Boreal Summer Intra Seasonal Oscillation (BSISO)
Researchers at the Indian National Centre for Ocean Information Services (INCOIS), Hyderabad have found a method to improve wave prediction and BSISO linked oceanic activity that affects behavior monsoon.
• Intra-seasonal oscillation (ISO) plays an important role in the onset and northward movement of the Asian summer monsoon, which is regulated regionally by rainy seasons.
• The Madden-Julian oscillation (MJO), is known as the intra-seasonal oscillation (ISO). It is the foremost method of intra-seasonal variability in the tropical climate system. It is a planetary scale, eastward-moving disturbance with a broad spectral peak around 40–60 days, which modulates the tropical deep convection, and hence the tropical precipitation.
• Under the Deep Ocean Mission of the Ministry of Earth Sciences, this aspect of monsoon (link with BSISO) would be studied to streamline the evidence-based forecasting.
o BSISO is stated as the movement of convection from Indian Ocean to western Pacific Ocean roughly every 10-50 days during the monsoon.
o The BSISO is known to affect climate variability, including the summer monsoon onset the active/break phases of the summer monsoon, extreme wet and dry events and climate predictability for precipitation.
o Active phase of BSISO induce high wave activity in north Indian Ocean and Arabian Sea. (Both water bodies affect monsoon at large- i.e.- Indian ocean Dipole) Waves induced by active phases of BSISO are nearly 0.5 meters higher than those which occur during other phases of BSISO. Wave forecast advisories based on the BSISO would be more useful for efficient coastal and marine management.
o An important feature of the BSISO is its northward propagation in the Asian summer monsoon region, which has an important impact on regions which are under influence of Monsoonal Rainfall.
1. BSISO‘s Relevance with India’s Monsoon
The BSISO exhibits more complex features-it involves interactions between Asian summer Monsoon circulation and convectively coupled equatorial waves. The BSISO tends to have a northward propagation over the Indian summer monsoon (ISM) region.
Northward propagation of the boreal summer intra-seasonal oscillation (ISO) has profound impacts on Northern Hemisphere extreme weather events. Monsoon is also a northern-ward movement of wet air that resulted into rainfall.
BSISO represents the monsoon’s ‘active’ and ‘break’ periods, in which weeks of heavy rainfall give way to brilliant sunshine before starting all over again. The active phase also enhances monsoon winds and hence the surface waves. The cooling and warming of Indian Ocean could be linked with the ‘active’ and ‘break’ periods of monsoon.
The active phases of BSISO occur between June and August which are the monsoon summer months. This finding has a great significance in developing seasonal and climate forecast service for waves and coastal erosion for India.
2. BSISO and ENSO
BSISO activity over the western Pacific is significantly weakened in El Niño decaying summer. Northward propagation (NP) of BSISO (equator to the north of 25° N) attributed to La Niña decaying summer, while the intensity of BSISO NP is rapidly weakened to the north of 15° N in El Niño decaying summer.
ENSO modulates BSISO activity by regulating circulation and moisture anomalies. Large-scale atmospheric circulation undergoes radical changes between El Niño and La Niña decaying summer.
India's monsoon is uncertain due to various complex climatic factors and inter relationship among them, predictability is still a practical problem in absence of reliable information and data. This undermine the approach to handle extreme weather events. Such research will give impetus to reliability of monsoonal forecasting. To a greater extend it would be going to help to improve wave predictions along India’s coasts, coastal management and mitigation of adverse impacts of high waves (coastal flooding, erosion, etc). Sea-navigation routes can also be better planned.
PEPPER IT WITH
Indian Ocean Dipole, Movement of ITCZ, Monsoon Trough, Monsoon ‘Break’, Pseudo Monsoonal Tendency