Summary: The very tall clouds that we see in satellite pictures of tropical cyclones (also known as hurricanes) fan out from the hurricane’s center over the course of each day, what we call a diurnal cycle. This is because a pulse of thunderstorms and rain forms near the hurricane center each night and steadily moves outward several hundred miles during the morning and afternoon. Although we see this in the images of the tops of the tall clouds, we don’t know whether there are also changes in winds and moisture near the surface. This study uses observations from hundreds of dropsondes – instruments that are dropped out of airplanes that measure pressure, temperature, moisture and wind as they fall to the surface – to see whether there are similar daily changes down low. This study helps us better understand how the diurnal cycle affects the structure of hurricanes near the surface
Important Conclusions:
- The hurricane also has a daily pattern near the surface, with stronger inflow (wind flowing toward the storm center) and increased moisture occurring in the overnight hours as compared to the rest of the day.
- These periods of increased inflow and moisture precede the outward-moving pulse of high clouds seen in satellite images.
- The diurnal cycle of tropical-cyclone low-level structure is strongest between 250-500 km (150-300 miles) from the hurricane’s center.
Read the study at https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019GL086206.