Why do we measure the atmosphere? The obvious answer is to predict the weather. We regularly record variables such as temperature and pressure because we want to and need to know what the weather will be. We must know the current state or condition of the atmosphere as well as changes in atmospheric conditions over a period of time in order to forecast weather events. We need to know of major weather systems that are elsewhere and heading our way. We need to know when a severe storm may develop near us or "pop up out of nowhere." We need to know the strength and duration of various weather systems so that we may adequately prepare in advance. If a drought is forecasted we may need to plan ahead for crops, livestock, and city water supplies. Evacuations may need to be executed in preparation for severe storms that could produce damaging winds or flooding. Our livelihood often depends on accurate weather forecasts.
A less obvious answer to the question above is to forecast air quality. Actually, forecasting air quality is still only part of the answer. You see, we cannot control the weather. There are ways that we can modify some aspects of weather events. We can increase and decrease to some degree the amount of rain a storm may produce, as well as the size of hailstones produced. But these modifications are usually not cost effective and they require adding chemicals that may later be detrimental. In contrast, we can often significantly control the quality of the air by limiting what we emit into the atmospere and when we emit it. When pollutants are released into the atmosphere, as we discussed in Session 1, they become part of the composition of the atmosphere. When the atmosphere moves, they move. When the wind blows, they are a part of the wind. Thus, wind patterns can tell us where pollutants will travel.
Atmospheric stability, determined from the measurements we take, can also help forecast pollutant concentrations at given locations. A stable atmosphere will trap pollutants, often at the surface, while an unstable atmosphere will enable them to mix and dilute with cleaner air. Storms can cleanse the atmosphere of many pollutants. Interestingly, all precipitation begins as an aerosol. But wait, in discussion of aerosols in Session 1 we said that liquid and frozen water were not considered aerosols. Water and ice are not aerosols. Rain, snow, sleet, and hail all form when water vapor either condenses or freezes onto a solid particle, often a pollutant. Those particles, whether pollutants or not, are called cloud condensation nuclei or CCN. When precipitation falls to earth, those particles are removed from the air. Wind speeds can influence pollutant deposition as well. Heavy particles will fall out of the air if winds are light while stronger winds will keep them aloft and in motion.
From this short discussion we begin to see why it is necessary to record regular atmospheric measurements. The more we understand about the atmosphere, the better we are able to predict not only the weather, but predict and control air quality as well. In this session, we will briefly discuss the varying properties of the atmosphere we can measure and introduce some of the more discreet parameters we can infer from them. We will also discuss where and how in the atmosphere the data is obtained. As in the case of many of the sciences, the study of meteorology requires learning many small pieces of information in order to build up to a complex process. It is often difficult to convey the significance of each piece until the process itself is better understood. Some of the material that follows is analogous to looking at individual pieces of a puzzle. You may not be able to grasp the importance of each piece until you see the whole puzzle completed. But keep in mind, each piece is important.
The Shodor
Education Foundation, Inc.