ESRL/PSD Seminar Series

Tropical Intraseasonal Air-Sea Interaction and the Madden-Julian Oscillation

Simon De Szoeke
Assistant Professor Earth, Ocean, and Atmospheric Science Oregon State University - Corvallis, OR

Abstract


Observations from the R/V Revelle during 3 intraseasonal convective events in DYNAMO test theories of the Madden Julian Oscillation (MJO). Local evaporation increased to 150 W m-2 from a mean of 110 W m-2, explaining about 10% of the precipitation in the convective phase of the MJO. Consistent with previous studies from TOGA-COARE and DYNAMO, the magnitude of these evaporation anomalies is not sufficient by itself to overcome processes drying the atmospheric column during the convective phase.



Column integrated moisture varied intraseasonally with an amplitude of ±2 cm from a mean of 6 cm liquid water equivalent. Column moisture increased before the intraseasonal convective phase, but high column moisture was not a sufficient condition for deep convection, nor did the observed precipitation simply discharge the moisture anomalies. Rather, column integrated moisture increased sharply on the days with highest precipitation at the beginning of the convective phase, and decreased gradually during weaker precipitation following later in the convective phase.



In addition to the surface flux anomalies, air-sea interaction also contibutes to the MJO through another mechanism. The sea surface temperature (SST) increases during low winds and high insolation in the suppressed phase of the MJO, and decreases in the convective phase. Peak SST occurs several days before the convective phase. Part of the warming is due to diurnal warm layers in the upper ocean. Assuming the atmospheric boundary layer is near thermal equilibrium with the SST anomalies, the warm SST anomalies induce hydrostatic low pressure in the boundary layer, driving winds. A rotating frictional model for boundary layer wind estimates long-lived horizontal boundary layer moisture convergence anomalies of 25 W m-2 in the Indian Ocean before the convective phase of the MJO. This value is comparable to horizontal moisture convergence anomalies computed from reanalysis in previous studies, suggesting that convergence due to SST anomalies contributes significantly to the supply of atmospheric column moisture before the MJO.


Wednesday Apr 08, 2015
1:00 pm
1D-403
Seminar Coordinator: Barbara (barbara.S.Herrli@noaa.gov)

SECURITY: If you are coming from outside the NOAA campus, you must stop at the Visitor Center to obtain a vistor badge. Please allow 10 extra minutes for this procedure. If you are a foreign national coming from outside the NOAA campus, please email the seminar coordinator at least 48 hours prior to the seminar to provide information required for security purposes.