Transcript ESCI 106 – Weather and Climate Lecture 1

Thanks to Martha Remos
QUIZ RESULTS – Overal Scores
QUIZ RESULTS – Individual Questions
ESCI 106 – Weather and Climate
Lecture 3
9-1-2011
Jennifer D. Small 
Weather Fact of the Day: September 1
 2008: A flash flood engulfed 4 hikers as they
were trekking along the banks of River PrietoRiver Blanco NW of Naguabo, PR.
 Two escaped the flood surge, but two were
swept away to their deaths
 ~1.5 in of rain had fallen on parts of the El
Yunque National Forest.
National Watches and Warnings
Temperature (from Chapter 2)
 Temperature is a
quantity that describes
how warm or cold an
object is.
 It can also be
described as:
 a measure of the
average kinetic energy
of the atoms or
molecules in a
substance
Temperature (from Chapter 2)
Temperature video from
online..
http://www.atmosedu.co
m/meteor/Animations/Te
mperatureMolecular.mov
Air Temperature –why it’s important
 It’s the first thing we
usually think about
when we talk about
“weather”
 Temperatures vary on
different time scales
Seasonally, daily and even
hourly
 Temperatures vary all
over the globe, by
quite a bit.
Isotherms
 We use Isotherms the distribution of temperature
over a large area.
They are lines that connect points on a map that have the
same temperature
Isotherms – Why do we care??
 Isotherms make it easier to read and analyze weather
maps
 By looking at patterns of temperature (and pressure) you
can determine weather conditions in the next few days.
Isotherm a Simplified Example
Let’s do an example together!
Air Temperature
 Daily mean temperature
Average of 24 hourly readings
Adding maximum and minimum
and dividing by two.
Example
Maximum Temperature: 96
Minimum Temperature: 42
Daily Mean Temperature: (96 + 42)/2 = 69
Air Temperature
Daily Temperature Range
The difference between the maximum and
minimum daily temperatures
Example
Maximum Temperature: 96
Minimum Temperature: 42
Daily Temperature Range: (96 - 42) = 54
February Daily
Mean Temperatures
Air Temperature
 Monthly mean
temperature
Adding together the
daily means for each
day of a month and
then dividing by the
number of days in that
month
Feb 1: 32
Feb 15: 40
Feb 2: 31
Feb 16: 42
Feb 3: 33
Feb 17: 45
Feb 4: 32
Feb 18: 47
Feb 5: 35
Feb 19: 47
Feb 6: 37
Feb 20: 52
Feb 7: 39
Feb 21: 51
Feb 8: 42
Feb 22: 53
Feb 9: 40
Feb 23: 55
Feb 10: 39
Feb 24: 58
Feb 11: 37
Feb 25: 54
Feb 12: 40
Feb 26: 53
Feb 13: 41
Feb 27: 52
Feb 14: 39
Feb 28: 50
 Example
Sum of Daily Means: 1216
Number of Days: 28
Monthly Temperature Mean: (1216/28) = 43.4
Air Temperature
 Annual Mean Temperature
Adding together the monthly
means and dividing by 12
Annual Means
January: 49
February: 47
March: 52
 Example
April: 60
May: 69
June: 75
July: 80
Sum of Monthly Means: 766
Number of Months: 12
August:: 83
September: 76
October: 65
November: 58
December 52
Annual Mean Temperature: (776/12) = 63.8
Air Temperature
 Annual Temperature
Range
The difference between the
warmest and coldest
monthly mean temperatures
 Example
Warmest Monthly Mean Temperature: 95
Coldest Monthly Mean Temperature: 25
Annual Temperature Range: (95 - 42) = 70
What controls air temperature?

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Differential Heating of land and water
Ocean Currents
Altitude
Geographic Position
Cloud cover and albedo
Land and Ocean – Differential Heating
 Different surfaces absorb, emit and reflect
different amounts of energy.
This causes variations in air above each
surface
Land and Ocean – Differential Heating
 In general: Land
HEATS more rapidly
and to HIGHER
temperatures than
Water.
 In general: Land
COOLS more rapidly
and to LOWER
temperatures than
Water.
Land and Ocean – Differential Heating
 Variations over Land
are GREATER than
variations over the
Ocean!!!
The land surface has
more variety….
 Trees
 Streets
 Buildings
 Fields
 Houses….
Ocean – Why is it more variable?
 Surface temperature of water rises and falls slower
than land
 Water is highly mobile and mixes easily (think mixing
red and blue dye… turns purple)
 Daily changes are about 6 meters deep
 Yearly ocean and deep lakes experience variations
through a layer between 200-660 m thick!
Land – Why is this the case?
 Heat does not penetrate deeply into soil or
rock; it remains near the surface.
 Rocks are not fluid… so no mixing
 Daily temperature changes are seen only 10
cm down
 Yearly temperature changes reach only 15
meters or less
Land and Ocean – Summer vs. Winter
 During summer a thick layer of water is
heated while only a thin layer of land is
heated.
 During winter the shallow layer of rock cools
rapidly while the deeply heated water takes
a longer time to cool.
 as surface water cools it becomes heavier and
sinks, replaced with warmer less dense water
from below….
 This means the surface temperture of water doesn’t
appear to change much
Land and Ocean – opaque vs. transparent
 Because land
surfaces are opaque
heat is absorbed
only at the surface
 Water is transparent
and lets energy from
the sun penetrate to
a depth of several
meters
Land and Ocean – Specific Heat
 The specific heat (the amount of heat needed
to raise the temperature of 1 gram of water by 1
degree Celsius) is greater (~3 times) for ocean
than land.
The OCEANS require
MORE heat to raise its
temperature the same
amount as an equal
quantity (grams) of land.
Land and Ocean – Evaporation
 Evaporation is
greater from Oceans
than from Land
There’s more water
molecules 
Energy is required to
evaporate water
When energy is used
to evaporate water it is
not available for
heating.
WATER WARMS
MORE SLOWLY
THAN LAND!!
Class Question??
 Which Hemisphere (north or south) has larger
temperature variations?
The Northern Hemisphere has greater variations
in temperature than the Southern Hemisphere
 Why??
There is more ocean than in the Southern
Hemisphere. There is little land to interrupt the
oceanic and atmospheric circulation. Thus, the SH
has smaller variations in temperature.
Ocean Currents
 Ocean currents are caused by
wind (interactions between the
atmosphere and ocean).
 Energy passes from the
atmosphere to the ocean via
friction.
The DRAG exerted be the wind
causes it to move
Ocean Currents
 The transfer of heat by winds and ocean currents
equalizes latitudinal energy imbalances
Ocean Currents – Poleward Currents
Have a MODERATING effect !!
 Warm water from the
tropics travels up the
coast via the Gulf
Stream
 It becomes the North
Atlantic Drift and helps
keep English and Irish
weather mild.
GULF STREAM!
Ocean Currents – Cold Currents
Have a COOLING effect !!
 Predominately
influence the tropics
during summer months
 Happen in regions of
costal upwelling
 Associated with cool
summers and fog
CALIFORNIA CURRENT
Altitude
 Atmospheric Lapse Rate: 6.5 C per km
 Cooler temperatures at greater heights
Altitude
However, additional heating of the LAND
(e.g. Mountain) causes the temperature to
be WARMER than predicted by the lapse
rate
 Absorbtion and
reradiation of solar
energy by the ground
surface keep places
like Quito, Ecuador
warmer than expected
Altitude
Again, atmospheric pressure and density
decreases too so it absorbs and reflect
less solar radiation.
Geographic Position
 Leeward: prevailing
winds blow TOWARDS
the Ocean
 Windward: prevailing
winds blow From the
Ocean to the SHORE
Lacks Ocean Influence, More like
Land Temperatures
Moderated by the Ocean air, cool
summers-mild winters
MORE VARIABLE TEMPERATURES
LESS VARIABLE TEMPERATURES
Cloud Cover and Albedo
 Clouds cool during
the day
High ALBEDO
Lower Maximum
 Clouds warm at night
Trap OUTGOING
Longwave radiation
 Higher Minimum
WORLD DISTRIBUTION OF
TEMPERATURES
JANUARY
 Decrease in
Temperature from
Equator to Poles
Warm colors to
Cool colors
JULY
WORLD DISTRIBUTION OF
TEMPERATURES
 Latitudinal Shifting
due to the seasonal
migration of the
Sun.
 “HOT SPOTS”
Differential heating
 Heating is largely a
function of
LATITUDE
JANUARY
JULY
WORLD DISTRIBUTION OF
TEMPERATURES
 The hottest and
coldest places are
over land.
 Warm ocean
currents moving to
the Poles warm the
air.
 Equatorial
bound currents
Help cool the air.
WORLD DISTRIBUTION OF
TEMPERATURES
Equatorial temperatures
do not fluctuate significantly
(there are no seasons).
Middle and higher latitudes
have much stronger seasonal
signals.
-40
25
-10
25
CYCLES of AIR TEMPERAUTRE
 Daily Temperature Variations
Magnitude of Daily Temp Changes Depends on
 Variations in Sun angle (location)
 Windward vs. leeward (location)
 Clouds or no clouds (weather)
 Amount of water vapor (weather)
 Annual Temperature Variations
Months with highest and lowest mean T do not
correspond to periods of max and min radiation
Shows that solar radiation isn’t the only thing governing
surface temperatures,
TEMPERATURE MEASUREMENT
Mechanical thermometers
Electronic thermometers
Instrument shelters
Mechanical Thermometers
Most substances EXPAND and
CONTRACT as a function of
temperature…
 Most thermometers use this principle.
Liquid-in-gas thermometers
Most common in daily use
Maximum Thermometers
Minimum Thermometers
Mechanical Thermometers
Bimetal strip
Consists of two thin strips of metal that
are bonded together and have different
expansion properties causing it to bend
and curl.
Mechanical Thermometers
Thermograph
Uses a bimetal strip
Continuously measures temperature as
the strip bends and flexes.
 Pen records temperature
on special paper.
 Not as accurate as liquid-inglass
Electric Thermometers
Thermistors are present in
electric thermometers
Thermal resistor
As temperature increase so does
the resistance, reducing the current
As temperature decreases, the
resistance decreases allowing
current to increase
Instrument Shelters
Where you take temperature matters
Instrument Shelters are:
White – for high albedo (reduce solar heating)
Ventilated – so it doesn’t get hot like your car
1 meter high – reduce longwave heating
Temperature Scales
Fahrenheit
Celsius
Kelvin
Fahrenheit
 Fahrenheit is the temperature
scale proposed in 1724 by, and
named after, the Dutch-GermanPolish physicist Daniel Gabriel
Fahrenheit
 Based on “Fixed Points” – coldest
temperature he could measure
and assumed human body temp.
 That’s why Freezing is at 32 and
Boiling is a 212.
Celsius
 Invented by Swede Anders
Celsius 28 years after
Fahrenheit (1742)
 Decimal Scale
 0 degrees = Freezing
 100 degrees = Melting
Kelvin
 Also called the “Absolute Scale”
 The Kelvin scale is named after the
Belfast-born engineer and physicist
William Thomson, 1st Baron Kelvin
(1824–1907), who wrote of the need
for an "absolute thermometric
scale".
 Same Spacing as Celsius – 100
divisions between boiling and
melting
 0 K = the temperature at which all
molecular motion is presumed to
cease
Converting between temperature scales
To go from Celsius to Fahrenheit
°F = (1.8 X °C) + 32
To go from Fahrenheit to Celsius
°C = (°F – 32) / 1.8
Converting between temperature scales
To go from Kelvin to Celsius
° C = K - 273.15
To go from Celsius to Kelvin
K = ° C + 273.15
Converting between temperature scales
To go from Kelvin to Fahrenheit
°F = (K - 273.15) * 9/5 + 32
To go from Fahrenheit to Kelvin
K = (°F - 32) * 5/9 + 273.15
APPLICATIONS of TEMP DATA
 Heating Degree-Days
When you turn the heat on
 Cooling Degree-Days
When you turn the AC on
 Growing Degree-Days
When plants can grow
 Temperature and Comfort
How temperature ACTUALLY feels
Heating Degree-Days
 Developed by Engineers in the
early 20th century
 A way to evaluate energy demand
Don’t need the “heat” if it is 65F or
warmer outside
Any degree BELOW 65 counts as a
heating degree-day
e.g. if it’s 50F out….
 That’s 65-50 = 15 heating degree-days
 Total it up for the whole year or
season
HEATING SEASON is defined as July
1st through June 30
Cooling Degree-Days
 Developed by Engineers in the
early 20th century
 A way to evaluate energy demand
for cooling a building
If its above 65 you need the AC on….
Any degree ABOVE 65 counts as a
Cooling degree-day
e.g. if it’s 85F out….
 That’s 85-65 = 20 cooling degree-days
 Total it up for the whole year or
season
COOLING SEASON is defined as
January 1st through December 31st
Growing Degree-Days (GDDs)
Used by farmers to determine the
approximate date to harvest their crops.
SUPER HANDY here in CA
Specific for each CROP
The number of GDDs for a crop on any day is
the difference between the daily mean
temperature and the base temperature of the
crop
Growing Degree-Days (GDDs)
Example:
Sweet Corn Base Temperature = 50 F
Peas Base Temperature = 40 F
If Mean Daily Temperature = 75 F
Sweet Corn GDDs = 75-50 = 25
Peas GDDs = 75-40 = 35
Thus, if 2000 GDDs are needed to mature a crop, you
just keep track of when you reach 2000 GDDs and
then harvest!
Growing Degree-Days (GDDs)
Temperature and Comfort
 How we perceive temperature matters to us
humans. It is affected by:
Relative humidity
Wind
Sunshine
 Heat Index
When it’s humid, evaporation doesn’t work as well and
we “Feel” hotter
 Windchill
Wind makes it “Feel” colder than it actually is
Temperature and Comfort