Winds:

1
Winds Global Systems

• This chapter discusses
• Models to examine general circulation of the
  atmosphere with average wind, precipitation, and
  pressure patterns
• Ocean - atmosphere interactions and global
  oscillations including El Nino

2
Single-Cell Circulation Model
The basis for average air flow around the earth
can be examined using a non-rotating, non-tilted,
ocean covered earth. Heating is more intense at
the equator, which triggers Hadley cells to
redistribute rising heat from the tropical low to
the polar highs.
Figure 11.1A
3
Three Cell Circulation Model
A rotating earth breaks the single cell into
three cells. The Hadley cell extends to the
subtropics, the reverse flow Ferrel cell extends
over the mid latitudes, and the Polar cell
extends over the poles. The Coriolis force
generates westerlies and NE trade winds, and the
polar front redistributes cold air.
Figure 11.2A
4
Observed Winds in January
Observed average global pressure and winds have
increased complexity due to continents and the
tilted earth. Differential ocean-land heating
creates areas of semi-permanent high and low
pressure that guide winds and redistribute heat.
Figure 11.3A
5
Observed Winds in June
Global pressure and wind dynamics shift as the
Northern Hemisphere tilts toward the sun,
bringing the inter-tropical convergence zone, the
Pacific high, and blocking highs in the southern
oceans northward.
Figure 11.3B
6
North American Winter Weather
Semi-permanent highs redirect North American
winds, such as cold interior southerly flow from
the Canadian high. The Polar front develops a
wave like pattern as air flows around lows.
Figure 11.4
7
Global Precipitation Patterns
Global low pressure zones around the equator and
60 latitude generate convergence at the surface,
rising air and cloud formation. Zones of high
pressure at 30 and the Poles experience
convergence aloft with sinking, drying air.
Figure 11.5
8
Coastal Summer Weather
Figure 11.6
The semi-permanent Pacific high blocks moist
maritime winds and rain from the California
coast, while the Bermuda high pushes moist
tropical air and humidity over the eastern states.
9
Coastal Winter Weather
During winter months, the Pacific high migrates
southward and allows for maritime winds with
moisture and rains to reach California. On the
east coast, precipitation is rather even
throughout the year.
Figure 11.7
10
January Winds Aloft
Land-sea temperature differences trigger ridges
and troughs in the isobaric surface.
Figure 11.8A
11
June Winds Aloft
Horizontal temperature gradients establish
pressure gradients that cause westerly winds in
the mid latitudes.
Figure 11.8B
12
Jet Stream
Figure 11.10
Figure 11.9
High velocity Polar and subtropical jet stream
winds are located in the lower tropopause, and
they oscillate along planetary ridges and troughs.
13
300 mb Winds Jets
300 mb pressure surface maps illustrate lines of
equal wind speed (isotachs) as the jets
meander. Jet streaks are the maximum winds,
exceeding 100 knots.
Figure 11.11
14
Simulation of Clear Turbulence
Figure 11.12
Clear turbulence is created by steep gradients of
changing wind speed near the jet, called shearing
winds, which generate fast flowing particles in
this simulation.
15
Polar Jet Formation
Steep gradients of temperature change at the
Polar front trigger steep pressure gradients,
which then forces higher velocity geostrophic
winds. This is the trigger for jet stream flow.
Figure 11.13A
16
Winds Angular Momentum
Angular momentum is the product of mass,
velocity, and the radius of curvature and it must
be conserved. As northward-flowing air
experiences a smaller radius, it increases in
velocity and augments the jet stream flow.
Figure 11.14
17
Surface Ocean Currents
Surface winds cause ocean water drift, a piling
up, and creation of pressure differences that
generates ocean circulation. Major ocean
currents are categorized as warm or cold, and
help to redistribute heat.
Figure 11.15
18
Gulf Stream Warmth
Color enhanced imagery shows an oceanic front at
the edge of the warm Gulf Stream current, where
eddies redistribute heat into cooler waters.
Figure 11.16
19
Cold Water Upwelling
Maps of west coast sea surface temperature
indicate regions of significantly cooler water
that has up welled from below.
Figure 11.17
20
Eckman Spiral Upwelling
Figure 11.19
Figure 11.18
The Coriolis force directs surface water to the
right of southward blowing winds along
California's coast. This creates an Eckman
spiral of ocean transport which removes water
from the coast, and is then replaced by the
upwelling of deeper water.
21
Ocean Oscillations
Figure 11.20A
In the southern Pacific Ocean, high pressure in
the east pushes surface winds, and waters, toward
the low in the west. This Walker Circulation
becomes disrupted during El Nino events, which
impacts upwelling and rains.
22
El Nino Kelvin Wave
Figure 11.21
Satellite imagery shows the eastward movement of
higher ocean levels, or Kelvin wave, in white and
red colors, caused by the reversal of the Walker
Circulation and El Nino event.
23
El Nino Ocean Temperature
Satellite data of sea surface temperature (SST)
illustrate the difference between a non-El Nino
year, with cool easterly waters, and the warmer
SST El Nino year.
Figure 11.22A
24
ENSO Index
Figure 11.23
El Nino Southern Oscillation (ENSO) intensity has
been tracked using 6 parameters, including air
and sea temperature, sea level pressure, wind
speed and direction, and cloudiness. A graph of
the ENSO index shows eastern Pacific warm El Nino
and cool La Nina years.
25
US El Nino Impacts
Figure 11.24A
US Winter weather is impacted by El Nino La
Nina events. During El Nino, a persistent trough
of low pressure in the north Pacific steers wet
weather in the southern US, while La Nina brings
a blocking high south of Alaska that pushes the
cold weather of the Polar jet into the western
states.
26
Global El Nino Impacts
The El Nino Southern Oscillation (ENSO) is part
of a planetary ocean-atmosphere interaction, and
can take several years to run its course. ENSO
causes abnormalities around the globe.
Figure 11.25
27
Pacific Decadal Oscillation
Figure 11.26A
28
Scientists recently discovered a 20 to 30 year
sea surface temperature (SST) reversal in a more
northern section of the Pacific. During the
warm, positive, phase, SSTs are warmer off the
Pacific Northwest coast, which strengthens the
Aleutian low and generates warmer
winters. During a cool phase, Pacific Northwest
coastal SSTs are cooler, causing colder winters.