At 07:13 PM 1/12/2013, Trent W. Buck wrote:
Craig Sanders wrote:
On Fri, Jan 04, 2013 at 08:53:09PM +1100, Andrew McGlashan wrote:
And whilst today is hot, you might expect that, we are as close [in distance] to the Sun as we'll be for the whole year.
you do realise that aphelion/perihelion has negligible affect on Earth's temperature, right? That the slightly elliptical orbit of the earth around the sun is NOT the cause of seasons?
Simpler proof: if it was so, both hemispheres would have winter at the same time.
True. Actually, the northern winter (which occurs at perihelion) is much more severe than the southern winter (which occurs at aphelion). At first this seems counter intuitive - afterall, shouldn't the more extreme summer occur in the hemisphere facing the sun at perihelion and the most severe winter in the hemisphere (which would be the same one) facing away from the at aphelion? The answer is to do with the distribution of land masses. The northern hemisphere has much more land mass, while the southern hemisphere has a lot less land and a lot more ocean. Water has a much higher heat capacity than land, and the large areas of water in the southern hemisphere moderate the seasons much more than the Earth's orbit makes them extreme. The heat capacity of the waters surround Australia is also one of the reasons behind the sudden onset of the Melbourne cool change. A northerly (or NW) wind blows off the outback, which has already heated up from months of solar heating. When the wind changes to SW, it's blowing over waters not much more than 20C just offshore, so the temperature immediately drops 20C or more. The same water also moderates the cold of the air mass, since it originates from Antarctica. Here in Bendigo, the cool change takes a little longer (maybe up to an hour or 2) to fully take effect, because the land in between here and the sea warms the air slightly, until the heat has been carried off by the wind. 73 de VK3JED / VK3IRL http://vkradio.com