Changes in water vapor transports of the ascending branch of the tropical circulation

Abstract

Recent studies have found contradicting results on whether tropical atmospheric circulation (TAC) has intensified or weakened in recent decades. Here we reinvestigate recent changes in TAC derived from moisture transports into the tropics using high temporal and spatial resolution reanalyses from ERA-Interim. We found a significant strengthening of both the lower-level inward transports and the midlevel outward transports over the recent two decades. However, the signal in the total budget is weak because the strengthening of the inflow and the strengthening of the outflow neutralize each other, at least to some extent. We found atmospheric humidity to be relatively stable, so we suggest that the intensification is mainly caused by an intensification of the wind-related circulation strength. The exact quantitative values were found to depend heavily on whether the calculations are based on mean or instantaneous values. We highlight the importance of using the instantaneous values for transport calculations, as they represent the coincidence of high wind speeds and high atmospheric humidity. © 2011 by the American Geophysical Union.