Environment

What is a Polar Vortex?

The polar vortex is an area of cold air and low pressure which always surrounds both the North and South poles.

The meaning of the term vortex refers to the fact that the flow of air moves eastwards which helps keep cold air near the Poles.

Sometimes in the winter months, the northern hemisphere’s polar vortex expands and this consequently sends cold air southward through the jet stream into North America.

This has happened on a number of occasions including January 2014 and several colder outbreaks during the Winters of 1977, 1982, 1985 and 1989.

Other countries have also experienced cold surges connected to the polar vortex like parts of Europe and Asia.

The North and South polar vortex is a large scaled and persistent low pressure zone.

It rotates anti-clockwise at the North Pole (which is known as a cyclone) and clockwise at the South Pole, meaning that both the polar vortices rotate eastwards around each pole.

The base of the vortices are located in the middle and upper troposphere which also extend up into the stratosphere. Under that lies a large mass of cold and dense Arctic air.

A polar vortex will get stronger during the winter and weaker during the summer months, because it depends on the different temperatures between the equator and the poles.

These two vortices span less than 1,000 kilometres (620 miles) in diameter. Just like other cyclones the rotation of these vortices are driven by the Coriolis effect.

The first recording of a polar vortex dates back to 1853, in an issue of Littell’s Living Age, which was a weekly literary periodical which started in 1844.

What is the Severn Bore?

The Severn bore is a large surge wave which is seen in the estuary of the River Severn and is considered as one of Britain’s truly natural phenomena.

It is a tidal range and is the second highest in the world, which on occasions can reach up to approximately 5 feet in height.

This is all due to the shape of the Severn estuary, which means that the water funnels into an ever decreasing narrow channel.

The estuary narrows from being 5 miles wide in Avonmouth to just 1 mile wide in nearby Lydney and by the time the estuary reaches the Gloucestershire village of Minsterworth on the north bank of the River Severn, it is less 100 yards wide!

The depth of the river changes quickly and when the incoming tide travels up the estuary, it is routed into an ever decreasing channel.

Consequently the surge wave or a “Severn Bore” as it is known, is created and large waves going upstream are caused.

There are about 60 bores that occur throughout the world and the Severn Bore is one of the largest in the world.

Around eight occur in the UK but bores are also knwon to happen on the Rivers Seine and Gironde in France and on the Amazon in Brazil.

The biggest bore in the world is on the Hang-chou-fe in China. When Spring tides occur the wave can reach up to heights of over 25 ft (7.5 metres) reaching speeds of between 13-15 knots, which lasting for up to 14 miles!

Image Credit: The Telegraph

What is a Shelf Cloud?

A shelf cloud is a horizontal wedge-shaped cloud which hangs low in the air, and is usually associated with thunderstorms. The shelf cloud will attached itself to the underside of a parent cloud.

The rising cloud motion looks severe as it rises but it is the lower cloud that appears turbulent and wind torn.

The cool sinking air from the downdraft of the shelf cloud spreads across the surface, and the leading edge is known as the gust front.

When the warm air is drawn into the storm’s updraft and it mixes with the cooler air, the moist air condenses and this creates a rolling effect people see which usually develops into a heavy rainstorm.

A shelf cloud is also known as a “Tsunami” cloud due to what looks like a rotating motion as the cloud draws nearer to the land.

When does our Summer Solstice occur and why?

Our Summer Solstice, which is also known as “the longest Day” is celebrated on June 21st and it happens when the tilt of the planet’s semi axis in either the southern or northern hemispheres is more inclined toward the star that it orbits.

The reason for this occurence between the 20th and 22 June is because the Earth’s axial tilt towards the Sun is at it’s maximum of 23 26′. This only occurs twice a year, the other occasion is between the 20th and 22nd Decemer, which becomes the shortest day and it is all due to each time the sun reaches it’s highest point in the sky as seen in the south or north pole and determines the number of daylight hours we receive.

It is believed in ancient history that this date in June helped the people to work out the time of year, especialy for planting and haresting crops.

At Stonehenge, some historians believe that this prehistoric momument in England is true evidence that humans used the Summer Solstice in June to erect a unique stone circle to establish the date of the longest day.

When viewed from its center, the Sun is shown to rise over a certain point on the horizon and can be clearly followed on the stone circle and used as a calendar. Again it helped the people establish what time of year it was to organise their calendars for the rest of the year.

What is the Rim of Fire?

The “Rim of Fire” lies around the rim of the Pacific Ocean.

There are a number of crustal plates that meet in this area, which results in frequent volcanic and earthquake activity.

There are 452 known volcanoes in this ring and 80 per cent of the world’s largest earthquakes occur here.