Spatio-temporal patterns of daily Indian summer monsoon rainfall

Abstract

The primary objective of this paper is to analyze a set of canonical spatial patterns that approximate the daily rainfall across the Indian region, as identified in the companion paper where we developed a discrete representation of the Indian summer monsoon rainfall using state variables with spatio-temporal coherence maintained using a Markov Random Field prior. In particular, we use these spatio-temporal patterns to study the variation of rainfall during the monsoon season. Firstly, the ten patterns are divided into three families of patterns distinguished by their total rainfall amount and geographic spread. These families are then used to establish 'active' and 'break' spells of the Indian monsoon at the all-India level. Subsequently, we characterize the behavior of these patterns in time by estimating probabilities of transition from one pattern to another across days in a season. Patterns tend to be 'sticky': the self-transition is the most common. We also identify most commonly occurring sequences of patterns. This leads to a simple seasonal evolution model for the summer monsoon rainfall. The discrete representation introduced in the companion paper also identifies typical temporal rainfall patterns for individual locations. This enables us to determine wet and dry spells at local and regional scales. Lastly, we specify sets of locations that tend to have such spells simultaneously, and thus come up with a new regionalization of the landmass.

A discrete view of the Indian monsoon to identify spatial patterns of rainfall

“…These patterns were identified from only 8 years (2000-2007) but they fit well on daily data from over a hundred years. In a companion paper, [17] we will discuss the temporal characteristics of these patterns, showing that some of them to be more frequent in the early and late monsoon months (June, September) while the others are more frequent in the peak monsoon months (July, August), and also study about homogeneous zones on the landmass which are also identified by this model.…”

“…The patterns we identify, and the sequence of their occurrence, provide an ideal platform to understand many features of the monsoon, and we make a beginning in the companion paper [17]. In that paper we collate the results of this paper, i.e., the spatial and temporal patterns, and thoroughly analyze various aspects of these patterns.…”

“…This paper presents a discussion of the spatial patterns illustrating the utility of the methodology developed here. Further analysis concerning the temporal evolution of the patterns identified in this paper forms one of the central aspects of the companion paper [17]. In particular, we study likely transitions of one spatial pattern to another within a monsoon season.…”

Spatio‐temporal relationships between rainfall and convective clouds during Indian monsoon through a discrete lens

“…While they differ in detail from our rainfall patterns, we see broad similarity in that the eight MISO phases too broadly fall into the three “families” (similar to those found by Mitra et al . (2019)) – (a) where the rainfall is restricted to the western coast and the north‐eastern regions, (b) rainfall covers central India, (c) rainfall covers eastern India and the Gangetic plains. By counting the pattern assignments from our method in a particular phase of MISO, we find that each pattern roughly overlaps with 3 MISO phases, generally from the same “family”.…”

“…The model then partitions the dataset into spatial and temporal clusters that maintain spatio-temporal coherence. Mitra et al (2019) identified temporal relationships between the patterns corresponding to each cluster. The number of clusters is estimated implicitly by the model and studying the corresponding patterns allows new physical insights to be inferred.…”