Rainbow sightings in Spring
Spring has sprung and it’s a great time of year for spotting rainbows, says Seven's national meteorologist David Brown.
They’re not only colourful but they’re a symbol of hope.
Meteorological speaking, rainbows are an optical phenomenon. They’re not a physical object like you and me and can’t be approached. So you’ll never find its end or a pot of gold. However, it doesn’t stop you from dreaming.
Did you know the turbulent nature of spring weather encourages rainbows? It’s common place to experience a mixture of sunshine, showers and torrential downpours all in one day and lots of rainbows too, more than in any other season in southern Australia.
The angle of the sun is just right in spring. In winter, it’s too low and in summer it’s too high. Autumn shine is just fine, but the weather is way too stable.
Rainbows are more likely in the early morning or late afternoon on showery days when breaks in the passing cloud allow the sun’s light to impact on raindrops. You see rainbows are the product of refracted and reflected sun light by millions and millions of falling rain drops.
The well-known proverb, ‘rainbow in the morning, sailors take warning; rainbow at night, a sailors delight’ works well in southern Australia, in fact in all middle and high latitude locations around the world. It relies on the assumption that weather systems move from west to east, an assumption that’s right 90 per cent of the time.
Have you noticed you can only see a rainbow when the sun is behind you? In the morning, when the sun is rising in the east, the showers will be to the west and moving towards you; therefore taking warning, it is likely to rain.
Conversely, in the late afternoon the sun will be to the west and the showers will be to the east moving away from you. Breaks in the cloud are vital for the sun's rays to impact on raindrops and therefore rainbows mostly occur with showery precipitation from convective cumulus cloud.
The bigger the rain drop, the better the rainbow. In fact, the most spectacular rainbows with the brightest colours are formed by thunderstorms.
A rainbow is actually two distinct bands of colour, one brighter than the other. The brightest is the primary bow. The outer and less distinct one is known as the secondary.
The primary bow has red colouring on the outside and the violet on the inside of the arch, while in the secondary bow, the colours appear as just the opposite.
You can make your own rainbows with a garden hose and a sprinkler head adjusted for a very fine spray. Having the sun in your back and spraying water in a broad stream at an angle between 40 and 50 degrees around the shadow of our head, you can see a rainbow.
Good luck and happy rainbow hunting.
