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Gabor Vali
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Russell C. Schnell
and
Gabor Vali

Abstract

In Part 1 (Vali and Schnell, 2024; VS24) we described the discoveries we and our associates made in the 1960s and 1970s about biological ice nucleators (bio-INPs). Bio-INPs are far more effective than mineral INPs at temperatures above −10°C. The bio-INPs were found in decayed vegetation and in ocean water, then bacteria were identified as being the most active source for this remarkable activity. In this Part 2, we recount how, within a few years, the worldwide distribution of bio-INP sources was shown to correlate with climate zones, as was the abundance of INPs in precipitation. Oceanic sources were further studied and the presence of bio-INPs in fog diagnosed. The potential for release of bio-INPs from to the atmosphere was demonstrated. Bacterial INPs were found to play a crucial role in a plant’s frost resistance. These and other early developments of biological INPs are described. A bibliography of related recent literature is presented in the online Part 1 Supplemental Material.

Open access
Gabor Vali
and
Russell C. Schnell

Abstract

An overview is given of the path of research that led from asking how hailstones originate to the discovery that ice nucleation can be initiated by bacteria and other microorganisms at temperatures as high as −2°C. The major steps along that path were finding exceptionally effective ice nucleators in soils with a high content of decayed vegetative matter, then in decaying tree leaves, and then in plankton-laden ocean water. Eventually, it was shown that Pseudomonas syringae bacteria were responsible for most of the observed activity. That identification coincided with the demonstration that the same bacteria cause frost damage on plants. Ice nucleation by bacteria meant an unexpected turn in the understanding of ice nucleation and of ice formation in the atmosphere. Subsequent research confirmed the unique effectiveness of ice nucleating particles (INP) of biological origin, referred to as bio-INPs, so that bio-INPs are now considered to be important elements of lower-tropospheric cloud processes. Nonetheless, some of the questions which originally motivated the research are still unresolved, so that revisiting the early work may be helpful to current endeavors. Part I of this manuscript summarizes how the discovery progressed. Part II (Schnell and Vali) shows the relationship between bio-INPs in soils and in precipitation with climate and other findings. The online supplemental material contains a bibliography of recent work about bio-INPs.

Open access

WANTED: MORE Ph.D.s

Graduate Enrollments in the Atmospheric Sciences

Gabor Vali
,
Richard Anthes
,
Dennis Thomson
,
David Houghton
,
Jack Fellows
, and
Susan Friberg

A recent survey of UCAR member institutions shows reason for concern about a possible decline in the number and quality of applicants entering graduate studies in the atmospheric and related sciences. If reported trends continue, a shortage of qualified Ph.D. graduates in the field in the next decade may be faced.

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Bjorn Stevens
,
Gabor Vali
,
Kimberly Comstock
,
Robert Wood
,
Margreet C. van Zanten
,
Philip H. Austin
,
Christopher S. Bretherton
, and
Donald H. Lenschow

Data from recent field studies in the northeast and southeast Pacific are used to investigate pockets of open cells (POCs) that are embedded in otherwise uniform stratocumulus. The cellular structure within a POC resembles broader regions of open cellular convection typically found further offshore. In both regions, cells are composed of precipitating cell walls and cell interiors with depleted cloud water and even clearing. POCs are long lived and embedded in broader regions of stratocumulus where average droplet sizes are relatively large. In contrast, stratiform, or unbroken, cloud formations tend to be accompanied by less, or no, drizzle, suggesting that precipitation is necessary for the sustenance of the open cellular structure. Because, by definition, open cells are associated with a reduction in cloud cover these observations provide direct evidence of a connection between cloudiness and precipitation—a linchpin of hypotheses that posit a connection between changes in the atmospheric aerosol and climate.

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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.

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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.

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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