1.Precipitation Flashcards
define hydrology
‘Hydrology is the science that treats the waters
of the earth, their occurrence, circulation, and
distribution, their chemical and physical
properties, and their reaction with their
environment, including their relation to living
things.’
During cretaceous: saskatoon was a ….
shallow inland sea
Saskatoon is in what river basin
South Saskatchewan River Basin
Describe a Hydrological schematic:
each rectangle is a storage compartment, arrows in between are called fluxes, circular rectangles are outputs
How much of the worlds water in the world is in the ocean ..%
(96.5%) and its saline
__% of fresh water is locked up in icecaps and sheets
70%
__% of fresh water is groundwater
30%
__% of fresh water is in surface, soil, and atmos
1.5
__% of the total water in the world is fresh
2.5
residence time/Water storage in different compartments takes differing ammounts of time dependent on where it is stored
Name Longest and Shortest
Longest:Groundwater-up to 4000 days
Shortest:
- Atmosphere-max 10 days
- Biological water 7 days
Measures of Water Vapour in the air(4)
- • Vapour pressure
- Absolute humidity
- Specific humidity
- Relative humidity
Vapour Pressure
– millibar (mb)
– Partial pressure contributed by water in atmosphere
-pressure from gases, mostly nitrogen, then oxygen(20%)
-each gas exerts a partial pressure contributing to total air pressure
-by looking at partial pressure of water vapour we get vapour pressure
Saskatoon Vapour pressure is about ___ mb
1000
Absolute Humidity
– g of water vapour per m3 of air
– Advantage
• Gives total amount of water present in air mass
• Useful for estimating possible precipitation
– Disadvantage
• Air expands as it rises
• Absolute humidity changes
– Even though all water vapour is still present
Absolute Humidity
– g of water vapour per m3 of air
– Advantage
• Gives total amount of water present in air mass
• Useful for estimating possible precipitation
– Disadvantage
• Air expands as it rises
• Absolute humidity changes
– Even though all water vapour is still present
- If air expand THEN HUMIDITY DECREASES AT IT IS SPREAD OUT OVER A GREATER SURFACE
Specific Humidity
g of water vapour per kg of air
– Advantage
•Does not change when air changes volume
Relative Humidity
– % – Percentage of maximum amount of water vapour the air can hold at certain temperature – RH = (ea / esat) * 100 %
To change relative humidity
• Changing amount of water vapour – Evaporation – Condensation . evaporation (humidifier) . condensation (dehumidifier) -HEATING AIR: RELATIVE HUMIDITY DECREASES -COOLING AIR: RELATIVE HUMIDITY INCREASES -cool to dewpoint At dewpoint: where condensation starts
• Changing temperature – Heating Relative humidity decreases – Cooling Relative humidity increases – Cool to dewpoint: RH = 100 %
Figure 2.1
Figure 2.1: Curve goes up to the right because hot air can HOLD more water
. Curve line is saturation line
.at the curve line is where that amount of air holds its maximum watercontent
Dew Point
how far the temperature has to go down to hit saturation
RH=
Saturation vapour pressure=1.5
Actual vapour pressure=4.25
(1.5/4.25)*100
33%
Why does ice have a different Evaporation vapour pressure?
.Over ice is lower saturated water pressure in comparison to over water
-ice releases less to evaporation then liquid water
Mechanism of Uplift(3)
. Mechanism of Uplift
- Cause precipitation by increasing humidity using uplift
1. Orographic
2. Convectional (Thunderstorm) - Figure 2.3: hot air rising surrounded by cold air like a hot air balloon
3. Cyclonic (Low pressure involved)
Atmospheric Air Pressure from North Pole to South Pole
- Polar High
- Subpolar lows
- Subtropical high
- Equitorial Low
- Subtropical High
- Subpolar Low
- Polar High
.equator heating causes rising motion while drawing in air from the north and south at the surface
-as air hits top of troposhphere it flows into northern and southern Hadley cells
-Subtropical high pressure belts develop from hot air coming from the equator which drive trade winds
Northeast Trades: because of rotation of the earth it rotates towards the southwest
SouthEast tradewinds: rotates towards Northwest
-These two create an equatorial trough(Low pressure system)
Poles: Cool down the atmosphere
-Polar High(cold air) flows out in the form of the polar Easterlies
-Boundary of westerlies and easterlies is POLAR FRONT(low pressure area)
Doldrums: Where Southeast and Northeast stop at the equator and little wind is present
Wind Paterns North Pole to South Pole
- Polar Outbreak/Front Easterlies
- Westerlies(Moving NE)
- Northeast Trade Winds(moving SW)
- Doldrum
- Southeast trades(moving NW)
- Westerlies(moving SE)
- Polar Easterlies(moving W)
global atmospheric circulation pattern from North Pole to South Pole
1.Polar Cell
2.Ferell Cell
3.Hadley Cell
Equator
4.Hadley Cell
5.Ferell Cell
6.Polar Cell
Environmental LapseRate:__degrees per 1000m
12
Rain Shadow
Adiabatic Cooling moving up the mountains causing warm/dry air coming over the leeward side in the form of a rain shadow
Siberian High
In January, it is over eastern Asia with arrows moving towards icelandic low
-does not appear in july
Aleutian Low
off the coast of Japan in January
-does not appear in july
Hawaiian High
off coast of California in January and moves a bit farther north in July
Azores High
remains on the coast of florida
-in january does not send arrows to canada
Figure 6.21
This is how a thunderstorm is formed
-On summer day, an air bubble which is hotter then surroundings rises and cools as it rises but it remains slightly warmer then surrounding air
-higher it goes, the bigger the difference in temp between air bubble and surroundings
-Environmental Lapse Rate(12 degrees/1000 meters) versus Wet adiabatic lapse rate(10 degrees/1000 meters)
-Environmental lapse rate can change dependent on day whereas Wet Adiabatic does not
.Lifting Condensation Level: is the altitude at which dew point occurs, and dew point is where relative humidity becomes 100%
Wet adiabatic lapse rate(__ degrees/1000 meters)
10
T OR F
Environmental lapse rate can change dependent on day whereas Wet Adiabatic does not
T
Lifting Condensation Level
.Lifting Condensation Level: is the altitude at which dew point occurs, and dew point is where relative humidity becomes 100%
For Thunderstorm/Figure 6,21 we need: 3
Warm surface, moist air, and an environmental lapse rate which is greater than the wet adiabatic lapse rate
Seasons affecting Global Circulation:
Seasons affecting Global Circulation:
.Most large terrestrial continents are in the northern hemisphere
-because of that, the pattern is highly messy
-southern hemisphere is much cleaner and easier to understand
.Winter: cools down a lot which creates HIGH pressure zones(ex: Siberian high pressure zone)
-oceans stay relatively warm compared to the continents so they remain a low pressure system (Ex: Aleutian Low)
-Bermuda High and Hawaiian high are subtropical highs in northern hemisphere
Summer:
. Instead of Siberian high you have the Asiatic low and the Hawaiian high and bermuda high which are bigger
In January ITC below equator
In June ITCabove the equator
-In Jan(Winter) its at its southern most position(farthest north over water and farthest south over continents)
-In July(Summer) it is much farther north(farthest north over continents and farthest south over water)
.Zones where Tradewinds come together is called the
ITC
Westerlies and Easterlies reaction
Westerlies are the warm wind and easterlies are cold
- these sheer past each other and create instabilities creating the polar front which bulges north and south
- where we get cyclonic rainfall
Low and High Pressure systems
L(984 hPa)= Rotating counter clockwise and inwards and upwards
-hPa increases away from low
H(1024)= Rotating outwards clockwise sending air outwards at the surface
-hPa decreases away from high as it moves toward lows
1013 hPa: IS STANDARD ________ PRESSURE
-ANYTHING ABOVE IS A HIGH, ANYTHING BELOW IS A LOW
Sea Level
Describe what happens as a cold front hits a warm front
What happens if a warm front hits a cold front
the cold air being denser pushes the warm air up swiftly causing hard precipitation
The warm air being less dense gradually rides up over the cold air while pushing it causing gradual calm preciitation
Describe what happens as a cold front hits a warm front
What happens if a warm front hits a cold front
the cold air being denser pushes the warm air up swiftly causing hard precipitation
The warm air being less dense gradually rides up over the cold air while pushing it causing gradual calm preciitation
.Cold Air is dense (balloon is freezer will shrink)
.as cold air moves underneath warm air a small area of hard precip occurs
.as warm air pushes away cold air it just slides over it and drags it along because it cant lift it off the ground
-uplift of warm air is gentle to the precip is more spread out and light
Figure 7.5
Highest precipitable water vapour is found between 30 N and 30 S
figure 3.23
Antarctica interferes with evaporation whereas the norther pole has a lot of open water
.Evaporation dip occurs at equator because the air is already humid at the equator
.subtropical highs has downward motion with adiabatic heating(temp goes up and humidity goes down) which results in very little moisture and evaporation increases compared to the equator
1 meter of snow will end up as ___cm of water
10
Precipitation over oceans vs. continents
Oceans:
- high precipitation at the equators
- low precipitation at the subtropics(deserts)
- 50 degrees(midlats) are at polar front, wave cyclones
- decrease towards the poles, no strong mechanisms(wave cyclones) to force water out of the atmos
Continents: less precip in toatality as water source from the ocean has already dumped before getting there
.same patterns as ocean except polar front is less highly expressed
-because wave cyclones originated over the ocean
.less landform/continents in southern hemisphere means that there is still high precip
Global Precipitation Regime 7
Global Precipitation regions: 7
.Big areas
1.Wet equatorial belt
- Trade Winds Coasts
- areas where the southeast or northeast winds it the coast
- wind moves over the ocean and gathers large amounts of water and continental uplift causes lots of precip - Tropical Desert(ex:sahara, ex: Northern Africa)
- subtropical high - Mid Lat deserts and steppes(grassland like sask)
- core areas of N.A and Asia
- dry because of continental effect, rain shadow, and westerlies
- mostly found in N.hemisphere because of more large continents - Humid Subtropical region
- dominant air movement is westerlies but the highs like the azores send humid air to the coasts
- reason for hurricanes coming in
- N.A east coast is perfect ex - Mid Lat West Coasts(ex: west coast Vancouver island)
- westerlies flow over ocean and carries water to west coast, Ireland and scotland the same
- southwest African coast is a desert and does not get this treatment because it is just a bit to far north to receive the westlies - Arctic Polar Deserts
- As dry and sahara desert
- little water vapour in atmos and no mechanisms to get water out of it
SASKATOON GETS ABOUT __ CM OF PRECIP A YEAR
30
Canadian Precipitation Regions 6
Precipitation regions of Canada:6
- Pacific Region
- Wet western zone: 325cm
- westerlies bring wet air
- combo of frontal, cyclonic, and orographic - Cordilleran Region
- interior valleys and mountain ridges
- sometimes get continental dry air from N and S that compliments westerlies - Prairie Region: 30 cm
- Area east of rockies
- rain shadow is very pronounced
- convection rainfall is significant portion because of high surface temps - Great Lakes-St.Lawrence region
- local moisture sources cause higher evaporation and high precip on eastside
- bermuda high effects this region and brings in wet air from the south - Atlantic Region is wet but not as wet as pacific: 150 cm
- dominated by Bermuda high and westerlies
- westerlies make location still continental despite maritime location, explaining why it doesn’t get as much rain as west cost - North is dry: 10cm
- Arctic region: way further north and not much energy
- Boreal Region: farther south and high prevalence of energy causing thunderstorms
3 Main Steps to Precipitaiton measurement
– Collect rainfall over a certain area
– Measure volume
– Calculate rainfall depth
– depth = volume / area
Depth = _____/_____
volume/area
3 types of recording rain gages
a-measures weight
b-measures depth of float
c-tipping bucket(standard one)
Resolution
.Resolution=the depth that the bucket can hold before tipping
-at high rainfall intensities its better to have a larger resolution
Ground Catch
.ground catch: true value fallen on ground
.gauge catch: what you get in gauge
-in a perfect world these would be the same, yet windspeed affects gauges accuracy
Canadian Nipher shielded rain gage is the best option because
.nipher shield gives air somewhere to go instead of deflecting up over rain gauges
-best option
Three main types of wind reducing shields for rain gages
- Nipher type shields
2. hinged altertype shields
Newest form of rcapturing rainfall
.RADAR: radiowaves bounce off rainfall and reflect back at antenna
.radisson,SK has a weather radar
Occurence of Snowfall dependent on:
Depends on factors such as latitude, altitude, and distance from water bodies
– Latitude and altitude • Control the temperature regime – Proximity to major water bodies • Affects atmospheric moisture supply – Uplift and cooling • Mountain ranges or fronts
Sublimation affecting snow depth
Sublimation: when ice crystals turn to watervapour which compacts snowfall, hence smaller snow depth
Density of snow varies between ___ and ___ kg m-3
50-120
density of rain fall is ___ kg m-3
1 gram per cubic cm or 1000 kg per cubic meter: DENSITY OF RAINFALL
Three most important physical aspects of snow
depth, density, and snow water equivalent
SWE equation is…
SWE = ds*ρs /ρw
– ds is snow depth (m) – ρs is density of snow (kg m-3) – ρw is density of water (kg m-3)
Following deposition, the density of snow ranges from ___to __ kg/m3
200 to 350
SWE can be defined as
ammount of water contained in the snowpack
To find the snow-water equivalent take SNOW DEPTH AND DIVIDE BY ___ FOR WATER
10
Measurement of Snow(3)
- Snow Ruler or graduated rod
- Sonar Device
3.Snow Gage
– Specialized gauge • Antifreeze melts snow and mass or volume is measured
T OR F
rain is more susceptible to wind disturbance than snow as its density is lower and allows it to move more easily
F
snow has a lower density which allows it to be moved easier
Measurement of Snow Density
Snow tubes is the STANDARD way, taking a core of snow
Measurements of SWE
- snow pillow filled with antifreeze measures density which fall atop of it
- flat sheet metal boxes go on top
2.Using snow tube with core of snow, requires melting or weighing
1 KG OF SNOW= 1 KG OF WATER
-we weigh snow instead of melting it because of easy conversion and use in the field
T OR F
1 KG OF SNOW= 1 KG OF WATER
T
Accuracy of Precipitation data is affected by:
- orifice size(funnel size)/heaight/wind shielding-really narrow is more effected by wind
- orientation- if rain comes in at an angle, its may not translate perfectly a measurement
- if trees or other obstructions are within the 90 degrees above it
- occult precipitation from low hanging clouds, will not register on rain gauges but is important
a ____ gage is used to capture occult precipitation
-harp gage with vertical Teflon covered wire to capture occult, you set it up perpendicular to the wind direction
When setting a precipitation gage a __ degree angle coming from the point of the intrument straight up should be clear of any obstructiions
90
Raingauge network is used to gain data on _____ rainfall
areal
Law of diminishing returns
- first rain gauge would have a lot of info, second gauge will add a lot but not as much as the first, third will add a bit but not as much as the second
- each rain gage makes info MORE accurate but the more you add, the less new information they give
Global precipitation gage placement followed _____
colonization from the monarchy’s
Areal Estimates
1.Arithmetic Mean: If all of the values are given the same weight, regular average
- Thiessen Polygons:(any shape that can be drawn in straight line segments ex:triangles) allow you to find the center of areas between gauges
- not all polygons will have the same area, weights are dependent on the size of the polygons
3.Surface Fitting:Isohyet lines: lines of equal rainfall
.Areas with low rainfall are displayed as lowlying while high rainfall in an area is presented by high lying
Interpolation
Interpolation is a procedure used to predict the values of cells at locations that lack sampled points.
Rules of Thumb for rainfall
- High intensity rainfall
- Low intensity rainfall
- Large amounts of rainfall
- Small amounts of rainfall
- High intensity rainfall – Short duration – Low frequency of occurrence
- Low intensity rainfall – Long duration – High frequency of occurrence
- Large amounts of rainfall – Low frequency of occurrence
- Small amounts of rainfall – High frequency of occurrenc
Return Period
probability that an event occurs
If an event has a probability of occuring once within a year of 1% the it is __/__
1/100
-this has a return period of every 100 years
a return period of 1/5 means __% chance of it occuring once this year
20%
-return period of 5 years
5 Temporal and Spatial Analysis
- Mean and standard deviation
- Depth-duration-frequency
- Intensity-duration-frequency
- Probable Maximum Precipitation (PMP)
- Areal coverage
Depth Duration Frequency
Depth=precipitation,duration=length of time period
. frequency= sort in order of decreasing magnitude (rank them)
-then find exceedance probability, ranking% divided by #ofobservations
-ex: 1/24=0.04
-96% of values are lower then this one
.make graph of x-axis(probability)=exceedance prob, y axis(log)= depth
-using logarithmic axis so that it wont be hugeeeee
-probability axis is symmetrical around 50% and stretches as you get farther away, never show 0 or 100
.longer period of time should be above shorter periods of time
.right side of graph is high occurrence, left is low occurrence
.this graph gives you a comparison between periods
- can then put into a graph with an x axis of duration(h) and y axis of depth
- also you can do a y-axis of intensityand x axis of duration
Probable Maximum Precipitation
ProbableMaximum Flood
Theoretically the greatest depth of precipitation for a given duration that is physically possible over a given size storm area at a particular geographical location at a certain time of year
– Largest flood that could occur from a given drainage basin
Figure 2.8
Why is there such high rates of hourly rain in the summer time in New Hamshire?
Figure 2.8: In July thunderstorms are created by surface heating and convection
In December there is not enough surface heating so no thunderstorms occur
secular means..
longterm
What are the limiting factorsof tree ring growth?
Water and Temperature
- .You can translate tree ring size/growth into predicitons for annual precipitation or temperature dependent on location
- even dead trees like those used in log cabins can be used
- overlap times series of older trees(like log cabin), dead trees, and live trees
Dominating factor in praries is..
Dominating factor in Mountains is…
WATER
Temperature
