What defines the weather? Is it the level of precipitation, or the temperature of the air? As a basic definition, weather is the state of the atmosphere. Most weather occurs in the troposphere, or the lowest layer of the atmosphere. Weather is made up of multiple parameters, including air temperature, atmospheric (barometric) pressure, humidity, precipitation, solar radiation and wind. Each of these factors can be measured to define typical weather patterns and to determine the quality of local atmospheric conditions.

Why measure weather? The environmental conditions produced by different weather parameters have an impact on the quality of the surrounding ecosystem. Weather elements form a chain reaction, as the impacts do not remain solely in the atmosphere. Temperature, pressure and humidity (moisture) can interact to form clouds. These clouds, in turn can reduce solar radiation for plants, or increase precipitation, which can runoff into a body of water. Consistently high temperatures can increase the heat transfer to local bodies of water in addition to heating the air. Likewise, a lack of precipitation affects not only weather conditions, but soil moisture and water levels due to evaporation. Wind speed and direction can be indicative of a front moving into the area, or it can create waves and encourage a stratified water column to mix.

Weather monitoring can establish a database of typical conditions. When one or more weather elements deviate from this standard, the information can be used to explain or predict weather events. Monitoring weather conditions is important not only as an environmental baseline, but to maintain quality working conditions, marine studies and recreational safety.

Each of the following chapters will discuss a different element of weather and atmospheric quality. These pages will define each parameter and explain why it is important to measure and monitor.

Weather and Atmosphere Chapters

• Air Temperature and Heat Index
• Barometric Pressure
• Humidity
• Precipitation
• Solar Radiation and Photosynthetically Active Radiation
• Wind Speed and Direction

Measurement methods and technology can be found in the Measurements section.