http://lawr.ucdavis.edu/ce_frost_protection.htm The presentations below will run automatically on your computer, and include recorded audio. 1. 2. 3. 4.
Active Frost Protection: Water Active Frost Protection: Wind Machines Passive Frost Protection Methods of Measuring Temperature
Las presentaciones abajo expuestas se abrirán automáticamente en su computadora, incluyendo sonido grabado. 1. 2. 3. 4.
La protección activa contra las heladas: Agua La protección activa contra las heladas: Viento La protección pasiva contra las heladas Los métodos para medir la temperatura
Mark Battany, Rhonda Smith, Gwen Tindula, Richard Snyder
National Weather Service
http://www.wrh.noaa.gov/sto/
Weather Tables
4
5
6
Methods of Heat Transfer Conduction- from molecule to molecule Heat Source
Metal bar
Convection - by movement of
Radiation - energy passing
heated air
from one object to another without a connecting medium Long wave loss from Earth Short wave gained from the sun
Earth 7
Methods of Heat Transfer Latent Heat - Chemical Heat Process 20oC to 0oC (68oF to 32oF) Freezing at 0oC (32oF) Evaporation
kJ kg-1 When water molecules evaporate, sensible heat is changed to latent heat and the temperature drops
84 H
335
O
H
-2500
One must cool and freeze six times as much water as evaporates to gain sensible heat 8
Inversion Formation
Temperature (oC) -5.0
5.0
0.0
35
10.0
10.0 30 4:00am
8:00pm
25 Height (ft)
8:00am
12:00am
4:00pm
20
6.0
15 4.0 10 2.0 5 0.0
0 20
25
30
35
40
Temperature (oF)
45
50
55
Height (m)
8.0
Freeze Injury 1. Intercellular Ice formation 2. Water is drawn out of the cells and condenses on the ice 3. Dehydration causes cell damage
Intercellular Ice Crystal Formation
Cells Ice
Prillieux (1869) cited by Levitt (1980)
Table of yield loss (%) for given temperatures Variety Peerless [F]
Stage
Temperature °F 21.9
23.0
24.1
25.0
26.1
27.0
28.0
100
75
45
25
50
25
79
50
14
1
petal fall
63
14
3
nut stage
46
45
9
19
14
3
45
27
10
Full bloom 100
showing pink
75
full bloom Peerless [C] NePlus Ultra [F]
full bloom
Mission [F]
showing pink
Drake [F] Nonpareil [F]
100
full bloom
80
60
100
75
showing pink
75
50
25
full bloom
75
60
40
showing pink
20
10
Nonpareil [C]
nut stage
Butte [C]
nut stage
F= field observation
100
75
50
50
25
28.9
25
20
90 C=growth chamber observation
Ice Nucleation Water Freezes below the Melting Point (0oC or 32oF) In the temperature range for Frost Damage, Bacteria cause 99% of Ice Nucleation
Passive Protection
INA Bacteria Site selection Cold air drainage Cover crops Soil water
COVER CROP Reflects Sunlight Dries Soil Less Conduction
Less Reflection Wetter Soil More Conduction
With Cover Tsurface ↓
colder
No Cover Tsurface ↑
warmer
Temperature
SOIL WATER CONTENT Reflects More Less Heat Capacity Less Conduction Dry Soil Tsurface ↓
Less Reflection Higher Heat Content More Conduction Wet Soil Tsurface ↑
Temperature
Active Protection Sprinklers Surface irrigation Helicopters
Sprinklers Heat from freezing water Add more energy from Freezing than lost to evaporation Start & stop based on Wet-bulb temperature
STARTING AND STOPPING 1. Air temperature initially drops to the wet-bulb temperature 2. If sprinklers stop, soil surface temperature drops to the wet-bulb 3. Between wetting, wet plant tissue cools to the wet-bulb
Starting and Stopping First night - Start before the wetbulb temperature falls to the critical damage temperature. Subsequent nights – Start before the wet-bulb falls to 0oC. Mornings - Stop when the sun is shining and the wet-bulb temperature is greater than 0oC.
SURFACE IRRIGATION
Start early enough Do not reuse cold water Run water near tree skirts Maximize the area Good flow rate
HELICOPTERS Frequent passes Talk to Pilot Load with water Use Marker lights Monitor Temperature