Multiple aircraft microwave observations of storms over the western Pacific Ocean


  • J. R. Wang,

  • J. Zhan,

  • P. Racette


During the second half (January–February 1993) of the intensive observation phase of the Tropical Ocean Global Atmosphere/Coupled Ocean-Atmosphere Response Experiment (TOGA/COARE), NASA deployed both DC-8 and ER-2 research aircraft in Townsville, Australia. A number of flights were made over the western Pacific Ocean with the objective of studying strong equatorial convection and clouds. A host of microwave radiometers operating in the frequency range of 10–220 GHz were placed on board both aircraft. Many other instruments were also present in both aircraft; among them was a 13.8-GHz radar in the DC-8 aircraft that provides reflectivity profiles of atmospheric hydrometeors essential for the present study. Observations were made by both aircraft on weather systems of convection as well as of cloud radiation. Some of these observations were conducted with both aircraft flying over the same regions at near coincidence but different altitudes. The nearly concurrent microwave radiometric measurements at comparable frequencies from the two aircraft at the altitudes of about 11 and 20 km provide a unique means to examine the properties of hydrometeors associated with storms. Three well-coordinated DC-8 and ER-2 aircraft flights over storms are described below. All of the microwave radiometers and the 13.8-GHz radar functioned normally during these flights. Some radiometers on the ER-2 and the DC-8 aircraft have comparable frequencies; signatures acquired by these radiometers from these flights are analyzed in detail. It is shown that storm-associated brightness temperature depressions observed at frequencies ≤90 GHz from two different altitudes are quite comparable. At high frequencies ≥150 GHz the brightness temperature depressions observed at 20-km altitude are significantly larger than those observed at 11-km altitude in some portions of the storms. This suggests the presence of hydrometeors in the 11- to 20-km altitude region that effectively scatter radiation at frequencies ≥150 GHz.