Reference Tables

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Table of Contents

Aerodynamic Roughness Values
Atmospheric Density
Characteristics of Gases
Ozone Predictors
Periodic Table
Rain Droplet Sizes
Saturation Values of Humidity vs. Actual Air Temperature
Standard Sea Level Pressure in Various units
UTC to Local Time Conversions
Weather Data Products
Satellite Image Interpretation Guide

Roughness Lengths for Various Surfaces

Type of Surface	z₀ (cm)
Fir Forest	283.0
Citrus orchard	198.0
Large City (Tokyo)	165.0
Corn Field	84.5
Wheat Field	23.0
Grass	10.0
Dry Lake Bed	0.003

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Standard atmospheric density at sea level, for a standard temperature 15 ^oC.

Value

Units

1.2250 kgm^-3

0.076474 lb_m/ft³

1.2250 g/liter

0.001225 g/cm³

kilograms per cubic meter

pounds-mass per cubic foot

grams per liter

grams per cubic centimeter

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Characteristics of Gases

Characteristics of gases in the air near the ground. Molecular weights are in g/mole. The volume fraction indicates the relative contribution to air in the earth's lower atmosphere. EPA is the USA Environmental Protection Agency.

Symbol

Name

Molecular Weight

Volume Fraction%

Constant Gases

N₂

O₂

H₂

Nitrogen

Oxygen

Argon

Neon

Helium

Hydrogen

Xenon

28.01

32.00

39.95

20.18

4.00

2.02

131.30

78.08

20.95

0.93

0.0018

0.0005

0.00005

0.000009

Variable Gases

H₂O

CO₂

CH₄

N₂O

Water vapor

Carbon dioxide

Methane

Nitrous oxide

18.02

44.01

16.04

44.01

0 to 4

0.035

0.00017

0.00003

EPA Air Quality Standards

SO₂

O₃

NO₂

Carbon monoxide

Sulfur dioxide

Ozone

Nitrogen dioxide

28.01

64.06

48.00

46.01

0.0035

0.000014

0.000012

0.000005

Mean Condition for Air

air

28.96

100.0

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Common predictors used in forecasting of ozone (O₃) concentrations.

VARIABLE	USEFULNESS
Maximum temperature	Highly correlated with ozone and ozone formation
Morning wind speed	Associated with dispersion and dilution of ozone precursor pollutants
Afternoon wind speed	Associated with transport of ozone
Cloud cover	Controls solar radiation, which influences photochemistry
Relative humidity	Surrogate for cloud cover
500-mb height	Indicator of the synoptic-scale weather pattern
850-mb temperature	Surrogate for vertical mixing
Pressure gradients	Causes winds and ventilation
Day of week	Emissions differences
Morning NOx concentration	Ozone precursor levels
Previous day's peak ozone	Persistence, carry-over
Aloft wind speed and direction	Transport from upwind region

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The Periodic Table

Rain Droplet Sizes

Droplet or Nuclei																																								Average Diameter (micrometers)
Typical CCN																																								0.2
Typical Cloud Droplet																																								20
Large Cloud Droplet																																								100
Typical Raindrop																																								2000

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(1) Saturation values of humidity vs. actual air temperature. -or- (2) Actual humidities vs. dew-point temperature.

Values are for over a flat surface of liquid water. r and q values are for sea level. e and p_v values are for any pressure. T is temperature, T_d is dew-point temperature, e is vapor pressure, r is mixing ratio, q is specific humidity, p_v is absolute humidity, and subscript s denotes a saturation value.

e_ss

r_s

q_s

p_vs

T_d

p_v

(^oC)

(kPa)

(g/kg)

(kg/m³)

-20

-18

-16

-14

-12

-10

-8

-6

-4

-2

0.127

0.150

0.177

0.209

0.245

0.287

0.335

0.391

0.455

0.528

0.611

0.706

0.814

0.937

1.076

1.233

1.410

1.610

1.835

2.088

2.371

2.688

3.042

3.437

3.878

4.367

4.911

5.514

6.182

6.921

7.736

8.636

9.627

10.717

11.914

13.228

0.78

0.92

1.09

1.28

1.51

1.77

2.07

2.41

2.80

3.26

3.77

4.37

5.04

5.80

6.68

7.66

8.78

10.05

11.48

13.09

14.91

16.95

19.26

21.85

24.76

28.02

31.69

35.81

40.43

45.61

51.43

57.97

65.32

73.59

82.91

93.42

0.78

0.92

1.09

1.28

1.51

1.76

2.06

2.40

2.80

3.25

3.76

4.35

5.01

5.77

6.63

7.60

8.70

9.95

11.35

12.92

14.69

16.67

18.89

21.38

24.16

27.26

30.72

34.57

38.86

43.62

48.91

54.79

61.31

68.54

76.56

85.44

0.00109

0.00128

0.00150

0.00175

0.00204

0.00237

0.00275

0.00318

0.00367

0.00422

0.00485

0.00557

0.00637

0.00728

0.00830

0.00945

0.01073

0.01217

0.01377

0.01556

0.01755

0.01976

0.02222

0.02494

0.02794

0.03127

0.03493

0.03896

0.04340

0.04827

0.05362

0.05947

0.06588

0.07287

0.08051

0.08884

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Standard (average) sea-level pressure in various units.

Value

Units

101.325 kPa

1013.25 hPa

101,325. Pa

101,325. Nm^-2

101,325 kg_mm^-1s^-2

1.033227 kg_fcm^-2

1013.25 mb

1.01325 bar

14.69595 psi

2116.22 psf

1.033227 atm

760 Torr

kiloPascals

hectoPascals

Pascals

Newtons per square meter

kg-mass per meter per s²

kg-force per square cm

millibars

bars

pounds-force / square inch

pounds-force / square foot

atmosphere

Torr

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UTC to Local Time conversions

Universal Time Convention (UTC)	Eastern Standard Time (EST)	Central Standard Time (CST)	Mountain Standard Time (MST)	Pacific Standard Time (PST)
any time	UTC - 5 hrs.	UTC - 6 hrs.	UTC - 7 hrs.	UTC - 8 hrs.
00:00 (midnight)	19:00 (7 pm)	18:00 (6 pm)	17:00 (5 pm)	16:00 (4 pm)
12:00 (noon)	7:00 (7 am)	6:00 (6 am)	5:00 (5 am)	4:00 (4 am)

Weather Data Products

Data Type	Variables	Forecasted/ Observed	Frequency
Surface Meteorological	Wind speed, wind direction, temperature, relative humidity, solar radiation, cloud cover, visibility, pressure	Observed	Hourly
Surface Air Quality	Ozone, nitrogen oxides, carbon monoxide, volatile organic compounds	Observed	Hourly
Upper air meteorology (rawindsondes, radar profilers, and sodars)	Vertical profiles of wind speed, wind direction, temperature, relative humidity	Observed	Twice-per-day to hourly
Aloft air quality observations (towers, mountains, and aircraft)	Ozone, nitrogen oxides	Observed	Variable
Weather charts	Surface: wind speed, wind direction, temperature, relative humidy, pressure 850-mb: wind speed, wind direction, temperature, height 700-mb: wind speed, wind direction, temperature, height 500-mb: wind speed, wind direction, temperature, height, others	Forecasted and observed	Twice per day
Weather radar	Precipitation	Observed	Hourly
Satellite	Cloud cover (visible and infrared)	Observed	Hourly and/or sub-hourly
Meteorological model forecasts	Temperature, relative humidity, wind speed, wind direction, cloud cover, visibility, precipitation, others at many levels	Forecasted	Twice per day
Text weather forecasts	Discussions	Forecasted and observed	Four or more times per day

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Guide to Interpreting Satellite Images

Types of Clouds

Image Type

Interpretation

Low Clouds

Visible

Infrared/Enhanced Infrared

Water Vapor

Low clouds look bright on visible images, since a significant amount of light is radiated back to the atmosphere. If you notice, most low clouds have a very dark base, signifying that light is not getting through to the surface.

Low clouds appear gray on IR/EnhIR images, since the tops of low clouds are relatively warm.

Since low clouds are so low in the atmosphere, they are detectable on water vapor images.

Cirrus Clouds

Visible

Infrared/Enhanced Infrared

Water Vapor

Cirrus clouds look a bit off-white in color, as compared with the brighter images of low clouds. Cirrus clouds as seen from the surface look white, meaning that light is getting through. Some light, however, is scattered back to the atmosphere, so the images appear as the characteristic off-white color.

Cirrus clouds are quite high in the atmosphere, so they are quite cold. On IR images, cirrus clouds appear bright white in color.

The high-altitude crystals that are found in cirrus clouds appear as white on water vapor images.

Tall Cumulus

Cumulonimbus

Visible

Infrared/Enhanced Infrared

Water Vapor

These clouds appear as bright white on visible images, since a significant amount of radiation is reflected or scattered back to the atmosphere.

The tops of these clouds are quite cold, so they appear as bright white on IR/EnhIR images.

As with cirrus clouds, these clouds emit cold (6.7 micron) radiation, so they appear as white images on water vapor images.

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