HURRICANE IKE CIRCULATION – LESSON 1

LEFT CLICK THESE IMAGES TO MAKE THEM LARGER.  YOU CAN ACHIEVE A NICE HIGH RESOLUTION VIEW OF THE IMAGE OF IKE ABOVE WITH A SECOND LEFT CLICK.

Inflow consists of the harder-edged clouds with sharp contrast – Outflow consists of the more diffuse cirrus and cirrostratus of the upper layer.

PLEASE REMEMBER THAT THOUGH THIS IS A TUTORIAL, THE LOCATIONS OF STORMS AS SHOWN ON THE GRAPHICS ARE TIME-SENSITIVE.  TO AVOID MISUNDERSTANDINGS, CONSULT THE DATE AND TIME OF THE POSTING.

With this post you can either simply enjoy the high resolution image of Ike and leave it at that point or explore deeper into the dynamics of storms such as this.

I have provided a large image (above) of Ike completed earlier today followed by smaller images contrasting the circulation below with the circulation above.  Thirdly, you will find below an image of what might seem like a very odd looking hurricane compared to what you have been looking at this season.  To see it, you must ask for more detail when the invitation appears at the end of the next paragraph.

Because of only a small amount of sheer and other factors, Ike is a well-formed system.  And – if you can get past its destructive character you might marvel at its beauty.  I speak of it as though it were a living thing.  In many respects, it is a separate entity with a life of its own.  We even talk about the life cycle of such a storm.  We personify it with a name, in this case a male name.  Its winds spiral because of the Coriolis effect and the whole storm’s path responds to the Coriolis effect – sometimes that is evident, sometimes it is not.  If you find yourself confused about the Coriolis effect, please be patient because I intend to post an item soon, with an explanation of certain aspects of hurricanes which might seem to be contradictions when they are not at all.  Believe me, misunderstandings about the Coriolis effect does cause considerable confusion.

Wind is the movement of air in response to a pressure gradient, almost always moving closer to lower pressure environs.  It doesn’t move perfectly with the gradient because of the Coriolis effect.  The degree to which the wind moves contrary to the gradient direction depends upon many factors which may be addressed at another time. Suffice it to say, for now, that the Coriolis effect is what causes the rotation both below and above.

Just as water flows downhill in response to a slope gradient, air flows from high to low in response to a pressure gradient.  The hotter the air and the greater the specific moisture content of the air – the less pressure it exerts.  The second half of that statement is paradoxical for many people because, sensibly, hot humid air “feels” stifling and heavy to us.  This paradox also will be discussed in a separate post soon.

Ike’s winds spiral inward toward a low pressure center cyclonically (counterclockwise in the Northern Hemisphere) and pick up velocity the closer to the eye wall because of the “conservation of angular momentum.”  That is illustrated when a figure skater spins faster as more mass approaches the axis of rotation.  This is achieved by him/her pulling in both arms and legs to spin faster.  Air rises within the storm, cools by expansion (forming cloud droplets once the dew point temperature is reached) and at some point very far up it becomes stable and then diverges outward anticyclonically (clockwise in the Northern Hemisphere).

The condensation of water vapor into cloud droplets within the rising air provides the primary source of energy for the storm, the latent heat of condensation.  That extra burst of heat makes the rising air even more unstable so that it has a tremendous positive buoyancy force – just as the heated air in a hot air balloon only far more exaggerated.  As it continues rising more air rushes in behind it.  Interestingly, that extra heat is “taken” from the sea surface in the evaporation process and then travels as potential energy “hidden” until the cloud-forming condensation occurs thus revealing it.  “Latent” means “hidden.”

If the “L” for low central pressure near the bottom of the storm and the “H” for high central pressure aloft puzzle you – the explanation is straight forward.  Please understand that in the graphic above comparing the incoming air of the storm with the outgoing air, the pressure at the surface is NOT lower than the pressure at the top of the storm.  You see, because I have a red “L” below and a blue “H” at the storm’s top you might think that to be true.  But – the pressure always drops with an increase in altitude.  So, why do I have an H above and an L below?  The pressure in the core region of the storm is low compared to the pressure away from the core at that same elevation.  Likewise, the pressure aloft at the middle of the storm is high compared to the pressure at the same elevation away from the middle.

There is considerable confusion about the terms cyclone/cyclonic and anticyclone/anticyclonic.  The latter set is often used incorrectly.

Hurricanes’ surface flow in the Northern Hemisphere is counterclockwise and they are cyclonic.  Hurricanes’ surface flow in the Southern Hemisphere is clockwise and they too are cyclonic.  Hurricanes are predominately rotating lows.  However, as you have seen, at the top they are anticyclonic – (rotating highs) but it’s the cyclonic component that is dominant and does the damage.  So, if you hear of a low pressure system rotating the “wrong” way (as do some tornadoes and waterspouts) do not make the mistake of calling them anticyclones.  They can’t be because they are rotating lows and, I repeat, anticyclones are rotating highs.  A great example of a rotating high is a cold air mass that moves into the U.S. from Canada.  They rotate clockwise around a central core of high pressure.  Instead of air converging and rising as it does in a hurricane, anticyclonic air sinks and diverges.

Hurricanes and extra-tropical cyclones (rotating lows that typically have fronts) are too large to rotate the wrong way for their respective hemispheres.  No such thing has ever been observed.  But, as previously mentioned, tornadoes and waterspouts can sometimes develop with a wrong-way rotation.

The image below is a cyclone even though it is rotating clockwise; it is very unusual hurricane located off the coast of Brazil.  Of course it is rotating clockwise because it is in the Southern Hemisphere where the Coriolis effect is opposite what it is in the Northern hemisphere.

LEFT CLICK FOR LARGER IMAGE

4 comments so far

  1. levi on

    wow… what could be its effect when it landforms.. i wonder

  2. shafi on

    hi a am student climatologiy
    a need help your in rainfall heavy and synoptic. can help me?
    thanks

    • cloudman23 on

      Dear Shafi,

      Before I take the time to communicate further with you, I request that you please provide me the following information:

      Are you formally engaged in a study of climatology? If so, where?
      What is your primary language?
      What is your age?
      What do you want to know about heavy rainfall?
      What do you want to know about synoptic weather?


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