Back in 2010, Russia experienced one of its most severe wildfires and heat waves while Pakistan witnessed its ‘superfloods’, of which the 2022 flash floods are a cruel reminder. While these two events were over 2000 kms apart, they were connected to a single *meteorological event - The Rossby Waves named after Carl Gustaf Arvid Rossby who first identified them. While th ese events were different in nature the waves caused a high pressure pattern over Russia while influencing downstream wind patterns in the Indian subcontinent leading to the floods.
But what are Rossby Waves and why have they gained relevance over the last decade?
Rossby or Planetary waves occur within the Earth’s ocean and atmosphere. They move continuously, along with the rotation of the planet. These can be classified into two categories - Oceanic and Atmospheric Rossby Waves
Unlike surface tidal waves which break as soon as they touch land, Oceanic Rossby waves are found along the thermocline or the layer where the warm surface waters mix with the cool deep water. They move about in slow undulating waves for hundreds of kilometers in the westward direction. It can take them a decade or more, to cover the surface area of the ocean. Their interaction with phenomena like the El Nino influences climate across the world, sometimes causing high tides and coastal flooding.
Atmospheric Rossby waves are high altitude winds in the mid latitudes. When the arctic jet stream becomes more wavy and flows into lower latitudes, that meandering is referred to as Rossby Waves. THIS MEANDERING HAS BEEN LINKED TO A WARMING ARCTIC, WHICH IS LEADING TO ANOMALIES IN THE JET STREAM. When they swing up, they transfer heat from the tropics to the poles and when they swing down they carry cold air towards the tropics to maintain some balance in the atmosphere. Any anomaly in Rossby Waves can cause disasters in seemingly disconnected parts of the Earth.
Normally, these waves move eastward, which implies that weather systems move with them. But if this eastward movement slows down or freezes, then high and low pressure areas persist over specific regions like they did in Russia, back in 2010. While the wildfires and superfloods did not happen together, their impacts were felt around the same time.
Rossby waves are composed of two intricately linked types - synoptic and forced waves. Synoptic waves move quickly, only formed by the atmosphere. But they also contain minor static/forced components. Forced waves are formed by interruptions of mountains and temperature differences across continents and oceans. These contain minor synoptic components.These two types interact with each other within an atmospheric channel called a ‘waveguide’. This interaction allows their strength to increase and influence the weather. This interaction is also called ‘wave resonance’.
While we do not have extensive historical data on Rossby waves, a lot of events like the 2003/2006/2015 European heatwave, Balkan floods of 2014, US heatwave of 2011 and North American heat wave of 2018 have been attributed to them. Research is still being conducted on the definitive influence of anthropogenic climate change on natural atmospheric phenomena like these.
It shows us how small and delicate changes in atmospheric events lead to catastrophic events affecting the environment and society at large.
*According to a study by William Lau and Kyu-Myong Kim, atmospheric scientists at NASA’s Goddard Space Flight Center in Greenbelt, Md.,published in the Journal of Hydrometeorology
