New cloud model could help with climate research

When clouds meet clear skies, cloud droplets evaporate as they mix with dry air. A new study involving researchers from the University of Gothenburg has succeeded in capturing what happens in a model. Ultimately, this could lead to more accurate climate modeling in the future.

The clouds in the sky have a significant impact on our climate.

Not only do they produce precipitation and provide shade from the sun, they also act as large reflectors that prevent the radiation of heat from the Earth -- commonly known as the greenhouse effect.

"Although clouds have been studied for a long time, they are one of the biggest sources of uncertainty in climate models," explains Bernhard Mehlig, Professor of Complex Systems at the University of Gothenburg.

"This is because there are so many factors that determine how the clouds affect radiation. And the turbulence in the atmosphere means that everything is in constant motion. This makes things even more complicated."

Focusing on the cloud edge

A scientific article in Physical Review Letters presents a new statistical model that describes how the number of water droplets, their sizes and the water vapour interact at the turbulent cloud edge.

The distribution of water droplets is important because it affects how clouds reflect radiation.

"The model describes how the droplets shrink and grow at the cloud edge when turbulence mixes in drier air," adds Johan Fries, a former doctoral student in physics and co-author of the study.

The researchers have identified the most important parameters, and have built their model accordingly.

In brief, the model takes into account the laws of thermodynamics and the turbulent motion of the droplets.

The model corresponds well with earlier numerical computer simulations, and explains their results.

The importance of evaporation

"But we're still a long way from the finish line," continues Professor Mehlig.

"Our model is currently able to describe what is happening in one cubic metre of cloud. Say, fifteen years ago it was only one cubic centimetre, so we're making progress."

When policymakers discuss climate change, great importance is attached to IPCC climate models.

However, according to the IPCC, the microphysical properties of clouds are among the least understood factors in climate science.

"Moreover, the evaporation of droplets is an important process, not only in the context of atmospheric clouds, but also within the field of infectious medicine. Tiny droplets that are produced when we sneeze can contain virus particles. If these droplets evaporate, the virus particles can remain in the air and infect others."

Professor Mehlig has also co-authored another study that describes how solid particles, such as ice crystals, move within clouds.

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Cloud clustering causes more extreme rain

Understanding cloud patterns in our changing climate is essential to making accurate predictions about their impact on society and nature. Scientists at the Institute of Science and Technology Austria (ISTA) and the Max-Planck-Institute for Meteorology published a new study in the journal Science Advances that uses a high-resolution global climate model to understand how the clustering of clouds and storms impacts rainfall extremes in the tropics. They show that with rising temperatures, the severity of extreme precipitation events increases.

Extreme rainfall is one of the most damaging natural disasters costing human lives and causing billions in damage.

Their frequency has been increasing over the last years due to the warming climate.

For several decades, scientists have been using computer models of the Earth's climate to better understand the mechanisms behind these events and to predict future trends.

In a new study, now published in the journal Science Advances, a team of researchers from the Institute of Science and Technology Austria (ISTA) and the Max-Planck-Institute for Meteorology (MPI-M) led by ISTA postdoc Jiawei Bao used a new state-of-the-art climate model to study how cloud and storm clustering impacts extreme rainfall events -- specifically in the tropics -- in more detail than has been possible before.

"This new type of model with a much finer resolution showed that, with a warmer climate, extreme rainfall events in the tropics increase in severity more than was expected from theory due to clouds being more clustered," Bao, who originally started this project during his previous postdoc position at the MPI-M, explains.

"We can see that when clouds are more clustered, it rains for a longer time, so the total amount of rainfall increases. We also found that more extreme rain over high-precipitation areas happens at the cost of expansion of dry areas -- a further shift to extreme weather patterns. This is due to how clouds and storms cluster together, which we could now simulate with this new climate model." This new model, first proposed in 2019, simulates the climate with a much higher resolution than previous ones.

Previous models could not factor in clouds and storms in as much detail, therefore missing much of the complex dynamics of air movement that create clouds and make them congregate to form more intense storms.

While the model simulates the whole world at once, the scientists focused their analysis on the area of the tropics around the equator.

They did this because cloud and storm formation there works differently than in other latitudes.

Caroline Muller, Assistant Professor at ISTA, adds, "Previous models have hinted at the influence of clouds clustering on precipitation extremes but could not provide the necessary data. In collaboration with our colleagues Bjorn Stevens and Lukas Kluft from the Max Planck Institute for Meteorology, our findings add to the growing body of evidence showing that cloud formation on a smaller scale has a crucial impact on the outcomes of climate change."

Collaborative Models

Researchers all over the world are collaborating on creating more detailed and realistic models of the world's climate to understand the effects of climate change.

Climate models divide the Earth's atmosphere into three-dimensional chunks, each with its own data about temperature, pressure, humidity, and many more physical properties.

They then employ physical equations to simulate how these chunks interact and change over time to create a representation of the real world.

As computing power and storage are not unlimited, these models have to introduce simplifications and scientist continuously work to making them more accurate.

Older generations of climate models use chunks of around 100 kilometers in horizontal length, which still result in tens to hundreds of thousands of them covering the whole globe.

Advances in algorithms and supercomputers enabled scientists to increase the resolution of the models more and more.

"We used a climate model developed at MPI-M and analyzed the data hosted at the German Climate Computing Centre in Hamburg with a resolution of just five kilometers which was very computationally expensive," Bao adds.

"All climate research is an immense collaborative effort by hundreds of people who want to contribute to our understanding of the world and our impact on it."

Bao, who first got interested in climate research during his PhD at the University of New South Wales, Australia, and who now works as an IST-BRIDGE postdoctoral fellow at ISTA, wants to continue his work on extreme precipitation events to find more evidence for their causes and impacts using additional models.

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Unlocking the secrets of a 'Hot Saturn' and its spotted star

Led by researchers from Université de Montréal's Trottier Institute for Research on Exoplanets (iREx), a team of astronomers has harnessed the power of the revolutionary James Webb Space Webb Telescope (JWST) to study the "hot Saturn" exoplanet HAT-P-18 b.

Their findings, published last month in the journal Monthly Notices of the Royal Astronomical Society, paint a complete picture of the HAT-P-18 b's atmosphere while exploring the great challenge of distinguishing its atmospheric signals from the activity of its star.

HAT-P-18 b is located over 500 light-years away with a mass similar to Saturn's but a size closer to that the larger planet Jupiter. As a result, the exoplanet has a "puffed-up" atmosphere that is especially ideal for analysis.

Passing over a spotted star

Observations from the JWST were taken while the HAT-P-18 b was passing in front of its Sun-like star. This moment is called a transit and is crucial to detect and further characterise an exoplanet from hundreds of light-years away with surprising precision.

Astronomers don't observe light that is being emitted directly by the distant planet. Rather, they study how the central star's light is being blocked and affected by the planet orbiting it, and so must try to disentangle signals caused by the presence of the planet from those caused by the star's own properties.

Just like our Sun, stars do not have uniform surfaces. They can have dark star spots and bright regions, which can create signals that mimic a planet's atmospheric attributes. A recent study of the exoplanet TRAPPIST-1 b and its star TRAPPIST-1 led by UdeM doctoral student Olivia Lim witnessed an eruption, or flare, on the surface of the star, which affected observations.

In the case of planet HAT-P-18 b, Webb caught the exoplanet right as it was passing over a dark spot on its star, HAT-P-18. This is called a spot-crossing event, and its effect was evident in the data collected for the new study. The iREx team also reported the presence of numerous other star spots on HAT-P-18's surface which were not blocked out by the exoplanet.

To accurately determine the exoplanet's atmospheric composition, the researchers had to simultaneously model the planet's atmosphere as well as its star's peculiarities. In their study, they point out that such consideration will be crucial in treating future exoplanet observations via the Webb to fully harness their potential.

"We found that accounting for stellar contamination implies the existence of spots and clouds instead of haze and recovers a water vapour abundance of almost an order of magnitude lower," said lead author Marylou Fournier-Tondreau.

"So considering the system's host star makes a big difference," added Fournier-Tondreau, who did the work as a master's student at iREx and is now pursuing a Ph.D. at the University of Oxford.

"It's actually the first time that we clearly disentangle the signature of hazes versus starspots, thanks to Canada's NIRISS (Near-Infrared Imager and Slitless Spectrograph) instrument, which provides wider wavelength coverage extending into the visible light domain."

H2O, CO2, and clouds in a scorching atmosphere

After modelling the exoplanet and the star in the HAT-P-18 system, the iREx astronomers performed a meticulous dissection of HAT-P-18 b's atmospheric composition. By inspecting the light that filters through the exoplanet's atmosphere as it transits its host star, the researchers discerned the presence of water vapour (H2O) and carbon dioxide (CO2).

The researchers also detected the possible presence of sodium and observed strong signs of a cloud deck in HAT-P-18 b's atmosphere, which appears to be muting the signals of many of the molecules found within it. They also concluded that the star's surface was covered by many dark spots that can significantly influence the interpretation of the data.

An earlier analysis of the same JWST data led by a team at Johns Hopkins University had also revealed a clear detection of water and CO2, but also reported the detection of small particles at high-altitudes called hazes and found hints of methane (CH4). The iREx astronomers paint a different picture.

The CH4 detection was not confirmed, and the water abundance they determined was 10 times lower than previously found. They also found that the previous study's detection of hazes could instead be caused by star spots on the star's surface, highlighting the importance of considering the star in the analysis.

Could the exoplanet support life? Not likely. While molecules like water, carbon dioxide, and methane can be interpreted as biosignatures, or signs of life, in certain ratios or in combination with other molecules, HAT-P-18 b's scorching temperatures of close to 600 degrees Celsius do not bode well for the planet's habitability.

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Mysterious missing component in the clouds of Venus revealed

What are the clouds of Venus made of? Scientists know it's mainly made of sulfuric acid droplets, with some water, chlorine, and iron. Their concentrations vary with height in the thick and hostile Venusian atmosphere. But until now they have been unable to identify the missing component that would explain the clouds' patches and streaks, only visible in the UV range.

In a new study published in Science Advances, researchers from the University of Cambridge synthesised iron-bearing sulfate minerals that are stable under the harsh chemical conditions in the Venusian clouds.

Spectroscopic analysis revealed that a combination of two minerals, rhomboclase and acid ferric sulfate, can explain the mysterious UV absorption feature on our neighbouring planet.

"The only available data for the composition of the clouds were collected by probes and revealed strange properties of the clouds that so far we have been unable to fully explain," said Paul Rimmer from the Cavendish Laboratory and co-author of the study.

"In particular, when examined under UV light, the Venusian clouds featured a specific UV absorption pattern. What elements, compounds, or minerals are responsible for such observation?"

Formulated on the basis of Venusian atmospheric chemistry, the team synthesized several iron-bearing sulfate minerals in an aqueous geochemistry laboratory in the Department of Earth Sciences.

By suspending the synthesized materials in varying concentrations of sulfuric acid and monitor the chemical and mineralogical changes, the team narrowed down the candidate minerals to rhomboclase and acid ferric sulfate, of which the spectroscopic features were examined under light sources specifically designed to mimic the spectrum of solar flares (Paul Rimmer and Samantha Thompson's FlareLab at the Cavendish Laboratory).

A photochemistry lab at Harvard collaborated in the research by providing measurements of the UV absorbance patterns of ferric iron under extreme acidic conditions, in an attempt to mimic the even more extreme Venusian clouds.

The scientists are part of the newly established Origins Federation, which promotes such collaborative projects.

"The patterns and level of absorption shown by the combination of these two mineral phases are consistent with the dark UV-patches observed in Venusian clouds," said co-author Clancy Zhijian Jiang, from the Department of Earth Sciences, Cambridge.

"These targeted experiments revealed the intricate chemical network within the atmosphere, and shed light on the elemental cycling on the Venusian surface."

"Venus is our nearest neighbour, but it remains a mystery," said Rimmer.

"We will have a chance to learn much more about this planet in the coming years with future NASA and ESA missions set to explore its atmosphere, clouds and surface. This study prepares the grounds for these future explorations."

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Not so silver lining: Microplastics found in clouds could affect the weather

From the depths of the seas to snow on mountains and even the air above cities, microplastics are turning up increasingly often. Now, in ACS' Environmental Science & Technology Letters, researchers have analyzed microplastics in clouds above mountains. They suggest that these tiny particles could play a role in cloud formation and, in turn, affect weather.

Microplastics -- plastic fragments smaller than five millimeters -- originate from a myriad of items used daily, such as clothing, packaging and car tires. As research in the field evolves, scientists are not only detecting microplastics in the atmosphere but also investigating how they may play a role in cloud formation. For example, a group of researchers recently detected plastic granules, which had water-attracting surfaces, in Japanese mountaintop clouds. So, to learn more, Yan Wang and colleagues set out to look for microplastics in mountain clouds, used computer models to figure out how they could have gotten there, and tested how the particles could have impacted -- and been impacted by -- the clouds.

Wang and the team first collected 28 samples of liquid from clouds at the top of Mount Tai in eastern China. Then they analyzed the samples and found:

• Low-altitude and denser clouds contained greater amounts of microplastics.
• Particles were made of common polymers, including polyethylene terephthalate, polypropylene, polyethylene, polystyrene and polyamide.
• The microplastics tended to be smaller than 100 micrometers in length, although some were as long as 1,500 micrometers.
• Older, rougher particles had more lead, mercury and oxygen attached to their surfaces, which the researchers suggest could facilitate cloud development.

To investigate where the plastic particles in the clouds originated, Wang and the team developed computer models that approximated how the particles traveled to Mount Tai. These models suggested that airflow from highly populated inland areas, rather than from over the ocean or other nearby mountains, served as the major source of the fragments. In laboratory experiments, the researchers demonstrated that microplastics exposed to cloud-like conditions -- ultraviolet light and filtered cloud-sourced water -- had smaller sizes and rougher surfaces than those exposed to pure water or air. Additionally, particles impacted by the cloud-like conditions had more lead, mercury and oxygen-containing groups. These results suggest that clouds modify microplastics in ways that could enable the particles to affect cloud formation and the fate of airborne metals. The researchers conclude that more work is needed to fully understand how microplastics affect clouds and the weather.

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Neptune's disappearing clouds linked to the solar cycle

Astronomers have uncovered a link between Neptune's shifting cloud abundance and the 11-year solar cycle, in which the waxing and waning of the Sun's entangled magnetic fields drives solar activity.

This discovery is based on three decades of Neptune observations captured by NASA's Hubble Space Telescope and the W. M. Keck Observatory in Hawaii, as well as data from the Lick Observatory in California.

The link between Neptune and solar activity is surprising to planetary scientists because Neptune is our solar system's farthest major planet and receives sunlight with about 0.1% of the intensity Earth receives. Yet Neptune's global cloudy weather seems to be driven by solar activity, and not the planet's four seasons, which each last approximately 40 years.

At present, the cloud coverage seen on Neptune is extremely low, with the exception of some clouds hovering over the giant planet's south pole. A University of California (UC) Berkeley-led team of astronomers discovered that the abundance of clouds normally seen at the icy giant's mid-latitudes started to fade in 2019.

"I was surprised by how quickly clouds disappeared on Neptune," said Imke de Pater, emeritus professor of astronomy at UC Berkeley and senior author of the study. "We essentially saw cloud activity drop within a few months," she said.

"Even now, four years later, the most recent images we took this past June still show the clouds haven't returned to their former levels," said Erandi Chavez, a graduate student at the Center for Astrophysics | Harvard-Smithsonian (CfA) in Cambridge, Massachusetts, who led the study when she was an undergraduate astronomy student at UC Berkeley. "This is extremely exciting and unexpected, especially since Neptune's previous period of low cloud activity was not nearly as dramatic and prolonged."

To monitor the evolution of Neptune's appearance, Chavez and her team analyzed Keck Observatory images taken from 2002 to 2022, the Hubble Space Telescope archival observations beginning in 1994, and data from the Lick Observatory in California from 2018 to 2019.

In recent years, the Keck observations have been complemented by images taken as part of the Twilight Zone program and by Hubble's Outer Planet Atmospheres Legacy (OPAL) program.

The images reveal an intriguing pattern between seasonal changes in Neptune's cloud cover and the solar cycle -- the period when the Sun's magnetic field flips every 11 years as it becomes more tangled like a ball of yarn. This is evident in the increasing number of sunspots and increasing solar flare activity. As the cycle progresses, the Sun's tempestuous behavior builds to a maximum, until the magnetic field beaks down and reverses polarity. Then the Sun settles back down to a minimum, only to start another cycle.

When it's stormy weather on the Sun, more intense ultraviolet (UV) radiation floods the solar system. The team found that two years after the solar cycle's peak, an increasing number of clouds appear on Neptune. The team further found a positive correlation between the number of clouds and the ice giant's brightness from the sunlight reflecting off it.

"These remarkable data give us the strongest evidence yet that Neptune's cloud cover correlates with the Sun's cycle," said de Pater. "Our findings support the theory that the Sun's UV rays, when strong enough, may be triggering a photochemical reaction that produces Neptune's clouds."

Scientists discovered the connection between the solar cycle and Neptune's cloudy weather pattern by looking at 2.5 cycles of cloud activity recorded over the 29-year span of Neptunian observations. During this time, the planet's reflectivity increased in 2002 then dimmed in 2007. Neptune became bright again in 2015, then darkened in 2020 to the lowest level ever observed, which is when most of the clouds went away.

The changes in Neptune's brightness caused by the Sun appear to go up and down relatively in sync with the coming and going of clouds on the planet. However there is a two-year time lag between the peak of the solar cycle and the abundance of clouds seen on Neptune. The chemical changes are caused by photochemistry, which happens high in Neptune's upper atmosphere and takes time to form clouds.

"It's fascinating to be able to use telescopes on Earth to study the climate of a world more than 2.5 billion miles away from us," said Carlos Alvarez, staff astronomer at Keck Observatory and co-author of the study. "Advances in technology and observations have enabled us to constrain Neptune's atmospheric models, which are key to understanding the correlation between the ice giant's climate and the solar cycle."

However, more work is necessary. For example, while an increase in UV sunlight could produce more clouds and haze, it could also darken them, thereby reducing Neptune's overall brightness. Storms on Neptune rising up from the deep atmosphere affect the cloud cover, but are not related to photochemically produced clouds, and hence may complicate correlation studies with the solar cycle. Continued observations of Neptune are also needed to see how long the current near-absence of clouds will last.

The research team continues to track Neptune's cloud activity. "We have seen more clouds in the most recent Keck images that were taken during the same time NASA's James Webb Space Telescope observed the planet; these clouds were in particular seen at northern latitudes and at high altitudes, as expected from the observed increase in the solar UV flux over the past approximately 2 years," said de Pater.

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Why do Earth's hemispheres look equally bright when viewed from space?

When seen from space, Earth's hemispheres -- northern and southern -- appear equally bright. This is particularly unexpected because the Southern Hemisphere is mostly covered with dark oceans, whereas the Northern Hemisphere has a vast land area that is much brighter than these oceans. For years, the brightness symmetry between hemispheres remained a mystery. In a new study, published in the Proceedings of the National Academy of Sciences (PNAS), Weizmann Institute of Science researchers and their collaborators reveal a strong correlation between storm intensity, cloudiness and the solar energy reflection rate in each hemisphere. They offer a solution to the mystery, alongside an assessment of how climate change might alter the reflection rate in the future.

As early as the 1970s, when scientists analyzed data from the first meteorological satellites, they were surprised to find out that the two hemispheres reflect the same amount of solar radiation. Reflectivity of solar radiation is known in scientific lingo as "albedo." To better comprehend what albedo is, think about driving at night: It is easy to spot the intermittent white lines, which reflect light from the car's headlights well, but difficult to discern the dark asphalt. The same is true when observing Earth from space: The ratio of the solar energy hitting the Earth to the energy reflected by each region is determined by various factors. One of them is the ratio of dark oceans to bright land, which differ in reflectivity, just like asphalt and intermittent white lines. The land area of the Northern Hemisphere is about twice as large as that of the Southern, and indeed when measuring near the surface of the Earth, when the skies are clear, there is more than a 10 percent difference in albedo. Still, both hemispheres appear to be equally bright from space.

In this study, the team of researchers, led by Prof. Yohai Kaspi and Or Hadas of Weizmann's Earth and Planetary Sciences Department, focused on another factor influencing albedo, one located in high altitudes and reflecting solar radiation -- clouds. The team analyzed data derived from the world's most advanced databases, including cloud data collected via NASA satellites (CERES), as well as data from ERA5, which is a global weather database containing information collected using a variety of sources in the air and on the ground, dating back to 1950. ERA5 data was utilized to complete cloud data and to cross-correlate 50 years of this data with information on the intensity of cyclones and anticyclones.

Next, the scientists classified storms of the last 50 years into three categories, according to intensity. They discovered a direct link between storm intensity and the number of clouds forming around the storm. While Northern Hemisphere and land areas in general are characterized by weaker storms, above oceans in the Southern Hemisphere, moderate and strong storms prevail. Data analysis showed that the link between storm intensity and cloudiness accounts for the difference in cloudiness between the hemispheres. "Cloud albedo arising from strong storms above the Southern Hemisphere was found to be a high-precision offsetting agent to the large land area in the Northern Hemisphere, and thus symmetry is preserved," says Hadas, adding: "This suggests that storms are the linking factor between the brightness of Earth's surface and that of clouds, solving the symmetry mystery."

Could climate change make one of the hemispheres darker?

Earth has been undergoing rapid change in recent years, owing to climate change. To examine whether and how this could affect hemispheric albedo symmetry, the scientists used CMIP6, a set of models run by climate modeling centers around the world to simulate climate change. One of these models' major shortcomings is their limited ability to predict the degree of cloudiness. Nevertheless, the relation found in this study between storm intensity and cloudiness enables scientists to assess future cloud amounts, based on storm predictions.

Models predict global warming will result in a decreased frequency of all storms above the Northern Hemisphere and of weak and moderate storms above the Southern Hemisphere. However, the strongest storms of the Southern Hemisphere will intensify. The cause of these predicted differences is "Arctic amplification," a phenomenon in which the North Pole warms twice as fast as Earth's mean warming rate. One might speculate that this difference should break hemispheric albedo symmetry. However, the research shows that a further increase in storm intensity might not change the degree of cloudiness in the Southern Hemisphere because cloud amounts reach saturation in very strong storms. Thus, symmetry might be preserved.

"It is not yet possible to determine with certainty whether the symmetry will break in the face of global warming," says Kaspi. "However, the new research solves a basic scientific question and deepens our understanding of Earth's radiation balance and its effectors. As global warming continues, geoengineered solutions will become vital for human life to carry on alongside it. I hope that a better understanding of basic climate phenomena, such as the hemispheric albedo symmetry, will help in developing these solutions."

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Clouds less climate-sensitive than assumed

In a major field campaign in 2020, Dr. Raphaela Vogel who is now at Universität Hamburg's Center for Earth System Research and Sustainability (CEN) and an international team from the Laboratoire de Météorologie Dynamique in Paris and the Max Planck Institute for Meteorology in Hamburg analyzed observational data they and others collected in fields of cumulus clouds near the Atlantic island of Barbados. Their analysis revealed that these clouds' contribution to climate warming has to be reassessed.

"Trade-wind clouds influence the climate system around the globe, but the data demonstrate behavior differently than previously assumed. Consequently, an extreme rise in Earth's temperatures is less likely than previously thought," says Vogel, an atmospheric scientist. "Though this aspect is very important for more accurately projecting future climate scenarios, it definitely doesn't mean we can back off on climate protection."

To date, many climate models have simulated a major reduction in trade-wind clouds, which would mean much of their cooling function would be lost and the atmosphere would consequently warm even more. The new observational data shows that this isn't likely to occur.

What is certain is that, as global warming progresses, more water on the ocean's surface evaporates and the moisture near the base of trade-wind clouds increases. In contrast, the air masses in the upper part of the clouds are very dry and only become slightly moister. This produces a substantial difference in moisture above and below. In the atmosphere, this is dispelled when the air masses mix. The previous hypothesis: drier air is transported downward, causing the cloud droplets to evaporate more rapidly and making it more likely that the clouds will dissipate.

The observational data from Barbados now offers the first robust quantification as to how pronounced the vertical mixing actually is, and how this affects moisture and cloud cover as a whole. As such, it is the first data to shed light on a process that is essential to understanding climate change. In brief: more intensive mixing does not make the lower layers drier or make the clouds dissipate. Rather, the data shows that the cloud cover actually increases with increasing vertical mixing.

"That's good news, because it means that trade-wind clouds are far less sensitive to global warming than has long been assumed," says Vogel. "With our new observations and findings, we can now directly test how realistically climate models portray the occurrence of trade-wind clouds. In this regard, a new generation of high-resolution climate models that can simulate the dynamics of clouds around the globe down to scales of one kilometer are particularly promising. Thanks to them, future projections will be more accurate and reliable."

The month-long field campaign EUREC4A (2020) was designed by the team members around extended flights with two research aircraft, which were equipped with different instruments and operated at different altitudes, and shipboard measurements from the R/V Meteor -- A German research vessel managed by the University of Hamburg. One plane was used to drop hundreds of atmospheric probes from an altitude of nine kilometers. As they fell, the probes gathered atmospheric data on the temperature, moisture, pressure and wind. The other plane surveyed clouds at their base, at an altitude of 800 meters, while the ship performed surface-based measurements. The result: an unprecedented database that will help to understand the unclear role of clouds in the climate system -- and to more accurately predict their role in future climate change.

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Cloud study demystifies impact of aerosols

Aerosol particles in the atmosphere have a bigger impact on cloud cover -- but less effect on cloud brightness -- than previously thought, new research shows.

Aerosols are tiny particles suspended in the atmosphere, and they play a key role in the formation of clouds.

With aerosols increasing due to human activities, numerous assessments by the Intergovernmental Panel on Climate Change (IPCC) have suggested they could have an important impact on climate change because clouds reflect sunlight and therefore keep temperatures cooler.

However, this cooling impact of aerosols on clouds is difficult to measure, and this has led to significant uncertainty climate change projections.

The new study -- led by the University of Exeter, with national and international academic partners and the UK's Met Office -- used the 2014 Icelandic volcano eruption to investigate this.

"This massive aerosol plume in an otherwise near-pristine environment provided an ideal natural experiment to quantify cloud responses to aerosol changes, namely the aerosol's fingerprint on clouds" said lead author Dr Ying Chen.

"Our analysis shows that aerosols from the eruption increased cloud cover by approximately 10%.

"Based on these findings, we can see that more than 60% of the climate cooling effect of cloud-aerosol interactions is caused by increased cloud cover.

"Volcanic aerosols also brightened clouds by reducing water droplet size, but this had a significantly smaller impact than cloud-cover changes in reflecting solar radiation."

Previous models and observations suggested this brightening accounted for the majority of the cooling caused by cloud-aerosol interactions.

Water droplets usually form in the atmosphere around aerosol particles, so a higher concentration of these particles makes it easier for cloud droplets to form.

However, as these cloud droplets are smaller and more numerous, the resulting clouds can hold more water before rainfall occurs -- so, more aerosols in the atmosphere can lead to more cloud cover but less rain.

The study used satellite data and computer learning to study cloud cover and brightness.

It used 20 years of satellite cloud images from two different satellite platforms from the region to compare the periods before and after the volcano eruption.

The findings will provide observational evidence of aerosols' climate impacts to improve the models used by scientists to predict climate change.

Jim Haywood, Professor of Atmospheric Science at the University of Exeter and part of the Global Systems Institute, and a Met Office Research Fellow, said: "Our earlier work had showed that model simulations could be used to disentangle the relative contribution of aerosol-cloud-climate impacts and potentially confounding meteorological variability.

"This work is radically different as it does not rely on models; it uses state-of-the-art machine learning techniques applied to satellite observations to simulate what the cloud would look like in the absence of the aerosols.

"Clear differences are observed between the predicted and observed cloud properties which can be used to assess aerosol-cloud-climate impacts."

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Could acid-neutralizing life-forms make habitable pockets in Venus’ clouds?

It's hard to imagine a more inhospitable world than our closest planetary neighbor. With an atmosphere thick with carbon dioxide, and a surface hot enough to melt lead, Venus is a scorched and suffocating wasteland where life as we know it could not survive. The planet's clouds are similarly hostile, blanketing the planet in droplets of sulfuric acid caustic enough to burn a hole through human skin.

And yet, a new study supports the longstanding idea that if life exists, it might make a home in Venus' clouds. The study's authors, from MIT, Cardiff University, and Cambridge University, have identified a chemical pathway by which life could neutralize Venus' acidic environment, creating a self-sustaining, habitable pocket in the clouds.

Within Venus' atmosphere, scientists have long observed puzzling anomalies -- chemical signatures that are hard to explain, such as small concentrations of oxygen and nonspherical particles unlike sulfuric acid's round droplets. Perhaps most puzzling is the presence of ammonia, a gas that was tentatively detected in the 1970s, and that by all accounts should not be produced through any chemical process known on Venus.

In their new study, the researchers modeled a set of chemical processes to show that if ammonia is indeed present, the gas would set off a cascade of chemical reactions that would neutralize surrounding droplets of sulfuric acid and could also explain most of the anomalies observed in Venus' clouds. As for the source of ammonia itself, the authors propose that the most plausible explanation is of biological origin, rather than a nonbiological source such as lightning or volcanic eruptions.

As they write in their study, the chemistry suggests that "life could be making its own environment on Venus."

This tantalizing new hypothesis is testable, and the researchers provide a list of chemical signatures for future missions to measure in Venus' clouds, to either confirm or contradict their idea.

"No life that we know of could survive in the Venus droplets," says study co-author Sara Seager, the Class of 1941 Professor of Planetary Sciences in MIT's Department of Earth, Atmospheric and Planetary Sciences (EAPS). "But the point is, maybe some life is there, and is modifying its environment so that it is livable."

The study's co-authors include Janusz Petkowski, William Bains, and Paul Rimmer, who are affiliated with MIT, Cardiff University, and Cambridge University.

Life suspect

"Life on Venus" was a trending phrase last year, when scientists including Seager and her co-authors reported the detection of phosphine in the planet's clouds. On Earth, phosphine is a gas that is produced mainly through biological interactions. The discovery of phosphine on Venus leaves room for the possibility of life. Since then, however, the discovery has been widely contested.

"The phosphine detection ended up becoming incredibly controversial," Seager says. "But phosphine was like a gateway, and there's been this resurgence in people studying Venus."

Inspired to look more closely, Rimmer began combing through data from past missions to Venus. In these data, he identified anomalies, or chemical signatures, in the clouds that had gone unexplained for decades. In addition to the presence of oxygen and nonspherical particles, anomalies included unexpected levels of water vapor and sulfur dioxide.

Rimmer proposed the anomalies might be explained by dust. He argued that minerals, swept up from Venus' surface and into the clouds, could interact with sulfuric acid to produce some, though not all, of the observed anomalies. He showed the chemistry checked out, but the physical requirements were unfeasible: A massive amount of dust would have to loft into the clouds to produce the observed anomalies.

Seager and her colleagues wondered if the anomalies could be explained by ammonia. In the 1970s, the gas was tentatively detected in the planet's clouds by the Venera 8 and Pioneer Venus probes. The presence of ammonia, or NH3, was an unsolved mystery.

"Ammonia shouldn't be on Venus," Seager says. "It has hydrogen attached to it, and there's very little hydrogen around. Any gas that doesn't belong in the context of its environment is automatically suspicious for being made by life."

Livable clouds

If the team were to assume that life was the source of ammonia, could this explain the other anomalies in Venus' clouds? The researchers modeled a series of chemical processes in search of an answer.

They found that if life were producing ammonia in the most efficient way possible, the associated chemical reactions would naturally yield oxygen. Once present in the clouds, ammonia would dissolve in droplets of sulfuric acid, effectively neutralizing the acid to make the droplets relatively habitable. The introduction of ammonia into the droplets would transform their formerly round, liquid shape into more of a nonspherical, salt-like slurry. Once ammonia dissolved in sulfuric acid, the reaction would trigger any surrounding sulfur dioxide to dissolve as well.

The presence of ammonia then could indeed explain most of the major anomalies seen in Venus' clouds. The researchers also show that sources such as lightning, volcanic eruptions, and even a meteorite strike could not chemically produce the amount of ammonia required to explain the anomalies. Life, however, might.

In fact, the team notes that there are life-forms on Earth -- particuarly in our own stomachs -- that produce ammonia to neutralize and make livable an otherwise highly acidic environment.

"There are very acidic environments on Earth where life does live, but it's nothing like the environment on Venus -- unless life is neutralizing some of those droplets," Seager says.

Scientists may have a chance to check for the presence of ammonia, and signs of life, in the next several years with the Venus Life Finder Missions, a set of proposed privately funded missions, of which Seager is principal investigator, that plan to send spacecraft to Venus to measure its clouds for ammonia and other signatures of life.

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Astronomers probe layer-cake structure of brown dwarf’s atmosphere

Maunakea, Hawaii -- Jupiter may be the bully planet of our solar system because it's the most massive planet, but it's actually a runt compared to many of the giant planets found around other stars.

These alien worlds, called super-Jupiters, weigh up to 13 times Jupiter's mass. Astronomers have analyzed the composition of some of these monsters, but it has been difficult to study their atmospheres in detail because these gas giants get lost in the glare of their parent stars.

Researchers, however, have a substitute: the atmospheres of brown dwarfs, so-called failed stars that are up to 80 times Jupiter's mass. These hefty objects form out of a collapsing cloud of gas, as stars do, but lack the mass to become hot enough to sustain nuclear fusion in their cores, which powers stars.

Instead, brown dwarfs share a kinship with super-Jupiters. Both types of objects have similar temperatures and are extremely massive. They also have complex, varied atmospheres. The only difference, astronomers think, is their pedigree. Super-Jupiters form around stars; brown dwarfs often form in isolation.

A team of astronomers, led by Elena Manjavacas of the Space Telescope Science Institute in Baltimore, Maryland, has tested a new way to peer through the cloud layers of these nomadic objects. The researchers used an instrument at W. M. Keck Observatory on Maunakea in Hawaii to study in near-infrared light the colors and brightness variations of the layer-cake cloud structure in the nearby, free-floating brown dwarf known as 2MASS J22081363+2921215.

The Keck Observatory instrument, called the Multi-Object Spectrograph for Infrared Exploration (MOSFIRE), also analyzed the spectral fingerprints of various chemical elements contained in the clouds and how they change with time. This is the first time astronomers have used MOSFIRE in this type of study.

These measurements offered Manjavacas a holistic view of the brown dwarf's atmospheric clouds, providing more detail than previous observations of this object. Pioneered by Hubble observations, this technique is difficult for ground-based telescopes to do because of contamination from Earth's atmosphere, which absorbs certain infrared wavelengths. This absorption rate changes due to the weather.

"The only way to do this from the ground is by using Keck's high-resolution MOSFIRE instrument because it allows us to observe multiple stars simultaneously with our brown dwarf," said Manjavacas, a former staff astronomer at Keck Observatory and the lead author of the study. "This allows us to correct for the contamination introduced by the Earth's atmosphere and measure the true signal from the brown dwarf with good precision. So, these observations are a proof-of-concept that MOSFIRE can do these types of studies of brown dwarf atmospheres."

She decided to study this particular brown dwarf because it is very young and therefore extremely bright. It has not cooled off yet. Its mass and temperature are similar to those of the nearby giant exoplanet Beta Pictoris b, discovered in 2008 near-infrared images taken by the European Southern Observatory's Very Large Telescope in northern Chile.

"We don't have the ability yet with current technology to analyze in detail the atmosphere of Beta Pictoris b," Manjavacas said. "So, we're using our study of this brown dwarf's atmosphere as a proxy to get an idea of what the exoplanet's clouds might look like at different heights of its atmosphere."

Both the brown dwarf and Beta Pictoris b are young, so they radiate heat strongly in the near-infrared. They are both members of a flock of stars and sub-stellar objects called the Beta Pictoris moving group, which shares the same origin and a common motion through space. The group, which is about 33 million years old, is the closest grouping of young stars to Earth. It is located roughly 115 light-years away.

While they're cooler than bona fide stars, brown dwarfs are still extremely hot. The brown dwarf in Manjavacas' study is a sizzling 2,780 degrees Fahrenheit (1,527 degrees Celsius).

The giant object is about 12 times heavier than Jupiter. As a young body, it is spinning incredibly fast, completing a rotation every 3.5 hours, compared to Jupiter's 10-hour rotation period. So, clouds are whipping around the planet, creating a dynamic, turbulent atmosphere.

Keck Observatory's MOSFIRE instrument stared at the brown dwarf for 2.5 hours, watching how the light filtering up through the atmosphere from the dwarf's hot interior brightens and dims over time. Bright spots that appeared on the rotating object indicate regions where researchers can see deeper into the atmosphere, where it is hotter. Infrared wavelengths allow astronomers to peer deeper into the atmosphere. The observations suggest the brown dwarf has a mottled atmosphere with scattered clouds. If viewed close-up, the planet might resemble a carved Halloween pumpkin, with light escaping from the hot interior.

Its spectrum reveals clouds of hot sand grains and other exotic elements. Potassium iodide traces the object's upper atmosphere, which also includes magnesium silicate clouds. Moving down in the atmosphere is a layer of sodium iodide and magnesium silicate clouds. The final layer consists of aluminum oxide clouds. The atmosphere's total depth is 446 miles (718 kilometers). The elements detected represent a typical part of the composition of brown dwarf atmospheres, Manjavacas said.

She and her team used computer models of brown dwarf atmospheres to determine the location of the chemical compounds in each cloud layer.

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Icy clouds could have kept early Mars warm enough for rivers and lakes

One of the great mysteries of modern space science is neatly summed up by the view from NASA's Perseverance, which just landed on Mars: Today it's a desert planet, and yet the rover is sitting right next to an ancient river delta.

The apparent contradiction has puzzled scientists for decades, especially because at the same time that Mars had flowing rivers, it was getting less than a third as much sunshine as we enjoy today on Earth.

But a new study led by University of Chicago planetary scientist Edwin Kite, an assistant professor of geophysical sciences and an expert on climates of other worlds, uses a computer model to put forth a promising explanation: Mars could have had a thin layer of icy, high-altitude clouds that caused a greenhouse effect.

"There's been an embarrassing disconnect between our evidence, and our ability to explain it in terms of physics and chemistry," said Kite. "This hypothesis goes a long way toward closing that gap."

Of the multiple explanations scientists had previously put forward, none have ever quite worked. For example, some suggested that a collision from a huge asteroid could have released enough kinetic energy to warm the planet. But other calculations showed this effect would only last for a year or two -- and the tracks of ancient rivers and lakes show that the warming likely persisted for at least hundreds of years.

Kite and his colleagues wanted to revisit an alternate explanation: High-altitude clouds, like cirrus on Earth. Even a small amount of clouds in the atmosphere can significantly raise a planet's temperature, a greenhouse effect similar to carbon dioxide in the atmosphere.

The idea had first been proposed in 2013, but it had largely been set aside because, Kite said, "It was argued that it would only work if the clouds had implausible properties." For example, the models suggested that water would have to linger for a long time in the atmosphere -- much longer than it typically does on Earth -- so the whole prospect seemed unlikely.

Using a 3D model of the entire planet's atmosphere, Kite and his team went to work. The missing piece, they found, was the amount of ice on the ground. If there was ice covering large portions of Mars, that would create surface humidity that favors low-altitude clouds, which aren't thought to warm planets very much (or can even cool them, because clouds reflect sunlight away from the planet.)

But if there are only patches of ice, such as at the poles and at the tops of mountains, the air on the ground becomes much drier. Those conditions favor a high layer of clouds -- clouds that tend to warm planets more easily.

The model results showed that scientists may have to discard some crucial assumptions based on our own particular planet.

"In the model, these clouds behave in a very un-Earth-like way," said Kite. "Building models on Earth-based intuition just won't work, because this is not at all similar to Earth's water cycle, which moves water quickly between the atmosphere and the surface."

Here on Earth, where water covers almost three-quarters of the surface, water moves quickly and unevenly between ocean and atmosphere and land -- moving in swirls and eddies that mean some places are mostly dry (the Sahara) and others are drenched (the Amazon). In contrast, even at the peak of its habitability, Mars had much less water on its surface. When water vapor winds up in the atmosphere, in Kite's model, it lingers.

"Our model suggests that once water moved into the early Martian atmosphere, it would stay there for quite a long time -- closer to a year -- and that creates the conditions for long-lived high-altitude clouds," said Kite.

NASA's newly landed Perseverance rover should be able to test this idea in multiple ways, too, such as by analyzing pebbles to reconstruct past atmospheric pressure on Mars.

Understanding the full story of how Mars gained and lost its warmth and atmosphere can help inform the search for other habitable worlds, the scientists said.

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Water on exoplanet cloud tops could be found with hi-tech instrumentation

 University of Warwick astronomers have shown that water vapour can potentially be detected in the atmospheres of exoplanets by peering literally over the tops of their impenetrable clouds.

By applying the technique to models based upon known exoplanets with clouds the team has demonstrated in principle that high resolution spectroscopy can be used to examine the atmospheres of exoplanets that were previously too difficult to characterise due to clouds that are too dense for sufficient light to pass through.

Their technique is described in a paper for the Monthly Notices of the Royal Astronomical Society and provides another method for detecting the presence of water vapour in an exoplanet's atmosphere -- as well as other chemical species that could be used in future to assess potential signs of life. The research received funding from the Science and Technologies Facilities Council (STFC), part of UK Research and Innovation (UKRI).

Astronomers use light from a planet's host star to learn what its atmosphere is composed of. As the planet passes in front of the star they observe the transmission of the stellar light as it skims through the upper atmosphere and alters its spectrum. They can then analyse this spectrum to look at wavelengths that have spectral signatures for specific chemicals. These chemicals, such as water vapour, methane and ammonia, are only present in trace quantities in these hydrogen and helium rich planets.

However, dense clouds can block that light from passing through the atmosphere, leaving astronomers with a featureless spectrum. High resolution spectroscopy is a relatively recent technique that is being used in ground-based observatories to observe exoplanets in greater detail, and the Warwick researchers wanted to explore whether this technology could be used to detect the trace chemicals present in the thin atmospheric layer right above those clouds.

While astronomers have been able to characterise the atmospheres of many larger and hotter exoplanets that orbit close to their stars, termed 'hot Jupiters', smaller exoplanets are now being discovered at cooler temperatures (less than 700°C). Many of these planets, which are the size of Neptune or smaller, have shown much thicker cloud.

They modelled two previously known 'warm Neptunes' and simulated how the light from their star would be detected by a high resolution spectrograph. GJ3470b is a cloudy planet that astronomers had previously been able to characterise, while GJ436b has been harder to characterise due to a much thicker cloud layer. Both simulations demonstrated that at high resolution you can detect chemicals such as water vapour, ammonia and methane easily with just a few nights of observations with a ground-based telescope.

The technique works differently from the method recently used to detect phosphine on Venus, but could potentially be used to search for any type of molecule in the clouds of a planet outside of our solar system, including phosphine.

Lead author Dr Siddharth Gandhi of the Department of Physics at the University of Warwick said: "We have been investigating whether ground-based high resolution spectroscopy can help us to constrain the altitude in the atmosphere where we have clouds, and constrain chemical abundances despite those clouds.

"What we are seeing is that a lot of these planets have got water vapour on them, and we're starting to see other chemicals as well, but the clouds are preventing us from seeing these molecules clearly. We need a way to detect these species and high resolution spectroscopy is a potential way of doing that, even if there is a cloudy atmosphere.

"The chemical abundances can tell you quite a lot about how the planet may have formed because it leaves its chemical fingerprint on the molecules in the atmosphere. Because these are gas giants, detecting the molecules at the top of the atmosphere also offers a window into the internal structure as the gases mix with the deeper layers."

The majority of observations of exoplanets have been done using space-based telescopes such as Hubble or Spitzer, and their resolution is too low to detect sufficient signal from above the clouds. High resolution spectroscopy's advantage is that it is capable of probing a wider range of altitudes.

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Satellite tracking shows how ships affect clouds and climate

By matching the movement of ships to the changes in clouds caused by their emissions, researchers have shown how strongly the two are connected.

When ships burn fossil fuels, they release airborne particles containing various naturally occurring chemicals, including sulphur. These particles are known to modify certain types of clouds, which can affect climate.

Better knowledge of how these particles, and particularly the sulphur components, affect clouds could help scientists create more accurate climate models.

In the latest study, satellite tracking was also used to show the impact of restrictions on sulphur in fuels, revealing the impact of ships on clouds largely disappears in restricted zones.

This information can be used to build a relationship between cloud properties and the sulphur content of shipping fuels. Importantly, this could help shipping companies monitor compliance with sulphur regulations that come into force on 1 January 2020.

The study, published today in Geophysical Research Letters, was led by researchers from Imperial College London, together with University College London and the University of Oxford.

Emissions from ships contain several chemicals, including sulphate aerosols -- small particles of sulphur and oxygen. The aerosols can act as 'seeds' around which water droplets accumulate, causing changes in cloud properties that are visible to satellites.

This means that ships can change clouds, leaving lines -- known as ship tracks -- in the clouds behind them as they sail.

However, exactly how these aerosols impact the properties of the clouds is not precisely known. This knowledge is important because the kinds of clouds that the emissions affect can influence climate warming, and is therefore important to capture in climate models.

Aerosol are emitted from many sources, such as factories and cars, but it has been difficult to match these outputs with the influence on clouds, as there are many other factors at play.

However, with ship tracks, the relationship is more straightforward, enabling researchers to tease out the links between aerosols and clouds more easily.

Lead researcher Dr Edward Gryspeerdt, from the Department of Physics at Imperial, said: "Ship tracks act like an experiment that would be impossible for us to do otherwise -- we cannot inject sulphate aerosols into the atmosphere at such scale to see what happens.

"Instead, restrictions on the amount of ship sulphate emissions can contain provide us with a perfect experiment for determining just how important the aerosols are in cloud formation. By analysing a huge dataset of ship tracks observed from satellites, we can see that they largely disappear when restrictions are introduced, demonstrating the strong impact of aerosols."

The team studied more than 17,000 ship tracks from satellite observations and matched them to the movements of individual ships using their onboard GPS.

The study period covered the introduction of emission control areas around the coast of North America, the North Sea, the Baltic Sea and the English Channel, which restricted sulphur in ship fuel to 0.5 percent, leading to fewer sulphate aerosol emissions.

The researchers found that in these areas, ship tracks nearly completely disappeared compared to before the restrictions, under similar weather conditions.

This shows that sulphate aerosols have the most significant impact on cloud formation, as opposed to other components of the ship exhaust, such as black carbon.

The result also means that a ship not in compliance with the regulations, by burning the current high-sulphur fuels without exhaust treatment, could be detected because it would create a measurable difference in the satellite-observed cloud properties.

Co-author Dr Tristan Smith, from UCL's Energy Institute, said: "Currently, it is hard for regulators to know what ships are doing in the middle of the ocean. The potential for undetected non-compliance with the 2020 sulphur regulations is a real risk for shipping companies because it can create commercial advantage to those companies who do not comply.

"This study shows that science and technology are producing significant advancements in the transparency of shipping, and helping to reduce risks and unfairness for responsible operators."

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Meteors help Martian clouds form

Mars.

How did the Red Planet get all of its clouds? CU Boulder researchers may have discovered the secret: just add meteors.

Astronomers have long observed clouds in Mars' middle atmosphere, which begins about 18 miles (30 kilometers) above the surface, but have struggled to explain how they formed.

Now, a new study, which will be published on June 17 in the journal Nature Geoscience, examines those wispy accumulations and suggests that they owe their existence to a phenomenon called "meteoric smoke" -- essentially, the icy dust created by space debris slamming into the planet's atmosphere.

The findings are a good reminder that planets and their weather patterns aren't isolated from the solar systems around them.

"We're used to thinking of Earth, Mars and other bodies as these really self-contained planets that determine their own climates," said Victoria Hartwick, a graduate student in the Department of Atmospheric and Ocean Sciences (ATOC) and lead author of the new study. "But climate isn't independent of the surrounding solar system."

The research, which included co-authors Brian Toon at CU Boulder and Nicholas Heavens at Hampton University in Virginia, hangs on a basic fact about clouds: They don't come out of nowhere.

"Clouds don't just form on their own," said Hartwick, also of the Laboratory for Atmospheric and Space Physics at CU Boulder. "They need something that they can condense onto."

On Earth, for example, low-lying clouds begin life as tiny grains of sea salt or dust blown high into the air. Water molecules clump around these particles, becoming bigger and bigger until they form the large puffs that you can see from the ground.

But, as far as scientists can tell, those sorts of cloud seeds don't exist in Mars' middle atmosphere, Hartwick said. And that's what led her and her colleagues to meteors.

Hartwick explained that about two to three tons of space debris crash into Mars every day on average. And as those meteors rip apart in the planet's atmosphere, they inject a huge volume of dust into the air.

To find out if such smoke would be enough to give rise to Mars' mysterious clouds, Hartwick's team turned to massive computer simulations that attempt to mimic the flows and turbulence of the planet's atmosphere.

And sure enough, when they included meteors in their calculations, clouds appeared.

"Our model couldn't form clouds at these altitudes before," Hartwick said. "But now, they're all there, and they seem to be in all the right places."

The idea might not be as outlandish as it sounds, she added. Research has shown that similar interplanetary schmutz may help to seed clouds near Earth's poles.

But she also says that you shouldn't expect to see gigantic thunderheads forming above the surface of Mars anytime soon. The clouds her team studied were much more like bits of cotton candy than the clouds Earthlings are used to.

"But just because they're thin and you can't really see them doesn't mean they can't have an effect on the dynamics of the climate," Hartwick said.

The researchers' simulations, for example, showed that middle atmosphere clouds could have a large impact on the Martian climate. Depending on where the team looked, those clouds could cause temperatures at high altitudes to swing up or down by as much as 18 degrees Fahrenheit (10 degrees Celsius).

And that climactic impact is what gets Brian Toon, a professor in ATOC, excited. He said that the team's findings on modern-day Martian clouds may also help to reveal the planet's past evolution and how it once managed to support liquid water at its surface.

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