The atmosphere is a layer of gasses that surrounds a planet. On Earth, the distance from the surface to the upper levels of the atmosphere is only about 97 kilometers (60 miles). While that may not sound like it is too far, imagine trying to observe a baseball game from that distance. It would be virtually impossible. That's why scientists need accurate and precise instruments to understand what happens there.
Thermometers and Barometers
One of the first pieces of technology ever used to observe the atmosphere was the thermometer, invented in Italy in the 1590s by Galileo Galilei. He designed a glass tube with a hollow bulb at one end. Galileo held the bulb end in his hands, allowing it to heat up, and then turned the device upside-down, tube end first, into a basin filled with water. The water then rose into the tube relative to the temperature of the surrounding air. Colder air made the water rise higher into the glass. Warm water did the opposite. In 1612, another Italian scientist improved upon Galileo's thermometer design by adding a number scale so that temperatures could be read.
Roughly 50 years later, one of Galileo's apprentices, Evangelista Torricelli, created the barometer—an instrument that measures the air pressure. Air pressure is the weight of the atmosphere pressing down on a location. Today, many scientists, including meteorologists, use barometers. They use air pressure readings to determine whether the atmosphere is stable (under high air pressure) or stormy (influenced by low air pressure).
We need thermometers, barometers, and other instruments to understand the conditions in the part of the where humans live. But what if scientists want to explore how the atmosphere might act hours or days into the future, or in another part of the world? For this, scientists depend on remote-sensing instruments. These are tools that obtain information from some distance away.
High in the atmosphere, the temperatures are below zero and the air is thin. Scientists have developed instruments that can collect observations in these conditions. One such instrument is the weather balloon, which floats to lofty heights while a device called a radiosonde follows close behind. As the radiosonde rises, its internal sensors measure temperature, pressure, and humidity. Every two seconds, a radio transmitter within the device relays this data back to scientists. They use this data (along with wind speed and wind-direction data, which are calculated by tracking the radiosonde's position) to create weather forecasts.
A weather balloon can only travel about 32 kilometers (20 miles) up from the surface, measuring data for only a third of the atmosphere. Above that height, the atmosphere's decreasing air pressure causes the balloon to rise and expand outward until it pops. To collect data at higher altitudes, scientists turn to satellites.
Weather Satellites and Radar
In the 1960s, NASA launched TIROS I, the nation's first weather satellite. Today, weather satellites continuously circle our planet hundreds of kilometers above its surface and are one of the most effective tools for studying Earth. From these locations, satellites are able to "see" atmospheric events around the globe. Not only do satellites collect data and relay it from space back to Earth's surface, they also capture images of what they see.
Satellites monitor clouds, lightning, snow, ice, and hurricanes. But they can also measure other events, such as wildfires, volcanoes, ocean temperatures, and solar flares. Satellites also assist scientists in monitoring the atmosphere's chemistry, such as ozone and air-pollution levels, and greenhouse-gas concentrations.
Radar is another form of technology that captures images of the atmosphere. Unlike weather balloons and satellites, which scan the atmosphere from above, radar works by scanning it from the ground. Radar sends out pulses of energy called radio waves and sees how the waves interact with objects in the air. This reveals the location of rain, snow, and other types of precipitation.
One kind of radar, called Doppler radar, can detect a storm's location and its movement too. It can tell whether a storm is approaching or moving out of a specific area. It can also see rotation, a sign of possible tornadoes.
You have likely heard meteorologists mention weather models when discussing the weather forecast. A weather model is essentially a computer program that uses data and math to make estimates and assumptions to predict the weather. As data, such as temperature, humidity, or pressure, is fed into the weather models the computer creates a model that predicts what will happen some time in the future. They can do this at speeds of quadrillions of calculations per second, weeks faster than can be done by hand. The model approximates what the atmosphere is likely to do before it actually does it.
Today's technologies allow us to explore the atmosphere in extremely fine detail.