Figure 7. Spatial reconstruction of Palmer Drought Severity Index (PDSI) at (a) secular trend and (b) El Nino/Southern Oscillation (ENSO) frequency (0.228 cycles/year). The length of the arrows represents the amplitude of the signal and the angle from the horizontal represents the phase lag. For easier interpretation the arrows are colored according to angle from the horizontal (black for 1 to 90 degrees, red for 91 to 180 degrees, blue for 181 to 270 degrees, and green for 271 to 360 degrees).
