Height profiles of the extinction and the backscatter coefficients in cirrus clouds are determined independently from elastic- and inelastic- (Raman) backscatter signals. An extended error analysis is given. Examples covering the measured range of extinction-to-backscatter ratios (lidar ratios) in ice clouds are presented. Lidar ratios between 5 and 15 sr are usually found. A strong variation between 2 and 20 sr can be observed within one cloud profile. Particle extinction coefficients determined from inelastic-backscatter signals and from elastic-backscatter signals by using the Klett method are compared. The Klett solution of the extinction profile can be highly erroneous if the lidar ratio varies along the measuring range. On the other hand, simple backscatter lidars can provide reliable information about the cloud optical depth and the mean cloud lidar ratio.

Independent measurement of extinction and backscatter profiles in cirrus clouds by using a combined Raman elastic-backscatter lidar

This paper examines the effects of the relationship between cirrus cloud ice water content and cloud temperature on climate change A simple mechanistic climate model is used to study the feedback between ice water content and temperature The central question studied in this paper concerns the extent to which both the radiative and microphysical properties of cirrus cloud influence such a feedback To address this question, a parameterization of the albedo and emissivity of clouds is introduced Observations that relate the ice water content to cloud temperature are incorporated in the parameterization to introduce a temperature dependence to both albedo and emittance The cloud properties relevant to the cloud feedback are expressed as functions of particles size re, asymmetry parameter g and cloud temperature and analyses of aircraft measurements, lidar and ground based radiometer data are used to select re and g It was shown that scattering calculations assuming spherical particles with a di

The Relevance of the Microphysical and Radiative Properties of Cirrus Clouds to Climate and Climatic Feedback

The development of the polarization lidar technique is reviewed, and the current capabilities and limitations of the technique for the cloud research are discussed. At present, polarization lidar is a key component of climate-research programs designed to characterize the properties of cirrus clouds and is an integral part of multiple remote-sensor studies of mixed-phase cloud systems such as winter mountain storms, making it possible to discriminate between cloud phases and to identify some particle types and orientations. Recent theoretical approaches involving ice crystal ray-tracing and cloud microphysical-model simulations are expected to increase the utility of the polarization lidar technique.

The Polarization Lidar Technique for Cloud Research: A Review and Current Assessment

We present a new parameterization of the optical properties of ice crystal clouds which is suitable for use in climate models. Five spectral intervals in the shortwave and five intervals in the infrared are employed, with the ice cloud optical properties parameterized in terms of ice water path (IWP) and the effective radius (re) of the ice crystal size distribution. The parameterization thus allows the flexibility of varying the ice water path and effective radius independently of each other. The parameterized optical properties are used to calculate the bulk reflectivity, transmissivity, and emissivity for cirrus clouds with realistic ranges of IWP and re. For a given change in cloud optical depth a change in re alone is more effective than a change in IWP alone in altering the shortwave reflectivity and therefore in altering the strength of the cloud albedo feedback.

A parameterization of ice cloud optical properties for climate models

Over the last 8 yr frequency and location of cloud observations have been compiled using multispectral High Resolution Infrared Radiation Sounder (HIRS) data from the National Oceanic and Atmospheric Administration polar-orbiting satellites; this work is an extension of the 4-yr dataset reported by D. Wylie et al. The CO 2 slicing algorithm applied to the HIRS data exhibits a higher sensitivity to semitransparent cirrus clouds than the cloud algorithm used by the International Satellite Cloud Climatology Project; the threshold for cloud detection appears to require visible optical depths (t vis) greater than 0.1. The geographical distributions of clouds in the 8-yr dataset are nearly the same as those reported from 4 yr of data. The detection of upper-tropospheric clouds occurs most often in the intertropical convergence zone and midlatitude storm belts with lower concentrations in subtropical deserts and oceanic subtropical highs. The areas of concentrated cloud cover exhibit latitudinal movement with the seasons as in other cloud datasets. HIRS finds clear sky in 25%, opaque cloud in 32%, and semitransparent cloud in 43% of all its observations. The effective emissivity of the all semitransparent clouds (t vis , 6) ranges from 0.2 to 0.6 with an average value of about 0.5. Time trends are reexamined in detail. A possible cirrus increase in 1991 reported by Wylie and coauthors in 1994 is found to be diminished upon reinspection. The revised 8-yr record has indications of an increase in high clouds in the northern midlatitudes (0.5% yr21) but little change elsewhere. The seasonal cycle of cloud cover in the Southern Hemisphere becomes very noticeable in 1993.

https://journals.ametsoc.org/doi/pdf/10.1175/1520-0442%281999%29012%3C0170%3AEYOHCS%3E2.0.CO%3B2

Eight Years of High Cloud Statistics Using HIRS

A lidar (0.694 μm wavelength) and a passive radiometer (10–12 μm) have been used together to remotely sense the optical properties and gross structure of cirrus (the LIRAD method). This article reports on observations of midlatitude cirrus taken during two extended experiments at Aspendale, Victoria, Australia, covering one winter season and one summer season and a six-week period of observations of tropical cirrus at Darwin, Northern Territory. Information has been obtained on the infrared emittance, optical depth, cloud depth, depolarization ratio, “anomalous” backscatter, the effective ratios of backscatter to extinction at the lidar wavelength and the visible to infrared extinction, and the backscatter profile of cirrus. The results show that the infrared emittance and volume absorption coefficient of midlatitude cirrus, when averaged over a year, are close functions of the midcloud temperature. Very similar relationships hold for tropical cirrus, taking into amount the limited samples. Mean ...

Remote Sounding of High Clouds. Part VI: Optical Properties of Midlatitude and Tropical Cirrus

The results of a ruby lidar (0.694 μm wavelength) and infrared radiometer (10–12 μm) study on cirrus clouds are reported for a period covering the autumn and winter months at Aspendale (38°S, 144°E). The lidar and radiometer data have been used to study the temperature dependence of the gross structure and optical properties of cirrus clouds. Well-defined correlations are found between the mid-cloud temperature and cloud depth, infrared absorption coefficient, infrared emittance, backscatter to extinction ratio and ratio of the visible extinction coefficient at 0.693 μm to the infrared absorption coefficient at 10–12 μm. For instance, as the mid-cloud temperature varies from −70 to −30°C, the mean cloud depth increases from 1 to 3.5 km and mean infrared absorption coefficient from 0.04 to 0,25 km−1. These two factors together cause a change in emittance from 0.11 to 0.42. The increase in absorption coefficient with temperature can be attributed to the presence of larger ice particles in the deepe...

A. C. Dilley

Papers

Remote Sounding of High Clouds. Part VI: Optical Properties of Midlatitude and Tropical Cirrus

Remote Sounding of High Clouds. IV: Observed Temperature Variations in Cirrus Optical Properties