After observing satellite surface winds in the area, oceanography experts from Flinders University have described a new type of tropical cyclone in the Indian Ocean near Sumatra.
The experts’ search for the trigger mechanisms of the Indian Ocean Dipole led to the discovery of SETIO Cyclone, a new type of atmospheric tropical cyclone forming in the South-East Tropical Indian Ocean (SETIO).
The Indian Ocean Dipole (IOD) is a coupled atmosphere-ocean interaction in the tropical Indian Ocean that has a significant impact on the climate and rainfall variability of neighbouring countries, including Australia.
SETIO Cyclone Function
Horizontal distributions for the IOD season (June–September) for the years 1988–2016 of
(a) climatological values of OLR (W m–2), arrows show average the surface-wind distribution;
(b) the standard deviation of daily OLR (W m–2); and
(c) the standard deviation of daily zonal wind speed (m s–1). Rectangles show the SETIO region (80–110°E, 0–10°S).
Credit: Ankit Kavi A and Jochen Kämpf CC-BY
The newly described cyclones, according to Flinders graduate Dr. Ankit Kavi and his Ph.D. supervisor Associate Professor Jochen Kaempf, include north-westerly winds along Sumatra’s west coast and westerly equatorial wind bursts.
They discovered that SETIO cyclones are short-lived weather-like events that frequently form during austral winter/spring and function to keep the region’s surface ocean warm.
“Dramatic changes happen in some years when SETIO cyclones fail to develop, and ambient winds trigger the appearance of cold seawater in a vast area strongly disturbing both winds and rainfall patterns over the Indian Ocean,”
Associate Professor Kaempf said.
Unexpected New Discovery
It is critical in the natural sciences to identify so-called trigger processes, such as SETIO cyclones, that link a cause to an effect. This is an unexpected new discovery that sheds new light on how the Indian Ocean Dipole operates.
To enhance the IOD forecasting, Associate Professor Kaempf hopes that this work will draw funding for additional studies that will examine the formation of SETIO cyclones in greater detail.
The western Indian Ocean alternately becomes warmer (positive phase) and then colder (negative phase) than the eastern part of the ocean during the irregular oscillation of sea surface temperatures known as the Indian Ocean Dipole (IOD), also referred to as the Indian Nino.
The IOD impacts the strength of the monsoons over the Indian subcontinent, in addition to its other effects. Climate scientists discovered the phenomenon for the first time in 1999.
Reference: Kavi Ankit, Kämpf Jochen (2022) Synoptic-scale atmospheric cyclones in the South-East Tropical Indian Ocean (SETIO) and their relation to IOD variability. Journal of Southern Hemisphere Earth Systems Science, 22 November 2022.
