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NATS 101 - 06

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Title: PowerPoint Presentation - NATS 101 - 06 Lecture 2 Density, Pressure & Temperature Climate and Weather Author: Emil Kursinski Last modified by – PowerPoint PPT presentation

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Title: NATS 101 - 06


1
NATS 101 - 06
  • Class listserve is now working
  • TA hours have changed from
  • 100-200 MWF
  • to 200-300 MWF
  • I need a notetaker volunteer.
  • Come see me after class
  • Make sure you bring 4x6 cards next class

2
Class LISTSERV
  • NATS101-06_at_listserv.arizona.edu
  • Use for any questions, comments, discussions that
    are general interest to the class.
  • kursinski_at_atmo.arizona.edu is reserved for
    personal requests not of general interest.
  • To subscribe go to http//listserv.arizona.edu/
    and click the link Subscribe to a list
  • http//listserv.arizona.edu/Subscribe.html
  • Follow straightforward instructions

3
LISTSERV
  • You can subscribe by sending an email to
    listserv_at_listserv.arizona.edu with the following
    as the only line in the body of the message.
  • subscribe xxxxxx Firstname Lastname Substitute
    the list you want to join for xxxxxx, i.e.
    kursinski_at_listserv.arizona.edu . Substitute your
    first name for Firstname Substitute your last
    name for Lastname

4
NATS 101 - 06Lecture 2Density, Pressure
TemperatureClimate and Weather

5
Two Important Concepts
  • Lets introduce two new concepts...
  • Density
  • Pressure

6
What is Density?
  • Density (?) Mass (M) per unit Volume (V)
  • ? M/V
  • ? Greek letter rho
  • Typical Units kg/m3, gm/cm3
  • Mass
  • molecules (mole) ? molecular mass (gm/mole)
  • Avogadro number (6.023x1023 molecules/mole)

7
Density Change
  • Density (?) changes by altering either
  • a) molecules in a constant volume
  • b) volume occupied by the same molecules

8
What is Pressure?
  • Pressure (p) Force (F) per unit Area (A)
  • Typical Units pounds per square inch (psi),
    millibars (mb), inches Hg
  • Average pressure at sea-level
  • 14.7 psi
  • 1013 mb
  • 29.92 in. Hg

9
Pressure
  • Can be thought of as weight of air above you.
  • (Note that pressure acts in all directions!)
  • So as elevation increases, pressure decreases.

Higher elevation Less air above Lower
pressure Lower elevation More air above Higher
pressure
Top
Bottom
10
Density and Pressure Variation
  • Key Points
  • Both decrease rapidly with height
  • Air is compressible, i.e. its density varies

Ahrens, Fig. 1.5
11
Why rapid change with height?
  • Consider a spring with 10 kg bricks on top of it
  • The spring compresses a little more with each
    addition of a brick. The spring is compressible.

12
Why rapid change with height?
  • Now consider several 10 kg springs piled on top
    of each other.
  • Topmost spring compresses the least!
  • Bottom spring compresses the most!
  • The total mass above you decreases rapidly
    w/height.

? mass
? mass
? mass
? mass
13
Why rapid change with height?
  • Finally, consider piled-up parcels of air, each
    with the same molecules.
  • The bottom parcel is squished the most.
  • Its density is the highest.
  • Density decreases most rapidly at bottom.

14
Why rapid change with height?
  • Each parcel has the same mass (i.e. same number
    of molecules), so the height of a parcel
    represents the same change in pressure ?p.
  • Thus, pressure must decrease most rapidly near
    the bottom.

?p
?p
?p
?p
15
A Thinning Atmosphere
Lower density, Gradual drop Higher
density Rapid decrease
NASA photo gallery
16
Pressure Decreases Exponentially with Height
  • Logarithmic Decrease
  • For each 16 km increase in altitude, pressure
    drops by factor of 10.
  • 48 km - 1 mb 32 km - 10 mb 16 km - 100
    mb 0 km - 1000 mb

1 mb
48 km
10 mb
32 km
100 mb
16 km
Ahrens, Fig. 1.5
17
Exponential Variation
  • Logarithmic Decrease
  • For each 5.5 km height increase, pressure drops
    by factor of 2.
  • 16.5 km - 125 mb 11 km - 250 mb 5.5 km - 500
    mb 0 km - 1000 mb

18
Water versus Air
  • Pressure variation in water acts more like
    bricks, close to incompressible, instead of like
    springs.

Air Lower density, Gradual drop Higher
density Rapid decrease
Top
Top
Water Constant drop Constant drop
Bottom
Bottom
19
Equation for Pressure Variation
  • We can Quantify Pressure Change with Height

20
What is Pressure at 2.8 km?(Summit of Mt. Lemmon)
  • Use Equation for Pressure Change

21
What is Pressure at Tucson?
  • Use Equation for Pressure Change
  • Lets get cocky
  • How about Denver? Z1,600 m
  • How about Mt. Everest? Z8,700 m
  • You try these examples at home for practice

22
Temperature (T) Profile
  • More complex than pressure or density
  • Layers based on the Environmental Lapse Rate
    (ELR), the rate at which temperature decreases
    with height.

Ahrens, Fig. 1.7
23
Higher Atmosphere
  • Molecular Composition
  • Homosphere- gases are well mixed. Below 80 km.
    Emphasis of Course.
  • Heterosphere- gases separate by molecular weight,
    with heaviest near bottom. Lighter gases (H, He)
    escape.

Ahrens, Fig. 1.8
24
Atmospheric Layers Essentials
  • Thermosphere-above 85 km
  • Temps warm w/height
  • Gases settle by molecular weight (Heterosphere)
  • Mesosphere-50 to 85 km
  • Temps cool w/height
  • Stratosphere-10 to 50 km
  • Temps warm w/height, very dry
  • Troposphere-0 to 10 km (to the nearest 5 km)
  • Temps cool with height
  • Contains all H2O vapor, weather of public
    interest

25
Summary
  • Many gases make up air
  • N2 and O2 account for 99
  • Trace gases CO2, H2O, O3, etc.
  • Some are very importantmore later
  • Pressure and Density
  • Decrease rapidly with height
  • Temperature
  • Complex vertical structure

26
Climate and Weather
  • Climate is what you expect.
  • Weather is what you get.
  • -Robert A. Heinlein

27
Weather
  • Weather The state of the atmosphere
  • for a specific place
  • at a particular time
  • Weather Elements
  • 1) Temperature
  • 2) Pressure
  • 3) Humidity
  • 4) Wind
  • 5) Visibility
  • 6) Clouds
  • 7) Significant Weather

28
Surface Station Model
Responsible for boxed parameters
  • Temperatures
  • Plotted ?F in U.S.
  • Sea Level Pressure
  • Leading 10 or 9 is not plotted
  • Examples
  • 1013.8 plotted as 138
  • 998.7 plotted as 987
  • 1036.0 plotted as 360

Ahrens, p 431
29
Sky Cover and Weather Symbols
Ahrens, p 431
Ahrens, p 431
30
Pressure Tendency
  • Change in pressure over the past 3 hours is also
    plotted.
  • Also called barometric tendency

Ahrens, p 432
31
Wind Barbs
  • Direction
  • Wind is going towards
  • Westerly ? from the West
  • Speed (accumulated)
  • Each flag is 50 knots
  • Each full barb is 10 knots
  • Each half barb is 5 knots

65 kts from west
Ahrens, p 432
32
SLP pressure
temperature dew point
cloud cover
Ohio State website
wind
33
Practice Surface Station
  • Temperate (oF)
  • Pressure (mb) Last Three Digits (tens, ones,
    tenths)
  • Dew Point (later) Moisture
  • Wind Barb Direction and Speed
  • Cloud Cover Tenths total coverage

34
Practice Surface Station
  • Sea Level Pressure
  • Leading 10 or 9 is not plotted
  • Examples
  • 1013.8 plotted as 138
  • 998.7 plotted as 987
  • 1036.0 plotted as 360

35
Surface Map Symbols
  • Fronts
  • Mark the boundary between different air
    masseslater
  • Significant weather occurs near fronts
  • Current US Map

Ahrens, p 432
36
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37
Radiosonde
  • Weather balloons, or radiosondes, sample
    atmospheric to 10 mb.
  • They measure temperature moisture pressure
  • They are tracked to get winds

Ahrens, Fig. 1
38
Radiosonde Distribution
  • Radiosondes released at 0000 and at 1200 GMT for
    a global network of stations.
  • Large gaps in network over oceans and in less
    affluent nations.
  • Stations 400 km apart over North America

39
Radiosonde for Tucson
  • Example of data taken by weather balloon released
    over Tucson
  • Temperature (red)
  • Moisture (green)
  • Winds (white)
  • Note variations of all fields with height
  • UA Tucson 1200 RAOB

stratosphere
tropopause
troposphere
temperature profile
moisture profile
wind profile
40
Upper-Air Model
Responsible for boxed parameters
  • Conditions at specific pressure level
  • Wind
  • Temperature (?C)
  • Moisture (Later)
  • Height above MSL
  • UA 500mb Analysis

Ahrens, p 431
Ahrens, p 427
41
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42
Climate
  • Climate - Average weather and range of weather,
    computed over many years.
  • Whole year (mean annual precipitation for Tucson,
    1970-present)
  • Season (Winter Dec-Jan-Feb)
  • Month (January rainfall in Tucson)
  • Date (Average, record high and low temperatures
    for Jan 1 in Tucson)

43
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44
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45
Climate of TucsonMonthly Averages
Individual months can show significant deviations
from long-term, monthly means.
46
Average and Record MAX and MIN Temperatures for
Date
47
Climate of TucsonProbability of Last Freeze
Cool Site Western Region Climate Center
48
Climate of TucsonProbability of Rain
Cool Site Western Region Climate Center
49
Climate of TucsonExtreme Rainfall
Cool Site Western Region Climate Center
50
Climate of TucsonSnow!
Cool Site Western Region Climate Center
51
Summary
  • Weather - atmospheric conditions at specific time
    and place
  • Weather Maps ? Instantaneous Values
  • Climate - average weather and the range of
    extremes compiled over many years
  • Statistical Quantities ? Expected Values

52
Reading Assignment
  • Ahrens
  • Pages 25-42
  • Problems 2.1-2.4, 2.7, 2.9-2.12
  • (2.1 ? Chapter 2, Problem 1)
  • Dont Forgot the 4x 6 Index Cards
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