Monday, October 18, 2010

This paper is "da bomb"

This month marks the 30th anniversary of one of the most important synoptic meteorology papers of the late 20th century.  Synoptic-Dynamic Climatology of the "Bomb" by Fred Sanders and John Gyakum not only has a great title, but it also set the stage for a blossoming of research on extratropical cyclone dynamics and evolution that culminated with the GALE and ERICA field programs.

Sanders and Gyakum (1980) credit Tor Bergeron for first characterizing cyclones that deepen at a rate of at least 1 mb/hr for 24 hrs as rapidly deepening.  Today, we use the term explosively deepening, which perhaps derives from Fred and John's use of "Bomb" in their article.

Some historical background is needed to put Sanders and Gyakum (1980) in perspective.  Today we are all products of the Internet age in which live satellite and high resolution (0.5 degree or better) global analyses with variational satellite radiance assimilation stream to us 24/7. In 1980, operational Geostationary satellite imagery was barely a decade old and the highest resolution model run by the National Meteorological Center (today's National Centers for Environmental Prediction) was the Limited Fine-mesh Model (LFM), which had horizontal grid spacings of 127 or 190.5 km depending on generation (Silberberg and Bosart 1982).

The LFM was the primary model used for forecasting when I started in college and we had various nicknames for it, the most family friendly being "Lousy Freaking Model."  Although cutting edge at the time, the LFM was indeed bad by today's standards.  A 72-hour forecast today has more skill than a 36-hour forecast in 1980.

Sanders and Gyakum (1980) includes several important findings that helped guide extratropical cyclone research in the 1980s and 1990s:
  1. Explosively deepening cyclones are primarily (but not exclusively) maritime phenomenon.
  2. Explosive deepening occurs preferentially in regions of strong SST gradients, such as along the Gulf Stream and Kiroshiro Current. 
  3. Quasigeostrophic dynamics cannot explain the rapid pressure falls.
  4. Current NWP models poorly forecast these events.
Anyone who lived on the eastern seaboard prior to about 1990 knew item four well!  Surprise nor'easters were commonplace.

Subsequent field programs (GALE and ERICA) examined the dynamics and evolution of marine cyclones, while a third, STORM-FEST examined continental systems.  Research spawned from these field programs illustrated the importance of air-sea interactions for preconditioning the atmosphere and subsequent condensational heating for explosive deepening.

In the 1980s some thought that explosively deepening cyclones were poorly forecast because the NWP models were missing a piece of key physics.  Instead, they were missing sufficient resolution to capture key non-linear dynamical processes, although advances in modeling and data assimilation have certainly contributed some to improved extratropical cyclone forecasts over the past three decades.

Today, events like Snowmaggedon are forecast days in advance.  Of course, we still have work to do in the Intermountain West...


  1. Jim, Thanks for remembering the bomb paper anniversary. This paper had a huge impact on meteorology. I think it is safe to say that if it wasn't for that paper, all the millions of dollars of funding that came from ONR and NSF wouldn't have happened. This is turn would have meant that you, me, and our colleagues (Greg Hakim, Gary Lackmann, Mark Stoelinga, Jon Martin) would have been off doing something different than extratropical cyclones for our thesis research.

    The impact of that single paper was immense.

  2. For sure Dave. Thanks for reminding me of how the paper spawned the development of human "infrastructure."