Space-Time Spectral Analysis of the Moist Static Energy Budget Equation

Kazuaki Yasunaga

Earth Science Division University of Toyama, Japan

Thursday, Jun 21, 2018, 11:00 am
DSRC Room 1D403

Abstract

The budget of column-integrated moist static energy (MSE) is examined in wavenumber-frequency transforms of longitude-time sections over the tropical belt. Cross spectra with satellite-derived precipitation (TRMM-3B42) are used to emphasize precipitation-coherent signals in reanalysis (ECMWF-Interim) estimates of each term in the MSE budget equation. These terms (partial tendencies, advection etc.) are normalized to units of % of the precipitation. Results reveal different mechanisms of MSE evolution in different types of convectively coupled equatorial waves (CCEWs) as well as the Madden–Julian oscillation (MJO), and tropical depression (TD)-type disturbances. The vertical advection is negatively correlated to precipitation and of order 10% in magnitude for all disturbances. This effect is overestimated by a factor of 2 or more if advection is computed using the time and zonal mean MSE, meaning that nonlinear correlations between ascent and humidity are important in reducing gross moist stability. Horizontal advection plays various roles; its imaginary component is hugely positive acting to advance the phase of TD-type disturbances, and is mildly positive for the MJO and Equatorial Rossby (ERn1) wave disturbances while almost negligible for the other CCEWs. The real component of horizontal advection is modest for most wave types, but substantially damps the MJO. Radiative heating has a positive real part, reinforcing precipitation for longer waves and reaching 14% for the MJO. Surface flux is a small effect, but acts to amplify MJO and ERn1 waves. The residual imaginary component is large and systematically positive, suggesting that the reanalysis model’s MSE sources would not propagate the precipitation-associated MSE anomalies properly.