The Amplification of East Pacific Madden–Julian Oscillation Convection and Wind Anomalies during June–November

Abstract

Madden?Julian oscillation (MJO) wind and convection anomalies are locally amplified over the northeast Pacific warm pool during June?November. Composite analysis using NCEP reanalysis data indicates that perturbation available potential energy (PAPE) production through the positive correlation of intraseasonal temperature and convective diabatic heating anomalies supports the local intensification of MJO-related east Pacific warm pool wind anomalies. PAPE production is maximum during periods of strong MJO convection and low-level westerly wind perturbations. PAPE is converted to perturbation kinetic energy through positive correlations between intraseasonal temperature and vertical velocity. Microwave Sounding Unit (MSU) temperature and NOAA outgoing longwave radiation data support the energy budget results derived from NCEP reanalysis. The amplified east Pacific circulation enhances surface convergence and latent heat flux anomalies during MJO convective periods. The surface convergence anomalies have a strong frictional component. Intraseasonal surface convergence and latent heat flux anomalies are strongly correlated (greater than 0.7) with the negative outgoing longwave radiation anomalies that is associated with east Pacific MJO convective regions. Surface latent heat and convergence variations may therefore be important in modulating MJO convective anomalies over the east Pacific during June?November. Enhanced surface flux and convergence anomalies associated with an enhanced surface circulation may intensify MJO convection, thereby creating a feedback loop that leads to the further intensification of local wind and convection anomalies. Work with mesoscale or general circulation models is needed to confirm that surface latent heat and convergence variations are indeed important for modulating east Pacific MJO convection. Enhanced MJO convection over the boreal summer east Pacific is accompanied by positive water vapor anomalies throughout the troposphere. Column precipitable water anomalies from both NASA Water Vapor Project (NVAP) and NCEP reanalysis are in phase with MJO convection anomalies over the east Pacific. These results support the observations of previous studies that the equatorial troposphere must be sufficiently moistened before significant MJO deep convection can occur. The strongest NCEP reanalysis specific humidity anomalies at lower levels are collocated with positive surface latent heat flux and surface convergence anomalies.