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  • Author or Editor: Dennis L. Hlavka x
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James D. Spinhirne
,
William D. Hart
, and
Dennis L. Hlavka

Abstract

A summary of experimental observations and analysis of cirrus from high-altitude aircraft remote sensing is presented. The vertical distribution of cirrus optical and infrared cross-section parameters and the relative effective emittance and visible reflectance are derived from nadir-viewing lidar and multispectral radiometer data for observations during the 1986 and 1991 FIRE cirrus experiments. Statistics on scattering and absorption cross sections in relation to altitude and temperature are given. The emittance and reflectance results are considered as a function of solar zenith angle. Comparative radiative transfer calculations based on the discrete-ordinate method were carried out for three representative cloud phase function models: a spherical water droplet, an ice column crystal cloud, and a Henyey-Greenstein function. The agreements between observations of the effective emittance and shortwave reflectance and the model calculations were a function of the solar zenith angle. At angles between 54° and 60° a Henyey-Greenstein (HG) function with an asymmetry factor of 0.6–0.7 produced the best comparison. At 66°–72° the ice column model was equally comparable to observations. Comparisons to the water cloud model wore poor in all cases. The effects of ice crystal microphysical variations on the observed results were not generally apparent, but one dramatic example of difference was found. In order to explain the variations noted for solar zenith angle, an instrument–the Tilt Scan CCD Camera radiometer–was developed to directly observe the shortwave bidirectional reflectance function for 1991 measurements. The results indicate a characteristic angular function of the visible reflectance of cirrus that is flatter than predicted by the ice column scattering model, but the overall asymmetry factor is comparable. The good agreement with values from an HG function at some angles is not generally applicable. The characteristics of the observed cirrus angular reflectance pattern correlate well with, and are explained by, the results that were found for the solar zenith angle dependence of the eminence and reflectance.

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John E. Yorks
,
Dennis L. Hlavka
,
William D. Hart
, and
Matthew J. McGill

Abstract

Accurate knowledge of cloud optical properties, such as extinction-to-backscatter ratio and depolarization ratio, can have a significant impact on the quality of cloud extinction retrievals from lidar systems because parameterizations of these variables are often used in nonideal conditions to determine cloud phase and optical depth. Statistics and trends of these optical parameters are analyzed for 4 yr (2003–07) of cloud physics lidar data during five projects that occurred in varying geographic locations and meteorological seasons. Extinction-to-backscatter ratios (also called lidar ratios) are derived at 532 nm by calculating the transmission loss through the cloud layer and then applying it to the attenuated backscatter profile in the layer, while volume depolarization ratios are computed using the ratio of the parallel and perpendicular polarized 1064-nm channels. The majority of the cloud layers yields a lidar ratio between 10 and 40 sr, with the lidar ratio frequency distribution centered at 25 sr for ice clouds and 16 sr for altocumulus clouds. On average, for ice clouds the lidar ratio slightly decreases with decreasing temperature, while the volume depolarization ratio increases significantly as temperatures decrease. Trends for liquid water clouds (altocumulus clouds) are also observed. Ultimately, these observed trends in optical properties, as functions of temperature and geographic location, should help to improve current parameterizations of extinction-to-backscatter ratio, which in turn should yield increased accuracy in cloud optical depth and radiative forcing estimates.

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Robert E. Holz
,
Steve Ackerman
,
Paolo Antonelli
,
Fred Nagle
,
Robert O. Knuteson
,
Matthew McGill
,
Dennis L. Hlavka
, and
William D. Hart

Abstract

An improvement to high-spectral-resolution infrared cloud-top altitude retrievals is compared to existing retrieval methods and cloud lidar measurements. The new method, CO2 sorting, determines optimal channel pairs to which the CO2 slicing retrieval will be applied. The new retrieval is applied to aircraft Scanning High-Resolution Interferometer Sounder (S-HIS) measurements. The results are compared to existing passive retrieval methods and coincident Cloud Physics Lidar (CPL) measurements. It is demonstrated that when CO2 sorting is used to select channel pairs for CO2 slicing there is an improvement in the retrieved cloud heights when compared to the CPL for the optically thin clouds (total optical depths less than 1.0). For geometrically thick but tenuous clouds, the infrared retrieved cloud tops underestimated the cloud height, when compared to those of the CPL, by greater than 2.5 km. For these cases the cloud heights retrieved by the S-HIS correlated closely with the level at which the CPL-integrated cloud optical depth was approximately 1.0.

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John E. Yorks
,
Matthew J. McGill
,
V. Stanley Scott
,
Shane W. Wake
,
Andrew Kupchock
,
Dennis L. Hlavka
,
William D. Hart
, and
Patrick A. Selmer

Abstract

The Airborne Cloud–Aerosol Transport System (ACATS) is a Doppler wind lidar system that has recently been developed for atmospheric science capabilities at the NASA Goddard Space Flight Center (GSFC). ACATS is also a high-spectral-resolution lidar (HSRL), uniquely capable of directly resolving backscatter and extinction properties of a particle from a high-altitude aircraft. Thus, ACATS simultaneously measures optical properties and motion of cloud and aerosol layers. ACATS has flown on the NASA ER-2 during test flights over California in June 2012 and science flights during the Wallops Airborne Vegetation Experiment (WAVE) in September 2012. This paper provides an overview of the ACATS method and instrument design, describes the ACATS HSRL retrieval algorithms for cloud and aerosol properties, and demonstrates the data products that will be derived from the ACATS data using initial results from the WAVE project. The HSRL retrieval algorithms developed for ACATS have direct application to future spaceborne missions, such as the Cloud–Aerosol Transport System (CATS) to be installed on the International Space Station (ISS). Furthermore, the direct extinction and particle wind velocity retrieved from the ACATS data can be used for science applications such as dust or smoke transport and convective outflow in anvil cirrus clouds.

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James R. Campbell
,
Dennis L. Hlavka
,
Ellsworth J. Welton
,
Connor J. Flynn
,
David D. Turner
,
James D. Spinhirne
,
V. Stanley Scott III
, and
I. H. Hwang

Abstract

Atmospheric radiative forcing, surface radiation budget, and top-of-the-atmosphere radiance interpretation involve knowledge of the vertical height structure of overlying cloud and aerosol layers. During the last decade, the U.S. Department of Energy, through the Atmospheric Radiation Measurement (ARM) program, has constructed four long-term atmospheric observing sites in strategic climate regimes (north-central Oklahoma; Barrow, Alaska; and Nauru and Manus Islands in the tropical western Pacific). Micropulse lidar (MPL) systems provide continuous, autonomous observation of nearly all significant atmospheric clouds and aerosols at each of the central ARM facilities. These systems are compact, and transmitted pulses are eye safe. Eye safety is achieved by expanding relatively low-powered outgoing pulse energy through a shared, coaxial transmit/receive telescope. ARM MPL system specifications and specific unit optical designs are discussed. Data normalization and calibration techniques are presented. These techniques, in tandem, represent an operational value-added processing package used to produce normalized data products for ARM cloud and aerosol research.

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Eric J. Jensen
,
Leonhard Pfister
,
David E. Jordan
,
Thaopaul V. Bui
,
Rei Ueyama
,
Hanwant B. Singh
,
Troy D. Thornberry
,
Andrew W. Rollins
,
Ru-Shan Gao
,
David W. Fahey
,
Karen H. Rosenlof
,
James W. Elkins
,
Glenn S. Diskin
,
Joshua P. DiGangi
,
R. Paul Lawson
,
Sarah Woods
,
Elliot L. Atlas
,
Maria A. Navarro Rodriguez
,
Steven C. Wofsy
,
Jasna Pittman
,
Charles G. Bardeen
,
Owen B. Toon
,
Bruce C. Kindel
,
Paul A. Newman
,
Matthew J. McGill
,
Dennis L. Hlavka
,
Leslie R. Lait
,
Mark R. Schoeberl
,
John W. Bergman
,
Henry B. Selkirk
,
M. Joan Alexander
,
Ji-Eun Kim
,
Boon H. Lim
,
Jochen Stutz
, and
Klaus Pfeilsticker

Abstract

The February–March 2014 deployment of the National Aeronautics and Space Administration (NASA) Airborne Tropical Tropopause Experiment (ATTREX) provided unique in situ measurements in the western Pacific tropical tropopause layer (TTL). Six flights were conducted from Guam with the long-range, high-altitude, unmanned Global Hawk aircraft. The ATTREX Global Hawk payload provided measurements of water vapor, meteorological conditions, cloud properties, tracer and chemical radical concentrations, and radiative fluxes. The campaign was partially coincident with the Convective Transport of Active Species in the Tropics (CONTRAST) and the Coordinated Airborne Studies in the Tropics (CAST) airborne campaigns based in Guam using lower-altitude aircraft (see companion articles in this issue). The ATTREX dataset is being used for investigations of TTL cloud, transport, dynamical, and chemical processes, as well as for evaluation and improvement of global-model representations of TTL processes. The ATTREX data are publicly available online (at https://espoarchive.nasa.gov/).

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