What to Know About the "Brown Ocean Effect" and Its Impact on Hurricanes and Tropical Cyclones

Researchers have recently discovered a fascinating phenomenon known as the "brown ocean effect," shedding light on how tropical cyclones can gain unexpected strength after making landfall. This weather occurrence has significant implications for understanding and predicting the behavior of hurricanes over land, challenging conventional assumptions about their decline once they reach inland areas.

Presenting their findings at the American Meteorological Society's meeting in Baltimore in January, scientists highlighted the brown ocean effect's role in revitalizing hurricanes over land. The phenomenon mirrors the ocean's ability to fuel tropical cyclones by supplying ample water and heat. Referred to as the "brown ocean" because it occurs over warm, waterlogged ground, this effect occurs when a tropical cyclone passes over already saturated soil.

Geologist Dev Niyogi and his research team from the University of Texas at Austin conducted a study on Hurricane Florence, a moderately weak storm that made landfall in the Carolinas in September 2018. Employing satellite measurements to analyze wind speeds, rainfall, and soil moisture, the scientists identified a potent feedback mechanism. As Hurricane Florence traversed over saturated soil, the intensity of its rains increased significantly, resulting in unprecedented levels of rainfall and subsequent flooding.

The brown ocean effect was initially proposed in 2013 by atmospheric scientist Marshall Shepherd and geographer Theresa Andersen. However, observational confirmation has been scarce until now. Niyogi's study on Hurricane Florence represents one of the first concrete pieces of evidence supporting this long-hypothesized phenomenon.

The research indicates that the intensity of the brown ocean effect depends on soil moisture, soil temperature, and the duration the soil has been wet before the storm arrives. Saturated soil provides a ready source of water vapor that, when condensed within the storm, releases heat, revitalizing the cyclone. The team discovered that the heaviest rains occurred over soil that had been saturated for approximately three days, emphasizing the importance of the duration of soil saturation.

Understanding the brown ocean effect is crucial for accurate weather forecasting, especially in predicting how hurricanes may behave over land. Incorporating this phenomenon into computer weather models is essential to enhance the precision of forecasts and anticipate the potential strengthening of inland hurricanes. The findings challenge the traditional understanding that hurricanes inevitably weaken after landfall, introducing a new dimension to the complex dynamics of tropical cyclones.