Understanding the Atlantic Hurricane Season: Technical Terms

By: Cavin Rawlins , 5:04 PM GMT on April 21, 2008

Technical Terms Simplified

I have compiled and simplified a list of technical terms that we will come across this hurricane season.

Tropical Cyclogenesis: is the technical term describing the development and strengthening of a tropical cyclone in the atmosphere.

Monsoon Trough: a convergence zone, like the ITCZ, that lies between the northeast trades and the monsoon southwesterlies.

Monsoon Southwesterlies: results when the southeast trades cross the equator and are deflected towards the northeast due to the Coriolis force.

African Easterly Wave: a synoptic feature that forms over Eastern Africa and moves westward as convective signatures.

Tropical Upper Tropospheric Trough (TUTT): an upper level trough that develops across the central Atlantic in the summer. It’s different from mid-latitude troughs in that it does not extend into the lower atmosphere and it’s mainly quasi-stationary.

Inverted V signature: a cloud pattern displayed by tropical waves in the Tropical Atlantic that resembles an upside-V.

African Easterly Jet (AEJ): a easterly flowing jet found in the lower part of the atmosphere over Africa that is responsible for the development of tropical waves.

Barotropic Cyclone: where both the temperature and pressure fields increase or decrease towards the center. Example, tropical cyclones.

Baroclinic Cyclone: a cyclone forming within a baroclinic environment and having asymmetric characteristics. Example, extratropical cyclones.

Baroclinic Environment: an environment characterized by vertical wind shear and temperature gradients.

INVEST: an area of disturbed weather persisting for more than 24 hrs outside diurnal variations that has potential to develop and/or threaten land. Invests are assigned by the NHC rotating from 90 to 99. The suffix "L" is assigned to invest in the Atlantic and "E" for eastern Pacific. Example: 90L, 91L, 92L, 93L, 94L, 95L, 96L, 97L, 98L, 99L, 90L, 91L, 92L, and so on.

Diurnal Convective Maximum: the time of the day when instability and convection is highest. It occurs around mid-late afternoon over land and around sunrise over water.

Diurnal Convective Minimum: the time of the day when instability and convection is the least. It occurs just after sunrise over land and around sunset over water.

The Madden-Julian Oscillation (MJO): is an eastward equatorial traveling pattern of anomalous rainfall and convection that is planetary in scale. When the MJO is positive, convection is enhanced and the likelihood tropical cyclone formation is increased.

Tradewind Inversion: an environment over the tropical Atlantic characterized by stable air in the mid-upper levels and stratocumulus or cumulus in the surface layer.

Saharan Air Layer (SAL): a layer of dust originating from West Africa that blows across the Tropical Atlantic.

The Azores High: an area of high pressure found the subtropical Atlantic. Depending its location it is sometimes called the Bermuda High.

Eye wall replacement cycle (EWRC): a process by which an outer eyewall forms, choking and breaking down the inner eyewall. Tropical cyclones often weaken during this process.

Heat of condensation: heat release when water vapor condenses into water droplets

Pressure level: a way of measuring altitude using pressure units.

Lower Level: that part of the atmoshphere between the surface and 600 hpa.

Mid-Level: that part of the atmophsere between 600 hpa and 400 hpa.

Upper Level: that part of the atmopshere above 400 hpa.

Diurnal Cycle (Max and Min) Visualized

Figure 1.The mean diurnal cycle of precipitation features identified from eight years of TRMM PR data over the tropical oceans (a, upper) and land (b, lower) (Image courtesy of Dr. Steve Nesbitt).

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5. cyclonekid
11:21 AM GMT on September 01, 2009
Thanks, 456 for answering my question...
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4. Cavin Rawlins
9:23 PM GMT on April 22, 2008
They are more of definitions than explanations. I could include a blog entry that would give additional information regarding the interaction with the tropics/subtropics.
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3. Ivansrvivr
8:22 PM GMT on April 22, 2008
I think (and this is just my opinion) your definitions should include more about how such things influence the the tropics. This is good blog though overall.
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2. Cavin Rawlins
11:10 AM GMT on April 22, 2008
thanks back atcha!
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1. sullivanweather
10:47 AM GMT on April 22, 2008

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With a Bachelors Degree in Environmental Sciences (2009), began tracking tropical storms in 2002 and is now a private forecaster.

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