The Moist Static Energy Budget on Intraseasonal Time Scales as Observed in NCEP Reanalysis Data

The intraseasonal vertically-integrated moist static energy (MSE) budget in a climate model was studied by Maloney (2009). The MSE budget associated with the Madden-Julian oscillation (MJO) was examined. An increasing trend in MSE occurs before the MJO rainy period, and MSE decreases during and after MJO rainfall onset. Horizontal advection of MSE dominates the MSE budget in the model, and has a strong meridional component which is dominated by synoptic eddy variability. An observed MSE budget for the MJO is presented here using NCEP (National Center for Environmental Prediction) reanalysis II data. Data are used for 16 years (the same length of time as by Maloney (2009)), from 1993 until 2008. MJO composites were made using the realtime multivariate MJO (RMM) index of Wheeler and Hendon (2004). MSE budget terms are composited for different MJO phases when RMM exceeds one standard deviation. Phase is defined such that the maximum rainfall at 155E occurs at 180 phase. Vertical integration is done from the surface to 100mb height. As previously observed, positive column-integrated MSE anomalies build before the peak MJO rainfall, and negative anomalies occur after peak rainfall. Many aspects of the observed MSE budget resemble those of Maloney (2009), with strong contributions from horizontal advection to recharging (discharging) column MSE before (after) MJO convection. Latent heat flux and radiative flux anomalies are also large and have a positive covariance with MJO precipitation. A difference from Maloney (2009) is that vertical advection appears to have a more dominant role in the MSE budget in observations than in the model. The longitudinal distribution of both MSE and specific humidity (q) have a similar eastward propagating pattern and magnitude as a function of phase, indicating that the time-change of MSE is mainly governed by q. From the calculations of the vertically integrated MSE budget, it is observed that a budget residual exists of the same order of magnitude as the MSE tendency. This suggests errors in moist physics of the reanalysis model. The anomalous meridional advection of MSE has higher amplitude than the zonal advection term. Meridional advection is dominated by advection of anomalous humidity by the perturbation flow. As in Maloney (2009), variability in synoptic eddy activity as a function of MJO phase dominates this horizontal advection term. Suppression of eddies in advance of MJO convection may contribute to preconditioning the atmospheric column.