A technical question for the board

[weatherwindow]

having read gray's explanation, i am still at a loss to understand the QBO's impact on the process of tropical cyclone intensification. can anyone shed any light on it?....thanks, rich

[MWatkins]

Little is really known for sure about the intensification process...and there are many variables that affect intensification. However, statistically, Dr Gray has been able to show that when the way way up high winds of associated with the QBO are westerly, years with this condition tend to have more major hurricanes.

The theory is that the relative amount of shear way up at the top of a hurricane is less...and I know this is counterintuitive...when they come from the west...on average of once every 3 hurricane seasons. This is because the amount of absolute wind shear on top of a hurricane is less...and creates a more favorable outflow channel and better vertical structure for developed hurricanes.

Again, the link is seasonal and does not apply to each storm...in other words operationally it really doesn't make since to check the QBO value when making a forecast, but instead a statistical correlation between anomalous (abnormal) QBO values and increased major hurricane frequency in the Atlantic. The reduced wind shear idea is a theory to explain the statistics...but isn't really known for sure. It's possible that there are other underlying things going on...that we just don't know about...during the western QBO phase that cause the increase in major hurricane frequency.

Hope this helps...

MW

[Stormsfury]

Also, I must add that during W QBO seasons, there TENDS to be a better than average chance of a higher degree of major hurricanes, but again, NOT an absolute ... the QBO is one of a complex factor of parameters that are factored into how soft or severe a season will turn out ...

SF

[Aslkahuna]

The QBO relates to stratospheric winds and when they are westerly, the compensation in the atmosphere results in easterlies in the upper troposphere. Since the lower trop has generally easterly flow in the ATL Basin you reduce the relative vertical shear in the troposphere by reducing or eliminating the directional component. Less shear improves the chances for development and intensification. With an easterly QBO, the high troposphere will then tend to have westerly winds which is a high vertical shear mode and death for TC's.

Steve

[weatherwindow]

thanks steve, that was exactly the crux of my question....just didnt make a lot of immediate intuitive sense....does now.....