Observation of a Saharan dust outbreak on 1-2 August 2007: determination of microphysical particle parameters

Paolo Di Girolamo1, Donato Summa1, Rohini Bhawar1, Tatiana Di Iorio2, Marco Cacciani2, Igor Veselovskii3, Alexey Kolgotin3

1 DIFA, Università degli Studi della Basilicata, Potenza, Italy, 2 Dipartimento di Fisica, Università degli Studi di Roma “La Sapienza”, Roma, Italy

3 Physics Instrumentation Center, Troitsk, Moscow Region, Russia

6th COPS Workshop, 27 – 29 February 2008University of Hohenheim, Stuttgart

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Particle Backscatter Ratio at 1064 nm, 1-2 August 2007

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Water Vapour Mixing Ratio

1-2 August 2007

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out-flow boundary

Measured parameters:

• particle backscattering coeff. @ 355, 532 and 1064 nm 3 • particle extinction coeff. @ 355 and 532 nm 2• depolarization ratio @ 355 & 532 nm, • atmospheric temperature• water vapour mixing ratio • relative humidity from simultaneous measurements of

temperature and water vapor mixing ratio

BASIL Raman Lidar

Raman lidar measurements (25 May – 30 August 2007)

More than 500 hours of measurementsdistributed over 58 days

particle size and microphysical parameters

COPS Web Pagehttp://www.cops2007.de/

Operational Products

The retrieval scheme employs Tikhonov’s inversion with regularization

Algorithm developed at the Physics Instrumentation Center

Inversion algorithm

Particle size distribution parameters:Mean radius rmean

Effective radius reff

Number concentration NSurface concentration SVolume concentration VComplex refractive index mr and mi

Parameters of a bimodal size distribution

3 + 2

In the solution of the inverse problem, particle size distribution f(r) is approximated by the superposition of base functions Bj(r) as:

where cj(z) are the weight coefficients.

Base functions have a triangular shape on a logarithmic-equidistant grid

Veselovskii et al., Appl. Opt. 41, 3685–3699, 2002.

Inversion with regularization

rmin=0.05 m, rmax=15 m

1.3 <mr< 1.6

0<mi<0.04

f(r)

Mean radius rmean

Effective radius reff

Number concentration NSurface concentration SVolume concentration V

numerically integrating f(r) over the radius interval [rmin, rmax]

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Particle Backscatter Ratio at 1064 nm, 1-2 August 2007

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Focus: two specific times when aerosol loading was higher21:00-21:30 UTC on 1 August 200700:00-00:30 UTC on 2 August 2007

(red dashed lines in figure)

1 August 2007, 21:00-21:30 UTC 2 August 2007, 00:00-00:30 UTC

averaging layers

1710-2100 m 2100-2490 m2490-2910 m2910-3210 m 3690-4110 m 4110-4500 m 4500-4920 m5310-5700 m

400 m thick

1 August 2007, 21:00-21:30 UTC 2 August 2007, 00:00-00:30 UTC

Particle size distribution

0.1 m <rmean< 0.2 m, 0.1 m <reff< 1.0 m5 m3/cm3 <V< 40 m3/cm3

Particle size distribution fine mode: 0.15-0.25 m

coarse mode: 1-4 m

1.44 <mr< 1.530.003 <mi< 0.008

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mR mI

Altitude

mR

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mI

1 August 2007, 21:00-21:30 UTC

Method: Inversion with regularization, performed by generalized cross-validation. In this retrieval, the combination of particle extinction and backscatter coefficients becomes especially important.The number of backscatter coefficients in the retrieval procedure should exceed the number of extinction coefficients by a factor of 2–3.

Backward trajectories ending at 00:00 UTC on 2 August 2007

NOAA-ARL HYSPLIT Lagrangian trajectory model

The air masses observed in Achern in the altitude region 3.5-5 km a.g.l. originated in the mixed layer over the Saharan desert

21:30 01:1523:22

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1-2 August 2007Dust particle hygroscopicity

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3-5.5 km

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Relative Humidity1-2 August 2007

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Particle backsc. coeff. at 355 nm vs RH, 1 August 07, 22:00-23:00 UTC, t=2min, 3-5.5 km

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Substantial increase in particle backscattering when RH > 75 %

Swelling tendency of hygroscopic aerosol particles at large RH values

Trend compatible with partially soluble aerosol particles

Back-trajectories show that airmasses originated in the Saharan desert transited for several days over the Atlantic Ocean

Aged dust particles presumably mixed with maritime aerosol during the advection to the meaurement site and partially coated with hygroscopic material

lidar dark bandfreezing level

radar bright band

freezing level

University of Manchester Radio Wind Profiler, 1290 MHz UHF Doppler radar

BASIL Raman Lidar

radar bright band

freezing level

MIRA 36, Radar Reflectvity at 36 GHz

radar bright band

freezing level

MIRA 36, Linear Depolarizatio Ratio

9 m/s4.5 m/s

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m)

radar bright band

freezing level

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Shear

IOP 9c – 20 July 07Passage of the frontal zone, with a Mesoscale Convective System inbedded

The waves like structures seen in the data just prior to the arrival of thethunderstorm are due to shear between inflow and outflow regions.

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Range corrected signals at 1064 nm

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BASIL – Rhine Valley Supersite(Lat: 48.64 ° N, Long: 8.06 E, Elev.: 140 m)

25-26 July 2007 – Water vapour mixing ratiog/kg

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mixing ratio [g/kg]

RadioSonde 01:15 Lidar 01:15-01:25

mixing ratio (g/kg)

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Range corrected signals at 1064 nm Water vapour mixing ratio

1064 532 355

355 532

Particle Backscatter Ratio at 1064 nm

Particle Backscatter Ratio at 532 nm

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r

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reff

rmean

1-D approach

2-D approach

mR