Global cloudiness map, based on data collected by the Aqua research satellite over more than a decade (2002-2015). Clouds are not distributed uniformly but rather concentrated in hot spots. Photo: NASA
Global cloudiness map, based on data collected by the Aqua research satellite over more than a decade (2002-2015). Clouds are not distributed uniformly but rather concentrated in hot spots. Photo: NASA
Tyler O'Neal, Staff Editor EARTH SCIENCES

Weizmann scientists solve a 50-year-old puzzle on why Earth’s hemispheres look equally bright when viewed from space

When looking at the Earth from space, its 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, Weizmann Institute of Science, Isreal, 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. (l-r) Prof. Yohai Kaspi and Or HadasAs 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. The 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.”

UK scientists find radioactive isotopes reach Earth by surfing supernova blast waves

Tyler O'Neal, Staff Editor EARTH SCIENCES

Scientists researching the origin of elements in our Galaxy have new insights into how they are transported to Earth, thanks to a new study led by authors at the University of Hertfordshire in the UK and the Konkoly Observatory, Research Centre for Astronomy and Earth Sciences (CSFK) in Hungary.

As well as understanding how our planet became enriched with these elements, the results could also help scientists uncover which exoplanets outside our solar system are most likely to contain life.

Many elements around us were produced either through stellar explosions called supernovae, or violent collisions of extremely dense objects called neutron stars. One of the questions puzzling scientists was how these heavy elements then reach us here on Earth – and in particular, how elements that originate in different places seem to have reached our planet at the same time.

Using sophisticated supercomputer modeling of the elements’ journey through space, scientists have now found that the heavy elements produced in collisions of neutron stars can “surf” on blast waves of other supernovae across our Galaxy and down to Earth.

The mystery was first raised in 2021 when radioactive isotopes discovered inside deep-sea rocks revealed a surprise for the scientists studying their origin. The isotopes did not originate inside our Solar System but in explosions of stars elsewhere in the Galaxy. Some of the detected isotopes especially raised eyebrows in the research community, because of their very different production sites.

Specifically, scientists found manganese-53 (associated with explosions of white dwarfs); iron-60 (produced in core-collapse supernovae); and plutonium-244 (which can usually only be produced by merging two extreme objects called neutron stars) sitting in layers of a similar depth in deep-sea rock samples.

To reach Earth, these isotopes would have rained down from the sky at some point during the last couple of million years. Since deep-sea sediments accumulate layer by layer over time to form rocks, researchers were very puzzled by the fact that these three isotopes, originating from different types of stellar explosions, were found in rock layers of similar depth. Finding them at similar depths means that they must have arrived on Earth together, even though their origin sites are so vastly different.

To understand how it was possible for these isotopes to arrive on Earth together, a team led by Dr. Benjamin Wehmeyer at the University of Hertfordshire in the UK, and the CSFK in Hungary, used supercomputer models to simulate how the isotopes travel from their Galactic production sites throughout space.

The study found that the ejected content of different astrophysical sites – from colliding neutron stars to exploding white dwarfs – are pushed around in the Galaxy by the shock waves of the much more frequent core-collapse supernovae. These supernovae are explosions of the cores of massive stars, which are much more common than explosions triggered by the merging of two neutron stars or explosions of white dwarfs.

Dr. Wehmeyer and his team observed that after they are produced, the isotopes can then “surf” on the shockwaves of these supernovae. This means that isotopes produced in very different sites can end up traveling together on the edges of the shock waves of core-collapse supernova explosions. Some of this swept-up material ends up on Earth, which can explain why the isotopes were found together within similar layers of deep-sea rocks.

The lead writer Dr. Wehmeyer explained, “Our colleagues have dug up rock samples from the ocean floor, dissolved them, put them in an accelerator, and examined the changes in their composition layer by layer. Using our computer models, we were able to interpret their data to find out how exactly atoms move throughout the Galaxy.

“It’s a very important step forward, as it not only shows us how isotopes propagate through the Galaxy but also how they become abundant on exoplanets – that is, planets beyond our solar system. This is extremely exciting since isotopic abundances are a strong factor in determining whether an exoplanet is able to hold liquid water – which is key to life. In the future, this might help to identify regions in our Galaxy where we could find habitable exoplanets”.

Dr Chiaki Kobayashi, Professor of Astrophysics at the University of Hertfordshire and co-writer of the study, adds: "I have been working on the origins of stable elements in the periodic table for many years, but I am thrilled to achieve results on radioactive isotopes in this paper. Their abundance can be measured by gamma-ray telescopes in space as well as by digging the rocks underwater on the Earth.

“By comparing these measurements with Benjamin's models, we can learn so much about how and where the composition of the solar system comes from”.

The full paper ‘Inhomogeneous enrichment of radioactive nuclei in the Galaxy: Deposition of live 53Mn, 60Fe, 182Hf, and 244Pu into deep-sea archives. Surfing the wave?’ is available now to read in Astrophysical Journal.

Daniel Floryan, Kalsi Assistant Professor of Mechanical Engineering at University of Houston, is reporting a method to describe complex systems with the least number of variables possible, sometimes reducing the possibility of millions to a minimal amount, and just one on rare occasions.
Daniel Floryan, Kalsi Assistant Professor of Mechanical Engineering at University of Houston, is reporting a method to describe complex systems with the least number of variables possible, sometimes reducing the possibility of millions to a minimal amount, and just one on rare occasions.

University of Houston's Floryan finds simplicity within complexity

Tyler O'Neal, Staff Editor EARTH SCIENCES

Mechanical engineer develops a method that can predict behavior, improve weather forecasting

Picture a tall stately grandfather clock, its long pendulum swinging back and forth, over and again, keeping rhythm with the time. Scientists can describe that motion with an equation or dynamical model, and though there are seemingly hundreds of factors contributing to the sway, (the weight of the clock, the material of the pendulum, ad infinitum) there is only one variable necessary to describe the motion of the pendulum and translate it into math: the angle of the swing. How long it took scientists and mathematicians to discover that is unknown. It could have taken years to test each variable in the equation to determine the single important variable for sway.  

Now a University of Houston researcher is reporting a method to describe these kinds of complex systems with the least number of variables possible, sometimes reducing the possibility of millions to a minimal amount and just one on rare occasions. It’s an advancement that can speed up science with its efficiency and ability to understand and predict the behavior of natural systems, and it has implications for speeding up an array of activities that use simulations from weather forecasting to the production of aircraft. 

“In the example of the grandfather clock, I can take a video of the pendulum swinging back and forth and from that video, automatically discover what is the right variable. Accurate models of system dynamics enable a deeper understanding of these systems, as well as the ability to predict their future behavior,” reports Daniel Floryan, Kalsi Assistant Professor of Mechanical Engineering.

To begin building the compact-yet-accurate models, one principle is fundamental: For every action, even those seemingly complex and random, there exists an underlying pattern that enables a compact representation of the system.  

“Our method finds the very most compact description that is mathematically possible, and that’s what differentiates our method from others,” said Floryan.  

Using ideas from machine learning and smooth manifold theory, the method makes simulations extremely fast and inexpensive. 

In one application, Floryan simulated a reaction between a couple of chemicals. The reaction resulted in complex behavior among the chemicals when they met: a repetitive rhythmic spiraling requiring more than 20,000 variables to simulate it. Floryan fed a video of the reaction into his algorithm, and it discovered he needed just one variable to understand the action. The necessary variable was the time the spiral took to come back to where it started, like a second hand on a watch. 

Regarding weather prediction, numerical models are supercomputer simulations of the atmosphere that use complicated physics and fluid dynamics equations. 

“For weather prediction and climate modeling, if you have something that is much faster you can better model the earth’s climate and better predict what’s going to happen,” said Floryan.