Sounding Station Parameters and Indices
SLAT
Station latitude in degrees
SLON
Station longitude in degrees; West longitude is negative
SELV
Station elevation in meters
SHOW
Showalter index
SHOW
= T500 - Tparcel
T500
= Temperature in Celsius at 500 mb
Tparcel
= Temperature in Celsius at 500 mb of a parcel lifted from 850 mb
LIFT
Lifted index
LIFT
= T500 - Tparcel
T500
= temperature in Celsius of the environment at 500 mb
Tparcel
= 500 mb temperature in Celsius of a lifted parcel with the average pressure, temperature, and dewpoint of the layer 500 m above the surface
LFTV
LIFT
computed by using
virtual temperature
.
SWET
SWEAT index
SWET
= 12 * TD850 + 20 * TERM2 + 2 * SKT850 + SKT500 + SHEAR
TD850
= Dewpoint in Celsius at 850 mb
TERM2
= MAX ( TOTL - 49, 0 )
TOTL
= Total totals index
SKT850
= 850 mb wind speed in knots
SKT500
= 500 mb wind speed in knots
SHEAR
= 125 * [ SIN ( DIR500 - DIR850 ) + .2 ]
DIR500
= 500 mb wind direction
DIR850
= 850 mb wind direction
KINX
K index
KINX
= ( T850 - T500 ) + TD850 - ( T700 - TD700 )
T850
= Temperature in Celsius at 850 mb
T500
= Temperature in Celsius at 500 mb
TD850
= Dewpoint in Celsius at 850 mb
T700
= Temperature in Celsius at 700 mb
TD700
= Dewpoint in Celsius at 700 mb
CTOT
Cross Totals index
CTOT
= TD850 - T500
TD850
= Dewpoint in Celsius at 850 mb
T500
= Temperature in Celsius at 500 mb
VTOT
Vertical Totals index
VTOT
= T850 - T500
T850
= Temperature in Celsius at 850 mb
T500
= Temperature in Celsius at 500 mb
TOTL
Total Totals index
TOTL
= ( T850 - T500 ) + ( TD850 - T500 )
T850
= Temperature in Celsius at 850 mb
TD850
= Dewpoint in Celsius at 850 mb
T500
= Temperature in Celsius at 500 mb
CAPE
Convective Available Potential Energy (J/kg)
CAPE
= GRAVTY * SUMP ( DELZ * ( TP - TE ) / TE )
SUMP
= sum over sounding layers from LFCT to EQLV for which ( TP - TE ) is greater than zero
DELZ
= incremental depth
TP
= temperature of a parcel from the lowest 500 m of the atmosphere, raised dry adiabatically to the LCL and moist adiabatically thereafter
TE
= temperature of the environment
CAPV
CAPE
computed by using
virtual temperature
.
CAPV
= GRAVTY * SUMP ( DELZ * ( TVP - TVE ) / TVE )
SUMP
= sum over sounding layers from LFCV to EQTV for which ( TVP - TVE ) is greater than zero
DELZ
= incremental depth
TVP
=
virtual temperature
. of a parcel from the lowest 500 m of the atmosphere, raised dry adiabatically to the LCL and moist adiabatically thereafter
TVE
=
virtual temperature
. of the environment
CINS
Convective Inhibition (J/kg)
CINS
= GRAVTY * SUMN ( DELZ * ( TP - TE ) / TE )
SUMN
= sum over sounding layers from top of the mixed layer to LFCT for which ( TP - TE ) is less than zero.
DELZ
= incremental depth
TP
= temperature of a parcel from the lowest 500 m of the atmosphere, raised dry adiabatically to the LCL and moist adiabatically thereafter
TE
= temperature of the environment
CINV
CINS
computed by using
virtual temperature
.
CINV
= GRAVTY * SUMN ( DELZ * ( TVP - TVE ) / TVE )
SUMN
= sum over sounding layers from top of the mixed layer to LFCV for which ( TVP - TVE ) is less than zero.
DELZ
= incremental depth
TVP
=
virtual temperature
. of a parcel from the lowest 500 m of the atmosphere, raised dry adiabatically to the LCL and moist adiabatically thereafter
TVE
=
virtual temperature
. of the environment
EQLV
Equilibrium level (hPa)
EQLV
= level at which a parcel from the lowest 500 m of the atmosphere is raised dry adiabatically to the LCL and moist adiabatically to a level above which the temperature of the parcel is the same as the environment. If more than one Equilibrium Level exists, the highest one is chosen.
EQTV
EQLV
computed by using
virtual temperature
.
LFCT
Level of Free Convection (hPa) by comparing temperature between a parcel and the environment
LFCT
= level at which a parcel from the lowest 500 m of the atmosphere is raised dry adiabatically to LCL and moist adiabatically to the level above which the parcel is positively buoyant. If more than one LFCT exists, the lowest level is chosen. If the parcel is positively bouyant throughout the sounding, the LFCT is set to be the same as the LCLP.
LFCV
LFCT
computed by using
virtual temperature
.
BRCH
Bulk Richardson number
BRCH
= CAPE / ( 0.5 * U**2 )
CAPE
= Convective Available Potential Energy
U
= magnitude of shear ( u2 - u1, v2 - v1 )
u1,v1
= average u,v in the lowest 500 m
u2,v2
= average u,v in the lowest 6000 m
BRCV
BRCH
computed by using
CAPV
BRCV
= CAPV / ( 0.5 * U**2 )
CAPV
= CAPE computed by using
virtual temperature
.
U
= magnitude of shear ( u2 - u1, v2 - v1 )
u1,v1
= average u,v in the lowest 500 m
u2,v2
= average u,v in the lowest 6000 m
LCLT
Temperature (K) at the LCL, lifted condensation level, from an average of the lowest 500 meters.
LCLT
= [1 / ( 1 / ( DWPK - 56 ) + LN ( TMPK / DWPK ) / 800 )] + 56
LCLP
Pressure (hPa) at the LCL, lifted condensation level, from an average of the lowest 500 meters.
LCLP
= PRES * (
LCLT
/ ( TMPC + 273.15 ) ) ** ( 1 / KAPPA )
Poisson's equation
MLTH
Mean mixed layer THTA (K)
MLTH
= average THTA in the lowest 500 m
MLMR
Mean mixed layer MIXR (g/kg)
MLMR
= average MIXR in the lowest 500 m
THTK
1000 mb to 500 mb thickness (meter)
THTK
= ( Z500 - Z1000 )
Z500
= Height of the 500 mb surface
Z1000
= Height of the 1000 mb surface
PWAT
Precipitable water (mm) for the entire sounding