Towers in the Tempest
Hundreds of miles above us, a fleet of NASA spacecraft constantly scans
the Earth. One of these has dramatically improved our ability to
study severe weather. TRMM, the Tropical Rainfall Measuring
Mission, observes weather systems with the world's only space based
precipitation radar. TRMM peers down through clouds revealing
their internal structure. Using TRMM measurements, scientists
identified a dramatic feature in the structure of Hurricane Bonnie.
Towering rain clouds close to the eye wall nearly reached the
stratosphere. These structures, called "hot towers", extended
higher than commercial jets
fly. Research into these observations has lead scientists to new
insights about hurricanes. Let's look at the role "hot towers"
play in hurricanes.
A hurricane's eye is an intense low pressure system. Near the
ocean's surface, air spirals
inward in an attempt to fill the low pressure region. As air
nears the eye, it rises rapidly until forced outward at the barrier
formed by the warm tropopause. The net effect is a cycle of air
moving inward near the ocean surface, upward at the eye wall, and
outward at high altitudes. The air picks up energy from the
warm ocean water through evaporation. This warm, moist air rises
in the eye wall and releases it's energy through condensation,
sustaining the hurricane. "Hot
towers" act like express elevators accelerating the movement of energy
into high altitude clouds. This energy boost tends to strengthen
What causes these "hot towers" to form?
There's a big
difference in wind speeds between the fierce eye wall and the
relatively calm winds inside the eye. These rapid changes in wind
speeds cause instabilities that can spin up intense vortices just
inside the eye wall. Near the surface, air spiraling inward
collides with these vortices forcing the air upwards creating an
updraft. A very strong updraft in the eye wall carries moisture
much higher than normal creating a "Hot Tower".
High resolution computer simulations of hurricanes show the formation
of "Hot Towers". In this simulation of Hurricane Bonnie, "Hot
Towers" are clearly visible.
The arrows show winds swirling near the surface where energy is picked
up from the warm ocean. Some of this air moves into the
tower and rises rapidly, boosting the
hurricane's strength. But, it's more complicated than that,
because hot towers move with the hurricane; and, there are often
multiple updrafts. When air passes into a hot tower, it rapidly
Conditions are more favorable for
vortices to form updrafts on one side of the hurricane because wind
shear amplifies colliding winds in that area. Wind shear causes these updrafts to weaken in other areas of the eye. Vortices can also pump high
energy air from the eye into the eye wall, boosting the strength of the
updrafts and intensifying the hurricane.
Scientists have confirmed a connection between hot towers and hurricane
intensification; but, forecasting intensification remains a difficult
satellite observations with super-computer simulations
provides a powerful tool for studying Earth's complex systems.