Search Results

You are looking at 31 - 34 of 34 items for

  • Author or Editor: Gabor Vali x
  • Refine by Access: All Content x
Clear All Modify Search
Zhien Wang
,
Jeffrey French
,
Gabor Vali
,
Perry Wechsler
,
Samuel Haimov
,
Alfred Rodi
,
Min Deng
,
Dave Leon
,
Jeff Snider
,
Liran Peng
, and
Andrew L. Pazmany

Clouds are a critical component of the Earth's coupled water and energy cycles. Poor understanding of cloud–radiation–dynamics feedbacks results in large uncertainties in forecasting human-induced climate changes. Better understanding of cloud microphysical and dynamical processes is critical to improving cloud parameterizations in climate models as well as in cloud-resolving models. Airborne in situ and remote sensing can make critical contributions to progress. Here, a new integrated cloud observation capability developed for the University of Wyoming King Air is described. The suite of instruments includes the Wyoming Cloud Lidar, a 183- GHz microwave radiometer, the Wyoming Cloud Radar, and in situ probes. Combined use of these remote sensor measurements yields more complete descriptions of the vertical structure of cloud microphysical properties and of cloud-scale dynamics than that attainable through ground-based remote sensing or in situ sampling alone. Together with detailed in situ data on aerosols, hydrometeors, water vapor, thermodynamic, and air motion parameters, an advanced observational capability was created to study cloud-scale processes from a single aircraft. The Wyoming Airborne Integrated Cloud Observation (WAICO) experiment was conducted to demonstrate these new capabilities and examples are presented to illustrate the results obtained.

Full access
Melanie A. Wetzel
,
Steven K. Chai
,
Marcin J. Szumowski
,
William T. Thompson
,
Tracy Haack
,
Gabor Vali
, and
Robert Kelly

Abstract

A field project was carried out offshore of central Oregon during August 1999 to evaluate mesoscale model simulations of coastal stratiform cloud layers. Procedures for mapping cloud physical parameters such as cloud optical depth, droplet effective radius, and liquid water path retrieved from Geostationary Operational Environmental Satellite (GOES) Imager multichannel data were developed and implemented. Aircraft measurements by the University of Wyoming provided in situ verification for the satellite retrieval parameters and for the forecast model simulations of the U.S. Navy's nonhydrostatic mesoscale prediction system, the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS). Case studies show that the satellite retrieval methods are valid within the range of uncertainty associated with aircraft measurements of the microphysical parameters and demonstrate how the gridded cloud parameters retrieved from satellite data can be utilized for mesoscale model verification. Satellite-derived products with applications to forecasting, such as temporal trends and composites of droplet size and liquid water path, are also discussed.

Full access
Paul J. DeMott
,
Ottmar Möhler
,
Olaf Stetzer
,
Gabor Vali
,
Zev Levin
,
Markus D. Petters
,
Masataka Murakami
,
Thomas Leisner
,
Ulrich Bundke
,
Holger Klein
,
Zamin A. Kanji
,
Richard Cotton
,
Hazel Jones
,
Stefan Benz
,
Maren Brinkmann
,
Daniel Rzesanke
,
Harald Saathoff
,
Mathieu Nicolet
,
Atsushi Saito
,
Bjorn Nillius
,
Heinz Bingemer
,
Jonathan Abbatt
,
Karin Ardon
,
Eli Ganor
,
Dimitrios G. Georgakopoulos
, and
Clive Saunders

Understanding cloud and precipitation responses to variations in atmospheric aerosols remains an important research topic for improving the prediction of climate. Knowledge is most uncertain, and the potential impact on climate is largest with regard to how aerosols impact ice formation in clouds. In this paper, we show that research on atmospheric ice nucleation, including the development of new measurement systems, is occurring at a renewed and historically unparalleled level. A historical perspective is provided on the methods and challenges of measuring ice nuclei, and the various factors that led to a lull in research efforts during a nearly 20-yr period centered about 30 yr ago. Workshops played a major role in defining critical needs for improving measurements at that time and helped to guide renewed efforts. Workshops were recently revived for evaluating present research progress. We argue that encouraging progress has been made in the consistency of measurements using the present generation of ice nucleation instruments. Through comparison to laboratory cloud simulations, these ice nuclei measurements have provided increased confidence in our ability to quantify primary ice formation by atmospheric aerosols.

Full access
Bjorn Stevens
,
Donald H. Lenschow
,
Gabor Vali
,
Hermann Gerber
,
A. Bandy
,
B. Blomquist
,
J. -L. Brenguier
,
C. S. Bretherton
,
F. Burnet
,
T. Campos
,
S. Chai
,
I. Faloona
,
D. Friesen
,
S. Haimov
,
K. Laursen
,
D. K. Lilly
,
S. M. Loehrer
,
Szymon P. Malinowski
,
B. Morley
,
M. D. Petters
,
D. C. Rogers
,
L. Russell
,
V. Savic-Jovcic
,
J. R. Snider
,
D. Straub
,
Marcin J. Szumowski
,
H. Takagi
,
D. C. Thornton
,
M. Tschudi
,
C. Twohy
,
M. Wetzel
, and
M. C. van Zanten

The second Dynamics and Chemistry of Marine Stratocumulus (DYCOMS-II) field study is described. The field program consisted of nine flights in marine stratocumulus west-southwest of San Diego, California. The objective of the program was to better understand the physics a n d dynamics of marine stratocumulus. Toward this end special flight strategies, including predominantly nocturnal flights, were employed to optimize estimates of entrainment velocities at cloud-top, large-scale divergence within the boundary layer, drizzle processes in the cloud, cloud microstructure, and aerosol–cloud interactions. Cloud conditions during DYCOMS-II were excellent with almost every flight having uniformly overcast clouds topping a well-mixed boundary layer. Although the emphasis of the manuscript is on the goals and methodologies of DYCOMS-II, some preliminary findings are also presented—the most significant being that the cloud layers appear to entrain less and drizzle more than previous theoretical work led investigators to expect.

Full access