPO The support of SAMUM is gratefully acknowledged. 18

19 SAMUM Target Areas SAMUM-1 SAMUM-2 Image of the Week - February 18,