The following definitions should be used
Mean errorĀ 

M = \frac{1}{M_w} \sum_{i=1}^n w_i (x_f - x_v)_i

where the sum of the weights

M_w = \sum_{i=1}^n w_i


Root mean square (rms) error

rms = \sqrt {\frac{1}{M_w} \sum_{i=1}^n w_i (x_f - x_v)_i^2 }


Correlation coefficient between forecast and analysis anomalies

r = \frac{\sum_{i=1}^n w_i (x_f-x_c-M_{f,c})_i (x_v-x_c-M_{v,c})_i}{\sqrt{\left(\sum_{i=1}^n w_i (x_f-x_c-M_{f,c})_i^2 \right) \left(\sum_{i=1}^n w_i (x_v-x_c-M_{v,c})_i^2 \right) }}

rms vector wind error

rms = \sqrt {\frac{1}{M_w} \sum_{i=1}^n w_i (\vec{V}_f - \vec{V}_v)_i^2 }

Mean absolute error

MAE = \frac{1}{M_w} \sum_{i=1}^n w_i | x_f - x_v |_i

rms anomaly

rmsa = \sqrt {\frac{1}{M_w} \sum_{i=1}^n w_i (x - x_c)_i^2 }

standard deviation of fieldĀ 

sd = \sqrt {\frac{1}{S_w} \sum_{i=1}^n w_i (x - M_x)_i^2 }

where

M_x = \frac{1}{M_w} \sum_{i=1}^n w_i x_i

S1 score

S_1 = 100 \frac{\sum_{i=1}^n w_i (e_g)_i}{\sum_{i=1}^n w_i (G_L)_i}


Where:

x_f
x_v
x_c
M_{f,c}
M_{v,c}
\vec{V}_f
\vec{V}_v