1. Part 2
2/24/2019

2. Week 16, 17, 18 and 19 The Atmosphere
Modules 3, 4, 7 and 8 in AP
The study of the Air and the Atmosphere and how we measure them
Movement of the Atmosphere - Air Masses, Winds and Storms
Weather Prediction
Next test: Week 19 T Jan 23/25 - covers the atmosphere and hydrosphere
Week 20 A Jan 30 - I will be away - analysis exercise
U of IL - Wx Course
Lyndon State Course
2/24/2019 2

3. Prep Questions Week 16 Week 17 Week 18 Week 19
(1) What role does the sun play in causing seasons and the weather?
(2) What is the composition of the air?
(3) What is the role of each component?
Week 17
(1) What are the 5 layers of the atmosphere?
(2) What is temperature?
(3) What is Ozone hole?
Week 18
(1) What factors influence the weather?
(2) What are the weather elements?
Week 19
(1) What are the factors that cause precipitation?
(2) What are the differences and common characteristics of a thunderstorm, tornado, hurricane and a nor'easter low pressure system?
2/24/2019

4. Current Weather Review 
Radar/Sat
US Radar
US Radar NWS
Goes Sat Page
US Sat IR
NRL Sat
US Sat Vis
NY VIS
Sfc Analysis NWS
Surface Plots
Surface 12 Hour Fcst
Surface 24 Hour Fcst
Surface 36 Hour Fcst
Surface 48 Hr Fcsts
Emergency
CURRENT SVR Wx RADAR
National Weather Situation Page  
Severe Weather Alert Link
Your Local Forecast
Local Fcsts
Rome NY 
 43.23°N 75.46°W 
Rome Griffiss Airfield
Lat:   Lon:   Elev: 504 ft Lat/Lon: 43.23°N 75.46°W   Elevation:482  
BGM Discussion 
Wx Maps
NAM
GFS
1. GFSx -Upper
2.GFSx-MRF- Precip
Long Range NWS Model
ECMWF
CPC
Datastreme
Climo
SYR CLIMO
CLIMO STAT CNY
ALB CLIMO
Other
NASA Solar Science
Solar-Sun Spot-Space-Wx
Sun & Moon Rise & Set Tables
Moon Phases
Your Sky Start Charts
Tides Maine
NOAA Space Wx
Forecast Central
2/24/2019

5. Atmospheric Pressure
- Weight (force of gravity) of air above a location.
- atmospheric pressure decreases with height.
- pressure density temperature relationship
- higher temperature more spread out the molecule the lower the density and pressure
- two way to change pressure at a given level – (hydro)dynamically through movement of air (wind) and thermodynamically – through temperature changes.
2/24/2019 5

6. Unit Area
14.7 lbs
2/24/2019

7. 2/24/2019 7

8. 2/24/2019 8

9. Values of Atm Pressure Atmospheric Pressure (AP: p55)
Pressure exerted by the atmosphere on all object within it.
In simple terms it is the measure of the concentration of weight of the air.
ATM (1 at sea level)
Lbs per square inch (14.7 at sea level)
Inches of Hg 29.92 mb pa
2/24/2019 9

10. Ways to measure atmospheric pressure
Barometers - instrument used to measure atmospheric pressure.
Types: Water, mercurial (see figure 3.2 p 59), aneroid:
Units: inches of Hg, mmHg, millbars, pascals, atm.
Types of Pressure Measurements:
Barometric pressure: The pressure as measure by a barometer.
Station Pressure: The barometric pressure at a given surface station.
Mean sea level pressure (MSLP) is the pressure at sea level or (when measured at a given elevation on land) the station pressure reduced to sea level assuming an isothermal layer at the station temperature.
2/24/2019 10

11. The Atmospheric Pressure as The vertical coordinate
Altimeter setting used in aviation, , is another atmospheric pressure reduced to sea level, but the method of making this reduction differs slightly.
2/24/2019 11

12. 2/24/2019 12

13. 2/24/2019 13

14. 2/24/2019 14

15. Water Vapor In the Air Terms:
Humidity is the water vapor or moisture content of air
Absolute humidity is the mass of water vapor contained in a certain volume of air
Dew point Temperature and Wet bulb Temperature are related directly and very practical indicators of humidity and impacts (i.e. will you have a frost)
Example Clear and 36/34 - no frost, 54/10 very likely to have a frosts
Relative humidity is the ratio of the mass of water vapor in the air at a given temperature to the maximum mass of water vapor the air could hold at that temperature, expressed as a percentage.
2/24/2019

16. Change of Phase - Heat Exchanges
Energy into water molecule cooling surfaces and air: melting, evaporation, sublimation
Energy out of water molecule warming surfaces and air: freezing, condensation, deposition
Water evaporates slowly under conditions of high humidity. Remember, the higher the humidity, the more water vapor that is already in the air. This makes it harder to put more water vapor in the air, which is what evaporation does.
Will sweating help cool you down when the humidity is 100%?
No, sweating will not cool you down. When the humidity is 100%, water will not evaporate, and that is what gives sweat its cooling effect.
We all know that ice melts because of heat. Why is it correct to say that ice also freezes because of heat?
Heat is energy that is being transferred. To freeze water, energy must be transferred from the water to the surroundings. Thus, water freezes because of heat!
2/24/2019

17. How does moisture (water vapor) impact atmospheric pressure?
Surprisingly adding water vapor  to dry air will make the air less dense and LOWER the PRESSURE as compared to dry air at the same temperature. This change is small but can be significant. Moisture changes are considered part of the thermodynamic forcing since moister air acts like warmer air.
% Composition of Air N2 78%, O2 21%, Other 1%
GAS: N2=28 AMU, O2 =32 AMU, Other = 26 AMU , Avg Dry is 29 AMU, H2O = 18 AMU
(AMU is Atomic Mass Units)
- Therefore, the lighter H20 will displace the heavier dry air molecules. Remember the atmosphere is not a rigid container. So the density and pressure of moist air must be less than dry air at the same temperature.
        - Adding moisture has the same effect on atmospheric stability as warming the air.
2/24/2019

18. The Water Vs Oxygen and Nitrogen Molecule18 32 O2
H20 28 N2
2/24/2019

19. The Water Molecule H2O - Very Unique Properties
Polar Molecule
Changes Phases with Normal Earth Temperature Ranges
Becomes less dense when it freezes
2/24/2019

20. 2/24/2019