Severe Weather In Australia

Tornadoes

A tornado is a rapidly rotating narrow region of low pressure. They usually form during a very intense thunderstorm. The wind speeds are as high as 70 to 300 mph and the pressure can be as low as 900 mb. The first process that occurs is a rotating body of air horizontal on the ground, which happens because of vertical wind shear. Drag and friction at the surface causes the air to move more slowly near the ground and the wind speed is higher at higher altitudes. The second process is that the horizontal mass of rotating is lifted off the ground by the strong updraft wind of a thunderstorm. Thunderstorms occur in a cumulonimbus cloud, which is a vertical cloud with strong updraft wind. When the rotating mass of air is lifted off the ground and almost vertically it is considered a mesocyclone. The mesocyclone is fully developed in the updraft of the thunderstorm. A tornado will develop when the mesocyclone descends from the slowly rotating “wall cloud” in the lower part of the cloud. Once it touches the ground it is called a tornado. Tornadoes in the US usually travel from southwest to northeast or from west to east. The reason for this direction is because this is the normal direction of the prevailing winds over the US.

In Australia there is a myth that tornadoes do not occur here, but that’s not essentially true. Tornadoes do happen, but far from how many that occurs in the US. It occur more than 1000 tornadoes per year in the US, while in Australia it occurs 16 tornadoes in average per year.

US tornadoes source:

http://www.ncdc.noaa.gov/climate-information/extreme-events/us-tornado-climatology

Australia tornadoes source:

http://www.abc.net.au/science/articles/2010/06/04/2918660.htm

In the link below there is a very good map that shows all tornadoes in Australia from 1795 to 2012. You can press play, or drag the time button on the timeline and all tornadoes will show the location and the intensity scale for each one.

http://www.theage.com.au/data-point/TornadoesInAustralia

By scooping through the timeline, we can see that there are very few tornadoes with big intensities. And almost everyone occurs south in on the continent. Most of the tornadoes occur in Victoria, New south Wales and South Australia. There also some occurrence south in the Western Australia. 

This is a graph from the U.S Annual Tornado Count. According to this graph the number of tornadoes has increased in the last 30 years. It seems strange that the amount tornadoes have increased in just a few years. I think the reason for this must be related to global warming, and it is a result from the humans. Since the increase of tornadoes is very big, I don’t think that is just random occurrences. I would guess it is related to global warming. 

Hurricanes.

There are three main requirements for a hurricane to form and that is: Consistent heating of the surface, high humidity and Cumulus and Cumulonimbus Clouds. Because of the high humidity and warm temperature requirements it is normal that hurricanes form near the equator. Most of the hurricanes in Australia happen in the North, which makes sense, because the northern part of Australia is located close to equator.

There are three main hurricane formation regions, and the word for a hurricane differs from what region in the world we are referring to. In the Atlantic and east pacific it is called hurricane. In the Indian Ocean and near Australia it is called cyclones, and off the coast of China and Indonesia it is called typhoons.

According to the map below the direction of the hurricanes in the US travel from southeast to northwest. After a lot of research I did not figure out why this is the direction.

In northern Australia hurricanes is not that rare. There is an average of 13 hurricanes (cyclones) that occurs in Australia every year, according to the link below.

http://australia101.com/australia/climate-in-australia/australian-cyclones/

I tried to find out how many that hits US every year, so I could have something to compare it with, but did not find anything on the internet, unfortunately. 


Other sources:

http://australia101.com/australia/climate-in-australia/australian-cyclones/

http://www.tropicalweather.net/where-do-hurricanes-occur.html