The air temperature is routinely measured in 2 meter height above ground by meteorological measurement stations (2m-Temperature). The temperature profile, that is the temperature variation with height, contains information about the atmospheric layers and is obtained e.g. from radiosonde launches. A global temperature field can be collected from the analysis of satellite observations.
The air pressure is routinely measured at ground level using stationary measuring instruments. This measured pressure is reduced to sea level pressure (barometric formula) and can then be used for isobar plots. A pressure profile is measured by radiosondes.
The atmospheric wind is measured with different instruments for example measurement stations or satellite remote sensing. Of interest are wind speed and wind directions. The wind direction is specified with the cartesian coordinates u (zonal component) and v (meridional component). The amount of the resulting wind vector is the wind speed.
Precipitation summarizes rain, snow, hail, graupel, dew and rime.
There are different measures for the moisture in the air: Absolute, relative and specific humidity, water vapor pressure or dew point temperature.
Clouds are one of the most well known (to us) atmospheric parameter - among temperature, wind and precipitation. Clouds consist of liquid water droplets and / or ice crystals. Depending on their vertical extent, growth history and water phase clouds obscure the sun partly or completely. They can cause more or less precipitation in various forms. Clouds play a fundamental role for the short- and long-wave radiation budget of the Earth's surface and the Earth as a whole. A cloud cover can both, "cool" and "warm" the Earth's surface, as it, e.g. during winter, reduces the outgoing long-wave radiation, and as it, e.g. during summer, reduces the amount of solar radiation incident at the Earth's surface.
Clouds are difficult to monitor because of the multitude of different forms they can have (shallow or convective, thick or thin, opaque or translucent). Different cloud layers occur which, depending on the cloud, may have different typical distributions and concentrations of cloud droplets and/or ice crystals. While we can either see the cloud base (from the ground) or the cloud top (from an airplane), satellite senors may, depending on the used frequency look into a cloud or even through a cloud.
Imagining satellite senors like the Advanced Very High Resolution Radiometer (AVHRR), the Moderate Resolution Imaging Spectroradiometer (MODIS), or the classical geostationary weather satellites: Meteosat, are suited to monitor total cloud cover - provided that the contrast between cloud and Earth's surface is large enough. This applies to both, the optical (only useful under daylight conditions) and the infrared spectral range: clouds exhibiting an albedo and/or surface temperature similar to the Earth's surface cannot be detected.
Profiling sensors scan the vertical structure of the clouds by coupling to changes in cloud composition (cloud particle phase), particle size distribution, and vertical cloud water distribution. Such sensors operate in the infrared spectral range such as the Atmospheric Infrared Sounder (AIRS) and the Infrared Atmospheric Sounding Interferometer (IASI). Actively profiling sensors like the CALIPSO Lidar and the CloudSat radar have allowed quite some progress in recent years with regard to resolving the vertical cloud structure in more detail.
The GEWEX Radiation Panel has been working on an assessment of currently available possibilities to remotely sense clouds; a preliminary report of this panel which illustrates current possibilities and limitations is given here.
Solar radiation and sunshine
The sunshine duration is measured in hours (h) and the intensity of radiation in Watt per square meter (W/m²).