Page 23 - NGTK2018

Number of sunshine hours in months is the sum of sunshine hours of the days in
the month. Numbers of sunshine hours are hours with direct solar radiation equal or
2
exceed 0.1 kw/m (≥ 0.2 cal/cm min.). Sunshine duration is measured by heliograph.
2
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.

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