Jim Hudson: Celebrating a Career in Cloud Physics

Jim Hudson: Celebrating a Career in Cloud Physics

Jim Hudson: Celebrating a Career in Cloud Physics

NOVEMBER 17, 2022

Cloud Physics
Cloud Condensation Nuclei
Atmospheric Science

Above: Throughout his career Jim Hudson, Ph.D., worked in planes such as the NCAR C-130 on several projects during his time at DRI.

Credit: Jim Hudson/DRI.

Research Professor Jim Hudson, Ph.D., the Institute’s longest-serving employee, recently retired from DRI after 51 years studying cloud condensation nuclei (CCN) – tiny particles around which cloud droplets form. Hudson originally came to DRI as a graduate student in 1970, following the completion of his Master’s degree in physics at the University of Michigan. Here, he worked under the direction of cloud physicist and Director of Atmospheric Sciences Patrick Squires and graduated with his Ph.D. in Atmospheric Physics from the University of Nevada, Reno, in 1976.

Hudson’s long and successful career at DRI has taken him from his current home base in Reno to 31 aircraft field projects around the globe. He developed the continuous flow diffusion cloud chamber, isothermal haze chamber, and five CCN spectrometers. He has led projects sponsored by the National Science Foundation (NSF), National Aeronautics and Space Association (NASA), Department of Energy (DOE), and others. He has co-authored 97 peer-reviewed publications in the Journal of Geophysical Research: Atmospheres, Journal of the Atmospheric Sciences, Journal of Applied Meteorology, Tellus, Atmospheric Chemistry & Physics, Atmospheric Physics, Atmospheric Science Letters, Journal of Atmospheric Chemistry, Geophysical Research Letters, Journal of the Meteorological Society of Japan, Bulletin of the American Meteorological Society, Aerosol Science and Technology, Atmospheric Environment, Journal of Atmospheric & Oceanic Technology, Idojaras, and Science, and delivered 146 conference presentations.

Although he officially retired in August 2021, Hudson is continuing at as an Emeritus Scholar at DRI. We sat down with Hudson to learn about some of his career highlights:

DRI: What inspired you to become a cloud physicist?

Hudson: I did not set out to be a scientist although I had a lot of science interests as a child and took all math and science courses offered in high school. Other interest were law and politics. When taking the Kuder vocational interest test in my junior year in spite of conscious efforts to score high in persuasion (for law or politics) I could not resist science responses.  Thus, I was dismayed that of the ten interest categories science tied with persuasion. Physical Science, biology, and chemistry in the first three high school years did not pique my interest but physics in the senior year with its more logical nature turned me to science. Despite feeling at the time that scientists are mere pawns to politicians and businessmen I majored in physics and mathematics in the Honors College of Western Michigan University (BA 1968).  An attraction of physics was great job prospects, but that crashed, especially for high energy physics that had attracted me to the University of Michigan.  Thus, in my last semester and summer there I drifted into aeronomy, which included a good deal of physics.  When I learned that clouds also have physics, I found a more interesting application of my background.  But the familiar down-to-Earth clouds were not studied at Michigan.  DRI in Reno was the place to study the clouds that concern weather.

Thus, I traded the study of atomic nuclei for cloud nuclei under a founding father of cloud physics, Patrick Squires.  At that time the main goal of cloud physics was understanding the onset of precipitation and perhaps controlling it. This leads to cloud seeding, which usually involved the ice phase, which was thought to be the origin of all precipitation until warm rain was discovered in the 1940s.  Being from Australia where the ice phase is less common directed Squires toward warm non-freezing clouds.

DRI: Which of your career accomplishments are you most proud of?

Hudson: In 2012 I finally realized that the DRI high-resolution CCN spectrometers often resolved two modes.  Although I and many others had known for decades that direct aerosol size distributions often displayed bimodality, I did not appreciate its importance until then.  Only then did I begin analyzing cloud microphysics (droplet and drop size distributions) in terms of CCN bimodality.  I have so far found opposite responses to CCN bimodality in stratus and cumulus clouds.  Bimodality seems to make more smaller droplets and less drizzle in stratus but fewer larger droplets and more drizzle in cumuli.

Jim Hudson and other male scientists

Jim Hudson, Ph.D. (left), poses for a picture with fellow scientists in September 1973 at a lab inside the Sage Building at UNR.

Credit: Jim Hudson/DRI.

DRI: What unanswered questions do you still want to solve?

Hudson: What’s known as the “indirect aerosol effect” continues to be the largest climate uncertainty. This is the interaction of air pollution with clouds and relates back to the 1950s discovery by Squires and Sean Twomey, that continental clouds differ from maritime clouds. They have more droplets, smaller droplets, and don’t precipitate as readily as maritime clouds. Why is that? Because there are more CCN over continents than oceans. Why are there more CCN over continents? That is a billion-dollar question. Are there significant natural continental sources or is it all anthropogenic?  This is such a difficult problem that most research dances around this question.  We actually know more about the unnatural sources, the man-made sources, than we do about the natural sources. The indirect aerosol effect is so important because to some yet to be known extent it probably counteracts the so-called greenhouse trace gas effect.  One does not need a degree to know that clouds are complicated.  We have known since the 1950s that CCN affect clouds though many have claimed that air motions (dynamics) are more important.  But when the effects of the clouds on the CCN are realized things get even more complicated.  Clouds thus are both a sink and a source of the CCN that in turn profoundly affect them.  This makes the foundation of science, cause and effect, especially challenging for clouds.

DRI: What are you working on as an Emeritus Scholar at DRI?

Hudson: I just want to further analyze the data I’ve collected over the last 30 or more years but now in terms of CCN bimodality.  Few atmospheric scientists delve into the extensive sets of aircraft data.  I’ve been in more than 30 cloud projects where we fly 10-20 research flights of 4-12 hours duration in a month or two.  Multitudes of data are collected throughout these flights, but only small fractions are analyzed or presented.  This is very time-consuming work much of which would be impossible if I were still employed.  These CCN cloud interactions are vitally important for the indirect aerosol effect and for fundamental cloud physics. I feel compelled to complete as much of this analysis as possible.

DRI: What has changed most at DRI during the course of your career?

Hudson: In the first, two or three decades of DRI partial contracts were not done.  In the 1970s there was actual pasting of letters and words onto paper.  Before the turn of the century proposals were hand delivered to parcel services.  Before the teens, Journals were printed onto paper and did not have supplementary material.

DRI: What advice do you have for future scientists?

Hudson: Look at the data. All of the data. Not just the data that you think is good, the data that fits your model. In all science, there’s always conflict between the theorists (modelers in cloud physics) and the experimentalists (observationalists). Peter Hobbs of University of Washington would say, “the modelers believe the data, and the observationalists believe the models.” Each are more aware of the pitfalls of their own area. I think he overstated that because he did not believe many models.  Conflicts between modelers and observationalists seem to be most intense in cloud physics. When I was in high energy physics 50 years ago there were articles about how theorists looked down on the experimentalists even though science is based on experiments.

DRI: Who have you most enjoyed working with at DRI?

Hudson: Of course, I did a lot of work with Squires in the beginning and then John Hallett for several field projects.  We must remember the engineers, who really built and maintained the CCN instruments, Gary Keyser, Rick Purcell, Norm Robinson, Dan Wermers and Morien Roberts. And then my students, Paul Frisbie, Xiaoyu Da, Hongguo Li, Yonghong Xie, Seong Soo Yum, David Mitchell, Subhashree Mishra, Samantha Tabor, Vandana Jha and Stephen Noble.  Fred Rogers was my fellow student under Squires.  In earlier years I worked with Dennis Lamb, Dick Egami, and Eric Broten.

male scientist in lab holding equipment

Jim Hudson, Ph.D., inventories the equipment in his lab space.

Credit: Jim Hudson/DRI.

Farm vehicles heavy as dinosaurs jeopardize future food security

Farm vehicles heavy as dinosaurs jeopardize future food security

Heavy farm machinery

May 17, 2022

Farm vehicles are heavy as dinosaurs, jeopardize future food security

Reposted from https://www.slu.se/en/ew-news/2022/5/farm-vehicles-heavy-as-dinosaurs-jeopardize-food-security/.

Farm vehicles are becoming so heavy that they jeopardize future food security in Europe, America and Australia. Larger and more flexible tires have limited the damage on the surface, but below the topsoil, the soil is becoming so compact that its long-term production capacity is threatened. These conclusions are made in a new global study, which also draws parallels to the sauropods, the heaviest animals that ever walked Earth.

The study, which was published in the Proceedings of the National Academy of Sciences (PNAS) yesterday, was conducted by Professor Thomas Keller from the Swedish University of Agricultural Sciences (SLU) and Agroscope in Switzerland, and Professor Dani Or from ETH Zurich in Switzerland and the Desert Research Institute in the USA.

Mechanization has greatly contributed to the success of modern agriculture, with vastly expanded food production capabilities achieved by the higher capacity of farm machinery. However, the increase in capacity has been accompanied by heavier vehicles that increase the risk of subsoil compaction.

While the total weight of laden combine harvesters could be around 4 tonnes in the late 1950s, we can today see modern vehicles weighing 36 tonnes in the fields, and the researchers behind the present study decided to investigate what this development has meant for arable land. The contact stress on the soil surface turned out to have remained constant at a low level during this period, which is due to the fact that the machines have been fitted with ever larger tires that distribute the weight over a larger surface. In the deeper soil layer, the subsoil, on the other hand, soil compaction has increased to levels that jeopardize the soil’s ability to produce food. This also has consequences for the soil’s ability to transport water and provide other important ecosystem services.

“Subsoil compaction by farm vehicles is a very serious problem, since once soils are compacted, they remain damaged for decades. This may be one of the reasons why harvests are no longer increasing and why we are now seeing more floods than before”, says lead author Professor Thomas Keller, from SLU in Sweden and Agriscope in Switzerland.

High risk of compaction in one fifth of the arable land globally

The researchers have also produced a map that shows how the risk of chronic subsoil compaction varies around the world and the risk turned out to be greatest in Europe, North and South America and Australia. Globally, about a fifth of all arable land is estimated to be at risk of far-reaching damage that is very difficult to repair. In other words, the chance that these soils will recover is small.

The risk is presently smaller in Asia and Africa, where the mechanization of agriculture has not reached the same high level yet.

“If the mechanization were to gain momentum in Asia and Africa, however, there is a risk of subsoil compaction also on these continents”, says Thomas Keller.

Vehicle manufacturers must pay more attention to subsoil compaction

To contribute to more sustainable agriculture, vehicle manufacturers need to be more concerned about the risk of subsoil compaction and its negative impact on the soil.

“Above all, the wheel loads of modern farm vehicles need to be reduced in order not to affect the subsoil to the same extent as today. The heavier the machines, the worse for the subsoils”, says Thomas Keller.

Did dinosaurs induce soil compaction?

The researchers also show that the heaviest farm vehicles used in modern agriculture approach the weight of the heaviest dinosaurs, the sauropods. This indicates that the sauropods probably induced soil compaction and affected the soil’s production capacity in the same way as modern farm vehicles.

“No one seemed to have wondered whether dinosaurs induced subsoil compaction, but since the sauropods were as heavy as modern farm vehicles, we thought this was a question that ought to be explored”, says Thomas Keller.

Like humans, sauropods depended on the soils ability to provide food, suggesting that they moved across the landscape in a way that reduced the risk of soil compaction. One possibility is that they restricted their movements to fixed “foraging trails” and grazed plants next to them with the help of their long necks. In this way, they could ensure that the surrounding land continued to produce the plant food they needed.

More information:

The full study, “Farm vehicles approaching weights of sauropods exceed safe mechanical limits for soil functioning,” is available from the Proceedings of the National Academy of Sciences: https://doi.org/10.1073/pnas.2117699119


About DRI

The Desert Research Institute (DRI) is a recognized world leader in basic and applied environmental research. Committed to scientific excellence and integrity, DRI faculty, students who work alongside them, and staff have developed scientific knowledge and innovative technologies in research projects around the globe. Since 1959, DRI’s research has advanced scientific knowledge on topics ranging from humans’ impact on the environment to the environment’s impact on humans. DRI’s impactful science and inspiring solutions support Nevada’s diverse economy, provide science-based educational opportunities, and inform policymakers, business leaders, and community members. With campuses in Las Vegas and Reno, DRI serves as the non-profit research arm of the Nevada System of Higher Education. For more information, please visit www.dri.edu.

MWA Welcomes Desert Research Institute as Newest MWA Member

Washington, DC (April 23, 2019) – The Millennium Water Alliance is pleased to announce that the Desert Research Institute, part of the Nevada System of Higher Education, has joined MWA as a new affiliate member organization.

“I am extremely pleased that the Desert Research Institute (DRI) has been made an affiliate member of the Millennium Water Alliance,” said Braimah Apambire, Senior Director, Center for International Water and Sustainability at DRI. “DRI builds capacity of NGO and government staff in developing countries, conducts basic and applied research, and applies technologies to improve the effective management of natural resources, especially water. We look forward to working with other MWA members to achieve the Sustainable Development Goal (SDG) 6 by 2030.”

MWA Executive Director Keith Wright welcomed DRI, noting that “DRI is a well-respected institution that brings a range of expertise from research to technology.  DRI joining MWA is an important contribution to MWA’s strategy to diversify our membership to include business, NGOs and academic institutions that are committed to SDG 6.“

DRI is well-known to the WASH community, working as a partner in multiple programs with WASH implementers in countries around the world. For more information about DRI’s WASH program: https://www.dri.edu/ciwas.

The Millennium Water Alliance, founded in 2003, now has 14 member NGOs: CARE, Catholic Relief Services, Desert Research Institute, El Porvenir, Food for the Hungry, HELVETAS, IRC WASH, Living Water International, Pure Water for the World, WaterAid America, Water 4, Water For People, Water Mission, and World Vision. Headquartered in Washington, DC, MWA is a permanent alliance that convenes opportunities and partnerships, accelerates learning and effective models, and influences the WASH space by leveraging the expertise and reach of its members and partners to scale quality, sustained WASH services globally. New member organizations are approved by a vote of the Board of Directors. For more information about MWA, visit: www.mwawater.org.

For more information, contact:

Keith Wright, Executive Director: keith.wright@mwawater.org

John Sparks, Director of Advocacy & Communications: john.sparks@mwawater.org

Meet Jim Hudson, Ph.D.

Meet Jim Hudson, Ph.D.

Jim Hudson, Ph.D., is a research professor of physics with the Division of Atmospheric Sciences at the Desert Research Institute in Reno. Jim specializes in cloud physics, and has worked throughout his career to gather and analyze field measurements of cloud condensation nuclei (CCN) from around the world. He is originally from Michigan, and holds bachelor’s degrees in physics and mathematics from Western Michigan University, a master’s degree in physics from University of Michigan, and a Ph.D. in atmospheric physics from the University of Nevada, Reno. Jim has been a member of the DRI community since 1970, when he started here as a graduate research assistant. In his free time, Jim can often be found at an ice rink; he is a passionate hockey player and carries his equipment wherever he goes. 

DRI: You are DRI’s longest serving employee. What initially brought you here to DRI?

JH: Yes, I’ve been here the longest of anybody – almost 50 years. I came as a grad student in 1970. I had been studying physics at the University of Michigan, looking at aurora and air glow, which is an upper atmospheric phenomenon. But my interests drifted, and the job situation drifted. I had seen brochures from DRI and UNR about lower atmospheric work, mainly to do with clouds, which I thought was a little more interesting. So, I applied and came as a graduate student in 1970, and continued on as a grad student for six years and got my Ph.D. My professor left shortly after I got my Ph.D., but I was able to stay and continue the work that he was doing here.

Jim Hudson examines an instrument screen inside of the Aerosol Physics Laboratory at DRI.

Inside of the Aerosol Physics Laboratory at DRI, Jim Hudson examines an instrument screen on the CCN spectrometer, used to measure cloud condensation nuclei. February 2019. Credit: DRI.

DRI: What is the focus of your research?

JH: I study cloud condensation nuclei (CCN), which are tiny particles in the atmosphere that cloud particles form on. In my work, I compare the measurements of the CCN with cloud droplet measurements and other characteristics of clouds. Over the years, I have worked with two or three different engineers to develop instruments that go on airplanes to measure the full spectrum of these cloud condensation nuclei. We make the CCN measurements while other instruments on the plane measure the cloud droplets. Then we compare them and write papers on our findings.

DRI: Why are cloud condensation nuclei important to measure and understand?

JH: Cloud condensation nuclei are actually the greatest uncertainty in climate, because many of these particles are manmade, from air pollution. If you have more cloud condensation nuclei, you have more cloud droplets. And if you have more cloud droplets, you reflect more sunlight back to space. This is a primary determinant of global climate.

At the moment, we don’t know how many of these CCN particles are manmade compared to how many are natural. We know that there are natural sources, because certainly there have been clouds long before human beings started perturbing the atmosphere, but we don’t understand the natural sources very well.

Jim Hudson stands near a CCN Spectrometer, an instrument designed by Jim and other DRI team members to measure cloud condensation nuclei from an aircraft.

Jim Hudson stands near a CCN Spectrometer, an instrument designed by Jim and other DRI team members to measure cloud condensation nuclei from an aircraft. February 2019. Credit: DRI.

DRI: Can you tell us about a project that you’re working on right now?

JH: My latest work, starting six years ago, focuses on the size spectrum of these CCN particles. We have enough resolution in our instruments to detect bimodality in the CCN spectrum, meaning that we are often seeing two different size classes of CCN. And we only see that under clouds. Where you don’t have any clouds, you don’t have this bimodality, you just have one mode (size class). A similar type of bimodality has been observed previously by scientists that measure particle size distributions, but our instrument is the first one that has seen this in the cloud condensation nuclei.

I’ve found that this bimodal spectrum of CCN is having different effects on different types of clouds. When we find the bimodal spectrum under stratus clouds, it tends to make clouds with more droplets but less precipitation, because the droplets are smaller and can’t get big enough to fall out. In cumulus clouds, it seems to be exactly the opposite – when you have the bimodal spectrum, you get fewer droplets and more precipitation. But these observations are only from two field projects. I want now to go back and do additional analysis using data that we’ve collected in about 25 other projects to see if this is a general thing that happens or how often it happens.

DRI: What has been your most memorable day on the job?

JH: That’s hard to say. I’ve been involved with 30 or so field projects over about three decades, all over the world. During those projects, we’d go off for a month or sometimes two months, often on islands, so that we could fly out over the oceans. I’m not a pilot, I would never do that. But I’ve logged thousands of hours flying. The Azores were very interesting. And in the Indian Ocean, the little island of Malé — that was very interesting because you had very polluted air coming off of India, but a few times we flew south, below the equator, and the air down there was very clean. So there was a big contrast.

I used to really enjoy doing fieldwork, but my last field project was in 2011. I thought that I would not be that interested in sitting around analyzing data, but I found that this latest work on the bimodal spectrum is extremely interesting. Looking at the data, analyzing the data – I’ve never had anything more interesting in my entire career.

For more information about Jim and his research, please visit: https://www.dri.edu/directory/jim-hudson

Climate Engine offers unprecedented access to Earth image datasets

Climate Engine offers unprecedented access to Earth image datasets

Reno, NV (Thursday, December 7, 2017): Working with large environmental datasets is a complex and time-consuming endeavor, often requiring huge amounts of data storage, specialized high-performance computers and technical knowledge. Climate Engine (ClimateEngine.org), a new, free web-based application created by a team of scientists at the Desert Research Institute (DRI), University of Idaho, and Google is aiming to change all of that.

New research published and featured on the cover of the November issue of the Bulletin of the American Meteorological Society (BAMS) outlines how Climate Engine improves the accessibility of climate and weather data by allowing users to create on-demand maps or graphs of various earth observation datasets using a standard web browser. Datasets are stored and processed in the cloud on the Google Earth Engine platform, eliminating the need for users to download, store and process large data files on their computers.

Climate Engine provides access to a variety of geospatial datasets that track vegetation, snow and water across the planet, as well as climate datasets that track temperature, precipitation and winds.

One of the web application’s greatest strengths, according to Dr. Justin Huntington, co-principal investigator of the Climate Engine project and associate research professor of hydrology at DRI, lies in the application’s ability to quickly and easily pair satellite imagery with different climate variables.

“We can process field-scale Landsat satellite imagery like we’ve never been able to before,” Huntington said. “For example, we can look at over 30 years of vegetation changes in a certain area and then pair those changes with the same historical record of climate, all within one platform, in a matter of seconds.”

In the paper Climate Engine: Cloud Computing and Visualization of Climate and Remote Sensing Data for Advanced Natural Resource Monitoring and Process Understanding, the authors describe the development, design and potential uses for this tool. The paper highlights various case studies related to drought, wildfire and agriculture, which each provide examples of how Climate Engine can be used to generate on-demand maps and time-series analyses of different conditions and extreme events.

The authors outline the capability of this cutting-edge tool to analyze temperature change in the Arctic, evaluate vegetation stress during a historic drought in the Great Plains, map fire danger and burned acreage in Idaho, monitor groundwater-dependent ecosystems in Nevada, and support famine early-warning efforts in Ethiopia.

Because Climate Engine is free and requires no specialized software to use, Huntington and his colleagues hope that it will be useful to researchers and decision-makers around the world.

“Our work allows decision makers unprecedented access to analyzing big data related to environmental monitoring on their desktops and tablets without needing a supercomputer by using cloud computing resources provided by Google,” said John Abatzoglou, co-principle investigator of Climate Engine and associate professor of geography at the University of Idaho. “The ability to analyze such data in real time will help fill an information void and improve our ability to sustain our environmental resources including water.”

After using the web application to create a map or graph, results can be downloaded or shared in common file formats, saving users hours of time that was once spent downloading and processing large data archives.

“That’s the beauty of Climate Engine,” Huntington said. “Instead of downloading archives to get to the answer, you can just download the answer.”

Climate Engine was originally unveiled at the White House Water Summit in 2016. In the time since the product launched, the web application has been used by more than 8,000 unique visitors across the globe.

Recently, Climate Engine team members Huntington and Dr. Katherine Hegewisch of the University of Idaho presented a talk at the Famine Early Warning System (FEWS) science meeting in Washington D.C., and Hegewisch hosted a workshop for African FEWS field scientists.

Climate Engine will also be on display at the upcoming American Geophysical Union Annual Fall Meeting in New Orleans. The event is the largest and preeminent Earth and space science meeting in the world.

In the future, the Climate Engine team plans to continue adding new datasets such as sea surface temperature and European satellite data. They are also planning to add agency-specific spatial averaging domains, such as agency management boundaries and crop zones, and also hope to continue expanding their education and outreach efforts.

The idea behind Climate Engine, says Huntington, is to make large datasets available to researchers, decision-makers, journalists, farmers, or anyone else who might benefit from the information – and in an easy-to-use, approachable and simple format.

Climate Engine was primarily funded by Google and federal programs of the National Integrated Drought Information System, Famine Early Warning System Network, U.S. Geological Survey’s Landsat Science Team, and Bureau of Land Management’s Nevada State Office.

For more information and use the Climate Engine web application visit – ClimateEngine.org


The Desert Research Institute (DRI) is a recognized world leader in investigating the effects of natural and human-induced environmental change and advancing technologies aimed at assessing a changing planet. For more than 50 years DRI research faculty, students, and staff have applied scientific understanding to support the effective management of natural resources while meeting Nevada’s needs for economic diversification and science-based educational opportunities. With campuses in Reno and Las Vegas, DRI serves as the non-profit environmental research arm of the Nevada System of Higher Education. For more information, please visit www.dri.edu.

The University of Idaho, home of the Vandals, is Idaho’s land-grant, national research university. From its residential campus in Moscow, UI serves the state of Idaho through educational centers in Boise, Coeur d’Alene and Idaho Falls, a research and Extension center in Twin Falls, plus Extension offices in 42 counties. Home to more than 11,000 students statewide, UI is a leader in student-centered learning and excels at interdisciplinary research, service to businesses and communities, and in advancing diversity, citizenship and global outreach. UI competes in the Big Sky Conference and Sun Belt Conference. Learn more at www.uidaho.edu.