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Đơn vị Hành chính, đất đai và khí hậu 19
or exceed 0.1 kw/m
2
(≥ 0.2 cal/cm
2
min.). Sunshine duration is measured by
heliograph.
Total number of sunshine hours in the year
is the total number of sunshine
hours of the days in the year.
Rainfall in months
is the total rainfall of the days in the month.
Rainfall
is the
thickness measured in millimeters (mm) of the floating water layer made by rain on
a flat surface at a site, which measured by rain-gauge/pluviometer.
Total rainfall in year
is the total rainfall of the days in the year.
Average humidity in months
is the average of average relative humidity of the
days in the month.
• Relative
humidity
is the ratio between the vapor in the air and saturation vapor
(maximum) at the same temperature. It is indicated in percentage (%). Humidity is
measured by hygrometer and hygrograph.
•
Daily average relative humidity
is calculated by the simple arithmetic mean
from the results of 4 main observations in the day at: 1 a.m., 7 a.m., 13 p.m., 19
p.m. or from the results of 24 observations at the time of 1 a.m., 2 a.m., 3 a.m.,... 24
p.m. of the hygrograph.
Average humidity in year
is the average of average relative humidity of all
days in the year.
The water level
is elevation of the water surface at the observation place in
relation to the sea surface, measured in centimeters (cm). A system of piles, rulers
and self-recording machines are used to monitor the water level.
Water flow
is the amount of water flowing through a cross section of the river
in a unit of time, measured in m³/s. Monthly average flow is the average value of
flow of the days in the month. Water flow is measured by flowmeters, drifting
buoys or ADCP machines.