Instruments Here on the Summit
2014-06-06 16:42:09.000 – Mike Dorfman, Weather Observer
Not a Bad Office View this Morning
It constantly amazes me how many different instruments we have here on the summit to measure various variables. Here is a brief description of the variables we measure and the instruments we use to measure them.
Wind Sensors: Our primary wind instruments here on the summit consist of a pitot tube anemometer and an alpine RM Young. The pitot tube measures wind speed by measuring the pressure of the wind, and the RM Young measures wind speed and direction with a spinning propeller. We also have a Hydrotek and 3-cup anemometer (both spinning anemometers) along with a Metek Sonic anemometer, which measures the wind (especially low winds) very accurately. In addition to this, we have a wind vane, which tells us wind direction, and we are testing an NRG heated wind direction sensor.
Temperature and Relative Humidity Sensors: Our most precise temperature sensor, the MET-2010 measures temperature very accurately. It measures dew point in a very elegant way-by measuring the reflection of a laser off of a cooled mirror. Once the mirror cools to a certain point, water will condense onto it, decreasing the intensity of the reflected laser. Other temperature and RH sensors we have here on the summit include the Campbell Scientific T-107 thermometer, HMP-45 temperature and RH sensor, and a Foxboro temperature sensor. We also read temperatures for our observations the same way we have for our existence here on the summit; off of alcohol and mercury thermometers.
Pressure sensors: Our official station pressure comes from Coastal Environmental System’s ‘PDB-1’ pressure sensor. We compare this to our outdoor barograph every 3 hours to assure its accuracy. We also house the second oldest barometer in use in the country, which we use to calibrate the barograph. This mercury barometer is extremely accurate and retains its accuracy much longer than most digital pressure sensors. In addition to these sensors, we have another digital barometer housed on the top of our tower.
Precipitation sensors: Although we have a precipitation sensor at our Auto Road Base remote station, we measure precipitation here on the summit the same way we have for over 80 years-with a can and a nipher screen to help minimize the effects of wind on precipitation.
Ceilometers: Located at the Cog Base and the Auto Road base, we use these to determine cloud height. They are basically large invisible lasers that shoot straight up to determine the distance between the ground and the cloud bases. These are extremely helpful as we report cloud heights on an hourly basis.
Electromagnetic Field Detectors: In simple words this is a lightning detector. In previous years, it has been mounted on the roof of the Sherman Adams building to give observers a better idea as to when it is safe to venture outside to take an observation.
Ice detector: Mount Washington is famous for its rime ice, which is formed from supercooled fog freezing on surfaces on the summit. We are lucky to be working together with CRREL on a project which analyzed cloud droplet size distribution. For this project, we need to know the rate of icing. The ice detector mounted on the tower contains a small metal piece which vibrates at an extremely high rate. Its vibration slows down as ice accrues on it and once a certain amount of ice builds up on the instrument it heats up very quickly, melting the small amount of rime off of it and starting the process over.
Observer FootnoteA reminder to register for Seek the Peak (http://seekthepeak.org/) our annual fundraiser to support our non-profit Observatory. While the date (July 18-19) is over a month away, it will be here faster than you know it!
Mike Dorfman, Weather Observer