Weather Instruments PPT
Download
Report
Transcript Weather Instruments PPT
Weather Instruments
Atmospheric Property
Instrument
Temperature
Thermometer
Atmospheric Pressure
Barometer
Relative Humidity
Psychrometer
Wind Speed
Anemometer
Wind Direction
Wind (Weather) Vane
Amount of Precipitation
Rain Gauge
Temperature
Measured with a thermometer.
Two temperature scales:
•degrees Fahrenheit, °F
•degrees Celsius, °C
Temperature Scale Conversions
°C °F
9
TF = TC 32 1.8TC 32
5
°F °C
5
TC = TF 32 .56TF 32
9
Examples of Temperature Conversions
Convert 20°C to Fahrenheit
TF 1.8TC 32
TF 1.820 32
TF 36 32
TF 68F
Convert 98.6°F to Celsius
TC .56TF 32
TC .5698.6 32
TC .5666.6
TC 37.3C
Temperature Records
Record High Temperatures
134°F
136°F
US:Death Valley, Calif., July 10, 1913
World: El Azizia, Libya, Sept. 13,1922
Record Low Temperatures
Contiguous US: Rogers Pass, Montana, Jan. 20, 1954
Alaska: Prospect Creek, Alaska, Jan. 23, 1971
World: Vostok, Antarctica, July 21, 1983
-70°F
-80°F
-129°F
Sudden Changes in Temperature (US only)
Drop: Browning, Montana, Jan, 23-24, 1916
Rise: Spearfish, SD, Jan. 22, 1943
+49F°
-100F° in 24 hrs
In 2 minutes!
7:30am = -4°F …
7:32am = 45°F
Mercury Barometer
h
ATMOSPHERIC PRESSURE
Depends on
Atmospheric Pressure
ATMOSPHERIC PRESSURE
Hg
Units: mmHg inHg
millibar, mb
Aneroid (without liquid) Barometer
Standard Atmospheric Pressure @ Sealevel
760mmHg
29.9inHg
1013mb
Relative Humidity
Amount of Water Vapor in the Air
Relative Humidity = Capacity of Air to Hold Water Vapor
Water vapor enters the air by :
Evaporation from wet surfaces
Transpiration from plants and animals
Capacity of Air to Hold Water Vapor
Absolute Humidity
Depends on Temperature
As temperature increases,Absolute Humidity increases
How does the relative humidity change as the temperature changes?
Consider a classroom where the number of students allowed is
determined by the number of seats available.
The number of seats available is determined by the temperature,
one seat for each F°.
Suppose we begin with the room at 80°F and 40 students present.
80 seats, 40 students…the room is 40/80 = 50% occupied.
Suppose we now cool the room to 70°F, 10 seats must be removed.
70 seats, 40 students…the room is now 40/70 = 57% occupied.
Suppose we now cool the room to 50°F, 20 seats must be removed.
50 seats, 40 students…the room is now 40/50 = 80% occupied.
Suppose we now cool the room to 40°F, 10 seats must be removed.
40 seats, 40 students…the room is now 40/40 = 100% occupied.
From this analogy we see that as a mass of air is cooled its relative
humidity increases.
When the relative humidity reaches 100% we say that the air is
saturated.
The temperature at which the relative humidity becomes 100% is
called the dew point.
If the air is cooled below the dew point some of the water leaves
the air by condensing back into droplets of liquid water if the
dew point is above freezing or ice crystals if the dew point is
below freezing.
If the water droplets/ice crystals condense above the
ground a cloud forms.
If the droplets/ice crystals condense directly onto the
ground dew/frost is formed.
Measuring Relative Humidity
Dry Bulb
Temperature
85°F
Wet Bulb
Temperature
75°F
Difference in
Temperatures
10F°
PSYCHROMETER
DRY BULB
WET BULB
90F
85F
80F
75F
70F
65F
60F
water evaporating
carries away heat
WATER
Psychometric Tables
1. Relative Humidity (%)
Air Temperature
(Dry Bulb) °F
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
105
110
Maximum
Moisture Capacity
( gr/ft 3 )
1.6
1.9
2.4
2.8
3.4
4.1
4.8
5.7
6.8
7.8
9.4
10.9
12.7
14.8
17.1
19.8
23.4
26.0
Degrees Depress ion of Wet Bulb Thermometer
(Difference Between Dry and Wet Bulb Temperatures)
1
87
89
91
92
93
93
94
94
95
96
96
96
96
96
96
96
97
97
2
74
78
81
83
86
87
88
89
90
90
91
91
92
92
93
93
93
93
3
62
67
72
75
78
80
82
83
85
86
86
87
88
89
89
89
90
90
4
49
56
63
68
71
74
76
78
80
81
82
83
84
85
85
86
87
87
5
37
46
54
60
64
67
70
73
75
77
78
79
80
81
82
83
83
84
6
25
36
45
52
57
61
65
68
70
72
74
75
76
78
79
80
80
81
7
13
26
36
45
51
55
59
63
66
68
70
72
73
74
75
77
77
78
Relative Humidity = 62%
8
1
16
27
37
44
49
54
58
61
64
66
68
69
71
72
73
74
75
9
10
15
20
25
30
6
19
29
38
43
49
53
56
59
62
64
66
68
69
70
71
73
10
22
31
38
43
48
52
55
58
61
62
65
66
68
69
70
10
19
26
31
36
40
44
46
49
51
54
55
57
5
12
19
24
29
32
36
38
41
43
46
3
9
15
20
24
27
30
33
36
3
8
13
17
21
23
26
2. Dew Point (°F)
Air Temperature
(Dry Bulb) °F
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
105
110
Maximum
Moisture Capacity
( gr/ft 3 )
1.6
1.9
2.4
2.8
3.4
4.1
4.8
5.7
6.8
7.8
9.4
10.9
12.7
14.8
17.1
19.8
23.4
26.0
Degrees Depress ion of Wet Bulb Thermometer
(Difference Between Dry and Wet Bulb Temperatures)
1
2
3
4
5
6
7
8
9 10 15
22 19 15 10
5
-3 -15 -51
27 25 21 18 14
8
2
-7 -25
33 30 28 25 21 17 13
7
0 -11
38 35 33 30 28 25 21 18 13
7
43 41 38 36 34 31 28 25 22 18
48 46 44 42 40 37 34 32 29 26
0
53 51 50 48 45 43 41 38 36 33 15
58 57 55 53 51 49 47 45 43 40 25
63 62 60 59 57 55 53 51 49 47 34
69 67 65 64 62 61 59 57 55 53 42
74 72 71 69 68 66 64 63 61 59 49
79 77 76 74 73 72 70 68 67 65 56
84 82 81 80 78 77 75 74 72 71 62
89 87 86 85 83 82 81 79 78 76 69
94 93 91 90 89 87 86 85 83 82 74
99 98 96 95 94 93 91 90 89 87 80
104 103 101 100 99 98 96 95 94 93 86
109 108 106 105 104 103 102 100 99 98 91
Dew Point = 71°F
20
25
30
8
14
26
36
44
52
59
66
72
78
84
-11
15
28
39
49
56
63
70
77
-7
19
32
43
52
61
68
Anemometer
measures wind speed
mi
Units:
hr
knots
nautical miles
hr
The highest surface wind speed ever officially recorded was 231 mph
at the Mount Washington (New Hampshire) Observatory in the US
on 12th April 1934.
The highest windspeed recorded was 316 mph measured during the
F5 tornado, in Moore, Oklahoma. It was measured 30 m (100 feet)
above ground.
Hurricanes are tropical cyclones with winds that exceed 64 knots (74
mi/hr) and circulate counter-clockwise about their centers in the
Northern Hemisphere (clockwise in the Southern Hemisphere).
Once a group of thunderstorms has come together under the right
atmospheric conditions for a long enough time, they may organize
into a tropical depression. Winds near the center are constantly
between 20 and 34 knots (23 - 39 mph).
Once a tropical depression has intensified to the point where its
maximum sustained winds are between 35-64 knots (39-73 mph), it
becomes a tropical storm. It is at this time that it is assigned a name.
During this time, the storm itself becomes more organized and
begins to become more circular in shape -- resembling a hurricane.
As surface pressures continue to drop, a tropical storm becomes a
hurricane when sustained wind speeds reach 64 knots (74 mph). A
pronounced rotation develops around the central core.
Hurricane Categories
Category Sustained Wind Speed
1
74-95mph
2
96-110mph
3
111-130mph
4
131-155mph
5
>155mph
Wind (weather) Vane
A wind vane is used to measure the direction of the
wind. A wind vane turns pointing into the direction
of the wind.
Rain (snow) Gauge
Units: inches
Record Rainfall: Alvin, Texas July 25-26,1979
43 inches in 24 hours!
What caused it?