Abstract
Monsoon in India is of particular importance for the $2 trillion economy, highly dependent on agriculture. Monsoon rains water two-thirds of India’s harvest. However, the monsoon season also causes large-scale flooding, resulting in loss of human life and economic damage estimated around $7 billion annually. Beryllium-7 is a tracer that can be used to monitor the intensity of stratosphere-troposphere exchange, which varies in accordance with the annual cycle of the global atmospheric circulation (Hadley, Ferrel and Polar cells). Based on the beryllium-7 data collected globally as part of the monitoring of the Comprehensive Nuclear-Test-Ban Treaty, the presented empirical method demonstrates the possibility to predict the start, withdrawal and intensity of the Indian monsoon season. Onset can be forecasted with an unprecedented accuracy of ±3 days, 2 months in advance compared to 1–3 weeks in advance by traditional methods. Applying this new method will enable better preparation for economic and natural hazard impacts of the monsoon season in India. This method can also be extended to other regions where the movement of Hadley cells governs monsoon onset and withdrawal.
Highlights
Beryllium-7 is one of the isotopes regularly detected by the radionuclide monitoring network of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO)[1]
A general increase or decrease of its concentration over time can be utilized as a proxy to monitor seasonal movement and general dynamics of atmospheric cells such as the Hadley-Ferrel Convergence Zones (HFCZ)[9,10,11]
Cross correlations of beryllium-7 activity concentrations at different monitoring stations can potentially serve as a suitable early warning index in monsoon regions governed by the HFCZ movements, with potentially several months of lead time prior to monsoon onset and withdrawal as demonstrated in the case study below on the Indian Monsoon
Summary
Lucrezia Terzi[1,2], Martin Kalinowski 3, Michael Schoeppner3,4 & Gerhard Wotawa 5. The close relationship between the position of the HFCZ and the monsoon as demonstrated in this study makes beryllium-7 a reliable indicator of monsoon onset and withdrawal forecasts It is a more reliable index than water content as it is linked to the root cause rather than the effects resulting from monsoon phenomena. Cross correlations of beryllium-7 activity concentrations at different monitoring stations can potentially serve as a suitable early warning index in monsoon regions governed by the HFCZ movements, with potentially several months of lead time prior to monsoon onset and withdrawal as demonstrated in the case study below on the Indian Monsoon. Unlike using statistics of local parameters where monsoon is expected, beryllium-7 concentration timeseries from two monitoring sites, north and south of the equator, are required These timeseries show a seasonal pattern directly linked to the Hadley circulation. Each data point represents the average of the past 15 days (top chart) and of the past 4 months (lower chart)
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