Measurement errors in cirrus cloud microphysical properties

Larsen, Howard; Gayet, J.-F.; Febvre, Guy; Chepfer, Hélène; Brogniez, Gérard

doi:10.1007/s005850050599

Cited by 3 publications

(5 citation statements)

References 18 publications

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“…The model gives also the estimated ice water content. Cirrus ice water content is important for studies of the clouds radiative impact [ Larsen et al , 1998].…”

Section: Modeling Of the Case Studymentioning

confidence: 99%

Isentropic modeling of a cirrus cloud event observed in the midlatitude upper troposphere and lower stratosphere

Montoux¹,

Keckhut²,

Hauchecorne³

et al. 2010

J. Geophys. Res.

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[1] This publication provides a detailed study of one cirrus cloud observed by lidar at the Observatory of Haute-Provence ($44°N) in January 2006 in the vicinity of the tropopause (12)(13)(14). The higher part of the air mass observed comes from the wet subtropics while the lower part comes from the midlatitudes. Both are advected by the Azores anticyclone, encounter cold temperatures ($205 K) above the North Atlantic Ocean, and flow eastward along the anticyclonic flank of the polar jet stream. A simulation of this cloud by an isentropic model is tested to see if synoptic-scale atmospheric structures could explain by itself the presence of such clouds. The developments made in the Modélisation Isentrope du transport Méso-échelle de l'Ozone Stratosphérique par Advection (MIMOSA) model to take into account the three phases of water and their interactions allow reproduction of the occurrence of the cirrus and its temporal evolution. MIMOSA-H 2 O reproduces the atmospheric water vapor structures observed with Atmospheric Infrared Sounder (AIRS) with, however, an apparent wet bias of around 50%. Reliable water vapor fields appear to be the main condition to correctly simulate such cirrus clouds. The model reproduces the cirrus cloud altitude for fall speeds around 1 cm/s and gives ice water content around 3-4 mg/m 3 . Fall speed is also a critical parameter, and a better parameterization with altitude or other atmospheric conditions in the modeling of such cirrus clouds is required. This study also shows that supersaturation threshold impacts strongly the vertical and horizontal extension of the cirrus cloud but more slightly the ice water path.

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“…The model gives also the estimated ice water content. Cirrus ice water content is important for studies of the clouds radiative impact [ Larsen et al , 1998].…”

Section: Modeling Of the Case Studymentioning

confidence: 99%

Isentropic modeling of a cirrus cloud event observed in the midlatitude upper troposphere and lower stratosphere

Montoux¹,

Keckhut²,

Hauchecorne³

et al. 2010

J. Geophys. Res.

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“…Our objective here is to examine data collected in situ to determine what assumptions are most reasonable for developing a cloud property retrieval algorithm that meets our needs. Specifically, we would like to determine what functional approximations are required to reproduce the observed size distributions to within at least their observational uncertainty [ Larson et al , 1998]. To determine this, we employ a functional fitting approach where each 5‐second averaged PMS 2DC size distribution is fitted with three functional approximations: a two‐parameter zeroth order gamma (exponential) function n e ( L ) = N e exp [‐λ e L ], a modified gamma function [ Gossard , 1994; Mace et al , 1998b] expressed in terms of the modal size of the distribution (i.e., N g is the number of particles per unit volume per unit length at the size L g where the function is a maximum), and a bimodal distribution composed of the summation of the exponential function for the smaller particle mode and the modified gamma function for the larger particle mode as suggested by Platt [1997].…”

Section: Analysis Of Aircraft‐observed Particle Size Spectramentioning

confidence: 99%

“…The value of 50% was chosen for two reasons. (1) Values such as IWC (second‐third moment of the particle spectrum) are known to vary by a factor of 1000 in natural cirrus between 10 −4 g m −3 and 10 −1 g m −3 and (2) the uncertainty of parameters derived from measurements of particle spectra by PMS probes is on the order of 30–50% [ Larson et al , 1998]. We therefore define those distributions where δ bimodal < 0.5δ unimoda l as being significantly bimodal.…”

Section: Analysis Of Aircraft‐observed Particle Size Spectramentioning

confidence: 99%

“…It is important to determine if this degree of complexity is required or if simpler two‐parameter functions provide a characterization of the cloud properties that is adequate with respect to our ability to observe them. The uncertainty in observing particle size distributions in cirrus clouds has recently been considered by Larson et al [1998]. An optimistic interpretation of their results suggests that the mass and mean size derived from a well‐calibrated PMS probe is generally on the order of 50% and 25%, respectively.…”

Section: Analysis Of Aircraft‐observed Particle Size Spectramentioning

confidence: 99%

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On retrieving the microphysical properties of cirrus clouds using the moments of the millimeter‐wavelength Doppler spectrum

2002

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[1] Techniques that use only measurements provided by millimeter-wavelength Doppler radar for retrieving the properties of clouds provide certain practical advantages over techniques that require measurements from multiple instruments. We concentrate on the capacity of the moments of the Doppler spectrum to provide information suitable for retrieving the microphysical properties of cirrus clouds. Specifically, we present an algorithm that uses the zeroth and first moments of the Doppler spectrum (radar reflectivity and mean Doppler velocity) to retrieve the cloud particle size distribution. We also discuss a methodology for evaluating the second moment of the Doppler spectrum for information related to the width of the particle size distribution. The properties of observed cirrus particle spectra are first examined to ascertain what degree of complexity is required of assumed functional representations of particle spectra in cirrus volumes. We find that although particle spectra with bimodal tendencies are common, single-mode functions are able to capture the essential characteristics of these spectra to within observational uncertainty for most cirrus. Furthermore, two-parameter functions such as the exponential function are shown to be adequate representations of cirrus particle spectra in situations where the radar reflectivity factor is less than about À5 dBZ e and the temperatures are colder than about 253 K. A technique for separating air motion contributions from the Doppler velocity is examined, and an approach for similarly processing the Doppler spectral width is introduced. In comparison to aircraft data, we find uncertainty in the derived quiet air velocity and spectrum width to be on the order of 20% and 40%, respectively. Using recent parameterizations of ice crystal terminal velocity, mass, and backscatter cross section, we present a straightforward algorithm for retrieving cirrus cloud microphysical properties from observations of radar reflectivity and Doppler velocity. A simulation experiment with variable particle habits and realistic observational error shows that the retrieval uncertainties are on the order of 60% and 40% for ice water content and mass median particle size, respectively. These uncertainty magnitudes are supported by comparison to aircraft data. Citation: Mace, G. G., A. J. Heymsfield, and M. R. Poellot, On retrieving the microphysical properties of cirrus clouds using the moments of the millimeter-wavelength Doppler spectrum,

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“…Irregular ice particles were the most predominant crystal shape sampled in the present mixed‐phase cloud, therefore, the bulk parameters were calculated assuming the following surface‐equivalent diameter relationships [ Gayet et al , 1993]:

For these empirical relations, d i eq are expressed in millimeter and A i in millimeter squared. The accuracy of derived microphysical parameters from 2D‐C data is given by Gayet et al [1993] and Larsen et al [1998].…”

Section: Aircraft Instrumentation Data Processing and Validationmentioning

confidence: 99%

Two case studies of winter continental‐type water and mixed‐phase stratocumuli over the sea 1. Microphysical and optical properties

et al. 2002

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[1] Collocated aircraft observations of microstructure and radiative properties of winter boundary layer clouds over the East China Sea and the Japan Sea have been carried out in January 1999 within the Japanese Cloud and Climate Study (JACCS) program. The first part of the paper describes the in situ measured microphysical and optical properties for two cases of boundary layer winter stratocumulus clouds, which concern, first, a rather uniform, supercooled water cloud contaminated by aerosols and, second, a highly heterogeneous, mixed-phase stratiform cloud. Using the Polar Nephelometer, a new instrument for measuring, in situ, the scattering phase function of cloud droplets and ice particles, the polluted, continental-type stratocumulus cloud can be optically regarded as a liquid water cloud because the measured scattering phase functions fitted very well with those calculated from Mie theory for the directly measured FSSP size distributions. In mixed-phase cloud, the measured scattering phase function shows that ice particles strongly affect optical properties of the cloud, where large number of liquid water droplets with higher extinction coefficient and asymmetry factor values were converted into a much smaller number of large ice crystals with lower extinction coefficient and asymmetry factor. Furthermore, a quasi-stable liquid-topped cloud layer with precipitating ice particles was noticed; the layer may, first, affect the cloud radiative properties and, second, seriously restrict the interpretation of satellite cloud composition retrievals.

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Measurement errors in cirrus cloud microphysical properties

Cited by 3 publications

References 18 publications

Isentropic modeling of a cirrus cloud event observed in the midlatitude upper troposphere and lower stratosphere

Isentropic modeling of a cirrus cloud event observed in the midlatitude upper troposphere and lower stratosphere

On retrieving the microphysical properties of cirrus clouds using the moments of the millimeter‐wavelength Doppler spectrum

Two case studies of winter continental‐type water and mixed‐phase stratocumuli over the sea 1. Microphysical and optical properties

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