This article on weather in science fiction & fantasy is part of the Science in Sci-fi, Fact in Fantasy blog series. Each week, we tackle one of the scientific or technological concepts pervasive in sci-fi (space travel, genetic engineering, artificial intelligence, etc.) with input from an expert. Please join the mailing list to be notified every time new content is posted.
The Expert: Candida Spillard
Candida Spillard obtained her PhD in “Transhorizon Microwave Propagation and its Relationship with Meteorological Conditions” before going on to two decades of research in the field, including pulling together work from all over Europe, part of which re-wrote the standards for radiocommunications from Unmanned Aerial Vehicles. See also her post on radio waves for sci-fi authors.
As a result of this international mingling she can order drinks and say “Cheers” in ten languages. She has been known to explain Bessel functions by sliding a glass of beer across a table.
Weather for Sci-Fi Authors
It is a truth universally acknowledged that an author in possession of a good story should never open with the weather.
Nevertheless, we often find weather as a plot driver. The parched climate of Frank Herbert’s ‘Dune’ underpins the inhabitants’ culture and mindset; the floods and ice-storms provide the drama in ‘The Day After Tomorrow’.
More subtly, we may find weather as a metaphor: the mist in which Hardy’s Tess is lost, or the storms which mirror the passions in Wuthering Heights.
In all these examples and more, weather acts in the tale in much the same way that a character might do.
And like any character, it will have its identity: physical description, goals or motivations – the forces driving it; and back-story – its origins. To portray its character with realism requires some understanding, right from the basics, of all these.
A team of intrepid space explorers have just landed on a planet much like Earth but with two differences: it rotates slowly – making for a very long day – and it has no seasons: every day, all year round, is exactly half daylight and half darkness.
Imagine our team near the planet’s equator. The sun, rising high in the sky, will heat up the ground and, via re-radiation, the lower atmosphere. The hot gases will rise, to be replaced with cooler ones from nearer the poles. This process, replicated over the whole planet, sets up a circulation of air rising at the equator, traveling to one or other pole, there to sink and eventually, traveling from pole to equator, return to start its circuit anew.
The result: everywhere on the planet will be subject, for most of the time, to a cool polar breeze.
Planet Rotation and Wind Flows
But our planet – the earth – is turning relatively rapidly: one eastward revolution every 24 hours. This has two effects on wind flows.
The first is that the wind appears deflected with respect to the land passing underneath it – towards the right in the Northern hemisphere, and the left in the southern. This – the Coriolis Effect – gives rise to the circulation patterns we see around areas of high and low pressure. Wind flows along lines of equal pressure (Isobars) rather than directly from areas of high to low pressure as it would on a non-rotating frame.
The second effect of rotation is to disrupt the atmospheric flow into ‘belts’. Air rising at the equator and flowing to the poles in a single circulation cell would break the law of conservation of angular momentum. Instead belts form, with alternating directions of flow: the faster the planet’s rotation (i.e. shorter its day) the narrower and more numerous the belts. Photographs of our solar system’s Gas Giants (Jupiter and Saturn have roughly ten-hour days) show these belts clearly.
On earth, we have three belts on each hemisphere, dividing the air-flow into six ‘doughnuts’ – the ‘trade winds’ which you likely learned about in Geography at school and which are depicted in loving detail at the UK Met office.
The polar belts, with winds from the North-East and air sinking over the poles, give relatively dry and predictable weather. Rain- and snowfall in Antarctica is so low that it counts as a desert. But Polar weather can also be unstable: ice storms can immobilize ships and disable infrastructure. The nearer to the poles, the more extreme is the variation in the lengths of days through the year (view exact times), with no winter sunlight, and no summer night, at the poles themselves.
The tropical belts, with air rising over the equator and sinking at latitudes 30o North and South, carry the most energy. With much of the tropical region being ocean, and with warm air able to hold more moisture than cold, the rising-air parts of these are the areas on earth where the strongest winds and the heaviest rainfalls occur. Wind speed is characterised on the Beaufort scale, and beyond Force 12 the five Saffir-Simpson categories for hurricanes. Islands and coasts are windier locations than inland, even including mountain summits.
The mid-latitude or Ferrel Cells flow counter to the Polar and Tropical cells, making them unstable by nature and giving rise to more changeable, ‘dynamic’ weather.
Gaze at a weather chart and you’ll see areas of high pressure (Anticyclones) and Lows with their associated fronts. Where the isobars curve around Highs winds are light; the air is stable and tends to be slowly subsiding. Settled conditions, especially over water, can produce particular acoustics, refracting sound causing it to carry long distances and have an echo-like quality. Mirages can occur in these conditions: light is refracted away from the heated air over hot surfaces. There are generally few clouds, but there can be mist or fog.
Air circulating in a depression, cyclone or storm is unstable, flowing in turbulent eddies and generally rising. The eddies, which range in size from tens down to fractions of meters, are felt as gusts in the wind. In the Ferrel cell rain and snow are associated with warm and cold fronts, which used to go by the more poetic names of steer lines and squall lines. The two can be distinguished, from the ground, by observing the types and relative motions of high and low altitude clouds. Cloud formations may allow a character familiar with their location to predict weather over the coming hours or days.
Land and coastal features affect weather. Downwind from hills one finds a ‘rain shadow’ where the air, having been forced upwards into colder layers, has lost much of its moisture. The föhn in the Alps is an extreme example. Similarly, wind coming in from over a cold sea, such as the Pacific off California, will be relatively dry. What little moisture there may be will arrive in the form of mist and fog. Wind coming in from a warm sea such as the Atlantic off the coast of Ireland is more likely to bring rain.
Mountain ranges may add to the weather’s seasonal variations: the Monsoon is partly driven by the fact that air flows round, rather than over, the Himalayas.
Local features may have their own microclimate – a dip may be the first area to experience frost in the autumn, for example, or a particular hill top (such as the appropriately-named Wetherlam in the English Lake District) may sit in its own cloud. This can give rise to local superstitions about a place being ‘cursed’ or ‘blessed’.
Physical and Psychological Effects of Weather
“Above this line exposed flesh freezes in 60 seconds” – this is a genuine piece of legend from a plot of wind chill. The line represents an effective temperature of -60oC and runs from a relatively calm but arctic 9mph at -40oC (-40oF) to a breezy 64 mph at -17oC (0oF). Learn more about wind chill in everybody’s favourite cool country.
Frostbite is damage to the cells caused by lack of circulation or superficial freezing, whereas hypothermia affects the entire body. The weather doesn’t have to be cold for the latter: an unfit person in wet clothes can be hypothermic in temperatures as mild as 15oC (60oF). A hypothermia victim is often confused, and can be the last to be aware of their state.
At the other extreme, heat stress occurs when a body cannot shed enough heat energy. Since we do this by evaporation, we feel damp heat as more uncomfortable than dry. Wet-bulb temperature (i.e. measured by a thermometer wrapped in damp gauze) reflects this: a reading of over 35oC (95oF) makes for a place unliveable by humans without constant technological assistance (such as air-conditioned space suits!).
When oxygen intake is reduced – either because of the nature of our new planet’s atmosphere or because of high altitude here on Earth – to below some 70% of what we are accustomed to (equivalent to some 3000 m/ 10,000 ft above sea level) this will affect our performance, causing confusion and even hallucinations, providing fertile ground for an unreliable narrator…
Weather can exert psychological effects. Long periods of darkness may result in moodiness or depression. The build up to a storm can increase irrational behaviour and sensitivity to pain. Weather may also change what we breathe: wind or rain may stir up particles or pests from the ground.
These last show the extent to which weather can influence mood – so opening a story with the weather, if done well, can set the tone admirably.
And there I must end, because it is a bright, cold morning and the clock
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