Moist Static Energy Budget Analysis on Various Time-scales during TOGA COARE

Abstract:

Temperature variability is small in the tropics, so anomalous moist static energy (MSE) is primarily due to anomalous moisture variability which is tightly connected with precipitation variability. Thus careful analysis of MSE budgets improves our understanding of the dynamics of tropical convection. Previous studies suggested that a recharge-discharge cycle of column-integrated MSE can be observed in the MJO life-cycle and life-cycles of equatorial Kelvin waves. Does this imply that the thermodynamics in the MJO is regulated by a similar process to that of higher frequency variability? To answer this question, we explore the recharge and discharge mechanisms of column-integrated MSE for various time-scales of variability using the TOGA COARE data set. We find that the MSE budgets behave in significantly different ways on the different time-scales. The relative contribution of each MSE budget term to the recharge-discharge mechanism gradually changes as the time-scale gets longer, making the MSE budget behavior on the MJO time-scale distinct from that on the shorter time-scales. For each frequency, we estimate the gross moist stability (GMS), which represents efficiency of MSE export via convection and associated large-scale circulations. The GMS has been used in many MJO studies. One of the popular usages is a linearization of vertical MSE advection in simplified MJO models with an assumption that the GMS is constant. In our analysis, we find that as the time-scale gets longer, the GMS, which is generally a highly variable quantity in a convective life-cycle, becomes a more constant quantity. We show that this more-constant GMS is primarily due to different patterns of the evolution of the vertical velocity profile.