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w_to_omega

Convert vertical velocity with units (m/s) to Pa/s.

Available in version 6.2.0 and later.

Prototype

load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"  ; This library is automatically loaded
                                                             ; from NCL V6.2.0 onward.
                                                             ; No need for user to explicitly load.

	function w_to_omega (
		w  : numeric,  ; float, double, integer only
		p  : numeric,  
		t  : numeric   
	)

Arguments

w

A variable of any dimensionality containing vertical velocity with units (m/s) Array size and shape must match p and t.

p

A variable containing pressure values (Pa). Array size and shape must match omega and t.

t

A variable containing temperature (K). Array size and shape must match omega and p.

Return value

A double array is returned if w is double, otherwise a float array of the same size and shape as w is returned.

Description

Converts vertical velocity (m/s), commonly denoted as w to vertical velocity (Pa/s), commonly denoted as omega. The approximate relationship used is: 


       rgas  = 287.058            ; J/(kg-K) => m2/(s2 K)
       g     = 9.80665            ; m/s2
       rho   = p/(rgas*t)         ; density => kg/m3
       omega = -w*rho*g           ; array operation

See Also

omega_to_w, wind_direction, wind_component

Examples

Example 1: If (a) w[*], p[*] and t[*]; (b) w[*][*][*], p[*][*][*] and t[*][*][*]; (c) w[*][*][*][*], p[*][*][*][*] and t[*][*][*][*] and all have the desired units then: 

       oa = w_to_omega(w, p, t)         ; oa[*] (Pa/s)
       ob = w_to_omega(w, p, t)         ; ob[*][*][*] (Pa/s)
       oc = w_to_omega(w, p, t)         ; oc[*][*][*][*] (Pa/s)

Example 2: Let w(time,lev,lat,lon) and t(time,lev,lat,lon) and plevel(lev) have units mm/day, degC and hPa, respectively. 

                                     ; change units: mm/day to Pa/s
       w       = w*/(1000.*86400.)   ; 1m/1000mm, 86400s/day; (mm/day)(day/86400s)(m/1000mm)    
       omega@units = "Pa/s

       t       = t + 273.15          ; degC -> degK
       t@units = "degK"
                                     ; make p[*] conform to w[*][*][*][*]
       P       = conform(w, p, 1)     ; P(:,:,:,:)
       P       = P*100               ; hPa -> Pa
       P@units = "Pa"
       
       omega   = w_to_omega(w, P, t)         ; omega[*][*][*][*] (Pa/s)
       
       delete(P)        ; no longer needed