Historical weather data is collected and studied in several ways to make sure the information is correct and useful. Here are the main ways this data is gathered:

1. Ground-Based Observations:

   • There are about 20,000 weather stations around the world that keep an eye on the weather all the time.
   • These stations check important things like temperature, humidity, wind speed, and how much it rains.

2. Remote Sensing:

   • Satellites, like those from NOAA (National Oceanic and Atmospheric Administration), track big weather patterns from space.
   • They use special tools to look at clouds, sea temperatures, and conditions in the air.

3. Meteorological Balloons:

   • Every day, around 900 balloons are released all over the globe to gather information from high up in the atmosphere.
   • They collect data on temperature, air pressure, and humidity at heights of up to 30 kilometers or more.

4. Data Assimilation:

   • This involves using smart math techniques to combine information from various sources to create clear datasets.
   • Weather models use computer programs to make better predictions by looking at past data.

5. Historical Records:

   • Studying old weather data, including things like ice cores and tree rings, helps scientists improve climate models.

By using these methods and making better computers and math tools, researchers can understand weather patterns and climate changes over many years.