12.05.2009

Why Not?

...and thus materializes another Blogspot blog. Because between all the strange pillars of activity that compose life, some web of connectivity must be drawn. Perhaps the digitally published pedestrian ramblings of an oft-underused intellect will serve as adequate glue, at least for a time.

The name, of course, refers to a major feature of severe thunderstorms in middle America: the phenomenon through which the most violent of these storms attain their peculiar level of power and ferocity. Said phenomenon is the mesocyclone, or the column of rotating air that forms the main updraft of severe thunderstorms. This updraft is what both drives the rapid rise and expansion of a nascent storm and stabilizes the mature storm when coupled with stable downdrafts, usually ahead of and behind ('forward flank' and 'rear flank', respectively) the updraft.

The updraft is the 'air intake' of the storm, whereby warm, moist air from the surrounding environment is drawn to heights of up to 60,000 feet, fueling convection, charge separation (for lightning production) and the development of hailstones up to softball size and beyond. This warm jet of air can reach incredible upward velocities in the stronger storms (100+ mph). When the air hits the tropopause, at which level jet stream winds blow continuously, it overshoots the wind at is sculpted into the familiar 'top of the anvil' shape. When it spreads out, the momentum and rapid cooling of the air cause it to curl back downwards forming the two downdrafts, both of which may carry huge hail and copious precipitation downwards to the the Earth below.

When the updraft rotates, it is known as a 'mesocyclone'. The recipe for their formation lies in variations in wind speed and direction with height in the atmosphere. Typically in America, winds at the surface are southwesterly as an approaching low pressure systems spins warm, moist air up from the Gulf of Mexico in the form of a Lower Level Jet. Winds aloft are usually westerly, which are 'backed' in relation to the lower level winds. The upper winds literally 'spin' the lower air mass, creating columns of rotating air 2 to 10km in diameter.

Atop this lower air mass is a 'capping inversion' of warm, dry air from west of the Rocky Mountains and atop this layer, the atmosphere cools rapidly. When the lower atmosphere heats sufficiently, the difference in moisture and temperature on either side of this inversion creates sufficient instability and the lower air breaks through the cap quite violently, releasing energy via condensation and quickly forming the huge convective cloud structures of thunderstorms.

To complete their development and remain relatively stable, these cumulonimbi require the constant infusion of warm, moist air in the form of the updraft. When the ambient air is rotating due to ambient wind shear, the storm will conserve the rotation as it draws the air into its updraft. If the downdrafts interfere with the main updraft, the storm will not reach full intensity. To further potentiate their development, the updrafts and downdrafts need to remain separate. This is achieved as the upper level winds blow the top of the storm forward of the main updraft. The cold air of the forward flank downdraft, which contains the storm's hail content, is thus offset from the warm air of the updraft, which allows the storm to maintain its diet of Gulf moisture.

Tornadoes form from mesocylones, although no one is completely sure of the exact mechanisms involved. Most theories and observations seem to indicate that they are a result in the conservation of momentum, transferring the rotational energy of the updraft to the ground some 600-1000 feet below. While the mesocyclone itself may be as large as 6-10km within the storm, the actual tornadoes are usually no more than 1/4 mile wide. This is akin to a spinning ice skater who uses her arms to shrink her profile, thus increasing her spinning speed. The strongest tornadoes, however, are often much larger; some have been observed to be more than 2km wide, with giant wedge-like profiles.

An 'inchoate' mesocyclone would be one in its initial stage of development, although this is probably a period of time so nebulous as to be non-existent. I'm not sure what particular appeal this pair of words has for me, but it probably stems from the metaphorical power even of a term so dryly scientific in nature, the suggestion of the formation of something beyond itself: more powerful, more demanding of attention.

But beyond the sinister implications of such self-gratifying titles, I like the wordage. Thus follows another haphazard publication, of interest probably to only those who know me and likely only a few of them at that...

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