One thing we have to remember about Australia is that it is in the southern hemisphere and consequently the "shapes" of its weather patterns are different from what we in the northern hemisphere are used to. For instance, while we're in the middle of winter, it's the middle of summer there. Consequently, temperatures are rather warm:
|Fig 1 -- Surface temperature analysis at 00Z, Jan. 16, 2011. From the Australian Bureau of Meteorology.|
|Fug 2 -- Surface MSLP and frontal analysis at 00Z, Jan 16, 2011. From the Bureau of Meteorology.|
- The cold air is located to the south instead of the north. So any cold air being dragged in with low pressure centers will come from the south.
- The Coriolis effect, which turns winds to the right in the northern hemisphere and explains why we have counter-clockwise flow around low pressure centers, turns winds to the left in the southern hemisphere. This means that winds flow clockwise around a low pressure center in the southern hemisphere.
|Fig 3 -- Simple diagram of the structure of a northern hemisphere extratropical cyclone. From Paragliding Weather website.|
|Fig 4 -- Simple diagram of the structure of a southern hemisphere extratropical cyclone at the surface. From the South African Climate Systems Analysis group.|
Note how I kept saying "clockwise" and "counter-clockwise" in terms of the winds instead of "cyclonic" or "anticyclonic". The term "cyclonic" is defined as the way the air moves around a cyclone (a low-pressure center). So in both the northern and southern hemisphere, the winds around the low pressure centers are technically "cyclonic". They may be going opposite directions from a clockwise/counter-clockwise perspective, but the term "cyclonic" definitely applies to both.
Anyhow, now that we're oriented a bit, it's kind of fun to see how this spin affects different things. You may have noticed in the surface analysis above that there's a feature called Severe TC "Zelia" to the northeast of Australia. This is indeed a tropical cyclone-- a category three, as a mater of fact. They are referred to as tropical cyclones in the southern hemisphere--"hurricane" is only used in the Atlantic basin. So "Severe TC Zelia" would translate to "Major Hurricane Zelia" if it were up here. Here's the forecast track from the Australian Bureau of Meteorology (the BOM):
|Fig 5 -- Track and forecast track for severe TC Zelia as of 00Z, Jan 16, 2011. From the BOM.|
One thing that's NOT different about mid-latitude weather systems in both hemispheres is their direction of movement--the prevailing jet streams (and consequently storm motion) are still from west to east. So just as hurricanes in the Atlantic move away from the equator and then get pushed around until they're moving to the east, so too do tropical cyclones in the southern hemisphere move away from the equator (south this time) and get pushed to the east the further they get from the equator. Pretty fun.
This cyclone has plenty of energy to work with, too--here's the latest sea surface temperatures off of Australia:
|Fig 6 -- Sea Surface temperatures off of Queensland and the Coral Sea from Jan 15, 2011. From the BOM.|
And finally, here's the latest IR satellite image over Australia:
|Fig 7 -- IR satellite image from 532Z. From the BOM.|
Remember what I said, though, about Australia being closer to the equator than the US? This explains why the main storm tracks (associated with the south polar jet) are well to the south of Australia--there's that parade of lows spinning around in the ocean south of Australia, rather far away from land. While the northern US would be hit by storms at those latitudes during our summers, Australia is just enough closer to the equator to miss out on most of those storm tracks. However, Australia extends close enough to the equator to get caught up in the tropical rain belts. Note the string of "cloud blobs" across the northern edge of Australia in the IR image above? Those are all tropical waves--the kinds of storms we'd usually see in the Caribbean. Australia is close enough to the equator that those impact the northern part of the country. In fact, on the surface analysis in figure 2, you can see the long dotted line running from east to west across the northern part of the continent. This persistent trough of low pressure brings lots of tropical rain to that belt during the summer.
So that was a quick look at something different--weather in the land down under. It's summer there, and I thought we could use a little break from our winter. Back to the US for my next post, though...