Determination of polar stratospheric cloud particle refractive indices by use of in situ optical measurements and T-matrix calculations.
A new algorithm to infer structural parameters such as refractive index and asphericity of cloud particles has been developed by use of in situ observations taken by a laser backscattersonde and an optical particle counter during balloon stratospheric flights. All three main particles, liquid, ice, and a no-ice solid (NAT, nitric acid trihydrate) of polar stratospheric clouds, were observed during two winter flights performed from Kiruna, Sweden. The technique is based on use of the T-matrix code developed for aspherical particles to calculate the backscattering coefficient and particle depolarizing properties on the basis of size distribution and concentration measurements. The results of the calculations are compared with observations to estimated refractive indices and particle asphericity. The method has also been used in cases when the liquid and solid phases coexist with comparable influence on the optical behavior of the cloud to estimate refractive indices. The main results prove that the index of refraction for NAT particles is in the range of 1.37-1.45 at 532 nm. Such particles would be slightly prolate spheroids. The calculated refractive indices for liquid and ice particles are 1.51-1.55 and 1.31-1.33, respectively. The results for solid particles confirm previous measurements taken in Antarctica during 1992 and obtained by a comparison of lidar and optical particle counter data.
Scarchilli
Claudio
C
Institute of Atmospheric Sciences and Climate, Italian National Research Council, Via Fosso del Cavaliere, 100-00133 Rome, Italy.
Adriani
Alberto
A
Cairo
Francesco
F
Di Donfrancesco
Guido
G
Buontempo
Carlo
C
Snels
Marcel
M
Moriconi
Maria Luisa
ML
Deshler
Terry
T
Larsen
Niels
N
Luo
Beiping
B
Mauersberger
Konrad
K
Ovarlez
Joelle
J
Rosen
Jim
J
Schreiner
Jochen
J
D000465:Algorithms; D001272:Atmosphere / Q000032:analysis*; D003081:Cold Climate; D003102:Colloids / Q000032:analysis; D004784:Environmental Monitoring / Q000379:methods*; D007834:Lasers; D010316:Particle Size; D012031:Refractometry / Q000379:methods*; D012542:Scattering, Radiation; D014867:Water / Q000032:analysis*; D014887:Weather
D003102:Colloids; D014867:Water