Effects of an Equatorial “Wall” on an Atmospheric Model

Abstract

The effect of an artificial lateral boundary (the wall) at the Equator on a simulated atmospheric circulation was studied numerically. By comparing the solutions of two 30-day integrations of a global model with and without the wall, we found that the discrepancies of the wind and temperature at the middle and high latitudes became appreciable at approximately 8 days and serious at approximately 12 days. This suggests that the wall (hemispheric) model may be applied as a forecast model for a maximum of about 12 days. The disagreement in the wind between the two cases starts just below the tropopause level at the Equator and spreads toward the higher latitudes. Eventually, the middle latitudes respond to this equatorial effect, and the disagreement is amplified to the natural variability level. Insertion of the wall considerably increases the condensation of water vapor in the Tropics for the winter hemisphere; the reverse is true for the summer hemisphere. The result is that, in the winter hemisphere, the tropical troposphere and the stratosphere are cooler and the higher latitude troposphere is warmer in the wall case than in the control case. The opposite is true for the summer hemisphere.