Tuesday, 9 January 2018
Exhibit Hall 3 (ACC) (Austin, Texas)
Reforecasts produced by the ECMWF Integrated Forecasting System (IFS) were used to study heating and moistening processes associated with three MJO events over the equatorial Indian Ocean during the Dynamics of the Madden-Julian Oscillation (DYNAMO) field campaign. Analyzed and derived variables from the IFS reforecast (IFS-RF) and observations over the DYNAMO sounding arrays agree reasonably well with each other, and they vary smoothly from western to eastern equatorial Indian Ocean. This lends confidence towards using IFS-RF as a surrogate of observations over the equatorial Indian Ocean outside the DYNAMO arrays. The apparent heat source Q1 and apparent moisture sink Q2 produced by IFS are primarily generated by parameterized cumulus convection, followed by microphysics and radiation. The vertical growth of positive Q1 and Q2 associated with the progression of MJO convection can be gradual, stepwise, or rapid depending on the event considered and its location over the broader equatorial Indian Ocean. The time for convective heating and drying to progress from shallow (800 hPa) to deep (400 hPa) can be <1 day to 6 days. It is usually short for convective processes alone, but becomes longer when additional microphysical processes are in play, such as evaporative moistening below convective and stratiform clouds. The ratio of radiative to convective heating is 10-20% during the buildup to peak MJO periods, and much greater during the decay period and in regions of weak precipitation. This suggests that this ratio alone does not measure the strength of cloud-radiative feedback, contrary to previous studies.
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