Characteristics of Orographic Rain Drop-Size Distribution at Cherrapunji, Northeast India

Fumie Murata,Laitpharlang Cajee,Hiambok Jones Syiemlieh,Kaustav Chakravarty,Toru Terao

doi:10.3390/atmos11080777

Abstract

The rain drop size distribution (DSD) at Cherrapunji, Northeast India was observed by a laser optical disdrometer Parsivel 2 from May to October 2017; this town is known for the world’s heaviest orographic rainfall recorded. The disdrometer showed a 30% underestimation of the rainfall amount, compared with a collocated rain gauge. The observed DSD had a number of drops with a mean normalized intercept log 10 N w > 4.0 for all rain rate categories, ranging from <5 to >80 mm h − 1 , comparable to tropical oceanic DSDs. These results differ from those of tropical oceanic DSDs, in that data with a larger N w were confined to the stratiform side of a stratiform/convective separation line proposed by Bringi et al. (2009). A large number of small drops is important for quantitative precipitation estimates by in-situ radar and satellites, because it tends to miss or underestimate precipitation amounts. The large number of small drops, as defined by the second principal component (>+1.5) while using the principal component analysis approach of Dolan et al. (2018), was rare for the pre-monsoon season, but was prevalent during the monsoon season, accounting for 16% (19%) of the accumulated rainfall (precipitation period); it tended to appear over weak active spells or the beginning of active spells of intraseasonal variation during the monsoon season.

Highlights

Rainfall over mountainous areas is important for the conservation of natural ecosystems and the management of human water resources, and with regard to natural hazards, such as flash floods and landslides [1]
The analysis period was from May to October 2017, and the total accumulated rainfall was 5313.0 or 9084.5 mm, as measured by a disdrometer or collocated rain gauge, respectively
The difference in the readings between the disdrometer and rain gauge was due to bad sensor conditions and underestimation of the rainfall by the disdrometer

Summary

Introduction

Rainfall over mountainous areas is important for the conservation of natural ecosystems and the management of human water resources, and with regard to natural hazards, such as flash floods and landslides [1]. The accurate monitoring of rainfall over the complicated topography is useful for the safety of human lives and infrastructures, mountainous areas are typically remote; in-situ rainfall observations are limited. A large variability in rainfall due to spatially non-uniform and complicated topography creates a challenge for accurate rainfall estimation. Remote sensing, such as ground radar and satellite-based observations, offers a powerful advantage for precipitation estimation over elevated terrain. The rain drop size distribution (DSD) provides information on the microphysics of precipitating clouds. The DSD determines the relationship between radar reflectivity (Z) and rain rate (R)

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Conclusion