GRIB2 - CODE TABLE 4.240

Type of Distribution Function

Revised 09/22/2025


Code Figure
 Meaning
0 No specific distribution function given
1 Delta functions with spatially variable concentration and fixed diameters Dl(p1) in meter (See Note 1)
2 Delta functions with spatially variable concentration and fixed masses Ml(p1) in kg (See Note 2)
3 Gaussian (Normal) distribution with spatially variable concentration and fixed mean diameter Dl(p1) and variance δ (p2) (See Note 3)
4 Gaussian (Normal) distribution with spatially variable concentration, mean diameter and variance (See Note 4)
5 Log-normal distribution with spatially variable number density, mean diameter and variance (See Note 5)
6 Log-normal distribution with spatially variable number density, mean diameter and fixed variance δ (p1) (See Note 6)
7 Log-normal distribution with spatially variable number density and mass density and fixed variance δ and fixed particle density ρ (p2) (See Note 7)
8 No distribution function. The encoded variable is derived from variables characterized by type of distribution function of type No. 7 (see above) with fixed variance σ (p1) and fixed particle density ρ (p2)
9-49151 Reserved
49152-65534 Reserved for Local Use
65535 Missing


Notes:

(1) Bin-Model or delta function with N concentration cl(r) in class (or mode) l.
Concentration-density function:
ƒ(r;d) = ∑l=1N cl(r) δ (d-Dl)

Where:
N - number of modes in the distribution
δ - delta-Function
d - diameter
Dl - diameter of mode l(p1)i

(2) Bin-Model or delta function with N concentration cl(r) in class (or mode) l.
Concentration-density function:
ƒ(r;m) = ∑l=1N cl(r) δ (m-Ml)

Where:
N - number of modes in the distribution
δ - delta-Function
m - mass
Ml - mass of mode (p1)

(3) N-Modal concentration-density function consisting of Gaussian-functions:
ƒ(r;d) = ∑l=1N cl(r) 1/ √ 2πδl  * e-((d-Dl)/δl)2
Where:
N - number of modes in the distribution
d - diameter
Dl - mean diameter of mode l(p1)
δl - Variance of Mode l ((p2)
with N fields of concentration cl(r)

(4) N-Modal concentration-density function consisting of Gaussian-functions:
ƒ(r;d) = ∑l=1Ncl(r)1/ √ 2πδl(r)  * e-((d-Dl)(r)/δl(r))2
with 3N fields of concentration cl(r), variance δl(r), and mean diameter Dl(r)

(5) N-modal log-normal-distribution for the number density:
ƒ(r;d) = ∑l=1Nnl(r)/ √ 2πlogδl(r) * e(log2d/Dl(r))/2log2δl(r)
Where:
d - diameter
with 3N fields of number density nl(r), variance δl(r), and mean diameter Dl(r)

(6) N-modal log-normal-distribution for the number density:
ƒ(r;d) = ∑l=1Nnl(r)/ √ 2πlogδl * e(log2d/Dl(r))/2log2δl
Where:
δl - variance of mode l (p1)
with 2N fields of number density nl(r) and mean diameter Dl(r)

(7) N-modal log-normal-distribution for the number density as in Note 6, but with a prescribed mass density ml(r), from which the diameter Dl(r) is calculated by:
Dl = ( ml(r) / nl(r) π⁄6 ρp,l e9⁄2log2δl )⅓
Where:
δl - variance of mode l (p1)
ρp,l - particle density (p2)
with 2N fields of number density nl(r) and mass density ml(r)



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