| Temperature |
temp |
Temperature measurements are made from self-registering
maximum and minimum thermometers set in a louvered, wooden shelter. The
shelter is mounted on a stand so that the thermometers are approximately
1.5 m above ground, which is usually a level, grassy surface. |
| Rainfall, Snowfall, And Precipitation |
precip |
Rain, drizzle, freezing rain, freezing drizzle and hail
are usually measured using the standard Canadian rain gauge, a
cylindrical container 40 cm high and 11.3 cm in diameter. The
precipitation is funneled into a plastic graduate which serves as the
measuring device. |
| Snow Depth |
snow_depth |
Snow cover is the depth of accumulated snow on the
ground, measured at several points which appear representative of the
immediate area, and then averaged. |
| Number Of Days With Specified Parameters |
days |
These elements give the average number of days per
month or year on which a specific meteorological event or parameter
threshold occurs. In the case of rainfall and precipitation, 0.2 mm or
more must occur before a “day with” is counted. The corresponding figure
for snowfall is 0.2 cm. |
| Degree-Days |
dd |
Degree-days for a given day represent the number of
Celsius degrees that the mean temperature is above or below a given
base. For example, heating degree-days are the number of degrees below
18° C. If the temperature is equal to or greater than 18, then the
number of heating degrees will be zero. Normals represent the average
accumulation for a given month or year. |
| Soil Temperature |
soil_temp |
Soil temperature measurements provide the climatology
of soil thermal characteristics such as the depth of frost penetration
into the soil and the duration that the soil remains frozen. It is of
interest to hydrologists because it affects surface runoff, infiltration
and snowmelt and to agriculturalists because it affects seed
germination. |
| Evaporation |
evaporation |
Evaporation refers to the calculated lake evaporation
occurring from a small natural open water-body having negligible heat
storage and very little heat transfer at its bottom and sides. It
represents the water loss from ponds and small reservoirs but not from
lakes that have large heat storage capacities. Lake evaporation is
calculated using the observed daily values of pan evaporative water
loss, the mean temperatures of the water in the pan and of the nearby
air, and the total wind run over the pan. |
| Frost And Freezing-Free Period |
frost |
Freezing occurs whenever temperatures fall to 0 deg C
or lower. Frost data normals are based on the occurrence of freezing
temperatures as recorded from minimum thermometers. The “Freezing-free
Period” is defined as the number of days between the last occurrence of
frost in spring and first occurrence of frost in the fall for a given
year. For the purposes of these calculations, “spring” is defined as
days on or before July 15, “fall” is defined as days after July 15 and
freezing or frost occurs on any day where the daily minimum temperature
(Tmin) is observed to be less than or equal to 0 deg C. |
| Hourly Data |
hours |
Some climate elements are observed on an hourly rather
than a daily basis. For these elements, the “3 and 5” rule for
completeness is inapplicable given the comprehensive volume of data.
Instead, to qualify for inclusion, hourly elements must have at least
90% of all available hours for a month complete where means or “days
with” statistics are calculated. As with daily elements, where average
totals are calculated, the record required 100% complete data. The
monthly mean was then assigned an annual code following the completeness
requirements. |
| Wind |
wind |
Most principal climatological stations are equipped
with a standard type U2A anemometer, taking one-minute or (since 1985)
two-minute mean speeds values at each observation. At other
wind-measuring sites, values are usually obtained from autographic
records of U2A or 45B anemometers. Averaging periods at these sites may
vary from one minute to an hour. |
| Bright Sunshine |
sun |
Bright sunshine observations are made using the
Campbell-Stokes sunshine recorder. It consists of a glass sphere that is
10 cm in diameter, mounted concentrically in a portion of a spherical
bowl. The sun’s rays are focused by the glass sphere on a card held in
position by a pair of grooves in the bowl. The focused rays scorch the
card or burn a trace right through it. The card size used depends on the
length of the day and is available in three classes corresponding to the
time of the year equinox, summer or winter solstice. |
| Humidex |
humidex |
Humidex is an index to indicate how hot or humid the
weather feels to the average person. It is derived by combining
temperature and humidity values into one number to reflect the perceived
temperature. For example, a humidex of 40 means that the sensation of
heat when the temperature is 30 degrees and the air is humid feels more
or less the same as when the temperature is 40 degrees and the air is
dry. |
| Wind Chill |
wind_chill |
Wind chill is an index to indicate how cold the weather
feels to the average person. It is derived by combining temperature and
wind velocity values into one number to reflect the perceived
temperature. For example, if the outside temperature is -10°C and the
wind chill is -20, it means that your face will feel more or less as
cold as it would on a calm day when the temperature is -20°C. |
| Humidity |
humidity |
Vapour pressure is the pressure exerted by the water
present in an air parcel. This pressure is one of the partial pressures
that make up the total pressure exerted by an air parcel. The vapour
pressure increases as the amount of water vapour increases. |
| Pressure |
pressure |
Pressure is the weight of a column of air of unit
cross-sectional area extending from the level of the observing station
vertically to the outer limit of the atmosphere. The standard instrument
for the measurement of atmospheric pressure is the mercury barometer, in
which the air pressure is balanced against the weight of a column of
mercury in a glass tube that contains a vacuum. |
| Solar Radiation |
rad |
Solar radiation is the measurement of radiant energy
from the sun, on a horizontal surface. There are several standardized
components of independent measurements. Each component is assigned a
different identifying number referred to as Radiation Fields (RF). The
standard metric unit of radiation measurement is the Mega Joule per
square metre (MJ/m2). |
| Visibility (Km) |
visibility |
Visibility in kilometers (km) is the distance at which
objects of suitable size can be seen and identified. Precipitation, fog,
haze or other obstructions such as blowing snow or dust can reduce
atmospheric visibility. |
| Cloud Amount |
cloud |
A cloud in the atmosphere is a visible collection of
minute particle matter, such as water droplets and/or ice crystals, in
the air. Condensation nuclei, such as smoke or dust particles, form a
surface around which water vapour can condense and create clouds. |
