Weather Answers

by Deb on November 25, 2011

Weather Answers

1.     La Nina means ‘the girl’ and is the companion or opposite of El Nino, the boy. The names come from South America and originally El Nino wasn’t literal – it was named because it tended to arrive at Christmas and the reference is to Christ. They are part of the Southern Oscillation climate pattern that impacts quite literally around the world.

In El Nino the temperature of the Pacific Ocean is slightly raised, in La Nina it is lower than normal. The temperature of water affects its density, which may not make much difference in your glass but is important in something as large as the Pacific. It affects ocean currents, winds and rainfall because less or more water evaporates.

The effects on either side of the Pacific are opposite – in Australia El Nino brings droughts and La Nina brings floods but it’s the other way around in South America. The long droughts the eastern states experienced up until 2010 were caused or exacerbated by El Nino, while the Queensland and related floods in 2011 were directly caused by La Nina.

If you follow me on Twitter you may have caught a few tweets along the lines of ‘La Nina is a bitch.’ Generally that’s when I’ve been sloshing my way out to rescue some of our animals from the spreading puddles, although seeing this is usually desert we don’t have any major concerns about flooding. However, if you live in Queensland or the catchment areas batten down the hatches and prepare for cyclones, because she’s back. She’s not expected to be as strong this year, but given how all the catchments in our area are still full from last year it could be fun. Good luck to everyone, let’s hope everyone is safe this year.

Have a look down the bottom for a great explanation of El Nino/La Nina.

2.     I bet most of you have children who have drawn pictures with beautiful raindrops in them. Or rather large and misshapen raindrops. Or you drew them yourselves if your kids are too young. But even if they were misshapen, they still had a point at the top and were round at the bottom, just like a drop teetering on the edge of a tap.

Unfortunately for our minds, there is no giant tap in the sky that drips out the rain. They have no need for the tail, and even if they did it would disappear as soon as they were released and they would turn into perfect spheres. And then things like wind resistance would come into play and they would flatten out a bit. So raindrops’ shapes depend on their size, the air pressure and their speed, but they are variations of balls or flying saucers.

3.     Clouds depend on three things – moisture, temperature and nuclei. They generally form when moist air rises and cools, then tiny droplets of water or ice crystals condense onto dust or ice. As the mass of air rises the moisture is fairly evenly spread throughout it, and the difference between what is ‘cloud’ and ‘not cloud’ really comes down to temperature. This is why they tend to have a flat bottom – it is the line between the temperature layers.

There are some moisture differences – the moist air mass that contains the cloud will be bordered by drier, cooler air. But within the mass the temperature differences are what’s important. We live in an area with very high humidity and monsoonal weather (see answer 1 above) and have watched clouds appearing and disapperaing. It’s amazing in a clear patch of sky to see a cloud coming and going.


4.     Windburn really should be labelled wind-drying – moving air cannot burn you (unless it’s moving out of an oven or something like that).  The most effect it has is usually on thin skin because it dries more easily, it often gives you chapped lips or sore eyelids. The red skin that many people label ‘windburn’ is really sunburn. It might be worse if you’re dried out as well, but the major damage is from the sun.

5.   The picture is Morning Glory Clouds in the Gulf of Carpenteria (the chunk taken out of northern Australia). They are roll clouds, and while they can occur in many different places the Gulf is the only place in the world where they can be seen semi-predictably. There are several theories why they form. One is that Cape York to the east has sea breezes form on both sides, they meet in the middle and push air up. Then at night the air mass cools and descends, going under the air from the Gulf. This starts a wave effect, the leading edge is going up but it is turbulent and rolls down again.

This is a bit long, but it is a very good explanation of El Nino/La Nina.

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