Some questions about meterology

[pilot_kenny]

Hi can I ask two questions here~?~ Thanks! :o)

1, Gradient Wind: non-geostrophic winds which blow parallel to isobars
In nouthern hemisphere, Why is it cyclonic for a L (anticlockwise) and anti for a H (clockwise)?
I saw in my book that it's because Coriolis foce > Pressure Gradient Force for a H --> clockwise and vice versa for a L
but in the above website, it also mentions centrifugal force (and in fact I dont understand the website much either ), what's the actual story?

2, what's wave/frontal depression? I've tried to understand from my book and search in the net, but failed to understand it well~

Thanks again!

[cyrex]

1) Well first, for "wind " to occur, its cause by horizontal pressure differences, thus "(pressure) Gradient Wind", this gradient wind will flow directly from a high pressure area to low pressure area (high seeks low) if theres no other force acting upon it. But due to earth's rotation, the 'wind' move over a moving body thus causing the coriolis effect. And as u said clockwise for high pressure and vice versa for low. Where Centrifugal force comes into play is actually with regards to wind speeds. As this force acts on a circulating flow of air around the high/low pressure areas, it tends to increase the wind speed in high pressure area and decrease it in the low pressure areas. Another force that can a play a factor with wind velocity is Surface Friction. Both friction from the airmasses and surface of the earth can slow the flow of air. When the wind speed decrease , the coriolis effect is reduce and thus causing wind to move across isobars at a slight angle inward towards center of the low pressure sys and outward from center of a high pressure sys.

2) Frontal depression= basically a front is the transition zone bewtween two airmasses. For Northern Hemp, vice versa for south, Frontal depression is cause by the interaction between the cold and dry airmasses from the north ( Polar or arctic air) with warm and moist airmasses from the south (tropical). YOu can further search online with regards to how differnt fronts (cold , warm, occluded, stationary ) works. Wave depression on the other hand is caused by orographical activity ( rising air blown up against a mountain) and as the warm mosit air rises its meets cooler and dryer air, thus causing interactions similiar to those of frontal depressions.

Hope this all helps..