NWC REU 2019
May 21 - July 30



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Evolution of the Diurnal Cycle of Tropical Rainfall associated with the Madden-Julian Oscillation

Leanne Blind-Doskocil and Naoko Sakaeda


What is already known:

  • The diurnal cycle of rainfall can be modulated by the Madden-Julian oscillation, an intraseasonal mode of tropical convective variability that propagates eastward across the Indian Ocean and west Pacific basins.
  • The DYNAMO field campaign took place in 2011 and 2012 to collect data for studying MJO initiation processes and cloud evolution.
  • The diurnal cycle typically peaks between midnight and early morning hours over the tropical ocean, but further investigation is needed to examine the diurnal cycle during DYNAMO.

What this study adds:

  • Analysis of rain estimates from TOGA radar during DYNAMO showed an afternoon peak in rainfall that appeared stronger when compared to the climatological diurnal cycle over the tropical ocean.
  • Rainfall amounts increased from the MJO suppressed to enhanced phase due to an increase in stratiform rain.
  • A strong afternoon maximum in rainfall was observed during the MJO enhanced phase which differs from observations by S-PolKa radar.


This study evaluates the impact of the Madden-Julian oscillation on the diurnal cycle of tropical rainfall and cloud populations by analyzing data from the TOGA radar aboard R/V Roger Revelle. The data was collected during the DYNAMO field campaign which investigated MJO initiation processes and cloud evolution. Rain rate and rain type data were examined to understand the diurnal cycle observed by the TOGA radar. The mean hourly time series of rainfall during the overall field campaign displayed a strong afternoon maximum in comparison to the climatological diurnal cycle that has been documented by satellite-based rain estimates. The diurnal cycle during the MJO enhanced phase shows a strong afternoon maximum when compared to S-PolKa radar. Large differences were observed in the time series of the diurnal cycles between the two MJO events that occurred during the observed period. This study aims to increase knowledge of the diurnal cycle with respect to the MJO by studying differences seen between the TOGA and S-PolKa radars.

Full Paper [PDF]