Category Archives: Earth Science

Hurricanes: ripped apart

Hurricane Katrina

Over the years Hurricanes have acquired the status of a devil, something that a common man should fear of!  Are hurricanes so mysterious? In this article I take you into the World of Hurricanes.

There are different atmospheric phenomena like cyclone, anti cyclone, tornado, etc, that are wrongly used interchangeably. Amongst them Hurricane is neither the largest nor the most intense; but it is the most destructive one. A hurricane is a storm of tropical origin with a cyclonic wind circulation of 74 mph or higher velocity. Let us rip it apart part by part. Let us go to Tropical oceans where they are born.

 

Life-stages of Hurricane:

I) Formative Stage:

Begins when an organized circulation develops in an Easterly wave or in vicinity of Intertropical Convergence Zone and ends when disturbance reaches Hurricane Intensity.

Hurricane formation is an Ocean phenomenon.They are formed in tropical region and move northwards in clockwise path,  spinning counter-clock wise in Northern Hemisphere. (Paths and spinning directions are opposite in southern hemisphere). Following are the favorable conditions for the formation of a hurricane:

  1. Existence of subnormal pressure in low latitude and above normal in high latitudes.
  2. An existing disturbance of some sort in the tropics
  3. Easterlies decreasing with height extending to 30000 feet or higher.
  4. The location of surface disturbance below 200 millibar pressure.
  5. Movement of disturbance at less than 20 mph.

At this stage hurricane becomes a self-feeding atmospheric phenomenon and continues to grow. It in engineering terms is nothing but a huge heat-engine.

shematic of Hurricane as a heat engine

 

Heat Engine cycle closely resembles Carnot efficiency=(T1-T0)/T1

where, T1= Sea surface Temperature=300K

T0= Stratospheric Temp = 200K

Mechanical energy (W) balances the frictional losses.

II) Stage of Immaturity: Hurricane continues to deepen and reaches its maximum intensity. It is most symmetric and small in area.

III)  Stage of Maturity: Isobars are expanding, with no further deepening. Area covered is maximum. Intensity is decreasing with time.

IV)  Stage of Decay: Occurs when hurricane moves inland, mainly because of two reasons: there is no source of warm water available anymore and secondly land friction.

This is how a typical journey of hurricane will look like:

We haven’t yet understood the hurricanes fully. We did a time journey with hurricanes, now let’s do a spatial journey into the hurricanes. Tighten your sit belts, we are about to enter a mature hurricane.

 

Parts of Hurricane

A hurricane is really a free-vortex, where the circumferential speed is inversely proportional to the radius.

Hurricane: opened up


  1. Outer Portion: Wind increases steadily from periphery(20-30 mph) towards center (120-150 mph)
  2. Region of maximum winds surrounding the eye.
  3. Eye: Size of 5-15 miles.

As the center of  eye is aproached wind diminishes with amazing rapidity from extreme violence to <15 mph.

Fast upward moving motions lift air right upto the base of Stratosphere(~15 km altitude)

The size of fully grown hurricane  is expressed in two ways:

1. Diameter of Hurricane winds(>74mph) : ~100 miles
2. Diameter of Gale winds(>40mph): 350-400 miles
Are the hurricanes so bad? May be not always…
Useful Effects of Hurricane

  1. A single hurricanes contains HUGE amount of energy. How much huge? Well, if we are talking only about the kinetic energy of winds, it amounts to  1.5 x 1012Watts, which is nearly half the planet’s energy consumption. If we get little more greedy and think in terms of including thermal energy also, we are talking about  6.0 x 1014 Watts of energy, which is 200 times the World’s energy needs. No one has till date succeeded in extracting energy out of hurricane. Wanna give it a try?
  2. Hurricanes bring rains with them as a consequence of condensing of sea water. This in other words brings fresh water supply to the large cities.
  3. Scientist see hurricanes as one of the possible means of preventing gradual cooling of Poles an gradual heating of Equators.
    What next???


    Future Research

Further work is needed in following fields

  • Understanding the mechanism of Hurricane completely
  • Accurate forecasting of hurricane movement
  • Further studies on Role of planetary circulation on development and re-curvature of hurricanes.
  • Harnessing useful effects of Hurricanes
  • To investigate distribution of energy in the hurricane.

If you stay in hurricane affected zone you should read these links about survival tips in a hurricane:

1.  http://www.pamlico-nc.com/emergency/hurricane.htm

2.  http://firstaid.about.com/od/emergencypreparation/bb/06_hurricane.htm

3.  http://www.prepare4disaster.com/Hurricanetips.html?NID=9408001&

That’s all from Ally’s end.  Would love to hear your experiences…

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