How the Earth’s tilt creates short, cold January days
Deanna Hence, Assistant Professor of Atmospheric Sciences, University of Illinois at Urbana-Champaign
Above the equator, winter officially begins in December. But in many areas, January is when it really takes hold. Atmospheric scientist Deanna Hence explains the weather and climate factors that combine to produce wintry conditions at the turn of the year.
How does the Earth’s orbit influence our daylight and temperatures?
As the Earth orbits the sun, it spins around an axis — picture a stick going through the Earth, from the North Pole to the South Pole. During the 24 hours that it takes for the Earth to rotate once around its axis, every point on its surface faces toward the sun for part of the time and away from it for part of the time. This is what causes daily changes in sunlight and temperature.
There are two other important factors: First, the Earth is round, although it’s not a perfect sphere. Second, its axis is tilted about 23.5 degrees relative to its path around the sun. As a result, light falls directly on its equator but strikes the North and South poles at angles.
When one of the poles points more toward the sun than the other pole, that half of the planet gets more sunlight than the other half, and it’s summer in that hemisphere. When that pole tilts away from the sun, that half of the Earth gets less sunlight and it’s winter there.
Seasonal changes are the most dramatic at the poles, where the changes in light are most extreme. During the summer, a pole receives 24 hours of sunlight and the sun never sets. In the winter, the sun never rises at all.
At the equator, which gets consistent direct sunlight, there’s very little change in day length or temperature year-round. People who live in high and middle latitudes, closer to the poles, can have very different ideas about seasons from those who live in the tropics.
As the Earth orbits the sun, sunlight strikes the surface at varying angles because of the planet’s tilt. This creates seasons.
There’s an old saying, “As the days lengthen, the cold strengthens.” Why does it often get colder in January even though we’re gaining daylight?
It depends on where you are in the world and where your air is coming from.
Earth’s surface constantly absorbs energy from the sun and stores it as heat. It also emits heat back into space. Whether the surface is warming or cooling depends on the balance between how much solar radiation the planet is absorbing and how much it is radiating away.
But Earth’s surface isn’t uniform. Land typically heats up and cools off much faster than water. Water requires more energy to raise and lower its temperature, so it warms and cools more slowly. Because of this difference, water is a better heat reservoir than land — especially big bodies of water, like oceans. That’s why we tend to see bigger swings between warm and cold inland than in coastal areas.
The farther north you live, the longer it takes for the amount and intensity of daylight to start significantly increasing in midwinter, since your location is tilting away from the sun. In the meantime, those areas that are getting little sunlight keep radiating heat out to space. As long as they receive less sunlight than the heat they emit, they will keep getting colder. This is especially true over land, which loses heat much more easily than water.
As the Earth rotates, air circulates around it in the atmosphere. If air moving into your area comes largely from places like the Arctic that don’t get much sun in winter, you may be on the receiving end of bitterly cold air for a long time. That happens in the Great Plains and Midwest when cold air swoops down from Canada.
But if your air comes across a body of water that keeps a more even temperature through the year, these swings can be significantly evened out. Seattle is downwind from an ocean, which is why it is many degrees warmer than Boston in the winter even though it’s farther north than Boston.
How quickly do we lose daylight before the solstice and gain it back afterward?
This depends strongly on your location. The closer you are to one of the poles, the faster the rate of change in daylight is. That’s why Alaska can go from having hardly any daylight in the winter to hardly any darkness in the summer.
Even for a particular location, the change is not constant through the year. The rate of change in daylight is slowest at the solstices — December in winter, June in summer — and fastest at the equinoxes, in mid-March and mid-September. This change occurs as the area on Earth receiving direct sunlight swings from 23.5 N latitude – about as far north of the equator as Miami – to 23.5 S latitude, about as far south of the equator as Asunción, Paraguay.
This satellite view captures the four changes of seasons. On the equinoxes, March 20 and Sept. 20, the line between night and day is a straight north-south line, and the sun appears to sit directly above the equator. Earth’s axis is tilted away from the sun at the December solstice and toward the sun at the June solstice, spreading more and less light on each hemisphere. At the equinoxes, the tilt is at a right angle to the sun and the light is spread evenly.
What’s happening on the opposite side of the planet right now?
In terms of daylight, folks on the other side of the planet are seeing the exact opposite of what we’re seeing. Right now, they’re at the peak of their summer and are enjoying the largest amounts of daylight that they’re going to get for the year. I do research on Argentinian hailstorms and Indian Ocean tropical cyclones, and both of those warm-weather storm seasons are well into their peaks right now.
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But there’s a key difference: The Southern Hemisphere has a lot less land and a lot more water than the Northern Hemisphere. Thanks to the influence of the southern oceans, land masses in the Southern Hemisphere tend to have fewer very extreme temperatures than land in the Northern Hemisphere does.
So even though a spot on the opposite side of the planet from your location may receive exactly as much sunlight now as your area does in summer, the weather there may be different from the summer conditions you are used to. But it still can be fun to imagine a warm summer breeze on the far side of the Earth — especially in a snowy January.
Deanna Hence receives funding from NASA, the National Science Foundation, and the Illinois Campus Research Board.
This article is republished from The Conversation under a Creative Commons license.
New Regency Productions
Conjuring images of snowy landscapes, barren trees, and frigid temperatures, winter weather imparts an instant and identifiable tone. It’s no wonder that a number of key films use this particular season as a constant backdrop. Rarely does the mere use of weather render such an immediate impact as it does when characters are exhaling steam as snow falls in an ever-present blanket around them. Indeed, audiences can practically feel the shivering cold through the screen.
Putting tone aside, winter often plays an even more direct role in the narrative. Films such as “Christmas Vacation” wouldn’t make much sense if they didn’t take place during the holiday season, after all. That’s not to mention the obstructive nature of snow and freezing temperatures in films such as “Cold Mountain,” “Fargo,” and “Force Majeure.” In John Carpenter’s horror classic “The Thing,” which takes place in the heart of Antarctica, the desolate winter weather mirrors the isolation characters face as the film progresses.
Meanwhile, audiences get to wrap themselves in warm blankets and sit next to the fire as they partake in the viewing experience. That makes winter-weather movies all the more appealing, as if they reinforce one’s own sense of comfort. It also helps that a number of these films are just downright great in their own right. Here are 20 of the best.
Stacker compiled a list of 20 great movies set in winter weather. To qualify, the film had to be primarily set in winter and have at least 20,000 votes and a 7.0 user rating on IMDb.
A benchmark of the proto-slasher sub-genre, Bob Clark’s cult classic takes place on a college campus during Christmas break. Against a wintry backdrop, a deranged serial killer stalks a group of sorority sisters. The film was shot on location in Toronto, where temperatures can drop as low as –20°C.
Adapted from the best-selling novel, this Civil War epic follows a wounded soldier (Jude Law) on a journey through perilous mountain terrain. Hostile winter weather is one among the many obstacles standing between the soldier and his wife (Nicole Kidman). Renée Zellweger won an Academy Award for Best Supporting Actress for the role of rugged individualist Ruby Thewes.
David Lean’s sweeping saga spans several decades and chronicles the romance between a Russian physician (Omar Sharif) and a married woman (Julie Christie). Adapted from a controversial novel, it clocks in at over three hours and touches on a number of historical events. Snow and frost provide the predominant backdrop, with a key scene taking place inside a famous ice palace. It won five Academy Awards.
Putting a surrealist spin on modern romance, this beloved dramedy stars Jim Carrey and Kate Winslet as a former couple trying to move past their break-up. In one of the most iconic scenes, they lie upon the cracked ice of a frozen lake while looking up at the stars. The ice itself could be viewed as a metaphor for their respective memories.
An expanse of snow sets the tone for this Coen Brothers classic, set in the midst of a harsh Midwestern winter. What starts as a harebrained kidnapping scheme gives way to a double homicide and other heinous crimes. Pregnant police chief Marge Gunderson (Frances McDormand) contends with cold weather and quirky personalities as she searches for answers. It won two Academy Awards.
A literal avalanche causes figurative disaster in this acclaimed Swedish black comedy from Ruben Östlund. The events unfold during a family ski trip, as the layers peel back on a seemingly happy marriage. It was later remade for American audiences as the critical and commercial dud “Downhill,” starring Julia Louis-Dreyfus and Will Ferrell.
Gifted with magical powers, a new queen accidentally turns her kingdom into a permanent winter wonderland. Hoping to lift the spell, the queen’s sister embarks on an epic adventure. Disney’s computer-animated musical was a blockbuster smash, earning over $1.2 billion at the global box office and spawning a hit sequel.
Auteur Wes Anderson took loose inspiration from the writings of Stefan Zweig when crafting this clever comedy. Set in the 1930s, it welcomes viewers to a lavish hotel perched deep within the snow-capped mountains of Europe. The movie’s unique visual palette was brought to life through a combination of traditional film and advanced digital technologies.
Bill Murray plays to his strengths as sarcastic but likable weatherman Phil Connors in this blockbuster comedy. On assignment in small-town Pennsylvania, Connors is forced to live the same day over and over again. Winter weather functions as both an uncontrollable obstacle and a motif as the story unfolds.
Director Christopher Nolan followed his breakout hit “Memento” with this remake of a 1997 Norwegian thriller. When a teenage girl is murdered in Northern Alaska, two Los Angeles detectives (Al Pacino and Martin Donovan) are called in to help with the investigation. A traumatic event and 24-hour sunlight spurs a bad case of insomnia for one of the detectives, who slowly loses his grip on reality.
This historical drama takes place during Christmas in the year 1183 A.D. and plays loosely on Shakespeare’s “King Lear.” Peter O'Toole stars as King Henry II, who must decide which of his three sons shall inherit the throne. It won three Academy Awards, including Best Actress for Katharine Hepburn in a rare tie.
Driving home from Colorado, author Paul Sheldon (James Caan) veers off an icy road and crashes his car. He’s saved from death by his number one fan (Kathy Bates), who gradually becomes his captor. Stephen King wrote the best-selling novel upon which this film is based, once describing it as an allegory for addiction.
The third installment of the “Vacation” franchise proves that the Griswold family are no less dysfunctional at home than they are on the road. From obnoxious relatives to an impromptu kidnapping, the holiday disasters just keep on coming. Comedy legend John Hughes wrote the screenplay and penned “Home Alone” the following year.
Leonardo DiCaprio went full survivalist when making this historical drama, sleeping in animal carasses and risking hypothermia. It tells the (supposedly) true story of 19th century frontiersman Hugh Glass, who’s left for dead after being mauled by a bear. His path of revenge plays out against a brutal terrain of dangerous weather and people alike. The film won three Academy Awards, including Best Actor for DiCaprio.
Winter is an alienating force and a deadly one, too, in this horror classic, which explores the line between psychological and supernatural terror. While caretaking the secluded Overlook Hotel, a struggling writer (Jack Nicholson) goes insane. It’s based on a novel by Stephen King, who famously took issue with director Stanley Kubrick’s interpretation of the material.
A failed experiment has kicked off the modern ice age in Bong Joon Ho’s futuristic thriller, based on a graphic novel. Aboard a perpetually moving train called the Snowpiercer, humanity’s survivors engage in class warfare. Writing for CinemaBlend, critic Kristy Puchko called it a “deeply beautiful movie, punctuated by edge-of-your-seat thrills and unexpected laughs.”
A critical and commercial disappointment upon its release, John Carpenter’s “The Thing” has since been reappraised as a sci-fi horror classic. The story takes place at a research station in the heart of Antarctica, where omnipresent snow and freezing temperatures are a way of life. With the introduction of a shape-shifting alien comes a deadly game of trust between its human prey. It was adapted from both a famous short story and a previous film.
Swedish auteur Ingmar Bergman often employs a cold and stark tonality, making winter weather a fitting backdrop for his work. This acclaimed drama makes up part of an informal trilogy about faith and takes place on a frigid Sunday. Already questioning his relationship with God, a small-town priest is thrown into further conflict by the love of a woman.
Drawing from stories by Chekhov and Dostoyevsky, this Turkish drama centers on a wealthy hotel owner in a snowy village. Literal storms are matched by metaphorical ones as the story unravels, exploring themes of family struggle and class division. It won both the Palme d'Or and the FIPRESCI Prize at the 2014 Cannes Film Festival.
Jennifer Lawrence delivers a breakout performance in this tense drama, playing destitute Ozark Mountain teen Ree Dolly. To save her family from homelessness, Ree must break with outlaw codes and locate her criminal father. Her subsequent journey plunges straight into the heart of darkness, where potential danger lurks behind every tattered door. The film’s use of cold weather drives home its dreary and despairing vibe.