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The Truth, the Hole Truth…

5 Jul

In October 2009, an otherworldly cloud formation appeared over Moscow. The Sun (the newspaper, not the yellow ball in the sky) promptly announced the appearance of a ‘mystery UFO halo’ and, before too long, internet message boards were awash with rumours of alien motherships and Russian weather weapons.

But sadly, this strange phenomenon is not the work of some little green men: a new study published in Science this week explains how these ‘hole punch clouds’ are created by aeroplanes, not UFOs, zipping through the sky.

The holey cloud formation over Moscow in October 2009 (left), nothing to do with little green men (right)

How to make a holey cloud

There are two key ingredients required for a holey cloud: supercooled water and a sudden temperature drop.

Supercooled water is water that seems to defy the laws of nature by remaining liquid at sub-zero temperatures. This happens in clouds at temperatures between 0 and -40°C when the surrounding air is so pure that no ice nuclei (e.g. dust particles) are present (the water droplets cannot crystallise).

However, a sudden drop in cloud temperature may help to kick-start ice formation. An aircraft can provide this cooling when it flies through a cloud, via air expansion behind the propeller tips or airflow over the wings.

A couple of hole punch clouds, observed over Antarctica (top) and Alabama (bottom). Credit: Eric Zrubek and Michael Carmody / Alan Sealls

The introduction of ice into a supercooled cloud triggers a domino effect of rapid ice formation, known in the meteorology world as the Bergeron-Findeisen process. When the ice becomes too heavy to remain in the cloud, it falls to the ground as snow, leaving behind a void. Et voilà…a holey cloud.

A hole new world

In their Science study, Andrew Heymsfield and colleagues from the National Centre for Atmospheric Research (NCAR in Colorado, USA) investigated satellite images of a holey cloud layer over Texas.

In total, 92 holes were spotted, produced by a wide variety of aircraft, including large passenger jets, military jets and turboprop aeroplanes. A typical hole grew for an hour after it was first detected, up to a maximum length of over 100 km in some cases (larger than the distance between London and Brighton). Several holes remained in the sky for more than four hours.

Unlike Heymsfield et al., Totoro and friends failed to notice the whopping great hole punch clouds floating around them (disclaimer: this image may have been photoshopped)

The scientists then used a computer model, configured to match the weather conditions in the Texas satellite observations, to show that there is more to holey clouds than previously thought.

They found that adding ice particles to the simulated cloud released latent heat, a form of energy associated with water changing state (e.g. from liquid to solid). This created updrafts near the hole centre that suspended the ice, allowing the hole to grow. Meanwhile, compensating downdrafts on the outer edges of the hole accelerated the evaporation of liquid water, causing the hole to widen rapidly.

Snow, glorious snow

And because cloud holes are often associated with snow, they can spell bad news for travellers, air traffic controllers, and people with an irrational fear of snowmen. Heymsfield and colleagues estimate that there is as much as a 6% probability of aircraft triggering ice formation near major airports.

If this happened during wintertime months, it could lead to rerouted flights, frantic de-icing, and grumpy passengers. Still, cloud spotters would argue that cranky holidaymakers are a small price to pay for these celestial beauties.

Based on an article written for Cosmos magazine.

This post was chosen as an Editor's Selection for ResearchBlogging.orgHeymsfield, A., Thompson, G., Morrison, H., Bansemer, A., Rasmussen, R., Minnis, P., Wang, Z., & Zhang, D. (2011). Formation and Spread of Aircraft-Induced Holes in Clouds Science, 333 (6038), 77-81 DOI: 10.1126/science.1202851

Extinction Poems

2 May

The Feral Theatre blog recently published a selection of poems on the topic of extinction, written by students at the South Camden Community School. Here’s a couple of my favourites, about the Steller’s sea cow and the thylacine (animals I hadn’t even heard of before, let alone know that they were extinct!).

Steller’s Sea Cow Speaks

Illustration of Steller's sea cows by F. John, 1902

Nature made me
But I feel as if I’ve lost protection

Nature made me
Yet I feel as if nature itself
doesn’t know who I am

Nature made me
But I’m under constant threat
from those superior to me

Nature made me
Somehow I had this natural feeling
that you too would care enough for me

Nature made me
So I thought you would love me
as your fellow companion

Nature made me
And for my fate there was zero creation
because now it ends.

By Fama, Y10

Eulogy to the Great Thylacine

Thylacine digital collage, by The Contextual Villains

O the great Thylacine
Your stripes are outstanding and worth looking at
Those mighty jaws of yours are very
So much that no-one would dare to look away.

You are your own animal
Nothing can match your unique looks.
You are the mighty king of all animals!
You will always be remembered.

The last Thylacine was killed by a human.
Please don’t take revenge on humans.

By Mahid Sulley and Yasmin Ahmed

Read all of the extinction-themed poems here, with, refreshingly, not a dodo in sight!


24 Jan

Beginning tomorrow (25th January) at London’s National Theatre is a new play, ‘Greenland’, that explores the issues around climate change. According to the website blurb, the production “draws together several separate but connected stories into a fast-paced and provocative new play.” The play was co-written by Moira Buffini, Matt Charman, Penelope Skinner and Jack Thorne, who spent six months researching the topic in the worlds of  science, politics, business and philosophy. A series of events have also been organised in tandem with the production.

Recently, climate change-related art and media projects have been cropping up all over the place – the Nordic RETHINK and British Cape Farewell initiatives are two examples. ‘Climate change theatre’, however, has seemed slow to get going. I guess it can’t be easy to create dramatic tension when the subject of the play is essentially a statistical trend that evolves on (at least) decadal timescales. Nevertheless, this article highlighted a recent spate of green plays that received a good critical response, so maybe it won’t be too long before we see a certain Lloyd Webber soundtracking the collapse of Larsen B.

Projects such as ‘Greenland’ open up new audiences to the big climate debate, and that can only be a good thing. Climate change is probably the area of science that stirs up the most controversy in the public domain. Ironically, it is also one of the topics that scientists most agree on…a study by Anderegg et al. (2010) found that “97–98% of the climate researchers most actively publishing in the field support the tenets of ACC (Anthropogenic Climate Change) outlined by the Intergovernmental Panel on Climate Change.”

This gap between scientific agreement and societal bewilderment is complex (maybe a question for psychologists?). However, scientists are increasingly being encouraged to come down from their ivory towers and communicate their results. After all, the general public’s understanding of climate change is formed by the media, not by specialist studies in scientific journals. Climate controversies such as the ‘Climategate‘ hullabaloo at the University of East Anglia demonstrate how the media can influence the public perception of scientists (and their work).

So hopefully this new play at the National Theatre will get people excited, help switch focus back to the important issues, and ignite some interesting debates. And hopefully the real life climate change drama won’t end up as a tragedy. Performances of ‘Greenland’ run from January 25th – April 2nd 2011.

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