WACCM Figures


Three WACCM simulations have been performed using observed SSTs for the period 1950-2000. The zonally averaged temperature differences between El Nino and La Nina years are shown for Northern winter months over the lower 100 km of the WACCM domain. An apparently significant response is found in the polar vortex strength, with El Nino years having a more disturbed and, consequently, warmer polar vortex. There is also a statistically significant response at the summer mesopause, particularly in January, driven by changes in parameterized gravity forcing. It is not clear whether this change is physically realistic, since derives largely from changes in gravity wave filtering due to modest changes in lower stratospheric winds.

The dynamical fields from one of the WACCM simulations was used to perform a five year chemistry and transport simulation with the MOZART III model. The top panels show the total column ozone (DU) during March for a La Nina year (1989, left) when the vortex is relatively undisturbed, and for an El Nino year (1992, right) when the vortex has less isolated. Much lower ozone concentration are found at high latitudes in an undisturbed vortex. The lower panels show time-height sections of the ozone mixing ration (ppmv) near the South (left, vertical lines on Oct 1) and North (right, vertical lines on March 1) poles. The South Pole has significant ozone depletion near 20 km every spring but the North Pole has significant depletion only in 1989 when the vortex is very isolated.