University of Washington
J. E. Tillman & N. C. Johnson
- Each pressure data point is a 1-minute average of 30 values ( 2 second
sample interval, resolved to 0.01 millibars).
The top frame contains the last 240 points of data taken. This
is normally 4 hours of one-minute averages. If these points include
gaps of any kind due to program failure, the time span will be greater
than 4 hours.
- The second frame is always
1 week in length and the last day is always the current day.
- The third frame is a plot of a 60 point running mean
of slopes of the pressure time series, d(Pressure)/d(Time).
- The abscissa times are Seattle local time and no adjustment to
sea level pressure has been made. The approximate adjustment to
obtain SLP is to add 4 millibars (note: this varies with atmospheric
- The range of the ordinate scale for the first and second plots is
a flexible quantity that varies with the range of the pressure data.
It changes at midnight when appropriate and whenever the data
approaches the upper or lower limits. The ordinate range of the third
frame is coded to be 2, 5, or 10 millibars.
- Continuous operation of this sensor began May 21, 1993. It
has been measured in its current location, approximately 33 meters
above sea level since July 1993.
- It was moved approximately 3 meters to a new location in
the same room, maintaining the same height to within 1 cm, on 29 July,
- The two Vaisala barometers were moved again, maintaining
the same height to well within 1 cm, on November 1, 2006.
- The Vaisala instrument directly produces ASCII in CGS units or
- Sampling, averaging, and other operations utilize a Campbell
Scientific, Inc., 21X programmable data logger.
- These plots were created using gnuplot, courtesy of the Free
- Meteorological analyses and pressure sensor intercomparisons are routinely
(see weekly and annual plots)
carried out using the statistical software Splus, courtesy of Statistical
Sciences, Inc. a division of MathSoft.
- This page provides dynamic refresh, which will include the
most recent pressure, via a client pull every 5 minutes to