Global Guide

## Global Guide to Tropical Cyclone Forecasting: Chapter 9: Ready Reckoner

### 9.7 DERIVED PARAMETERS

#### 9.7.1 Definition of Terms

 b empirical constant. cg gravity wave phase speed. cp specific heat of dry air at constant pressure. c1, c2 empirical constants.
 e base of natural logarithm. f Coriolis parameter. h,H atmospheric scale height. I inertial frequency. k unit vector perpendicular to the earth surface. L latent heat of condensation.
 Lr Rossby radius of deformation. ln natural logarithm. Ma absolute angular momentum. N Brunt Vaisala frequency, total number in population sample. p air pressure.
 pc central (minimum) pressure of a tropical cyclone. pn representative environmental pressure for a tropical cyclone. q specific humidity. R universal gas constant. Rd gas constant for dry air.
 Ro Rossby number. r radius. rm radius of maximum winds. T temperature. t time.
 u wind component, either zonal or radial. V velocity. v wind component, either meridional or azimuthal. vg geostrophic wind. vm maximum wind speed.
 x empirical parameter. z height above the earth surface. gradient operator. partial derivative. overbar denotes mean.
 ! factorial. relative vorticity. potential temperature. E equivalent potential temperature. latitude, azimuthal angle.
 air density. summation convention. standard deviation. earth angular velocity.

#### 9.7.2 Derived Parameters

Angular Momentum:

where f0 is evaluated at the cyclone centre (Holland, 1983).

Brunt Vaisala Frequency (Static Stability):

Coriolis Parameter:

Divergence:

Equation of State:

Equivalent Potential Temperature:

Inertial Frequency (Inertial Stability):

Mean:

Poisson Distribution: The discrete probability distribution

which has the properties of mean= and standard deviation, =½.

Potential Temperature:

Rossby Number:

Standard Deviation:

Thermal Wind:

Vorticity:

Wind Balance:

For cyclones, the positive (negative) root is used in the northern (southern) hemisphere.

Wind Profiles: (Holland, 1980)

Wind/Pressure Relationships (ms-1):

Note that the Fletcher (1955) formulation has an error in it and will overpredict wind speeds (Myers, 1957).

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