Wayne Yuan-Huai Tsai

Weather and Climate Systems

Wayne Yuan-Huai Tsai

Prediction Skills of Rainfall Diurnal Cycle over the Maritime Continent and the Influences from Madden-Julian Oscillation in ECMWF and NCEP S2S Reforecasts

April 24th, 2024

3:00 pm

NWC 1350

Abstract: The Maritime Continent is one of the rainiest regions globally, where the diurnal cycle of rainfall contributes significantly to rainfall variability and is modulated by the Madden-Julian Oscillation (MJO). However, our understanding of prediction skills for the diurnal cycle and its relevance to the MJO in subseasonal forecast models is still limited. This study evaluates subseasonal prediction skills of rainfall diurnal cycle characteristics over the Maritime Continent using ECMWF and NCEP S2S models and explores the influences of MJO activity on prediction skills. The evaluated diurnal cycle characteristics include the daily mean, diurnal amplitude, and phase. Generally, the reforecast skills of diurnal rainfall characteristics become lower and stabilize after 10 days, but aggregation over longer periods can sustain or enhance prediction accuracy compared to the daily timescale. Errors over land are attributed to earlier peaks and stronger amplitudes than observations, w
hile over the sea are typically along the coastlines and some far ocean regions such as the northern West Pacific. Furthermore, we stratify the forecasted rainfall diurnal cycle by MJO phase at forecast initiations to examine MJO’s impacts on prediction skills in S2S models. The predictions become worse than climatology when MJO’s convection reaches the Maritime Continent, which is hypothesized to be related to the barrier effect. This study contributes to understanding the subseasonal prediction skill of the rainfall diurnal cycle and the role of MJO in rainfall predictions over the Maritime Continent.Â

Keywords: Sub-seasonal to seasonal (S2S) forecast, Maritime Continent, rainfall diurnal cycle, Madden-Julian Oscillation (MJO).