Month: August 2023

A recent study published in the journal Geology attempts to interpret the patterns of dunes, which are sand mounds frequently formed by aeolian (wind) processes and range in size from small ripples observed on beaches to massive structures observed in the desert. Specifically, the researchers focused on patterns of dune crestlines, which are the top of the dunes. Different dune crestline patterns might appear as mundane features, but their formations are often the result of a myriad of influences, including climate change, surface processes, and atmospheric phenomena.

However, questions pertaining to the processes responsible for the different crestline patterns have baffled scientists. But the findings from this recent study could provide researchers insights into environmental variances not only on Earth, but other dune-harboring planetary worlds in our own solar system. These currently include three of the four terrestrial planets, Venus, Earth, and Mars; smaller bodies such as Jupiter’s volcanic moon, Io; Saturn’s largest moon, Titan; and even dwarf planet Pluto.

“When you look at other planets, all you have is pictures taken from hundreds to thousands of kilometers away from the surface,” said Dr. Mathieu Lapôtre, who is an assistant professor of Earth and planetary sciences in the Stanford Doerr School of Sustainability, and a co-author on the study. “You can see dunes – but that’s it. You don’t have access to the surface. These findings offer a really exciting new tool to decipher the environmental history of these other planets where we have no data.”

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Dune interactions are defined as when their crestlines are near one another, and it’s these interactions result in the dunes establishing a balance, or equilibrium, with their surrounding environment. Therefore, the researchers hypothesized that a large amount of dune interactions could be interpreted as recent or nearby changes regarding those confined conditions.

For the study, the researchers analyzed changes in specific known environmental conditions, including sand quantity and wind direction, using orbital images of dune field sites numbering 30 and 16 on Earth and Mars, respectively. Examples of Earth dune field sites included Rice Valley, White Sands, the Namib Desert, and the Tengger Desert. Examples of Martian dune field sites included Nili Patera, Kaiser Crater, Rabe Crater, and Hargraves Crater.

Examples of active dune fields within Nili Patera on Mars. Dunes like these were examined for this study in hopes of giving scientists better insights into how their interactions are influenced by a planet’s climate. (Credit: NASA/JPL-Caltech/Univ. of Arizona)

Example of dune activity in Rabe Crater on Mars, one of the locations for this recent study investigating dune interactions. (Credit: NASA/JPL-Caltech/UArizona)

Example of dune activity in Kaiser Crater on Mars, one of the locations for this recent study investigating dune interactions. (Credit: NASA/JPL-Caltech/UArizona)

For Earth, the researchers flattened a dune field in China’s Tengger Desert to establish a baseline prior to analyzing satellite imagery between 2016 and 2022 of how this flat terrain evolved into large dunes as they slowly reached a state of equilibrium with their surrounding environment. This was followed by the team examining how wind conditions in the Namib Desert resulted in increased dune interaction as the dunes migrated throughout a valley whose landscape transitions from unrestricted to restricted then unrestricted afterwards.  

“As both sand and winds get funneled into the valley, the dunes feel a change in their boundary conditions, and their pattern needs to adjust,” said Colin Marvin, who is a PhD student in the Department of Earth and Planetary Sciences at Stanford, and lead author of the study. “They move into the portion outside the valley, and they again readjust to their unconfined conditions, and we see a drop in the number of interactions. This trend is exactly what we expected to see.”

Time-lapse images of the Nili Patera dune field on Mars observed between 2007 and 2010. These images indicate dune ripple movement and are an example of what scientists observed in the Namib Desert on Earth for this study. (Credit: NASA)

For Mars, the researchers used orbital imagery to discover similar dune patterns, specifically near the Martian north pole where the researchers observed minor amounts of dune interactions. This was due to the dunes reaching a state of equilibrium with their surrounding environment, resulting in relative spacing from each other and similar characteristics for both appearance and size. However, dunes observed in slightly lower latitudes exhibited greater amounts of interactions due to changing winds and local surface frost. But once these dunes migrate closer to the north pole, their patterns settle out resulting in decreased interactions.

“We have an upper bound on the time that it takes for a given dune to adjust to changes in environmental conditions, and that is the time it takes for a dune to migrate by a distance of one dune length,” said Marvin. “We can use this to diagnose recent changes in environmental conditions on planetary bodies where we don’t have any information other than images taken from orbit or radar for example.” 

Dr. Lapôtre noted that gaining insights about dune patterns on Mars could not only help better understand Mars’ recent climate, but also assist in locating subsurface water ice that could be excavated by future astronauts on the Red Planet.

As stated earlier, other planetary bodies besides Earth and Mars possess dunes that could be used to better understand climates on those worlds, with one such world being Saturn’s largest moon, Titan. In addition to its dunes, Titan is the only moon that possesses a thick atmosphere, which makes it a target for astrobiology and the search for life beyond Earth. This large moon was extensively investigated by NASA’s Cassini throughout the 2000s and 2010s with the European Space Agency’s Huygens probe touching down on Titan’s surface in January 2005. This made Huygens the first spacecraft to land on a planetary body in the outer solar system and the first landing on a moon aside from Earth’s Moon. While Huygens only transmitted data and images back to Earth for approximately 90 minutes, it provided scientists with a first-time, up-close look at one of the most intriguing moons in the solar system.

This most recent study has helped scientists lay the foundation for helping us better understand dune interactions on other worlds, but NASA’s upcoming Dragonfly mission to Titan hopes to confirm these findings when it lands on the moon’s surface sometime in the 2030s. With this mission, Dragonfly will become only the second rotorcraft sent to another world—the first being NASA’s Ingenuity helicopter on Mars—and will mark the first powered flight on any moon. During its multi-year science mission, Dragonfly will perform short flights around Titan in hopes of determining its prebiotic chemistry and potential for extraterrestrial life but should also provide scientists an up-close investigation of its dunes, which have thus far only been observed from orbit.

What new discoveries about dune interactions on Earth and other worlds will scientists make in the coming years and decades? Only time will tell, and this is why we science!

As always, keep doing science & keep looking up!

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From NOT A LOT OF PEOPLE KNOW THAT

By Paul Homewood

Ed Miliband announced Labour’s new Energy Policy at the Party Conference last year. Its centrepiece is a commitment to totally decarbonise power generation by 2030, to be achieved by doubling onshore wind, trebling solar power and quadrupling offshore wind.

You may recall the computer modelling work done by John Brown a few weeks ago, which used 2022 generation data to assess how much wind power capacity we would need if electrolysis was employed to provide hydrogen to back up the grid.

John and I have used the same model to plug in Labour’s plans for wind and solar. Unsurprisingly, but frighteningly, it shows that Miliband’s numbers simply don’t stack up.

First, a few basic assumptions:

• Demand in 2030 is 20% higher than now, factoring in EVs and heat pumps. This figure will, of course, rise dramatically in the following years, but for now we are concentrating only on 2030.
• The model is based on BMRS data, which does not include embedded generation, such as small wind and solar farms. Instead these appear as lower demand as far as BMRS is concerned. The model results however are not affected.
• We have assumed that, on top of wind and solar, the UK has 10 GW of dispatchable capacity, such as nuclear, biomass and hydro.
• There is no electricity generated from hydrogen – there seems to be no way that bulk hydrogen infrastructure –  electrolysers, steam reformers, distribution networks and a 50GW fleet of new hydrogen burning power stations – could be ready by 2030.
• Equally there is no Carbon Capture power generation available.
• There are no electricity imports. (See discussion below)
• There is no major expansion of battery storage to the scale needed.

A few basic numbers:

• Peak demand is 56.5 GW
• Average demand is 35.8 GW, adding up to 314 TWh
• Wind, Solar and Others generation are 204, 33 and 88 TWh respectively, giving a total of 325 TWh

You can probably see Labour’s thinking, that there is enough generation to meet demand!

But, as we know, the wind does not always blow, and the sun does not always shine. And this is where the model gets interesting, and not a little scary.

Using 2022 data, the model finds that the power deficit peaks at 41 GW, a 5-minute period when demand is 56 GW and generation 15 GW. It is of course possible to smooth the peaks to a small extent with the help of demand side response and battery storage.

But more critical is the fact that there was a 19-day period last December when there was a rising cumulative power deficit of about 7TWh, at an average of 15.7 GW. Although within this period there were short spells when generation exceeded demand, the net balance remained negative. Put simply, even with smoothing and storage there would not have been enough electricity to go round.

This spell unsurprisingly coincided with the cold snap that month. And as we know too well, we could be facing much colder weather, and over a much longer period than 19 days in years to come. Our model shows that we need at least 7 TWh of storage, but a proper safety reserve would need much more than that.

The model also finds that there would be a shortage of power for 48% of the year, and a surplus for 52%.

As well as the deficit side of the equation, we must not forget that over the year a surplus of 531 TWh builds up, peaking at 44 GW. Without hydrogen infrastructure, most of this will either have to be exported or thrown away.

The model does not allow for imports of electricity. Currently we have 7.4 GW of interconnector capacity, excluding the Irish ones – (If we are short of wind power, it is a pretty good bet Ireland will be as well!). According to DESNZ, this could grow to 17 GW by 2030.

According to our model though, the power deficit would be above 17 GW for more than a tenth of the year, so clearly we cannot simply rely on imports, which in any case would be incredibly risky and make a nonsense of claims of energy security.

For instance, during that 19 day spell in December, there was one 9-hour period when the power deficit averaged 22 GW. Other days were similarly bad.

And just as we will still be critically short of power even with interconnectors, they will not have enough capacity to get rid of all of the surplus electricity produced.

Demand will of course carry on increasing in the years after 2030, as more EVs and heat pumps appear on the scene. Power shortages will therefore become more frequent and larger, even if more wind farms are built.

For more on Net Zero and UK politics go to our ClimateTV section on the subject.

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