After reading this thread and other threads and the VP2 console User Manual my brain is all wrapped in knots over the different pressures that are discussed. The pressures discussed in these sources are atmospheric pressure, SLP, barometric pressure, altimeter and pressure as reported by MesoWest. The VP2 console User Manual states in Appendix A that the console measures atmospheric pressure and converts it to barometric pressure. It also states in the Weather Data Specifications that barometric pressure readings are standardized to sea level. I live just outside Ottawa, Kansas. The local airport is Ottawa Municipal Airport, ID KOWI. MesoWest reports Pressure and Altimeter. I have the following questions:
1. Is the value that the VP2 console displays and reports the same as SLP?
2. Is what the VP2 console User Manual calls barometric pressure the same as SLP? (Probably the same question as question 1.)
3. Is the Pressure value that MesoWest reports the same as what the VP2 console User Manual calls atmospheric pressure?
4. When following the Calibrating Barometric Pressure instructions in the VP2 console User Manual are you entering what the manual refers to as atmospheric pressure or barometric pressure (SLP?)?
5. The distance between my location and the airport is approximately 11 miles and the difference in elevation is approximately 25 to 30 feet. Can I use the data in the MesoWest report to calibrate the pressure in my console?
Thanks in advance.
I feel your pain. I do.
re: definition of barometric presure:
Wikipedia: Atmospheric pressure, also known as barometric pressure
NOAA & NWS : Barometric Pressure - the pressure of the atmosphere as indicated by a barometer.
As you can see, the use of the term “barometric pressure” is somewhat ambiguous. So is the term “SLP”. In the U.S. it appears that barometric pressure can refer to either atmospheric pressure or SLP. In academia, SLP can refer to either Altimeter( setting)/QNH or QFF.
Although personal preferences and common/popular usage can be different, once you add regional and country differences you have a Tower of Babel scenario. In Europe, SLP and Altimeter are not used in METAR(some military airfields excepted). It is just QNH over there but in Europe, “air pressure” is commonly used.
I think the aviation world is far more clear. They use the "Q"codes. No confusion with QFE, QNH and QFF.
For meteorological purposes for our personal weather stations (pws), I prefer the following terminology. Note the absence(intended) of barometric pressure, atmospheric pressure and air pressure.
Pressure/Station pressure = calibrated station pressure at your sensor elevation. Unlike airports, we assume that sensor pressure = station pressure.
Altimeter/QNH = station pressure that is elevation corrected.
SLP/MSLP/QFF = station pressure that is elevation and temperature corrected (sometimes there are additional corrections for humidity and plateau effect)
Your Davis console (unless you have the Vue console) calculates SLP only so I suspect your manual's "barometric pressure" is probably referring to SLP.
"Atmospheric pressure" is reported as "Pressure" in Mesowest.
I do not own a Davis weather station but I believe when you are in "adjust barometer mode" you are adjusting atmospheric pressure/station pressure.
Perhaps a Davis owner can confirm this.
The elevation difference between you and your airport is immaterial as SLP normalizes all pressures down to sea level elevation. SLP is a calculated value - calculated by your console.