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| 2083 "Moisture Conveyors" Pixels Link |
In "The Main Veil of the Weather Dance - The Warm Conveyor Belt" I made the case for the Warm Conveyor Belt as the prima ballerina in the weather ballet and the "Conveyor Belt Conceptual Model". In "What do Smoke Rings have to do with Croquet?" I described how the leading edge veil of the Warm Conveyor Belt was a stretchy three dimensional deformation zone fabric that contained the flow of the atmospheric river. Using the smoke ring analogy I then showed how the vorticity ring evolved into a croquet hoop on the warm side of the surface warm front. I then alluded to using this croquet hoop as a forecasting tool. This is how I did that.
The precipitation associated with a storm is the result of
both the intensity and the duration of the precipitation. These
characteristics can be quickly estimated by looking at the croquet hoop representation
of the warm conveyor belt. I will use a graphic to try to save a lot of words.
The moisture in the warm conveyor belt travels northward, rising for free on the constant energy surfaces meteorologists call isentropic surfaces. This view is looking northward along that path through the croquet hoop just south of the surface warm front.
A brief explanation of the important features of the croquet hoop are included in the graphic. Pressure is the weight of the air above a point. The rising air of the cyclonic swirl of the croquet hoop causes pressure falls. Precipitation processes releases energy that fuels the rapid rise of air in this cyclonic croquet leg. Meanwhile the sinking air along the anticyclonic peg results in rising pressure. The pressure difference between these two legs determines the wind speed of the conveyor belt delivering heat and moisture energy to the storm. This current of energy is often called an atmospheric river and the pressure difference across the river keeps it flowing and determines the current.
The orientation of the warm conveyor belt as revealed by the plane of the croquet hoop is also vitally important. The following graphic might help explain this better but it all has to do with the atmospheric frame of reference and the direction of flow of that atmospheric river. The importance of the atmospheric frame of reference was made in the very first post in this series "Cloud Shapes and Lines in the Atmosphere".
The tilt of the cyclonic vorticity tube that is the rising swirl of the croquet hoop will typically be the same as the orientation of the warm conveyor belt. If this cyclonic vorticity tube tilts to the northwest expect a slow moving or stationary weather system where both duration and intensity of the precipitation will be a concern.
Now for some fun... A time tested "rule of thumb" at the Ontario Storm Prediction Centre in Toronto is to count the isobars originating from the warmth and moisture of the Gulf of Mexico. If you should count four isobars (drawn at 4 millibar intervals) directed from this huge energy source then you can simply predict significant precipitation in Toronto in 24 hours. A significant atmospheric river requires 16 millibars of pressure difference from bank to bank.
There was a tendency during my meteorological career to shun these techniques as "cook book meteorology" in favour of numerical modeling of the atmosphere. My response was that even the best chefs refer to a reference guide especially if these were based on solid science and knowledge.
My illustrations for this application of the croquet hoop guide to the warm conveyor belt follow. They are computer generated. I am retired and was looking for a case to illustrate the atmospheric river approach to the warm conveyor belt and croquet hoop. I stopped doing hand drawn analyses long ago even though it was my favourite task and where I really learned about the weather.
The analysis image on the left showed at least five isobars drawn at 2 millibar intervals (10 to 12 millibars of pressure difference across the atmospheric river) coming off the Gulf of Mexico . The 24 hour forecast chart on the right showed the rain well into Southern Ontario. Indeed, it poured and produced major spring flooding across the province
Why think of these things? Trying to understand how the real world works is way better than the other options. The weather is a beautiful ballet and not a battle.
There is much more to come...
Warmest regards,
Phil the Forecaster Chadwick
PS: The orientation of the warm conveyor belt related to event duration described is intended as a generalization - but one that applies well for central and eastern Canada. There is a well-known and strong and nearly stationary atmospheric river that points northeastward to the west coast. This "Pineapple Express" imports a lot of moisture and heat energy from the tropical Pacific around Hawaii into the west coast and duration is the problem.
The orientation of the warm conveyor belt as revealed by the plane of the croquet hoop is also vitally important. The following graphic might help explain this better but it all has to do with the atmospheric frame of reference and the direction of flow of that atmospheric river. The importance of the atmospheric frame of reference was made in the very first post in this series "Cloud Shapes and Lines in the Atmosphere". The tilt of the cyclonic vorticity tube that is the rising swirl of the croquet hoop will typically be the same as the orientation of the warm conveyor belt. If this cyclonic vorticity tube tilts to the northwest expect a slow moving or stationary weather system where both duration and intensity of the precipitation will be a concern.
Now for some fun... A time tested "rule of thumb" at the Ontario Storm Prediction Centre in Toronto is to count the isobars originating from the warmth and moisture of the Gulf of Mexico. If you should count four isobars (drawn at 4 millibar intervals) directed from this huge energy source then you can simply predict significant precipitation in Toronto in 24 hours. A significant atmospheric river requires 16 millibars of pressure difference from bank to bank.
There was a tendency during my meteorological career to shun these techniques as "cook book meteorology" in favour of numerical modeling of the atmosphere. My response was that even the best chefs refer to a reference guide especially if these were based on solid science and knowledge.
The analysis image on the left showed at least five isobars drawn at 2 millibar intervals (10 to 12 millibars of pressure difference across the atmospheric river) coming off the Gulf of Mexico . The 24 hour forecast chart on the right showed the rain well into Southern Ontario. Indeed, it poured and produced major spring flooding across the province
Why think of these things? Trying to understand how the real world works is way better than the other options. The weather is a beautiful ballet and not a battle.
There is much more to come...
Warmest regards,
Phil the Forecaster Chadwick
PS: The orientation of the warm conveyor belt related to event duration described is intended as a generalization - but one that applies well for central and eastern Canada. There is a well-known and strong and nearly stationary atmospheric river that points northeastward to the west coast. This "Pineapple Express" imports a lot of moisture and heat energy from the tropical Pacific around Hawaii into the west coast and duration is the problem.
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