Constraints to the tropical low-cloud trends in historical climate simulations

Abstract

Given the importance and difficulty in evaluating long-term trends in the tropical low-cloud amount (Cl), we examined mechanisms that determine the Cl trend in 20th century experiments using two different versions of the climate model called the Model for Interdisciplinary Research on Climate (MIROC). The Cl trend patterns are coherent with trends in vertical velocity (ω) and lower-tropospheric stability (LTS). While the mean LTS trend varies and gives a stronger constraint to the Cl trends, the ω trend cannot do so due to mass conservation. Two of three reanalysis products support the positive LTS trend, but it is inconclusive because of the diversity in pattern and sign. © 2011 Royal Meteorological Society © 2011 Royal Meteorological Society.