Jialin Lin, Brian Mapes, Minghua Zhang, and Matthew Newman
Submitted to JAS, November 2002
The contribution of stratiform precipitation to the vertical profile of heating in the Madden-Julian Oscillation (MJO) is examined. Heating profiles in a strong MJO event in 1992-3 are calculated from the Tropical Ocean Global Atmosphere (TOGA) Coupled Ocean Atmosphere Response Experiment (COARE) sounding array data. Long-term heating estimates, derived from vorticity budgets in NCEP reanalysis, support the notion that this well-observed event was representative. Convective/stratiform precipitation estimates are obtained from the Tropical Rainfall Measurement Mission (TRMM) satellite. All datasets are filtered using a 30-70 day bandpass filter. The long-term MJO composites are constructed using linear correlation and linear regression with respect to time series of surface precipitation. The observed MJO anomalous vertical heating profile is very top-heavy at the time of maximum precipitation. TRMM data show that the anomalous stratiform precipitation contributes more than 50% to the anomalous total precipitation in the MJO. This large fraction of stratiform precipitation significantly increases the anoma- lous heating in the upper troposphere and decreases the anomalous heating in the lower troposphere. This helps to make the heating profile top-heavy. The MJO anomalous vertical heating profiles in several GCMs and other models are shown to differ from the observations. The model heating profiles are generally middle-heavy. Based on the above results, it is hypothesed that the weak and fast MJO in the current GCMs may be partly caused by their middle-heavy anomalous vertical heating profiles.