A recent study conducted by climate scientist Indrani Roy at University College London (UCL) sheds light on the intricate relationship between the Indian monsoon and two climate phenomena known as El Nino-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD). Roy’s research indicates that a positive IOD, coupled with a warm phase of ENSO, can enable a normal Indian monsoon.
The Indian summer monsoon (ISM) is greatly influenced by ENSO, which is characterized by periodic variations in sea surface temperatures (SST) in the tropical Pacific. When SST warms, it results in an El Nino phase, while cooling generates a La Nina phase. The ISM experiences reduced rainfall during warm ENSO phases and increased rainfall during cold ENSO phases. Drought years in India often coincide with El Ninos, while floods align with La Ninas. The east-west Walker circulation that originates in the tropical Pacific also plays a role in this teleconnection.
In addition to ENSO, Roy’s research highlights the impact of the Indian Ocean Dipole (IOD) on the Indian summer monsoon. The IOD Index, which measures differences in sea surface temperature anomaly between the western equatorial and southeastern equatorial portions of the Indian Ocean, reveals that during a positive IOD phase, India receives more rainfall. Conversely, a negative IOD phase results in less rainfall. Both ENSO and IOD exert countervailing effects on India’s monsoon, with El Nino suppressing rainfall and a positive IOD enhancing it.
The discovery of the IOD in 1999 added a new dimension to our understanding of the Indian monsoon. Roy explains that ENSO teleconnection is particularly pronounced in Central North East (CNE) India, where the Inter-Tropical Convergence Zone (ITCZ) and the east-west Walker circulation converge with the north-south Hadley air circulation.
Roy’s study utilizes the Coupled Model Inter-Comparison Project to analyze climate models, demonstrating that around 80% of the models agree on the strength of the regional teleconnection around CNE, further solidifying the relationship between the ISM and ENSO. These models also indicate that improved predictions of monsoon rainfall can benefit millions who rely on the monsoon for their agricultural livelihoods.
The research also highlights the influence of external factors such as volcanic eruptions on the monsoon. In the late 20th century, two powerful volcanic eruptions, El Chichon in 1982 and Pinatubo in 1991, occurred during strong solar cycles, affecting the Moduki ENSO. These eruptions disrupted the ISM-ENSO teleconnection by triggering a preferential alignment of the North Atlantic Oscillation (NAO) and fluctuations in atmospheric pressure over the North Atlantic, resulting in changes in Central Pacific warming, North Atlantic cooling, and Eurasian sector warming. These changes affected the north-south Hadley circulation, illustrating the significance of natural drivers in the Indian monsoon.
Understanding the complex interplay between these climate phenomena is crucial for accurate monsoon predictions, as the Indian monsoon has far-reaching impacts on agriculture, water resources, and the economy of the region. Roy’s research illuminates the significance of the ENSO-ISM teleconnection and the role of the IOD, providing valuable insights for policymakers, farmers, and researchers.
As climate change continues to disrupt weather patterns, studying and comprehending these teleconnections becomes increasingly important. By investigating different mechanisms and drivers, scientists aim to enhance climate models and improve monsoon forecasting, enabling better preparation and adaptation strategies for regions dependent on the Indian monsoon.
Overall, the study conducted by Indrani Roy at UCL underscores the importance of considering multiple factors, including ENSO and the IOD, to accurately predict and understand the Indian summer monsoon. By unraveling the complexities of these teleconnections, scientists can help safeguard communities and ecosystems impacted by the monsoon, supporting sustainable and resilient development in the face of climate change.
