Australian Weather

14 May 2024, 3:01AM UTC

Auroras lit up the skies on the weekend amid one of the strongest geomagnetic storms in years, but did this display impact aeroplanes and the aviation industry?  The spectacular exhibit was the aurora borealis/australis, or northern and southern lights seen in both hemispheres.      Images: Aurora Australis on Saturday, May 11 from Bendleby Ranges, SA (top), source: @bendlebyranges and Ricketts Point, Vic (bottom), source: @dayofthedreamer  These lights are typically only seen in the polar latitudes, but this weekend they were spotted in the Southern Hemisphere as far north as Mackay in Queensland. This was caused by the strongest solar flare and storm seen in over 20 years.  This auroral display was caused by a solar flare and multiple coronal mass ejections (CMEs) which erupted from the sun over a few days last week. Charged particles were then carried from the sun to earth by a solar wind.   When these particles reached earth, they interacted with our planet’s magnetic field and were driven towards the magnetic poles.   In the upper layer of the atmosphere called the ionosphere (90km above the surface) the solar wind collides with oxygen and nitrogen in this layer and produces a colorful display.  The southern lights typically occur between 50 and 800km above the surface, well above the layer of atmosphere that planes typically fly in.   So, do they impact aviation despite occurring well above the flight level?   Yes, space weather events like this can impact aviation communications, navigation and surveillance systems. They can also increase the radiation exposure of aircraft in the air.       Images: Aurora Australis from Virgin plane cockpit on Saturday, May 11. Source: @shelbytillett  The charged particles caused by CMEs can modify the upper layer of earth's atmosphere called the ionosphere, which can impact our technology systems.   High frequency radio communication depends on the ionosphere reflecting radio waves back down to earth.  Satellite communication, navigation and surveillance rely on the transmission of signals through the ionosphere.   According to the Bureau of Meteorology’s space weather department, >Space weather events that modify the density and/or structure of the ionosphere can therefore significantly impact the performance of HF COM, SATCOM and SATNAV systems". While communication and navigation can be impacted by the modification of the ionosphere, the electricity network can also be impacted. The storms can induce currents in power lines, overheating transformers, which can potentially cause power outages.   The strongest geomagnetic storm ever recorded occurred during September 1859, called the Carrington Event. This event caused multiple fires of telegraph systems across Europe and North America.  There have been no reports of negative major impacts of this solar storm, it was merely a spectacular display that captivated people across the world.   Unfortunately, auroras are notoriously difficult to forecast as they need multiple factors to line up for these beautiful lights to occur.  Looking ahead, the sun is nearing its solar maximum, which means we could see more sunspots on the sun's surface this year. This could increase our chance of seeing more spectacular displays in the coming months.

07 May 2024, 11:23PM UTC

Earlier this year destructive thunderstorms and winds equivalent to a category two cyclone lashed Victoria, bending towers and toppling trees and poles.  So, how can thunderstorms damage energy infrastructure, and are these events getting worse?   This event occurred during mid-February 2024, when a strong cold front generated severe thunderstorms and localised wind gusts of 130km/h after a prolonged period of extreme heat. The image below shows a squall line around 1,500km long causing lightning across four states in February.  Image: Himawari-9 satellite image, lightning and radar on Tuesday, February 13 at 3pm AEDT.  The destructive winds were caused by microbursts, which bent towers and toppled trees and poles in Vic, leaving thousands without power.   Image: Damaged transmission towers at Anakie, Source: AAP  Microbursts are a localised column of sinking air (downdraft) within a thunderstorm and is usually less than 4km wide. The cold, heavy air within this downdraft descends rapidly to the surface and then spreads out in all directions as it hits the ground. The image below shows how wind gusts are produced in thunderstorms.    Microbursts can be destructive and cause wind gusts above 100 km/h, which can be a risk for power infrastructure. The force applied to the structure is roughly proportional to the speed squared.  Fierce wind gusts from thunderstorms can:  Knock down trees, which can fall onto power lines  Topple poles  Knock out transmission towers.  Microbursts typically occur during the warmer months of the year and, unfortunately, they can develop rapidly and last for only a short period of time, making them difficult to predict and warn communities about.   Have these thunderstorm events become more severe in Victoria?   The severe thunderstorm season across southern Australia occurs during the warmer months of the year, between November and April.   While thunderstorms are more common across northern Australia, Qld, and NSW, they do occur frequently in the summer months. The map below shows the annual average lightning density in Vic between July 2014 and June 2023, with the most lightning occurring in the northeast high country each year.      Image: Weatherzone’s Total Lightning Network Annual lightning density mean between July 2014 and June 2023.  You can see in the map above that lightning is common to the north of Ballarat near Learmonth and Miners Rest, with the region seeing 37.7 pulses per year. The high country near Benalla and Whitfield recorded an average of 28.1 pulses, Thorpdale in Gippsland saw 24.5 pulses, and Melbourne only 8.2 pulses per year.    Research has shown that the warming climate is increasing the risk of heatwaves and bushfires, which can impact energy infrastructure. Unfortunately, it is unknown how global warming will affect thunderstorms and their associated destructive winds. To research climate change's impact on thunderstorms, we would need quality data that dates back well into history. Unfortunately, detecting lightning is a fairly new phenomena, so a solid climate base to compare data to is not currently existent.   According to the University of Melbourne researchers and Watt Clarity, ‘The evidence we do have suggests continued climate change may potentially increase the risk of extreme winds from thunderstorms. This is partly due to more moist and unstable air, which are essential for thunderstorms to form. We think these conditions could occur more often with climate change, in part because warmer air can hold more moisture.’   Indeed, much of Australia had an unusually stormy summer 2023/24, with Melbourne, Canberra and Brisbane all seeing 5 to 6 extra storm days a season. The map below shows that an unusually high number of thunder days were seen over most of Qld, NSW, SA, Vic, the ACT and Tas during the summer of 2023/24 compared to the average of the most recent nine years.  Image: Thunder day anomalies for summer 2023-24 versus the average thunder days for the nation’s nine most recent summers (2014/15 to 2022/23).