Geophysical Phenomena

Extratropical cyclones, often referred to as mid-latitude or frontal cyclones, are a prevalent weather phenomenon occurring mainly in the middle and high latitudes. Forming outside the tropical zones, these cyclones are significant weather systems with vast influences on the climate and weather patterns of the regions they affect.

Meteorological Conditions Associated with Extratropical Cyclones

• Temperature Contrast: They prominently occur where there is a significant temperature contrast, generally where polar and tropical air masses converge. Eg: in the North Atlantic region, the sharp temperature gradients leading to the “Nor’easters” in the northeastern U.S.
• Frontogenesis: Frontogenesis, a process defining the birth or strengthening of a weather front, plays a pivotal role. During the 1993 “Storm of the Century” in the U.S., frontogenesis was witnessed with a rapid intensification of fronts, bringing about severe snowfalls.
• Jet Streams: These cyclones often form and intensify near the jet streams, characterized by fast-flowing narrow air currents. Eg: the European windstorm “Kyrill” in 2007, fueled by the jet streams, showcased how these atmospheric rivers can enhance a cyclone’s development.
• Cold and Warm Fronts: The dynamic interaction between cold and warm fronts leads to the formation of occluded fronts as the cyclone matures. Eg: during the historic “Ash Wednesday Storm” of 1962, which witnessed the merging of such fronts, resulting in extreme weather conditions.
• Wind Patterns: As these cyclones develop, they induce specific wind patterns with winds spiraling inward and converging at the center. The “Great Appalachian Storm of 1950” in the U.S. showcased this wind pattern, with severe winds wreaking havoc over a large geographical expanse.
• Rossby Waves: Rossby waves, large waves in the jet stream, significantly influence the lifecycle of extratropical cyclones. For instance, during the North Atlantic Oscillation (NAO) events, Rossby waves play a crucial role in determining the cyclones’ pathway and intensity.

Distinctive Characteristics of Extratropical Cyclones

• Broad Spatial Extent: These cyclones have a substantial spatial presence, often overshadowing their tropical counterparts. Eg: the “Great Storm of 1987” affected a vast area across the UK and France, showcasing the extensive geographical reach of extratropical cyclones. The Spatial Extent of Extratropical Cyclones ranges from 500 kms to 2500 kms.
• Seasonal Variability: The “Winter of 2013-14” in North America saw a spate of extratropical cyclones, highlighting the seasonal predisposition of these weather events, significantly impacting regions with massive snowfalls and cold waves.
• Asymmetric Structure: They frequently display an asymmetric structure, having divergent meteorological dynamics on different sides. Eg: the “1993 Superstorm” in the US, where one side experienced heavy snowfall while the other side encountered severe thunderstorms.
• Variable Precipitation Patterns: They exhibit a diversity in precipitation patterns, encompassing rain, snow, or mixed phases. Eg: the “North American Blizzard of 2009” showcased varying precipitation patterns, including a mix of heavy snowfall and rain across different regions.
• Complex Lifecycle: It is intricate, passing through stages from inception to occlusion. The series of cyclones impacting the UK in winter 2013-14 witnessed complex life cycles, evolving through various stages, showcasing the complexity in the developmental phases of these cyclones.
• Impact on Weather: They substantially affect weather patterns, inducing sudden and drastic alterations in weather conditions over expansive areas. The “Derecho of 2020” (USA) brought about significant weather alterations, highlighting the transformative impact of these cyclones.

Extratropical cyclones are dynamic weather systems which play a pivotal role in shaping the weather and climate of mid and high latitude regions. Understanding the meteorological conditions and distinctive characteristics of these cyclones is vital in weather forecasting and climate studies to mitigate their impacts effectively.