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brunt_vaisala
Compute the Brunt-Vaisala frequency which is a measure of bouyancy
Available in version 6.4.0 and later.
Prototype
load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl" function brunt_vaisala ( th : numeric, ; float, double, integer only z : numeric, dim [1] : integer ) return_val [dimsizes(th)] : float or double
Arguments
thPotential temperature (K).
zGeometric height (m). Same dimensionality as th.
dimThe dimension number of z which corresponds to th.
Return value
An array of the same size and shape as th. The output will be double if th or z is of type double.
Description
The Brunt-Vaisala frequency (1/s) is a measure of bouyancy. In a continuously stratified fluid, it is the natural frequency of the vertical oscillation of fluid parcels.
For plotting, the returned values which have units (1/s) are often multiplied by 86400 (s/day) to get units of (1/day).
See Also
coriolis_param, pot_temp, static_stability, eady_growth_rate, rigrad_bruntv_atm
Examples
Example 1: Read data from a WRF file and calculate assorted quantities.
;---------------------------------------------------------- ; WRF DATA ;---------------------------------------------------------- a = addfile("wrfout_d01_2013-05-17_12","r") ;[Time|1]x[bottom_top|40]x[south_north|324]x[west_east|414] ; 0 1 2 3 th = wrf_user_getvar(a,"theta",-1) ; potential temperature (degK) z = wrf_user_getvar(a,"z",-1) ; model height ua = wrf_user_getvar(a,"ua" ,-1) ; u at mass grid points brunt = brunt_vaisala_frq(th, z, 1) printVarSummary(brunt) printMinMax(brunt, 0) xlat = a->XLAT ; [Time|1]x[south_north|324]x[west_east|414] printVarSummary(xlat) XLAT = conform(th, xlat, (/0,2,3/)) ; (1,40,324,414) egr = brunt_vaisala(th, ua, z, XLAT, 1) printVarSummary(egr) printMinMax(egr, 0) ; print all vertical values at an arbitrarily chosen grid point ix = 20 ; arbitrary jy = 21 dimTimes = getfilevardimsizes(a,"Times") ntim = dimTimes(0) print( sprintf("%7.1f", z(ntim-1,:,jy,ix)) \ + sprintf("%15.5e",brunt(ntim-1,:,jy,ix)) \ + sprintf("%15.5e",egr(ntim-1,:,jy,ix)) )The (edited) output is:
Variable: brunt
Type: float
Total Size: 20925216 bytes
5231304 values
Number of Dimensions: 4
Dimensions and sizes: [Time | 1] x [bottom_top | 39] x [south_north | 324] x [west_east | 414]
Coordinates:
Number Of Attributes: 3
long_name : Brunt–Vaisala (buoyancy) frequency: atm
units : 1/s
info : http://glossary.ametsoc.org/wiki/Brunt-v%C3%A4is%C3%A4l%C3%A4_frequency
(0) Brunt-Vaisala (buoyancy) frequency: atm: min=0 max=0.0743625
Variable: xlat
Type: float
Total Size: 536544 bytes
134136 values
Number of Dimensions: 3
Dimensions and sizes: [Time | 1] x [south_north | 324] x [west_east | 414]
Coordinates:
Number Of Attributes: 5
FieldType : 104
MemoryOrder : XY
description : LATITUDE, SOUTH IS NEGATIVE
units : degree_north
stagger :
Variable: egr
Type: float
Total Size: 20925216 bytes
5231304 values
Number of Dimensions: 4
Dimensions and sizes: [Time | 1] x [bottom_top | 39] x [south_north | 324] x [west_east | 414]
Coordinates:
Number Of Attributes: 3
_FillValue : 1e+20
long_name : maximum eady growth rate
units :
(0) maximum eady growth rate: min=6.5775e-13 max=0.00406928
------------------------------------------
Z BRUNT EGR
(0) 29.2 0.00000e+00 1.00000e+20
(1) 99.1 0.00000e+00 1.00000e+20
(2) 192.9 0.00000e+00 1.00000e+20
(3) 313.0 0.00000e+00 1.00000e+20
(4) 463.0 3.77258e-03 3.49967e-06
(5) 647.4 1.02118e-02 1.24992e-05
(6) 872.0 1.06960e-02 1.05712e-05
(7) 1142.9 1.34968e-02 2.63051e-06
(8) 1463.4 1.98726e-02 3.39886e-06
(9) 1835.1 1.83999e-02 4.34887e-06
(10) 2258.8 1.26123e-02 2.34866e-06
(11) 2733.7 1.07150e-02 5.76828e-07
(12) 3259.3 9.99975e-03 3.18521e-06
(13) 3835.0 1.02520e-02 4.51157e-06
(14) 4442.5 1.24183e-02 2.02051e-06
(15) 5057.9 1.37012e-02 9.44995e-07
(16) 5674.7 1.16770e-02 1.08149e-06
(17) 6292.0 8.31896e-03 5.79138e-06
(18) 6907.9 9.73829e-03 1.05950e-05
(19) 7523.3 1.10047e-02 5.64395e-06
(20) 8139.1 1.07249e-02 3.27011e-07
(21) 8755.4 1.01392e-02 8.26907e-07
(22) 9372.1 9.75036e-03 3.56708e-06
(23) 9988.7 1.10250e-02 7.66039e-06
(24) 10606.4 1.13320e-02 1.39343e-05
(25) 11225.7 1.00888e-02 1.61388e-05
(26) 11845.9 7.97759e-03 1.17152e-05
(27) 12465.8 8.47375e-03 4.51332e-06
(28) 13085.9 1.04011e-02 5.23316e-06
(29) 13707.9 1.33597e-02 1.15163e-05
(30) 14335.0 1.68360e-02 7.09510e-06
(31) 14971.9 1.79719e-02 5.89672e-06
(32) 15621.2 2.00726e-02 6.78411e-06
(33) 16288.0 2.13622e-02 4.65560e-06
(34) 16976.2 2.06080e-02 4.16494e-06
(35) 17686.4 2.01936e-02 4.20652e-06
(36) 18420.1 2.23056e-02 2.95023e-06
(37) 19185.4 2.51125e-02 2.68033e-06
(38) 20094.5 2.53134e-02 3.04996e-06