A term that is important to know - a Rossby wave, rain that fell over Japan disrupted the jet stream, moved with it to the east and crashed into a high pressure area that stayed over North America and how is this related to the fact that during a drought in southeastern Australia there are floods in the north
On June 25, 2021, it rained over the western Pacific near Japan. There was nothing particularly noteworthy about this rain event, but it hit waves twice.
First, it created an atmospheric disturbance in exactly the way it created a wavelike oscillation in the jet stream - a river of very strong winds in the upper atmosphere - which atmospheric scientists call a Rossby wave (or planetary wave). The wave was then directed east by the jet stream towards North America.
Along the way the wave intensified, then broke just as an ocean wave breaks as it approaches the shore. When the wave broke it created an area of high pressure that remained stationary over northwestern North America for the last week of June.
Here's where our innocuous rain event hit waves again: The locked area of high pressure started one of the most unusual heat waves we've ever seen, shattering temperature records along the northern US West Coast and western Canada, as far north as the Arctic. Layton in British Columbia reached 49.6℃ this week before a devastating fire hit it.
What causes a heat wave?
This heat wave is unusual in many respects, but in its formation and development there was a familiar sequence of events that creates heat waves.
Heat waves occur when there is high air pressure in the ground. The high pressure is a result of air sinking through the atmosphere. As the air descends, the pressure increases, compressing the air and heating it, just like a bicycle pump.
Sinking air has a large heating effect: the temperature rises by one degree for every 100 meters that the air is pushed down.
The heat wave in North America caused fires to spread throughout the area.
High pressure systems are an integral part of the Rossby wave in the atmosphere, and they move along with the wave. Heat waves occur when high pressure systems stop moving and affect a certain area for a considerable period of time.
When this happens, the warming of the air by the sunset alone can become more intense because the ground warms the air - and this is especially powerful if the ground was already dry. In the northwestern United States and western Canada, the heat waves are exacerbated by the warming created by sinking air after it crosses the Rocky Mountains.
How Rossby waves affect the weather
Two questions remain: what causes a high pressure system, and why does it stop moving?
As we mentioned earlier, a high pressure system is usually part of a specific type of wave in the atmosphere - a Rossby wave. These waves are very common, and are created when air moves north or south over mountains, other weather systems, or large areas of rain.
Rossby waves are the factors that most influence the weather outside the tropics, including the volatile weather in the southern half of Australia. Sometimes the waves get so big that they capsize and break. The breaking of the waves is closely related to their becoming stationary.
It is important to note that, as in the last event, the source of the Rossby waves that caused the heat waves is several thousand kilometers west of their location. As for the American Northwest, it is the western Pacific Ocean. Heat waves in Australia are usually caused by events in the Atlantic Ocean west of Africa.
Another important feature of heat waves is that they are often accompanied by a large amount of rain closer to the equator. When there are heat waves in southeast Australia, northern Australia usually has rain. These rain events are not just side effects, they actively strengthen and prolong the heat waves.
to the article on The Conversation website
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