Thursday, October 4, 2012

Eastern Pacific "modon" block

Over the northeastern Pacific Ocean right now there is a great example of a Rex block, which I prefer to refer to as a "modon" block, for reasons that I will mention shortly. These blocks consist of a high-over-low pattern, which is evident in the 500 hPa chart for today (lines are 500 hPa geopotential height every 30 m, and colors are absolute vorticity; credit).

I call this a modon block because its structure is very close to analytical solutions known as modons. Here's an example from Muraki and Snyder (2007), showing the streamfunction (like geopotential height):

Modon solutions are known for the barotropic and quasi-geostrophic equations, on the plane and on the sphere. What makes them truly remarkable is that they are exact solutions of the full nonlinear equations, which is a rare. Perhaps more important is that they are useful for understanding the dynamics of weather systems! The low-over-high version is a good model of a jet streak, which is discussed in Chapter 6 of the book(see Figs. 6.12, 6.16 and 6.17).

As can be seen from the figures above, the high-over-low version is a good model for blocking, and this subject is explored in Matlab problem M6.5, which uses the QG model and diagnostic package that come with the book. I will have more to say about those tools in future posts, because I think they provide a really cool way for students to explore dynamic meterology.

No comments:

Post a Comment