1. No category

Surface Inversions, Atmospheric
Stability, and Spray Drift
Surface Temperature Inversions:
• Are very common
• Are easy to recognize
• Affect the dispersal of very small spray droplets
suspended in the air
• Do not increase the amount of off-site movement
• Can increase the potential for offsite affects &
the distance at which affects can be observed
Atmospheric Stability
• Inversions cause STABLE atmospheric
conditions
• The concept of atmospheric stability helps
understand how inversions affect drift
• Close to the ground, atmospheric stability
changes regularly between STABLE,
NEUTRAL, & UNSTABLE
55 F
60 F
65 F
70 F
75 F
80 F
The large scale trend in
the atmosphere is that
temperature decreases
with height
55 F
60 F
65 F
70 F
75  F
80  F
Where there is a decrease in
temperature with height greater
than the adiabatic rate the
atmosphere is UNSTABLE
55 F
60 F
65 F
70 F
75  F
80  F
Droplets
or
particles
suspended
in
When the atmosphere is
the
air
will
be
dispersed/diluted
UNSTABLE air parcels near the
surface will rise and expand
because they are warmer & less
dense than the air above
105 foot temperature monitoring tower
105’ 38°F
Cloud of 5-25 u oil
droplets generated under
unstable conditions
64’ 40°F
32’ 40°F
16’ 41°F
8’
41°F
105’ 38°F
105’ 38°F
64’ 40°F
64’ 40°F
32’ 40°F
32’ 40°F
16’ 41°F
16’ 41°F
8’ 41°F
8’
41°F
o
65 F
o
60 F
A temperature inversion is an
area where temperature
increases with height.
o
55 F
o
50 F
o
45 F
o
40 F
It can begin at the ground.
50°F
o
30 F
48°F
46°F
o
40 F
44°F
42°F
o
50 F
40°F
38°F
o
60 F
40°F
42°F
o
70 F
44°F
46°F
o
80 F
48°F
Or it can begin above the ground.
A temperature inversion
is an area where
temperature increases
with
this will
is area
is
These
aloftheight,
inversions
be discussed
inversion
layer
at thethe
end
of the program
55
o
65 F
o
60 F
When temperature increases
with height the atmosphere is
STABLE.
o
55 F
o
50 F
o
45 F
o
40 F
Vertical mixing of the air and
dispersion of small droplets is
suppressed.
o
65 F
o
60 F
o
55 F
o
50 F
o
45 F
o
40 F
A
parcel
of
air
near
the
surface
is
If forced down by a current of air,
always
cooler
&
more
dense
than
it will immediately rise back.
the air above, so it can’t rise and
disperse.
o
65 F
o
60 F
o
55 F
o
50 F
o
45 F
o
40 F
If forced up by a current of air, it
will immediately sink back.
o
65 F
o
60 F
o
55 F
o
50 F
o
45 F
o
44 F
The parcel of air can’t rise and
disperse, but it can be move
laterally in the light variable
winds typical of a surface
inversion
Temperature Profile
105’
64’
32’
16’
8’
Wind 0.6 mph
35°F
30°F
29°F
28°F
26°F
Surface Inversion - STABLE CONDITIONS
Temperature Profile
105’
64’
32’
16’
8’
35°F
30°F
29°F
28°F
26°F
Surface Inversion - STABLE CONDITIONS
105’ 33°F
64’
32’
16’
8’
32°F
31°F
29°F
27°F
Surface Inversion - STABLE CONDITIONS
Temperature Profile
105’
64’
32’
16’
8’
43°F
36°F
32°F
30°F
28°F
Cold air drainage down a slope
Surface Inversion - STABLE CONDITIONS
Temperature Profile
105’
64’
32’
16’
8’
43°F
36°F
32°F
30°F
28°F
Cold air drainage down slope
Surface Inversion - STABLE CONDITIONS
o
65 F
o
60 F
55 F
o
50 F
o
45 F
o
40 F
A Surface
can extend
Height
(of Inversion
the inversion)
doesn’t
upwards 5, 50, 100, 500 ft or
matter:
more.
If the application is made within
the inversion it, the effects will
be similar.
Layering observed when oil droplets released at ground level or
top of tower. Clouds moving in different directions.
105’ 35°F
64’
32’
16’
8’
30°F
29°F
28°F
26°F
Surface inversion extending above the tower
Cloud is dispersing
2.5 mph wind
105’ 38°F
.5 mph wind
Shallow surface inversion
STABLE conditions up to 64’
NEUTRAL conditions at 105’
64’
32’
16’
8’
38°F
37°F
36°F
33°F
55 F
60 F
65 F
70 F
75 F
80 F
Surface Inversions are
part of the daily cycle
unless wind or cloud
cover intervene
During the night, unless clouds or wind intervene, the ground loses
heat cooling the air above.
Unless wind intervenes the surface inversion will continue until the
sun begins to heats the ground
During the day when cloud cover is light, the sun heats the ground
warming the air above. This causes in unstable conditions unless
wind intervenes.
As the sun sets the ground begins to lose more heat than it gains,
cooling the air above. In the absence of heavy cloud cover and/or
wind a surface inversion will begin to form.
50
105’ temperature
40
30
20
64’
temperature
16’
32’temperature
temperature
8’ temperature
Solar energy
10
0
M
M
M
M
0P
8:0
M
0P
4:0
PM
:00
12
0A
8:0
0A
4:0
A
:00
12
Time of Day
0.700
0.600
0.500
0.400
0.300
0.200
0.100
0.000
Solar Energy (Kw/m2)
Temperature (°F)
60
Temperature (°F)
60
50
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Inversion - Stable
40
30
20
10
Sunset
Sunrise
0
8:0
0P
M
M
PM
0P
:00
M
0A
105' temp
4:0
12
8:0
AM
M
0A
:00
4:0
12
8' temp
solar energy
Solar Emergy (Kw/m2)
Daily Cycle
11/9/93 Inversion - Stable
Unstable
How to recognize a surface inversion
•
•
•
•
•
•
•
Sunset to just after sunrise
Windless to low wind conditions (<2-3 mph)
Clear to partly cloudy skies
Ground fog (if sufficient humidity exists)
Dust hanging over a roadway
Smoke from a chimney forming a layer
Dew or frost (if sufficient humidity exists)
Signs of a surface
inversion in the
early morning
Lack of heavy cloud cover
Windless or light
variable wind
Ground Fog
Frost (or dew)
Smoke from a chimney forming a layer
Surface inversion - early morning
How to recognize the potential for a
surface inversion
• Sun is getting low in the sky
• Wind is becoming light and variable
• Clear to partly cloudy skies
Surface Inversions don’t:
• Increase the amount of spray droplets
moving off-site
Surface Inversions can:
• Decrease the dispersion of droplets too
small to quickly settle out.
• Result in a higher air concentration of these
small droplets.
• Increase the potential for off-target effects.
• Increase the distance at which off-target
effects can be observed.
• Increase the size of the area affected.
• Cause the direction of drift to be
unpredictable
Reducing the effects of Surface
Inversions on Spray Drift
• Minimizing production of very small drops
• Using equipment the minimizes the number
of small drops suspended in the air
• Morning applications are likely to have
shorter exposure to STABLE conditions
than evening applications
o
80 F
o
80 F
o
80 F
o
80 F
o
80 F
o
80 F
When the atmospheric stability is
NEUTRAL,
there
is little
or
Vertical mixing
is not
suppressed
change
temperature
with and
as underinSTABLE
conditions,
height.
Low heavy
cloud
cover
the turbulence
of even
a 5 mph
wind iswind
effective
in dispersing
and/or
contribute
to
suspended small
droplets.
NEUTRAL
conditions.
Temperature Profile
105’
64’
32’
16’
8’
32°F
33°F
33°F
33°F
32°F
Wind 4.5 mph
NEUTRAL CONDITIONS
Temperature Profile
105’
64’
32’
16’
8’
32°F
33°F
33°F
33°F
32°F
Wind 4.5 mph
NEUTRAL CONDITIONS
Surface Inversion
No wind
Temperature Profile
105’
64’
32’
16’
8’
43°F
36°F
32°F
30°F
28°F
7:00 AM
Neutral Conditions
4.5 mph wind
8:30 AM
Temperature Profile
105’
64’
32’
16’
8’
32°F
33°F
33°F
33°F
32°F
Neutral conditions can be the best
time to spray
• Wind direction if often consistent
• Good dispersion of droplets too small to
quickly settle out.
50°F o
30 F
48°F
46°F o
40 F
44°F
42°F o
50 F
40°F
38°F o
60 F
40°F
42°F o
70 F
44°F
46°F o
80 F
48°F
Aloft Inversions
A
temperature
inversion
• Are not likely to effect applications to
is an area
where
agricultural
crops
increasescan affect
• Lowtemperature
altitude aloft inversions
with
height,
this is area is
aerial
forestry
application
inversion
layer are often
• Lowthe
altitude
aloft inversions
surface inversions in the process of
dissipating & 55
are therefore short lived
Surface Temperature Inversions:
• Are very common
• Are easy to recognize
• Affect the dispersal of very small spray droplets
suspended in the air
• Do not increase the amount of off-site movement
• Can increase the potential for offsite affects &
the distance at which affects can be observed