Sindex {aiRthermo}

Showalter Instability Index

Description

This function computes Showalter instability index (Celsius) from given parameters from a vertical sounding pressure (Pa), temperature (K) and mixing ratio (kg/kg).

Usage

Sindex(Ps, Ts, ws, deltaP, doLog = 0)

Arguments

Ps

A vector with pressure values in Pa.

Ts

A vector with temperature values in Kelvin.

ws

A vector with mixing ratio values in kg/kg.

deltaP

The width (Pa) of the layers used in the numerical solution of the vertical evolution.

doLog

Use logarithmic vertical interpolation between sounding levels. A default value is 0.

Details

If the needed levels (850 hPa or 500 hPa) are not exactly found in the input sounding, logarithmic/linear vertical interpolation is run to get the corresponding T/w from the Ps/Ts/ws depending on the value of doLog (TRUE or FALSE).

The evolution of the lifted particle is computed by integrating the dT/dP ordinary differential equation (applying the Runge Kutta 4th order method) that represents the vertical adiabatic evolution from 850 hPa to 500 hPa using a pressure step dP > 0 (Pa). The vertical adiabatic evolution is either dry (before saturation) or pseudoadiabatic at every vertical step with a correction for moisture in the specific heat at constant pressure c_p during the dry steps (as in Tsonis, eq 7.11).

If the sounding does not enclose the needed levels and the interpolation fails, the function returns -99999999.

Value

This function returns the Showalter instability index (Celsius).

References

Djuric D. (1994). Weather Analysis, Prentice Hall, New Jersey.

See Also

LIindex

Examples

data(RadiosondeA)
aPs<-RadiosondeA[,1]*100
aTs<-C2K(RadiosondeA[,3])
aws<-RadiosondeA[,6]/1000
S<-Sindex(aPs,aTs,aws,5,0)