Deep Tropical Ice Clouds

There are some notable differences between midlatitude cirrus and tropical ice clouds from anvils and dissipating thick stratiform precipitation regions:

  • Vertical velocities near deep convection in the tropics can be very high (m s-1)
  • While there may be small particles near cloud top, large crystals are often present at sizes of mm to cm
  • Habits are much more complex than in midlatitude cirrus; riming often occurs near convective regions

Examples

The data shown in these examples were collected primarily in tropical anvils and dissipating thick stratiform precipitation regions.

The figure below depicts examples of particles vs. altitude (km) and temperature (oC) in three size ranges (< 100, 400-600, >800 microns) by the Cloud Particle Imager (CPI) probe on August 22, 1999 during KWAJEX (Kwajalein Experiment; Kwajalein, Marshall Islands). The magnification between the different size ranges is not the same. Figure taken from Heymsfield et al., 2002. In this particular case, the cloud sampled was in close proximity to convection. The particles observed were rimed in the intermediate and large sizes with some aggregration evident. Analysis of measured radar reflectivities indicated vertical velocities above a few meters per second, which indicated the presence of deep updrafts. Strong updrafts led to in turn to extensive riming and complex ice crystal shapes often associated with the freezing of cloud droplets at low temperatures. In other words, riming was probably acquired in the convective regions, and subsequently the particles were advected into the anvil.

The figure below depicts examples of particles vs. altitude (km) and temperature (oC) in three size ranges (< 100, 400-600, >800 microns) by the Cloud Particle Imager (CPI) probe. The upper panel depicts data collected on 021799 (February 17, 1999) during LBA (Large Scale Biosphere-Atmosphere Experiment in Brazil) while the bottom figure is from 990823 (August 23, 1999) during KWAJEX. The 021799 case shows riming, which tends to occur near strong convection. The 082399 case shows pristine cirrus-type crystals reflecting short-lived convective elements and low temperatures. Figure taken from Heymsfield et al., 2002.


Relevant References

Heymsfield, A. J., A. Bansemer, P. R. Field, S. L. Durden, J. L. Stith, J. E. Dye, W. Hall, and C. A. Grainger: Observations and parameterizations of particle size distributions in deep tropical cirrus and stratiform precipitating clouds: Results from in situ observations in TRMM field campaigns. J. Atmos. Sci., 59, 3457-3491, 2002. View


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