Ice clouds and Asian dust studied with lidar measurements of particle extinction-to-backscatter ratio, particle depolarization, and water-vapor mixing ratio over Tsukuba

Tetsu Sakai; Tomohiro Nagai; Masahisa Nakazato; Yuzo Mano; Takatsugu Matsumura

doi:10.1364/AO.42.007103

Applied Optics
Vol. 42,
Issue 36,
pp. 7103-7116
(2003)
•https://doi.org/10.1364/AO.42.007103

Ice clouds and Asian dust studied with lidar measurements of particle extinction-to-backscatter ratio, particle depolarization, and water-vapor mixing ratio over Tsukuba

Tetsu Sakai, Tomohiro Nagai, Masahisa Nakazato, Yuzo Mano, and Takatsugu Matsumura

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Tetsu Sakai, Tomohiro Nagai, Masahisa Nakazato, Yuzo Mano, and Takatsugu Matsumura, "Ice clouds and Asian dust studied with lidar measurements of particle extinction-to-backscatter ratio, particle depolarization, and water-vapor mixing ratio over Tsukuba," Appl. Opt. 42, 7103-7116 (2003)

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Abstract

The tropospheric particle extinction-to-backscatter ratio, the depolarization ratio, and the water-vapor mixing ratio were measured by use of a Raman lidar and a polarization lidar during the Asian dust seasons in 2001 and 2002 in Tsukuba, Japan. The apparent (not corrected for multiple-scattering effects) extinction-to-backscatter ratios (S _p) showed a dependence on the relative humidity with respect to ice (RH_ice) obtained from the lidar-derived water-vapor mixing ratio and radiosonde-derived temperature; they were mostly higher than 30 sr in dry air (RH_ice < 50%), whereas they were mostly lower than 30 sr in ice-supersaturated air (RH_ice ≥ 100%), where the apparent extinction coefficients were larger than 0.036 km^-1. Both regions showed mean particle depolarization ratios of 20%–22%. Comparisons with theoretical calculations and the previous experiments suggest that the observed dependence of S _p on RH_ice is attributed to the difference in the predominant particles: nonspherical aerosols (mainly the Asian dust) in dry air and cloud particles in ice-supersaturated air.

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Particles	Observation		Theoretical Calculation
Particles	Value (sr)	Description	Value (sr)	Description
Asian dust	47± 18a	This study (RH_ice < 50% or T ≥ 273.15 K)	89 (35–102)b	Ellipsoids (b/a = 1.4, h/a = 0.2–1.0)
	42–73	Over Japan (HSRL and Raman lidar)33	58	Semiempirical34,35
	39–45	Over Japan (Raman lidar)36
	40–55	Over Yellow Sea and Sea of Japan (nephelometer)37
Clouds	17± 14a	This study (RH_ice ≥ 100%)	16–19	Hexagonal columns (maximum tilt angle γ = 1°)38
	5–20	Cirrus over Germany (Raman lidar at 308 nm)8	70–86	Imperfect hexagonal columns (γ = 30°)38
	10–30	Cirrus over Arctic (Raman lidar at 355 nm)39	19	Water droplets (C1 model40)
	∼25	Cirrus over Wisconsin, U.S. (HSRL)41	5–15	Regular hexagonal column and plate (L/2a = 8/20,c 300/120 µm,42 20/20–750/160 µm,43 1000/400 µm44)
	∼24	Cirrus over Utah, U.S. (LIRAD at 694 nm)45	∼10	Bullet rosettes (1/2a = 120/60 µm)46
	39–79	Cirrus over midlatitude in southern hemisphere and tropics (LIRAD at 694 nm)47	∼10	Dendrites (L/2a = 32/80 µm)46
	<1	Horizontally oriented ice plates22	∼6	Aggregates (maximum dimension of 200 µm)48
			∼170	Hollow columns (L/2a = 200/100 µm with depth randomly selected 0–100 µm)48
			>120	Small (a few micrometers) crystals49

Particles	Observation		Theoretical Calculation
Particles	Value (%)	Description	Value (%)	Description
Asian dust	20± 7a	This study (RH_ice < 50% or T ≥ 273.15 K)	25 (21–33)b	Ellipsoids (b/a = 1.4, h/a = 0.2–1.0)
	20–30	Over Japan33,36,50
	∼17c	Over Utah, U.S. (694 nm)4
Clouds	22± 7a	This study (RH_ice ≥ 100%)	31–32	Hexagonal columns (maximum tilt angle γ = 1°)38
	∼25± 7a,c	Cirrus over Utah, U.S. (at 694 nm)51	35–36	Imperfect hexagonal columns (γ = 30°)38
	13–18c	Cirrus over midlatitude in southern hemisphere (at 694 nm)47	0	Water droplets (C1 model40)
	21–23c	Cirrus over tropics (at 694 nm)47	25–36	Regular hexagonal plate to column with L/2a d ranging from 8/80 to 400/80 µm51
	13–38	Cirrus over Arctic (at 355 nm)39	∼33	Bullet rosettes (1/2a = 120/60 µm)46
	∼18	Cloud over Antarctica (midcloud temperature below 243 K)52	∼26	Dendrites (1/2a = 32/80 µm)46
			22–34	Aggregates (maximum dimension of 200 µm)48
			19–35	Hollow columns (L/2a = 200/80 µm with hollow depth decreases from 100 to 0 µm)46
			∼10	Small (a few micrometers) crystals53
			0	Horizontally oriented columns and plates23

Particles	Observation		Theoretical Calculation
Particles	Value (sr)	Description	Value (sr)	Description
Asian dust	47± 18a	This study (RH_ice < 50% or T ≥ 273.15 K)	89 (35–102)b	Ellipsoids (b/a = 1.4, h/a = 0.2–1.0)
	42–73	Over Japan (HSRL and Raman lidar)33	58	Semiempirical34,35
	39–45	Over Japan (Raman lidar)36
	40–55	Over Yellow Sea and Sea of Japan (nephelometer)37
Clouds	17± 14a	This study (RH_ice ≥ 100%)	16–19	Hexagonal columns (maximum tilt angle γ = 1°)38
	5–20	Cirrus over Germany (Raman lidar at 308 nm)8	70–86	Imperfect hexagonal columns (γ = 30°)38
	10–30	Cirrus over Arctic (Raman lidar at 355 nm)39	19	Water droplets (C1 model40)
	∼25	Cirrus over Wisconsin, U.S. (HSRL)41	5–15	Regular hexagonal column and plate (L/2a = 8/20,c 300/120 µm,42 20/20–750/160 µm,43 1000/400 µm44)
	∼24	Cirrus over Utah, U.S. (LIRAD at 694 nm)45	∼10	Bullet rosettes (1/2a = 120/60 µm)46
	39–79	Cirrus over midlatitude in southern hemisphere and tropics (LIRAD at 694 nm)47	∼10	Dendrites (L/2a = 32/80 µm)46
	<1	Horizontally oriented ice plates22	∼6	Aggregates (maximum dimension of 200 µm)48
			∼170	Hollow columns (L/2a = 200/100 µm with depth randomly selected 0–100 µm)48
			>120	Small (a few micrometers) crystals49

Particles	Observation		Theoretical Calculation
Particles	Value (%)	Description	Value (%)	Description
Asian dust	20± 7a	This study (RH_ice < 50% or T ≥ 273.15 K)	25 (21–33)b	Ellipsoids (b/a = 1.4, h/a = 0.2–1.0)
	20–30	Over Japan33,36,50
	∼17c	Over Utah, U.S. (694 nm)4
Clouds	22± 7a	This study (RH_ice ≥ 100%)	31–32	Hexagonal columns (maximum tilt angle γ = 1°)38
	∼25± 7a,c	Cirrus over Utah, U.S. (at 694 nm)51	35–36	Imperfect hexagonal columns (γ = 30°)38
	13–18c	Cirrus over midlatitude in southern hemisphere (at 694 nm)47	0	Water droplets (C1 model40)
	21–23c	Cirrus over tropics (at 694 nm)47	25–36	Regular hexagonal plate to column with L/2a d ranging from 8/80 to 400/80 µm51
	13–38	Cirrus over Arctic (at 355 nm)39	∼33	Bullet rosettes (1/2a = 120/60 µm)46
	∼18	Cloud over Antarctica (midcloud temperature below 243 K)52	∼26	Dendrites (1/2a = 32/80 µm)46
			22–34	Aggregates (maximum dimension of 200 µm)48
			19–35	Hollow columns (L/2a = 200/80 µm with hollow depth decreases from 100 to 0 µm)46
			∼10	Small (a few micrometers) crystals53
			0	Horizontally oriented columns and plates23

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Applied Optics