Arctic aerosol and clouds studied by bistatic lidar technique

Abstract

[1] Aerosol and cloud studies were carried out with a polarimetric bistatic lidar setup at the Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR) in Andenes (69°N, 16E°), Norway. The measurements were performed from 10 to 23 October 2006 and covered altitudes between 1.5 and 11 km, corresponding to scattering angles between 130 and 170°. The degree of linear polarization, P L , calculated from the experiments was compared with light scattering calculations using Lorenz-Mie theory for spherical particles, the T-matrix approach for nonspherical rotationally symmetric particles, and a geometric optics ray-tracing method. Average P L values between 0.61 and 0.72 were obtained for the background aerosol under cloud-free conditions. The aerosol results may be qualitatively reproduced by standard aerosol types if a suitable combination of coarse-and fine-mode spherical particles is assumed. The P L values obtained for thin and mildly opaque clouds were in the range from 0.21 to 0.38. These results were not well described by spherical particles, and the results for relatively small prolate and oblate particles studied with the T-matrix method tended to be slightly higher than the experimental values. Geometric optics calculations for hexagonal column ice particles with surface roughness were able to reproduce the experimental cloud data. This does not rule out contributions from other types of particles, and particle orientation effects may also have influenced the results. We conclude that the experimental results are consistent with earlier in situ studies of cirrus clouds, and the further development and application of the bistatic lidar technique is discussed.

Comprehensive T-matrix reference database: A 2012–2013 update

“…T-matrix modeling of scattering properties of carbonaceous and soot aerosols and soot-containing aerosol and cloud particles [6,107,110,146,227,249,250]. [103,135,145,177,180,193,194,196,226,227]. [7,10,19,20,33,46,60,97,104,105,115,116,130,136,163,179,187,195,203,204,214,224,225,245,248,251,253,254].…”

“…T-matrix calculations for Chebyshev and generalizedChebyshev particles[105,121,128,129,203,204,230,252].2.13. T-matrix calculations for finite circular cylinders[21,36,51,57,61,67,78,80,103,128,129,145,147,149,158,180,211,219,222,226,227,235,237,240,241,252]. ,[13][14][15]25,[28][29][30][31]37,40,41,44,45,[48][49][50]54,72,74,82, 92,93,102,110,112,119,120,122,123,...…”

Lidar studies of the polar troposphere

“…In 2006 a polarization‐sensitive bistatic lidar receiver was used to study the ice crystals in cirrus clouds. The bistatic arrangement allowed measurements of scattering angles 130–170° along with the backscatter as collected by the regular detection system (Olofson et al , 2009).…”

“…A similar system has recently been installed at Summit in Greenland, which measures linearly‐polarized returns parallel, perpendicular, and at 45° to the transmitted beam (Neely et al , 2010). Another method for accessing scattering phase function information has been demonstrated at ALOMAR where Olofson et al (2009) used a bistatic depolarization lidar. A bistatic system is one where the receiver is physically removed from the transmitter, in this case the receiver was 2.1 km distant.…”

“…The backscatter coefficient, β π (λ, z ), is the product of the concentration of scatterers in the sampled volume and their differential backscatter cross‐section. The π will be dropped for clarity and indeed it should be noted that for bistatic lidars the scattering cross‐section at an angle other than π is possible (Olofson et al , 2009 for example). The exponential term is the two‐way fractional transmission of light through an atmosphere with an extinction coefficient α.…”