The daily dance of flowers tracking the sun is more fascinating than most of us realise

Julien Christ/Unsplash

Gregory Moore, The University of MelbourneWhen I was a child, I was intrigued by the Queensland box (Lophostemon confertus) growing in our backyard. I noticed its leaves hung vertical after lunch in summer, and were more or less horizontal by the next morning.

This an example of heliotropism, which literally means moving in relation to the sun. We can see it most clearly as spring arrives and various species burst into flower — you might even get the feeling that some flowers are watching you as they move.

Many of us probably first got to know of heliotropism at home, kindergarten or primary school by watching the enormous yellow and black flowering heads of aptly name sunflowers, which moved as they grew.

These flowers track the course of the sun spectacularly on warm and sunny, spring or summer days. Sometimes they move through an arc of almost 180⁰ from morning to evening.

So with the return of sunny days and flowers in full bloom this season, let’s look at why this phenomenon is so interesting.

The mechanics of tracking the sun

A number flowering species display heliotropism, including alpine buttercups, arctic poppies, alfalfa, soybean and many of the daisy-type species. So why do they do it?

This is Heliotropium arborescens, named for its heliotropism. They were very popular in gardens a century or more ago, but have fallen from favour as they can be poisonous and weedy.

Flowers are really in the advertising game and will do anything they can to attract a suitable pollinator, as effectively and as efficiently as they can. There are several possible reasons why tracking the sun might have evolved to achieve more successful pollination.

By tracking the sun, flowers absorb more solar radiation and so remain warmer. The warmer temperature suits or even rewards insect pollinators that are more active when they have a higher body temperature.

Optimum flower warmth may also boost pollen development and germination, leading to a higher fertilisation rate and more seeds.

Read more:
Why there’s a lot more to love about jacarandas than just their purple flowers

So, the flowers are clearly moving. But how?

For many heliotropic flowering species, there’s a special layer of cells called the pulvinus just under the flower heads. These cells pump water across their cell membranes in a controlled way, so that cells can be fully pumped up like a balloon or become empty and flaccid. Changes in these cells allow the flower head to move.

Venus fly trap
Fly traps have somewhat similar mechanics to heliotropism.

When potassium from neighbouring plant cells is moved into the cells of the pulvinus, water follows and the cells inflate. When they move potassium out of the cells, they become flaccid.

These potassium pumps are involved in many other aspects of plant movement, too. This includes the opening and closing of stomata (tiny regulated leaf apertures), the rapid movement of mimosa leaves, or the closing of a fly trap.

But sunflowers dance differently

In 2016, scientists discovered that the pin-up example of heliotropism — the sunflower — had a different way of moving.

They found sunflower movement is due to significantly different growth rates on opposite sides of the flowering stem.

A sunflower facing a setting sun
Sunflowers move differently to other heliotropic flowers.
Aaron Burden/Unsplash

On the east-facing side, the cells grow and elongate quickly during the day, which slowly pushes the flower to face west as the daylight hours go by — following the sun. At night the west-side cells grow and elongate more rapidly, which pushes the flower back toward the east over night.

Everything is then set for the whole process to begin again at dawn next day, which is repeated daily until the flower stops growing and movement ceases.

Read more:
The secret life of puddles: their value to nature is subtle, but hugely important

While many people are aware of heliotropism in flowers, heliotropic movement of leaves is less commonly noticed or known. Plants with heliotropic flowers don’t necessarily have heliotropic leaves, and vice versa.

Heliotropism evolves in response to highly specific environmental conditions, and factors affecting flowers can be different from those impacting leaves.

The leaves of Queensland box, Lophostemon confertus, which track the sun.
Krzysztof Ziarnek, Kenraiz/Wikimedia Commons, CC BY-SA

For example, flowers are all about pollination and seed production. For leaves, it’s for maximising photosynthesis, avoiding over-heating on a hot day or even reducing water loss in harsh and arid conditions.

Some species, such as the Queensland box, arrange their leaves so they’re somewhat horizontal in the morning, capturing the full value of the available sunlight. But there are also instances where leaves align vertically to the sun in the middle of the day to minimise the risks of heat damage.

Plants are dynamic

It’s easy to think of plants as static organisms. But of course, they are forever changing, responding to their environments and growing. They are dynamic in their own way, and we tend to assume that when they do change, it will be at a very slow and steady pace.

Heliotropism shows us this is not necessarily the case. Plants changing daily can be a little unsettling in that we sense a change but may not be aware of what is causing our unease.

As for me, I still keep a watchful eye on those Queensland boxes!

Read more:
It is risen: the story of resurrection ferns and my late colleague who helped discover them in Australia

The Conversation

Gregory Moore, Doctor of Botany, The University of Melbourne

This article is republished from The Conversation under a Creative Commons license. Read the original article.

The sunlight that powers solar panels also damages them. ‘Gallium doping’ is providing a solution


Matthew Wright, UNSW; Brett Hallam, UNSW, and Bruno Vicari Stefani, UNSWSolar power is already the cheapest form of electricity generation, and its cost will continue to fall as more improvements emerge in the technology and its global production. Now, new research is exploring what could be another major turning point in solar cell manufacturing.

In Australia, more than two million rooftops have solar panels (the most per capita in the world). The main material used in panels is silicon. Silicon makes up most of an individual solar cell’s components required to convert sunlight into power. But some other elements are also required.

Research from our group at the University of New South Wales’s School of Photovoltaics and Renewable Energy Engineering shows that adding gallium to the cell’s silicon can lead to very stable solar panels which are much less susceptible to degrading over their lifetime.

This is the long-term goal for the next generation of solar panels: for them to produce more power over their lifespan, which means the electricity produced by the system will be cheaper in the long run.

As gallium is used more and more to achieve this, our findings provide robust data that could allow manufacturers to make decisions that will ultimately have a global impact.

The process of ‘doping’ solar cells

A solar cell converts sunlight into electricity by using the energy from sunlight to “break away” negative charges, or electrons, in the silicon. The electrons are then collected as electricity.

However, shining light on a plain piece of silicon doesn’t generate electricity, as the electrons that are released from the light do not all flow in the same direction. To make the electricity flow in one direction, we need to create an electric field.

Read more:
Curious Kids: how do solar panels work?

In silicon solar cells — the kind currently producing power for millions of Australian homes — this is done by adding different impurity atoms to the silicon, to create a region that has more negative charges than normal silicon (n-type silicon) and a region that has fewer negative charges (p-type silicon).

When we put the two parts of silicon together, we form what is called a “p-n junction”. This allows the solar cell to operate. And the adding of impurity atoms into silicon is called “doping”.

An unfortunate side effect of sunlight

The most commonly used atom to form the p-type part of the silicon, with less negative charge than plain silicon, is boron.

Boron is a great atom to use as it has the exact number of electrons needed for the task. It can also be distributed very uniformly through the silicon during the production of the high-purity crystals required for solar cells.

But in a cruel twist, shining light on boron-filled silicon can make the quality of the silicon degrade. This is often referred to as “light-induced degradation” and has been a hot topic in solar research over the past decade.

The reason for this degradation is relatively well understood: when we make the pure silicon material, we have to purposefully add some impurities such as boron to generate the electric field that drives the electricity. However, other unwanted atoms are also incorporated into the silicon as a result.

One of these atoms is oxygen, which is incorporated into the silicon from the crucible — the big hot pot in which the silicon is refined.

When light shines on silicon that contains both boron and oxygen, they bond together, causing a defect that can trap electricity and reduce the amount of power generated by the solar panel.

Unfortunately, this means the sunlight that powers solar panels also damages them over their lifetime. An element called gallium looks like it could be the solution to this problem.

A smarter approach

Boron isn’t the only element we can use to make p-type silicon. A quick perusal of the periodic table shows a whole column of elements that have one less negative charge than silicon.

Adding one of these atoms to silicon upsets the balance between the negative and positive charge, which is needed to make our electric field. Of these atoms, the most suitable is gallium.

Gallium is a very suitable element to make p-type silicon. In fact, multiple studies have shown it doesn’t bond together with oxygen to cause degradation. So, you may be wondering, why we haven’t been using gallium all along?

Well, the reason we have been stuck using boron instead of gallium over the past 20 years is that the process of doping silicon with gallium was locked under a patent. This prevented manufacturers using this approach.

Gallium-doped silicon heterojunction solar cell.
Robert Underwood/UNSW

But these patents finally expired in May 2020. Since then, the industry has rapidly shifted from boron to gallium to make p-type silicon.

In fact, at the start of 2021, leading photovoltaic manufacturer Hanwha Q Cells estimated about 80% of all solar panels manufactured in 2021 used gallium doping rather than boron — a massive transition in such a short time!

Does gallium really boost solar panel stability?

We investigated whether solar cells made with gallium-doped silicon really are more stable than solar cells made with boron-doped silicon.

To find out, we made solar cells using a “silicon heterojunction” design, which is the approach that has led to the highest efficiency silicon solar cells to date. This work was done in collaboration with Hevel Solar in Russia.

We measured the voltage of both boron-doped and gallium-doped solar cells during a light-soaking test for 300,000 seconds. The boron-doped solar cell underwent significant degradation due to the boron bonding with oxygen.

Meanwhile, the gallium-doped solar cell had a much higher voltage. Our result also demonstrated that p-type silicon made using gallium is very stable and could help unlock savings for this type of solar cell.

To think it might be possible for manufacturers to work at scale with gallium, producing solar cells that are both more stable and potentially cheaper, is a hugely exciting prospect.

The best part is our findings could have a direct impact on industry. And cheaper solar electricity for our homes means a brighter future for our planet, too.

Read more:
It might sound ‘batshit insane’ but Australia could soon export sunshine to Asia via a 3,800km cable

The Conversation

Matthew Wright, Postdoctoral Researcher in Photovoltaic Engineering, UNSW; Brett Hallam, Scientia and DECRA Fellow, UNSW, and Bruno Vicari Stefani, PhD Candidate, UNSW

This article is republished from The Conversation under a Creative Commons license. Read the original article.

You may have heard the ‘moon wobble’ will intensify coastal floods. Well, here’s what that means for Australia


Mark Gibbs, Australian Institute of Marine ScienceExtreme floods this month have been crippling cities worldwide. This week in China’s Henan province, a year’s worth of rain fell in just three days. Last week, catastrophic floods swept across western Germany and parts of Belgium. And at home, rain fell in Perth for 17 days straight, making it the city’s wettest July in 20 years.

But torrential rain isn’t the only cause of floods. Many coastal towns and cities in Australia would already be familiar with what are known as “nuisance” floods, which occur during some high tides.

A recent study from NASA and the University of Hawaii suggests even nuisance floods are set to get worse in the mid-2030s as the moon’s orbit begins another phase, combined with rising sea levels from climate change.

The study was conducted in the US. But what do its findings mean for the vast lengths of coastlines in Australia and the people who live there?

A triple whammy

We know average sea levels are rising from climate change, and we know small rises in average sea levels amplify flooding during storms. From the perspective of coastal communities, it’s not if a major flood will occur, it’s when the next one will arrive, and the next one after that.

But we know from historical and paleontological records of flooding events that in many, if not most, cases the coastal flooding we’ve directly experienced in our lifetimes are simply the entrée in terms of what will occur in future.

Flooding is especially severe when a storm coincides with a high tide. And this is where NASA and the University of Hawaii’s new research identified a further threat.

Researchers looked at the amplification phase of the natural 18.6-year cycle of the “wobble” in the moon’s orbit, first identified in 1728.

The orbit of the moon around the sun is not quite on a flat plane (planar); the actual orbit oscillates up and down a bit. Think of a spinning plate on a stick — the plate spins, but also wobbles up and down.

Read more:
Predators, prey and moonlight singing: how phases of the Moon affect native wildlife

When the moon is at particular parts of its wobbling orbit, it pulls on the water in the oceans a bit more. This means for some years during the 18.6-year cycle, some high tides are higher than they would have otherwise been.

This results in increases to daily tidal rises, and this, in turn, will exacerbate coastal flooding, whether it be nuisance flooding in vulnerable areas, or magnified flooding during a storm.

View of Earth from the Moon
The moon’s orbit isn’t on a flat plane. It oscillates up and down, like a plate would when it spins on a stick.

A major wobble amplification phase will occur in the mid-2030s, when climate change will make the problem become severe in some cases.

The triple whammy of the wobble in the moon’s orbit, ongoing upwards creep in sea levels from ocean warming, and more intense storms associated with climate change, will bring the impacts of sea-level rise earlier than previously expected — in many locations around the world. This includes in Australia.

So what will happen in Australia?

The locations in Australia where tides have the largest range, and will be most impacted by the wobble, aren’t close to the major population centres. Australia’s largest tides are close to Broad Sound, near Hay Point in central Queensland, and Derby in the Kimberley region of Western Australia.

However, many Australian cities host suburbs that routinely flood during larger high tides. Near my home in Meanjin (Brisbane), the ocean regularly backs up through the storm water drainage system during large high tides. At times, even getting from the front door to the street can be challenging.

Derby, WA, has one of the biggest tidal ranges in Australia.

Some bayside suburbs in Melbourne are also already exposed to nuisance flooding. But a number of others that are not presently exposed may also become more vulnerable from the combined influence of the moon wobble and climate change — even when the weather is calm. High tide during this lunar phase, occurring during a major rainfall event, will result in even greater risk.

Read more:
High-tide flood risk is accelerating, putting coastal economies at risk

In high-income nations like Australia, sea-level rise means increasing unaffordability of insurance for coastal homes, followed by an inability to seek insurance cover at all and, ultimately, reductions in asset values for those unable or unwilling to adapt.

The prognosis for lower-income coastal communities that aren’t able to adapt to sea-level rise is clear: increasingly frequent and intense flooding will make many aspects of daily life difficult to sustain. In particular, movement around the community will be challenging, homes will often be inundated, unhealthy and untenable, and the provision of basic services problematic.

What do we do about it?

While our hearts and minds continue to be occupied by the pandemic, threats from climate change to our ongoing standard of living, or even future viability on this planet, haven’t slowed. We can pretend to ignore what is happening and what is increasingly unstoppable, or we can proactively manage the increasing threat.

Some coastal communities, such as in Melbourne’s bayside suburbs, may experience flooding, even if they never have before.

Thankfully, approaches to adapting the built and natural environment to sea-level rise are increasingly being applied around the world. Many major cities have already embarked on major coastal adaptation programs – think London, New York, Rotterdam, and our own Gold Coast.

However, the uptake continues to lag behind the threat. And one of the big challenges is to incentivise coastal adaptation without overly impacting private property rights.

Read more:
For flood-prone cities, seawalls raise as many questions as they answer

Perhaps the best approach to learning to live with water is led by the Netherlands. Rather than relocating entire communities or constructing large barriers like sea walls, this nation is finding ways to reduce the overall impact of flooding. This includes more resilient building design or reducing urban development in specific flood retention basins. This means flooding can occur without damaging infrastructure.

There are lessons here. Australia’s adaptation discussions have often focused on finding the least worst choice between constructing large seawalls or moving entire communities — neither of which are often palatable. This leads to inaction, as both options aren’t often politically acceptable.

The seas are inexorably creeping higher and higher. Once thought to be a problem for our grandchildren, it is becoming increasingly evident this is a challenge for the here and now. The recently released research confirms this conclusion.

Read more:
King tides and rising seas are predictable, and we’re not doing enough about it

The Conversation

Mark Gibbs, Principal Engineer: Reef Restoration, Australian Institute of Marine Science

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Where do meteorites come from? We tracked hundreds of fireballs streaking through the sky to find out

Patrick M Shober, Curtin UniversityIf asked where meteorites come from, you might reply “from comets”. But according to our new research, which tracked hundreds of fireballs on their journey through the Australian skies, you would be wrong.

In fact, it is very likely that all meteorites — space rocks that make it all the way to Earth — come not from icy comets but from rocky asteroids. Our new study found that even those meteorites with trajectories that look like they arrived from much farther afield are in fact from asteroids that simply got knocked into strange orbits.

We searched through six years’ worth of records from the Desert Fireball Network, which scans the Australian outback for flaming meteors streaking through the sky. None of what we found came from comets.

That means that of the tens of thousands of meteorites in collections around the world, likely none are from comets, leaving a significant gap in our understanding of the Solar System.

When the Solar System formed, more than 4.5 billion years ago, a disc of dust and debris was swirling around the Sun.

Over time, this material clumped together, forming larger and larger bodies — some so large they swept up everything else in their orbit, and became planets.

Yet some debris avoided this fate and is still floating around today. Scientists traditionally classify these objects into two groups: comets and asteroids.

Asteroids are rockier and drier, because they were formed in the inner Solar System. Comets, meanwhile, formed further out, where ices such as frozen water, methane or carbon dioxide can remain stable — giving them a “dirty snowball” composition.

The best way to understand the origin and evolution of our Solar System is to study these objects. Many space missions have been sent to comets and asteroids over the past few decades. But these are expensive, and only two (Hayabusa and Hayabusa2) have successfully brought back samples.

Read more:
The Hayabusa2 spacecraft is about to drop a chunk of asteroid in the Australian outback

Another way to study this material is to sit and wait for it to come to us. If a piece of debris happens to cross paths with Earth, and is large and robust enough to survive hitting our atmosphere, it will land as a meteorite.

Most of what we know about the Solar System’s history comes from these curious space rocks. However, unlike space mission samples, we don’t know exactly where they originated.

Meteorites have been curiosities for centuries, yet it was not until the early 19th century that they were identified as extraterrestrial. They were speculated to come from lunar volcanoes, or even from other star systems.

Today, we know all meteorites come from small bodies in our Solar System. But the big question that remains is: are they all from asteroids, or do some come from comets?

Read more:
Asteroid dust brought back to Earth may explain where our water came from with hydrogen clues

In total, scientists around the world have collected more than 60,000 meteorites, mostly from desert regions such as Antarctica or Australia’s Nullarbor Plain.

We now know most of these come from the main asteroid belt – a region between Mars and Jupiter.

But might some of them have come not from asteroids, but from comets that originated in the outer reaches of the Solar System? What would such meteorites be like, and how would we find them?

Fireball observatory operated by the Desert Fireball Network in South Australia.

Fortunately, we can actively look for meteorites, rather than hoping to stumble across one lying on the ground. When a space rock is falling through the atmosphere (at this stage, it’s known as a meteor), it begins to heat up and glow — hence why meteors are nicknamed “shooting stars”.

Larger meteors (at least tens of centimetres across) glow brightly enough to be termed “fireballs”. And by training cameras on the sky to spot them, we can track and recover any resulting meteorites.

The largest such network is the Desert Fireball Network, which features around 50 cameras covering more than 2.5 million square kilometres of the Australian outback.

The network’s data has resulted in the recovery of six meteorites in Australia, and two more internationally. What’s more, by tracking a fireball’s flight through the atmosphere, we can not only project its path forwards to find where it landed, but also backwards to find out what orbit it was on before it got here.

Orbital data of debris in the inner Solar System detected by the Desert Fireball Network between 2014-2020.

Our research, published in The Planetary Science Journal, scoured every fireball tracked by the DFN between 2014 and 2020, in search of possible cometary meteorites. In total, there were 50 fireballs that came from comet-like orbits not associated with a meteor shower.

Unexpectedly, despite the fact that just under 4% of the larger debris was from comet-like orbits, none of the material featured the hallmark “dirty snowball” chemical composition of true cometary material.

A meteorite fragment recently found in the Cotswolds town of Winchcombe. Researchers at Curtin University worked with collaborators in the UK to help recover this rare carbonaceous meteorite.

We concluded that debris from comets breaks up and disintegrates before it even gets close to becoming a meteorite. In turn, this means cometary meteorites are not represented among the tens of thousands of objects in the world’s meteorite collections.

The next question is: if all meteorites are asteroidal, how did some of them end up in such weird, comet-like orbits?

For this to be possible, debris from the main asteroid belt must have been knocked from its original orbit by a collision, close gravitational encounter, or some other mechanism.

Meteorites have given us our most profound insights into the formation and evolution of our solar system. However, it is now clear that these samples represent only part of the whole picture. It is definitely an argument for a sample-return mission to a comet. It’s also testament to the knowledge we can gain from tracking fireballs and the meteorites they sometimes leave behind.The Conversation

Patrick M Shober, Planetary Science PhD Candidate, Curtin University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

China’s Tiangong space station: what it is, what it’s for, and how to see it

China Manned Space Engineering Office

Paulo de Souza, Griffith UniversityChina’s space program is making impressive progress. The country only launched its first crewed flight in 2003, more than 40 years after the Soviet Union’s Yuri Gagarin became the first human in space. China’s first Mars mission was in 2020, half a century after the US Mariner 9 probe flew past the red planet.

But the rising Asian superpower is catching up fast: flying missions to the Moon and Mars; launching heavy-lift rockets; building a new space telescope set to fly in 2024; and, most recently, putting the first piece of the Tiangong space station (the name means Heavenly Palace) into orbit.

What is the Tiangong space station?

Tiangong is the successor to China’s Tiangong-1 and Tiangong-2 space laboratories, launched in 2011 and 2016, respectively. It will be built on a modular design, similar to the International Space Station operated by the United States, Russia, Japan, Canada and the European Space Agency. When complete, Tiangong will consist of a core module attached to two laboratories with a combined weight of nearly 70 tonnes.

The core capsule, named Tianhe (Harmony of Heavens), is about the size of a bus. Containing life support and control systems, this core will be the station’s living quarters. At 22.5 tonnes, the Tianhe capsule is the biggest and heaviest spacecraft China has ever constructed.

The Tianhe module will form the core of the space station, with other modules to be added later to increase the size of the station and make more experiments possible.
Saggitarius A / Wikimedia, CC BY-SA

The capsule will be central to the space station’s future operations. In 2022, two slightly smaller modules are expected to join Tianhe to extend the space station and make it possible to carry out various scientific and technological experiments. Ultimately, the station will include 14 internal experiment racks and 50 external ports for studies of the space environment.

Tianhe will be just one-fifth the size of the International Space Station, and will host up to three crew members at a time. The first three “taikonauts” (as Chinese astronauts are often known) are expected to take up residence in June.

Read more:
How to live in space: what we’ve learned from 20 years of the International Space Station

A troubled launch

Tianhe was launched from China’s Hainan island on April 29 aboard a Long March 5B rocket.

These rockets have one core stage and four boosters, each of which is nearly 28 metres tall - the height of a nine-storey building - and more than 3 metres wide. The Long March 5B weighs about 850 tonnes when fully fuelled, and can lift a 25-tonne payload into low Earth orbit.

During the Tianhe launch, the gigantic core stage of the rocket – weighing around 20 tonnes – spun out of control, eventually splashing down more than a week later in the Indian Ocean. The absence of a control system for the return of the rocket to Earth has raised criticism from the international community.

Read more:
A giant piece of space junk is hurtling towards Earth. Here’s how worried you should be

However, these rockets are a key element of China’s short-term ambitions in space. They are planned to be used to deliver modules and crew to Tiangong, as well as launching exploratory probes to the Moon and eventually Mars.

Despite leaving behind an enormous hunk of space junk, Tianhe made it safely to orbit. An hour and 13 minutes after launch, its solar panels started operating and the module powered up.

Completion and future

Tianhe is now sitting in low-Earth orbit (about 400km above the ground), waiting for the first of the ten scheduled supply flights over the next 18 months that it will take to complete the Tiangong station.

A pair of experiment modules named Wentian (Quest for Heavens) and Mengtian (Dreaming of Heavens) are planned for launch in 2022. Although the station is being built by China alone, nine other nations have already signed on to fly experiments aboard Tiangong.

How to see the Tiangong space station

Tianhe is already visible with the naked eye, if you know where and when to look.

A video shot from New Zealand shows the tumbling chunk of rocket from Tianhe’s launch, followed by the bright dot of the space station module itself.

To find out when the space station might be visible from where you are, you can check websites such as, which show you the station’s current location and its predicted path for the next 10 days. Note that these predictions are based on models that can change quite quickly, because the space station is slowly falling in its orbit and periodically boosts itself back up to higher altitudes.

The station orbits Earth every 91 minutes. Once you find the time of the station’s next pass over your location (at night – you won’t be able to see it in the daytime), check the direction it will be coming from, find yourself a dark spot away from bright lights, and look out for a tiny, fast-moving spark of light trailing across the heavens.The Conversation

Paulo de Souza, Professor, Griffith University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Climate explained: how particles ejected from the Sun affect Earth’s climate

Earth’s magnetic field protects us from the solar wind, guiding the solar particles to the polar regions.

Annika Seppälä


Climate Explained is a collaboration between The Conversation, Stuff and the New Zealand Science Media Centre to answer your questions about climate change.

If you have a question you’d like an expert to answer, please send it to

When the Sun ejects solar particles into space, how does this affect the Earth and climate? Are clouds affected by these particles?

When we consider the Sun’s influence on Earth and our climate, we tend to think about solar radiation. We are acutely aware of the skin-burning dangers of ultraviolet, or UV, radiation.

But the Sun is an active star. It also continuously releases what is known as “solar wind”, made up of charged particles, largely protons and electrons, that travel at speeds of hundreds of kilometres per hour.

Some of these particles that reach Earth are guided into the polar atmosphere by our magnetic field. As a result, we can see the southern lights, aurora australis, in the southern hemisphere, and the northern equivalent, aurora borealis.

Aurora Australis
Aurora australis observed above southern New Zealand.

This visible manifestation of solar particles entering Earth’s atmosphere is a constant reminder there is more to the Sun than sunlight. But the particles have other effects as well.

Read more:
Why is the sun’s atmosphere so hot? Spacecraft starts to unravel our star’s mysteries

Solar particles and ozone

When solar particles enter the atmosphere, their high energies ionise neutral atmospheric nitrogen and oxygen molecules, which make up 99% of the atmosphere. This “energetic particle precipitation”, named because it’s like a rain of particles from space, is a major source of ionisation in the polar atmosphere above 30km altitude — and it sets off a chain of reactions that produces chemicals that facilitate the destruction of ozone.

The impact of solar particles on atmospheric ozone was first observed in 1969. Since the early 2000s, thanks to new kinds of satellite observations, we have seen growing evidence that solar particles play an important part in influencing polar ozone. During particularly active times, when the Sun releases large amounts of particles into space, up to 60% of ozone at altitudes above 50km can be depleted. The effect can last for weeks.

Lower down in the atmosphere, below 50km, solar particles are important contributors to the year-to-year variability in polar ozone levels, often through indirect pathways. Here, solar particles again contribute to ozone loss, but a recent discovery showed they also help curb some of the depletion in the Antarctic ozone hole.

How ozone affects the climate

Most of the ozone in the atmosphere resides in a thin layer at altitudes of 20-25km — the “ozone layer”.

But ozone is everywhere in the atmosphere, from the Earth’s surface to altitudes above 100km. It is a greenhouse gas and plays a key role in heating and cooling the atmosphere, which makes it critical for climate.

In the southern hemisphere, changes in polar ozone are known to influence regional climate conditions.

Satellite image of Earth's atmosphere
Solar particles ionise nitrogen and oxygen molecules in the atmosphere, which leads to other chemical reactions that contribute to ozone destruction.

Its depletion above Antarctica had a cooling effect, which in turn pulled the westerly wind jet that circles the continent closer. As the Antarctic hole recovers, this wind belt can meander further north and affect rainfall patterns, sea-surface temperatures and ocean currents. The Southern Annular Mode describes this north-south movement of the wind belt that circles the southern polar region.

Ozone is important for future climate predictions, not only in the thin ozone layer, but throughout the atmosphere. It is crucial we understand the factors that influence ozone variability, be it man-made or natural like the Sun.

The Sun’s direct influence

The link between solar particles and ozone is reasonably well established, but what about any direct effects solar particles may have on the climate?

We have observational evidence that solar activity influences regional climate variability at both poles. Climate models also suggest such polar effects link to larger climate patterns (such as the Northern and Southern Annular Modes) and influence conditions in mid-latitudes.

The details are not yet well understood, but for the first time the influence of solar particles on the climate system will be included in climate simulations used for the upcoming Intergovernmental Panel on Climate Change (IPCC) assessment.

Read more:
Solar weather has real, material effects on Earth

Through solar radiation and particles, the Sun provides a key energy input to our climate system. While these do vary with the Sun’s 11-year cycle of magnetic activity, they can not explain the recent rapid increase in global temperatures due to climate change.

We know rising levels of greenhouse gases in the atmosphere are pushing up Earth’s surface temperature (the physics have been known since the 1800s). We also know human activities have greatly increased greenhouse gases in the atmosphere. Together these two factors explain the observed rise in global temperatures.

What about clouds?

Clouds are much lower in the atmosphere than where most solar particles penetrate. Particles know as galactic cosmic rays (coming from the centre of our galaxy rather than the Sun) may be linked to cloud formation.

It has been suggested cosmic rays could influence the formation of condensation nuclei, which act as “seeds” for clouds. But recent research at the CERN nuclear research facility suggests the effects are insignificant.

This doesn’t rule out some other mechanisms for cosmic rays to affect cloud formation, but thus far there is little supporting evidence.The Conversation

Annika Seppälä, Senior Lecturer in Geophysics

This article is republished from The Conversation under a Creative Commons license. Read the original article.