portion of the
systems.
depths between
feet,
The lowest of these, extending from the surface up to about 20,000
is the well known trade wind current.
The Trades are deepest and strong-
tographs show
est during the winter months, December through February,
iy
at the surface of about 19 knots from an east-northeasterly direction.
Halimeda
with an average strength
Maximum
speeds occur at about the four to five thousand foot level, where speeds greater
‘eet
in depth.
than 25 knots are not uncommon.
The top of the current during this season may
he surface,
often extend to 30,000 feet or more,
C per mile,
become gradually weaker and more variable.
Ik Atoll.
most typical direction veers from east~northeasterly to easterly.
During August
an and in 1930 |
and September the average surface wind is 1]1 knots from the east.
During these
coconuts, and
two months,
niwetok Atoll
southeast,
nd because of
rent becomes shallowest, often not extending above the 8,000 or 9,000-foot level.
At the same time their average or
frequent periods of very light winds,
During March,
are often observed.
especially coming from the
April and May the trade wind cur-
Figure 4, on which is plotted the zonal or east-west component of the wind as a
At
masses,
During the spring and summer the Trades
10 natives
function of height and of month, shows these different changes.
‘with Ameri.
statistics by month are given in Table I.
persong
Surface wind
Above the trades and extending up to the tropopause, which is generally
veral hun-
located between 55,000 and 60,000 feet,
purposes
called the Upper Westeriies.
are westerly winds which are usually
This wind stream may be thought of as the southward
' On FRED
extension of the strong circumpolar jet stream of mid-latitudes.
ding from
of Eniwetok this southward extension of the polar westerlies overlies the trade
es,
wind current.
At the latitude
The Upper Westerlies are quite variable due to the presence of
numerous cyclonic and anticyclonic vortices which are typically carried along in
the basic current.
lands area
The upper westerly current, whose core is normally located at about the 40,000-
f the
foot level,
fent a
hE othaataa
Se
in
h of the
tC wind
is strongest in the spring,
deepest and most well developed.
autumn,
at
from the month of March through May,
which time average velocities reach 25 knots.
ar with
belt,
in the proper position relative to Enlwetok,
often produces east winds for periods of two to four days at these upper levels.
x III), at
,
Such a vortex,
At the same time this current is
As the season progresses through summer into
the thickness and strength of the current diminishes to average values
of about 5 knots with extremely high variability.
In mid-winter the Upper West-
erlies often do not extend as far south aloft as Eniwetok.
Above the tropopause and situated in the lower stratosphere is
wind stream, which is an easterly and very steady current.
the third
These winds are
Vo er oe rome