Isotope Meteorology

Precipitation isotopes and hydro-meteorological processes

Monsoon processes and precipitation isotopes

Wind circulation plays an essential role in determining atmospheric processes. The seasonal reversal of wind is typically observed all over the world. However, it is well developed in certain regions of Earth and is the most dramatic in the Indian subcontinent. Such kind of wind reversal is commonly known as the monsoon. Monsoon manifests through complex interactions among ocean, atmosphere, land, vegetation, ice sheet, etc over a broad spectrum of spatial and temporal scale. The agricultural and economic activities of the Indian subcontinent, are greatly influenced by the monsoon rainfall. Hence a better understanding of the monsoon processes aimed at developing predictive capability is an active research area in meteorology and atmospheric science. Monsoon is characterized by different modes of variability. It varies from intra-seasonal to multi-millennium time scales. Long-term rainfall data is required to examine the monsoon processes. Instrumental data is used to study the short-term processes, while proxy data is required to examine its long-term periodicities.

Both observational methods and numerical models are used to study the monsoon system. A variety of instruments are used to quantify the various attributes of the monsoon. Starting from simple rain gauges to complex instruments like weather radars are used to measure different parameters of clouds and precipitation. Satellite-based remotely sensed instruments are increasingly being used to better characterize the monsoon processes. Measurements of water isotopes, that is 18O/16O and 2H/1H isotopic ratios in precipitations and atmospheric moistures, are being used to understand the atmospheric processes from a different perspective.

FIgure-1 Precipitation sampling network.

The isotopic analysis of rainfall has been widely used to address a variety of hydrological problems and moisture transport processes. In the Indian context, the hydrological characteristics are intricately linked to the monsoon processes and hence it is important to understand how the precipitation isotopes are controlled by the monsoon rainfall and its associated variables. Hence, it is important to understand how the precipitation isotopes respond to different attributes of the monsoon system. Precipitation is the primary attribute of monsoon, but the precipitation isotopes do not show strong sensitivity with precipitation amount. Hence the relation between the precipitation isotopes with other parameters of the monsoon system needs to be examined.

Towards this we have established a precipitation sampling network across India (FIgure-1). Precipitation samples are collected in these sites and are analyzed at the Stable Isotope Laboratory of IITM, Pune.