Horizontal velocity structure functions in the upper
troposphere and lower stratosphere: 1. Observations
We compute horizontal velocity structure functions using quasiglobal
data accumulated by specially equipped commercial aircraft on 7630
flights from August 1994 to December 1997. Using the ozone
concentration measurements, we classify the results as tropospheric or
stratospheric. We further divide the results into four absolute
latitude bands. For separation distance r between 10 and 100
km, the lower stratospheric diagonal third-order structure functions
are proportional to negative r. This implies a downscale
energy cascade, and we estimate the mean energy dissipation rate to be
< epsilon > ~ 6 x 10-5 m2 s-3. For
r between 300 and 1500 km, a positive r3
dependence was visible for the polar stratospheric data. This may be
the result of a 2D turbulence downscale enstrophy cascade, and we
estimate the average enstrophy flux to be Piomega ~ 2 x
10-15 s-3 and the energy spectral constant to be
K ~ 2. The negative sign of these third-order functions at
mesoscales in both the upper troposphere and lower stratosphere
provide no support for an inverse energy cascade 2D turbulence. At
scales above ~ 100 km, the second-order structure functions increase
with latitude in the troposphere and decrease with latitude in the
stratosphere. The off-diagonal third-order functions in the
stratosphere show a remarkably clean negative r2
dependency from 10 to 1000 km in scale.
Send e-mail to
j y n c @ m i t . e d u for a copy of
the complete article.
Return to publications list.