Wednesday, October 31, 2012

Superstorm Sandy and the tropopause

Among the many remarkable aspects of Superstorm Sandy is the evolution of the tropoause during the event. Lacking time for a full post on that right now, I will share the most recent view of potential temperature on the tropoause, which shows a plume of very warm air (>340K) over the North Atlantic ocean.

The plume has been stretched, with one blob over  the central Atlantic and the other over eastern North America. These blobs are connected by a thin ribbon over the North Atlantic. An animation of over the past seven days shows the evolution of the tropical plume, and the thinning filament. One gets no hint of this detail from a 500 hPa map (NOAA/ESRL)

which shows an omega-type blocking pattern (slightly different time, but that doesn't matter). There's no hint of the tropical air over eastern North America, or the filament.

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.

Monday, October 1, 2012

Companion web page for the book

The companion website for the book is located here. This page provides all online support for the text, including all figures, MATLAB scripts, and a solutions manual for instructors.

These pages are under continual development, so you will see new features appear over time. In particular, we plan to add additional color figures to the image bank and links to other resources.

Please note that equation references in the comments of Matlab scripts have not yet been updated to the 5th edition, but will soon.