Abstract

Ascending convective plumes of inhomogeneous warm air interspersed with regions of air that are remarkably free from temperature fluctuations are sometimes observed in the lower layers of the atmosphere. A close correlation is demonstrated between intervals of good optical seeing along an upward-slanting path 20 m long and such periods of below average, air-temperature fluctuation. This correlation is sensitive to the azimuthal angle between wind direction and the vertical plane containing the optical path. The occurrence of temperature-quiescent periods at a given height is also shown to require the horizontal wind speed to be less than a critical value, and there is evidence that the thermal structure tends to be elongated in the direction of the wind. The range of amplitudes of image dancing observed in these experiments is comparable with that encountered in solar observations. The atmospheric temperature structure coefficients calculated from these optical experiments compare favorably with independent direct measurements.

© 1967 Optical Society of America

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References

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  1. E. K. Webb, Appl. Opt. 3, 12, 1329 (1964).
    [CrossRef]
  2. R. J. Bray, R. E. Loughhead, Aust. J. Phys. 14, 14 (1961).
    [CrossRef]
  3. E. K. Webb, C. E. Coulman, Nature 212, 58 (1966).
    [CrossRef]
  4. C. H. B. Priestley, Turbulent Transfer in the Lower Atmosphere (University of Chicago Press, Chicago, 1959).
  5. R. J. Taylor, Aust. J. Phys. 11, 168 (1958).
    [CrossRef]
  6. E. K. Webb, Nature 193, 840 (1962).
    [CrossRef]
  7. R. E. Loughhead, R. J. Bray, Z. Astrophys. 63, 101 (1966).
  8. C. E. Coulman, J. Opt. Soc. Am. 55, 896 (1965).
    [CrossRef]
  9. C. E. Coulman, J. Opt. Soc. Am. 56, 1232 (1966).
    [CrossRef]
  10. Reference 4, p. 71.
  11. J. L. Lumley, H. A. Panofsky, The Structure of Atmospheric Turbulence (Interscience Publishers, New York, 1964), Chap. 5.
  12. J. Warner, J. W. Telford, J. Atmos. Sci. 20, 313 (1963).
    [CrossRef]
  13. J. V. Ramsay, Opt. Acta 6, 344 (1959).
    [CrossRef]
  14. R. E. Hufnagel, N. R. Stanley, J. Opt. Soc. Am. 54, 52 (1964).
    [CrossRef]
  15. V. M. Bovsheverov, M. A. Kallistratova, Astron. Zh. 41, 550 (1964).

1966 (3)

E. K. Webb, C. E. Coulman, Nature 212, 58 (1966).
[CrossRef]

R. E. Loughhead, R. J. Bray, Z. Astrophys. 63, 101 (1966).

C. E. Coulman, J. Opt. Soc. Am. 56, 1232 (1966).
[CrossRef]

1965 (1)

1964 (3)

E. K. Webb, Appl. Opt. 3, 12, 1329 (1964).
[CrossRef]

R. E. Hufnagel, N. R. Stanley, J. Opt. Soc. Am. 54, 52 (1964).
[CrossRef]

V. M. Bovsheverov, M. A. Kallistratova, Astron. Zh. 41, 550 (1964).

1963 (1)

J. Warner, J. W. Telford, J. Atmos. Sci. 20, 313 (1963).
[CrossRef]

1962 (1)

E. K. Webb, Nature 193, 840 (1962).
[CrossRef]

1961 (1)

R. J. Bray, R. E. Loughhead, Aust. J. Phys. 14, 14 (1961).
[CrossRef]

1959 (1)

J. V. Ramsay, Opt. Acta 6, 344 (1959).
[CrossRef]

1958 (1)

R. J. Taylor, Aust. J. Phys. 11, 168 (1958).
[CrossRef]

Bovsheverov, V. M.

V. M. Bovsheverov, M. A. Kallistratova, Astron. Zh. 41, 550 (1964).

Bray, R. J.

R. E. Loughhead, R. J. Bray, Z. Astrophys. 63, 101 (1966).

R. J. Bray, R. E. Loughhead, Aust. J. Phys. 14, 14 (1961).
[CrossRef]

Coulman, C. E.

Hufnagel, R. E.

Kallistratova, M. A.

V. M. Bovsheverov, M. A. Kallistratova, Astron. Zh. 41, 550 (1964).

Loughhead, R. E.

R. E. Loughhead, R. J. Bray, Z. Astrophys. 63, 101 (1966).

R. J. Bray, R. E. Loughhead, Aust. J. Phys. 14, 14 (1961).
[CrossRef]

Lumley, J. L.

J. L. Lumley, H. A. Panofsky, The Structure of Atmospheric Turbulence (Interscience Publishers, New York, 1964), Chap. 5.

Panofsky, H. A.

J. L. Lumley, H. A. Panofsky, The Structure of Atmospheric Turbulence (Interscience Publishers, New York, 1964), Chap. 5.

Priestley, C. H. B.

C. H. B. Priestley, Turbulent Transfer in the Lower Atmosphere (University of Chicago Press, Chicago, 1959).

Ramsay, J. V.

J. V. Ramsay, Opt. Acta 6, 344 (1959).
[CrossRef]

Stanley, N. R.

Taylor, R. J.

R. J. Taylor, Aust. J. Phys. 11, 168 (1958).
[CrossRef]

Telford, J. W.

J. Warner, J. W. Telford, J. Atmos. Sci. 20, 313 (1963).
[CrossRef]

Warner, J.

J. Warner, J. W. Telford, J. Atmos. Sci. 20, 313 (1963).
[CrossRef]

Webb, E. K.

E. K. Webb, C. E. Coulman, Nature 212, 58 (1966).
[CrossRef]

E. K. Webb, Appl. Opt. 3, 12, 1329 (1964).
[CrossRef]

E. K. Webb, Nature 193, 840 (1962).
[CrossRef]

Appl. Opt. (1)

E. K. Webb, Appl. Opt. 3, 12, 1329 (1964).
[CrossRef]

Astron. Zh. (1)

V. M. Bovsheverov, M. A. Kallistratova, Astron. Zh. 41, 550 (1964).

Aust. J. Phys. (2)

R. J. Taylor, Aust. J. Phys. 11, 168 (1958).
[CrossRef]

R. J. Bray, R. E. Loughhead, Aust. J. Phys. 14, 14 (1961).
[CrossRef]

J. Atmos. Sci. (1)

J. Warner, J. W. Telford, J. Atmos. Sci. 20, 313 (1963).
[CrossRef]

J. Opt. Soc. Am. (3)

Nature (2)

E. K. Webb, C. E. Coulman, Nature 212, 58 (1966).
[CrossRef]

E. K. Webb, Nature 193, 840 (1962).
[CrossRef]

Opt. Acta (1)

J. V. Ramsay, Opt. Acta 6, 344 (1959).
[CrossRef]

Z. Astrophys. (1)

R. E. Loughhead, R. J. Bray, Z. Astrophys. 63, 101 (1966).

Other (3)

C. H. B. Priestley, Turbulent Transfer in the Lower Atmosphere (University of Chicago Press, Chicago, 1959).

Reference 4, p. 71.

J. L. Lumley, H. A. Panofsky, The Structure of Atmospheric Turbulence (Interscience Publishers, New York, 1964), Chap. 5.

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Figures (11)

Fig. 1
Fig. 1

(a) Typical profiles of mean potential temperature θ with height z on logarithmic scale in the three regions discussed in the text. (b) Typical records of temperature fluctuations in the regions of (a). This figure is adapted from Webb1 (1964).

Fig. 2
Fig. 2

A simplified sketch of the model proposed by Webb1 (1964) to account for intermittent periods of good and bad solar seeing in the presence of ascending thermal convection plumes in the lower atmosphere. Adapted from Webb1 (1964).

Fig. 3
Fig. 3

An image of the point source S is formed at the focus of the lens O. Rapid response thermometers T2, T4, and T10 are located almost vertically beneath the source S at heights of 2 m, 4 m, and 10 m, respectively.

Fig. 4
Fig. 4

A typical section of the experimental records. The modulus and argument of the optical transfer function (OTF) have been recorded simultaneously with the horizontal wind speed at 2 m height and the air temperatures at 2 m, 4 m, and 10 m above ground. Quiescent periods in the temperature records correlate with reduced fluctuation of arg (OTF) (or image motion) and increased mean value of mod (OTF) (or image contrast). There is often a small time displacement between quiescent periods on the temperature and optical records because the thermometers are not located at the centroid of the optical path. The anemometer calibration is linear; 25 cycles/min on the records denotes a wind speed of 1 m/sec.

Fig. 5
Fig. 5

(a) The relative frequencies of occurrence of temperature quiescent intervals (at z = 4 m) are shown according to their durations. (b) The relative frequencies of occurrence of quiescent periods on the record of arg (OTF), or image movement, are shown according to duration. It is noticeable that only about 50% of the shortest group of temperature quiescent events (0–10 sec) yield periods of reduced image movement. The percentage is higher for the longer duration temperature quiescent events.

Fig. 6
Fig. 6

Correlation between quiescent periods on the temperature traces and the arg (OTF) trace as a function of wind speed for wind direction |φ| < 30°. ⊗ denotes r(τ4; τopt), from the 4-m thermometer. ⊕ denotes r(τ10, τopt), from the 10-m thermometer. The standard errors of coefficients r(τ10, τopt) are shown by vertical lines. Similar standard errors are true for r(τ4, τopt).

Fig. 7
Fig. 7

Correlation between quiescent periods on the temperature traces and the arg (OTF) trace for wind direction |ψ| > 30°. The behavior of the correlation coefficients with wind speed is different from that in Fig. 6.

Fig. 8
Fig. 8

The incidence of occurrence of periods of reduced amplitude of image motion varies with wind speed in the manner shown. This result refers to a telescope and light source arrangement as shown in Fig. 3. Standard deviations are shown by vertical lines. 0 for |ψ| < 30°. × for |ψ| > 30°.

Fig. 9
Fig. 9

The variation of incidence of occurrence of temperature quiescent periods at z = 4 m with wind speed.

Fig. 10
Fig. 10

As Fig. 9 but the data refer to z = 10 m.

Fig. 11
Fig. 11

A typical section of experimental record illustrating the range of variation in duration of the temperature quiescent periods.

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