Abstract

The available diffraction-corona theory for the interpretation of the cloud iridescence phenomenon is reviewed and applied to photographic observations of an iridescent contrail. It is concluded that the simple-diffraction theory qualitatively explains the occurrence of corona and iridescence under the cloud microphysical conditions with which these phenomena are typically associated, and that the theoretical predictions of cloud droplet diameters of 1–3 μm during initial contrail formation appear to be reasonable for a highly supersaturated environment. However, additional Mie theory simulations utilizing narrow droplet size distributions should be performed to assess the impact of anomalous diffraction in realistic cloud compositions in order that iridescence observations may be more precisely interpreted for cloud microphysical studies.

© 1979 Optical Society of America

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References

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  1. W. J. Humphreys, Physics of the Air (McGraw-Hill, New York, 1929).
  2. M. Minnaert, The Nature of Light and Color in the Open Air (Dover, New York, 1954).
  3. R. A. R. Tricker, Introduction to Meteorological Optics (American Elsevier, New York, 1970).
  4. H. C. van de Hulst, Light Scattering from Small Particles (Wiley, New York, 1957).
  5. See H. Appleman, “The formation of exhaust condensation trails by jet aircraft,” Bull. Am. Meteorol. Soc. 31, 14–20 (1953), for a discussion of the meteorological aspects of contrail formation. Note, however, that these contrails appeared to form at a temperature several degrees warmer than the predicted critical temperature required to produce water saturation under the conditions derived from the sounding.
  6. The simulation through ray tracing methods of most ice crystal refraction phenomena provides a means to sense remotely the types and orientations of the ice crystals present in each case (see, e.g., Ref. 3).
  7. G. C. Simpson, “Coronae and iridescent clouds,” Q. J. R. Meteorol. Soc. 38, 291–299 (1912).
    [Crossref]
  8. Although ice crystals are to be expected to produce coronas on the basis of diffraction theory using simplified ice particle shapes (see Refs. 1 and 4), this has apparently not been observed to be the case in the atmosphere. It may be that the proper conditions of minute, monodispersed ice crystal populations with the same shape and orientation are rarely, if ever, realized in atmospheric ice clouds.
  9. A first step in such a program was recently discussed byF. E. Barmore, R. Crouch, and R. Lloyd at the Topical Meeting on Meteorological Optics [see“Iridescence in an aircraft contrail,” Technical Digest Topical Meeting on Meteorological Optics, Keystone, Opt. Soc. Am., MB3-1-2 (1978)].

1953 (1)

See H. Appleman, “The formation of exhaust condensation trails by jet aircraft,” Bull. Am. Meteorol. Soc. 31, 14–20 (1953), for a discussion of the meteorological aspects of contrail formation. Note, however, that these contrails appeared to form at a temperature several degrees warmer than the predicted critical temperature required to produce water saturation under the conditions derived from the sounding.

1912 (1)

G. C. Simpson, “Coronae and iridescent clouds,” Q. J. R. Meteorol. Soc. 38, 291–299 (1912).
[Crossref]

Appleman, H.

See H. Appleman, “The formation of exhaust condensation trails by jet aircraft,” Bull. Am. Meteorol. Soc. 31, 14–20 (1953), for a discussion of the meteorological aspects of contrail formation. Note, however, that these contrails appeared to form at a temperature several degrees warmer than the predicted critical temperature required to produce water saturation under the conditions derived from the sounding.

Barmore, F. E.

A first step in such a program was recently discussed byF. E. Barmore, R. Crouch, and R. Lloyd at the Topical Meeting on Meteorological Optics [see“Iridescence in an aircraft contrail,” Technical Digest Topical Meeting on Meteorological Optics, Keystone, Opt. Soc. Am., MB3-1-2 (1978)].

Crouch, R.

A first step in such a program was recently discussed byF. E. Barmore, R. Crouch, and R. Lloyd at the Topical Meeting on Meteorological Optics [see“Iridescence in an aircraft contrail,” Technical Digest Topical Meeting on Meteorological Optics, Keystone, Opt. Soc. Am., MB3-1-2 (1978)].

Humphreys, W. J.

W. J. Humphreys, Physics of the Air (McGraw-Hill, New York, 1929).

Lloyd, R.

A first step in such a program was recently discussed byF. E. Barmore, R. Crouch, and R. Lloyd at the Topical Meeting on Meteorological Optics [see“Iridescence in an aircraft contrail,” Technical Digest Topical Meeting on Meteorological Optics, Keystone, Opt. Soc. Am., MB3-1-2 (1978)].

Minnaert, M.

M. Minnaert, The Nature of Light and Color in the Open Air (Dover, New York, 1954).

Simpson, G. C.

G. C. Simpson, “Coronae and iridescent clouds,” Q. J. R. Meteorol. Soc. 38, 291–299 (1912).
[Crossref]

Tricker, R. A. R.

R. A. R. Tricker, Introduction to Meteorological Optics (American Elsevier, New York, 1970).

van de Hulst, H. C.

H. C. van de Hulst, Light Scattering from Small Particles (Wiley, New York, 1957).

Bull. Am. Meteorol. Soc. (1)

See H. Appleman, “The formation of exhaust condensation trails by jet aircraft,” Bull. Am. Meteorol. Soc. 31, 14–20 (1953), for a discussion of the meteorological aspects of contrail formation. Note, however, that these contrails appeared to form at a temperature several degrees warmer than the predicted critical temperature required to produce water saturation under the conditions derived from the sounding.

Q. J. R. Meteorol. Soc. (1)

G. C. Simpson, “Coronae and iridescent clouds,” Q. J. R. Meteorol. Soc. 38, 291–299 (1912).
[Crossref]

Other (7)

Although ice crystals are to be expected to produce coronas on the basis of diffraction theory using simplified ice particle shapes (see Refs. 1 and 4), this has apparently not been observed to be the case in the atmosphere. It may be that the proper conditions of minute, monodispersed ice crystal populations with the same shape and orientation are rarely, if ever, realized in atmospheric ice clouds.

A first step in such a program was recently discussed byF. E. Barmore, R. Crouch, and R. Lloyd at the Topical Meeting on Meteorological Optics [see“Iridescence in an aircraft contrail,” Technical Digest Topical Meeting on Meteorological Optics, Keystone, Opt. Soc. Am., MB3-1-2 (1978)].

The simulation through ray tracing methods of most ice crystal refraction phenomena provides a means to sense remotely the types and orientations of the ice crystals present in each case (see, e.g., Ref. 3).

W. J. Humphreys, Physics of the Air (McGraw-Hill, New York, 1929).

M. Minnaert, The Nature of Light and Color in the Open Air (Dover, New York, 1954).

R. A. R. Tricker, Introduction to Meteorological Optics (American Elsevier, New York, 1970).

H. C. van de Hulst, Light Scattering from Small Particles (Wiley, New York, 1957).

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Figures (2)

FIG. 1
FIG. 1

Results of predictions of the dependence of drop diameter on solar separation angle derived from the simple diffraction-corona theory for the first- and second-order red bands. The dashed line gives precise Mie theory results which undulate about the simple theory predications owing to the effect of anomalous diffraction.

FIG. 2
FIG. 2

Predicted drop diameters at the approximate distances behind the aircraft at which the first- and second-(solid circle) order red bands were observed (from Table I), derived from the simple diffraction-corona theory. Approximate droplet growth rates dr/dt were calculated with an assumed aircraft speed of 300 ms−1.

Tables (1)

Tables Icon

TABLE I Angular separation in degrees between the generating aircraft tail and the center of each colored band, derived from photographs of the contrails at the indicated angular separation angles from the sun (θ).

Equations (1)

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sin θ = ( n + 0.22 ) λ / d ,