Predicting disaster: better hurricane forecasts buy vital time for residents

Jeffrey David Kepert, Australian Bureau of Meteorology and Andrew Dowdy, Australian Bureau of Meteorology

Hurricane Irma (now downgraded to a tropical storm) caused widespread devastation as it passed along the northern edge of the Caribbean island chain and then moved northwards through Florida. The storm’s long near-coastal track exposed a large number of people to its force.

At its peak, Hurricane Irma was one of the most intense ever observed in the North Atlantic. It stayed close to that peak for an unusually long period, maintaining almost 300km per hour winds for 37 hours.

Both of these factors were predicted a few days in advance by the forecasters of the US National Hurricane Center. These forecasts relied heavily on modern technology – a combination of computer models with satellite, aircraft and radar data.

Read more: Irma and Harvey: very different storms, but both affected by climate change

Forecasting is getting better

Although Irma was a very large and intense storm, and many communities were exposed to its force, our capacity to manage and deal with these extreme weather events has saved many lives.

There are many reasons for this, including significant construction improvements. But another important factor is much more accurate forecasts, with a longer lead time. When Tropical Cyclone Tracy devastated Darwin in 1974, the Bureau of Meteorology could only provide 12-hour forecasts of the storm’s track, giving residents little time to prepare.

These days, weather services provide three to five days’ advance warning of landfall, greatly improving our ability to prepare. What’s more, today’s longer-range forecasts are more accurate than the short-range forecasts of a few decades ago.

We have also become better at communicating the threat and the necessary actions, ensuring that an appropriate response is made.

The improvement in forecasting tropical cyclones (known as hurricanes in the North Atlantic region, and typhoons in the northwest Pacific) hasn’t just happened by good fortune. It represents the outcome of sustained investment over many years by many nations in weather satellites, faster computers, and the science needed to get the best out of these tools.

Tropical cyclone movement and intensity is affected by the surrounding weather systems, as well as by the ocean surface temperature. For instance, when winds vary significantly with height (called wind shear), the top of the storm attempts to move in a different direction from the bottom, and the storm can begin to tilt. This tilt makes the storm less symmetrical and usually weakens it. Irma experienced such conditions as it moved northwards from Cuba and onto Florida. But earlier, as it passed through the Caribbean, a low-shear environment and warm sea surface contributed to the high, sustained intensity.

In Irma’s case, forecasters used satellite, radar and aircraft reconnaissance data to monitor its position, intensity and size. The future track and intensity forecast relies heavily on computer model predictions from weather services around the world. But the forecasters don’t just use this computer data blindly – it is checked against, and synthesised with, the other data sources.

In Australia, government and industry investment in supercomputing and research is enabling the development of new tropical cyclone forecast systems that are more accurate. They provide earlier warning of tropical cyclone track and intensity, and even advance warning of their formation.

Still hard to predict destruction

Better forecasting helps us prepare for the different hazards presented by tropical cyclones.

The deadliest aspects of tropical cyclones are storm surges (when the sea rises and flows inland under the force of the wind and waves) and flooding from extreme rainfall, both of which pose a risk of drowning. Worldwide, all of the deadliest tropical cyclones on record featured several metres’ depth of storm surge, widespread freshwater flooding, or both.

Wind can severely damage buildings, but experience shows that even if the roof is torn off, well-constructed buildings still provide enough shelter for their occupants to have an excellent chance of surviving without major injury.

By and large, it is the water that kills. A good rule of thumb is to shelter from the wind, but flee from the water. combines weather data from the Global Forecast System, North American Mesoscale and the European Centre for Medium-Range Weather Forecasts to create a live global weather map.

This means that predicting the damage and loss caused by a tropical cyclone is hard, because it depends on both the severity of the storm and the vulnerability of the area it hits.

Hurricane Katrina in 2005 provides a good illustration. Katrina was a Category 3 storm when it made landfall over New Orleans, about as intense at landfall as Australian tropical cyclones Vance, Larry and Yasi. Yet Katrina caused at least 1,200 deaths and more than $US100 billion in damage, making it the third deadliest and by far the most expensive storm in US history. One reason was Katrina’s relatively large area, which produced a very large storm surge. But the other factor was the extraordinary vulnerability of New Orleans, with much of the city below normal sea level and protected by levées that were buried or destroyed by the storm surge, leading to extensive deep flooding.

We have already seen with Hurricane Irma that higher sea levels have exacerbated the sea surge. Whatever happens in the remainder of Irma’s path, it will already be remembered as a spectacularly intense storm, and for its very significant impacts in the Caribbean and Florida. One can only imagine how much worse those impacts would have been had the populations not been forewarned.

The ConversationBut increased population and infrastructure in coastal areas and the effects of climate change means we in the weather forecast business must continue to improve. Forewarned is forearmed.

Jeffrey David Kepert, Head of High Impact Weather Research, Australian Bureau of Meteorology and Andrew Dowdy, Senior Research Scientist, Australian Bureau of Meteorology

This article was originally published on The Conversation. Read the original article.


The secrets of Titan: Cassini searched for the building blocks of life on Saturn’s largest moon

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Cassini captures Saturn’s largest moon, Titan.

Courtney Ennis, La Trobe University

Lakes and seas of liquid methane, rain from hydrocarbon clouds, and evidence of poisonous hydrogen cyanide in the atmosphere of Titan were just some of the discoveries the Cassini probe made of Saturns’s largest moon.

The space probe has now made its final pass of Titan as it heads towards its grand finale plunge into the ringed planet later this week.

Dubbed Cassini’s “goodbye kiss” by NASA, Titan has been the subject of much scrutiny by the probe, with 127 flybys on its 13-year mission exploring the planetary system.

Read more: A look back at Cassini’s incredible mission to Saturn before its final plunge into the planet

One of Cassini’s greatest feats is its contribution to untangling the complicated chemistry of Titan, no doubt one of the more chemically diverse objects in our Solar System.

One last look at Titan on Cassni’s final journey.

We have known for some time that the combination of ultraviolet rays from the Sun and particle bombardment has altered the mainly nitrogen and methane atmosphere over time.

This chemistry has sustained a thick, orange smog layer surrounding the entire body, shrouding Titan’s oceans and landscape from view prior to Cassini’s arrival.

The murky orange disk of Saturn’s moon Titan.
NASA/JPL/Space Science Institute

Probing Titan

With Cassini’s toolkit of advanced sensing instruments – combined with atmospheric sampling by the Huygens probe during its 2005 descent to the surface – the mission has developed a comprehensive picture of Titan’s chemistry.

Touchdown on Titan with the Huygens probe.

Intriguingly, on top of the hundreds of molecules accounted for, chemical models developed here on Earth incorporating Cassini data predict the existence of even more complex material.

Of potential significance to biochemistry, these molecules have evaded observation over the relatively short Cassini mission, being either out of view or present at levels below the detection limits of the equipment.

Even if only formed in small quantities in the atmosphere it is plausible that these life-bearing species have built up on the surface over Titan’s history.
So what are these chemicals and how do they come to be?

This composite image shows an infrared view of Saturn’s moon Titan from Cassini’s flyby in November 2015. The near-infrared wavelengths in this image allow Cassini’s vision to penetrate the haze and reveal the moon’s surface.
NASA/JPL/University of Arizona/University of Idaho

Cyanide snow

Unlike Earth, oxygen atoms are rather scarce in Titan’s atmosphere. Water is locked as surface ice and there appear to be no abundant sources of O₂ gas.

In oxygen’s place, we see nitrogen play a more significant role in Titan’s atmospheric chemistry.

Here, common products of nitrogen reactions are the cyanide family of compounds, of which hydrogen cyanide (HCN) is the simplest and most abundant.

As the numbers of cyanide molecules build up at lower, colder altitudes they form cloud layers of large floppy polymers (tholins) and budding ice aerosols.

As the aerosols descend to the surface, shells of methane and ethane ice form further layers on the exterior. This acts to protect the inner organic material on its descent to the surface before being dispersed in hydrocarbon lakes and seas.

Cassini’s view of Titan’s high northern latitudes in May 2012, the lakes on the left are full of liquid hydrocarbons while those on the top right are only partially filled, or represent saturated ground or mudflat.

Surprisingly it is these cyanide compounds, chemicals closely associated with toxicity and death to Earthly lifeforms, that may actually provide avenues for life-bearing biomolecules to form in space environments.

Some simulations predict that cyanides trapped in ices and exposed to space radiation can lead to the synthesis of amino acids and DNA nucleobase structures – the building blocks of life on Earth.

Excited by these predictions and their implications toward astrobiology, chemists have rushed to explore these reactions in the laboratory.

Synchrotron experiments: Titan-in-a-can

Our contributions to astrochemistry have focused on simulating the atmosphere of Titan and its cyanide haze.

With a specialised gas cell installed at the Australian Synchrotron, we are able to replicate the cold temperatures associated with Titan’s cloud layers.

Cassini’s spectrum view of the southern polar vortex shows a signature of frozen hydrogen cyanide molecules (HCN).
NASA/JPL-Caltech/ASI/University of Arizona/SSI/Leiden Observatory and SRON

By injecting cyanides (the friendlier variety) into our cell we can determine the size, structure and density of Titan aerosols as they grow over time; probing with infrared light from the facility.

These results have provided us with a list of signatures for which we can locate cyanide aerosols using infrared astronomy.

The next step will be to seed these aerosols with organic species to determine if they can be identified in extraterrestrial atmospheres.

Perhaps these signals will act as a beacon for future explorations designed to search for complex organic material in more remote space locations – potentially even on the “giant Earth” exoplanets in distant star systems.

Life off Earth

Space provides us a unique perspective to turn back the pages of chemistry.
Among the planets, moons and stars – and the not quite emptiness between – we can study the initial reactions thought to have started chemistry here on Earth.

Using ever more sensitive telescopes and advanced spacecraft, we have uncovered chemical nurseries – pockets of gas and ice exerted to harsh space radiation – in our Solar System and beyond.

Such cold, icy objects as Titan, the moons of Jupiter, Trans-Neptunian Objects (such as Pluto and other minor bodies in the Kuiper belt and beyond), as well as microscopic interstellar dust particles, all generate higher-order organic molecules from simple chemical ingredients.

Read more: Cloudy with a chance of life: how to find alien life on distant exoplanets

As far as we know, the lack of heat and liquid water precludes life to exist at these worlds.

However, we can look for clues regarding life’s origins on a primitive Earth. Were life-bearing chemicals delivered via comet impact, or made in-house near the early ocean shores or deep sea volcanoes? Observing the chemistry of distant objects could one day provide the answers.

The ConversationThese forays into our chemical history have been enabled by the significant steps we have taken in our exploration of space including, as a glowing example, the resounding success of Cassini’s exploration of Titan.

Courtney Ennis, Research Fellow, La Trobe University

This article was originally published on The Conversation. Read the original article.