Shared Flashcard Set


Wind Science
Wind Science
Undergraduate 3

Additional Geography Flashcards




Prairie Drylands and wind

Low moisture + High wind trasnport potential = landscape highly susceptible to aeolian processes


*Canada has two dryland regions (Okanagan and Palliser). The larger area in the prairie ecozone occurpies 46.7 million ha, including 60% of canada's cropland and 80% of it's rangeland.

Surface cover (vegetation) and Wind

Generally limits entrainment of soil and snow by wind- but disturbed surfaces and various land use activities increase the susceptibility to aeolian transport.


Offers :

1)Cover and protection

2)Momentum extraction (z0) from air

3)Trapping of soil particles

Drylands and Wind Erosion- So What?

Mainly an issue of land surface cover sensitivity

-Dryland climates are typically associated with thin or patchy (creosote) vegetation cover

-These vegetation types are more easily disturbed/removed than forested areas. Thus, drylands have increased potential for direct exposure of sediment to wind = higher susceptibility to wind erosion


-Vegetation cover is also more susceptible to natural and anthropogenic disturbances (fire, over-grazing, drought)

-Soils are relatively dry and more readily entrained when exposed

Why is it so windy in Lethbridge and far less so in Calgary?

1.Lower regional surface roughness


2.Higher proportion of storm tracks, particularly AB clippers


3.Higher proportion chinooks


4.Orographic characteristics.. more abrupt mtn/prairie transition in S.AB (leads to well-formed downslope flows)


5.Preferrential occurrence of lee trough development and cyclogenesis


6.High winds in summer largely depend on convective activity


**there is a gap in the rockies around mid AB/BC where the mountains are not as tall (to west of leth, they are 3000-3500m)

-on the mesoscale, cyclones appear to form preferentially to the lee of the highest topography (S. Rockies)

-Most lee cyclones can be traced to an upstream precursor over the Pacific Ocean

-A major lee trough develops, driving srong westerly surface winds


Windiest area is just to the west of lethbridge.. egg shape


What is the broader relevance of wind?

Biological dispersal (pollen, seeds, birds)

Surface energy transfers – evaporation

Climate – fronts, chinooks, clippers, etc

Pollution transport – emissions modeling & monitoring

Erosion – agricultural soil loss (not replaced as fast as lost

Energy – multi-billion dollar industry

Aerodynamics – urban design

Health – particulate matter, pollution, chinooks)

Genetic Drift – Monsanto vs. Schmeiser

Transportation – snow, wind shear

Hydrology – snow translocation, resource heterogeneity

Hazards – blow downs, derechos

Infrastructure – wind loads

Surface Energy Balance - Evaporation

Dalton (1802) established a law which expresses the evaporation rate from a water surface , depending on the air saturation deficit (esat - eair) and on the wind speed (u). This law has the following expression:


Evap = f(u) (esat - eair)



(esat - eair) = the saturation vapr deficit (esat is the saturated vapor pressure in mb and eair is the vapor pressure of air in mb)


f(u) is an empirical wind function in units of mm/hr/mb:


f(u) = 0.0169(u)0.4998


where u is the wind speed in m/s



Canada soil degredation
Canada is one of the few countries that has made an estimate of income foregone due to soil degradation. For the prairie provinces, that figure is about one billion annually. Wind erosion is the costliest

In 1977 an estimated 209 million hectares in the 10 Great Plains states were eroded by wind with an average loss of 11.9 t/ha. 61 percent occurs on cropland, 38 percent on rangeland. Losses vary from 2.9 to 33.4 t/ha.

One-fifth to 1/3 of the worlds cropland is losing topsoil at a rate that is undermining long term productivity. The inherent productivity of 34 percent of U.S. cropland is falling because of loss of topsoil


gas flaring
removal of unwanted byproducts associated with oil/gas extraction and refining
Gaussian Plume

Concentrations vary with distance from stack, and horizontal and vertical dimensions of the plume


-affected by wind speed, heigh of stack, presence of inversion, etc.


What is the effect of varying Wind Speed on ground level pollution downwind of a stack??

-The main effect of increasing WS is that the effective stack heigh lowers and ground level concentration is higher near the stack (effective height is height of plume)

Building design and snow build-up

Interesting building aerodynamics exist

-bubble of low wind speed forms on wind-side of building

-highest speeds on top and around wind-side of building

-slowest speeds behind building


Can design wind deflector to limit snow buildup and entrance


Hinkel and Hurd- Permafrost Destabilization and Thermokarst following snow fence installation

*Ground warming caused by thick winter snow cover!!


Wind Forecasts

Western N.Am and NW USA:

North America, Europe and elsewhere:

The Weather Office (Environment Canada):


pressure: force per unit area


atmospheric pressure: the force per unit area exerted against a surface by the weight of air above that surface


-in most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point

-low pressure areas have less atmospheric mass above their location, whereas high pressure areas have more atmospheric mass above their location

-Similarly, as elevation increases there is less overlying atmospheric mass, so that pressure decreases with increasing elevation.


**atm pressure decreases exponentially with altitude

Recording of Pressure

**Spatial variations in ATM presure drive wind!!


-Recording stations are reduced to sea level pressure equivalents so we can compare pressures on a constant elevation surface

-mean sea level pressure = 1013.2mb

SLP (sea level pressure) = surface pressure corrected for elevation (gives equivalent pressure if you moved parcel of air down to sea level). Allows us to compare pressure everywhere. Need to correct measured pressure using temp and elevation

Vertical Pressure Gradients

Average vertical pressure gradients are usually greater than even extreme examples of horizontal pressure gradients as pressure always decreases with altitude


At sea level, p=1000mb

at 10km p=300mb


Therefore, gradient = (1000-300)/10km



VPG about 6000 times more than HPG in this example



Answer: hydrostatic equilibrium

-the downward force of gravity is balanced by a strong vertical pressure gradient (VPG)-- creates hydrostatic equilibrium (exception is convective storms... up and down drafts)

Laws of Horizontal Motion:

Four major controls on horizontal movement of air near the Earth's surface:


1.Pressure gradient force (PGF)

2.Coriolis force

3.Centripetal Acceleration

4.Frictional Forces


Primary cause of wind (mass transfer) is pressure gradient.


pressure gradient force


-the PGF initiates movement of atmospheric mass, wind, away from areas of high pressure to areas of lower pressure

-horizontal wind pseeds are a function of the strength of the pressure gradient


-pressure differences exist due to unequal heating of earth's surface!!

-spacing b/w isobars indicates intensity of gradient

-flow is perpendicular to isobars

Coriolis force

Once air has been set in motion by PGF, it is defectd rom its path. This apparent deflection is called the Coriolis force and is a result of the earth's rotation.


The magnitude of deflection is proportional to latitude --- the effect is thus maximum at poles and decreases towards the equator.


Te Coriolis Force always acts at right angle to wind - to the right in N. Hem and the left in S. Hem

Geostrophic Wind

Is the balance of PGF and coriolis.


Observations of upper winds (those far enough from the effects of surface friction) show that wind blows more-or-less orthogonal to PGF.


Upper level ATM wind blowing parallel to isobars is known as the geostrophic. This condition, however, is only present where isobars are straight and evenly spaced.


In most cases isobars are curved, particularly owing to ridges and troughs that dominate the upper ATM in the N.Hem and due to High and Low pressure centres.


This changes the geostrophic winds s that they are no longer geostrophic but are instead in gradient wind balance. They still blow parallel to the isobars, but are no longer balanced by only the pressure gradient and Coriolis forces, and do not have the same velocity as geostrophic winds.

Gradient Wind

-centripetal acceleration


When isobars are curved, there is a third force, the centrifugal force. This apparent force, pushes objects away from the center of a circle.


In the case of a low pressure system or trough, the gradient wind blows parallel to the isobars at a less than geostrophic (subgeostrophic) speed


In a high pressure system or ridge, the gradient wind blows parallel to the isobars faster than geostrophic (supergeostrophic) speed.

Wind @ Surface

Geostrophic wind blows parallel to the isobars because the Coriolis Forces and PGF are in balance. However it should be realized that the actual wind is not always geostrophic, especially near the surface.


Close to the surface (within 500m) a variety of elements slow and deflect wind.


Ekman spiral


*increasing friction deflects wind towards the PGF (low pressure area). Reduces effect of coriolis force.

Planetary Boundary Layer



Below this frictional effects are important.

However, above the level of surface frictional effects the wind speed increases and becomes more or less geostrophic. When vorticity occurs due to ridging and troughing, the wind is more or less gradient (subgeostrophic or supergeostrophic)


Primary cause of wind is PGF, all other controls are modifying factors

Variations of pressure and wind velocity with height

Pressure cells (highs and lows) can exhibit different characteristics in the vertical according tothe surface temperature of the cell.


When surface is relatively cold, usually low pressure aloft, and either high or low at the ground. Common in winter.

cold cyclone: low aloft, low ground. Cold core intensifies aloft.

cold anticyclone: low aloft, high at ground. Leads to downward contraction of pressure aloft.


When surface is relatively warm, usually high pressure aloft, with low or high at ground. Common in summer.

warm cyclone: high aloft, low at ground. Weakens aloft and may be replaced by H-pressure.

warm anticyclone: High above, high below. Causes pressure surfaces to bulge upward.


**isobaric surface is depressed where cold air occurs near surface

*isobaric surface is raised where warm air occurs near surface

Cyclones, Anticyclones, Troughs, and Ridges

High pressure areas (anticyclones) - clockwise airflow in the Northern Hem (opposite in South)

-characterized by descending air which warms creating clear skies.


Low prssure areas (cyclones) - counerclockwise airflow in NHem (opposite in S)

-air converges toward low pressure centers, cyclones are characterized by ascending air which cools to form clouds and possibly precipitation.


In the upper atmosphere, ridges correspond to surface anticyclones (high) while troughs correspond to surface cyclones (low)



**Isobars usually not closed off at highest levels (troughs/ridges)

**isobars usually closed off at lowest levels (cyclones, anticyclones)

Upper ATM and 500mb chart


-we often use the spatial distribution of the height of a constant pressure (500mb) to examine upper ATM winds

-upper air pressure gradients are best determined throug the heights of constant pressure due to density considerations

-constant pressure surfaces of cooler air will be lower in altitude than those of warmer air


The 500 mb chart represents weather conditions in the mid- troposphere, at a level where approximately half the mass of the atmosphere lies below this level. This level is at an altitude of approximately 5,500 meters. This level is often used to represent upper level flow conditions because the level is well above the effects of topography and friction and the level is below the region in the upper troposphere where the air flow may experience strong accelerations and decelerations when in the vicinity of the upper jet streams. Since many weather systems tend to follow the wind flow at this level, this level is often considered to symbolize the steering level of these systems.


For a variety of reasons, the change in temperature with latitude is not even, but is instead rather sudden across the boundary between the tropical and polar air. This boundary, between the two contrasting air masses, is known as the Polar Front.

The steep pressure-gradients that occur aloft in association with this major, active air-boundary can result in narrow bands of very strong high-altitude winds. These are known as jet streams or, specifically in association with the Polar Front, the Polar Jet.


The jet is not a static feature:

-It displays marked latitudinally-undulating or longwave (ridge-trough) structurer in N.Hem (land-ocean contrast)

-Strong Longwave patterns are more prevalent in winter than in summer owing to more pronounced latitudinal temperature gradients.

.....hence the stronger winds in S.AB in winter.

Upper (500mb) vs lower (SLP) pressure maps

Why do we discriminate b/w upper/low level pressure?

...because the uper level systems control the major traxks of lower level systems.


In other words: Lower level pressure tells us about winds near the surface - upper levels tell us about the movement of ridges/troughs/fronts responsible for the lower level winds.

Global Driving Forces of Wind

At a fundamental level, global imbalances of heating (radiation) drive pressure variation, and, hence, wind.


Vertical and Horizontal Circulation patterns:

Hadley Regime (cells): heat-driven gobal circulation pattern; drives global wind patterns.


Air moves under pressure gradients, and is modified by the Coriolis Force and friction, so as to rise, move laterally, and fall depending on its density. This circulation pattern is term a cell, or in some instances a convection cell. A non-rotating Earth would, in principle, experience at the surface a warming of air in the low latitudes and a cooling of air near the poles. The higher pole pressures drive the air towards the equator. There the warm air rises and cools, and then is driven poleward. This sets up an upper atmosphere flow towards the poles, where the air, now further cooled, sinks. That air is once again driven near the surface back towards the equator. This produces a single circulation cell,



Equator: Low @ surface; converging/rising air. High aloft; diverging air. Equatorial low (ITCZ) shifts with season.


Subtropical Region: Cool air subsides into subtropics (low aloft). High at surface... diverging air.


Subtropical Surface Highs (anticyclones) migrate north/south according to seasons.


ITCZ draws surface winds that deflect eastward according to coriolis force (trade winds).

Several high pressure centers develop in the subtropical zones (cancer/capricorn).

North/southward divergence of mass @ subtropical high combined with coriolis produces mid-lat westerlies.

Velocity of Air Mass

V = (1/(2wsinop))*(dp/dn)


w= angular velocity


p=air density

dp/dn = pressure gradient

Distribution of pressure on globe

Poles are High pressure


Equator is Low pressure (doldrums)


Horse latitudes are high pressure (convergence at subtropics) (30 degrees)


subpolar low cnvergence at jet stream (60 degrees)


The doldrums are due to a belt of LOW pressure which surrounds the earth in the equatorial zone as a result of the average overheating of the earth in this region. The warm air here rises in a strong convection flow.

Two belts of HIGH pressure and relatively light winds occur symmetrically around the equator at 30oN and 30oS latitude. These are called the subtropical highs.

There are then two more belts of LOW pressure which occur at perhaps 60oS latitude and 60oN latitude, the subpolar lows. In the Southern Hemisphere, this LOW is fairly stable and does not change much from summer to winter. This is expected because of the global encirclement by the southern oceans at these latitudes. In the Northern Hemisphere, however, there are large land masses and strong temperature differences between land and water. These cause the LOWs to reverse and become highs over land in the winter (the Canadian and Siberian highs). At the same time the lows over the oceans, called the Iceland low and the Aleutian low, become especially intense and stormy low pressure areas over the relatively warm North Atlantic and North Pacific Oceans.

The westerlies are well defined over the Southern Hemisphere because of lack of land masses. Wind speeds are quite steady and strong during the year, with an average speed of 8 to 14 m/s. The wind speeds tend to increase with increasing southerly latitude, leading to the descriptive terms roaring forties, furious fifties, and screaming sixties.

Mean Upper Air Patterns

A broad Ridge (H) and Trough (L) structure dominates the Northern Hemisphere

THese longwave patterns in the opper ATM flow are known as the Rossby Waves

The Rossby regime is also a product of Ocean-Land differenecs in the N.Hem, which manifest into a more pronounced surface temperature variatons.

In the S.Hem there is 80% ocean, so variations (longwaves) are less developed and the upper air pressure pattern is more zonal


Pressure patterns during certain periods of the year may be radically different from long-term seasonal averages.

Zonal Index (35-60 deg N)

-Westerlies evolve into long waves with ridge/trough patterns, periodically splitting into discrete cells.

Low wave-like pattern = strong upper winds and a High Zonal Index.

Cellular pattern = low upper winds and Low Zonal Index


A zonal flow over a wide region lessens the likelihood of storm development and is indicative of relatively uniform longitudiunal temperature
Conversely, highly meridional flow reflects the existence of temperature heterogeneity and implies favorable conditions for storms
The upper flow gives us a useful idea of storm motion: storms tend to move along the direction of the 500 mb flow, but at about half the speed.

baroclinic instability

While the Hadley regime is a significant driver of global winds, it is not the only driver (inefficient northward advection of heat)

Cyclone/anticyclone eddying is one important mechanism for northward heat transport (referred to as baroclinic instability)


Baroclinic zone
boundary of two contrasting air masses (also called a frontal zone (front))
Air Masses

Mass of air whose physical properties, expecially temperature, moisture and lapse rate are more or less uniform horizontally for 100s of kilometers

Defining Factors:

1)Source area (from which air mass obtains properties)

2)Direction of movement and changes in properties as it moves over long distances

3)Age of air mass


-air masses interact at fronts (boundaries), which themselves move or dissipate over time


cA (continental arctic) - very cold and dry

cP (cont. polar) - cold and dry

cT (cont trop) - warm and dry

mT (maritime tropical) - warm and moist

mE (maritime equatorial) - very warm, very moist

mP (maritime polar) - cool and moist

Cold Front

The cold air moves rapidly against warm air, creating convergence within the baroclinic zone between the tow air masses.

baroclinic - ATM condition in which isbaric and constant-density surfaces are not parallel


Convergence forces the warm, moist air to ascend along the frontal surface. The deveoping cloud band is inclined rearward with height

The main zone of cloudiness and precipitation is located behind the surface front.

Extent of clouds and rate of precipitation is determined by properties of Warm air mass.


As front emerges, winds shift to northerly or westerly, but most often NWerly in S.AB


Dec19 2004: A strong low pressure system moving across northern alberta pushes a cold front across central and southern regions of the province, marking the leading edge of a cooler airmass moving in from the NW


Typical sequence of events during the passage of a cold front:

Temp goes from warm to sudden cooling to cold and getting colder.


ATM pressure goes from decreasing steadily to leveling off to increasing steadily.


Winds go from south/southeast to variable and gusty to west/northwest.


Precip goes from showers to heavy rain or snow to showers and clearing


Clouds go from cirrostratus to cumulus and cumulonimbus to cumulus

Warm Front

Warm moist air moves against colder dry air.


At the boundary of these two air masses the warm air tends to slide up over the wedge of colder air.


This process causes the frontal cloud band, and the associated precipitation, found mainly in front of the surface front.


The warm air glides up and over the cold air masss. Precipitation is strung out over a much broader area and thick nimbostratus and other stratified cloud types are characteristic.

Typical Sequence of events during the passage of a warm front:

Temp goes from cool to warming suddenly to warmer then leveling


ATM pressure goes from decreasing steadily to leveling off to slight rise followed by a decrease


Winds go from south/SE to variable to S/SW


Precip goes from showers/snow/sleet/drizzle to light drizzle to none


Clouds go from stratuses to clearing

Air masses, frontogenesis and wind

depressions: lows and cyclones


Mid-latitude depressions (cyclones) begin life as a wave or kink in the front dividing cool polar air from the warmer tropical air mass.

As the wave grows the pressure at the centre of the depression drops and the system intensifies and begins to rotate.

The depression migrates from west to east and forms a characteristic comma shaped mass of cloud.

Starting at the centre the cold front starts to catch up with the warm front forming an occluded front



Many mid-continental cyclones track with the jet stream.

SFC winds (around a depression) circulate counter-clockwise in an attempt to overcome pressure gradients.

Identifying a cold front.

Cold fronts are not always identifiable by simply examining the temperature field alone.

-wind speed

-wind direction


Another indication of a possible frontal passage is  a change in the air's relative humidity. The air mass ahead of a cold front is typically more moist than the air mass behind it.

Weather map symbols

Lecture 6 Slide 15.. know this!


Cloud type

Surface wind speed

Surface wind direction

Surface temp

cloud cover

Surface pressure (if leading digit is 7,8,9 place 9 in front. If leading digit is 0,1,2 place a 10 in front)


Pacific cyclone off west coast

Risingand latent heat release (WALR)

Air descends (DALR)


Westerly winds that condense and precipitate their moisture when ascending the Roxkies, and then compressionally warm and dry when descending, are described as chinooks or foehs.


Some distinguishing surface characteristics:

-increased air temp

-decreased relative humidity

-increased wind speed

-increased westerly wind component

*all increase wind erosion

Chinook conditions


1)continental arctic (cA) air mass centered east of Rockies (often a cold-cored High)


2)Maritime Polar (mP) air mass driven eastward by westerlies with enhanced temperature and moisture upon reaching coastal BC


3)Limited interaction/mixing of two contrasting air masses



-coastal low, and 2nd low over Hudson Bay

-high pressure over Idaho

-counter cw circulation around low and clockwise around high support strong westerly fow = substantially accelerated winds over Roxkies, and centripetal acceleration around Idaho High = supergeostrophic



-Arctic front (High @ surface, low aloft) moves east due to eastward migration of BC low around Hudson Bay

-SW-NE gradient admits warm Pacific air from west of Rockies into S.AB

-Chinook will persist until trough (low aloft) off coastal BC  crosses continental divide

-Chinook termination marked by return of northerly winds at surface


Wind trends in Prairies...

-Southern stations show NE resultant

-Northern Stations show SE resultant

Downslope wind wing analogy

Flow accelerates over top of airplane wing in order to keep up with flow along shorter path under wing.


Bernoulli relation indicates pressure must be lower at top of wing.


**Low pressure zone shifts downwind as scale of ridge increases (ie. rocky mountains)

-for 1m hill, low pressure in middle, for 10km (mountains), low pressure on lee side.


Streamlines indicate upward deflection of upper winds on stoss side of Mtn range and downward deflection on lee side

-Surface pressure increases on stoss and decreases on lee side

-surface winds decrease on stoss side and increase on lee side

-Surface pressure and winds recover some distance in the lee of the mtns


*lenticular clouds develop commonly on lee side - representing leewave.


*break in high cloud cover in lee of Rockies is sign of adiabatic compression of descending air


*maritime air slowly penetrates continental arctic air in chinook, with early stages on chinook conditions aloft, and gradually pushing cold airmass away.

Hydraulic Jump analogy

Wind accelerates down lee side of Mtns, initially creating a shooting flow, but then encounters cold dense air on prairies = hydraulic jump


Wind is prevented from moving up due to overlying inversion (like gravity for water)


Lethbridge gets huge #s chinooks... about 50 days per winter.

-gets almost 300 days a year with 50km/h or higher wind

Chinook Recap

Chinooks are favored by lower/upper level trough (Low) off BC coast (moving inland) and presence of High (ridge) over Idaho
Strong westerly flow produces Low or trough @ surface in lee of Rockies
Wind is deflected down lee side of mtns by overlying inversion and by strong pressure gradient (towards Low)
Winds tend to be strongest near foot of mtns and decrease to east (i.e., higher winds at Pincher than Lethbridge; even slower @ Medicine Hat
Analogy to water flow: hydraulic drop down mtn slopes and hydraulic jump where warm air confronts cooler air mass in prairies


Canadian coast and Rocky Mtn ranges lie downstream of Pacific storm track


Cyclolysis common on windward side

Cyclogenesis common to lee


Lee cyclones can usually be traced to a Pacific trough or cyclone

-very high frequency of cyclogenesis in lethbridge area

-on the mesoscale, cyclones appear to form preferentially to the lee of the highest topography

-most lee cyclones can be traced to an upsream prcursor over the Pacific Ocean (Gulf of Alaska)

-Cyclone development or evolution is "masked" by the topography


Composite evolution of AB cyclones


Alberta cyclogenesis is preceded by the landfall of a Pacific cyclone and associated upper-level trough.

-Mesoscale lee trough forms to lee of Rockies in response to increased cross-barrier flow

-Upper level trough begins to move over rockies



Upper-level trough moves over Rockies
Cyclonic vorticity advection (CVA) and downslope flow at surface contribute to low level cyclonic vorticity production. CVA is significant because it creates forced lift in the atmosphere. This forced lift, in the presence of conditions favorable for atmospheric convection, can lead to precipitation
Cyclogenesis occurs east of the Rockies within lee trough
The lee trough develops southward and broadens in scale
Major low center remains over Gulf of Alaska


Upper-level trough and downstream CVA move east of Rockies

Cross-barrier flow weakens

Orography plays a less prominent role in cyclone development

Northern portion of lee trough moves away from mountains while

southern portion remains fixed to topography

Cyclogenesis 6 stages

Stage A

Cross barrier flow associated with Pacific cyclone results in development of a mesoscale lee trough

Stage B

Cyclogenesis occurs as upper-level trough moves over Rockies

Stage C

Cyclone deepens, lee-side baroclinic zone intensifies
Confluence along lee trough between subsided air from Rockies and air from over plains

Stage D

Cyclone and northern portion of lee trough move eastward

Cold advection develops behind lee trough

Arctic front begins to rotate round low center

Stage E

Cold advection overtakes lee trough, forming warm occlusion-like structure

Stage F

Cyclone begins to develop a more classical appearance (in terms of surface thermal structure)

AB clipper


A clipper originates when warm, moist winds from the Pacific Ocean come into contact with the mountains in the provinces of British Columbia and then Alberta. The air travels down the lee side of the mountains, often forming a chinook in Alberta, then develops into a storm over the Canadian prairies when it becomes entangled with the cold air mass that normally occupies the region in winter. The storm then slides southward and gets caught up in the jet stream, sending the storm barreling into central and eastern areas of North America

“… the strongest winds are usually located on the western side of the Alberta clipper in the region between the surface cyclone and the often-intense anticyclone trailing the clipper.


Generally go from NW mostly to E but a little S as well


AB clippers develop in December!

Lethbridge average monthly wind speed

Trends in mean annual wind speed at Lethbridge... Historical decrease of monthly WS by 0.3 m/s (prairie region)


WS anomaly plot

-substract the long-term average for each of the 12 months from the number of records of each month (used to isolate monthly variability)

Climate and wind

Just as with other aspects of climate, wind statistics are subject to natural variability on a wide range of time scales. Decadal and multi-decadal variability in wind speed statistics currently introduce an element of risk into the decision process for citing new wind power generation facilities.


Impacts will affect the stats (max, min, mean, and variance) of all meteorological variables.


While GCM predictions of changes in wind speed are readily available, these results are not commonly reported in the climate change literature as wind speed is oly of secondary importance to most affected ecosystems.

Breslow and Sailor (2002)

-Application of two GCMs to estimate future changes in wind speed, and, hence, wind power (Hadley and Canadian Climate Centre – CCC)
- Vegetation Ecosystem Modeling and Analysis Project (VEMAP) – historical, seasonal, grided (0.5° by 0.5°) wind data – derived from wind resource atlas. VEHMAP is used to compare actual conditions with GCM output
-Constant roughness value over time

Used two focus regions:
R1 - covers all N and S Dakota
R2 - covers the panhandle of Texas, western Oklahoma, and the SW corner of Kansas

-the CCC predicts generally lower wind speeds than suggested by the Hadley model.

The Hadley model shows very little change over entire period of analysis. The CCC model, however, shows a decrease in wind speeds that grows over the period of analysis to 8 or 10% for all seasons except winter, where the decrease is less than 4%.


The results from the Hadley model suggest minimal climate change impact on wind resources, while the results from the Canadian model suggest reductions in mean wind speeds on the order of 10 to 15%.

Considering that wind power generation is a function of the cube of the wind speed, these decreases in wind speed correspond to potential reductions in wind power generation on the order of 30 to 40%.

It is clear from the model output that a large degree of uncertainty remains.

QUESTION: is the uncertainty too much to consider this study as informative and accurate?


Mean wind speed in Lethbridge area is highest in the country... around 20 km/hr

St. George and Wolfe

El Nino stills winter winds across the southern Canadian Prairies

Analysis of long-term terrestrial wind speed (u) records demonstrates that inter-annual variability is a major component of near-surface wind dynamics in the southern Canadian Prairies (SCP). Since the early 1950s, there have been several periods when negative anomalies in regional u persisted for 8 to 13 consecutive months, with anomalies for individual months exceeding -1 m s-1. Calm conditions on the SCP usually coincided with negative u anomalies across much of western Canada, and nearly all low-wind events occurred during a ‘moderate’ or ‘stronger’ El Nino. Wind energy facilities in the SCP have been built during a period of relatively stable wind conditions, and the next El Nino may test their ability to maintain expected energy outputs. El Nino may affect u in other parts of the North American wind corridor and be useful for predicting seasonal or inter-annual changes in regional wind energy production.


The southern Prairies (roughly bounded by 101°W to 114°W and 49°N to 51°N) are one of the windiest parts of Canada, and are the northern limit of the North American wind corridor that begins in Texas and extends northward through the American Great Plains. This region also hosts 12 active wind farms, which have a total installed capacity of 779 megawatts

Goals of study:

Examine inter-annual variability of mean monthly wind speed over the last 5 decades and relate the observations to ENSO


Winds on the southern Prairies are strongest during winter. In spring, winds slacken modestly (by roughly 0.2 m/s) and continue to decline as the region warms, reaching a minimum during mid-summer (July and August). Mean u during the shoulder seasons (spring and autumn) are approximately equal. Over the region, the amplitude of the seasonal cycle in u is roughly 1 m/s.


Mean monthly u decreased significantly at stations in the southern Canadian Prairies between 1953 and 2006. The mean u of the last decade of observations (1997 to 2006) is roughly 0.3 m/s lower than mean of the first decade of observations (1953 to 1962).


Anomaly graph shows strong seasonal signal. Persistent weak winds also occurred in 1982-83 (12 consecutive months of negative anomalies), 1992-93, and 1997-98 (13 consecutive months). Low-wind periods always include very weak winds between December and March


Six years with anomalously weak winter winds: 1969, 1978, 1983, 1993, 1995 and 1998. Anomaly maps show that, during low-wind winters, weak winds are not restricted to the southern Prairies but instead extend across much of western Canada.

The low-wind event during the 1997/98 winter was most exceptional. Weak winds were observed at almost every station on the Prairies. Low mean annual u were also reported for 1998 at five tall-tower sites in Minnesota, suggesting that anomalous u conditions prevailed over a large portion of the North American interior

Winds on the southern Prairies appear to be connected to the positive phase of ENSO. With the exception of the 1968-69 event, all low-wind events identified in the last 50 years occurred during a ‘moderate’ or ‘stronger’ El Niño. Mean u on the southern Prairies is roughly 0.5 m/s slower during El Niño winters than during all other winters

****Not all El Ninos are associated with weak winds across the region

Low-wind winters on the Prairies coincide with anomalously weak winds aloft (250 MB level) across most of southern Canada.

Mean winter (DJFM) scalar wind anomalies at the 250 millibar

level during (a) low-wind winters on the southern Canadian Prairies and (b) El Niño events. Anomalies are relative to 1968 – 1996 climatology.


The strong likelihood of similar events occurring in the future may be viewed as a negative, particularly by the wind energy industry, but the connection to El Niño might also allow their prediction several months in advance.

El Niños may signal an increased risk of low-wind winters affecting the southern Prairies and could lead to u reductions over a large portion of western Canada.

It appears that wind energy facilities in this region have been planned and developed during a period characterized by unusually favorable wind conditions. It is not known if the u decreases associated with these low wind events are large enough to have a major impact on the amount of energy produced from wind farms – effectively, whether they could cause something equivalent to a drought in the wind.

Stilling and wind energy in canada stats/facts



-Wind supplies less than one percetof the country's electricity, but wind energy has increased more than tenfold since 2002 and is projected to produce 12000 MW by 2016


-The 'stilling phenomenon': the observation that near-surface winds have weakened at many locations around the planet during the past 30 to 50 years. Decreases in u have been observed in Australia, China, Europe, and the United States.


In a comprehensive national study of 117 u records, Wan et al. (in press) showed that mean u has declined over most of southern canada since mid-1950s

What other synoptic-scale controls on wind speed in the great plains could account for a trend towards decreasing speed?

1. Equator to pole temperature gradients (north-south pressure gradient)


2. Atmospheric circulation indices [North Atlantic Oscillation (NAO), Pacific North America (PNA), El Nino Southern Oscillation (ENSO)] ???


3. Frequency of cyclogenisis: Evidently, several recent studies have determined that the frequency of Northern Hemisphere mid-latitude cyclones and anticyclones has decreased in the last half of the 1900s (Serreze et al., 1997; Key and Chan,1999; McCabe et al., 2001)


Klink (2007, p.454): The relationship demonstrated here between mean monthly 70-m wind speeds in Minnesota and the large-scale circulation suggests that it is possible to make probabilistic forecasts of the low-frequency variability of above- and below-average wind speed (and thus wind power) from months-ahead forecast models, particularly forecasts of 500-hPa heights.”

Improving soil salinity
Experiments show that you can trap snow in saline areas to reduce salinity
measures wind speed and direction
Wanglor Fork Sensor

-designed for manufacturing asembly lines to recognize defects

-has laser end and photo sensor on other end

-can measure at least 2000 particles passing through per second

-connect it to a data logger


Lethbridge and dust

Our region is NOT semi-arid, it is dry sub-humid


trough = low pressure cell

-slowed down... subgeostrophic


-in summer, most winds associated with convective storms (not chinooks, as jetstream shifts)


-taller mountains means greater trough!!

sand or snow.. kind of ribbons
stokes formula
how fast matter settles out of a fluid

a fungus that is transported by aeolian processes from deserts and contributes to "sea fan disease" of the world's coral reefs

-living microorganisms carried across pacific by dust (Sahara)

-chemical contaminants may also come (also from China).... pesticies, pharmaceuticals, heavy metals (known carcinogens and endocrine disruptors)

CFD and thermokarst definitions

CFD= computational fluid dynamics


thermokarst.. thawing of permafrost

wind barbs/air density at 25C

barbs = little forks on wind map


rowe symbol (p) denotes air density

-is 1.22kg/m2 at 25C


Average sealevel pressure

1000mb (approx)


Gradient wind is parallel to geostrohpic wind, but is either faster or slower!!

Wind uniformity on global level

Altered by water/land

-water has higher specific heat capacity

-differential heating

-also friction... makes slower in north


Kinks in upper atmosphere are manifestation of water/land differential/contrast

-kinks are ridge/troughs

-much more dominant in the Northern Hemisphere


Diagnostics of a chinook:

-air temp

-wind speed

-relative humidity

-air pressure

-inversion is a good ingredient!


*worst chinooks/downslope winds are in Wyoming/Colorado!


**troughing on lee side of mountains could be cyclogenesis or a chinooks (low pressure)


***Compare and contrast cyclone with a chinook

relative high and low pressure

high= more air under 500mb surface

low= less air under 500mb surface

Converting to km/h
mutiply m/s by 3.6 to get km/h
Paper- Hinkel and Hurd

"Permafrost Destabilization and Thermokarst following Snow Fence Installation"


-2.2km/4m snow fence in Alaska

-attracts large drift

-monitored soil temp at 5,30,50cm 6yrs

**soil temperatures beneath drift are 2-14C warmer than control on tundra!!

-snow insulates

-mean soil temperature over 6-yr period has warmed 2-5C, and upper permafrost has thawed

*both direct warming and indirect effects of ponding contribute to thermokarst


-on average, snow went from 10-90cm

-at the end of a 5yr period, active layer was 2.5 times(6.5m) deeper than control


-after 6 yrs, big difference at 30cm, none at 50cm

-increased warming, each year, due to insulation

-even though snow stays into summer, does not counterbalance and keep cool

-pre-existing ponds became larger and deeper



1)a 4m drift forms each year on the lee side of fence, and a 1.5m forms upwind


2)Soil temperatures near top of permafrost range from 2-14 degrees warmer than control in winter


3)drift persists 4-8weeks after snow has melted from the open tundra. This delays onset of soil thaw and limits soil warming in summer.


4)Increased ponding in summer

Canada-Wide Standards for Particulate Matter (PM) and Ozone

PM10 refers to airborne particles 10microns or less diameter

PM2.5 ..2.5 or less

PM10-2.5 refers to those in between


PM2.5 has greatest effect on human health.



A CWS for PM2.5 of 30micrograms/cubic meter, 24 hour average time by 2010.

-achievements to be based on the 98th percentile ambient measurement annually, averaged over 3 years



A CWS of 65ppb, 8 hour averaging time, by 2010

-achievement to be based on the 4th highest measurement annually, averaged over 3 consecutive years

-specific provisions related to transboundary flow of ozone are ....



-develop jurisdictional plan

-implementation of continuous improvement, pollution prevention, and keeping areas clean programs

-establishment and maintenance of the PM and ozone monitoring networks needed to characterize the PM and ozone air quality problms across Canada

Fletcher 1988

"Fohn illness" and human biometeorology in the Chinook area of Canada


Data evaluated to determine if well-being was weather related

Meteorological parameters:

-8 48h weather types






-Expected increase in fohn illness symptoms during the frequent warm chinook and decrease at times of cold non-chinook weather were not present.


However with the cool chinook (temp slightly below freezing) several adverse symptoms were positively correlated with wind velocity.

**No widespread "chinook illness" comparable to the fohn illness was found.


Fohn illness from Europe... intensifies with age/exposure








-circulatory dysfunctions




-surgeons postpone operations


Apparently it requires several years of exposure to the fohn for its adverse influence to be sufficiently strong to be effective or at least recognized.

"confirmedthe fact that fohn sensitivity does not become evident until years after one has moved into the area"



-Air Temperature and change

-Atmospheric Pressure (low pressure 'alerts')

-Air Humidity (dry anyways)

-Wind (people like chinooks)

-Atmospheric ionization (excess of positive ions harmful) (always low though)



-no widespread chinook illness compareabe to the fohn illness was found.

-cool chinooks of any duration were associated with the most symptoms


So why do some people believe that they feel unwell for a day or two before the arrival of the fohn/chinook even though there were no extremes of or rapid changes in the five meteorological parameters surveyed in this paper.

Could short-term pressure fluctuations or atmospherics play a role?

Nkemdirim 1996

"Canada's Chinook Belt"


-latent heat converted to sensible heat

temperature signal: the difference between the highest temperature attained during a chinook event and the daily maximum.

numerical frequency: number of days in the winter with, at least, 1h of chinook wind.


-mean point values of the signal range from 13-25K

-Mean seasonal frequency varies from 43-52 winter days

-the cores for these two statistics do NOT coincide


Highest frequencies occurr in the pass

Strongest signals found further east in Brooks area.

Both show strong decadal functions (80s chinook strong, 70s chinook poor)


The general macroscale patterns required for a chinook are:

1)the establishment of a strong pressure gradient towards the north-east, enabling esterly flow of maritime air into southern AB

2)a surface presure pattern that includes a high pressure system in NW USA and troughs of low pressure in N BC, AB, SK

3)an upper air disturbance in combination with 1) + 2) which promotes the establishment of a strong zonal flow


-on west side, cools at DALR until dewpoint, then cools at around 0.6K/100m

-air gains sensible heat as precipitation removes moisture

-on lee, warms at DALR (1K/100m)


Temp Enhancement Factors:

1)altitude of place determines the amount of adiabatic warming realized

2)position of point relative to chinook wave (those positions that intersect the trough will be warmed)



1)signal is strongest to south and to east

-weakest on rockies

2)The maximum chinook signal does not appear to be correlated with the distribution of heights at the continental divide

3)Average chinook signal peaks in january

4)Leth is in the max zone of "chinook days per year", and just outside of max # of hours/yr zone

5)In terms of frequency, the chinook belt is more homogeneous than thought originally

-the systems that produce chinooks cover large areas

6)SW AB receives the most chinooks



-average chinook signal is 6.5K and maximum is 25.3K

-average 45-52 days/winter (small variation)

-freq/sig show similar decadal variability, both quantitatively and spatially

Piorecky et. al 1997

"Effect of Chinook Winds on the Probability of Migraine Headache Occurrence"


Objective was to determine if Chinook weather conditions in the Calgary area increase the probability of headache attacks in migraine sufferers.

-looked at diaries of 13 migraine patients

-probability of migraine headache onset was greater on days with Chinook weather (17%) than on non-Chinook days (14.7%) (p=0.042). Older patients appeared more weather sensitive than younger patients.

-For patients over the age 50, p=0.007


-in contrast to other studies, targeted those affected by migraines

-increased wind speed, falling barometric pressure, and rising temperature might all play a role

-different patients might have different migraine triggers

Paper - Breslow and Sailor

Vulnerability of Wind Power Resources to Climate Change in the Continental United States


-look at impacts of climate change on wind speeds/power across contnental US

-GCM from CCC and Hadley Center used


-The models were generally consistent in predicting that the US will see reduced wind speeds of 1-3.2% in next 50 years, and 1.4-4.5% over 100


-canadian model predicted larger decreases



-agreed best tool for assessing likely climate response to increasing CO2 levels

-not very good resulution (2-4 degrees latitude)

CCC's GCM1 and UK Hadley Center's GCMII used


VEMAP - Veg Ecosystem modeling + Anal. Proj.

-resolution at 0.5 degrees



According to Wind Energy Resource Atlas, there are seven regions in the contiguous US that have sufficient annual wind power for supporting wind power generation facilities.


Comparison of models and observed:

In R1, GCM1 is similar to historical, and GCMII is lower

In R2, both are lower than historical



-Results from GCMII (Hadley) suggest minimal change

-Results from GCMI (CCC) suggest reductions in wind speeds on the order of 10 to 15% (over 100yrs)

**A large amount of uncertainty remains!!

Paper - St George and Wolfe

El Nino stills winter winds across the southern Canadian Prairies


Since 50s there have been several periods when negative anomalies in regional wind speed persisted for 8 to 13 consecutive months, with anomalies for individual months exceeding -1m/s.

-Nearly all low-wind events occurred during a moderate or stronger El Nino.


-acquired monthly u observations from national db



-reductions in u often uccur during winter

-Next strong El Nino will provide another chance to evaluate the apparent association between winds in western Canada and the ENSO system.

Paper - Chinooks/Foehns - Hugenholtz

Names include foegn, ibe, zonda, berg, nor'wester


env effects: wind erosion, reduced air quality, vegetation mortality, adverse health-related effects


synoptic conditions: surface ridge of high pressure on the windward side, trough of low pressure on lee side


-Pincher reported 25.5C increase in 1 hour


the layer of air influenced by surface friction (planetary boundary layer)


The mixing depth of PBL can increase as:

a)air becomes more unstable (heats)

b)terrain roughens

c)wind speeds increase


-surface obstructions slow surface winds, which due to viscosity creates eddies in a much thicker layer.

-the vertical depth of these eddies and gusting winds thickens with surface wind velocity



Dunes and depressions

Dunes and other landforms project into the boundary layer, altering the streamlines and resulting in secondary flow modifications (lee separation, re-circulation, stoss acceleration, etc.)


Modification of Wind Speed Within a Snall Hollow/Depression

-expansion and deceleration at the entrance, compression and acceleration at the exit

-non-logarithmic profiles indicate complex flow separation

-ends up faster than entry point at 0.3m and slow at 2m


Oblique winds are more effective in eroding and deepening of the hollow. Westerly winds are more effective in evaluating sand owing to flow acceleration

Vegetation interaction with the boundary layer

Wind speeds increase with elevation above earth's frictional surface, where stronger winds sculpt an denude branches of tres


Shelterbelts may protect downwind property, but may also create unwanted turbulent eddies


Vegetation acts as a "living" wind shelter, reducing wind speed appreciably for some distance downwind in the sheltered "wake" region. The effectiveness depends on the porosity, lateral extent, and heigh [H] of veg

**flow recovery is about 25-25 times H


Local Winds Produced by Differential  Surface Heating and Cooling

Changes in air temperature causing warm air to rise and cool air to sink can generate horizontal winds


Rising warm air creates a surface low and upper level high. Sinking cool air creates a surface high and upper level low.


Land heats more quickly than water, creating land-water temperature differences along a coastline.


During the day the land's warm-core thermal low draws a sea breeze, while at night, the warmer sea draws a land breeze

-Table Mountain in Cape Town is a good example



Water is smoother than the land surface, permitting increases in wind velocity. These increased speeds mean 1)a greater Coriolis force and deflection, 2)divergence and sinking of air at the upwind water surface with convergence at the downwind end



Similar to land/sea wind in its diurnal cycle are the valley and mountain winds. Valley winds occur in the day because air along mtn slopes is heated more intensely than air at the same elevation over a valley floor (anabatic winds)

Rapid radiational heat loss in the evening reverses the process to produce a mountain or a down valley wind (katabatic wind).. this is density driven


Montain snow cover creates a thin layer of high pressure cold air that rushes into lower valleys

-Elevated plateaus with snow cover may foster development of a thin layer of high pressure cold air

-Pressure gradient winds are triggered due to lower pressure above the adjacent valley, pushing cold air into the lower valley.

Modification of wind within the PBL

-Vertical profiles of wind speed

-Surface roughess

-Surface roughness change

-Flow over hills - orographic speed-up

-sheltering by obstacles


-height increases exponentially with regards to wind speed (frictional forces most distinct closer to ground)

Prandtl-von Karman equation

Wind speed at heigh z for neutral conditions in surface layer


u(z) = (u*/k)*(ln(z/z0))


u* = friction velocity (velocity scale, surface stress)

k= von Karman constant (0.4)

z= height above ground

z0 = aerodynamic roughness length (height at which wind speed is no longer zero... ie it starts to increase)

-seas and lakes have z0 of around zero


u*^2 times air density = absolute value of [t?]


-how quickly wind speed increases with height (lower value means quicker increase)


-sea/lakes is around zero

-flat land is around 0.03m

-a few hills/a few trees is 0.1m

-0.4m would be many windbreaks separated by a few hundred metres


-snow is around 0.001

-grass around 0.002

-grassland around 0.02m

-trees around 0.4m

-suburban around 2-4m

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