NASA's Tropical Cloud Systems and Processes Mission in Costa Rica
Steve Roy, Marshall Space Flight Center

NASA’s ER-2 airplane departs the San Juan Santa Maria airport in San José, on July 6, 2005. As Hurricane Dennis collapses along the southern shores of the United States, and millions of coastal residents breathe a sigh of relief, NASA and the National Oceanic and Atmospheric Administration (NOAA) are busy studying data gathered during the early days of the hurricane that threatened much of the southern Atlantic and Gulf of Mexico.

Researchers conducted their second coordinated flight to study Tropical Storm Dennis on the evening of July 6. The ER-2 overflew the developing eye and "rain bands" of the tropical storm using coordinates relayed by the TCSP science team monitoring satellite imagery on the ground. The ER-2, which flew at 65,000 feet, was joined a few hours later by the NOAA P-3 Orion, flying at 14,000 feet. During the mission, the National Hurricane Center upgraded Tropical Storm Dennis to Hurricane Dennis at Category 1 intensity.

The NASA and NOAA planes flew coordinated passes over the eye of the storm for more than an hour. Both aircraft monitored precipitation structures as the eye became more tightly concentric, and rain bands increased in intensity with each pass. The P-3 Orion continued to monitor the storm's eye wall and rain band development for several more hours after the ER-2 returned to base, making five passes over the eye. At one point, the storm pressure dropped 12 millibars in a two-hour period -- equivalent to the amount that a garden-variety low pressure system over the United States may intensify in about 24 hours.

The TCSP missions to document developing tropical cyclones are providing rare datasets that will help unravel the mysteries about why so few tropical weather disturbances intensify into full-fledged hurricanes. For instance, "rapid deepening" -- a phenomenon in which the minimum sea-level pressure of a tropical cyclone drops by 1.75 millibars per hour, or 42 millibars in 24 hours -- is still poorly understood and is not captured well by hurricane forecast models. In the case of Dennis, the data captured exceptionally rapid deepening of the storm's central pressure, as well as documenting the eye in the process of closing off into a complete circle.

The 28-day TCSP mission is sponsored by NASA's Science Mission Directorate at NASA Headquarters in Washington. The primary goal of the mission is to document "cyclogenesis" in action -- the interaction of temperature, humidity, precipitation, wind and air pressure that creates ideal birthing conditions for tropical storms, hurricanes and related phenomena.

TCSP participants include NOAA-HRD, five NASA centers, 10 American universities and partner agencies in Costa Rica.