Characteristics of Precipitation Diurnal Cycle over a Mountainous Area of Sumatra Island including MJO and Seasonal Signatures Based on the 15-Year Optical Rain Gauge Data, WRF Model and IMERG

Marzuki Marzuki,Helmi Yusnaini,Abdul Azim Bin Amirudin,Mutya Vonnisa,Ravidho Ramadhan,Fredolin Tangang,Hiroyuki Hashiguchi,Toyoshi Shimomai

doi:10.3390/atmos13010063

Marzuki Marzuki, Helmi Yusnaini + Show 6 more

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https://doi.org/10.3390/atmos13010063

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In this study we investigate the characteristics of the diurnal precipitation cycle including the Madden–Julian oscillation (MJO) and seasonal influences over a mountainous area in Sumatra Island based on the in situ measurement of precipitation using the optical rain gauge (ORG). For comparison with ORG data, the characteristics based on the Global Precipitation Measurement (GPM) mission (IMERG) and Weather Research and Forecasting (WRF) simulations were also investigated. Fifteen years of ORG data over a mountainous area of Sumatra, namely, at Kototabang (100.32° E, 0.20° S), were analyzed to obtain the characteristics of the diurnal cycle of precipitation in this region. The diurnal cycle of precipitation presented a single peak in the late afternoon, and the peak time difference was closely related to the rain event duration. The MJO acts to modulate the diurnal amplitude but not the diurnal phase. A high precipitation amount (PA) and frequency (PF) were observed during phases 2, 3, and 4, along with an increase in the number of longer-duration rain events, but the diurnal phase was similar in all MJO phases. In terms of season, the highest PA and PF values were observed during pre-southwest and pre-northeast monsoon seasons. WRF simulation reproduced the diurnal phase correctly and more realistically than the IMERG products. However, it largely overestimated the amplitude of the diurnal cycle in comparison with ORG. These disagreements could be related to the resolution and quality of IMERG and WRF data.

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We examined the ability of the Weather Research and Forecasting (WRF) model to reproduce the diurnal cycle of the precipitation in the mountains of Sumatra, using a smaller simulation grid of 5 km
The diurnal precipitation cycle at Kototabang presented a single peak in the late afternoon, and the peak time was closely related to the duration of rain events
The peak time of short-duration rain events came earlier than those of medium- and long-duration events, which is consistent with the evolution of the mesoscale convective system (MCS)

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Introduction

The estimation of precipitation at high altitudes in Indonesia, including Sumatra, is challenging because in situ measurements remain scarce. Sumatra is one of the largest islands in Indonesia, and is directly adjacent to the Indian Ocean (see Figure 1). It is considered important in global atmospheric circulation because its position is almost perpendicular to the propagation of winds and clouds from the Indian Ocean [1,2,3]. The combination of mesoscale variability with topography and the coastline controls diabatic heating in Indonesia, including Sumatra [4]. The Barisan mountain range in Sumatra, with an average altitude of 2000 m, plays an essential role in the convection process in this

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