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.

Thursday, September 27, 2012

Overview of changes from the 4th edition

I finally have the book in my hands, which feels really good after working on this project for so long. I didn't get to do all that I planned, but most of the major changes in the book proposal are represented in the 5th edition.

I view this book as having a "book within a book" involving the first six chapters. Those six chapters are essential for students studying dynamic meteorology, ranging from an introduction to the fundamental equations, to their simplification and application to understanding weather systems. I tried to restructure the book so that progression flows logically.

You can read about the details of the changes in the preface to the 5th edition, but here's a brief summary of the highlights for the first six chapters.

  • In Chapter 1, there's a new section on kinematics, the analysis of motion without reference to forces. This material introduces basic aspects of the structure of wind systems, and defines quantities used to measure those aspects throughout the book, such as vorticity and divergence.
  • Chapter 2 has new sections on the Boussinesq approximation and moist thermodynamics. These are used extensively later in the book, so I thought it made sense to elevate their status to the "basic conservation laws" chapter.
  • In Chapter 4, potential vorticity is given a richer treatment, including a simple derivation from the Kelvin circulation theorem, and an introduction to tropopause maps, which provide a modern perspective for extratropical dynamics.
  • Wave motions are vitally important in dynamic meteorology, so what was formerly Chapter 7 is now Chapter 5. Rossby waves, both stationary and propagating, are given expanded treatment, and the properties of these waves that distinguishes them from inertia-gravity waves are used to motivate the quasi-geostrophic equations that follow in Chapter 6.
  • Chapter 6 has been mostly re-written from the 4th edition. The goal was to provide a streamlined, accessible, introduction to quasi-geostrophic theory. The basic elements of the theory are relatively simple, but it is easy to make QG theory seem very complicated and abstract.  Two perspectives are given: "PV Thinking" and "W Thinking." PV Thinking provides a concise and powerful view of extratropical dynamics, but lacks a connection to vertical motion. W Thinking promotes the importance of vertical motion and the role of ageostrophic circulations in changing momentum, vorticity, and potential temperature. These concepts are illustrated with idealized disturbances modeled on archetypal weather disturbances found in midlatitudes (short-wave troughs and jet streaks). Moreover, MATLAB codes, including a QG model and diagnostic package, are provided for students to explore these ideas on their own. Students that master both perspectives have a powerful arsenal for explaining the existence of large-scale cloud patterns, and understanding the interaction of extratropical weather systems and their components. 
So overall, the changes are meant to bring the book up to date, and to enrich the text with bits of synoptic meteorology that should help students make the leap from the text to the real atmosphere.

Tuesday, June 19, 2012

Announcing the 5th edition of James R. Holton's classic text

Hello, World.

This blog is devoted to the book entitled, An Introduction to Dynamic Meteorology by James R. Holton and Gregory J. Hakim. We'll use this space for a variety of purposes, including discussing the content and its use in the classroom, errata, plans for future editions, current weather, and anything else that makes sense in the world of atmospheric dynamics.

The main announcement at the current time is that the 5th edition of the book is in the final stages of preparation, and pre-orders are now accepted.

Please add this page to your reader, or check back for future updates.