The monthly mean PNA index is constructed by following modified pointwise method:
PNA = Z*(15°N-25°N,180-140°W)-Z*(40°N-50°N,180-140°W)
+Z*(45°N-60°N,125°W-105°W)-Z*(25°N-35°N,90°W-70°W),
where Z* denotes monthly mean 500 mb height anomaly that is obtained by subtracting the calendar mean value for each month during 1950-2000 base period.
The index is normalized using 1950-2000 base period statistics.
The correlation coefficients between PNA indices using different methods for the 1950-2000 base period.
|
REOF |
Modified Pointwise |
Pointwise |
REOF |
|
0.92 |
0.92 |
Modified Pointwise |
|
|
0.98 |
cf) The PNA index using Pointwise method following Wallace and Gutzler (1981):
PNA = Z*(20°N,160°W)-Z*(45°N,165°W)+Z*(55°N,115°W)-Z*(30°N,85°W).
|