Imagine our weather if Earth were completely motionless, had a flat dry landscape and an untilted axis. This of course is not the case; if it were, the weather would be very different. The local weather that impacts our daily lives results from large global patterns in the atmosphere caused by the interactions of solar radiation, Earth's large ocean, diverse landscapes, and motion in space.
A storm darkens the sky at the mouth of the Russian River, north of Bodega Bay, Calif. The storm was driven largely by an "atmospheric river" over California. (Image credit: NOAA)
Global winds
Earth’s orbit around the sun and its rotation on a tilted axis causes some parts of Earth to receive more solar radiation than others. This uneven heating produces global circulation patterns. offsite link For example, the abundance of energy reaching the equator produces hot humid air that rises high into the atmosphere. A low pressure area forms at the surface and a region of clouds forms at altitude. The air eventually stops rising and spreads north and south towards the Earth's poles. About 2000 miles from the equator, the air falls back to Earth's surface blowing towards the pole and back to the equator. Six of these large convection currents cover the Earth from pole to pole.
NOAA studied about four decades of tropical cyclones revealing the surprising result that reducing particulate air pollution in Europe and North America has contributed to an increase in the number of tropical cyclones in the North Atlantic basin and a decrease in the number of these storms in the Southern Hemisphere. The study also found that the growth of particulate pollution in Asia has contributed to fewer tropical cyclones in the western North Pacific basin.
Air masses
These global wind patterns drive large bodies of air called air masses. Air masses are thousands of feet thick and extend across large areas of the Earth. The location over which an air mass forms will determine its characteristics. For example, air over the tropical ocean becomes exceptionally hot and humid. Air over a high latitude continent may become cold and dry. You have probably noticed the temperature rapidly dropping on a nice warm day as a cold air mass pushed a warm one out the way.
Fronts
The location where two air masses meet is called a front. They can be indirectly observed using current weather maps, which can be used to track them as the move across the Earth. Cold fronts, generally shown in blue, occur where a cold air mass is replacing a warm air mass. Warm fronts, shown in red, occur where warm air replaces cold air.
The term jet stream is used increasingly in both weather forecasts and news reports of extreme events, from cold spells and flooding to heatwaves and droughts. But what is the jet stream, and why do we care about it so much?
Jet streams
The local weather conditions that we experience at the Earth's surface are related to these air masses and fronts. However the environment far above us impacts their movement. High in the atmosphere, narrow bands of strong wind, such as the jet streams, steer weather systems and transfer heat and moisture around the globe.
Coriolis effect
As they travel across the Earth, air masses and global winds do not move in straight lines. Similar to a person trying to walk straight across a spinning Merry-Go-Round, winds get deflected from a straight-line path as they blow across the rotating Earth. In the Northern Hemisphere air veers to the right and in the Southern Hemisphere to the left. This motion can result in large circulating weather systems, as air blows away from or into a high or low pressure offsite link area. Hurricanes and nor'easters are examples of these cyclonic systems.
EDUCATION CONNECTION
Students should understand that weather events that they experience do not just occur at random but are dependent upon scientific principles and processes. The clouds, temperature, precipitation, winds and storms that you and your students observe are dependent on interactions between global systems and your local conditions such as geography, latitude, moisture levels and solar energy absorption. This collection provides real-world and real-time resources to help educators develop students' understanding of the interactions of these Earth systems.