APPENDIX J ____________________________________________________PRESSURE TENDENCY
VAISALA ________________________________________________________________________ 101
APPENDIX J PRESSURE TENDENCY
The World Meteorological Organization (WMO) publication Manual on Codes
Vol. I.1, International Codes, Part A - Alphanumerical Codes, 1995 Edition,
WMO - No. 306. Section C, Code Table 0200: a - Characteristic of pressure
tendency during the 3 hours preceding the time of observation describes the
pressure tendency as follows:
Code figure
0 Increasing, then decreasing; atmospheric
pressure the same or higher than three hours
ago
1 Increasing, then steady; or increasing, then
increasing more slowly; atmospheric pressure
now higher than three hours ago
2 Increasing (steadily or unsteadily);
atmospheric pressure now higher than three
hours ago
3 Decreasing or steady, then increasing; or
increasing then increasing more rapidly;
atmospheric pressure now higher than three
hours ago
4 Steady; atmospheric pressure the same as
three hours ago
5 Decreasing, then increasing; atmospheric
pressure the same or lower than three hours
ago
6 Decreasing, then steady; or decreasing, then
decreasing more slowly; atmospheric pressure
now lower than three hours ago
7 Decreasing (steadily or unsteadily); atmospheric pressure now lower than
three hours ago
8 Steady or increasing, then decreasing; or decreasing then decreasing
more rapidly; atmospheric pressure now lower than three hours ago
In addition to this the PTB220 series barometers output code * when the
pressure tendency has not yet been calculated i.e. less than three hours have
elapsed since power-up of the barometer. The absence of the pressure trend is
indicated in the similar manner, too.
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