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Mobile (Moving) Polar Highs and the Weather

Marcel Leroux, an empirically oriented meteorologist/climatologist in France, developed the theory that the main aspects of the weather are created by moving polar highs (MPH's) that spin away from the polar regions. An MPH has higher pressure than the surrounding atmosphere and therefore the winds tend to move outward from the center. This outward movement in combination with the rotation of the Earth results in the MPH turning in the opposite direction from the rotation of the Earth. In the Northern Hemisphere this is clockwise and in the Southern Hemisphere it is anticlockwise. For more on this see Wind Directions. Actually to be more precise the wind direction is outward from the center at the Earth's surface. The divergence at the surface must be matched by a convergence in the upper atmosphere and down flow at the center. This means that at the edge of the MPH there must be an upward flow of air. With the cooling associated with the rising air there would be condensation. This is vividly illustrated by the following image.

Leroux believes that the MPH's stay within sectors delimited by mountain chains and other topographic features. This means that the weathers of the differents sectors are largely independent of each other. Leroux is an empiricist and I trust his observations. This is in contrast to the climate modelers whom I do not trust. The climate modelers have all the credibility of used car salesmen; i.e., they usually, but not always, avoid telling barefaced lies but they can easily mislead with half truths and quarter truths. As Stephen Schneider put it, he strikes a balance between effectiveness and honesty.

But back to Marcel Leroux, a honest meteorological empiricist. Granted the validity of his observations the next step is to find explanations for the process. Leroux asserts that MPH's are thrown off of the polar regions by centriful force. Since all of the atmosphere is subject to the so-called centrifugal force due to the Earth's rotation one might expect that a natural pressure gradient between the equator and the poles would develop which would counterbalance the centrifugal force. However the number one axiom in climatology is to not mistake theory for reality. One must look at the data. Here is the graph of sea level pressures versus latitude for the Northern Hemispheric winter (DJF).

There is no pressure impediment to GPH's moving from the arctic into the high temperate zone and even a pressure gradient push in the antarctic. But at about 45°N and 75°S there are pressure gradients which would impede the passage of the GPH's to the south. However below 30° N and S the pressure gradient reverses. This would segregate weather conditions in the tropics. This reversal cannot be accounted for by centrifugal force. It could perhaps be accounted for by the higher moisture content of the atmosphere in the tropics. But the pressure gradient would drive tropical cyclones (hurricanes, typhoons, etc.) into the temperate zones.

This shows once again how complex the real world is compared to the theory. Theory should be a flashlight to aid in looking for the truth and should not be mistaken for the truth itself.

There is another kinematic effect besides centrifugal force which would drive MPH's toward the equator. Cyclones and anticyclones have angular momentum about their spin axes. The rotation of the Earth creates a forced precession of this angular momentum which generates a global torque. For a gyroscope the imposition of a torque creates a precession. A forced precession creates a torque. This torque due to forced precession creates a force which moves hurricanes and typhoons toward the North Pole. Anti-cyclones like the MPH's would be subject to the same torque which would move them in the direction of the equator.

When hurricanes and typhoons move north they are subject to the so-called Coriolis force which moves them to east so their trajectories go from a westward movement to a northwestward movement, a recurvature and finally a northeastward trajectory.

Anticyclones moving south would subject to a Coriolis force moving them to the west but they would move into winds moving to the east and their net movement could be to the east or to the west. Leroux observes their net movement being to the east. The Coriolis and wind forces could balance in the east-west direction. The pressure gradient which starts at about 60°N could bring about a stationarity for anticyclones that is not possible for cyclones. This would explain the existence of the quasistationary high pressure systems such as in the Mid-Pacific (Hawaian) and around the Azores. These quasistationary high pressure systems Leroux calls anticyclonic agglutinations (aggregations).

The oceanic anticyclonic agglutinations are located on the eastern margins of their oceans where continents obstruct the path of MPH's. They are named after the islands within their areas. Their names are Azores, Easter Islands, Hawaii, Mascarene and St. Helena. There are also continental anticyclonic agglutinations but they are more seasonal and less well identified. One is in the Turan Basin of central Asia. Another is a Mediterranean-Sahara cell in the summer which becomes a Saharan cell in the winter. There is also a seasonal Arabian cell.

The anticyclonic agglutinations are maintained by new MPH's merging with them and maintaining their coolness with respect to the surrounding atmosphere.

The Trajectories of the Mobile Polar Highs (MPH's)

Leroux identifies major paths of the MPH's as they move from the poles to toward the meteorological equator. These are determined by topographic features such as large islands and mountain chains. The paths are described in terms the motion of the centers of the anticyclone but they are so large, being on the order of two thousand kilometers in diameter, that their effects are spread far beyond their centers. A few of these trajectories are given below.

From the studies of the Laboratory of Physical Geography there is a tabulation of the number of MPH's following the above trajectories over the period from 1989 to 1993.

All Arctic
From: M. Leroux, Dynamic Analysis of Weather and Climate, Praxis Publishing Ltd., 1998, pp. 29-41.

In the above table there is a discrepancy between the figures for the three trajectories and the total for the Arctic. Any shortfall between the total for the three trajectories and the total is easily accounted for by a fourth trajectory that goes through the Bering Strait into the north Pacific. However in several cases the total for the three trajectories is greater than the figure for the total. These discrepancies are perhaps accounted for by the total being for the MHP's formed in the Arctic Basin whereas it is possible that some northern MPH's are formed outside of the Arctic Basin. In any case, the significant thing is that there is, on average, about one MPH formed per day.

(To be continued.)

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