Abstract

The spatiotemporal mean rain rate (MR) can be characterized by the rain frequency (RF) and the conditional rain rate (CR). We computed these parameters for each season using the TMPA 3-hourly, 0.25° gridded data for the 1998–2017 period at a quasi-global scale, 50°N~50°S. For the global long-term average, MR, RF, and CR are 2.83 mm/d, 10.55%, and 25.05 mm/d, respectively. The seasonal time series of global mean RF and CR show significant decreasing and increasing trends, respectively, while MR depicts only a small but significant trend. The seasonal anomaly of RF decreased by 5.29% and CR increased 13.07 mm/d over the study period, while MR only slightly decreased by −0.029 mm/day. The spatiotemporal patterns in MR, RF, and CR suggest that although there is no prominent trend in the total precipitation amount, the frequency of rainfall events becomes smaller and the average intensity of a single event becomes stronger. Based on the co-variability of RF and CR, the paper optimally classifies the precipitation over land and ocean into four categories using K-means clustering. The terrestrial clusters are consistent with the dry and wet climatology, while categories over the ocean indicate high RF and medium CR in the Inter Tropical Convergence Zone (ITCZ) region; low RF with low CR in oceanic dry zones; and low RF and high CR in storm track areas. Empirical Orthogonal Function (EOF) analysis was then performed, and these results indicated that the major pattern of MR is characterized by an El Niño-Southern Oscillation (ENSO) signal while RF and CR variations are dominated by their trends.

Highlights

  • Precipitation is a key factor in most atmospheric and hydrologic interactions

  • This study investigates the dataset from 1 September 1998, to 28 February 2017 (18.5 years) and the precipitation parameters are calculated for each season in the study period

  • The distribution of mean rain rate (MR) is consistent with previous studies and shows the major rain features, such as the Inter Tropical Convergence Zone (ITCZ), South Pacific Convergence Zone (SPCZ), and storm tracks off the west coasts of the Atlantic and Pacific

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Summary

Introduction

Precipitation is a key factor in most atmospheric and hydrologic interactions. It interacts with other components of the climate system such as the biological and chemical cycles. Precipitation has a huge influence on human activities and various aspects of daily life, such as transportation [5], food security [6], and spread of disease [7,8]. Reanalyzed precipitation products contain uncertainties introduced by the following aspects: the inter-model indeterminacies due to the discrepancies in the responses from different models under a warming climate, and internal variability of a climate model due to its own uncertainty components [10].

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