Seasonal Variability of Vertical Eddy Diffusivity
in the Middle Atmosphere,
Part I: Three-Year Observations by the MU Radar
Shoichiro Fukao, Manabu D. Yamanaka, Naoki Ao
Radio Atmospheric Science Center, Kyoto University,
Uji, Kyoto 611, Japan
Wayne K. Hocking
Department of Physics, University of Western Ontario,
London, Ontario N6A 3K7, Canada
Toru Sato
Department of Electrical Engineering II, Kyoto University,
Sakyo, Kyoto 606, Japan
Mamoru Yamamoto, Takuji Nakamura, Toshitaka Tsuda and Susumu Kato
Radio Atmospheric Science Center, Kyoto University,
Uji, Kyoto 611, Japan
Journal of Geophysical Research ,
Vol. 99 , No.D9, pp.18,973-18,987
First draft: November 17, 1991;
Submitted: September 13, 1993;
Received: September 24, 1993;
Revised: March 11, 1994;
Recieved: March 24, 1994;
Accepted: April 1, 1994
Published: September 20, 1994
ABSTRACT ,
CONTENTS ,
CORRECTIONS ,
FIGURES ,
REFERENCES ,
CITATIONS
Abstract
The vertical eddy diffusivity K due to atmospheric turbulence
with spatial scales of $10^{0}-10^{2}$ m has been computed
from the echo power spectral width observed by the MU radar
for almost every month from January 1986 to December 1988.
The method of analysis follows Lilly et al. [1974],
Sato and Woodman [1982] and Hocking [1983a, 1985, 1988],
and the contamination due to beam broadening,
vertical shear and transience has been removed.
Although observations for horizontal wind speeds larger than
approximately 40 m/s,
such as occur near the tropopause jet stream in winter,
have been omitted because of excessive beam broadening,
sufficient numbers of observations have been accumulated
to produce a reasonable climatology
for the upper troposphere and lower stratosphere (6-20 km altitude)
and for the mesosphere (60-82 km altitude).
The monthly median of K
shows a local maximum near the tropopause jet stream altitude.
It becomes larger in the mesosphere,
increasing gradually with height.
Maxima of K are observed in winter near the tropopause and
in summer in the mesosphere,
and the seasonal variability of K reaches approximately an order of
magnitude.
A semiannual variability is apparent in the mesosphere with minima
in the equinoctial seasons.
Contents
- 1. Introduction
- 2. Observational Principle
- 2.1. The MU Radar
- 2.2. Observational Limit due to Spectral Broadening Effects
- 2.3. Estimation of Vertical Eddy Diffusivity
- 2.4. Method of Calculation
- 3. Upper Troposphere and Lower Stratosphere
- 4. Mesosphere
- 5. Summary and Discussions
Corrections and Additional Remarks
(Nothing)
List of Tables and Figures
- Table 1.
List of the GRATMAC standard observations.
- Table 2.
Parameters of the MU radar for the GRATMAC standard observations.
- Table 3.
Summary of observations.
- Fig. 1.
Vertical scales of the inertial subrange of turbulence
($L$: the outer scale, $\ell$: the inner scale),
adapted from Hocking [1985] with modifications.
Observable scales with the MU radar ($\Delta z$: the sampled volume thickness,
$\lambda / 2$: half the radar wavelength) are hatched.
The density scale height ($H$),
the predominant vertical wavelength ($IGW$; to be discussed in Part II),
and the maximum vertical scale ($Z$; given by the altitude itself)
are also indicated.
- Fig. 2.
The observational principle and beam-broadening contamination due to
a background wind.
(a) Schematic vertical cross-section of a radar scattering volume in which
$\lambda / 2$-scale eddies are advected by larger scale turbulence;
the background wind (thick horizontal arrow) produces an inhomogeneous
radial velocity field which appears as beam broadening
in the observed Doppler spectra.
(b) Calculated relationship between the background horizontal wind velocity
and the minimum spectral width observed by the MU radar
(zenith angle: 10\degr ).
- Fig. 3.
Scatter plots of experimental spectral half-power half-width of
oblique beams at 10\degr azimuth vs the beam-broadening contaminations
for the upper troposphere and lower stratosphere.
The three upper panels show the winter case,
and the three lower panels show the summer case.
- Fig. 4.
Same as Fig. 3,
but for the mesosphere.
- Fig. 5.
Seasonal-vertical variations of the monthly medians
of vertical eddy diffusivity K observed by the MU radar in the upper
troposphere and lower stratosphere in (a) 1986, (b) 1987 and (c) 1988,
respectively.
Unite are in m$^{2}$/s.
- Fig. 6.
Seasonal-vertical variations of the mean kinetic energy dissipation rate
$\epsilon$ calculated from routine meteorological observations (twice a day)
at the Shionomisaki Weather Station of the Japan Meteorological Agency.
- Fig. 7.
Vertical profiles of the annual medians of vertical eddy diffusivity
K observed by the MU radar during 1986-88
in the upper troposphere and lower stratosphere,
in comparison with a standard model profile
[ Massie and Hunten, 1981].
- Fig. 8.
Vertical profiles of the seasonal medians of vertical eddy diffusivity K
observed by the MU radar during 1986-88 in the upper troposphere and
lower stratosphere,
in comparison with a standard model profile
[ Massie and Hunten, 1981].
- Fig. 9.
Same as Fig. 5,
but for the mesosphere.
- Fig. 10.
Scatter plots of the hourly medians and the vertical profiles of
annual medians of vertical eddy diffusivity K observed by the MU radar
in the mesosphere for (a) 1986,
(b) 1987 and (c) 1988,
in comparison with a standard model profile
[ Ogawa and Shimazaki, 1975].
- Fig. 11.
Vertical profiles of the seasonal medians of vertical eddy diffusivity K
observed by the MU radar in the mesosphere during 1986-88.
Hourly-median values for each season in 1987 are plotted by dots,
66\% of which are ranged between a pair of thick broken curves.
- Fig. 12.
Comparison of the present observations
(the variability of the annual medians is shown by the hatched areas)
with previous studies
($A$ [ Allen et al., 1981],
$BS$ [ Blum and Schuchardt, 1978],
$C$ [ Crutzen, 1974],
$H$ [ Hocking, 1985b],
$J$ [ Justus, 1973],
$JW$ [ Johnson and Wilkins, 1965],
$L$ [ L\"{u}bken et al., 1993],
$M$ [ McElroy et al., 1974],
$MH$ [ Massie and Hunten, 1981],
$OS$ [ Ogawa and Shimazaki, 1975],
$TB$ [ Teitelbaum and Blamont, 1977],
$S$ [ Strobel et al., 1987]
and $Y$ [ Yamazaki, 1989]).
The seasonal variabilities obtained by the present observations
(as the ranges of the seasonal medians) and by the study of
Blum and Schuchardt are shown by arrows.
An approximate profile of the molecular diffusivity is also indicated
by broken curve.
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Citations by Subsequent Papers
(Under construction !!!!!)
List of Original Papers
by M. D. Yamanaka
Bibliography
by any authors
M. D. YAMANAKA homepage (English)
E-mail : yamanaka@kurasc.kyoto-u.ac.jp