LIindex {aiRthermo}

Lifted index

Description

This function calculates the instability parameter Lifted index (Celsius) from pressure, temperature and mixing ratio values described by a vertical sounding.

Usage

LIindex(Ps, Ts, ws, Psurface, deltaP, PWIDTH, doLog = 0)

Arguments

Ps

Pressure (Pa) of the sounding.

Ts

Temperature (K) of the sounding.

ws

Mixing ratio (kg/kg) of the sounding.

Psurface

Surface pressure (Pa). If not available, the first level of the sounding can be used.

deltaP

The width (Pa) of the layers used in the numerical solution of the vertical evolution (integration of the ODE). A default value of 5 Pa is used. It must be positive.

PWIDTH

PWIDTH represents the width (Pa) of the lower layer that will be averaged for P, T and w in order to calculate a "mixed-layer" average parcel that will be used for the vertical evolution. Typically 5000-10000 Pa are used.

doLog

Use logarithmic vertical interpolation between sounding levels if doLog=1. It is not used by default (doLog=0).

Details

If the 500 hPa needed level is 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 0/1.

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 the initial condition to 500 hPa using a pressure step deltaP (Pa). The vertical adiabatic evolution is either dry (before saturation) or pseudoadiabatic at every vertical step with a correction for moisture in c_p using the value of the mixing ratio (c_{pm} as in Tsonis, eq 7.11).

If the sounding does not enclose the needed level of 500 hPa and the interpolation fails, the function returns -99999999.

Value

This function returns the LI index (Celsius).

References

Tsonis, A. A. (2002). An Introduction to Atmospheric Thermodynamics, Cambridge University Press, Cambridge. Eq. 7.11.

Examples

data(RadiosondeA)
aPs<-RadiosondeA[,1]*100
aTs<-C2K(RadiosondeA[,3])
aws<-RadiosondeA[,6]/1000
LIindex(aPs,aTs,aws,max(aPs),5,2500,0)