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Investigation 9A: WESTERLIES AND THE JET STREAM 1. "The Northern Hemisphere’s upper-air westerlies flowing through topographical ridges
exhibit clockwise (anticyclonic) curvature as seen from above. As shown in Figure 1, the
ridge axis line divides the ridge into two roughly symmetrical sectors. Note that west of the
ridge axis, winds are from the southwest (a warm weather direction) and east of the ridge
axis, winds are from the northwest (a cold weather direction). We can conclude that winds to
the west of a ridge axis favor ________ air advection while winds to the east of a ridge axis
favor cold air advection." cold warm
2. "The Northern Hemisphere’s upper-air westerlies flowing through topographical troughs
exhibit counterclockwise (cyclonic) curvature as seen from above. As shown in Figure 1, the
trough axis line divides the trough into two roughly symmetrical sectors. Note that west of the trough axis, winds are from the northwest (a cold weather direction) and east of the
trough line, winds are from the southwest (a warm weather direction). We conclude that
winds west of a trough axis favor ________ air advection while winds east of a trough line
favor warm air advection." cold warm
3. "Upper-air winds steer low-pressure systems as well as air masses. A surface Low that is
centered to the east of a trough axis and west of a ridge axis will be expected to move
toward the ________." southeast northeast 4. "When the upper-air flow pattern is zonal, the source region for much of the air over the
coterminous U.S. is the Pacific Ocean. On the other hand, when the upper-air flow pattern is
meridional, the source regions for air masses over the lower 48 states are Canada (where
winds are from the northwest) or Mexico or the Gulf of Mexico (where winds are from the
southwest). Hence, from west to east across the lower 48 states, temperatures are likely to be
more variable with a ________ flow pattern." meridional zonal
5. "Fundamental to the formation of the polar-front jet stream within the westerlies is the
physical property that warm air is less dense than cold air when both are at the same
pressure. Air pressure drops ________ rapidly with increasing altitude in cold air than in
warm air." less
more 6. "In the Northern Hemisphere, when the polar-front jet stream is south of a locality, the
weather at that location is relatively ________." warm cold
7. "As a component of the planetary-scale upper-air westerlies and similar to the winds at 500
mb, the polar-front jet stream steers low pressure systems. Hence, middle latitude storms
generally move from ________." east to west west to east 8. "The pattern of winds in Figure 4 indicates a ________ over the central U.S. states. The
flow pattern across the country is meridional." ridge trough
9. "On average, one would expect temperatures at similar latitudes to be similar. Zonal wind
patterns, as in Figure 3, would exhibit this relationship. However, given the wind pattern of
Figure 4, at 00Z on 18 NOV 2015, surface air temperatures in the central plains states of
South Dakota and Nebraska are likely to be ________ than surface temperatures over Ohio
and Kentucky." lower higher 10. "Knowledge of the location of the jet stream and upper-air winds in general is very
important for commercial aviation and can result in fuel savings and shorter flight times. At
Figure 4 map time, an airline flight from Austin, Texas to International Falls, Minnesota
would take ________ time than a flight along the same route from International Falls to
Austin." less more Applications 11. "Wind directions at station models near isobar lines across the country were generally
seen to flow ________ with the circulation of the Ontario Low best defined as a lowpressure system." parallel to surface isobars at angles across isobars
12. "Surface wind speeds across the coterminous U.S. were generally less than Billings, in
south central Montana, which reported a speed with three feathers denoting ________
knots." 15
30
50 13. "Figure 6 is the 500-mb constant-pressure map for 12Z 01 NOV 2015, the same time as
the Figure 5 surface map. The mid-tropospheric flow pattern shown by the contour lines
on the 500-mb map, displayed ________." a trough over the Great Lakes a closed circulation within a trough over Texas a generally west-to-east flow over the northwestern and north-central U.S. all of these features 14. "Recall that the heights at which the radiosondes detected 500-mb of pressure are
reported in the upper right position of the upper-air station models on the map. Also, the
heights are plotted in tens of meters, so that a “0” needs to be added to the digits for the
actual height. The height of the 500-mb pressure level plotted at Buffalo, in western New
York, was ________ meters above sea level." 5420 5560 5630 15. "Compare the heights of the 500-mb pressure surface across the southern portion of the
U.S. to those along the northern portion on the map. As latitude increases (one moves
poleward), the height of the 500-mb surface generally ________." increases remains constant decreases
16. "The highest wind speeds plotted on the 500-mb map were reported at Buffalo. Those
winds were generally from the southwest at about ________ knots (a pennant, four long
and one short feathers)." 55 95 120
17. "The 500-mb wind directions often provide guidance on storm movements. The 500-mb
wind directions over the Great Lakes region indicate the storm center seen on the Figure
5 surface map would generally move toward the ________ over the next day or so. The
winds over the southern surface storm were generally light and mixed in direction,
indicating little movement was expected." northwest northeast southeast southwest
18. "Figure 7 is the 300-mb constant-pressure map for 12Z 01 NOV 2015, the same time as
the surface and 500-mb maps. The 300-mb pressure level occurs in the upper
troposphere. The 300-mb station model heights are also plotted in tens of meters. The
height of the 300-mb pressure level at Buffalo, NY, was ________ meters above sea
level." 9290 9450 9770 19. "The general 300-mb contour pattern at 12Z on 01 NOV exhibited an upper air flow with
________." a deep trough in the south-central U.S. a weak trough centered over the Great Lakes a generally west-to-east flow over the northwestern and north-central U.S. all of these features
20. "Comparing the heights of the 300-mb pressure surface generally across the southern
portion of the U.S. to those along the northern portion on the map, as latitude increases
(one moves poleward), the height of the 300-mb surface generally ________. This pattern
is the same as that found at 500 mb." increases remains constant decreases
21. "From the 300-mb station models, the highest wind speed plotted on the Figure 7 map
was at 155 knots at ________." Flagstaff, AZ Charleston, SC Buffalo, NY
22. "Survey the map for wind speeds of 70 knots or more. Using this arbitrary wind speed
threshold to define the existence of a jet stream, we can therefore conclude that there
________ evidence of a jet stream on the Figure 7, 300-mb constant-pressure map
curving across the U.S." was was not
23. "Now compare the wind speeds plotted on the 12Z 01 NOV 2015, 500-mb constantpressure map (Figure 6) with those of the corresponding areas on the Figure 7, 300-mb
map. The comparison implies that wind speeds typically ________ as altitude increases
(upward to lower pressures) in the troposphere." decrease remain the same increase
24. "As was seen at the 500-mb constant-pressure level in Investigation 8B, higher wind
speeds at 300 mb are also located where the spacings of height contours are relatively
________. Furthermore, the relationship is consistent with that on surface weather maps
between wind speeds and the spacings of isobars." far apart close together 25. "Compare the 500-mb and 300-mb wind flows. The pattern of wind directions also shows
that the winds generally flow ________. This directional relationship is particularly
evident at higher wind speeds." “parallel” to the contour lines across contours at large angles
26. "Also note the relatively high wind speed area within the 90-kt isotach over the West
Coast from Washington State to northern California extending eastward to western
Montana. The wind speed at Medford, in southern Oregon, was plotted with two pennants
and a half feather indicating ________ knots." 85 105 135
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