In my last post, I noted how observations are one of three critical elements of weather and climate research (along with theory and computer modeling). Observing the atmosphere may seem like a simple task--and in fact, some types of observations are quite straightforward. Most of us are familiar with temperature, humidity, wind, and air pressure, the measurements typically included as "current conditions" on daily weathercasts. These have been measured for hundreds of years in situ (in place) through basic weather instruments. Today, digital versions of these instruments are used in many locations, but the idea is still the same: provide a snapshot of the most important weather variables at one point in space and time.
Some other aspects of weather and climate are very difficult to measure. For example, how prevalent are clouds throughout Earth's atmosphere? Some types of clouds can be "seen" by satellite images that detect sunlight reflecting off clouds (so-called visible satellite images). Clouds can show up even at dark with the help of infrared sensors. But most satellites can't easily see through multiple layers of clouds, so even though we have a good idea of how much of the planet is cloud-covered at any given time, it's much harder to gauge the sum total of cloudiness in three dimensions. Innovative new satellites, such as NASA's CloudSat and CALIPSO spacecraft, are helping get past this roadblock, but it will take time to develop a true 3-D system for measuring clouds. The location and prevalence of clouds has huge implications for climate change, so this is a very important goal.
The basic weather variables noted above are much easier to measure, but these observations need to be as bias-free as possible, and sustained for as long as possible, in order to be most useful for studying climate change. There are thousands of weather stations across the United States, including both public and private networks, but not all of these stations are up to the standards needed for long-term climate assessment. Some have been affected by changes in buildings and tree cover, a point recently acknowledged by NOAA. (It's important to keep in mind that this does not negate the vast body of evidence that Earth has been warming in recent decades!)
To help ensure that a select group of weather stations is maintained with long-term climate in mind, NOAA's U.S. Climate Reference Network program has been building a network of more than 100 carefully built and monitored observing stations over the last seven years. Scientists are also working on "networks of networks" in order to link the nation's growing set of regional observing networks (often called mesonets), a goal recently examined by the National Research Council.
Because rainfall and snowfall vary so much across small areas, they are among the toughest weather variables to measure. This is where the public comes in! A program called CoCoRaHS (Community Collaborative Rain, Hail, and Snow Network), which started in Colorado, has quickly spread to include most of the United States in the last few years. More than 12,000 CoCoRaHS volunteers ranging from grade school children to senior citizens have installed simple, inexpensive equipment at home (a rain gauge and, in some states, hail pads). They use these backyard stations to measure each day's rain, snow, and liquid equivalent of snow. Volunteers post their report on the Web at 7:00 a.m. local time each morning, and the data are pooled in maps that allow you to see thousands of precipitation readings across the nation and zoom in to areas of interest. Every U.S. state except for Minnesota is participating (Arizona is joining this year). It's easy to sign up, and by participating, you can do your part to advance weather and climate research.