The news in late November 2009 made much of the presence of icebergs heading north out of the Southern Ocean. There is an impressive photo of one of the icebergs here. The story got me thinking again about the amazing properties of water, so I will continue the thread of a previous post by focusing on ice.
How the Sun moves across the sky
As we approach summer in NZ, the Sun gets higher in the sky and increasingly warms the Earth and the air around us. In the early 1600s Galileo Galilei explained that the Earth goes around the Sun, but there's no reason why we can't discuss the apparent movement of the Sun across the sky, as you see it from a frame of reference fixed to the Earth. Let's do that, and investigate the different ways that the Sun drives our seasons.
As I indicated at the end of the recent post about surface tension, I've started a new thread about the amazing properties of water. This time I'll write about saturation, what it is and what it isn't. The reason I included the bit about "what it isn't" is that a close friend once asked what saturation actually was - they thought that if the air were "saturated" it was like walking through a swimming pool. Not an unreasonable deduction based on our everyday meaning of "saturation".
We've just had some very strong winds over NZ, so I'm writing this short post to give some background to it. First of all, check out these peak northwesterly wind speeds from the morning of Wednesday 4 November:
mean wind (including gusts and lulls) strongest gust South West Cape (Stewart Island) 143 km/h183 km/hCastlepoint (Wairarapa coast)109 km/h161 km/hPuysegur Point (bottom of Fiordland)100 km/h144 km/h
Water is an amazing substance. It has many properties that have a big impact on our lives and, I think, are quite useful for us to know about. One of these is the property of surface tension, which water shares with other less prevalent liquids. So what is surface tension? Wikipedia describes it as being caused by "the attraction between the liquid's molecules" which acts at the surface of the liquid to "diminish the surface area".
The Structure of Highs
After writing two blog posts about lows or depressions, I thought it would be a good idea to also write something about highs or anticyclones. After all, one is just the opposite of the other, isn't it?? Well, in some ways yes, but there are some important differences too.
With a superb view over Wellington and the harbour from the MetService building in Kelburn, we're often (and quite appropriately) treated to some fantastic weather related vistas. Here's a little sample, snapped on Monday 26 October 2009 as a few light showers passed over the city in a northerly flow late afternoon.
The Snow of '39
Ranfurly Shield Rugby in the Snow. Source: The Weekly News, August 1939
The Structure of Lows - part II
In my previous blog post I pointed out that tropical lows and cyclones don't have fronts like the lows we're used to around NZ, but rather, a core of warm air near the centre. I'd like to follow up by further contrasting tropical and mid-latitude lows, and looking a bit more closely at tropical cyclones and how they can affect our weather in New Zealand.
When tropical lows fully develop into cyclones they become the most damaging of tropical weather features. There are three main reasons for this:
Puysegur Point Storms
Years ago, I heard the wife of a lighthouse keeper talking on the radio about the weather at Puysegur Point, on the south coast of Fiordland, where she and her husband had been stationed for a time. Six months or so before they arrived there, a fishing boat had gone down in a storm with all hands. One day, as she walked along the black stony beach, something white caught her eye. Bending over, she picked up a single human tooth.