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ESCI 106

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Title: ESCI 106 Weather and Climate Lecture 1 Author: Jenny Last modified by: Jenny Created Date: 8/17/2011 4:20:55 AM Document presentation format – PowerPoint PPT presentation

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Title: ESCI 106


1
Thanks to Martha Remos
2
QUIZ RESULTS Overal Scores
3
QUIZ RESULTS Individual Questions
4
ESCI 106 Weather and Climate Lecture 3
  • 9-1-2011
  • Jennifer D. Small ?

5
Weather Fact of the Day September 1
  • 2008 A flash flood engulfed 4 hikers as they
    were trekking along the banks of River
    Prieto-River 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.

6
National Watches and Warnings
7
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

8
Temperature (from Chapter 2)
  • Temperature video from online..
  • http//www.atmosedu.com/meteor/Animations/Temperat
    ureMolecular.mov

9
Air Temperature why its important
  • Its 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.

10
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

11
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.

12
Isotherm a Simplified Example
13
Lets do an example together!
14
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
15
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
16
Air Temperature
February Daily Mean Temperatures February Daily Mean Temperatures
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
  • 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
  • Example

Sum of Daily Means 1216 Number of Days 28
Monthly Temperature Mean (1216/28) 43.4
17
Air Temperature
  • Annual Mean Temperature
  • Adding together the monthly means and dividing by
    12
  • Example

Annual Means
January 49
February 47
March 52
April 60
May 69
June 75
July 80
August 83
September 76
October 65
November 58
December 52
Sum of Monthly Means 766 Number of Months 12
Annual Mean Temperature (776/12) 63.8
18
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
19
What controls air temperature?
  • Differential Heating of land and water
  • Ocean Currents
  • Altitude
  • Geographic Position
  • Cloud cover and albedo

20
Land and Ocean Differential Heating
  • Different surfaces absorb, emit and reflect
    different amounts of energy.
  • This causes variations in air above each surface

21
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.

22
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.

23
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!

24
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

25
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
    doesnt appear to change much

26
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

27
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.

28
Land and Ocean Evaporation
  • Evaporation is greater from Oceans than from Land
  • Theres 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!!
29
Class Question??
  • Which Hemisphere (north or south) has larger
    temperature variations?
  • Why??

The Northern Hemisphere has greater variations in
temperature than the Southern Hemisphere
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.
30
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

31
Ocean Currents
  • The transfer of heat by winds and ocean currents
    equalizes latitudinal energy imbalances

32
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!
33
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
34
Altitude
  • Atmospheric Lapse Rate 6.5 C per km
  • Cooler temperatures at greater heights

35
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

36
Altitude
  • Again, atmospheric pressure and density decreases
    too so it absorbs and reflect less solar
    radiation.

37
Geographic Position
  • Windward prevailing winds blow From the Ocean
    to the SHORE
  • Leeward prevailing winds blow TOWARDS the Ocean

WIND DIRECTION
WIND DIRECTION
Lacks Ocean Influence, More like Land
Temperatures MORE VARIABLE TEMPERATURES
Moderated by the Ocean air, cool summers-mild
winters LESS VARIABLE TEMPERATURES
38
Cloud Cover and Albedo
  • Clouds cool during the day
  • High ALBEDO
  • Lower Maximum
  • Clouds warm at night
  • Trap OUTGOING Longwave radiation
  • Higher Minimum

39
WORLD DISTRIBUTION OF TEMPERATURES
JANUARY
  • Decrease in Temperature from Equator to Poles
  • Warm colors to Cool colors

JULY
40
WORLD DISTRIBUTION OF TEMPERATURES
JANUARY
  • Latitudinal Shifting due to the seasonal
    migration of the Sun.
  • HOT SPOTS
  • Differential heating
  • Heating is largely a function of LATITUDE

JULY
41
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.

42
WORLD DISTRIBUTION OF TEMPERATURES
-40
Equatorial temperatures do not fluctuate
significantly (there are no seasons).
25
-10
Middle and higher latitudes have much stronger
seasonal signals.
25
43
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 isnt the only thing
    governing surface temperatures,

44
TEMPERATURE MEASUREMENT
  • Mechanical thermometers
  • Electronic thermometers
  • Instrument shelters

45
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

46
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.

47
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-in-glass

48
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

49
Instrument Shelters
  • Where you take temperature matters
  • Instrument Shelters are
  • White for high albedo (reduce solar heating)
  • Ventilated so it doesnt get hot like your car
  • 1 meter high reduce longwave heating

50
Temperature Scales
  • Fahrenheit
  • Celsius
  • Kelvin

51
Fahrenheit
  • Fahrenheit is the temperature scale proposed in
    1724 by, and named after, the Dutch-German-Polish
    physicist Daniel Gabriel Fahrenheit
  • Based on Fixed Points coldest temperature he
    could measure and assumed human body temp.
  • Thats why Freezing is at 32 and Boiling is a
    212.

52
Celsius
  • Invented by Swede Anders Celsius 28 years after
    Fahrenheit (1742)
  • Decimal Scale
  • 0 degrees Freezing
  • 100 degrees Melting

53
Kelvin
  • Also called the Absolute Scale
  • The Kelvin scale is named after the Belfast-born
    engineer and physicist William Thomson, 1st Baron
    Kelvin (18241907), 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

54
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
55
Converting between temperature scales
  • To go from Kelvin to Celsius

C K - 273.15
  • To go from Celsius to Kelvin

K C 273.15
56
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
57
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

58
Heating Degree-Days
  • Developed by Engineers in the early 20th century
  • A way to evaluate energy demand
  • Dont need the heat if it is 65F or warmer
    outside
  • Any degree BELOW 65 counts as a heating
    degree-day
  • e.g. if its 50F out.
  • Thats 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
59
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 its 85F out.
  • Thats 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
60
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

61
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!
62
Growing Degree-Days (GDDs)
63
Temperature and Comfort
  • How we perceive temperature matters to us humans.
    It is affected by
  • Relative humidity
  • Wind
  • Sunshine
  • Heat Index
  • When its humid, evaporation doesnt work as well
    and we Feel hotter
  • Windchill
  • Wind makes it Feel colder than it actually is

64
Temperature and Comfort
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