The energy in waves

Blame the Sun. Blame the Sun for all your surfing-related problems—because that giant nuclear fireball, 150 million km (93 million miles) away, is surely to blame.

Like almost everything else on Earth, surfing is solar-powered: the energy that shoots you over the sea comes indirectly from the Sun. And what a lot of energy beams our way: theoretically, up to 1000 watts of solar power per square feet of land. But the interesting thing is not where this energy comes from, but where it goes. Earth’s lopsided tilt means the planet cooks unevenly in sunlight, like a spit-roasting joint we’ve stupidly propped at the wrong angle. The tropical bits can blacken and char to the point of forest fires while the polar caps (for now, at least) stay locked in ice. Because energy likes to even itself out, Earth has a turbulent atmosphere and an equally dynamic ocean. And where the howling winds meet the tumbling water, we get waves. Lots of waves.

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What are waves anyway?

You know the answer to this question both in theory and in practice. In theory, because you can still remember flipping through the pages of your old school textbook: amplitude, wavelength, and frequency—those are officially the measure of waves. Now you’re older and a surfer, and you spend a significant part of your life bouncing up and down the sea surface, waves mean something different: breaking waves make your day. They’re no longer two-dimensional scientific abstractions—wiggly black lines drawn on white paper—but colourful, three-dimensional memories, vividly tied to places and times, burned in your memory till the day you die. Every science book explains waves the same way: as energy in motion, shooting from place to place while the medium (water, air, or whatever it might be) goes nowhere. But every surfer—even every beach-bound wave watcher—knows better than to reduce practical waves to a simple theory. Because, in glorious surfing reality, every wave is slightly different from every other wave that has ever broken in exactly the same place.

The waves surfers care about happen at the interface between the atmosphere and oceans, although they’re not the only waves you’ll find in either the air or the water. High above your head, there are waves shooting through the sky; that’s one of the reasons you’ll sometimes see cool, repetitive patterns formed in clouds (instead of the random lumpy cotton-wool you might be used to). There are also waves that travel deep underwater, but—intriguingly—often visible from high up in space.

How do waves form?

We all know the simple answer is “when the wind blows across the sea”, so the energy that was in the air is systematically transferred to the water. But how does that transfer take place? Is it like stirring a cup of coffee, except with friction from the wind dragging the water surface and tugging it along? It’s not hard to think of all kinds of ways the wind might stir up the water—but what does the science say?

Credit: Wind makes waves, so it's no surprise that the biggest waves are in the windiest places. This image of wave heights around the world was snapped from space by the TOPEX/Poseidon satellite in 1992. The red and yellow areas show that wave hotspots occur in places like the Roaring Forties where the winds are strongest. Photo courtesy of NASA Jet Propulsion Laboratory (public domain).

Imagine the surface of the ocean is flat and glassy with not a wave in sight. Peer close enough and the water-air interface you see is no different from the mirror surface of a pond, where cunning insects float and scamper on invisible skin. Water has surface tension, just like a drum, and if you deform it slightly, the pulling force between neighboring water molecules will spring it rapidly back again. This is the first key bit of science in a glorious sequence of events that build the waves for surfing. Because as the wind starts to blow over water, it creates minuscule ripples called capillary waves, barely a foot high. The water’s own elasticity—surface tension—tries to destroy them immediately by tugging them back into place.

But with a steady wind blowing, it’s already too late: the water surface is roughening up. Now friction kicks in and the wind can get more of a grip, systematically building up the ripples to make wind chop and swell that will eventually clean itself up into perfectly formed surf in a voyage that could last hundreds or thousands of miles. Once waves grow beyond capillary size, surface tension can’t stop them. Now they’re at the mercy of the most persuasive long-range force in the Universe: gravity. Where surface tension does its best to rid the ocean of puny capillary waves, gravity is responsible for wrecking every surfer’s fun by cleaning away the bigger waves: it’s the force that determines the life and death of every ocean wave as it constantly tries to smooth out the sea.

A swell party

If you’ve ever played at making surf in your bored, Sunday afternoon bath-tub, by flipping your hand back and forth in the water, you’ll have figured out that there are three ways to make bigger waves: you can flip your hand faster, further, or for longer. The wind in a storm zone works exactly the same way when it’s making waves. If it blows faster, longer, or over a greater distance (technically called the fetch), it creates bigger waves. Why? Because bigger waves need more energy to create them (you have to lift more water up against the force of gravity, for one thing) and a faster wind blowing for longer, or over a bigger area of sea, is the way to get that energy into the water. That’s one key reason why open coastlines are so much better for surfing. The simple rule is that it takes energy, time, and distance to make great surf. The 20ft waves that delighted southern California surfers in August 2014, courtesy of Hurricane Marie, had had 800 miles to get their act together.

That begs another interesting question: just how big can waves ever be? If a hurricane blew for weeks or months over a long enough fetch of open water, would we get ridiculously big waves? “Yes” is the simple answer, but there’s still a scientific limit to how much waves can grow. Like houses of cards, waves are unstable structures that gravity is determined to collapse, sooner or later—with the added complication that they’re moving in the turbulent interface between the atmosphere and the ocean. Seven decades of oceanographic research has determined that waves don’t build beyond a certain steepness: the ratio of their length (measured between one wave crest and the one following behind) to their height (measured from crest to trough, or maximum to minimum) can never be more than seven to one. Waves break on the shore when the rising slope of the beach (or reef) increases their steepness beyond that critical ratio; out in the open ocean, the same limit applies, and we get white caps forming as gravity forces excessively steep waves into premature collapse.

In practice, when the wind blows across the water in a perfect-surf-creating storm, we reach an equilibrium. The wind keeps on adding more energy to the water, but the waves keep collapsing. At this point, we have what the oceanographers call a fully developed sea. The waves are as big as they’re ever going to get. All they have to do now is get themselves to the shore, where the surfers are waiting.

The birth of surf science

Surfing is essentially a 20th-century invention, and so is surf science. But who first had the idea to turn the wonder of waves into a scribble of mathematics —and why?

Surf science owes its birth to military manoeuvres. The pioneers of surf forecasting, Norwegian oceanographer Harald Sverdrup (head of the famous Scripps Institution) and his young American student Walter Munk, figured out how to predict wave heights from the wind speed, fetch, and duration while working for the US military during World War II. Fortunately, they also had loads of data to test their theory and quickly honed their equations enough to make accurate predictions. Although no-one knew it at the time, this crucial work was used by the Allied forces to select the best days for the famous beach landings. It was first used to pick a calm day for an assault on North Africa on 8 November 1942 and, subsequently, for the D-Day landings in Europe in June 1944. Surfing science, in other words, changed history.

Sverdrup and Munk completed their work in 1943, but it remained classified until after the War, finally appearing in March 1947 as US Navy Hydrographic Office Publication Number 601, “Wind, Sea, and Swell: Theory of Relations for Forecasting”. Later refined and extended by Charles Bretschneider, the revised theory became known as the SMB (Sverdrup, Munk, Bretschneider) model. Though it’s only a basic explanation of how the wind makes waves, it’s still widely referred to today, but it’s now been superseded by decades of more detailed research.

How much energy is there in waves?

It’s worth quantifying the energy in waves for all kinds of practical reasons. From an environmental point of view, it tells us how feasible it is to build things like renewable wave-energy systems—and whether we can harvest more energy from the hidden heat in ocean water (the temperature difference between the ocean surface and its depths) than from its mechanical energy (the back-and-forth, up-and-down movement of water caused by tides and waves). From a surfing point of view, asking this question tells us exactly which waves are rideable and what you can do on them. Everyone knows you can’t catch a small wave on a surfboard (or even a boogie board)—and the simple scientific reason for that is that a rideable wave needs to contain a minimum amount of energy to lift your body against the force of gravity and accelerate you to its own speed.

Go figure

Let’s try to guesstimate how much energy there is in a medium-sized wave crashing down on top of us as we stand in the surf. I must emphasize that this is “back-of-the-envelope” physics and not in any sense rigorous or correct oceanography. It’s what’s technically referred to as “just a bit of fun”! I’m not going to attempt to use the complex equations that are really needed to do this properly. For now, let’s see how far we can get with the kind of basic science we learn at school.

We know the total energy is the sum of the wave’s kinetic energy (because the water is moving) and potential energy (because the crest is lifted up above the mean water level). Let’s not get too bogged down, though: let’s simplify everything as much as we can to the point of basic, school-level physics.

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Suppose we have a 1m width of a wave that closes out completely, with the water coming to an impossible, screeching halt (so effectively it loses all its kinetic and potential energy when it breaks). According to Willard Bascom (one of the founding fathers of surf science), the speed of a decent surfing wave is about 25mph or 11 m/s. For easy sums, let’s assume the wavelength (the distance between one wave peak and the next one) is 2m and the amplitude (the height of the wave) is also 2m, so the volume of water above the mean sea level that we’re interested in (the dark grey bit in the figure is roughly 1 x 1 x 0.6 = 0.6m3 = 600 liters, which weighs about 600kg. Simplifying very greatly indeed (I know, I know… but bear with me), that gives us potential energy of mgh = 600 x 10 x 1 = 6000 joules and kinetic energy of ½mv2 = 300 x 11 x 11 = 37,000 joules, making a grand total of about 43,000 joules—or call it 50 kilojoules to keep things simple. This is a rough estimate of how much useful (non-heat) energy there is per foot of a simple breaking wave—and the actual value is likely to be less than this because of all the simplifications I made (a real wave isn’t this steep; it doesn’t stop completely when it breaks; it has an ever-changing, irregular volume; its total mass is not all concentrated at exactly the same height, and so on).

Catching waves

Do the numbers tell us anything useful? Suppose you weigh 70kg (not including the weight of your board). If you want to travel at 11m/s, you need kinetic energy of ½mv2 = 35 x 11 x 11 = 4235 joules. To ride a meter above the ocean surface, you’ll also need potential energy of mgh = 70 x 10 x 1 = 700 joules, so you’ll need about 5000 joules of energy altogether. Let’s say it takes you 5 seconds to catch the wave. The power your muscles and the wave need to supply for you to start surfing is the total energy needed to be divided by the time it takes, so that makes an average power of about 1000 watts to reach 5000 joules in 5 seconds—as much as a typical clothes washing machine. Could you get that from a 1ft wave? Maybe yes, maybe no. My estimate of about 50 kilojoules was for the total energy in 1ft width of a wave, which sounds like it’s 10 times more than enough—but, remember, you wouldn’t get all that energy from the wave (it keeps moving and doesn’t break) and you’re not tapping into a 1ft width of water (maybe only the width of your board).

Kids, lucky things, can catch smaller waves than adults because they weigh about half as much and they can accelerate faster. The potential and kinetic energy of a surfer are both linearly related to body mass, so if you have less mass, you need correspondingly less energy—making it more likely the wave will sweep you along. By the same token, if a wave is big enough, you can (theoretically) surf it in or on whatever you like.

How exactly does paddling help? If you’re paddling as you catch a wave, you’ve already given your body a certain amount of kinetic energy and momentum, so any oncoming wave has to provide you with less of the total energy you need to get moving: paddling, put very simply, gives you a head-start in terms of kinetic energy and momentum. It doesn’t help you with potential energy: unless you’re lying prone on a bodyboard, you’ve still got to get upright!

But different waves deliver very different force even if they contain the same amount of energy. Why? Waves that break faster produce more force, which is why a plunging wave that closes out in a shore-dump is more dangerous than a wave that peels gradually across its width. Simple physics tells us why: if two waves contain exactly the same amount of energy but one breaks five times faster than the other, it can (theoretically) deliver five times the force (because F=mv/t and if t is five times smaller, f is five times greater).

Please donate

Oceanography is a very important discipline for understanding the oceans, which are essential for all life on Earth and cover the majority of the Earth’s surface.

“Oceanography is extremely multidisciplinary, covering the physics, chemistry, geology and biology of the world’s oceans. No understanding of Earth’s climate or the chemical cycles essential to life is complete without the insights of oceanography.”

I started surfing when I was 12 years old and I have been obsessed with ocean waves ever since. Ever since I first started school I wanted to learn the “birth, life, and death of an oceanic swell.” I started with Meteorology so I could understand the birth of the swell; that is, the storms that create the swells. I am now studying Physical Oceanography to understand swell propagation as well as the surf zone dynamics.

Please help me stay at the University of Hawaii. This past semester I wasn’t able to continue with school due to financial concerns. I have used all my student loans allowed, l and currently looking for grants. You can use paypal (my PayPal is barrjohnm@gmail.com) Anything will help, even $1.00!

When I started school I was 30 years old, and I was completely illiterate! It took many years just to get to college status, but I am proud of all my accomplishments as when I first started school 5/1=5 really confused me, and now I understand partial differential equation (PDEs) and in fact my undergraduate degree of Atmospheric Sciences (Meteorology) pretty much including PDEs all thoroughout the degree, below is a common equation in Meteorology:

If you have ever seen warm or cold fronts on a weather map this is the equation for it. Really cool, right?

As, I said above I have been obsessed with ocean waves ever since I started surfing. My first step was to discover how the waves were formed and now I am studying what happens when they leave their original area.  I will finally study what happens when the ocean waves enter the beach zone and become surf, which will no doubt be the most difficult part of my study.

I am very dedicated to going to graduate school for Physical Oceanography at SOEST at the University of Hawaii, Money is the only thing standing in my way. I am studying by myself at home which is challenging since I just finished my undergraduate degree.

Here are my thoughts on my subset of Physical Oceanography:

Physical Oceanographers

Physical oceanographers apply theory and observation to study the circulation of oceans. As heat, salt, and other dissolved chemicals move through the oceans and into lakes and rivers, these scientists are able to track this movement. They also study tides and waves to see how these things affect the atmosphere and nearby ecosystems. Once the data is collected, physical oceanographers may then build computer simulations that mimic the movement of the ocean.

Job responsibilities of a physical oceanographer include:

  • attempting to lessen the impact on ocean life of pollution carried by currents
  • testing water and soil samples for pH balances
  • studying the sea ice and polar ice sheets to understand the distribution of these features and attempt to preserve them
  • ensuring a balance between the human use of ocean resources and conservation

Climate Change in Hawaii

The Aloha state of Hawaii is located in the middle of the Pacific Ocean, approximately 2,600 miles west of California.

“As the only state in the United States that is an island, Hawaii is unquestionably vulnerable to changes in climate“

Like many islands across the world, Hawaii is susceptible to sea level rises, coastal flooding and a whole host of other impacts caused by climate change. According to the global climate change report on the United States (U.S. climate change report), islands have been experiencing rising air temperatures and sea levels in recent decades. Scientific evidence strongly suggests that these trends are very likely to continue into the foreseeable future.

According to the U.S. climate change report, small islands are considered among the most vulnerable to climate change because extreme events have major impacts on them. Changes in weather patterns and the frequency and intensity of extreme events, sea-level rise, coastal erosion, coral reef bleaching, ocean acidification, and contamination of freshwater resources by salt water are among the impacts small islands face. In addition, the availability of freshwater is likely to be reduced, with significant implications for island communities, economies, and resources.

Climate change and global warming are likely to have adverse potential impacts on Hawaii’s environment, health, economy and natural resources. Sea-level rise explains the disappearance of Whale Skate Island, a small island formerly located in Hawaii’s northwest region. Its disappearance wiped out habitats for birds, turtles and other fish and wildlife. In general, the Northwestern Hawaiian Islands, which are low-lying and therefore at great risk from increasing sea levels, have a high concentration of endangered and threatened species, some of which exist nowhere else. The loss of nesting and nursing habitats is expected to threaten the survival of already vulnerable species, and unusually high temperatures and increased frequency of heat waves could very likely lead to a rise in heat-related deaths, particularly among the elderly, in a situation similar to what befell Europe in 2003, when several thousands more died above normal death rates.

The scientific evidence for sea-level rise is strong and unequivocal. As the U.S. climate change report indicates, “Recent global sea-level rise has been caused by the warming-induced expansion of the oceans, accelerated melting of most of the world’s glaciers, and loss of ice on the Greenland and Antarctic ice sheets. A warming global climate will cause further sea-level rise over this century and beyond.” Based upon data furnished at a presentation given at a National Oceanic and Atmospheric Administration (NOAA) meeting in San Francisco, sea levels are projected to rise three feet along the coast of Oahu during the rest of this century due to global warming. Clearly, islands and other low-lying coastal areas will face increased risk from coastal inundation due to sea-level rise and storm surge, with major consequences for coastal communities, infrastructure, natural habitats, and resources.

Generally, Hawaii’s beaches are not subject to any significant erosion thanks to coral reefs, which act as barriers to incoming waves. With documented warming of the seas, coral reefs will be subject to adverse environmental conditions which are harming their ecosystems, growth and sustainability. Without the protective quality of these coral reefs, which are the source of the island’s white, sandy beaches, Hawaii’s coastline will very likely undergo erosion over time.

According to Next Generation Earth, a group associated with the Earth Institute at Columbia University, the cost of replenishing these beaches to prevent sea-level rise will range anywhere from $350 million to $6 billion. Based upon a study issued by NOAA along with several other government and research agencies, ocean water temperature increases are expected to amplify the frequency and severity of coral-bleaching events. Most of Hawaii’s coral reefs are in fair to good condition, but this status will change for the worse if effective ecosystem management measures are not taken.

According to a United States Geological Survey report, warmer temperatures in Hawaii are having adverse affects on native bird species. Warmer temperatures expand the range of mosquitoes into higher mountain elevations. For birds such as the honeycreeper that live in higher, cooler mountain refuges, this will introduce new stresses and disease vectors into their environment. Without resistance to malaria, honeycreeper birds in their current habitats may face extinction as a result of the spread of mosquitoes and mosquito bites. As ecosystems move and change, other diseases are likely to migrate into regions of warmer temperature. Saving the honeycreepers and other bird species will require active environmental management of those areas they currently inhabit and the elimination or containment of mosquito populations.

Climate change impacts in Hawaii have an economic dimension with effects felt in the tourism industry and fisheries trade. As the U.S. climate change report notes, “coral reefs sustain fisheries and tourism, have biodiversity value, scientific and educational value, and form natural protection against wave erosion. For Hawaii alone, net benefits of reefs to the economy are estimated at $360 million annually, and the overall asset value is conservatively estimated to be nearly $10 billion.” Although further evidence is necessary, warmer seas may also promote toxic algae, leading to harmful algae blooms known as red tides. These blooms are toxic to habitat and shellfish nurseries as well as humans. In addition, clean-up costs must be taken into consideration.

Any environmental problems or disasters may have a net negative effect on Hawaii’s tourism industry, as tourists will be dissuaded from visiting an unstable, environmentally risky destination. In 2008, over 6.8 million visitors came to Hawaii and spent $11.4 billion, which accounted for 18% of Hawaii’s gross domestic product. Sea-level rises and flooding contribute to submergence of beaches, and that will be a factor Hawaii policymakers must grapple with in planning the future of Hawaiian tourism. In recent decades, as sea levels have risen and more beaches have overflowed with seawater, more sea walls have been built along the famous Waikiki beachfront to stem the rise in ocean levels. As a possible consequence, many affected parts of the islands may experience declines in real estate values.

Unlike many small, developing island nations, as part of the United States, Hawaii has the capacity and resources to mount a credible defense against environmental impacts caused by climate change. Hawaii has exhibited foresight in anticipating climate change impacts. In 1998, the state issued a lengthy report on the effects of climate change on the islands. Recommendations and action plans to improve energy efficiency and reduce greenhouse gas emissions over a broad range of industries were included in the report. Hawaii is proactive and has positioned itself to combat climate change and reduce greenhouse gas emissions.

In 2007, Hawaii enacted “A Global Warming Solutions Act 234″ to cap greenhouse gas emissions to the 1990 level by 2020. In 2008, Hawaii launched a Clean Energy Initiative with the goal of creating a 70 percent clean-energy economy within a generation. As a result of its location and lack of fossil fuel resources, Hawaii is the most oil-dependent state in the nation, getting 90 percent of its energy needs from imported oil. In a memorandum of understanding signed in 2008, the Department of Energy (DOE) will assist Hawaii to achieve the goal of reducing its dependence on oil for electricity generation.

Hawaii has at its disposal a plethora of renewable energy options to transition to a renewable energy economy including biomass, hydro, wind, geothermal, ocean waves and, of course, solar. In its favor, Hawaii emits only 0.4 percent of the total U.S. greenhouse gas emissions and is therefore one of the lowest state emitters in the country. Hawaii is also part of the EPA’s Clean Energy State Partnership Initiative to support the introduction and use of clean, renewable energy. The Sierra Club reports that Hawaii also recently imposed a $1 surcharge on each barrel of oil imported into the state. Funds collected here will be earmarked for the development of clean, renewable energy. Last but not least, the Governor of Hawaii, Linda Lingle, recently signed an energy bill into law mandating that 25 percent of Hawaii’s electricity must come from renewable energy sources by 2020 and 40 percent by 2030.

The scientific evidence for climate change in Hawaii is strong. Rising sea levels and temperatures are increasingly affecting coastal areas, natural habitats, and will potentially have harmful effects on human health and the economy. To spotlight the severity of the problem with climate change and rising sea levels, the President of the Maldives, Mohamed Nasheen, recently conducted an underwater cabinet meeting to point out one possible future scenario for island nations if little or no action is taken to deal with climate change. With foresight and planning, Hawaii is taking appropriate steps to adapt to changing conditions, strengthen its natural defenses and mitigate future climate troubles. It is highly unlikely that Hawaii would have to take the astonishing step of performing an instance of official government business underwater like the Maldives to bring awareness of the issue to a wider global audience. Given its global impact, the warming of the oceans and other climate changes are obviously beyond the sole control of the state and will present continuous challenges well into the foreseeable future. In this sense, Hawaii shares vulnerability with other small island nations in that its environmental resilience and destiny is as much determined by its own actions as it is dependent upon the actions of others in other parts of the world.

The Jet Stream

What It Is and How It Affects Our Weather

You’ve probably heard the words “jet stream” many times while watching weather forecasts on TV. That’s because the jet stream and its location is key to forecasting where weather systems will travel. Without it, there would be nothing to help “steer” our daily weather from location to location.

Rivers of Rapidly Moving Air 

Named for their similarity to fast-moving jets of water, jet streams are bands of strong winds in the upper levels of the atmosphere. Jet streams form at the boundaries of contrasting air masses. When warm and cold air meet, the difference in their air pressures as a result of their temperature differences (recall that warm air is less dense, and cold air, more dense) causes air to flow from higher pressure (the warm air mass) to lower pressure (the cold air mass), thereby creating high winds. Because the differences in temperature, and therefore, pressure, are very large, so too is the strength of the resulting winds.

Jet Stream Location, Speed, Direction 

Jet streams “live” at the tropopause (about 6 to 9 miles off the ground) and are several thousand miles long. Jet stream winds range in speed from 120 to 250 mph but can reach more than 275 mph. Oftentimes, the jet houses pockets of winds that move faster than the surrounding jet stream winds. These “jet streaks” play an important role in precipitation and storm formation. (If a jet streak is visually divided into fourths, like a pie, its left front, and right rear quadrants are the most favorable for precipitation and storm development. If a weak low-pressure area passes through either of these locations, it will quickly strengthen into a dangerous storm.)

Jet winds blow from west to east, but also meander north to south in a wave-shaped pattern. These waves and large ripples (known as planetary, or Rossby waves) form U-shaped troughs of low pressure that allow cold air to spill southwards and upside-down U-shaped ridges of high pressure that bring warm air northwards.

Discovered by Weather Balloons 

One of the first names associated with the jet stream is Wasaburo Oishi. A Japanese meteorologist, Oishi discovered the jet stream in the 1920s while using weather balloons to track upper-level winds near Mount Fuji. However, his work went unnoticed outside of Japan. In 1933, knowledge of the jet stream increased when American aviator Wiley Post began exploring long-distance, high-altitude flight. Despite these discoveries, the term “jet stream” was not coined until 1939 by German meteorologist Heinrich Seilkopf.

Meet the Polar and Subtropical Jets 

While we typically talk about the jet stream as if there was only one, there are actually two: a polar jet stream and a subtropical jet stream. The Northern Hemisphere and the Southern Hemisphere each have both a polar and a subtropical branch of the jet.

  • The Polar Jet: In North America, the polar jet is more commonly known as “the jet” or the “mid-latitude jet” (so-called because it occurs over the mid-latitudes).
  • The Subtropical Jet: The subtropical jet is named for its existence at 30°N and 30°S latitude—a climate zone known as the subtropics. It forms at the boundary temperature difference between air at mid-latitudes and warmer air near the equator. Unlike the polar jet, the subtropical jet is only present in the wintertime—the only time of year when temperature contrasts in the subtropics are strong enough to form jet winds.

The subtropical jet is generally weaker than the polar jet. It is most pronounced over the western Pacific.

Jet Position Changes With the Seasons 

Jet streams change position, location, and strength depending on the season.

In the winter, areas in the Northern Hemisphere may get colder than normal periods as the jet stream dips “lower” bringing cold air in from the polar regions. Although the height of the jet stream is typically 20,000 feet or more, the influences on weather patterns can be substantial as well. High wind speeds can drive and direct storms creating devastating droughts and floods. A shift in the jet stream is a suspect in the causes of the Dust Bowl.

In spring, the polar jet starts to journey north from its winter position along the lower third of the U.S., back to its “permanent” home at 50-60°N latitude (over Canada). As the jet gradually lifts northward, highs and lows are “steered” along its path and across the regions where it’s currently positioned. Why does the jet stream move? Well, jet streams “follow” the Sun, Earth’s primary source of heat energy. Recall that in spring in the Northern Hemisphere, the Sun’s vertical rays go from striking the Tropic of Capricorn (23.5° south latitude) to striking more northerly latitudes (until it reaches the Tropic of Cancer, 23.5° north latitude, on the summer solstice). As these northerly latitudes warm, the jet stream, which occurs near boundaries of cold and warm air masses, must also shift northward to remain at the opposing edge of warm and cool air.

Locating Jets on Weather Maps 

On surface maps: Many news and media that broadcast weather forecasts show the jet stream as a moving band of arrows across the U.S., but the jet stream isn’t a standard feature of surface analysis maps.

Here’s an easy way to eyeball the jet position: since it steers high and low-pressure systems, simply note where these are located and draw a continuous curved line in-between them, taking care to arch your line over highs and underneath lows.

On upper-level maps: The jet stream “lives” at heights of 30,000 to 40,000 feet above Earth’s surface. At these altitudes, atmospheric pressure equals around 200 to 300 mb; this is why the 200 and 300 mb level upper air charts are typically used for jet stream forecasting.

When looking at other upper-level maps, the jet position can be guessed by noting where pressure or wind contours are spaced close together.

Quantum Physics and Surf Forecasting

At the moment the wave charts are not looking too epic. However, in about a week’s time things are due to improve as the general situation over the North Pacific  changes.

“That’s all I can say. Why? Because the best way to look at the long-term charts is to just get a general picture and not try to be too specific; otherwise you’ll be frustrated when the forecast keeps changing.”

Forecasting is a trade-off between three parameters: precision, accuracy and length. If we want a really detailed forecast it needs to be short-term; otherwise it won’t be accurate. Likewise, if we want an accurate long-term forecast we mustn’t specify too many details.

As our understanding of the atmosphere and ocean improves, and computing power increases, forecasts will, of course, get better. But there are several reasons why they will never be perfect: the most fundamental of which has to do with their dependence on initial conditions.

Atmospheric and oceanic prediction models rely on initial measured values of parameters such as pressure, windspeed and temperature. The more accurate these measurements are, the better the prediction will be.

The ocean-atmosphere system is highly complex and behaves in a non-linear way, with feedback loops, tipping points and snowball effects. Any slight errors in the initial measurements will not only feed through to the end result, but will be amplified. As the forecast length increases, so does the amplification of errors, so that the forecasts end up diverging uncontrollably.

So, all we need to do to get that perfect forecast is to measure those initial conditions perfectly. In fact, this is what the great French physicist Pierre-Simon Laplace (1749-1827) had in mind. He postulated that, if we could somehow measure the exact position and velocity of every particle in a system, we could use Newton’s laws of motion to predict their next position and velocity, and the next, and so on. As long as we knew the present, we could predict the future

Laplace’s hypothesis – called determinism – was proved wrong about a century later. Scientists like Werner Heisenberg (1901-1976) started discovering the paradoxes of quantum mechanics, one of which is that you cannot measure the position and velocity of a particle at the same time.

This means you can never describe the present state of anything with 100 per cent accuracy. And if you can’t describe the present state with total accuracy, you’ll never be able to make an error-free prediction of the future.

So, bearing in mind that there are inevitably going to be errors, the best thing we can do is to know how precise to be, and when. The MSW ‘probability’ parameter helps us do that by giving us an idea of how confident we can be of a particular forecast. You’ll notice that it doesn’t just change with forecast length – but I’ll talk more about that in a future article.