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Remote Sounding of High Clouds. V: Infrared Properties and Structures of Tropical Thunderstorm Anvils

C. M. R. PlattCSIRO Division of Atmospheric Research, Aspendale, Victoria, 3195, Australia

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A. C. DilleyCSIRO Division of Atmospheric Research, Aspendale, Victoria, 3195, Australia

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J. C. ScottCSIRO Division of Atmospheric Research, Aspendale, Victoria, 3195, Australia

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I. J. BartonCSIRO Division of Atmospheric Research, Aspendale, Victoria, 3195, Australia

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G. L. StephensCSIRO Division of Atmospheric Research, Aspendale, Victoria, 3195, Australia

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Abstract

The infrared properties and structures of some anvils emanating from local thunderstorms were studied by lidar and infrared radiometry at Darwin, tropical Northern Australia. The anvils were typically from 1 to 2 km deep, at altitudes from 7 to 16 km and at temperatures from −15 to −70°C. There was a rough dependence of infrared emittance on temperature, but there was also a dependence on the age of the anvil. The average altitude and calculated wide-band greybody flux emittance were 11 km and 0.65 respectively.

One dense cloud appeared “superblack” when observed from below, due to reflection of upwelling warm radiation from the surface. The magnitude of the effect agreed within experimental error with that predicted from computations on a model cloud of ice cylinders, but was about twice that computed for a model of ice spheres.

Calculated rates of heating in the very cold clouds were very high, reaching 4°C h−1 near cloud base. The survival of these clouds for several hours suggests that the absorbed radiant heat was converted largely into sensible heat in the atmosphere rather than causing evaporation of the crystals.

Abstract

The infrared properties and structures of some anvils emanating from local thunderstorms were studied by lidar and infrared radiometry at Darwin, tropical Northern Australia. The anvils were typically from 1 to 2 km deep, at altitudes from 7 to 16 km and at temperatures from −15 to −70°C. There was a rough dependence of infrared emittance on temperature, but there was also a dependence on the age of the anvil. The average altitude and calculated wide-band greybody flux emittance were 11 km and 0.65 respectively.

One dense cloud appeared “superblack” when observed from below, due to reflection of upwelling warm radiation from the surface. The magnitude of the effect agreed within experimental error with that predicted from computations on a model cloud of ice cylinders, but was about twice that computed for a model of ice spheres.

Calculated rates of heating in the very cold clouds were very high, reaching 4°C h−1 near cloud base. The survival of these clouds for several hours suggests that the absorbed radiant heat was converted largely into sensible heat in the atmosphere rather than causing evaporation of the crystals.

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