Forecasting the Future

Конспект урока

Педагогика и дидактика

The process of compiling and interpreting this data -- in other words, preparing a forecast -- is comparable to assembling a jigsaw puzzle. The more data available, the easier it is to see what's going on in the atmosphere and to know what the weather will do next.



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Lesson 8: Forecasting the Future

Observations, Computer Models, and Weather Satellites

A weather observation tells you what's happing in the atmosphere -- temperature, relative humidity, wind speed, wind direction, precipitation, cloud cover, and atmospheric pressure -- at a specific place and time. It's one small piece of a much larger picture. All across the globe, thousands of observations are made at the same times throughout each day, both by human observers and by automated sensors.

The process of compiling and interpreting this data -- in other words, preparing a forecast -- is comparable to assembling a jigsaw puzzle. The more data available, the easier it is to see what's going on in the atmosphere and to know what the weather will do next.

There are so many pieces to the puzzle that we still can't see the complete picture, which is why you sometimes have to shovel five inches of snow out of your driveway on a supposedly "partly sunny" day. In fact, such a "complete picture" may forever be impossible for human knowledge to grasp, despite technological advances. Still, innovations such as Doppler radar and weather satellites are making forecasts more reliable than ever before.

  •  The National Weather Service installed a grid of Doppler radar stations in the 1990s, replacing an older generation of radar. Radio waves reflect off particles in the air, such as raindrops. Doppler radar can detect where storms are and how fast they're moving.
  •  Geostationary weather satellites orbit the Earth from fixed points over the equator at an altitude of about 22,500 miles. "Geostationary" means that the satellites travel in orbit at the same speed the Earth is rotating beneath them. They provide information about wind, liquid water content, and temperature in clouds thatýallows meteorologists to make better forecasts.
  •  Information from the latest weather observations provides a "snapshot" of the atmosphere at a particular time. All that information is then fed into supercomputers, capable of completing billions of calculations per second. How will all the billions of components in the atmosphere interact with each other? To find out, a computer model takes the current data and runs a simulation of what it anticipates the atmosphere will look like a few minutes later. Repeating the process, the model eventually provides a forecast for the next several days.

Ice Cores, Sediment Deposits, and Tree Rings

Meteorology is the study of what weather's doing right now, right here and an attempt to predict what it will do in the immediate future. Climatology looks at the big picture, deciphering large-scale weather patterns over the course of hundreds or thousands of years.

We have reliable, scientifically calibrated weather observations going back only a century or two, and only from certain parts of the world. That doesn't mean the climate of the past is a complete mystery. If you've ever wondered how scientists know what they're talking about when they say things like, "This was the warmest decade in the last 100,000 years," here's how:

  •  Ice cores. Gasses trapped in the ice of Antarctica and Greenland can tell us a lot about past climates and the composition of the atmosphere. An annual cycle preserves the pattern of the past in the ice. For instance, the ratio of oxygen isotopes -- oxygen-16 and oxygen-18 -- in the ice reveals much about the temperatures of past ages. The evidence shows that carbon dioxide levels were lower during eras with cooler temperatures and expanding ice sheets.
  •  Tree rings. In general, a healthy tree grows a wider ring. For certain types of trees, a wide ring indicates a warmer, moister year. Diseases and pest infestations sometimes can throw a wrinkle into this method of reading the past. But by comparing how historical records match up with tree rings for the past 100 to 200 years, scientists have a sort of Rosetta Stone for decoding the tree rings of past millennia.
  •  Sediment deposits. As a September 2000 article by Constanza Villalba in Weatherwise magazine explains, temperature determines whether the spring thaw is a roar or a trickle. Meltwater that surges with greater force carries larger particles, which then settle on the lakebed. A fine-grained layer of sediment indicates a relatively cool summer that year while a coarse-grained layer is a sign of higher temperatures.

Learn More

See Weather: How it Works and Why it Matters, pages 110 to 111, for an account of how scientists use tree rings to peer into the past.

El Nino and La Nina

In 1997, the phenomenon known as El Niño (Spanish for "the child") was blamed for everything from floods in California to tornadoes in Texas to blizzards in the Midwest. The way El Niño kept showing up in newspaper headlines and casual conversation, you'd think it was responsible for traffic jams and the budget deficit, too.

In an El Niño year, an area of semi-permanent high pressure over the Southern Pacific weakens and the easterly trade winds slacken. Warm water pushes against the coast of South America warming the air above it. As a result, worldwide weather patterns can shift, with unusually heavy rain hitting California while a drought is inflicted on Brazil. An El Niño develops every few years. It transfers enormous quantities of heat from the oceans to the atmosphere.

La Niña refers to a cooling down of the surface waters in the Pacific. Here are some weather trends to keep in mind during En Niño/La Niña years:

  •  The Atlantic Ocean seems to produce fewer hurricanes during El Niño years.
  •  Tornado outbreaks in the "Tornado Alley" section of the United States tend to decrease during El Niño years and increase during La Niña years. A strong subtropical jet stream exists during El Niño years, which may make things stormy in the southern United States in the winter, but also tends to "block" warm, moist tropical air -- a necessary ingredient for thunderstorms and tornadoes -- south of the Gulf of Mexico in the summer.

El Niño and the Oceanic Food Chain

The weather can affect every aspect of our lives, including the economy. In a non-El Niño year, the easterly trade winds push surface waters in the Pacific toward the west, allowing deeper, colder, more nutrient-rich waters to well up from the ocean depths, much to the delight of fish -- and Peruvian fishermen. The warm waters of an El Niño season are not as nutrient-rich and the fish population dwindles

Wrapping Things Up

Weather affects how we dress (a wool sweater on a July afternoon is usually out of the question, except perhaps in New England in 1816), how we spend our weekends (a downpour might change your plans to go on a picnic on Saturday), and many other aspects of our lives. It can change the outcome of ballgames, raise the price of heating oil, make roads slippery, and affect our moods. As the old saying goes, "Everyone talks about the weather . . ."

Here are a few more rules of thumb for predicting the weather from your own back yard. No matter how much the climate may change, you can take some comfort in the fact that the underlying rules that govern weather will always stay the same.

  •  Dew on the grass in the morning probably means that a cool, but mostly sunny day is in store. Dew forms most often when the previous night was clear and fairly dry. This is somewhat surprising at first glance. Dew on the grass requires moisture, so you'd expect it to form when there's high humidity. For dew to appear, though, water vapor in the air must cool enough to condense on the grass. Too much moisture in the air actually helps keep the surface relatively warm at night. The ground cools more on nights that are clear, calm, and dry.
  •  "Flowers smell best before a rain" is a fairly reliable weather proverb. Remember that low pressure results in rising air, releasing odors from the soil. High humidity -- such as when a storm is approaching -- allows water vapor to bind with molecules released by flowers and grasses, making it easier for sensitive cells in our noses to detect them.
  •  The faster the wind is blowing, the more quickly -- and dramatically -- the weather will change. A strong wind indicates sharp pressure differences between one air mass and another.

More on Meteorology

To learn more about weather, or to follow the weather in your area and around the world, there are plenty of resources. Online, you can always check:

  •  The Weather Channel, for latest maps and updates: www.weather.com 
  •  National Weather Service: www.nws.noaa.gov 
  •  Mount Washington Observatory, including archives of the syndicated radio show The Weather Notebook: www.mountwashington.org 
  •  The Weather Doctor: www.islandnet.com 
  •  A good general interest magazine about weather is Weatherwise. For more information see their Web site at www.weatherwise.org.

I hope you enjoyed this introduction to meteorology. Keep watching the sky -- there's a lot going on up there.

Assignment 8: Forecasting the Future

Drawing on what you’ve learned in the previous eight lessons, make your own weather forecast tomorrow morning. Don’t look at the newspaper or the TV weather report. Go outside and observe the temperature, clouds, wind speed, and direction. Is there dew (or it’s frozen equivalent, frost) on the ground? Are the winds backing or veering? If you have a barometer, check that too. Write down all your observations.
Later that same day, perhaps during your lunch break, make another detailed observation of the sky and write down what you see. Compare it to your morning observation and see what has changed in the past few hours. Finally, write down your prediction for tonight and tomorrow. Temperature, wind direction, wind speed, precipitation, cloud cover -- include them all. Once you’ve written down your forecast, you can cheat and see if the TV weather report agrees.
Final reading assignment: Read Chapter 13 of
Weather: How it Works and Why it Matters for a brief, but technical look at El Niño. As a conclusion to this course, I recommend Chapter 2, “Pinwheel,” in Tying Down the Wind.


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