| dc.description.abstract | 300 mb. mean wind speeds and directions
o were extracted at 5 latitude/longitude grid points
In a region between latitudes 300N and 300S around
the globe for the months of January, April, July
and October. The streamline-isotach charts (The
Upper Tropospheric Circulation over the Global
Tropics) prepared by Sadler (1975) were used for
this purpose.
The zonal and meridional wind components
were used for the computation of the horizontal
velocity divergence~ relative vorticity, their
component terms and absolute vorti~ity.
The horizontal velocity divergence and
relative vorticity were used to decompose the
wind vector into the divergent and rotational
components by the Liebmann reiaxationprocedure
and Version II of-Hawkins and Rosenthal (1965)
scheme for boundary values.
A number of other dynamical computations
were made which include a comparlson of the divergent
and rotational wind components, an examination of the
computable quantities occurring In the divergence
and vorticity equations and a determination of their
- Xl -
Fourier amplitudes and phase angles In the zonal
direction. These computations were also used to
verify the validity of the classical scale analysis
technique, wherever possible.
The results of this study show that:
(i) For total wind vector V, the magnitude of
the zonal wind component is larger than that
of the Deridional wind component. The zonal
component is smallest in the equatorial
latitudes and increases towards the subtropics.
It is largest in the winter hemisphere-
The magnitude of the meridional component
shows very little variation with latitude.
gradients occur in the winter hemisphere.
(ii\ Large positive values of velocity divergence
general_f occur around the equator and large
negafi~e values of divergence occur in the
sub-tropical latitudes above the surface
position of the sub-tropical ridge line. The
largest divergence viiues'occur roughly above
the surface position of the Intertropical
Convergence Zone (ITC~).
Ciii) The relative vorticity field 1S dominated by
anticyclonic vorticity e~cept in the regions
of mid-oceanic cyclonic troughs. The largest
values of relative vorticity and its meridional
(.IV,) "I'he magnitudes 0f aaxu and aayv vary very 1·1tt1e
with latitude. Each is of the same order of
magnitude as the horizontal velocity
divergence.
(v) The magnitude of
av
than that of ax. is generally much larger
au
The largest values of ay
occur in the winter hemisphere and its smallest
- values occur in the equatorial region.
have does not vary much with latitude.
(vi) The absolute vorticity is positive in the
northern hemisphere and negative in the southern
hemisphere except within about 50 latitude
from the equator, where the position of zero
absolute vorticity isopleth fluctuates around
the equator, being confined more into the
winter hemisphere than into the summer
hemisphere.
(vii) The velocity potential field shows several
closed zonally oriented-·centres of mass
sources and sinks. The major mass sources
are generally found in the summer hemisphere
corresponding to the surface position of the
Inter-tropical Convergence Zone. The major
mass sinks are found in the winter hemisphere.
(viii) The stream function field is in good agreement
with the corresponding streamline analysis
pattern, with positions of the major cyclonic
and anticyclonic systems nearly coinciding.
Cix) The magnitude of the meridional divergent
wind component v ls generally larger than
that of the zonal divergent wind component
u. v is about twice u in the sub-tropical
latitudes and nearly equal in the equatorial
latitudes.
(x) The magnitude of the zonal rotational wind
component u~ is small in the equatorial
latitudes and very large in the sub-tropical
latitudes.
(xi) The magnitude of the meridional rotational
wind component is smaller than that of the
zonal rotational wind component use, and it
does not vary much with latitude.
(xii) The magnitude of the divergent wind vector
varies very little with latitude. It is
smaller than that of the:rotational wind
vector , by about an order of magnitude.
The rotational vector wind is largest in the
,
sub-tropical latitudes.
(xi i i.) The magnitude of absolute
by the divergent wind (is comparable
to that by the rotational wind
(xiv) The magnitude of absolute vorticity advection
by the total wind is about three
times the magnitude of the product of absolute
vorticity and horizontal wind divergence
, within 50 of equator; elsewhere
they are nearly equal.
(xv) The magnitude of the Jacobian term
is generally less than both
the relative vorticity term Ifs\jJa1nd the Beta
termlu\jJBlbY an order of magnitude in the
tropical region and by even two orders of
magnitude in the sub-tropical latitudes.
(xvi) The deformation term !(A~+B~) increases from
,the equatorial latitudes towards the subtropical
latitudes.
(xvii) The relative vorticity term increases
from the equatorial towards the sub-tropical
latitudes.
(xviii) The Fourier amplitude~~ of relative vorticity
S, meridional divergent wind v , zonal rotational wind 'meridinal rotational wind
deformation term 1 (A2+B2) and vorticity
term - !S~ are large and have peaks in the
planetary scale waves (~ave numbers 1 to 4).
The amplitudes are generally small for synoptic
scale waves (wave numbers 5 to 18).
(xix) The large Fourier amplitudes of the horizontal
wind divergence V-V, zonal divergent wind Ux
and Jacobian term 2J(v~,u~) are spread between
wave numbers 1 to 10. There are two peaks;
a major peak is between wave numbers 1 to 5 and
a Minor peak between wave numbers 7 and 9.
(xx) The winter hemisphere Fourier amplitudes
are generally larger than the summer hemisphere
amplitudes. The amplitudes decrease In
magnitude towards the equator from the subtropical
latitudes.
(xxi) The scale analysis values for the horizontal
velocity divergence, relative vorticity and
Jacobian term are generally smaller than their
corresponding observed values. The difference
is much larger for wave numbers less than 5 and
not as large for wave numbers 6 to 10. The
scale analysis values are comparable to the
observed values for wave numbers greater than
10. | en |
