101: Conveyor Belt Model

 

Some time ago I wrote a post on the Norwegian Cyclone Model and how great it is. Well, it actually has some major flaws. A large portion of these flaws stem from the limited number of available observations the Bergen School had to work with when developing their model in the early 1900s. Essentially, their data only represented the weather found over the northeast Atlantic and Western Europe. Therefore, it completely lacks data on storms such as those that rapidly develop near the east coast of North America (i.e. Nor’easters) or those that form in the lee of the Rockies and move across central U.S. Another source of the problems associated with the Norwegian Model is that aside from some aspects of fronts and air masses, it is mostly described in 2-D. A likely cause for this oversight was the fact that little research had been done on upper level dynamics. At that time, meteorologists did not have access to technologies we now take for granted such as radar and satellite imagery. Even phenomena as critical as jet streams were unknown, in fact the jets were not identified until high altitude bombing missions over the Pacific during the latter part of WWII. Clearly, the Model needed some adjustment.

As a result of its shortcomings, many weather features that are now observed every day are simply impossible to explain using the Norwegian Model. As an example, check out the MODIS image below of an intense Mid-Latitude Cyclone (MLC) in the Gulf of Alaska from October of 2005. At this time the system featured warm, cold, and occluded fronts and packed Hurricane Force winds. I will be using this impressive system as a great example throughout this post.

 

Notice the two highlighted regions; these are both examples of features not found in the Norwegian Model. However, it should be noted that these are just two examples, not the only examples of features absent in the Model.

 

This image highlights a region of the storm where the air flow has wrapped around the low center several times. Much of the outer parts of the spiral happen to contain the end of the Occluded Front. This complex spiral is not described in the Norwegian Model, which depicts a developed low such as this as having a very strong cold front that continues as a short occluded front and makes only a small portion of a spiral into the low’s center.
 

In this image, a portion of the scattered convection on the cold side (west) of the MLC is clearly enhanced relative to the surrounding cloud field. This region is likely the beginnings of a Comma Cloud. A comma cloud is small system that often looks a bit like a MLC, but much smaller and without fronts. These formations are important to follow because they can have a large effect on the main MLC and its cold front if it interacts with them.

 

All of these features are depicted above. This image consists of a simple version of the MODIS image above, overlaid with the surface map from about the same time.

So, what have scientists done about these issues? Answer: they devised a new model that adjusts and builds upon the Norwegian Model named The Conveyor Belt Model. In the next 101 post I’ll describe this model in more detail, but for now, consider the diagram of a MLC as a teaser.