Gservo
20th January 2003, 03:00 AM
NASA scientists have successfully devised a way to get a complete picture of the anatomy of an evolving tropical thunderstorm. Using sophisticated radar equipment, they have been able to do a "full-body scan" that is expected to help verify satellite rainfall measurements, improve computer models of storms, and make the skies safer for aircraft.
David Atlas of NASA's Goddard Space Flight Center gathered the data collected from an unusual storm over the Amazon rainforest in February 1999 and arranged it into an intriguing image of the storm clouds' inner workings.
The research, co-authored by University of Colorado's Christopher Williams, appears in the January 2003 American Meteorological Society's Journal of the Atmospheric Sciences
Storms typically produce precipitation in one of two ways; either by forming rain at lower altitudes or by forming frozen particles higher in the atmosphere. The storm that Atlas examined was unusual in that both processes were seen to operate as the event evolved.
In the tropics, the air is warm even at considerably high altitudes, meaning that rain can occur in high clouds by forming liquid droplets without freezing first. During the warm rain stage only the larger drops fall quickly enough to overcome the strength of the updraft, but the smaller ones are carried very high into the clouds, where they freeze into snow and hail. This particular storm possessed a very strong updraft and also formed frozen precipitation in its upper levels, even as rain fell closer to the ground.
"While such a two-phase process should occur in many vigorous storms, it has rarely been observed in a single storm," said Atlas.
The research provides new insight into the intensity of storms and the theats they pose to aircraft. "Even the aircraft used in this study did not go into the core of the storm because of the hazards," explained Atlas.
At the higher altitudes, cold temperatures created larger frozen particles that were able to fall through the updraft. The smaller ones continued to rise, colliding with those coming down. These collisions caused friction and electrical charges that generated lightning.
Radar was the primary means used to generate the "body scan". A team of scientists from NASA, the National Oceanic and Atmospheric Administration (NOAA), the National Center for Atmospheric Research (NCAR), and several universities used radar equipment sensitive enough to detect the different kinds of particles from the storm's base up to its top, some 14 km (8.7 miles) above the jungle floor.
Different types of radar were used to examine various aspects of the storm. These included a scanning Doppler radar, often seen on television weather broadcasts, that is specially designed with the capability to measure particle types and sizes and rain rates; and a vertically oriented Doppler radar, which measures particle motion and size, and vertical air motions.
The analysis was also aided by measurements within the storm made by a jet aircraft operated by the University of North Dakota. NASA provided funds for the use of the two radars and the operation of the jet aircraft during this field experiment.
One purpose of the study was to validate the Tropical Rainfall Measuring Mission (TRMM) satellite measurements. Satellites like TRMM provide data about how these storms operate and help atmospheric scientists better understand how wind circulates above the planet. A continuous array of these evolving tropical thunderstorms around the world acts as a heat engine that warms the upper atmosphere. That warming maintains a gradient of temperature and pressure from the tropics to the poles, driving the global wind circulation.
"Our particular study attempted to validate what the satellites were showing us with an up-close view," says Atlas. "The validation of TRMM data will help to fine-tune and set the stage for the Global Precipitation Mission (GPM) satellite, which is planned to succeed TRMM."
David Atlas of NASA's Goddard Space Flight Center gathered the data collected from an unusual storm over the Amazon rainforest in February 1999 and arranged it into an intriguing image of the storm clouds' inner workings.
The research, co-authored by University of Colorado's Christopher Williams, appears in the January 2003 American Meteorological Society's Journal of the Atmospheric Sciences
Storms typically produce precipitation in one of two ways; either by forming rain at lower altitudes or by forming frozen particles higher in the atmosphere. The storm that Atlas examined was unusual in that both processes were seen to operate as the event evolved.
In the tropics, the air is warm even at considerably high altitudes, meaning that rain can occur in high clouds by forming liquid droplets without freezing first. During the warm rain stage only the larger drops fall quickly enough to overcome the strength of the updraft, but the smaller ones are carried very high into the clouds, where they freeze into snow and hail. This particular storm possessed a very strong updraft and also formed frozen precipitation in its upper levels, even as rain fell closer to the ground.
"While such a two-phase process should occur in many vigorous storms, it has rarely been observed in a single storm," said Atlas.
The research provides new insight into the intensity of storms and the theats they pose to aircraft. "Even the aircraft used in this study did not go into the core of the storm because of the hazards," explained Atlas.
At the higher altitudes, cold temperatures created larger frozen particles that were able to fall through the updraft. The smaller ones continued to rise, colliding with those coming down. These collisions caused friction and electrical charges that generated lightning.
Radar was the primary means used to generate the "body scan". A team of scientists from NASA, the National Oceanic and Atmospheric Administration (NOAA), the National Center for Atmospheric Research (NCAR), and several universities used radar equipment sensitive enough to detect the different kinds of particles from the storm's base up to its top, some 14 km (8.7 miles) above the jungle floor.
Different types of radar were used to examine various aspects of the storm. These included a scanning Doppler radar, often seen on television weather broadcasts, that is specially designed with the capability to measure particle types and sizes and rain rates; and a vertically oriented Doppler radar, which measures particle motion and size, and vertical air motions.
The analysis was also aided by measurements within the storm made by a jet aircraft operated by the University of North Dakota. NASA provided funds for the use of the two radars and the operation of the jet aircraft during this field experiment.
One purpose of the study was to validate the Tropical Rainfall Measuring Mission (TRMM) satellite measurements. Satellites like TRMM provide data about how these storms operate and help atmospheric scientists better understand how wind circulates above the planet. A continuous array of these evolving tropical thunderstorms around the world acts as a heat engine that warms the upper atmosphere. That warming maintains a gradient of temperature and pressure from the tropics to the poles, driving the global wind circulation.
"Our particular study attempted to validate what the satellites were showing us with an up-close view," says Atlas. "The validation of TRMM data will help to fine-tune and set the stage for the Global Precipitation Mission (GPM) satellite, which is planned to succeed TRMM."