If the first discussion on climate services and their inhomogeneities didn’t scare you enough, let me just throw this out there:
The U.S. measures surface observations at 1.5 meters above the ground while the rest of the world measures at 2 meters above.
O.k., o.k., but let’s talk about specifics. You’ve also hopefully also reviewed all the limitations in current data and the considerations to take when setting up a weather or climate station in Climate Change 101: Observing the Climate Itself, so we should be ready to talk about the equipment itself!
First off, location is key
An observation station should be in a large, homogeneous area so that it properly represents its geographic sampling. Place it far away from any possible developments and preferably on even, open clearings. The sensors themselves should sample at 1.5 meters, due to the cycle of heating and cooling that occurs on the Earth’s surface. At 1.5 meters, there is a near-perfect balance that avoids that heating and cooling bias.
Early temperature sensors, used in COOP and the first order weather stations (see Climate Change 101: U.S. Observation Networks), were not automated. Minimum temperature was recorded by an alcohol thermometer while maximum temperature was recorded by the mercury thermometer. Each thermometer was able to maintain the max/min in a unique way.
Modern temperature sensors, thermistors, are called maximum minimum temperature systems (MMTS). The sensor itself is housed in a small, beehive looking case outside to protect it from direct radiation.
When installing rain gauges, consider the amount of wind. The more wind, the more error. Gauges should, however, not be shielded by buildings or trees if possible either. So how can we accommodate these finicky things? Try to place them in a site where wind is controlled in all directions, such as an opening in a grove of trees. Some people even build screens around their gauges that look like wooden fences.
The most common rain gauge is fashionably called the Standard Rain Gauge (SRG). You’ll find these employed on COOP stations. They consist of a metal cylinder, cunnel top, and a measuring tube in the middle. It typically holds up to 2 inches before the rain overflows into an outer cylinder. During the winter, it can be adjusted to measure snow fall by removing that inside tube.
The Fischer and Porter Rain Gauges measure the actual weight of rain as it is collected in a metal bucket. It sits on a mechanism that can convert the weight into inches, fancy! Every 15 minutes, it punches holes to record the amount into a piece of paper tape. The observer will then remove that tape at the end of the month and send it to a local National Weather Station (NWS) office, who will in turn send it to the National Center for Data Collection (NCDC). Some COOP stations employ this method as well for hourly measurements.
What many people may have heard of is the Tipping Bucket Rain Gauge. Here, precipitation falls into one of two small buckets. Once the first small bucket fills, it tips into the second bucket and sends a signal to the recorder. This indicates intensity of rainfall as well. The Automatic Surface Observing Stations (ASOS) employ this rain gauge.
Snowfall and Snow Depth Sensors
Snow is difficult to measure. It melts when it hits the ground, or it drifts and settles into a compact layer.
Some observers use “snowboards“. It’s rudimentary, but does the trick. Lay a piece of plywood on the ground measuring 3 sq. feet and attach a perpendicular ruler in the middle. Sit that in an open space and wait for your snow fall! After each measurement, the observer will brush off the previously accumulated snow.
Another method is a snow pillow. I know, this is getting a bit silly, but hear me out. Snow pillows are designed for automatic recordings. They measure the hydrostatic pressure that is created by layers of fallen snow. They’re also larger in size than snowboards, measuring at about 3 sq. meters.
Remember that measuring climate variables is very difficult. Many factors can skew or create a bias in your recordings, including place, space, time, instrumentation, and even the weather itself!
Remember that, if you wish to record or use the data collected, to consider the spatial and temporal scale of the phenomena that your observing. Get the metadata, which should describe the type of equipment employed and it’s maintenance and calibration. Also look at the geographical representation of the site to see if it is in a largely homogeneous area that accommodates the footprint of the instruments used.