| Atmospheric Pressure
|
Pressure (force per unit area) exerted by the
atmosphere on any surface by virtue of its weight;
it is equivalent to the weight of a vertical column
of air extending above a surface unit area to the
outer limit of the atmosphere. |
| Average Temperature Calculator
|
Tool to calculate average daily maximum, daily
minimum and daily average temperature from period
specified by user and compared to past years and
climatological averages. |
| Chilling Hours
|
The number of hours of winter temperature below
45 oF |
| Chilling Hours Calculator
|
Tool to calculate number of chilling hours for
a period specified by user and compared to previous
years. |
| Cooling Degree Day
|
A from of degree day used in estimating the
amount of energy necessary to reduce the effective
temperature of warm air. Computed by subtracting
72 oF from the specified day's average
temperature. |
| Cooling Degree Day Calculator
|
Tool used to calculate the number of cooling
degree days for a period specified by user and compared
to previous years and climatological averages.
|
| Degree Day
|
Difference between the mean temperature of a
particular day and a pre-determined reference temperature
(60 oF). |
| Degree Day Calculator
|
Tool to calculate number of degree days for
period specified by user and compared to previous
year |
| Dew Point
|
Temperature to which a volume of air must be
cooled at constant pressure and constant moisture
in order to reach saturation; any further cooling
causes condensation. |
| Evapotranspiration
|
Vaporization of water through direct evaporation
from wet surfaces and the releases of water vapor
by vegetation |
| Heating Degree Day
|
A form of degree day used as an index for fuel
consumption computed by subtracting day's average
temperature from 65 oF |
| Heating Degree Calculator
|
Tool used to calculate number of heating degree
days for period specified by user and compared to
previous years and climaltological average. |
| Heat Index
|
An index that combines air temperature and relative
humidity to determine apparent temperature—how it
feels. |
| Humidity |
Water vapor content of air. |
| Minimum Temperature Estimator |
The dewpoint is the temperature at which water
vapor condenses as dew on grass, the roof top of
cars or leaves on a tree. The dewpoint has an effect
on the amount and rate of heat lost to the atmosphere,
especially noticeable in cold weather. Knowing the
dewpoint can give growers a rough estimate of minimum
temperature. During a radiation frost, when the
dewpoint is reached, the latent heat released as
water vapor condenses into water and slows the rate
of temperature drop significantly.
Growers can estimate the minimum temperature at
their location on a cold night by using the air
temperature and dewpoint at sunset. The Brunt equation
uses this method. The grower should use the sunset
temperature directly in his grove as air temperature
can vary wildly depending on elevation and topography.
Dewpoint temperatures do not vary greatly over a
distance of several miles, therefore the grower
can use the calculated sunset dew point from the
nearest GAEMN site. While the GAEMN dew point will
not be the exact dewpoint of the grove, it should
provide a close approximation. This method for estimating
the minimum temperature was designed to be used
for a stable air mass of uniform moisture. Significant
errors can occur if dry air moves in or winds increase.
The GAEMN minimum temperature estimator provides
a minimum temperature estimate for each site. If
a grower wants an estimation for a particular site,
the sunset dewpoint of the closest GAEMN site should
be used along with the air temperature of the specified
site. These readings can then be inserted into the
estimator to calculate the minimum temperature of
a specified site. The Burnt estimator calculates
minimum temperatures; actual minimum temperature
can vary several degrees over short distances depending
on nighttime conditions . This Brunt estimator should
be one of several sources used to manage a cold
protect program. |
| Rainfall Calculator
|
Tool to calculate total rainfall in inches and
number of rainy days for a period specified by the
user and compared to past years and climatological
averages. |
| Relative Humidity
|
A ratio, expressed in percent, of the amount
of atmospheric moisture present relative to the
amount that would be present if the air were saturated.
|
| Soil Moisture
|
Moisture contained in that portion of the soil
which lies above the water table, including water
vapor contained in the soil pores. |
| Soil Temperature
|
Temperature at variable depths in the soil.
|
| Soil Temperature Calculator
|
Tool to calculate average daily soil temperature
at 2", 4" and 8" for a period specified by user
and compared to past years. |
| Solar Radiation
|
A measure of the intensity of the sun's radiation
reaching the earth's surface. Radiation with wavelengths
from 0.3 to about 4um |
| Temperature |
The degree of hotness or coldness of a substance
as measured by a thermometer. |
| Water Balance
|
The comparison of actual and potential evapotranspiration
with amount of precipitation |
| Water Balance Calculator
|
Tool to calculate difference between precipitation
and evapotranspiration for period specified by user
and compared to previous users and climatological
averages. |
| WBGT (Wet Bulb Globe Temperature)
Index |
The Wet Bulb Globe Temperature is
usually used as guidance for environmental heat
stress to help prevent heat stroke while at work
or during physical exercise. WBGT determines heat
stress in humans on the job in harsh environment.
-
WBGT index of 78 oF (26 oC)
Cautions is advised as extreme intense physical
exercise could lead to heat stroke or heat exhaustion.
-
WBGT index of 82 oF (28 oC)
Heavy exercise for unseasoned personnel is cautioned.
-
WBGT index of 85 oF (29 oC)
During first three weeks of training strenuous
exercise for unseasoned personnel should be
suspended. After second week of training, training
activities may be continued at a reduced scale.
-
WBGT index of 88 oF (31oC)
For those with less than 12 week of training
in hot weather, strenuous exercise should be
discontinued. Those, who have been acclimatized
each season, can continue limited activity at
a WBGT of 88 oF to 90 oF
(31 oC - 32 oC) for six
hours or less each day.
-
WBGT index of 90 oF (32 oC)
+
Physical training and strenuous exercise should
be discontinued for all persons.
The following simplified formula is used:
WBGT = 0.567 Td
+ 0.393 e + 3.94
where:
WBGT = Wet Bulb Globe Temperature (oC)
Td = Dry bulb temperature
(oC)
e = Water vapor pressure (hPa)
|
| Wet Bulb Temperature |
- Isobaric wet-bulb temperature: the temperature
an air parcel would have if cooled adiabatically
to saturation at constant pressure by evaporation
of water into it, all latent heat being supplied
by the parcel.
- Adiabatic wet-bulb temperature (or pseudo
wet-bulb temperature): the temperature an air
parcel would have if cooled adiabatically to
saturation and then compressed adiabatically
to the original pressure in a moist-adiabatic
process. This is the wet-bulb temperature as
read off the thermodynamic diagram and is always
less than the isobaric wet-bulb temperature,
usually by a fraction of a degree centigrade.
- The temperature read from the wet-bulb thermometer.
We use the following
steps and equations to calcuate Wet-bulb temperature:
- Compute e as [es(T)*rH/100]
where es(T) = 0.611*EXP(17.27*T/(T+237.3)) in
kPa
T is drybulb temp in oC
e = (rH/100)*0.611*EXP(17.27*T/(T+237.3))
where e is ambient vapor pressure in kPa
- Compute dewpoint temperature (Td)
Td = [116.9+237.3ln(e)]/[16.78-ln(e)] in oC
- Compute wet bulb temperature (Tw)
Tw = [(GAMMA*T)+(DELTA*Td)]/(GAMMA+DELTA)
GAMMA = 0.00066*P
where P is ambient barometric pressure in kPa
DELTA = 4098*e/(Td+237.3)2
This method should be close, especially when
Tw is close to Td (DELTA should be evaluated
at (Tw+Td)/2.
Jensen et al. (1990) ASCE Manual No. 70 (see pages
176 & 177)
|
| Wind |
Air motion relative to the Earth's surface.
Unless otherwise specified, only the horizontal
component is considered. |
| Wind Chill
|
The combined effect of wind and temperature
on exposed human flesh. |
