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R. Wood
,
S. Irons
, and
P. R. Jonas

Abstract

Any population of cloud droplets forming on polydisperse condensation nuclei is thermodynamically unstable. There is no value of the supersaturation for which the growth rate of all the droplets is zero, so that if some droplets are in equilibrium, then some must have positive and some negative growth rates. Droplets with positive growth rates will continue to grow at the expense of those with negative growth rates. This effect has been termed the ripening process, and has been postulated to be a potential mechanism to explain broad droplet size distributions in stratiform clouds. In this paper multiple parcel trajectories are used, derived using a simple representation of the turbulent dynamics, to examine the time evolution of the droplet size distribution in a nonentraining stratiform cloud. It is shown that the magnitude of the effect is critically dependent upon the mean parcel in-cloud residence time. The simulations suggest that, for a stratiform clouds of h = 400 m thickness, and a vertical wind standard deviation of σ w = 0.6 m s–1 (typical for stratocumulus clouds in a fairly vigorous, well-mixed boundary layer), the ripening effect is negligible, in that the droplet size distribution changes little with time. However, clouds with low σ w = 0.2 m s–1 (typical of weaker stratus clouds) show a marked spectral ripening effect over a period of several hours. Ripening is observed in the numerical model in both clean and polluted aerosol distributions. Autoconversion rates calculated from the droplet size distributions increase markedly with time as ripening takes place. It is suggested that to accurately model droplet size distributions in stratus cloud, it may be necessary to take into account the distribution of in-cloud parcel residence time.

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R. Wood
,
I. M. Stromberg
,
P. R. Jonas
, and
C. S. Mill

Abstract

A system has been developed for use on a light aircraft for the measurement of the turbulent wind vector components that does not rely on the use of either an inertial navigation system (INS) or Doppler radar. The system described here uses a five-hole probe to measure the wind vector relative to the aircraft. A GPS system, a vertical gyroscope for aircraft pitch and roll angles, a gyrocompass system, and a strap-down three-axis accelerometer system are used to obtain aircraft motion. Flight tests and results of an intercomparison with the United Kingdom Meteorological Office C-130 are presented. Under conditions of straight and level flight, the estimated rms errors are 0.3 m s−1 for the vertical wind component and 2 m s−1 for the horizontal components.

Full access
G. M. Martin
,
D. W. Johnson
,
D. P. Rogers
,
P. R. Jonas
,
P. Minnis
, and
D. A. Hegg

Abstract

Decoupling of the marine boundary layer beneath stratocumulus clouds and the formation of cumulus clouds at the top of a surface-based mixed layer (SML) have frequently been observed and modeled. When such cumulus clouds penetrate the overlying stratocumulus layer, the cloud microphysics and hence the radiative properties of the cloud are altered locally. Observations made during a series of Lagrangian experiments in the Azores as part of the Atlantic Stratocumulus Transition Experiment (ASTEX, June 1992) have been analyzed to ascertain how the properties of a stratocumulus layer with which cumulus clouds are interacting differ from those of an unaffected cloud layer. The results suggest that in regions where cumulus clouds penetrate the cloud layer, the stratocumulus is thickened as the cumuli spread out into its base. Transport of air from the SML into the cloud by convective updrafts is observed, and the increase in available moisture within the penetrating cumulus clouds results in increased liquid water content and hence changes in the droplet size spectra. The greater liquid water path results in a larger cloud optical depth, so that regions where cumulus are interesting with the stratocumulus layer can be observed in satellite measurements. Therefore, it is likely that the surface energy budget may be significantly altered by this process, and it may be necessary to parameterize these effects in large-scale numerical models.

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Tim Li
,
Abdallah Abida
,
Laura S. Aldeco
,
Eric J. Alfaro
,
Lincoln M. Alves
,
Jorge A. Amador
,
B. Andrade
,
Julian Baez
,
M. Yu. Bardin
,
Endalkachew Bekele
,
Elisangela Broedel
,
Brandon Bukunt
,
Blanca Calderón
,
Jayaka D. Campbell
,
Diego A. Campos Diaz
,
Gilma Carvajal
,
Elise Chandler
,
Vincent. Y. S. Cheng
,
Chulwoon Choi
,
Leonardo A. Clarke
,
Kris Correa
,
Felipe Costa
,
A. P. Cunha
,
Mesut Demircan
,
R. Dhurmea
,
Eliecer A. Díaz
,
M. ElKharrim
,
Bantwale D. Enyew
,
Jhan C. Espinoza
,
Amin Fazl-Kazem
,
Nava Fedaeff
,
Z. Feng
,
Chris Fenimore
,
S. D. Francis
,
Karin Gleason
,
Charles “Chip” P. Guard
,
Indra Gustari
,
S. Hagos
,
Richard R. Heim Jr.
,
Rafael Hernández
,
Hugo G. Hidalgo
,
J. A. Ijampy
,
Annie C. Joseph
,
Guillaume Jumaux
,
Khadija Kabidi
,
Johannes W. Kaiser
,
Pierre-Honore Kamsu-Tamo
,
John Kennedy
,
Valentina Khan
,
Mai Van Khiem
,
Khatuna Kokosadze
,
Natalia N. Korshunova
,
Andries C. Kruger
,
Nato Kutaladze
,
L. Labbé
,
Mónika Lakatos
,
Hoang Phuc Lam
,
Mark A. Lander
,
Waldo Lavado-Casimiro
,
T. C. Lee
,
Kinson H. Y. Leung
,
Andrew D. Magee
,
Jostein Mamen
,
José A. Marengo
,
Dora Marín
,
Charlotte McBride
,
Lia Megrelidze
,
Noelia Misevicius
,
Y. Mochizuki
,
Aurel Moise
,
Jorge Molina-Carpio
,
Natali Mora
,
Awatif E. Mostafa
,
uan José Nieto
,
Lamjav Oyunjargal
,
Reynaldo Pascual Ramírez
,
Maria Asuncion Pastor Saavedra
,
Uwe Pfeifroth
,
David Phillips
,
Madhavan Rajeevan
,
Andrea M. Ramos
,
Jayashree V. Revadekar
,
Miliaritiana Robjhon
,
Ernesto Rodriguez Camino
,
Esteban Rodriguez Guisado
,
Josyane Ronchail
,
Benjamin Rösner
,
Roberto Salinas
,
Amal Sayouri
,
Carl J. Schreck III
,
Serhat Sensoy
,
A. Shimpo
,
Fatou Sima
,
Adam Smith
,
Jacqueline Spence
,
Sandra Spillane
,
Arne Spitzer
,
A. K. Srivastava
,
José L. Stella
,
Kimberly A. Stephenson
,
Tannecia S. Stephenson
,
Michael A. Taylor
,
Wassila Thiaw
,
Skie Tobin
,
Dennis Todey
,
Katja Trachte
,
Adrian R. Trotman
,
Gerard van der Schrier
,
Cedric J. Van Meerbeeck
,
Ahad Vazifeh
,
José Vicencio Veloso
,
Wei Wang
,
Fei Xin
,
Peiqun Zhang
,
Zhiwei Zhu
, and
Jonas Zucule
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